Upload
ngongoc
View
225
Download
0
Embed Size (px)
Citation preview
March 2003 MEIT-2003 / Section 10 / Page 1
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
Section 10
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
Richard DeLombardAcceleration Measurement Discipline Scientist
NASA Glenn Research Center
March 2003 MEIT-2003 / Section 10 / Page 2
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
Acceleration measurements for experiments• Experiments in microgravity are disturbed by accelerations
(e.g. vibrations, shocks, gravity gradient, linear motion)
• Experiments in ground laboratories are disturbed by accelerations also
• Gravity (very pervasive!)• Elevator motions in laboratory building • Traffic nearby building (e.g. street, loading dock) • Air conditioning equipment (e.g. compressor, fans, etc.)• Clumsy lab assistants
• Accelerations should be measured during experiment ground operations - not just during orbital operations
March 2003 MEIT-2003 / Section 10 / Page 3
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
10-2 10-1 100 101 10210-7
10-6
10-5
10-4
10-3
10-2
10-1One-Third Octave Band Comparison
Frequency (Hz)
ISS REQs GRC 2.2 GRC ZGF JAMIC Mir 1996 Shuttle IML-2 KC-135 Bolted KC-135 Free-Float Sounding Rocket Bremen (Drop Axis Only)
RM
S A
ccel
erat
ion
(gR
MS)
Residual acceleration for various microgravity facilities
(from Ross, 2001)
March 2003 MEIT-2003 / Section 10 / Page 4
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
Methods of creating ‘zero-g’ or microgravity• Center of Earth’s mass (ge ~ 0 m/s2)
• Impractical location for experiment operations
• Very distant from Earth or other celestial body (ge= 10-6 m/s2)• Impractical location for experiment operations
• Free fall • Zero horizontal velocity ------> drop tower (ge = 9.8 m/s2)• 400 kph horizontal velocity ------> aircraft (ge = 9.8 m/s2)• 30,000 kph horizontal velocity ------> orbital (ge ~ 9 m/s2)• Where ge is the acceleration due to Earth’s gravitational pull
• The reduced gravity features comes from free fall, not the absolute reduction or elimination of Earth’s gravitational acceleration!
March 2003 MEIT-2003 / Section 10 / Page 5
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
Ground-based facilities with zero horizontal velocity• Seismic mass / vibration isolation
• Not free-fall but vibrationally quiet- Still 1-g environment
• Isolated floor mass • Vibration isolation platform
• Drop tower• Carrier containing experiment is dropped• Experiments may be complex
• Drop tube• Sample material only is dropped • Most often sample is molten metal drops
March 2003 MEIT-2003 / Section 10 / Page 6
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
Ground Facilities with zero horizontal velocity
2.2 Second Drop TowerNASA Glenn
Drag shield being assembled for an experiment drop
Seismic MassPlum Brook Station
Base of huge vacuum chamber (illustrative of method to utilize
vibration-quiet laboratory conditions)
March 2003 MEIT-2003 / Section 10 / Page 7
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
SPF Seismic Mass Characterization
• Figure 10-1 illustrates the conditions existing on a large mass of concrete
• Concrete foundation of world’s largest vacuum chamber • The X-axis was vertical • a = F/m implies low levels of acceleration with large value of
mass with nominal forces from ground and wind
March 2003
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
• 1-g condition• Gravity effects are apparent when a retarding force
disturbs free fall• Beaker exerts a force to stop water from falling • Floor exerts a force on people (felt as their weight)
• Microgravity condition in a free fall• Gravity effects are not apparent in free fall • Beaker falls with the fluid
- beaker is no longer exerting a retarding force on water- sedimentation and buoyancy are reduced- surface tension & capillary forces are ‘revealed’
