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Slide 1 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
OLYMPUS and the 1993 PerseidsLessons for the LeonidsDoug CaswellOLYMPUS Spacecraft ManagerApplications DirectorateTelecommunications DepartmentEuropean Space Agency, ESTEC, Noordwijk, The Netherlands
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 2 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
The early morning of August 12 1993 was predicted to be the peak of the Perseids Meteoroid Shower
A colleague at work had said to me, the OLYMPUS Spacecraft Manager, that “OLYMPUS dies at midnight”, as I left work
At 23:55 Zulu on August 11, the OLYMPUS Satellite lost earth pointing and began spinning
By the end of August 1993, OLYMPUS had been put into a graveyard orbit and the spacecraft was safed and shutdown
This presentation will reveal what we discovered
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 3 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
OLYMPUS was the largest civilian telecommunications satellite when it was launched in July 1989
Payloads included:
Direct to Home TV for the BBC and the RAI
Regular HDTV Transmissions
Digital Broadcasting
Specialised Business Services
Ka band Services and Propagation Investigations
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 4 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Investigations were conducted by:
British Aerospace, Prime Contractor
GEC Marconi Avionics, Gyro Supplier
Telespazio, Spacecraft Ground Control
University of Kent at Canterbury, Impact Physics
ESOC ESA, Ground Control
ESTEC ESA, Programme
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 5 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Mission Background
Launch, 12 July 1989 - last ARIANE 3
Earth Sensor Midnight Problem - Gyros used 6 hours per day
Loss of South Solar Drive and Solar Array Power in 1991
Hardware problems and Operator error resulted in a frozen spacecraft and round-the-world journey - loss of fuel in 1991
Loss of North Solar Array Section in January 1993
Algorithms reprogrammed, Gyro use for midnight phase, no North/South Stationkeeping, Fixed South Solar Array, Limited Power, careful Payload Operations scheduling
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 6 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Operational Status prior to August 11
6 months of trouble free operation
Plan was to continue operations for one more year
Last year more customers and demonstrations than ever
InterSatellite link to Eureca in LEO was demonstrated
Sufficient fuel to perform the planned mission with allowance for reorbiting to a Graveyard Orbit
But, no fuel margin for anomalies
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 7 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Preparations for August 11/12
Risk analysis performed for interception with stream
NASA announced the delay of Shuttle Mission
Reassessment of risk
Microaccelerometer put in operation
Additional support personnel sent to Ground Station
Extra staff on alert for event support
Payload operations performed as normal
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 8 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Anomaly Events:
23:32 Zulu Roll gyro spin down
23:40 Roll attitude diverged
23:53 Earth Presence lost (>15 degrees)
00:20 Automatic Reconfiguration
Earth Sun Acquisition Safe Mode failed capture
Spacecraft spinning about roll axis
Anomaly in North Array telemetry for position
Loss of Telemetry in Fucino for 7 minutes
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 9 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Operations:
Spacecraft despin was not possible with biprop as monomethyl hydrazine was spun from outlet
Operate system in cold gas mode to despin
Spin rate reduced from 2.1 revolutions per minute
MMH reprimed at .9 revolutions per minute
Quick Thermal Gauging determined remaining fuels
3 Kilograms of MMH and almost no NTO
Decision made to end mission and enter a graveyard orbit
Final burn only lasted 38 seconds verifying fuel estimate
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 10 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Graveyard Orbit
Following anomaly and despin, satellite was in an orbit with apogee 195 km below GEO and perigee 390 km below
End of life tests were performed
Final fuels and gas expended with apogee below 200 km
Spacecraft electrically safed and telemetry turned off
The OLYMPUS mission was over
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 11 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Investigations:
Roll Gyro Turn Off
Gyro turned on with no problems
Difficult to fail only one of three operating gyros
Spacecraft umbilical gave external access to gyros
Umbilical interface uncovered
Gyros operational during launch phase
