Download - COMPARISON OF THE HUYGENS MISSION AND THE SM2 TEST FLIGHT FOR HUYGENS ATTITUDE RECONSTRUCTION
COMPARISON OF THE HUYGENS MISSION AND THE SM2 TEST FLIGHT FOR HUYGENS COMPARISON OF THE HUYGENS MISSION AND THE SM2 TEST FLIGHT FOR HUYGENS ATTITUDE RECONSTRUCTIONATTITUDE RECONSTRUCTION
ENGINEERINGENGINEERING
PROPERTIESPROPERTIES Huygens Flight Module
SM2 Drop Test
Inner & Outer Structure ~ Identical
( no HASI booms on SM2 )
mass Identical ~ 300 kg
balance “similar“ moments of inertia
Descent Control SubSystem Identical
mechanisms Identical
spin vanes Identical design
3° inclination 2.2° inclination
main parachute Identical DGB double gap
stabilizer parachute
DGB
double gap
DGB
single gap
recovery parachute (no swivel)
A. Sarlette(1), M. Pérez-Ayúcar, O. Witasse, J.-P. LebretonPlanetary Missions Division, Research and Scientific Support Department, ESTEC-ESA, Noordwijk, The Netherlands.
(1) Stagiaire from February 1 to April 29; student at Liège University, Belgium Email: [email protected], [email protected], [email protected], [email protected]
AABSTRACTBSTRACTThe Huygens probe is the ESA’s main contribution to the Cassini/Huygens mission, carried out jointly by NASA, ESA and ASI. It was designed to descend into the atmosphere of Titan on January 14, 2005, providing surface images and scientific data
to study the ground and the atmosphere of Saturn’s largest moon.
In the framework of the reconstruction of the probe’s motions during the descent based on the engineering data, additional information was needed to investigate the attitude and an anomaly in the spin direction.
Two years before the launch of the Cassini/Huygens spacecraft, in May 1995, a test probe called SM2 (Special Model 2) was dropped in the Earth’s atmosphere from the balloon launch site of Kiruna, Sweden, to verify proper operation during the descent and especially the parachute deployments sequence. It featured a flight standard structure and DCSS (Descent Control SubSystem) and, unlike the Huygens probe, was fully instrumented to monitor the orientation of the descent module (3-axes
accelerometers and gyroscopes).
On this poster, we describe how a comparison between the SM2 test flight and the Huygens mission provides some information about the Huygens probe’s behaviour. After briefly discussing the spin direction, we focus on the tip and tilt.
The final conclusions of this comparison are still of qualitative nature, but the results are a starting point for better interpretation of the engineering data in terms of attitude to derive the probe’s orientation.THE HUYGENS MISSION
The Huygens probe is the ESA’s main contribution to the Cassini/Huygens mission, carried out jointly by NASA, ESA and ASI. It was designed to descend into the atmosphere of Titan on January 14, 2005, providing surface
images and scientific data to study the ground and the atmosphere of Saturn’s largest moon
THE SM2 TEST FLIGHT
Two years before the launch of the Cassini/Huygens spacecraft, in May 1995, a test probe called SM2 (Special Model 2) was dropped in the Earth’s atmosphere from the balloon launch site of Kiruna, Sweden, to verify proper
operation during the descent and especially the parachute deployments sequence.
FLIGHT CHARACTERISTICS FLIGHT CHARACTERISTICS
INSTRUMENTS FOR INSTRUMENTS FOR
ATTITUDE & AZIMUTHATTITUDE & AZIMUTH
RECONSTRUCTIONRECONSTRUCTION
Measurement Resolution
Time Resolution
Huygens Flight Data
CASU (vertical acc.) ± 0.2 m/s2 1 Hz
RASU (radial acc.) ± 0.0024 m/s2 4 Hz
On HASI, SSP, DISR (see Scientific Instruments´ teams)
SM2 Drop Test Data
X-accelerometer (vertical) ± 0.2 m/s2 200 Hz
Y-acc. & Z-acc. (horizontal) ± 0.15 m/s2 200 Hz
X-gyroscope (spin) ± 0.1 °/s 40 Hz
Y-gyro & Z-gyro (horizontal)
[High / Low range]
± 2.4 ± 0.24 °/s40 Hz
Video Recordings Up & Down (separation phases)
PROBE CHARACTERISTICSPROBE CHARACTERISTICS
1. Huygens mission spin profile 1. Huygens mission spin profile (cfr. M.Pérez et al., “Huygens attitude
reconstruction based on engineering parameters”)
~ 7.5 rpm through entry phase (spin induced at Cassini ejection) Spin annihilation at direction reversal
2. SM2 test flight spin rate 2. SM2 test flight spin rate ( X-axis gyroscope )
Spin movement starts after front shield release (spin vanes active)Spin movement starts after front shield release (spin vanes active) Constant direction under main chute and stabilizer chute, Constant direction under main chute and stabilizer chute, no annihilationno annihilation Oscillations under recovery chute (no swivel Oscillations under recovery chute (no swivel suspension cable suspension cable acts as torsional spring) around acts as torsional spring) around -1.4 rpm-1.4 rpm ( = parachute spin rate?) ( = parachute spin rate?)
