STS-71 Shuttle Mir Mission Report

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STS-71 Shuttle/Mir Mission Report L1'aTOuC

July 31,1995

Douglas J. Zimpfer

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Ac k n o w led g emen t sThe efforts documented here reflect th e work of numerous individuals, from multipleorganizations. The auth or wo uld like to acknow ledge the efforts of these people and apologize foranyone who may have been missed. In the flight control design, analysis and flight supportactivities, from NASA, Nancy Smith and Ken Lindsay, from the Draper Laboratory, KimKirchwey, Mark Jackson, Dave Hanson, Rami Mangoubi, Tim Henderson, Ray Barrington, RobHall, Neil Adams and Darryl Sargent, from Rockw ell International, Bob Friend, DemetriousZaferias and Janet Hou, from Honeyw ell Internationa l, Bob W illms, Tom Gederberg and RogerWacker. In the flight design and operations activites, Ken Bain, Dave G ruber, Leroy Cain, SedraSpruell, Stan Schaefer, Jeff Davis, Lyn da Gav in, Malise Fletcher, Joel Montelbano, JeahnetteKirinich and Robbie Gest. From RSC-E, Y. Kasnecheev, A. Patsiora, S. Shitov and V.Stashkov. In the loads and dynam ics, James Dagen, Tamm y Long, Steve Yahata and Glen Funk.

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Table of ContentsTable of Contents iiTable of Figures iiiTable of Tables iv1. Summary 12. Mission Overview 13. Stability & Control Performance 84. Increased Propellant Consumption Summary 13

4.1. Control Response to Acceleration Difference 154.2. Analysis of Modeling Errors 174.3. Analysis of Possible Control System Solutions 19

5. RME 1301 - Mated PRCS Firing Test 206. DTO1120-Free Drift Test 257. Mir ACSPerformance 278. Conclusions &Lessons Learned 319. References 3310. Attachments 36

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Table of FiguresFigure 1 - Ultra Robust Notch Filter Frequency Response 8Figure! - Pitch Rate Estimate (GMT 180/19:43:35- 180/19:47:30) 9Figure 3 - Estimated Rate during Maneuver to IO1.1A (GMT 180/13:15 -180/13:40).. .10Figure 4 - Limit Cycle Response During IO Hold (GMT 180/19:20 - 20:20) 11FigureS - Limit Cycle Response During GOHold (GMT 181/13:00- 181/14:00) 12Figure6 - Undesired Accelerations (GMT 180/21:00- 180/22:40) 14Figure 7 - Negative Pitch Response (GMT 180/17:59 - 180/18:00) 15Figure 8 - Ideal DAP Limit Cycles 16Figure 9 - STS-71 DAP Limit Cycles (GMT 180/19:20 - 180/20:20) 16Figure 10 - Center of Gravity Locations 18Figure 11 - Results from Part 1, negative pitch firing 21Figure 12 - PSD of detrended pitch attitude 22Figure 13 - Pitch rate comparison 22Figure 14 - Effect of negative pitch firings at 10.96 sec interval 23Figure 15 - I-loaded notches with observed mode 24Figure 16 - Shuttle Attitude Deviation Free Drift Test (GMT 184/09:30 184/13:45) 25Figure 17 - Shuttle Rate Errors Free Drift Test (GMT 184/09:30 184/13:45) 26Figure 18 - Inertial Hold Rates (GMT 183/11:40-'183/15:00) 28Figure 19 - Gravity Gradient Hold Rates (GMT 183/10:10 - 183/11:40) 29Figure 20 - Desaturations during Inertial Hold (GMT 183/11:40 -183/15:00) 29Figure 21 - Inertial Mir Attitude Misalignment (GMT 183/11:40 - 183/15:00) 30Figure 22 - LVLH Mir AttitudeMisalignment (GMT 183/10:10 - 183/11:40) 30

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Table of TablesTable 1 - On-orbit Flight C ontrol Activity Timeline 2Table 2 - Separation Timeline 7Table 3 - Actual vs. Predicted P ropellant Consumption Obs/hr) 14Table 4 - Pitch Acceleration byEleven Postion (7sec2) 17Table5 - RME 1301 timeline... 20

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STS-71 Mission ReportCSDL-R-2699July 31,1995

1. SummaryThe on-orbit flight control system (PCS) performed nominally during all phases of the STS-71mission, including approach, mated operations an d separation. No dynamic interaction stabilityconcerns were observed. All planned flight tests (RME1301 and DTO 1120) were completedsuccessfully. All new OI-24 software capabilities performed as expected, including the PostContact Thrusting (PCT) sequence. During periods of inertial attitude hold, the M C C PROP teamnoted the propellant consum ption rates were 70% higher than pre-flight predictions. This wasdetermined to be the result of an actual in-flight negative pitch acceleration 25% lower tha n thatcalculated by the on-board softwa re and was not related to the flexible dynam ics of the stack. Thisdiscrepancy is believed to be a result of modeling error in the aft down-firing VRC S jets, mostlikely due to the modeling o f plume impingem ent. Additional periods of GO attitude holds wereplanned an d propellant margins remained positive, so no further action was taken to improvepropellant consumption during the flight. Analysis of the Shuttle downlisted data indicated the MirAC S control performance w as nominal, although , data indicated performance did not match pre-flight predictions.Performance of the autopilot during mated operations demonstrates that the Shuttle can control andstabilize large space station sized structures, such as the Mir and planned International SpaceStation (ISS) assembly stages. Valu able data was obtained on the performance of the vehicleduring control of these large structures and will be incorporated into the on-going design an danalysis of the assembly operations of the ISS. One lesson learned from this flight is thatsufficeint margin should be built into ISS assembly control performance to account for systemtolerance an d errors, such as the jet modeling discrepancy u ncovered during this flight. Furtherflight tests will be planned for upcoming Phase I Mir flights to minimize the possibility ofdiscovering additional modeling or system problems du ring IS S assembly.

2. Mission OverviewThe on -orbit control system perform ance dur ing all phases of the STS-71 flight w as nom inal.Table 1 provides a timeline of the significant control activities durin g the flight.On Flight Day (FD) 2, two tests of the flight control system were performed. The first was an in-flight firing of the PC T sequence, w hich mimicked the firings performed during pre-flight SA ILtesting. Data indicated the PC T sequen ce performed nom inally. The second w as the uplink and

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STS-71 Mission ReportCSDL-R-2699July 31, 1995verification of the notch filters and mass property I-loads required to support operations followingSoyuz separation. These values were uplinked into CNTL AC C EL 8, which was then selectedwith the DAP in free drift to verify successful completion of the uplink. No problems wereencountered during this process. Also on FD2, a concern was raised over a fax sent to theRussians outlining the effects of Orbiter Docking System (ODS ) freeplay on mated stack structuralfrequencies. Direct discussions between NA SA and Russian flight control and loads counterpartsindicated there was no concern over the effects of freeplay outlined in the fax and the go ahead wasgiven to proceed w ith the planned flight operations (CHIT 008).

Table 1 - On-orbit Flight C ontrol Activity T imelineEvent

PCTTestCNTL ACCEL 8 UplinkDockingVRCS C ontrol InitiatedR M E Pa r t iR M E Pa r t 2MirACSH/OSTS H/OFree Drift DTO1 120DB CollapseShuttle Undock

GMT Time179/15:03179/15:10180/13:00180/13:20182/12:34182/14:00183/10:10183/14:55184/09:19185/10:42185/11:09

On FD3 the Sh uttle successfully docked with the Mir and mated operations began. During theapproach, at a range of approxim ately 270 feet the Mir m aneuvered from the inertial attitude to anOSC attitude for docking, and w hen the Shuttle had reached 50 feet, the gyrodins were m anuallydesaturated to reduce the probability of an automatic desaturation firing during final approach.RSC E data indicates the gyrodine m om entum remained low th roug hou t the approach. Nearly atthe exact planned time, Atlantis's crew initiated the PCT firing, the O DS indicated capture and theShuttle and Mir were docked. Fifteeen m inute s later follow ing retraction of the dockingmechanism and hook closure, daploads A12 and B12 w ere loaded. Since the docking had nulledthe vehicle rates to -0.01, -0.02, 0 deg/sec in roll, pitch and yaw respecitvely and an inertialattitude was planned, rate damping in the INRTL mode was not required. The DAP was moded to

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STS-71 Mission ReportCSDL-R-2699July 31,1995AUTO and the vehicle maneuvered to the IO1.4B inertia! attitude. Control performance during themaneuver was nominal and no dynamic response was noted in the DA P rate estimate, indicatingthe notch filters were succesfully attenuating any structural excitation induced by the verneirthrusters. Several additional inertial ma neuvers were performed and the DAP remained in inertialholds for the entire initial day of mated operations.During the initial period of inertial operations, the MC C PROP team reported that the propellantconsum ption rates were exceeding the pre-flight predictions by nearly 70%. Simultaneously theM ER flight control team observed negative pitch limit cycle rates higher than expected based onpre-flight simulations, i.e., the DAP w as commanding je t firings to induce larger negative pitchrate w henever the positive attitude deadband was exceeded. These higher than expected rates werecausing the increased propellant consumption. To assess the DAP performance the roll an d pitchundesired accelerations were added to the variable downlist (CHIT 22). The undesired accelerationvalues were consistent with the DAP limit cycle rates, indicating the software was performingnom inally. The longer jet firings were traced to large transients in the undesired acceleration due toan actual acceleration 25% lower than the on-board calculated acceleration.On FD 4, the Russians agreed to increase the amount of time spent in the GO attitudes, if anadditional period of GO 1.2 orientation was added prior to crew sleep to observe Mir solar arraypower performance. Indications were the Mir was generating sufficeint power during this periodof attitude hold and it was agreed to remain in the attitude during the crew sleep period.Attachment 1 provides a summary of the attitudes maintained during the entirity of mated flight.Since the only adequate solutions to resolve the increase in propellant would require a GMEM ofthe flight software and the Russians agreed to increase the duration of time spent in the GO(minimum disturbance) attitudes which provided positive propellant m argins, it was decided tosimply operate with the degraded, albeit acceptable DAP performance. Control performance at theGO attitudes was quite nominal, with few deadband exceedances requiring control firings,indicating that the mass properties had been we ll predicted in determining the GO attitudes pre-flight. During the crew sleep period, control remained quite stable and insufficeint firings of theforward VRCS jets were required, resulting in low temperatures and a false F5R fail leakindication. To avoid further false leak annunciations the GO1.1 attitude was biased by two degreesin pitch to increase the num ber of thruster firings and maintain adequate jet temperatures. Also,during the n ight the circulation pum ps were activated and the inboard elevons were driven to thefull down positions, +21, decreasing the -pitch acceleration to 35% lower than the onboardcalculations.