Tests inconclusive, roll gyro probably more marginal
Probably spurious electrical event entering via umbilical
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 12 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Investigations:
Microaccelerometer
“Microphone”, listen for impact
Nothing major in signal
7 events in 11 seconds were recorded 2 minutes prior to Roll Gyro shutdown
Not correlated to onboard activity
Impact on Solar Array would not be heard due to attenuation
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 13 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Investigations:
Wheel Speed
Pitch Wheel speed change due to Gyro run down
Failure of Safing Mode
Earth Sun Acquisition Mode should have captured
Failure somewhere in control loops
Most likely, short circuit in capacitor
Possibly connection to space through sun sensor
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 14 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Investigations:
North Solar Array position anomaly
Problem disappeared, likely bit error
Loss of Ground Telemetry
Wrong position in ground antenna due to change of orbit
Telemetry fringing effects due to spinning spacecraft
Roll Thruster Firings
Planned firings to desaturate wheels loaded by the fixed South Solar Array occurred a few seconds before Gyro off
Exhaust gases would be in area of umbilical and sun sensor
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 15 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Investigations:
Possible Perseid Impact
Previous years about 50 meteoroids an hour for 2 to 3 days Peaking around 100
These visual meteors (magnitude greater than 6.5) mass of 1 mg or greater
After 1988, peak about 400, predicted 10000 possibly 1993
Increased activity due to last close pass of Comet Swift-Tuttle in 1862
The peak occurred around 03:30 Zulu At 23:30 rate was 100
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 16 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Investigations:
Possible Perseid Impact
Sporadic Meteoroid rate is 10
Sporadics at approximately 20 km per sec
Perseids about 60 km per sec
For same visual magnitude, Sporadic is 100 times mass
For the same mass, the Sporadic flux is 10 times Perseid
Probability of impact is driven by Sporadic
For equal damage however, similar probability
Plasma production, 1 mg Perseids equals 50 mg Sporadics
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 17 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Investigations:
Possible Perseid Impact
At the time of “impact?”, the plasma risk was at least 5 times higher than normal Sporadic
Sporadic impact rate is approximately 1.5 impacts per year of .1 mg particles
OLYMPUS exposed surface area up to 140 m2
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 18 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Investigations:
Spacecraft Flux for Perseid Stream
East 58degrees 1.94 sq. m.
West nil
South nil
North 34 2.89
Earth 78 1.29
Aft nil
South Array (fixed) 73 8.48
North Array 94 1.73
Most Probable Impact Area is Fixed South Solar Array
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 19 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Conclusions:
We could not prove that the anomaly was the result of impact from a Perseid meteor,
We did not hear it,
We did not measure it on the wheels
There was no apparent significant damage
The impact seems most probable for dust intersecting the South Solar Array, generating a plasma which was augmented by the thruster firing in the area of the umbilical and the sun sensor which shut down the roll gyro and failed a capacitor in the safing control circuit. The rest is history when OLYMPUS had no fuel.
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 20 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Recommendations:
For Meteoroid Showers,
1. Minimise cross section to Stream for peak period
2. Prepare operational contingency plans for recovery. Augment Support Teams
3. Set up to monitor for impacts
4. Protect from external plasmas through electrical windows (pre-launch)
5. Ground and cover all interface points such as umbilical(pre-launch)
6. If your spacecraft is weak and fragile, shut down the mission for the peak duration
OLYMPUS and the 1993 Perseids -
Lessons for the Leonids
Slide 21 Doug Caswell Leonids Threat Conference Manhattan Beach April 26/27 1998
Spaceraft are impacted by orbit debris, man-made and natural
Some areas are very critical
Larger spacecraft receive more impacts in their sweep of space
Meteoroid storms have a bigger effect due to higher velocities
Plasma is produced
Large spacecraft should exercise caution during showers to minimise the risk
Designs must be robust to this operational hazard
Reference: Pages 139-150 International Journal of Impact Engineering Vol 17, Caswell et al 1995 0734-743X 95 S9.50-0.00