NEAR Shoemaker Report 19 May 2000

MISSION OPERATIONS:

NEAR Shoemaker remained in Operational Mode with Flight Computer #1 and
Attitude Interface Unit #2 in control of spacecraft attitude. Except
for
the Near-Infrared Spectrometer (NIS), the spacecraft instrument suite
remained “ON” and operational this week. The NIS instrument had a
“high
energy current” problem last Saturday. NIS was turned “OFF” and has
remained “OFF” during the week. Several key members of the NIS team
were
on travel and only mid-week were all available for planning a “turn-on”
scenario.

NEAR Shoemaker is presently in a nominal 50 km circular orbit around
Eros.
The spacecraft entered this orbit April 30, 2000 at 16:15 UTC when
Orbit
Correction Maneuver 6 (OCM 6) was executed. According to the current
long
term trajectory plan, NEAR Shoemaker will remain in this orbit
conducting
Science observations until July 7, 2000 at 18:00 UTC when Orbit
Correction
Maneuver 7 (OCM 7) will initiate the 50 km x 35 km transfer orbit.

Since the next planned OCM is not scheduled until July 7, weekly
Momentum
Correction Maneuvers (MCM) are required to manage spacecraft system
momentum. Beginning May 10, these maneuvers are scheduled every
Wednesday
until June 28. The second MCM of this period, MCM 4, was successfully
executed this past Wednesday, May 17, at 13:00 UTC. The achieved
momentum
was well within operational tolerances, and the imparted delta V was
minor.

Revised XGRS PIN Diode autonomy rules and macros which were loaded last
week are functioning well. Performance evaluation of these rules may
dictate minor tweaks to the PIN diode threshold voltage set point
and/or
desaturation timer duration.

A workaround for the Flight Computer Scan Enable anomaly has been
identified and incorporated into MOPS planning software. The first
command load to incorporate this workaround is 00143 which starts at
the
end of the high gain antenna track this coming Monday, DOY 143. When a
Scan Enable command is requested, the workaround issues the command 4
times with a .25 second delay between successive commands.

The NIS instrument was disabled last Saturday, DOY 134, when an
excessive
power converter current was detected. When discovered, the real-time
flight operations team contacted the NIS lead engineer who, upon
evaluation of telemetry, recommended the instrument be disabled.
Operation of the Magnetometer, which shares a common Data Processing
Unit
(DPU) with the NIS, was not effected. For the near future, the NIS
will
remain disabled, pending further telemetry evaluation and instrument
state
assessment.

Except for the NIS, science activities conducted this week included
Eros
observations by the full instrument suite: MSI, MAG, NLR and XGRS.
Please
consult science timelines for more details.

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:

May 24 Momentum Correction Maneuver 5

July 7 Eros Orbit Correction Maneuver 7 (50km x35km transfer orbit)

July 14 Eros Orbit Correction Maneuver 8 (35km orbit circularization)

July 24 Eros Orbit Correction Maneuver 9 (35km x50km transfer orbit)

July 31 Eros Orbit Correction Maneuver 10 (50km orbit circularization)

NAVIGATION:

Navigation generated a new plan, named #05/16/00, which modified the
July
low altitude segment to accommodate critical opnavs immediately
following
the circularization burn at 35km. The effect of this was to move OCM-9
and OCM-10 one day later than the previous plan. An integrated SPK
file
representing the new plan from April 2000 until the end of mission was
placed on the SDC and a formal delivery notice was issued.

Operational tests of the LIDAR data are being performed. The data from
50km orbit has resulted in another improvement in our shape model and
gravity model which in turn improves our orbit accuracy. Differences
between the LIDAR based and optical landmark/DSN based orbits are now
only
a few tens of meters. Having these complementary data types has been a
boon for verifying the nav system and improving its accuracy.

An alternate low-phase flyover orbit that gives several passes at about
24
degrees phase at about 60km radius have been developed. These
integrated
orbits are available for planning purposes, but the nominal plan still
has
the single flyover orbit at about 200km radius. The nominal plan will
not
be changed until and unless the project decides to change this orbit.