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STS-71 Mission ReportCSDL-R-2699July 31,1995The m ated PRC S firing structural model verification test, RM E 1301, was successfully performedon FD 5. This test commanded a series of open loop PRCS je t firings followed by queiscentperiods to observe the structural response. The response was compared to pre-flight predictionsbased on the finite element model. Part I of the test commanded single pulse firings, wh ile Part IIcommanded two pulses separated by the Alt mode delay time. Part I firings provided excellentcomparison to the expected results, well w ithin the 20% frequency and 6db amplitude uncertaintiesused in control system design. Part II demonstrated the delay time had been correctly selected toinsure that a series of PRC S firings would not resonate the primary bending modes. Given theresults observed from the test, CHIT 35 was w ritten to accept contingency use of the Alt PRCS inthe event of a VRC S jet failure.Also, to insure that th e forward VRCS jet temperatures would not again fall below leakannunication levels and have false annunication wake the crew, the attitude deadband was reduced.CHIT 36 was transmitted to allow the "use of a 3 deadband to increase the likelihood of firings, butto not excessively increase propellant consumption. The lower deadband was still above the 1value found acceptable for Shu ttle separation. Since this deadband still did not assure adequate je tfirings, it was used for an orbit prior to crew sleep and all indications were it would maintainadequate forw ard VRC S jet temperatures. Yet, to insure forward thruster temperatures above theleak values, a DEU equivalent comm and load wa s created to reduce the deadband to 1, to inducefirings, and then to increase the deadband back to 3 once the jets had w armed to acceptable levels.Again, this procedure w as reviewed by the ME R flight control team and it was approved based onreducing the maneuver rate to O.T/sec to match the plann ed deadband collapse of separation. Thecrew reduced the maneuver rate and a test of the load was performed successfully prior to the sleepperiod. During the remainder of mated operations the reduced deadband an d biased attitudeprovided sufficeint firings to avoid further false leak annunciations and the DEU equivalentcommand was not required.The high light of FD 6 was the demo nstration of the Mir Attitude C ontrol System. The Mirassumed control of the stack at the GO2.1 attitude used during the Shuttle water dump andmaneuv ered the stack to the GO 1.1 attitude and performed a 1.5 hour period of attitude hold ongyrodines. An RC S maneuv er was then performed to the IO1.2 attitude and a two hou r period ofgyrodine inertia! hold performed . Mir AC S performa nce was monitored via Shuttle downlist of theestimated rates and Un iversal Pointing total errors. All indications were the system performedwell. It was noted that the Mir appeared to have approximately 2-3 of inertial platformmisalignment, required desaturations during the inertial hold period at rates twice as often aspredicted pre-flight and that the gyrodine system bandwidth appeared lower than expected.

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STS-71 Mission ReportCSDL-R-2699July 31,1995Conversations with Yuri Kasnecheev confirmed the indications of the Shuttle downlist.Additionally, Mr. Kasnecheev indicated that the Mir estimate of mass properties implied the flightvalues were within 3% of the predicted values, but the inertia values used in the gyrodine controlloop had not been updated to reflect the mated S huttle/Mir values.During the M ir control demonstration the Shuttle elevens were parked at the 7.5 up position at therequest of the Mir flight control team (C HIT 37). This provided a third data point on the effects ofeleven position on VRC S aft down-firing jet acceleration and self impingemen t off the elevens. Asexpected, the acceleration was increased (i.e., plume was decreased) resulting in a flight value only16% below the onboard calculation. The limit cycle perform ance improved and propellantconsumption was reduced from a first day average of 38 Ibs/hr to 27 Ibs/hr (it should be noted thatpost-flight analysis has shown the decreased consumption to be a function of the varying IOattitudes). Since adequate con sum ables existed, the Aero Surface Assembly (ASA ) remainedpow ered up, keeping the elevens at the 7.5 up position for the remainder of the mated operationsand until the OPS 8 PC S checkout was performed to support deorbit.Shuttle control during the waste water dum p at the GO2.1 attitude was nominal.The final flight test of the mated operations phase was performed on FD 7 with the successfulcompletion of DTO1120, Free Drift Test. The test perform ed at the GO 1.1 biased attitude was todemo nstrate the stability of the selected attitude. All pre-flight predictions had been performedbased on the nominal GO1 attitudes, but a real-time simulation performed based.on the flightattitude and rates, without aerodynamic effects of the Mir solar arrays, indicated stableperformance. Althou gh, all flight indications were the attitude was stable, the yaw attitude errorshowed a slight increase over the duration of the test, exceeding pre-flight predictions of 5, butnot the 10 test limit. Roll and pitch also showed larger than expected attitude deviations, but didnot indicate a growing attitude instability. A review of the Mir configuration post-test showed anasymmetrical solar array configuration due to the problems encountered pre-flight w ith the Kvant-1, Kvant-2 an d Spektr arrays, imp lying the planned attitude may not have been a true torqueequilibrium (TEA) attitude. Pos t-flight discussion s w ith the Russian s also uncovered that theSoyuz jets had been com manded on during the test as part of a Soyuz checkout for undocking.Following completion of the free drift test the Shuttle was returned to automatic control. Tocommand sufficeint je t firings to warm the forward thrusters, DAP B was selected with the lower1 attitude deadband. This was an example of performing the deadban d collapse required prior toSoyuz separation on the follow ing day. During this deadband collapse the D AP initiated a

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STS-71 Mission ReportCSDL-R-2699July 31, 1995maneuver to attitude, overshot the desired attitude and commanded a maneuver cycle. Themaneuver was terminated via re-selection of DAP A before the maneuver cycle had completed. Areview of the DAP performance during this deadband collapse indicated that the reduced -pitchacceleration was causing performance worse than seen in pre-flight simulations which did notincorporate jet modeling error. Since the maneuver cycle had been terminated via reselection ofDAP A, no flight data existed to determine the time that would have been required to fully null theovershoot and determine if convergence would have occurred. To provide confidence in the pre-flight separation analysis, a simulation was performed utilizing the reduced pitch acceleration andverified convergence of the attitude within the time alloted in the separation timeline. To protect fora possible timeline exceedance due to the reduced acceleration, a plan was developed to reselectDAP A if the DAP had not converged on attitude at least 90 seconds prior to going Free Drift tosupport Soyuz separation. This would terminate any on-going maneuvers and damp residual rates.This was discussed with the Rendezvous and Proximity Operations team and determined to be anacceptable option. This contingency procedure was not required.During the crew post-sleep period on FD8, an erroroneous command caused the Mir ACS toattempt to activate. The Shuttle was moded toFree Drift, to avoid a possible force fight, but theMir did not actually issue any control commands because the second logical command to activatethe RCS and gyrodine effector systems had not been issued. Once the Mir system was determinedto be in free drift (indicator mode), the Shuttle was moded to Manual Inertial and then auto tomaneuver to the GO 1.1 separation attitude.A summary of the actual separation timeline is compared to the planned timeline in Table 2. Asplanned the deadband was collapsed to 1 via selection of DAP B12. A maneuver was initiated tonull the attidue errors and a maneuver cycle was observed. The overshoot was nulled and themaneuver terminated within the alloted time. The rate errors were damped to -0.001, -0.023,0.005 Vsec when the DAP was moded to Free Drift. This moding occured approximately twominutes early. The Soyuz separation was nominal at the planned time of PET-15 minutes (wherePET = 0 was Shuttle separation). The CNTL ACCEL was changed to 8 to select the "No Soyuz"mass properties and notch filters. The DAP was moded back to AUTO/B12 approximately 3mintues after Soyuz separation. The early selection of Free Drift allowed anattitude error ofnearly17 to grow requiring the DAP to maneuver back to attitude, which was accomplished withoutaproblem. The maneuver was completed and the rates damped in the reduced time alloted (due tothe late reselection of auto following Soyuz separation) prior to moding to Free Drift to supportShuttle separation. The Shuttle rate errors were only 0.005, 0.005, 0 Vsec at selection of FreeDrift, well below the desired 0.02/sec limit.

