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This device provides non-invasivebeat-to-beat blood pressure measure-ments and can be worn over the upperarm for prolonged durations. Phase andwaveform analyses are performed on fil-tered proximal and distal photoplethys-mographic (PPG) waveforms obtainedfrom the brachial artery. The phaseanalysis is used primarily for the compu-tation of the mean arterial pressure,while the waveform analysis is used pri-marily to obtain the pulse pressure. Real-time compliance estimate is used to re-fine both the mean arterial and pulsepressures to provide the beat-to-beatblood pressure measurement.

This wearable physiological monitorcan be used to continuously observe thebeat-to-beat blood pressure (B3P). It canbe used to monitor the effect of pro-longed exposures to reduced gravita-tional environments and the effective-ness of various countermeasures.

A number of researchers have usedpulse wave velocity (PWV) of blood inthe arteries to infer the beat-to-beatblood pressure. There has been docu-mentation of relative success, but a de-vice that is able to provide the requiredaccuracy and repeatability has not yetbeen developed. It has been demon-strated that an accurate and repeatableblood pressure measurement can be ob-tained by measuring the phase change(e.g., phase velocity), amplitude change,and distortion of the PPG waveformsalong the brachial artery. The approachis based on comparing the full PPGwaveform between two points along the

artery rather than measuring the time-of-flight. Minimizing the measurementseparation and confining the measure-ment area to a single, well-defined arteryallows the waveform to retain the gen-eral shape between the two measure-ment points. This allows signal process-ing of waveforms to determine the phaseand amplitude changes.

Photoplethysmography, which mea-sures changes in arterial blood volume,is commonly used to obtain heart rateand blood oxygen saturation. The digi-tized PPG signals are used as inputs intothe beat-to-beat blood pressure measure-ment algorithm. The algorithm consistsof the following main components:• First harmonic isolation bandpass fil-

ters take the raw PPG signals and sepa-rate out the first harmonics.

• Three harmonic lowpass filters takethe PPG signal and filter out all spec-tral components outside the first threeharmonics. The first three harmonicsare used for regeneration of the pulsepressure waveforms.

• Phase analysis engine takes the firstharmonics of the PPG signals and com-putes the phase difference betweenthem in real time using a cross-correla-tion-based algorithm. The phase dif-ference is to the first order correlatedto the MAP (mean arterial pressure).

• Compliance estimation engine takesinformation on the general shape ofthe waveforms and the phase delay tocompute the local compliance of theartery. The higher the arterial pres-sure, the higher the Young’s modulus

and thus the lower the compliance.• MAP computation engine obtains the

phase delay and compliance informa-tion and provides the mean arterialpressure.

• Waveform analysis engine takes thePPG signal containing the first threeharmonics and provides the signal pro-cessing needed for compliance (elas-ticity) estimation and pulse pressurecomputation.

• Pulse pressure computation enginetakes the filtered PPG signal and an es-timate of the arterial compliance to re-generate the pulse waveform.

• B3P computation engine takes theMAP and the pulse pressure computa-tions and combines them with a bloodpressure model and calibration data toproduce the final signal of interest —the beat-to-beat blood pressure.This work was done by Yong Jin Lee of

Linea Research Corporation for Johnson SpaceCenter. For more information, download theTechnical Support Package (free whitepaper) at www.techbriefs.com/tsp under theBio-Medical category.

In accordance with Public Law 96-517,the contractor has elected to retain title to thisinvention. Inquiries concerning rights for itscommercial use should be addressed to:

Linea Research Corporation1020 Corporation WaySuite 216Palo Alto, CA 94303Refer to MSC-24601-1, volume and num-

ber of this NASA Tech Briefs issue, and thepage number.

Beat-to-Beat Blood Pressure MonitorThis invention is applicable to all segments of the blood pressure monitoringmarket, including ambulatory, home-based, and high-acuity monitoring.Lyndon B. Johnson Space Center, Houston, Texas

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Improving Balance Function Using Low Levels ofElectrical Stimulation of the Balance OrgansA device based on this technology may be used as a miniature patch worn by peoplewith disabilities to improve posture and locomotion, and to enhance adaptability orskill acquisition.Lyndon B. Johnson Space Center, Houston, Texas

Crewmembers returning from long-duration space flight face significantchallenges due to the microgravity-in-duced inappropriate adaptations in bal-ance/sensorimotor function. The Neu-roscience Laboratory at JSC isdeveloping a method based on stochas-tic resonance to enhance the brain’sability to detect signals from the balanceorgans of the inner ear and use them forrapid improvement in balance skill, es-pecially when combined with balancetraining exercises. This method involvesa stimulus delivery system that is wear-able/portable providing imperceptibleelectrical stimulation to the balance or-gans of the human body.

