LCROSS en route Options

[NGC3314]

While we're waiting for Those Pictures, here are a couple of shots of LCROSS from our campus observatory last night (0221, 027 UT on 15 July). 4 minute exposures tracking expected motion from the Horizons ephemeris, within 20 degrees of the southern horizon and fighting summertime haze as well as city lights. I wanted to catch it before its inclined orbit takes it too far south, after which it spends a week or so as a predawn object. The range was about 563,000 km, and the Centaur is no bigger than a CSM/LM combination, so this is a more difficult target than spotting an Apollo enroute was. (On the other hand, nobody had CCD imagers in 1969).

[Astro0]

In response to the Spaceflight Now article, this response from the LCROSS team...

During a communications session on Aug. 22, it was discovered that a fault had been triggered in the spacecraft's inertial reference unit, or IRU. The IRU is used by the probe's attitude control system to determine its orientation in space.
The fault in the IRU caused LCROSS to switch to its star tracker for attitude information. Noise in the star tracker resulted in the spacecraft's attitude control system firing the spacecraft's thrusters excessively, consuming a substantial amount of propellant.

The mission operations team was able to correct the situation and stop the excessive thruster firing. Mission engineers determined what went wrong and uploaded software updates that should prevent such an incident from recurring.

The big issue was determining how much propellant was lost and how much was required to successfully complete the mission. The good news out of all of this is that the problem was caught and corrected in time so that the spacecraft still maintains a positive propellant margin; we still have more than enough propellant to successfully complete the mission. However, our extra margin of propellant is not nearly as much as it was previously. Mission management and the operations team want to maintain a prudent propellant margin for the rest of the mission and are therefore looking at the schedule of upcoming maneuvers to determine which are really necessary and which we can do without.

The bottom line here is:
1. An anomaly occurred which caused excessive use of propellant on the spacecraft.
2. The anomaly was detected and corrected.
3. Even after the anomaly, we have enough propellant to complete the mission.
4. We are still on target for a October 9 impact at 11:30 UT.

I know we promised you an exciting mission, but we are all looking forward to toning down the excitement until impact!

...End Message.