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STS-71 Mission ReportCSDL-R-2699July 31,1995Table! - Separation Timeline

EventDAP B 12 DB CollapseFree Drift (Soyuz Sep)Soyuz SeparationDAP AutoFree Drift (Shuttle Sep)Shuttle Separation

Planned PET-29:00-21:00-15:00-12:00-4:000:00

Flight PET-28:00-23.30-15:00-10:00-4:300:00

All times are in min utes, wh ere PET = 0 was S huttle separation.The effects of the Soyuz and Shuttle separations were evident in the DAP rate estimate. The S oyuzimparted a pitch rate on the stack, while the Shuttle separation resulted in a roll rate and a pitch rate.The roll rate indicates the separation sp rings did not symmetrically effect the Orbiter. The DAPwas correctly moded to A9/B9 w ith CNTL ACC EL set to 0 (Orbiter Alone ma ss properties). NoDAP problems were reported during the Shu ttle separation and fly around.Du ring the Soyuz redocking the M ir AC S experienced a problem. An errorenous solar arrayuplink overw rote a segement of com puter memory and moded the control system to free drift. TheMir was nearing the completion of the maneuver to the docking attitude and had reduced themaneuver rates to the pre-completion levels. An attempt to restore the computer memory w asunsuccessful, and the Soyuz re-docked to the Mir immediately. No problems were observed indocking to the freely rotating station. Due to the Mir rotation, adequate power was maintained onthe solar arrays, allowing for a non-dam aging de-spin of the gyrodines. The backup compu tersystem was not utilized and the Mir remained in a drift mode until the system was restored on FD9.After control system reselection, RC S control was utilized until all of the gyrodines had been spunup to nominal operating speeds. The adqua te pow er levels allowed the magnetic supensionsystems on the gyrodines to operate nominally and the spin down and up was performed in acontrolled manner to minimize disturbances on the station.On FD9, a -pitch firing was performed for the Orbiter withou t the Mir to assess the acceleration ofthe minu s pitch VRC S jets (CHIT 44). The results of this test indicated a close m atch between thepredicted and actual accelerations.

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STS-71 Mission ReportCSDL-R-2699July 31,19953. Stability & Contro l Per formanceThe principal flight control concerns in preparation for the STS-71 mated operations were theShuttle's ability to control the mated stack, stabilize the mated system structural vibrations an densure that RC S firings would not exceed loading constraints. C ontrol of the mated stack wasbased on pre-flight simulation u tilizing high fidelity flexible m odels to insure that the Shuttlecontrol system could maneuver the mated stack and maintain attitude hold within acceptablepropellant limits for the planned orientations without exceeding vehicle constraints on RC Sperformance (on time and pulsing) and loads constraints on Alt PRC S delay times. The stability ofthe control system was based on insuring tha t the flexible dynamics of the system would notadversely interact w ith the control system and was achieved by developing notch filters to attenuatethe structural modes effect on the control system feedback loop. Figure 1 provides the "ultrarobust" notch filters utilized during all mated operations. These filters were designed to providerobustness to 30% frequency uncertainty and 9 db amplitude unc erta inty [1]. Finally, the flightcontrol system was configured when using the PRCS to the Alt mode and a delay was enforcedbetween firings to insure that worse case firings can not violate loads constraints. The planned AltPRC S delay time was 10.96 seconds.

Ultra Robust Notch Design

-100 10"Freq (Hz) 10"

Figure 1 - U ltra Robu st Notch Filter Frequency ResponseThe performance of the VRC S control system during the mated portions of the flight was nominaland no failures occured eliminating any requirement to perform closed-loop Alt PRCS control.The system was able to success fully re-orient the mated stack between various required attitudesan d maintian these orientations within the propellant and hardware constraints. No dynamic

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STS-71 Mission ReportCSDL-R-2699July 31,1995interaction instabilities were observed and the effects of the vehicle dyna mics on performance werenegligble. Figure 2 of the estimated rate response from a pitch firing during mated control clearyshow s that notch filter design adequately attenua ted any flexure during VRC S control. A latersection describes that the notch filters also provide adequate attenuation to the dynamic responsefrom the RME 1301 PRCS firings and indicates the pre-flight models accurately represented theflight response.

Rate Est (deg/sec)0.03

0.02

0.01

-0.01

-0.02

-0.031450 1500 1550Time (sec) 1600 1650

Figure! - Pitch Rate Estimate (GMT 180/19:43:35 -180/19:47:30)Figure 3 provides the rate estimate response from the initial maneuver to inertial attitude. Thecontrol system response w as nominal and the autopilot had no difficulty controlling the matedstack. The transient seen near the completion of the maneuver in Figure 3 is due to the group Bpower down completed during the maneuver. An I/O Reset was performed causing the DAP to re-initialize. Adequ ate perform ance w as main tained dur ing this reset, but this re-initialization of theDAP during maneuvers should be avoided wh enever possible.As expected periods of VRC S jet pulsing in the control system phase plane shelf w ere noted duringflight. One period of extremely high jet pulsing was observed immediately following the firstma neuv er to the IO1.4B attitude . This high period of jet pu lsing was exacerbated by the inertialattitude held, the reduced acceleration filter gains and the low control accelerations. Low frequencyperiodic pu lsing of LSD and R5D was observed in the pitch axis shelf as the control system offsetthe orbital disturbance. This was followed by a period of high frequency pulsing of F5R, LSD,R5R and R5D as a roll firing was comm anded. W hen the roll command was terminated the pitch

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STS-71 Mission ReportCSDL-R-2699July 31,1995axis w as driven off the shelf and the pulsing terminated. Analysis of the RC S firings during a 40minute period including this pulsing, indicated that no individual jet w as commanded for more than375 firings, and therefore the firing constraint of 1000 pulses / hour was not in jeopardy of beingexceeded.

0.05

-0.05

R a t e s (deg/sec)

200 400 600 800 1000 1200 1400 1600

0.1: 0IL-0.1

-0.2 J.

10 RESET

200 400 600 800 1000 1200 1400 1600

0.10.05

-0.05 200 400 600 800 1000 1200 1400 1600Time (sees)

Figure 3 - Estimated Rate during Man euver to IO1.1A (GMT 180/13:15 -180/13:40)Prior to the flight ES/RI [2] had predicted tha t the pitch frequencies of the mated Shuttle / M ir maybe am plitude dependent as a result of freeplay in the Orbiter D ocking Sy stem attachment to theOrbiter. Pre-flight analysis [3] show ed the control design w as robust to the non-linearity, but thisamp litude dependency was not observed in the flight results and therefore had no effect on thecontrol performance.During the first periods of inertial attitude hold, h igher than expected negative pitch limit cycle rateswere observed (see Figure 4) and higher than predicted propellant consumption was reported.This was traced to a modeling error in the aft down firing VRCS jet control authority and isexplained in detail elsewhere in this report. The control system demon strated significantrobustness to ma intain it's nom inal capabilities in the presence of a 2 5% low acceleration error.This error impacted control performance by increasing propellant consumption, causing longer

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STS-71 Mission ReportCSDL-R-2699July 31,1995firings during auto maneuvers and increasing the probability of overshoots during the deadbandcollapse prior to separation. The increased propellant consumptionwas caused by transients in theestimation of the disturbance acceleration, while the longer firings and overshoots are caused bythe requirement to fire longer to acheive and null rates. There also was an interaction between thenotch filters and the acceleration error. The notch filters will tend to induce lag between the rateestimate and the actual vehicle rate (rigid body), while an acceleration error can provide lead (lessacceleration than predicted onboard) or lag (more acceleration than predicted onboard). The errorseen during the STS-71 flight, resulted in an over prediction of the acceleration and thereforeestimate lead, which combined with the lag of the notch filters, resulted in nearly ideal rateestimates. Although this assisted in the general stability and control of the vehicle it had an adverseeffect on limit cycle performance as described later.

0.05

-0.05

0.05

-0.05

0.05

-0.05

Rates (deg/sec)

0 500 1000 1500 2000 2500 3000 3500

0 500 1000 1500 2000 2500 3000 3500

0 500 1000 1500 2000 2500 3000 3500Tim e (sees)

Figure 4 - Limit Cycle Response DuringIOHold (GMT 180/19:20 - 20:20)While maintaining the GO1.2 attitude during the crew sleep period following FD4, F5R wasannunicated failed leak. This false annunciationwas caused by the stable GO attitude requiring aninsufficeint number of jet firings to maintain adequate forward je t temperatures. To avoid thisproblem, the GO attitudes were biased by two degrees to increase the number of jet firings during

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STS-71 Mission ReportCSDL-R-2699July 31,1995FD5. Observation of the jet tempartures while maintaining GO holds indicatied that a falseannunication was again possible during the crew sleep period. To avoid this, the deadband wasreduced to 3 (from 5) to increase the jet firing frequency, while minimizing the impact topropellant consumption. Since this reduction did not insure jet firings, because the deadband (3)was still larger than the attitude bias (2),a procedure was developed to allow the ground tocommand DEU equivalents to reduce the deadbands further. This deadband reduction, to 1,would insure jet firings. Once the jets had warmed to an acceptable level a second commandwould be issued to reinstate the 3 attitude deadband. Analysis [4] had been completed pre-flightto support separation which indicated that it was acceptable to reduce the attitude deadbands as lowas 1, if the maneuver rate was reduced to O.r/sec. The assumptions and guidelines of thisanalysis were followed in developing this jet warming deadband collapse. Although the DEUequivalent deadband collapse was not required during sleep periods, a deadband collapse wasmanually performed subsequent to the completion of the free drift DTO 1120.