Stochastic resonance (SR) is a phe-nomenon whereby the response of anonlinear system to a weak periodicinput signal is optimized by the presenceof a particular non-zero level of noise.This phenomenon of SR is based on theconcept of maximizing the flow of infor-mation through a system by a non-zerolevel of noise. Application of impercep-tible SR noise coupled with sensoryinput in humans has been shown to im-

prove motor, cardiovascular, visual, hear-ing, and balance functions. SR increasescontrast sensitivity and luminance detec-tion; lowers the absolute threshold fortone detection in normal hearing indi-viduals; improves homeostatic functionin the human blood pressure regulatorysystem; improves noise-enhanced mus-cle spindle function; and improves de-tection of weak tactile stimuli using me-chanical or electrical stimulation. SRnoise has been shown to improve pos-tural control when applied as mechani-cal noise to the soles of the feet, or whenapplied as electrical noise at the kneeand to the back muscles.

SR using imperceptible stochasticelectrical stimulation of the vestibularsystem (stochastic vestibular stimula-tion, SVS) applied to normal subjectshas shown to improve the degree of as-sociation between the weak input peri-odic signals introduced via venousblood pressure receptors and the heart-rate responses. Also, application of SVSover 24 hours improves the long-termheart-rate dynamics and motor respon-siveness as indicated by daytime trunk

activity measurements in patients withmulti-system atrophy, Parkinson’s dis-ease, or both, including patients whowere un responsive to standard therapyfor Parkinson’s disease. Recent studiesconducted at the NASA JSC Neuro-sciences Laboratories showed that im-perceptible SVS, when applied to nor-mal, young, healthy subjects, leads tosignificantly improved balance perfor-mance during postural disturbances onunstable compliant surfaces. Thesestudies have shown the benefit of SRnoise characteristic optimization withimperceptible SVS in the frequencyrange of 0–30 Hz, and amplitudes ofstimulation have ranged from 100 to400 microamperes.

This work was done by Jacob Bloombergand Millard Reschke of Johnson Space Cen-ter; Ajitkumar Mulavara and Scott Wood ofUSRA; Jorge Serrador of Dept. of Veterans Af-fairs NJ Healthcare System; Matthew Fiedler,Igor Kofman, and Brian T. Peters of Wyle;and Helen Cohen of Baylor College. For fur-ther information, contact the JSC InnovationPartnerships Office at (281) 483-3809.MSC-25013-1

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Several technological enhancementshave been made to METI’s commercialEmergency Care Simulator (ECS) withregard to how microgravity affectshuman physiology. The ECS uses both asoftware-only lung simulation, and anintegrated mannequin lung that uses aphysical lung bag for creating chest ex-cursions, and a digital simulation oflung mechanics and gas exchange.METI’s patient simulators incorporatemodels of human physiology that simu-

late lung and chest wall mechanics, aswell as pulmonary gas exchange.

Microgravity affects how O2 and CO2are exchanged in the lungs. Proce-dures were also developed to take intoaffect the Glasgow Coma Scale for de-termining levels of consciousness byvarying the ECS eye-blinking functionto partially indicate the level of con-sciousness of the patient. In addition,the ECS was modified to provide vari-ous levels of pulses from weak and

thready to hyper-dynamic to assist in as-sessing patient conditions from thefemoral, carotid, brachial, and pedalpulse locations.

This work was done by Nigel Parker andVeronica O’Quinn of Medical EducationTech, Inc. for Johnson Space Center. Formore information, download the TechnicalSupport Package (free white paper) atwww.techbriefs.com/tsp under the Bio-Medicalcategory. MSC-23922-1

Developing Physiologic Models for Emergency MedicalProcedures Under MicrogravityLyndon B. Johnson Space Center, Houston, Texas

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A flexible, organic polyurea-basedaerogel insulation material was devel-oped that will provide superior thermalinsulation and inherent radiation protec-tion for government and commercial ap-plications. The rubbery polyurea-basedaerogel exhibits little dustiness, goodflexibility and toughness, and durabilitytypical of the parent polyurea polymer,yet with the low density and superior in-sulation properties associated with aero-gels. The thermal conductivity values ofpolyurea-based aerogels at lower temper-ature under vacuum pressures are verylow and better than that of silica aerogels.

