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(meteorobs) Fwd: "NEAR Update, 10 April 2000" and "NEAR Moves to Next Stage"
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From: Ron Baalke <BAALKE@KELVIN.JPL.NASAdot gov>
Date: Tue, 11 Apr 2000 14:53:26 GMT
Subject: [ASTRO] NEAR Update - April 10, 2000
NEAR Mission Status Reports - http://near.jhuapldot edu
April 10, 2000
MISSION OPERATIONS:
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.
NEAR Shoemaker is presently in a nominal 200 km x 100 km transfer orbit
around Eros. The spacecraft was placed in this orbit April 2, 2000 at
9:03 p.m. EST when Orbit Correction Maneuver 3 (OCM 3) was executed. NEAR
Shoemaker will remain in this transfer orbit conducting Science
observations until April 11, 2000 at 5:12 p.m. EST when Orbit Correction
Maneuver 4 (OCM 4) will circularize the orbit at 100 km. As OCM 4 is
refined, this burn time could move as much as +/- 1 hour.
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.
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.
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)
NAVIGATION:
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.
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From: Ron Baalke <BAALKE@KELVIN.JPL.NASAdot gov>
Date: Wed, 12 Apr 2000 15:25:33 GMT
Subject: [ASTRO] NEAR Mission Moves to the Next Stage
NEAR Mission Moves to the Next Stage
http://near.jhuapldot edu/news/flash/000411.html
April 11, 2000
The NEAR mission moved smoothly to its next stage after
a 5-second engine burn on April 11 nudged NEAR Shoemaker
into a circular orbit about 62 miles (100 kilometers)
from asteroid Eros. At the time of the engine burn, the
spacecraft was about 128 million miles (206 million
kilometers) from Earth.
Getting its best look at Eros so far, the spacecraft
will remain at this orbital distance for 11 days, moving
around the asteroid three times at just under 5 miles
per hour. Another maneuver on April 22 will start
lowering the spacecraft into its prime scientific orbit,
which starts April 30, when the spacecraft is 31 miles
(50 kilometers) from Eros' center.
NEAR Shoemaker has circled Eros five times since meeting
up with the asteroid on Feb. 14, providing data on the
space rock's surface, shape and composition that has
exceeded scientists' early expectations.
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