0.02

-0.02

Rate Est (deg/sec)

500 1000 1500 . 2000 2500 3000 3500

Q.-

500 1000 1500 2000 2500 3000 3500

0.02-0

-0.02500 1000 1500 2000 2500 3000 3500T i m e (sec)

Figure 5 - Limit Cycle Response DuringGOHold (GMT 181/13:00 -181/14:00)

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STS-71 Mission ReportCSDL-R-2699July 31, 1995

4. Increased Propellant C o n s u mp t i o n SummaryDuring the first periods of inertial attitude hold, higher negative pitch limit cycle rates and increasedpropellant consumption were observed. Table 3 provides a comparison of propellant consumptionto pre-flight predictions for the initial periods of inertial attitude hold. The IO1.1A attitude shows a70% increase over perflight predictions while most other attitudes remained close. Although pre-flight simulations had not been performed for comparison, significant propellant consumption wasalso observed at the IO1.1B attitude. Data review also indicated that the DAP negative pitch limitcycle rates were higher than desired and higher then seen in pre-flight simulations. To assess thelimit cycle performance, a variable downlist patch was implemented to add the roll and pitchundesired accelerations, which indicated that the autopilot was commanding rates to offset aperceived disturbance as seen in Figure 6. This perceived disturbance was the result of a negativepitch acceleration approximately 25% lower than the acceleration calculated onboard. The flightpitch acceleration was derived from the rate as shown in Figure 7. Similar calculations on thepositive pitch response indicated acceleration close to that calculated onboard. Simulationscompleted with the aft-down firing VRCS acceleration reduced by 25% duplicated the flightperformance [5]. Several factors that could contribute to the the errors seen in the negative pitchacceleration, including mass property errors and jet modeling errors were investigated, and severalpossible solutions to resolve the propellant increase were assessed, including updating to lessrobust notches, modification of DAP deadbands, and patching (GMEM) the software. Since theRussians agreed to remain at the GO attitudefor longer periods of time, which provided improvedpropellant consumption and increased propellant margins, no effort was made to implement any ofthe software solutions assessed. Analysis of the derived accelerations and the various causesindicate the principal contributor to the modeling error was inaccurate modeling of the Shuttleplume self impingement. This has been partially validated by off-line analysis completed post-flight [6]. To prevent a recurence of this problem on future Shuttle/Mir flights an investigation ofthe plume modeling errors will be undertaken and an analysis of enabling the inhibit logic in theDAP acceleration estimator will be completed to support STS-74.

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STS-71 Mission ReportCSDL-R-2699July 31, 1995Table 3 - Actual vs. Predicted Propellant C onsumption (Ibs/hr)

AttitudeIO1.1IO1.1A(with -25%)IO1.2(with -25%)GO 1.2GO2.1(water dump)IO1.4BIO1.1B

FlightTot26.338.425.93.513.6

22.754.9

Fwd8.510.78.3

1.44.5

8.818.2

Aft17.827.717.62.19.1

13.936.7

PredictedTot

25.422.839.626.530.66.017.3

N/AN/A

Fw d9.69.012.39.410.02.77.1

N/AN/A

Aft15.813.827.317.120.63.310.2N/AN/A

x10 Undes Acce l (deg/sec/sec)

0.5

-0.5-1 1000 2000 3000 4000 5000 6000

x 1 0

0.80.6f0.4

0.21000 2000 3000Time (sec) 4000 5000 6000

Figure 6 - Undesired Accelerations (GMT 180/21:00 -180/22:40)

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STS-71 Mission ReportCSDL-R-2699July 31,1995Rate Est (deg/sec)

0.02

ay = dw / dt = -0.05 / 26.08 = 0,0019 deg/sec/sec

-0.04 30Time (sec)

Figure 7 - Negative Pitch Response (GMT 180/17:59 - 180/18:00)

4.1. Control Response to Acceleration DifferenceThe increased propellant consumption was caused by the acceleration difference adverselyimpacting the control systems estimate of the disturbance acceleration. Toprovide the desired one-sided and two-sided limit cycles seen in Figure 8, the DAP estimates the slowly varyingaccelerations of gravity gradient, aerodynamic, euler coupling and venting disturbances. In theabsence of large disturbances the control system will commandjet firings resultingin low rate two-side limit cycles, but when disturbances are present the DAP will command efficient one-side limitcycles. The estimate of the undesired disturbance acceleration is the principal component used todetermine the S11 swithing curve which determines the limit cycle target rate. The error betweenthe actual negative pitch acceleration and that calculated onboard results in a large transient in theestimate of the disturbance acceleration during the firing, as the DAP perceives a large disturbancecausing the vehicle to respond slower than predicted. This transient, which decays once the firinghas terminated, drives the target rate down in the phase plane to induce a one-side limit cycle tooffset the perceived disturbance, but since a real disturbance is not present, this results in the highrate two-sided limit cycle seen in Figure 7. This highly inefficeint limit cycle results in morefrequent firings, wastingaf t propellant to command the higher rates an d then forward propellant toremove them when the opposite attitude deadband is reached.

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STS-71 Mission ReportCSDL-R-2699July 31,1995A software solution to resolve these limit cycles by inhibitingthe acceleration calculation during jetfirings was implemented in the OI-23 software, but had been disabled for the STS-71 flight. Thisinhibit which significantly reduces the acceleration transient in the presence of the jet firingacceleration errors, was disabled to avoid an unstable interaction with the Alt PRCS tail only mode.Pre-flight analysis [7] indicated the roll modes of the mated stack could be sufficeintly excited tocorrupt the acceleration filter during periodic Alt PRCS firings, a phemonena noted duringfeasibility analysis of Shuttle control during Space Station assembly[8].

Attitude Error (deg) Attitude Error (deg)

FigureS - Ideal DAP Limit CyclesPhase Plane

Figure 9 - STS-71 DAPLimit Cycles (GMT 180/19:20 -180/20:20)

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STS-71 Mission ReportCSDL-R-2699July 31,19954.2. Analysis of Modeling ErrorsReview of the possible modeling errors has indicated the most likely source of the error is OrbiterRC S self impingement. Although,not believed to be principal contributors to the problem, severaladditional errors sources were investigated, including jet mounting errors, jet thrust errors andmass property errors. During the flight, data was obtained for several je t firings and Orbiter elevenlocations (see Table 4).

Table 4 - Pitch Acceleration byEleven Postion (7sec2)Eleven+21.60.0-7.5

I-Load-0.0026-0.0026-0.0026

Actual-0.0017-0.0019-0.0022

Jet mounting an d thrust errors were eliminated as principal contributors. The MER propulsiongroup reported that the thrust profiles of the VRCS jets were all nominal. An analysis of themounting error [9] required to induce the acceleration differences seen indicated this was anunlikely source. If no thrust error was present, it would take 20 mounting error, while for a 15%reduced thrust, a 10 mounting error was still required. These errors were determined to beoutside of feasible tolerances.Mass property errors were eliminated as principal contributors. All indications from the GOattitude holds were that the GO attitudes based on pre-flight predicted mass properties were verynear to the minimum gravity gradient attitudes providing confidence in the inertia values. TheRussians also reported [10] that based on their estimates, the mass properties were within 3% ofthe pre-flight predictions. Finally, an analysis to determine the combination of pitch inertia changeand X eg shift that could result in a 25% acceleration error in minus pitch and no error in positivepitch was completed [11]. The derived values resulted in a non-physical inertia value, as therequired pitch inertia (lyy) was greater than the sum of roll (Ixx) and yaw (Izz) inertias.:All indications are the principal contributorto the acceleration difference is a modeling error in theself impingement for the aft down-firing VRCS jets. As the eleven w as repositioned the jetacceleration also changed, indicating that the plumeeffects varied as a function of eleven, which isno t included in the current model. A long VRCS firing was completed following undocking,which indicated the model provides valid answers for nominal Orbiter configurations. The VRCS

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STS-71 Mission ReportCSDL-R-2699July 31,1995jet model has a value of force and torque abou t a reference point. The torque value is thentranslated to the actual center of gravity by summing the reference torque and the cross product ofthe difference between the center of gravity and the reference point and the reference force. Figure10 provides the relationship betw een the C G for the Shu ttle / M ir stack, the reference point and theOrbiter alone C G. It is obvious there was a much larger offset between the mated CG and thereference point, than for Orbiter alone, which would increase the significance of the referenceforces. Rough calculations indicate it only takes a small amount (4-6 Ibs) of unmodeled X force toprovide the differences seen in flight.To support the hypothesis that plume impingement was causing the error, EG3 completed ananalysis to determine the plume impingem ent values based on the updated plume model an dupdated Orbiter geometry. Preliminary results indicate the model shou ld be updated and the valuesseen in flight fall within shadowing tolerances of the newly calculated data. The results alsoindicated there is a larger X force than predicted by the previous model. It is currently planned tovalidate the updated plume model against additional flight data (from STS-74 and possibly STS-76) prior to updating the onboard software Kloads of the jet force and torque.

CG Locations vs Ref CG

-45

"uc

X

*X

2

Reference CGSTS-71 Mated CGHST-61Cap/RelHST-31 App Dply/y\ \

0 40 6

I +\

' X: K

0 80 1CXov (ft)

11

x) n

/

20 14

Figure 10 - Center of Gravity Locations

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STS-71 Mission ReportCSDL-R-2699July 31, 19954.3. Analysis of Possible Control System Solut ionsSeveral updates to the control configuration and/or operations were assessed during the flight tomitigate the effects of the decreased pitch acceleration. The only solutions that were determined toprovide adequate resolution required patches or uplinks to the software. Given adequate Mirpower and Shu ttle propellant in the GO a ttitudes, none of these solutions were implemented. Thefollowing provides a brief summ ary of each option assessed.Decreasing the rate deadband would have resulted in an indeterminate impact on propellantconsumption. It would have reduced the duration of the -pitch firings, but may have causedadditional roll and/or y aw firings. Add itionally, it wou ld have reduced flight control stabilitymargin.