Flexible, rubbery polyurea-based aero-gels are able to overcome the weak andbrittle nature of conventional inorganicand organic aerogels, including polyiso-cyanurate aerogels, which are generallyprepared with the one similar compo-nent to polyurethane rubber aerogels.Additionally, with higher content of hy-drogen in their structures, the polyurearubber-based aerogels will also provideinherently better radiation protectionthan those of inorganic and carbon aero-gels. The aerogel materials also demon-strate good hydrophobicity due to theirhydrocarbon molecular structure.

There are several strategies to over-coming the drawbacks associated with

the weakness and brittleness of silicaaerogels. Development of the flexiblefiber-reinforced silica aerogel compos-ite blanket has proven to be one promis-ing approach, providing a convenientlyfielded form factor that is relatively ro-bust in industrial environments com-pared to silica aerogel monoliths. How-ever, the flexible, silica aerogelcomposites still have a brittle, dustycharacter that may be undesirable, oreven intolerable, in certain applicationenvironments. Although the crosslinkedorganic aerogels, such as resorcinol-formaldehyde (RF), polyisocyanurate,and cellulose aerogels, show very highimpact strength, they are also very brit-tle with little elongation (i.e., less rub-bery). Also, silica and carbon aerogelsare less efficient radiation shielding ma-terials due to their lower content of hy-drogen element.

The invention involves mixing atleast one isocyanate resin in solventalong with a specific amount of at leastone polyamine hardener. The hard-ener is selected from a group of poly-oxyalkyleneamines, amine-based poly-ols, or a mixture thereof. Mixing isperformed in the presence of a catalystand reinforcing inorganic and/or or-ganic materials, and the system is then

subjected to gelation, aging, and super-critical drying. The aerogels will offerexceptional flexibility, excellent ther-mal and physical properties, and goodhydrophobicity.

The rubbery polyurea-based aerogelsare very flexible with no dust and hy-drophobic organics that demonstratedthe following ranges of typical proper-ties: densities of 0.08 to 0.293 g/cm3,shrinkage factor (raerogel/rtarget) = 1.6to 2.84, and thermal conductivity valuesof 15.2 to 20.3 mW/m K.

This work was done by Je Kyun Lee ofAspen Aerogels, Inc. for Johnson Space Cen-ter. For more information, download theTechnical Support Package (free whitepaper) at www.techbriefs.com/tsp under theMaterials & Coatings category.

In accordance with Public Law 96-517,the contractor has elected to retain title to thisinvention. Inquiries concerning rights for itscommercial use should be addressed to:

Aspen Aerogels, Inc.30 Forbes Road, Building BNorthborough, MA 01532Phone No.: (508) 691-1111Fax No.: (508) 691-1200 Refer to MSC-24214-1, volume and num-

ber of this NASA Tech Briefs issue, and thepage number.

Polyurea-Based Aerogel Monoliths and CompositesThese aerogels can be used in portable apparatus for warming, storing, and/or transporting food and medicine, and can be recycled for fillers forconventional plastics.Lyndon B. Johnson Space Center, Houston, Texas

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Force sensing is an essential require-ment for dexterous robot manipulation,e.g., for extravehicular robots makingvehicle repairs. Although strain gaugeshave been widely used, a new sensing ap-proach is desirable for applications thatrequire greater robustness, design flexi-bility including a high degree of multi-plexibility, and immunity to electromag-netic noise.

This invention is a force and deflec-tion sensor — a flexible shell formedwith an elastomer having passagewaysformed by apertures in the shell, withan optical fiber having one or moreBragg gratings positioned in the pas-sageways for the measurement of forceand deflection.