• Acapulco cliff divers feel weightless during their free-fall to the ocean
Free-fall vs. 1-g1-g
µg
March 2003 MEIT-2003 / Section 10 / Page 9
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
• Drop towers attempt to minimize external forces• Air drag is a large external force
- Steady force which gradually increases with increasing velocity• Several mechanisms are used to counteract air drag
- Drag shield - Experiment package surrounded by free falling container
- Vacuum operation- Evacuate air from the chamber in which the experiment is dropped
- Drag force compensation- Apply compensating force (thrust) to experiment carrier
• Keys for a ‘quiet’ drop - Smooth release mechanism to minimize initial transient vibration- Structural relaxation depends on design of carrier and
experiment - Dynamically balance moving experiment and carrier
components
Drop Towers & Tubes
March 2003
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
• NASA GRC 2.2 Second Drop Tower uses a drag shield
• Capture in an air bag
Drag Shield
Drag Shield
Experiment package
Velocity
March 2003
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
NASA GRC 2.2 Second Drop Tower
Experiment rig assemblyDrag shield preparation
March 2003 MEIT-2003 / Section 10 / Page 12
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
Vacuum Operation• Vacuum drop towers include:
• Zero Gravity Research Facility at NASA GRC- Capture in foam pellet container
• ZARM facility at University of Bremen, Germany - Capture in foam pellet container
ZARM tower
exteriorExperiment capture in Zero Gravity Research Facility
March 2003 MEIT-2003 / Section 10 / Page 13
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
Drag Force Compensation• Japan Microgravity Center
• Inner & outer capsule (i.e. drag shield)- Vacuum drawn between inner & outer capsules
• Acceleration added to outer capsule for drag compensation- Cold-gas jet
• Capture accomplished with air pressure then mechanical brake
JAMIC
March 2003 MEIT-2003 / Section 10 / Page 14
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
Drop Tower Comparison• NASA GRC 2.2 Second Drop Tower
• 2.2 seconds 24.1 m 10-4 g
• ZARM Drop Tower• 4.74 seconds 123 m 10- 5 g
• NASA GRC Zero Gravity Research Facility• 5.18 seconds 145 m 10-5 g
• Japan Microgravity Center • 10 seconds 490 m 10-5 g
ZARM
March 2003 MEIT-2003 / Section 10 / Page 15
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
Acceleration Environment Features of Drop Towers• Release
• Step change transition from 1-g to sub-milli-g level • Transition occurs over very short time that the mechanism
actually releases carrier
• Vibrations from release mechanism• The release transition is similar to ringing a bell
- Step change causes (unwanted) vibration in experiment carrier- The ‘bell ringing’ is damped by carrier and experiment mechanical design
• May persist for major portion of microgravity time
• Figure 10-2
March 2003 MEIT-2003 / Section 10 / Page 16
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
Acceleration Environment Features of Drop Towers• Vibrations from experiment equipment operation, such as:
• Camera shutters• Film transport• Solenoid and relay actions• Pumps• Motor-driven fluid mixers• Figure 10-3
• High level of deceleration at capture • Levels depend on capture mechanism and final velocity • Figures 10-2 and 10-4
March 2003 MEIT-2003 / Section 10 / Page 17
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
Non-orbital flight platforms (~ 200 mph horizontal velocity)
• KC-135 aircraft (NASA)• Operated by NASA Johnson Space Center• Each parabola provides 15-20 seconds of reduced gravity
environment• Periodic free-fall interspersed with high-g pull-out• Approximately 40-50 parabolas per flight (campaign)
• Terrier-Black Brant sounding rocket• Achieves free-fall conditions on the order of 500 seconds after
motor burn-out • One of several types of sounding rockets
March 2003 MEIT-2003 / Section 10 / Page 18