Decreasing the attitude deadband wo uld have reduced the ma gnitude of the -pitch firings, butincreased limit cycle frequency. More propellant may have been required to control roll and yaw.The deadband could not be decreased for maneu vers, unless the man euver rate was also decreased.This decrease in maneuver rate w ould have increased m aneuver time.Uplinking new notch filters would have decreased propellant consumption in general, but wouldnot explicitly minimize the effects of the disturbance transient. It would have decreased themagnitude of the -pitch limit cycle if the notch induced lag were reduced significantly. To achievea performance improvement stability robustness would been compromised. Although RM E dataindicated the pre-flight predictions were close, u ncertain ty remained in the system due to thepossible presence of freeplay.A single variable GM EM could hav e been used to set the acceleration filter inhibit counter to 31.Reenabling the inhibit logic would significantly reduce the transients seen in the disturbanceacceleration by disabling the calculation of the distrubance durin g jet firings. This w ould havesignificantly improved propellant consumption, but may have had an adverse effect on Alt PRCScontrol if required to offset a VRCS failure. Analysis of this solution for STS-74 have indicatedlarge Alt PRC S transients may have been encoun tered, and a filter inhibit count of 2 is currentlyplanned for STS-74 to reduce the VRC S transient during the firing and the Alt PRCS transients ofperiodic firings.The jet force and moment K -loads could hav e been updated via GMEM to provide a closer matchto flight data. This wo uld have required modifying twelve parameters (Fx, Fy, Fz and MX , My,

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STS-71 Mission ReportCSDL-R-2699July 31,1995MZ for both jets). Additionally, it was unknown what the correct values were and updating toincorrect values may have adversely impacted separation and "Obiter Alone" operations.


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STS-71 Mission ReportCSDL-R-2699July 31, 1995X 1 C T Power Spectral Density (Unfiltered)

AngularAmplitude(deg)

O*OlO>

\AID'Frequency(Hz)

Figure 12 - PSD of detrended pitch attitude.

0.02

0.015

0.010.005

5,


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STS-71 Mission ReportCSDL-R-2699July 31,1995Similar results were derived for the higher frequency roll modes which were shown to beinconsequential to the attitude control system.Effects of Firings at the Alt Delay PeriodOne of the primary goals of Part 2 of the test was to show that firings spaced by the planned Altmode delay time w ould not resonate the primary modes. Figure 14 shows the flight results fromthe second set of pitch firings in part 2. Exam ination of the filtered attitude and rate plots in thefigure shows that firing at the Alt mode delay time (10.96 seconds) reduced the amplitude of theresponse, and thus did not further excite the mode. Firing pairs in other axes appeared to hav enegligible effects on the other modes.

< 0.02o -0.02S (&"5 5i0.02

0Q.T3 -0.02

0.02

"8 -0.028 (

10 15 20Time (sec) 25 30

10 15Time (sec) 20 25 30

10 15Time (sec) 20 25 30

Figure 14 - Effect of negative pitch firings at 10.96 sec interval.Evaluation of Notch Design Based on Flight DataFigure 15 shows the I-loaded notch design. These notche s were created to be robust to 9 dBamp litude variations and 30% frequen cy variations in the model. The asterisk on the plotrepresents the attenua tion required to guaran tee stability against the observed mode at the observedfrequency. The horizontal line adds 6 dB amp litude uncertainty and 20% frequency uncertainty to

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STS-71 Mission ReportCSDL-R-2699July 31, 1995this mode. These were the nominal uncertainty factors used fo r baseline designs. The plotindicates that the notch filters were appropriately placed an d were sufficiently conservative.C onservatism in the design could have been reduced with a notch redesign/uplink, bu t this was notrequired since the improved propellant margins would have been negligible.

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STS-71 Mission ReportCSDL-R-2699July 31,19956. DTO1120 - Free Drift TestThe free drift test, DTO1120, was initiated at 184/09:30:00 GMT. The purpose of this test was todemonstrate the dynamic stability of the mated stackatgravity gradient stable attitudes to determinethe feasibility of planning long duration periods of free drift to conserve propellant consumption.The stack orientation must remain stable to insure adequate Mir power generation from the solararrays, ground communications and Orbiter thermal requirements. Control of the mated stackwastransferred to the Mir at the biased GO1.1 attitude. The Mir nulled attitude and rate errors about thisattitude, dumped momentumand then moded to drift (indicator mode). The mated stack was thenleft to drift for approximately 3 orbits. As seen in the plot of the attitude error from the predictedstable attitude, Figure 16, the Shuttle pitch and roll attitudes remained within the five degree errorpredicted pre-flight, but the yaw axes deviated to near eight degress. All three axes had oscillationscentered withina degree of the predicted stable attitude. A review of the rates (Figure 17) showedthat several distinct rate changes occured duringthe test. Although the attitudes did deviate furtherthan predicted pre-flight, they showed a stable nature indicating that it may be possible to utilizefree drift to conserve propellant when stable attitudes provide sufficeint station power. This will befurther assessed with a longer drift period on STS-74.

10

-5

Attitude Error (deg)

2000 4000 6000 8000 10000 12000 14000 16000

t10

-10

2000 4000 6000 8000 10000 12000 14000 16000

"0 2000 4000 6000 8000 10000 12000 14000 16000Time (sec)

Figure 16 - Shuttle Attitude Deviation Free Drift Test (GMT 184/09:30 184/13:45)

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0.02o 0

-0.02

0.01

-0.01

0.01

Rate Error (deg)

2000 4000 6000 8000 10000 12000 14000 16000

2000 4000 6000 8000 10000 12000 14000 16000

-0.01-0.02 2000 4000 6000 8000 10000 12000 14000 16000Time (sec)

Figure 17 - Shuttle Rate Errors Free Drift Test (GMT 184/09:30 184/13:45)Post-flight review of the drift test results has resolved some of the issues with the test, but hasbeen unable to duplicate the exact test results to date. A contributor to the larger yaw attitudedeviation is the non-sym metrical n ature of the Mir solar arrays. Prior to flight several problemswere encountered in configuring the solar pane ls for STS-71. The +Zb Spectr array was unable tobe deployed, the -Yb Krystall array was not completly retracted and the -Zb Kv ant-2 array motionwas restricted to a "feathered for approach" orientation. Each of these contribute additionalaerodynamic disturbance in the Shuttle yaw axis. An updated model of the aerodynamics wasdeveloped indicating this should have contributed a negligble vehicle torque in yaw ofapproximately, 0.0109sin(cot)+0.0235 ft-lb, where (fl is orbital rate. The distinct rate change inpitch was traced to an unscheduled check out of the Soyuz during the test resulting in a firing of theSoyuz reaction control system. It appears the the roll/yaw rate change may be related to the effectsof sunrise on the solar arrays, or possibly another disturbance occuring at an orbital period.Further analysis w ill be conducted on STS-74 to determine the feasibility of long periods of drift toconserve propellant du ring International Space Station operations.The Russians have also assessed the results of the drift test [15] and have been unable tocompletely duplicate the results. They did conclude that the Mir ACS had not fully nulled the rates

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STS-71 Mission ReportCSDL-R-2699July 31, 1995prior to selection of indicator mode, and the time allocated to null the rates will be increased forSTS-74 to insure m inimal initial transients.

7. Mir ACS PerformanceMir control performance throu ghou t the joint operations was nominal. The Mir m aintained the IO2attitude, until the Sh uttle approached a range of approxim ately 300 ft. At this range, w hile theShuttle was station keeping the Mir maneuvered to the OSC-5 docking attitude at GMT 180/10:55,arriving at the attitude at GMT 180/11:12, approxim ately 50 minutes ahead of schedule. At a rangeof approximately 50 feet the gyrodines werre manually desaturated from Hxyz=-787, 14, 2012Nmsec to Hxyz=192, 995, 394 Nmsec to minim ize the probability of S huttle plumes inducingsaturation during the final approach. Alth ou gh , the resultan t attitude and rate deviation fromdesaturation would not have affected piloting for the STS-71 configuration, the manualdesaturation demonstrated the capability for STS-74 and subsequ ent flights. The m om entum levelat capture, H Xyz=71 5, 502, 170 Nmsec, was well below saturation value (~5700 Nmsec RSS).The Mir control system performance during the mated operations w as nominal. The performancewas monitored via Shuttle downlist of the rate and attitude errors. At 183/10:13, the Mirmaneuvered from the GO2.1 attitude to the GO1.1 attitude utilizing RC S. GO1.1 w as held undergyrodine control for approximately 85 minu tes. The M ir then performed an RCS maneuv er to theIO1.2 attitude and maintained that attitude un der gyrodine control for nearly 3 hours. The M irdemonstrated it could maneu ver the m ated stack utilizing the RC S and m aintain both inertial andgravity gradient attitude holds with the gyrodins. Figures 18, 19 and 20 provide the rates duringthe IO and GO control periods. Note: All of the data is in Shuttle body axes reference, w hereXs=Yb,Ys=-ZbandZs=-Xb.During the inertial hold the gyrodines required desaturation periods at least fou r times an orbit, asopposed to the RSC -E pre-flig ht predictions of twice an orbit. Given the availability of only 9gyrodines for control and the twice orbital rate frequency of the gravity gradient disturbing torque,this could be expected. Additiona lly, Mir inertial platfo rm misalignmen ts were o bserved in theShuttle attitude error data. Given the tight poin ting control of the Mir gyrodines, most of theattitude error observed is due to misalignments between the Shuttle and Mir inertial platforms. TheShuttle IMU's were aligned during the flight and were reported to be quite accurate, w hile it wasknow n tha t the M ir was relying on the Sun sensors and the magnetom eter to provide setting of thenavigation basis. During the IO1.2 control period the data (Figure 21) indicated a staticmisalignment of -0.25, 1.5 and 2.75 degrees in the S huttle pitch, yaw and roll axes respectively,

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STS-71 Mission ReportCSDL-R-2699July 31,1995while during the GO1.1 control period the misalignments were cyclic with orbital rate (Figure 22).A review of the Mir Xb desaturation control in Figure 19, indicated that the Mir gyrodine controlsystem bandwidth and damping were lower than the values derived from the control gainsprovided to NASA. These gains are scaled by a constant value of inertia in the gyrodine controllaw to provide the appropriate bandwidth as a funciton of varying inertia. The results from thisflight indicate that the inertia values were not updated in the gyrodine control law and the loadedroll inertia was 1/4 of the actual mated Shuttle/Mir roll inertia. The derived bandwidth from theflight data was 0.007 Hz compared to an expected value of 0;014 Hz based on the controller gainsprovided by RSC-E.Additional comparisons will be made to validate the NASA model of the Mir control system.These results should be able to provide good comparisons for the checkout of the RCS hold andmaneuver capability and the gyrodine hold capability, including the response to automaticdesaturation firings.

