# Presentation: 095273

## SPACECRAFT ACCIDENTS:  EXAMINING THE PAST, IMPROVING THE FUTUREMars Climate Orbiter (MCO) and Mars Polar Lander (MPL) 

- Bryan Palaszewski
- working with the
- Digital Learning Network
- NASA Glenn Research Center

## Mars Climate Orbiter (1/2)

- Launched from Earth
- December 11, 1998
- Payload on spacecraft
- Camera and other sensing instruments investigating the atmosphere and possible subsurface ices

**Notes:**
MCO failure report

## Mars Climate Orbiter (2/2)

- Payload on spacecraft (continued)
- Similar to but smaller payload than Mars Observer that was lost in 1993
- Arrival at Mars
- September 23, 1999
- Planned to use rocket engine to slow into Mars orbit

**Notes:**
MCO failure report

## Slide 4

**Notes:**
ftp://ftp.hq.nasa.gov/pub/pao/reports/1999/MCO_report.pdf

On September 27, 1999, the operations navigation team consulted with the spacecraft
engineers to discuss navigation discrepancies regarding velocity change DV) modeling
issues. On September 29, 1999, it was discovered that the small forces DV’s reported by
the spacecraft engineers for use in orbit determination solutions was low by a factor of
4.45 (1 pound force=4.45 Newtons) because the impulse bit data contained in the AMD
file was delivered in lb-sec instead of the specified and expected units of Newton-sec.

Finally, after the fact navigation estimates, using all available data through loss of signal, with corrected values for the small forces DV’s, indicated an init ial periapsis (lowest point of orbit) of 57 km which was judged too low for spacecraft survival.

## Slide 5

**Notes:**
ftp://ftp.hq.nasa.gov/pub/pao/reports/1999/MCO_report.pdf

On September 27, 1999, the operations navigation team consulted with the spacecraft
engineers to discuss navigation discrepancies regarding velocity change DV) modeling
issues. On September 29, 1999, it was discovered that the small forces DV’s reported by
the spacecraft engineers for use in orbit determination solutions was low by a factor of
4.45 (1 pound force=4.45 Newtons) because the impulse bit data contained in the AMD
file was delivered in lb-sec instead of the specified and expected units of Newton-sec.

Finally, after the fact navigation estimates, using all available data through loss of signal, with corrected values for the small forces DV’s, indicated an init ial periapsis (lowest point of orbit) of 57 km which was judged too low for spacecraft survival.

## MCO Root Cause 

- Failure to use metric units in the coding of a ground software file, “Small Forces,” used in trajectory models

**Notes:**
MCO failure report

## MCO Contributing Causes (1/2)

- Undetected mis-modeling of spacecraft velocity changes
- Navigation Team unfamiliar with spacecraft
- Trajectory correction maneuver number 5 not performed
- System engineering process did not adequately address transition from development to operations.

## MCO Contributing Causes (2/2)

- Inadequate communications between project elements
- Inadequate operations Navigation Team staffing
- Inadequate training
- Verification and validation process did not adequately address ground software.

## MCO Recommendations (1/3)

- Verify the consistent use of units throughout the MPL spacecraft design and operations.
- Conduct software audit for specification compliance on all data transferred between JPL and Lockheed Martin Astronautics.
- Verify Small Forces models used for MPL.

## MCO Recommendations (2/3)

- Compare prime MPL navigation projections with projections by alternate navigation methods.
- Train Navigation Team in spacecraft design and operations.
- Prepare for possibility of executing trajectory correction maneuver number 5.

## MCO Recommendations (3/3)

- Establish MPL systems organization to concentrate on trajectory correction maneuver number 5 and entry, descent, and landing operations.
- Take steps to improve communications.

## Mars Polar Lander (1/2)

- Launched from Earth
- January 3, 1999
- Payload on spacecraft
- Camera and other sensing instruments looking for volatiles (water, etc.) and investigating the climate at the Martian South Pole

## Mars Polar Lander (2/2)

- Arrival at Mars
- December 3, 1999
- Planned to use Mars’ atmosphere for initial braking and then rocket engines for the final landing on Mars.

## Slide 14

## Slide 15

## Slide 16

## Slide 17

## MPL Findings: Most Probable Cause Of Loss Of Mission (1/3)

- Premature shutdown of descent engines
- The software — intended to ignore touchdown indications prior to the enabling of the touchdown sensing logic — was not properly implemented, and the false touchdown indication was retained.

## MPL Findings: Most Probable Cause Of Loss Of Mission (2/3)

- The touchdown sensing logic was enabled at 40 meters altitude, and the software would have issued a descent engine thrust termination at this time in response to a (false) touchdown indication.

## MPL Findings: Most Probable Cause Of Loss Of Mission (3/3)

- At 40 meters altitude, the lander had a velocity of about 13 meters per second (m/s), which with no thrust is accelerated by Mars gravity to an impact velocity of about 22 m/s.
- The planned touchdown velocity was 2.4 m/s.
- At this impact velocity, the lander could not have survived.

## MPL Findings (1/2)

- The flight software was not subjected to complete fault-injection testing.
- Problems with post-landing fault-response algorithms were uncovered in the course of the investigation.
- The touchdown sensing software was not tested with the lander in the flight configuration.

## MPL Findings (2/2)

- Because of this, the software error was not discovered during the verification and validation program.

## Slide 23

## Slide 24