SPIN RATESPIN RATE
Main Chute
Stabilizer Chute
Stabilizer Chute
Main Chute
Recovery Chute
Under Balloon & Gondola
Pilot & Main Chute Deployments
Stabilizer Chute Deployment
Recovery Chute Deployment
Landing
Front Shield Release
SPIN DIRECTIONSPIN DIRECTIONAfter the spin direction anomaly was confirmed on Huygens, the SM2 spin direction was also investigated
1. According to X-gyroscope, SM2 was spinning clockwise as seen from above (see positive gyroscope measurement and axes definitions on the right)
2. On video recording, sun ray is moving clockwise (up-looking) probe is moving counterclockwise (up-looking), which is clockwise seen from above, confirming the result:
SM2 Acc. and Gyro axes definitionsSM2 Acc. and Gyro axes definitions
SM2 up-looking video camera – Main chute releaseSM2 up-looking video camera – Main chute releaseConsecutive pictures a) – d) cover an interval of about 4s
Spin direction anomaly present on SM2
Check of spin vane Check of spin vane orientation on the SM2 orientation on the SM2 probe: probe: seems to induce counterclockwise torque
SIMULATIONS to fit SIMULATIONS to fit CASU / RASUCASU / RASU
Based on the identified frequencies of about 1 Hz -- which should correspond to attitude motions according to the SM2 comparison.
The effect on the Huygens accelerometers of pendulum-like and coning-like probe motions was simulated and compared to the mission measurements.
Variables:Variables: Amplitude Amplitude Fix point height Fix point height ll
[ discarding what happens above [ discarding what happens above l l ]]
Results:Results: Most plausible fixed point:
~ 10 cm above accelerometers Most plausible aperture angles:
- Main chute: 0 – 4°
- Beginning stabilizer chute: 4 – 9°
- End stabilizer chute: 1 – 5°
PLANETPLANET
PROPERTIESPROPERTIES Huygens
(Titan)
SM2
(Earth)
Gravity 1.354 m/s2 9.81 m/s2
Atmosphere
Temperatures 70 – 200 K ~ 270 K
Surface pressure 1.5 bar 1 bar
Typical vsound 200 m/s 330 m/s
Typical scale factor 20 km
(nearly no validity)
8 – 9 km
FLIGHTFLIGHT
PROPERTIESPROPERTIES Huygens Mission Flight
SM2 Drop Test
Main chute phase duration 15 mn 6 mn
altitudes 155 – 111 km 34 – 14.6 km
Stab. chute phase duration 2 h 13 mn 3 mn 30 s
altitudes 111 – 0 km 14.6 – 4.8 km
Typical Re ~ 107 ~ 106
Qdyn Descent initiation 316 Pa 300 Pa
Front shield release 34 Pa 90 Pa
Mach Descent initiation 1.465 0.9
Front shield release 0.4 0.4
Main Main chutechute
Stabilizer Stabilizer ChuteChute
SM2 Test FlightSM2 Test Flight 2.1 Hz 2.6 Hz
Huygens missionHuygens mission 0.75 – 0.8 Hz 1 Hz
FREQUENCY DOMAIN FREQUENCY DOMAIN COMPARISONCOMPARISON
SM2 Z-axis accelerometer spectrumSM2 Z-axis accelerometer spectrum
Huygens RASU spectrumHuygens RASU spectrum
Similarities:Similarities:
Calm descent under main chute, noisy under stabilizer chute Dominant horizontal frequency lines:
Differences:Differences:
Varying line decreasing from 1 Hz to 0.6 Hz under stabilizer on Huygens, absent on SM2 Progressive damping of oscillations under stabilizer on Huygens, no damping on SM2
( but SM2 stabilizer phase much shorter)
SM2 gyroscopes SM2 gyroscopes confirm that the SM2 confirm that the SM2 frequency lines are reflecting attitude motionsfrequency lines are reflecting attitude motions
Frequency comparison:Frequency comparison:
fSM2 / fHuygens = 2.77 (Main) ; 2.6 (Stabilizer)
~ ( g Earth / g Titan )1/2 = 2.7
It is likely that the same type of It is likely that the same type of movement was observed for the SM2 test movement was observed for the SM2 test
flight and for the Huygens missionflight and for the Huygens mission
Still to be explained: Still to be explained: - parachute influence- parachute influence- presence of decreasing frequency line on RASU - presence of decreasing frequency line on RASU
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