0.10.05

>0

-0.05

0.1c 0

-0.2(

0.1

"-0.1 h-0.2

Rate (deg/sec)

2000 4000 6000 8000 10000 12000

2000 4000 6000 8000 10000 12000

1 T^i^j i2000 4000 6000 8000Time (sec) 10000 12000

Figure 18 - Inertial Hold Rates (GMT 183/11:40 -183/15:00)

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STS-71 Mission ReportCSDL-R-2699July31,19950.01

e o

Rate (deg/sec)

-0.011000 1500 2000 2500 3000 3500 4000 4500 50000.07

0.065Q.

0.0611000 I I1500 2000 2500 3000 3500 4000 4500 5000

0.01

-0.011000 1500 2000 2500 3000 3500 4000 4500 5000Time(sec)

Figure 19 - Gravity Gradient Hold Rates (GMT 183/10:10 -183/11:40)

0.01 Rate (deg/sec)

-0.012000 3000 4000 5000 6000 7000 8000 9000 10000 11000 120000.01

-0.0' J o1JjL-u -v|p"

i

"""*ww* .iu.JtnU NT v . x k ju/* * - | p -wriOO 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000

0.01

-0.012000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000T i m e (sec)

Figure 20 - Desaturationsduring Inertial Hold (GMT 183/11:40 -183/15:00)-29-


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2.92.82.7

Alt Err (dag)

M4pi ite3000 4000 5000 6000 7000 8000 9000 10000

-0.15-0.2.-0.252000 3000 4000 5000 6000 7000 8000 9000 10000

1.6ll.

12?)00 3000 4000 5000 6000 7000 8000 9000 10000Time (sec)

Figure 21 - Inertial Mir Attitude Misalignment (GM T 183/11:40 -183/15:00)At t E r r (deg)

"lOOO 1500 2000 2500 3000 3500 4000 4500 5000

0.4

!0.2

1000 1500 2000 2500 3000 3500 4000 4500 5000

-21000 1500 2000 2500 3000 3500 4000 4500 5000Time (sec)

Figure 22 - LVLH Mir Attitude Misalignm ent (GMT 183/10:10 -183/11:40)

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8. Conclusions & Lessons LearnedThe STS-71 Shuttle/Mir flight control joint operations were extremely successful. Both the Shu ttleand M ir control systems demonstrated the capability to perform mated stack reorientation an dattitude maintenance. The results of the flight indicate that the methods and process used areadequate to perform analysis and flight of the Internation al Space Station. All pre-flight objectiveswere succesfully completed including :

1.) Demonstrated Shu ttle can stabilize and control mated stack.2.) Demonstrated Mir can stabilize and control m ated stack.3.) Demonstrated Mir m anua l desaturation capability.4.) C ompleted RME1301 to validate structural models for control design and analysis.5.) C ompleted DTO1120 to dem onstrate ability to maintain the mated stack in a stable gravity

gradient attitude to conserve control system propellant.6.) Demonstrated capability of Shu ttle to collapse attitude deadbands for separation.7.) Successful performance of post contact thrusting software.

The results of the flight also have demonstrated m any of the Shuttle capabilities required for controlof the early International Space S tation assembly flights. Also, lessons were learned that can beapplied to future Shuttle/Mir flights.

1.) Substan tial structural bending was observed as predicted during the PRC S jet firings.2.) Notch filters were able to adequately atte nu ate bending, w hile maintaining acceptable flight

control performance.3.) U pdated modeling is required to account for RC S self imping emen t.4.) Mated stack can be maintained in stable orientations, but larger deviations than predicted

may be encountered due to unmodeled effects.5.) Frequency identification tools can adequately identify observable vehicle structural

dynamics.6.) C ontrol system upgrades developed for Space S tation Assem bly perform as predicted.

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STS-71 Mission ReportCSDL-R-2699July 31, 19957.) Process used for development of flight control system mission specific designs worked

well and can be used for the ISS assembly analysis.8.) Margin should be built into the ISS assembly design to account for unknown modeling

errors.9.) Tests of ISS assembly control designs and operations should be performed on later

Shuttle/Mir flights.10.) D uring maneuv ers avoid operations that cause D AP reinitialization.

Based on these lessons learned some modifications will be made to future mission designs.1.) An analysis will be com pleted to assess reenabling the acceleration filter inhibit logic until

updated jet force an d mom ent K-loads can be verified an d incorporated into the flightsoftware.

2.) Notch filter robustness for STS-76 and su bseque nt missions will be reduced in am plitudebased on the results of RME1301 perfo rmed on STS-71 and STS-74.

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STS-71 Mission ReportCSDL-R-2699July 31, 1995

9. References1. Hanson, D., Zimpfer, D., and Jackson, M., "STS-71 Mated Mir 05 Right Cycle NotchFilters", Draper Laboratory Memo E41-95-030, March 14, 1995.2. Yahata, S., datafax on Rockwell assessment of freeplay gaps by S. Lo dated 5/19/95,

faxed June 7, 1995.3. Zimpfer, D. and Kirchwey, K., "Risk Mitigation of Freeplay Violation of Notch Filter

Design Criteria", Draper Laboratory Memo E41-95-093, June 20,1995.4. Zimpfer, D., "Shuttle Control during STS-71 Soyuz/Shuttle Separation Operations",

Draper Laboratory Memo E41-95-111, June 27,1995.5. Kirchwey, K., "Simulation of mated inerital hold with reduced VRCS acceleration", Data

fax to D. Zimpfer, June 30,1995.6. Park, J., "VRCS Plume Data", Electronic Mail to D. Zimpfer, August 14, 1995.7. Kirchwey, K., "Results of OCFS Simulation Verification of Nominal STS-71 Orbiter/MirConfiguration Flight Control Performance", Draper Memo E41-95-029, February 15 ,1995.8. DeBitetto, P., "Analysis of Disturbance Acceleration Estimation for Space StationFreedom", Draper Memo ESC-93-109, March 28, 1993.9. Kirchwey, K., "Graphical Representation of Jet Mounting Error", Data Fax to D. Zimpfer,July 1, 1995.10. Kasnecheev, Y., "RSC-E Assessment of Mir Control Performance", Phone Conversation

with D. Zimpfer, July 3, 1995.11 . Kirchwey, K., "Non-plausible Inertia Values", Phone conversation with D. Zimpfer, July

1, 1995.12 . Jackson, M ., "Identification of Mated Shuttle/Mir Structural Characteristics for FlightControl Analysis During RME 1301 on STS-71", Draper Laboratory Memo, E41-95-122,

August 13, 1995.13. Henderson, T., "Updated MIR Models [11/30/94]", Draper Memo ESC-94-207,November 30, 1994.14 . Lepanto, J., "Description of the frequency identification tool", Draper Memo SSV-95-046,May 18, 1995.

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STS-71 Mission ReportCSDL-R-2699July 31,199515. Sazonov, V., Belyaev, M., Efimov, N., Stazhkov, V., "Passive Movement of Mir-AtlantisStack in the Gravitational Orientation M ode", RSC -E Report, Au gust 1995.16. WG -3/RSC E/NASA/3402-1, Shuttle-M ir Physical C haracteristics STS-71", M arch 1995.17. WG -3/RSC E/NASA/3408-1, C ontrol of Shu ttle and Mir in Mated C onfiguration STS-71",March 1995.18 . WG -3/RSC E/NAS A/3409-1, Structu ral Loads an d M utual C onstraints STS-71", March1995.19. WG -3/RSC E/NAS A/3243-1, Attitude Plan STS-71, March 1995.20 . Blagov, V., "Condition/Status of the onboard System of the Mir Station", Data Fax to R.Castle, July 5, 1995.21. Friend, R., "Shuttle/Mir Mated Free Drift DTO Simulation Analysis" , Rockwell

International I nterna l Letter 292-600-JO-94-92, October 26,1994.22. RKK Energia, "Brief Summary of the Results of Shuttle/Mir M ated Free Drift SimulationAnalysis", Integration M eeting Data Transmittal, December 1994.23. Zimpfer, D., "STS-71 On-orbit Flight C ontrol D ata Sum mary" , Draper Lab memo ESC-94-097, June 15, 1994.24. Hanson, D.,"STS-71 Mated Mir 05 Drift Channel Stability Screening," Draper MemoESC-94-152, September 9, 1994.25. Jackson, M., "Assessment of aerodynamic torques on mated Shuttle-Mir configuration forSTS-71", Draper Lab mem o ESC -94-163, October 11,1994.26. Zimpfer, D., "Updated STS-71 Flight Cycle On-Orbit DAP I-loads", Draper Memo E41-95-017, January 23, 1995.27. Hanson, D., Zimpfer, D., and Jackson, M., "STS-71 Mated Mir 05 Flight Cycle NotchFilters", Draper Memo E41-95-030, March 14,1995.28. Dagen, J., "Proposed Revisions to the Sh uttle PRC S Test Firings", Message 4385, April26, 1995.29. Zimpfer, D., "STS-71 Flight Version Daploads", Draper Memo E41-95-060, April 27,1995.30. Barrington, R., "STS-71 PCS Final Load SAIL Test Report" Draper Memo SSV-95-040,May 18,9531. Zimpfer, D., "Effect of Inertia Uncertainty on STS-71 Mated Shuttle / Mir Attitudes",Draper Mem o E41-95-066, May 19,1995.32. Jackson, M., "STS-71 M ated Shuttle/Mir Parametric Stability Study" , Draper Mem o E41-95-076, SSV-95-045,.May 25, 1995.

