NEAR Science Update

On February 2, the NEAR spacecraft resumed normal
science operations after a brief hiccup. During
preparations for a scheduled rocket engine burn, the
spacecraft entered a safe hold. The safe hold is a
pre-programmed, automatic response by the spacecraft to
an unplanned event which requires immediate corrective
action. In this case, the spacecraft stopped all routine
operations, pointed its medium gain antenna at Earth,
and awaited further instructions. Recovery from the safe
hold and return to normal operations occurred on the
afternoon of February 2, and the spacecraft successfully
executed a revised engine burn on February 3 at noon EST
(17:00 UT).

The cause of the safe hold was incorrect data input to
the spacecraft attitude control system as onboard
accelerometers were powered up, which resulted in a
small autonomous engine firing. Fuel expenditure was
insignificant. With the successful engine burn today,
the NEAR spacecraft is back on course for arrival at
Eros as planned on February 14.

We did, however, lose science observations that were
scheduled to take place during the time that the
spacecraft was in safe hold. After another heroic effort
on the part of our sequencing team and operations team,
a new set of commands has been loaded on the spacecraft
to recover the most critical of these observations,
which include image sequences of Eros and an infrared
spectrometer mirror geometry test. The image sequences
will be used for optical navigation to pin down the
trajectory of the spacecraft now that the engine burn
has been completed. The infrared spectrometer test was
needed to determine accurately the look direction of the
instrument, which uses a scan mirror. This mirror
functions like a periscope – we turn the mirror to scan
the instrument field of view through a 140 degree arc.
The test will use Eros as a source of light to calibrate
the viewing direction versus the scan mirror position.
For the test to work, Eros cannot be too close or too
far – hence the need to perform the test this week. Both
the recovery image sequences and mirror geometry test
are scheduled to occur over the next few days.