One object of the invention is light-weight, rugged appendages for a robotthat feature embedded sensors so thatthe robot can be more “aware” of loadsin real time. A particular class of opticalsensors, fiber Bragg grating (FBG) sen-sors, is promising for space robotics andother applications where high sensitiv-ity, multiplexing capability, immunity toelectromagnetic noise, small size, andresistance to harsh environments areparticularly desirable. In addition, thebiosafe and inert nature of optical fibersmakes them attractive for medical ro-botics. FBGs reflect light with a peakwavelength that shifts in proportion tothe strain to which they are subjected.

Multiple FBG sensors can be placedalong a single fiber and optically multi-plexed. FBG sensors have previouslybeen surface-attached to or embeddedin metal parts and composites to moni-tor stresses.

An exoskeletal force sensing robot fin-ger was developed by embedding FBG sen-sors into a polymer-based structure. Multi-ple FBG sensors were embedded into thestructure to allow the manipulator tosense and measure both contact forcesand grasping forces. In order to fabricatea three-dimensional structure, a newshape deposition manufacturing (SDM)process was developed. The sensorizedSDM-fabricated finger was then character-ized using an FBG interrogator. A force lo-calization scheme was also developed.

A sensor is formed from a thin shell offlexible material such as elastomer toform an attachment region, a sensing re-gion, and a tip region. In one embodi-ment, the sensing region is a substan-tially cylindrical flexible shell, and has aplurality of apertures forming passage-ways between the apertures. Opticalfiber is routed through the passageways,with sensors located in the passagewaysprior to the application of the elas-tomeric material forming the flexibleshell. Deflection of the sensor, such as bya force applied to the contact region,causes an incremental strain in one ormore passageways where the optical

fiber is located. The incremental strainresults in a change of optical wavelengthof reflection or transmittance at the sen-sor, thereby allowing the measurementof force or displacement.

The ability to route a single opticalfiber through the passageways of theouter shell of the sensor, combined withthe freedom to place Bragg grating-based sensors in desired locations of theshell, provides tremendous flexibility insensing force in three axes, as well as thepossibility of providing a large numberof sensors for more sophisticated mea-surement modalities, such as torque andshell deflection in response to multi-point pressure application.

This work was done by Yong-Lae Park,Richard Black, Behzad Moslehi, MarkCutkosky, and Kelvin Chau of IntelligentFiber Optic Systems Corp. for Johnson SpaceCenter. For more information, download theTechnical Support Package (free whitepaper) at www.techbriefs.com/tsp under thePhysical Sciences category.

In accordance with Public Law 96-517,the contractor has elected to retain title to thisinvention. Inquiries concerning rights for itscommercial use should be addressed to:

Intelligent Fiber Optic Systems Corp.424 Panama MallStanford, CA 94305Refer to MSC-24501-1, volume and num-

ber of this NASA Tech Briefs issue, and thepage number.

Multiplexed Force and Deflection Sensing ShellMembranes for Robotic ManipulatorsThis technology can be used to enhance precision in robotic surgery.Lyndon B. Johnson Space Center, Houston, Texas

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A concept has been developed for anew fuel cell individual-cell-voltage mon-itor that can be directly connected to amulti-cell fuel cell stack for direct sub-stack power provisioning. It can also pro-vide voltage isolation for applications inhigh-voltage fuel cell stacks. The tech-nology consists of basic modules, eachwith an 8- to 16-cell input electrical mea-surement connection port. For eachbasic module, a power input connectionwould be provided for direct connectionto a sub-stack of fuel cells in series withinthe larger stack. This power connectionwould allow for module power to beavailable in the range of 9-15 volts DC.

The relatively low voltage differencesthat the module would encounter fromthe input electrical measurement con-nection port, coupled with the fact thatthe module’s operating power is sup-plied by the same substack voltage input(and so will be at similar voltage), pro-vides for elimination of high-common-mode voltage issues within each module.Within each module, there would be op-tions for analog-to-digital conversionand data transfer schemes.

Each module would also include adata-output/communication port. Eachof these ports would be required to beeither non-electrical (e.g., optically iso-

lated) or electrically isolated. This is nec-essary to account for the fact that theplurality of modules attached to thestack will normally be at a range of volt-ages approaching the full range of thefuel cell stack operating voltages. A com-munications/data bus could interfacewith the several basic modules. Optionshave been identified for command in-puts from the spacecraft vehicle con-troller, and for output-status/data feedsto the vehicle.

