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).

[nprev]

Sweet!!!

What's your campus scope, anyhow? (Type, aperature, etc.)

[NGC3314]

0.4m Ritchey-Chretien, using one of the big Santa Barbara Instruments CCDs for this. Details here. I have been very pleased with its performance (installed about 5 years ago, replacing a vintage-1950 refractor). With our summer climate, I am also very pleased that it can be operated from an air-conditioned control room! Perspiration is bad for the logbook, not to mention keyboard.

[Lewis007]

An article on the "cold side bake-out" process (to get rid of water contained in the Centaur stage's foam layer) can be found here: http://www.spaceflightnow.com/lcross/090810bakeout/
Two bakeouts have been completed, with at least one more to go.
The target crater for the impat will be decided upon early September, and NASA tentatively plans to announce the target crater around Sept. 10.

Last week, LCROSS looked back at Earth as part of an calibration of its science payload. More details can be found here: http://www.nasa.gov/mission_pages/LCROSS/main/

Attached thumbnail(s)

 

[mps]

LCROSS experienced an anomaly: http://www.nasa.gov/mission_pages/LCROSS/main/index.html

[Guest_Zvezdichko_*]

Oh, this is BAD! But they are optimistic that the mission will be fulfilled despite the problem.

[nprev]

Wow. Is the IRU in question part of the Centaur itself? That would sort of make sense of such a dramatic fault, since booster components ordinarily aren't expected to operate longer than a few hours at the most.

[ugordan]

Hmm, I thought star trackers were the de facto method of maintaining/figuring out attitude with gyros only as backups for periods when star trackers are unavailable?

[John Moore]

There were some initial problems with the star tracker (STA) and the IRU (June 26) after launch, however, these were minor, expected, problems -- according to the Flight Director's Blog.

As far as I understand, the ACS Attitude Control System is "based primarily on LRO hardware and software in the same arrangement". Tried finding some images of the IRU, the ACS, however, no luck -- assuming that they are on the LCROSS R4 (Attitude Control & Communications Electornics) panel.

John
A Moon Site

[Lewis007]

On August 17, LCROSS took additional images of the moon and earth, as part of the process to calibrate its instruments. See page http://www.nasa.gov/mission_pages/LCROSS/main/index.html

[Marz]

Here's a Spaceflight article explaining the recent startracking-frenzy anomaly:
http://spaceflightnow.com/lcross/090825fuel/

summary: Half the fuel is gone, but it should be just enough to complete the mission. LCROSS may have to cancel some activities not crucial to the mission to save the fuel for other unexpected contingencies.

[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.

[nprev]

Good info, all (thanks for the late-breaking, Astro0!) Yes, by all means, let's save the rest of the excitement for The Day.

Didn't realize that LCROSS' ACS was designed to torque the entire stack around...amazing engineering, and undoubtedly some pretty unique control algorithms at work there.

[climber]

More good news: http://www.spaceref.com/news/viewsr.html?pid=32291

[Astro0]

Nice memo to the LCROSS team and well deserved.
I am sure that they know how much effort the DSN put in also providing continuous coverage for LCROSS.
Also, how other missions made way in the schedule for them.

On UMSF we get to see the pretty pictures and data, but the effort that goes in to getting this stuff for us is incredible.
I've watched our comms teams during spacecraft emergencies and I can tell you it's incredible to watch so many people come together to solve sometimes seemingly unsolvable problems and all in real-time (and even two-way light travel time!).

I'm going to have to write a book one day about all the backroom happenings