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
Aircraft Facilities
SAMS-FF / KC-135Linear acceleration sensors and fiber optic gyro sensor
Parabolic Aircraft Rating System
Linear acceleration sensors and software processing
KC-135
March 2003 MEIT-2003 / Section 10 / Page 19
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
SAMS-FF / Sounding RocketLinear acceleration sensors and
fiber optic gyro sensor
Sounding Rockets
Terrier-Orion
March 2003 MEIT-2003 / Section 10 / Page 20
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
KC-135 Environment Characterization
• Figure 10-5 illustrates the KC-135 overall environment over multiple parabolas during a typical campaign
• Figure 10-6 is a detailed plot of the KC-135 environment during the reduced gravity portion of the parabola
• Figure 10-7 is a plot of KC-135 parabola recorded in support of SAL experiment. Shows free-float of SAL test equipment and timelines the activity within the parabola
• Figure 10-8 is a detailed plot of the free-float period of the parabola
March 2003 MEIT-2003 / Section 10 / Page 21
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
Sounding Rocket Environment Characterization
• Terrier-Black sounding rocket DARTFire flight timeline is shown in the graphic in Figure 10-9
• Figure 10-10 illustrates the acceleration vector magnitude for the time period when the sampling rate was 25 samples per second
• environment measured to be less than 30 micro-g root sum square (RSS) for the time interval analyzed
• Figure 10-11 is the RSS power spectral density for the time period when the sampling rate was 25 samples per second
• frequency domain characteristics track known disturbance sources from the DARTFire equipment
- Intensified Multispectral Imager filter wheel operates at 5 Hz- Infrared Imager filter wheel operates at 1 Hz
March 2003 MEIT-2003 / Section 10 / Page 22
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
References• Zero Gravity Research Facility
• http://microgravity.grc.nasa.gov/zero-g/index.html
• 2.2 Second Drop Tower• http://microgravity.grc.nasa.gov/drop2/
• ZARM Drop Tower• http://www.zarm.uni-bremen.de/main.htm
• ZARM Drop Tower Bremen - Users Manual, Version 28, April 2000• JAMIC Drop Tower
• http://www.jamic.co.jp/ENG/JAMIC/3.html
• Microgravity Carrier Summary• http://microgravity.msfc.nasa.gov/NASA_Carrier_User_Guide.pdf
• Ross, H. D. (2001) Microgravity Combustion, Academic Press
March 2003 MEIT-2003 / Section 10 / Page 23
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
Figure 10-1: Ground Testing – SPF data
March 2003 MEIT-2003 / Section 10 / Page 24
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
1.400
-1 .400
-1 .200
-1 .000
-0 .800
-0 .600
-0 .400
-0 .200
0 .000
0 .200
0 .400
0 .600
0 .800
1 .000
1 .200
9 .05 .0 5 .5 6 .0 6 .5 7 .0 7 .5 8 .0 8 .5
accel data (g)
Data from the vertical axis in NASA GRC 2.2 Second Drop Tower facility.
0 .0 0 5
- 0 .0 0 5
- 0 .0 0 4
- 0 .0 0 3
- 0 .0 0 2
- 0 .0 0 1
0 .0 0 0
0 .0 0 1
0 .0 0 2
0 .0 0 3
0 .0 0 4
7 .55 .0 5 .5 6 .0 6 .5 7 .0
accel data (g) Low-g portion of dropComplete drop
1-g
0-g
Figure 10-2: Acceleration level for drop tower test
5-mg
0-mg
Time (sec)
Time (sec)
Acc
eler
atio
n le
vel (
g)
Acc
eler
atio
n le
vel (
g)
March 2003 MEIT-2003 / Section 10 / Page 25
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
PSD of Residual Acceleration,Bremen Drop Tower, Weight of Capsule: 500kg
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50
Freq / Hz
PSD / 10-12 g02 / Hz
Figure 10-3: Power Spectral Density plot during drop (ZARM)(note: release disturbances not included)
Equipment operation
March 2003 MEIT-2003 / Section 10 / Page 26
Microgravity Environment of Ground-based Facilities and Non-orbital Flight Platforms
Deceleration Forces at Bremen Drop Towerz-axis
-10
0
10
20
30
40
50
4,7 4,8 4,9 5 5,1 5,2 5,3 5,4 5,5
time [s]
g0
Figure 10-4: Deceleration at capture (ZARM)
Peak > 40-g (!)