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STS-71 Mission ReportCSDL-R-2699July 31, 199533 . Harrington, R. and Zimpfer, D.,, "STS-71 New DAP Values for No Soyuz", DraperLaboratory Mem orandum, RDB-95-012, June 14, 1995.34 . Willms, R., "Results of HI Deadband Collapse Simulation", Data transmittal to D.

Zimpfer, July 3, 1995.35. Hanson, D., "U ltra-less Notch Design,", Electronic Mail to D. Zimpfer, June 30,1995.

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10. AttachmentsAttachment 1 Attitude TimelineAttachment 2 Flight CHIT'sAttachment 3 Flight Data Summary

-36-


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Attachment 1

Attitude Timeline for Mated Operations

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AtMET/GMT23001/17:28:00 MET180/13:00:19 GMT

26001/17:48:00 MET18:05:10180/13:20:19 GMT37:29

27001/18:39:00 MET58:03180/14:11 :19 GMT30:22

28001/20:44:41 MET45:46180/16:17:00 GMT18:05

29001/23:04:50 MET06:36180/18:37:09 GMT

38:5530001/23:45:02 MET46:48180/19:17:21 GMT19:07

31 002/17:10:00 MET27:27181/12:42:19 GMT59:46

32003/12:00:00 MET17:37182/07:32:19 GMT49:56

33003/16:00:00 MET14:48182/11 :32:19 GM T47:07

34004/11:30:00 MET40:00183/07:02:19 GMT12:19

35004/14:38:00 MET183/10:10:19 GMT

36004/14:40:00 MET50:00183/10:12:19 GMT22:19

** * ALL ATTITUDES*** PYR EULER SEQUI

M N V R OPTION

INR TL R=244.00M N V R P=109.00Y= 80.00

INR TL R=127.00MN V R P=353.00Y=311.00

INRTL R=121 .00M N V R P=345.00Y=319.00

INR TL R=130.00M N V R P=347.00Y=305.00

INR TL R = 1 2 1 .00M N V R P=345.00Y=319.00

TGT=2BV=5Po240.00Y= 0.00OM= 0.00INR TL R=136.00M N V R P= 0.00Y=304.00

TGT=2BV=5P=238.00Y= 0.00OM=180.00TGT=2BV=5P-240.00Y = 0.00OM=270.00TGT=2BV=5P=240.00Y= 0.00OM=270.00TGT=2BV=5P=240.00Y= 0.00OM=180.00

i t u d e T i m e l i n eb'APA6INRTALT

A12AUTOV E R N

A12AUTOV E R N

A12AUTOV E R N

A12AUTOV E R N

A12AUTOV E R N

A12AUTOV E R N

A12AUTOV E R N

A12AUTOV E R N

A12AUTOv e n n

A 1 2AUTOV E R N

A 1 2AUTOV E R N

RATE 0.2000DB AT 5.00DB RT 0.070

RATE 0.1500DB AT 5.000DB RT 0.050

R ATE 0.1500DB AT 5.000DB RT 0.050

R ATE 0.1500DB AT 5.000DB RT 0.050

R A T E 0.1500DB AT 5.000DB RT 0.050

R ATE 0.1500DB AT 5.000DB RT 0.050

R ATE 0.1500DB AT 5.000DB RT 0.050

R ATE 0.1500DB AT 5.000DB RT 0.050

R ATE 0.1500DB AT 5.000DB RT 0.050

RATE 0.1500DB AT 5.000OB R l 0.050

RATE 0.1500DB AT 5.000DB RT 0.050

R ATE 0.1500DB AT 5.000DB RT 0.050

E/SSUNR 28.4P 167

SUNR 180P 33

SU NR 360P 137

SUNR 0P 127

SUNR 360P 140

SUNR 0P 127

EAR THR 180P 120

SUNR 360P 147

EAR THR 180P 122

EARTHR 180P 120

EARTHR 18 0P 120

EAR THR 180P 120

R EF ATT/REMARKSIN RTL R=258.02HOLD P= 40.51Y=290.26

LVLH R= 0.00P= 30.00Y= 0.00

LVLH R=180.00P=148.00Y= 0.00

LVLH R= 90.00P= 90.00YaSOO.OO

LVLH R= 90.00P= 90.00Y=300.00

LVLH R=180.00P=150.00Y= 0.00

EVENTDOCKED

10 1 .4BPOST DOCKHATCH CHECK

10 1.1

10 1.1A

10 1.1BMIR VIP Event

10 1.1A

GO 1.2

10 1.1

G O 1 . 1 B i a s e d

GO 2.1Wa s t e Dump

H/0 to MIR

GO 1.1 - MIR

N MEAN OF 1950 *** 5-1 AS FLOWN ATL=NCE **

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A t t i t u d e T i m e l i n eMET/GMT37004/16:13:00 MET30:03"""1H33SH * H f

3$004/19:23:00 MET04183/14:55:19 GMT23

39005/02:00:00 MET13:17183/21:32:19 GMT45:36

40005/13:45:00 MET;184/09:17:19 GMT

41 005/13:46:41 MET184/09:19:00 GMT

42005/18:00:00 MET

184/13:32:19 GMT

43006/02:30:00 MET45:58184/22:02:19 GMT1 8 : 1 7

44006/11:48:00 MET51:59185/07:20:19 GMT24:18

45006/12:00:00 MET11:09185/07:32:19 GMT43:28

46006/15:23:00 MET

185/10:55:19 GMT

47006/15:37:00 MET

185/11:09:19 GMT

M N V R OPTIONIN RTL R = 54.61MNVR P=111.03Y314.55

IN RTL R = 55.00M N V R P=111.00Y=315.00

TGT=2BV=5P=238.00Y= 0.00OM=180.00

TGT=2BV=5P=238.00Y= 0.00OM=180.00

TGT=2BV =5P=238.00Y= 0.00OM=180.00TGT=2BV=5P=238.00Y= 0.00OM=180.00

IN RTL R = 57.29M N V R P=111.77Y=320.04

INRTL R= 93.00M N V R P=129.00Y=339.00

TGT=2BV=5P=240.00Y= 0.00OM=180.00

DAPA 1 2AUTOV E R N

A 1 2AUTOV E R N

A 12AUTOV E R N

A 1 2AUTOV E R N

A1 2F R E EV E R N

A 1 2AUTOV E R N

A 1 2AUTOV E R N

A 1 2AUTOV E R N

A 12AUTOV E R N

ASI N R TV E R N

R A T E 0.1500DB AT 5.000DB RT 0.050

R A T E 0.1500DB AT 5.000DB RT 0.050

RATE 0.1500DB AT 5.000DB RT 0.050

R ATE 0.1500DB AT 5.000DB RT 0.050

R A T E 0.1500DB AT 5.000DB RT 0.050

R A T E 0.1500DB AT 5.000DB RT 0.050

R A T E 0.1500DB AT 5.000DB RT 0.050

R A T E 0.1500DB AT 5.000DB RT 0.050

RATE 0.1500DB AT 5.000DB RT 0.050

R A T E 0.2000DB AT 1 .000DB RT 0.020

E/SSUNR 0P 149

SUNR 360P 149

EARTHR 180P 122

EA RT HR 180P 122

EA RT HR 180P 122

EA RT HR 180P 122

SUNR 0P 143

SUNR 330P 119

EARTHR 180P 120

SUNR 352P 95

R EF A T T / R E M A R K S

LVLH R=180.00P=148.00Y= 0.00

LVLH R=180.00P=148.00Y= 0.00

LVLH R=180.00P=148.00Y= 0.00

LVLH R=180.00P=148.00Y= 0.00

LVLH R=180.00P=150.00Y= 0.00

INRTL R=106.01HOLD P= 44.87Y= 19.27

EV EN T10 1.2 - MIR

H/0 to SHUTTLE

G O 1 . 1 B i a s e d/

H/0 to MIRG O 1 . 1 B i a s e d

Free D r i f t Test

G 0 1 . 1 B i a s SHTL

10 1.2

F R E E D R I F T

G O 1 . 1

SOYUZ U N D O C K6/15:23Ground AOS -30

SHUTTLE UNDOCK6/15:37

* * * ALL ATTITUDES IN M E A N OF 1950 "* * * PYR E U L E R SEQUENCE *** 5-2 AS FLOWN ATL

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Gov t

Attachment 2

STS-71 Mission CHIT's

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Gov'tSTS-071 MISSION AC TION REQU EST (CHIT) Launch DateVehicle ID 06/27OV-1 04 (GMT TIME179:16:08:10

REQUESTOR G CSR RESPONSEO R G MOD CONTRL 008N U M B E R UUOACTION REQUESTED BY (TIME): INFO ONLYREQUESTER: CSR/Draper Labs/D.ZimpferRESPONDER: RIO/C. ArmstrongSUBJECT: EFFECTS OF ODS FREEPLAY

SPAN OP SPaul Maley

179:16:18:24C SR MANAGER

Jeffrey G.Williams179:16:27:27

SPAN SYSTEMSLaura Stallard179:19:56:04

SPAN MANAGERTom Kwiatkowski

179:19:55:33REQUEST 1 Pages in hardcopy file. 0 Graphical Attachments. Page 1The attached fax has been transmitted to RSC-E. The fax describes the effect of freeplay on stack bendingmode fre quen cy. A teleconference was conducted with RSC-E at 8am C DT June 28,1995, to discuss theeffects of this freeplay on Mir control performance and Mir loads. Participants in the telecon includedV.Blag ov, A.Patsiora, S.Timokov, V.Mezch in/RSC -E, and from NASA G.Lange, J.Dagen, D.Zimpfer andJ.Montalbano. At this telecon RS C -E specialists, said they had NO ISSUES with the effect of the freeplay onMIR STACK CONTROL CAPABILITY OR MIR LOADS and the Mir could meet planned STS-71objectives. An official responose will be provided through the RIO.

