Preparations and testing of OCM 4, which will place NEAR Shoemaker in a 100 km circular orbit, continue. Final burn parameters and the timing update will be loaded on the spacecraft when these values are available, in the next few days.

Overall NEAR Shoemaker continued to operate nominally this past week in orbit around the asteroid 433 Eros. NEAR Shoemaker remained in Operational Mode with Flight Computer #1 and Attitude Interface Unit #2 in control of spacecraft attitude. The spacecraft instrument suite remained "ON" and operational this week.

Problems with the Multispectral Imager (MSI) Data Processing Unit (DPU) flight application software have been corrected by the software patch that was successfully loaded March 30, 2000. During this past week, the MSI has performed flawlessly.

Science activities conducted this week included Eros "high altitude" ~200 Km x 100 km observations with the MSI, NIS, MAG, NLR and XGRS instruments. Please consult science timelines for more details.

Navigating In Deep Space
Navigation generated SPK files for new Eros orbit plan and placed them on the NEAR Shoemaker SDC server at JHU-APL this week. This delivery used the best current estimate for Eros mass, gravity, spin-state, and ephemeris files that were sent to the SDC in March. The new orbit plan gives times of future maneuvers and an associated reference trajectory until January 10, 2001. The plan label is 3-23-00.

The use of optical landmark tracking for the NEAR Shoemaker orbit phase has been validated and is working as predicted. The current landmark database contains over 700 individual landmarks (craters). Landmarks are being added as the sun lights up more of the Southern Hemisphere of Eros. Post fit landmark residuals are good to about 60 m in the 200 km circular orbit; the precision should be even better than this in the lower orbits planned for the future.

Navigation has processed all available lidar data in combination with the DSN radio metric tracking and the optical landmark data. Processing this data allowed navigation to improve its internal shape model much earlier than expected which in turn improved the processing of the optical landmarks. The improved shape model was also used to generate a spherical harmonic gravity field model (based on an assumed uniform density for Eros) which is being used as a priori for estimates of lower orbits and as a field for predicting the behavior of the upcoming low orbits.

Navigation is studying the feasibility of lowering the orbit to 35 km circular some time after July 4, but before August 8. This orbit geometry would provide early measurements of the high degree and order gravity harmonics before we return to this altitude for a longer period in December. This provides processing and analysis time to determine a good gravity model before entering the low orbits planned for the end of mission. Science team and project concurrence will be obtained before inserting this orbit into the current plan.

Upcoming Spacecraft Activities:

In addition to regular Eros Science and Optical Navigation, the following, are operationally significant activities planned for the NEAR Shoemaker mission operation:

• April 11: Eros Orbit Correction Maneuver 4 (100 km orbit circularization)

• April 22: Eros Orbit Correction Maneuver 5 (100 km x 50 km transfer orbit)

• April 30: Eros Orbit Correction Maneuver 6 (50 km orbit circularization)