This work was done by Arturo Vasquez ofJohnson Space Center. For further informa-tion, contact the JSC Innovation PartnershipsOffice at (281) 483-3809. MSC-24592-1

Fuel Cell/Electrochemical Cell Voltage Monitor Lyndon B. Johnson Space Center, Houston, Texas

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NASA is in the process of moderniz-ing its communications infrastructure toaccompany the development of a CrewExploration Vehicle (CEV) to replacethe shuttle. With this effort comes theopportunity to infuse more advancedcoded modulation techniques, includ-ing low-density parity-check (LDPC)codes that offer greater coding gainsthan the current capability. However, inorder to take full advantage of thesecodes, the ground segment receiver syn-chronization loops must be able to oper-ate at a lower signal-to-noise ratio (SNR)than supported by equipment currentlyin use.

At low SNR, the receiver symbol syn-chronization loop will be increasinglysensitive to transmitter timing jitter. Ex-cessive timing jitter can cause bit slips inthe receiver synchronization loop,which will in turn cause frame lossesand potentially lead to receiver and/ordecoder loss-of-lock. Therefore, it isnecessary to investigate what symboltiming jitter requirements on the satel-lite transmitter are needed to supportthe next generation of NASA codedmodulation techniques.

Measurements of ground segmentreceiver sensitivity to transmitter bit jit-ter were conducted using a satellitetransponder and two different com-mercial staggered quadrature phase-shift keying (SQPSK) re ceivers. Thesymbol synchronizer loop transferfunctions were characterized for eachreceiver. Symbol timing jitter was intro-duced at the transmitter. Effects of si-nusoidal (tone) jitter on symbol errorrate (SER) degradation and symbol slipprobability were measured. These mea-surements were used to define regionsof sensitivity to phase, frequency, andcycle-to-cycle jitter characterizations.An assortment of other band-limitedjitter waveforms was then appliedwithin each region to identify peak orroot-mean-square measures as a basisfor comparability.

Receiver clock recovery loops that op-erate in low SNR ratio environments re-quire that transmit clock jitter be con-strained by several measures ondifferent dimensions and operating re-gions. In this work, effects of transmitphase jitter (PhJ), frequency jitter (FJ),and cycle-to-cycle jitter (CCJ) were stud-

ied for sinusoidal and multi-tone jitterprofiles on receiver performance. It wasdemonstrated that the receiver musthave a loop bandwidth tight enough toavoid cycle slips, but loose enough totrack some movement in the data signal.Movement that a tight loop cannot trackis usually manifested first as intersymbolinterference (ISI) (SER degradation)and then ultimately as cycle slipping inthe receiver.

Results from the tests indicate that thereceiver symbol synchronization loop ismore sensitive to certain types of symboljitter and jitter frequencies, dependingon the selection of the loop filter anddamping ratio. A framework is providedto properly compose a transmit jittermask depending on receiver design pa-rameters such as damping ratio in orderto limit receiver performance degrada-tion at low SNR regions.

This work was done by Chatwin Lans-downe and Adam Schlesinger of JohnsonSpace Center. For more information, down-load the Technical Support Package (freewhite paper) at www.techbriefs.com/tspunder the Physical Sciences category. MSC-24810-1

Measurement Techniques for Clock JitterNew approach offers more advanced coded modulation techniques.Lyndon B. Johnson Space Center, Houston, Texas

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This new release of MBDyn is a soft-ware engine that calculates the dynamicsstates of kinematic, rigid, or flexiblemultibody systems. An MBDyn multibodysystem may consist of multiple groups ofarticulated chains, trees, or closed-looptopologies. Transient top ologies are han-dled through conservation of energy andmomentum. The solution for rigid-bodysystems is exact, and several configurablelevels of nonlinear term fidelity are avail-able for flexible dynamics systems.

The algorithms have been optimizedfor efficiency and can be used for both

non-real-time (NRT) and real-time (RT)simulations. Interfaces are currently com-patible with NASA’s Trick Simulation En-vironment. This new release represents asignificant advance in capability and easeof use. The two most significant new addi-tions are an application programming in-terface (API) that clarifies and simplifiesuse of MBDyn, and a link-list infrastruc-ture that allows a single MBDyn instanceto propagate an arbitrary number of in-teracting groups of multibody top ologies.

MBDyn calculates state and state de-rivative vectors for integration using an

external integration routine. A Trick-compatible interface is provided for ini-tialization, data logging, integration,and input/output.