***END OF REQUEST***RESPONSE 0 Pages in hardcopy file. Page 1Thank you.

*** END OF RESPONSE ***

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U.S. Gov t

To: Mr. MezhinMr. Kaznacheev

From: Mr. DagenMr. ZimpferSubject: Freeplay :Effect On The Shuttle Dynamic Loads ModelRecent discussions internal to NASA have identified a structural gap(freeplay) in the interface between the airlock and the Shuttlepayload bay side walls. This gap has the effect of changing themated vehicle natural frequencies dependent on the amplitude of thedynamic pscillations. The most significant effect is on the beambending:mode:at 0.14 hertz (Shuttle pitch motion). Attached is agraph which shows the expected natural frequency versus amplitudeat the Shuttle control system sensor feedback location in the nose ofthe Shuttle, We are prepared to discuss this topic with you if it hasany effect on, Mircontrol system stability and performance. Thepreviously transmitted maximum loads remain applicable, since thenatural frequency will be unchanged at the high amplitude levelcommensurate;with; these loads.:>; ; . , ; , , iBest Regards

0.14 I Nominal >Frq ti

20% Low Freq

-A2.3-0.2 0.4 0.6 0.8 1 1.2Amplitude (dg/sc) , 1.4 1.6 1.8


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u.s. Gov tSTS-071 MISSION ACTION REQUEST (CHIT) L av u e n h t i ? a r o ov-foGMT TIME180:20:26:31

REQUESTO R G MER RESPONSEO R G MOD CONTROLNUMBER 022ACTION REQUESTED BY (TIME): 180:22:28:00REQUESTER: MER/D. ZimpferRESPONDER: GNC/S. SchaeferSUBJECT: Downlist DAP Variable

TEAM LEADER VE/VGREP CONTRACT REP MER MANAGERW. Arceneaux180:20:45:07

SPAN SYSTEMSJoseph G. Fanelli

181:03:34:59

SPAN MANAGERBrian K. ToddNASA X47125181:03:35:14

REQUEST 2Pagesinhardcqpy:.flle.i / / > , iQ graphical Attachments. Page 1The MER GNC Console requests that.DAP Hal Variable CGCV-UndesiredrAccel be included in the variabledownlist.' Attached is the Hal :st'at listing of this .variable. i ; ; ' > ' ' ' ' ' ' ' ! ,,, ; : '

WKEND.&F REQUEST***RESPONSE P'Pages iriihardcopy file. Page 1The variably downlist"has>beeniUpdated to include these parameters.

* * "; > 'S u * ' ! Vt ' . - "-. "-' 'I-

i . , , ' < < ' . ( i i ; t i l j i : 4 j.'f'AF V , 1 1 1 , n U ;- ' , ' ' . . < > , . ' ' : .

P A G E is

: - A2.4 -:,..


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G o v tSTS-071 MISSION ACTION REQUEST (CHIT) Ov T o 4G M T TIME ;182:19:40:00

'REQUESTOR G "' MER RESPONSEO R G M O D CONTROLNUMBER 035ACTION REQUESTED BY (TIME): INFO ONLYREQUESTER: MER/James DaganRESPONDER: SPAN/B. K. ToddSUBJECT: Mated Vehicle PRCS attitude control using Alt DAP

TEAM LEADER VE/VGREP ' ' ' ' !

CONTRACT REP M ER MANAGERW . Arceneaux182:20:55:49

SPAN SYSTEMSI.E. Conner182:21:00:31

SPAN MANAGERBrian K. ToddNASA \47125182:21:00:35

REQUEST 0 Pages in hardcopy file. 0 Graphical Attachments. Page 1Shuttle Alt DAP, PRC S control is acceptable for use in the mated configuration if vernier jet con trol is lost.

*.** END OF REQUEST***RESPONSE 0 Pages in hardcopy file. Page'lThanks.

i I , *?*\END O F RESPONSE * * *

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Gov tSTS-071 MISSION ACTION REQUEST (CHIT)GM T TIME182:21:04:00

REQUESTOR G MER

RESPONSEQRG MOD CONTROL n~NUMBER 036

ACTION REQUESTED BY (TIME): INFO ON LYREQUESTER: MER/CSDL/D. ZimpferRESPONDER: SPAN/B. K. ToddSUBJECT: VRCS Attitude Deadband Decrease

TEAM LEADER VE/VGREP CONTRACT REP MER MANAGERW. Arceneaux182:23:15:05

. ' i

SPAN SYSTEMSJ.E. Conner182:23:18:38

SPAN MANAGERBrian K. ToddNASA X47125

182:23:18:44REQUEST 0 Pages m /hardcppy f i l e ; ; / , > 0 Graphical Attachments. Page 1To increase the probability of commanding-forward VRC S jets during crew sleep period.to avoid false leakannunciations, the MER concurs that1attitude deadband can1 be ;decreased from 5,degrees to 3 degrees.

. . I - . . . . ' ' - - - I \ i ' . M - . . ' a : < , . . ' , | . t i MPre-flight analysis indicates that ai 3'degree attitude deadbandj'and 0.05 degree/second rate deadband is a stableand controllable DAP configuration; \TTiisicpnrigur^atidn should NOT be used for attitude 'maneuvers.lii the event'the temperature of the; forward; VRC S jets do near the leak annunciation level, a further deadbandcollapse td^ l degree is acceptable:. The y&CS nianeuver rate m ust be reduced from 0.15 degree/second (DAPA 1 2 ) to 0.1 degree/second to meet?limits (determined during pre-flight analysis for separation deadbandcollapse. , . . ' , ' - . ' i . - . | ' r ' . ' ' ; / ' . . , ' . - " ' " . ' ; ' ' : " . i v V ; : . ' ' i . ! : ; '

*** END, OF REQUEST ***RESPONSE 0 Pages in hardcopy file. PagelThanks.

. ; . ' ' , ' - - , : i i , . I?*-*.END&FiRESPpN$E>***; 1 , ' ' * . .'!./ 1 '' ! ' " i ' ' : ' " ; ' ' ' ' ' ' ^ ' 1 " ' ' ! ' \ ' V i '

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U.S. Gov'tSTS-071 MISSION ACTION REQUEST (CHIT) Launch Date 06/27/9Vehicle ID OV-104(15GMT TIME182:23:11:40

REQUESTO R G MER RESPONSEO R G MOD CONTROLNUMBER 037ACTION REQUESTED BY (TIME): 183:12:02:00REQUESTER: MER/R. Friend/MER/RIRESPONDER:SUBJECT: Eleven Repositioning for Jet Impingement Analysis

TEAM LEADER VE/VG REP CONTRACT REP1 t

" '

MER MANAGERW. Arceneaux182:23:35:37

SPAN SYSTEMS SPAN MANAGER

REQUEST 0 Pages in hardcop y file. 0 Graphical Attachments. PagelThe MER requests thatthe elevens be,driven tb op'ne'ap the fol^ 'iip-pcisiiipri to ai'id'in analysis of the minuspitch acceleration delta. It would be foptim al to maintain |this .configuration while holding an IO attitude. Asan option, if procedural constraints prevent positioning tb! full'up^'the "MER requests jtliat 'the elevens be drivent o me-7T5jjd!gr0e^^ jJ^ . . >? ' '

: - ' ' i : r . . : ; ; i l . : ' . ' i " ; U ; ; i : i i V ' ; l ! M > : i ) : i^'il:i':^M ' " ' ' ' ' " ' ; '. ;, :,'Y,r lu'.ivi:.i!MV;M:. ; '

RESPONSE 0 Pages in hardcopy file. Pagel

*** END OF RESPONSE**?*

', , ' f ^ r ,, ' M , ' . , ,nv;-. . . 1' ' ' T ( '

ORSGINAL PAGE ISOF POOR QUALITY


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U.S. Gov tSTS-071 Launch Date 06/27/Vehicle ID OV-1 04 (1

GMT TIME183:22:10:00

REQUESTORG MER RESPONSE MOD CONTROLN U M B E R 044

ACTION REQUESTED BY (TIME): 185:12:00:00REQUESTER: MER/FCS/R. FriendRESPONDER: GNC/S. SpruellSUBJECT: Minus Pitch Acceleration Verification After Undock

TEAM LEADER VE/VG REP, CONTRACT REP MER MANAGER: W.Arceneaux

183:22:19:23

SPAN SYSTEMSLaura Stallard'184:18:12:19 ;

SPAN MANAGERTom Kwiatkowsk

184:18:12:28REQUEST ' O'Pages in hardcopy file. ; , 0 Graphical Attachments. PagelThe MER requests that an Orbiter minus pitch rotation be performed as soon as possible after separation and

' '.l! i ; '

flyaway from the Mir. The requested rotation should be performed with the elevens parked at -7.5 degreesand the.DAiP in FREE mode. 'Usinga Rotation PulsCjSIize:,$$& 26 or 46) of 0.2 deg/seci deflect the RHC inminus pitch. This Will provide an'LSD/RSD firing approximately 15seconds in length. Following completionof the pulse, wait 5 seconds before resuming control in AUTO/TAIL (ALT). This avoids expenditure offorward propellant while accomplishing th e request. .;

***'* END OF REQUEST ***R E S P O N S E ^ , > 1 Pages in hardcopy file. Page 1The Vernier Pitch Test (L5D/R5D firing) will be.scheduled after the Mir'flyaroundds complete and prior toPCS C/O (elevens move from -7.5deg during PCS C/0). The procedure is attached. Note that the rotationpulse size was-updated to 0.3 deg/sec per subsequent request from MER PCS personnel.

***END OF RESPONSE ***


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U.S. Gov t

; > ; . VERNIER PITCH TEST

Documents

STS-71 Shuttle Mir Mission Report