Figure 10-5
−1
−0.5 0
0.5 1
1.5 2
2.5 3
Original Mean=−5.27e−02 gRMS Value=5.27e−02 g
X−Axis Acceleration (g)
−1
−0.5 0
0.5 1
1.5 2
2.5 3
Original Mean=6.83e−03 gRMS Value=9.71e−03 g
Y−Axis Acceleration (g)
050
100150
200250
300−
1
−0.5 0
0.5 1
1.5 2
2.5 3Original Mean=1.09e+00 gRMS Value=8.06e−01 g
Z−Axis Acceleration (g)
Tim
e (seconds)
Multiple K
C−
135 Parabolas Without D
e−M
eaningM
ET
Start at 055/15:09:59.992
Head C
, 5.0 Hz
fs=25.0 sam
ples per secondK
C−
135K
C−
135 Coordinates
T=
300.0 seconds
MA
TL
AB
: 13−A
ug−1998, 10:35 am
Figure 10-6
02
46
810
1214
1618
20−
0.4
−0.2 0
0.2
0.4
Tim
e (sec)
X−Axis (g)
Original Mean = −2.87e−02 g
RMS Value = 8.75e−02 g
Head SA
MS−
FF DA
TA
, 209.6 Hz
fs= 800 sam
ples per seconduSE
G M
issionSA
MS−
FF Coordinates
MA
TL
AB
: 15−Jun−
1998, 04:41 pm
ME
T Start at 02/27/1998 10:35:52
uSEG
Mission: R
educed Gravity Portion of K
C−
135 Parabola Without D
e−M
eaning
02
46
810
1214
1618
20−
0.4
−0.2 0
0.2
0.4
Tim
e (sec)
Y−Axis (g)
Original Mean = 2.01e−03 g
RMS Value = 2.95e−02 g
02
46
810
1214
1618
20−
0.4
−0.2 0
0.2
0.4
Tim
e (sec)
Z−Axis (g)
Original Mean = 5.24e−04 g
RMS Value = 1.89e−02 g
FREE-FLOATDATE: 04-27-99, FILE #0031
SAMS-FF, 26.2 Hzfs=100 samples per second
KC-135-FREE FLOATKC-135 Coordinates
T=25.0 seconds
MA TLA B: 1 0 -Jan -2 0 0 0 , 0 7 :1 1 am
0 5 10 15 20 25-1.5
-1
-0.5
0
0.5
1
1.5
Time (seconds)
Acc
eler
atio
n (g
)
pickup rig from floor
test conductor adjustments
release
bump
capture
reposition rig
place rig back on floor mounts
free-float
X-AxisY-AxisZ-Axis
Figure 10-7
SAMS-FF Data Recorded in Support of SAL Experiment Showing Free-Float Interval
Figure 10-8
12 12.5 13 13.5 14 14.5 15 15.5 16−1.5
−1
−0.5
0
0.5
1
1.5x 10
−4Enhancement of Free Float Interval for Z−Axis
Data Set #31
Time (Seconds)
Acc
eler
atio
n (g
)
Head SAMS−FF, 50 Hzfs=100 samples per second
KC−135 Free FloatApril 27, 1999
Figure 8−7: Enhancement of the Free Float Period for the Z−Axis
Figure 10-9
TS
H
RM
S
y
(µg
)z
(µ
g)
376405
243x
(µ
g)
50 MIL
ES
TS
H
RM
S
y
(µg
)z
(µ
g)
89
91
37
58
22
x
(µg
)
TS
H
RM
S
y
(µg
)z
(µ
g)
58
16
82
38
x
(µg
)
200 MIL
ES
150 MIL
ES
200 SA
MP
LE
S P
ER
SE
CO
ND
0 MIL
ES
SA
MS
-FF
DA
RT
Fire
RM
S V
alues fo
r Each
TS
H S
amp
ling
Rate
100 MIL
ES
400 SA
MP
LE
S P
ER
SE
CO
ND
TS
H
RM
S
y
(µg
)z
(µ
g)
13
13
10
x
(µg
)
TS
H
RM
S
y
(µg
)
11
5
x
(µg
)z
(µ
g)
4
Figure 10-10
020
4060
80100
120140
160
0
0.5 1
1.5 2
2.5 3x 10
−5
Tim
e (sec)
Acceleration Vector Magnitude (g)
Head SA
MS−
FF DA
TA
, 6.55 Hz
fs= 25 sam
ples per second
DA
RT
Fire Mission
SAM
S−FF C
oordinates
MA
TL
AB
: 11−A
ug−1998, 06:02 pm
ME
T Start at 000/00:02:05.027
Acceleration V
ector Magnitude for Fs=
25
Figure 10-11
02
46
810
12
10−
14
10−
13
10−
12
10−
11
10−
10
10−
9
10−
8
RSS PSD Value (g2/Hz)
Frequency (Hz)
Head SA
MS−
FF DA
TA
, 6.55 Hz
fs= 25 sam
ples per second
dF= 0.048828 H
z
DA
RT
Fire Mission
SAM
S−FF C
oordinates
T=
179.988 sec
MA
TL
AB
: 11−A
ug−1998, 06:05 pm
ME
T Start at 000/00:02:05.027, H
anning k=8
RSS Pow
er Spectral Density for Fs=
25