This work was done by John Maclean,Thomas Brain, Leslie Quiocho, An Huynh,and Tushar Ghosh of Johnson Space Center.For more information, download the Techni-cal Support Package (free white paper) atwww.techbriefs.com/tsp under the Softwarecategory. MSC-24925-1

Linked-List-Based Multibody Dynamics (MBDyn) EngineLyndon B. Johnson Space Center, Houston, Texas

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Plug-in Plan Tool v3.0.3.1Lyndon B. Johnson Space Center, Houston, Texas

The role of PLUTO (Plug-in Port UTi-lization Officer) and the growth of theInternational Space Station (ISS) haveexceeded the capabilities of the currenttool PiP (Plug-in Plan). Its users (crewand flight controllers) have expressedan interest in a new, easy-to-use tool witha higher level of interactivity and func-tionality that is not bound by the limita-tions of Excel.

The PiP Tool assists crewmembers andground controllers in making real-timedecisions concerning the safety andcompatibility of hardware plugged intothe UOPs (Utility Outlet Panels) on-board the ISS. The PiP Tool also pro-vides a reference to the current configu-ration of the hardware plugged in to theUOPs, and enables the PLUTO andcrew to test Plug-in locations for con-straint violations (such as cable connec-tor mismatches or amp limit violations),to see the amps and volts for an enditem, to see whether or not the end itemuses 1553 data, and the cable length be-tween the outlet and the end item. Asnew equipment is flown or returned, thedatabase can be updated appropriately

as needed. The current tool is a macro-heavy Excel spreadsheet with its owndatabase and reporting functionality.

The new tool captures the capabili-ties of the original tool, ports them tonew software, defines a new dataset,and compensates for ever-growingunique constraints associated with thePlug-in Plan. New constraints were de-signed into the tool, and updates to ex-isting constraints were added to providemore flexibility and customizability. Inaddition, there is an option to associatea “Flag” with each device that will letthe user know there is a unique con-straint associated with it when they useit. This helps improve the safety and ef-ficiency of real-time calls by limiting theamount of “corporate knowledge” over-head that has to be trained and learnedthrough use.

The tool helps save time by automat-ing previous manual processes, such ascalculating connector types and decid-ing which cables are required and inwhat order.

This project provides a better on-board tool for the crew to safely test

ideas for reconfigurations before call-ing the ground, and send the changesdirectly. The layout provides clear de-tail for power channels, module loca-tions, and data ports, and allows for in-tuitive “drag-and-drop” connectionsfrom the database. The software willallow only compatible connections tooccur, and will flag violations if theyexist. It also allows the user to flagunique constraints that might not becaught by the software’s existing rulesand calculations.

The PiP Tool includes reporting capa-bilities that allow the user to export data-base information and configuration in-formation to Excel to share with othersor run detailed comparisons andsearches as needed.

This work was done by Kathleen E. An-drea-Liner, Brion J. Au, Blake R. Fisher,Watchara Rodbumrung, Jeffrey C. Hamic,Kary Smith, and David S.Beadle of theUnited Space Alliance for Johnson Space Cen-ter. For more information, download theTechnical Support Package (free whitepaper) at www.techbriefs.com/tsp under theSoftware category. MSC-24872-1

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Ascent/Descent Software Lyndon B. Johnson Space Center, Houston, Texas

The Ascent/Descent Software Suite hasbeen used to support a variety of NASAShuttle Program mission planning andanalysis activities, such as range safety, onthe Integrated Planning System (IPS)platform. The Ascent/Descent SoftwareSuite, containing Ascent Flight Design(ASC)/Descent Flight Design (DESC)

Configuration items (Cis), lifecycle docu-ments, and data files used for shuttle as-cent and entry modeling analysis and mis-sion design, resides on IPS/Linuxworkstations. A list of tools in Navigation(NAV)/Prop Software Suite representstool versions established during or afterthe IPS Equipment Rehost-3 project.

This work was done by Charles Brown,Robert Andrew, Scott Roe, Ronald Frye,Michael Harvey, Tuan Vu, Krishnaiyer Bal-achandran, and Ben Bly of the United SpaceAlliance for Johnson Space Center. For furtherinformation, contact the JSC Inno vationPartnerships Office at (281) 483-3809.MSC-24960-1