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 -

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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 -

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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 -

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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 -

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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 -

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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 -

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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 -

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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

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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

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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