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LCROSS Set For Lunar Impact Oktober 9 : HD WALLPAPERS AND VIDEO
NASA_LCROSS_2009_
nasa_lcross
Our last day in flight promises to be the most challenging and the most rewarding for the project. Our 112 days in orbit are focused entirely on the last four minutes, after the Centaur impacts our target crater and raises a plume of lunar material for the LCROSS Shepherding Spacecraft to observe for signs of water, but before the Shepherd also impacts the moon.
From a Flight Team perspective, the LCROSS impact sequence is a dream occasion, and yet provides some cause for trepidation. Many things can go wrong, and with so little time, there is only so much that can be done.
During you day tomorrow, I thought it might be fun for you to know what the Flight Team will be doing in lead-up to the event. To put it plainly, we won’t be idle! Enjoy!
A Recent Development: TCM 9 put LCROSS On-Target
The latest data from our Navigation team indicates that TCM 9 has already put LCROSS on target to hit the designated impact area, without the need for executing TCM 10 on Thursday evening. Our predicted impact point is already within our target 3.5 km diameter circle, and our team will only make very small adjustments to improve our impact accuracy. This alters our original plan for Thursday.
Instead of performing TCM 10, the team will plan and execute a very slow rotation by feeding the spacecraft new target attitudes each minute (see “Once More Around the Earth” for a description of our “quaternion creep” attitude change) to minimally disturb the current orbit while turning to an orientation that is optimal for Separation. At Separation, LCROSS will use the velocity imparted by the springs between the LCROSS Shepherding Spacecraft and the Centaur (adding an estimated 15 cm/s to the Centaur) as a final means of nudging the Centaur toward the center of our target. Analysis of the Centaur separation springs, along with actual tests of the system conducted to simulate very harsh conditions of space (far harsher than LCROSS has actually experienced) indicate the separation will impart a fairly precise change in velocity to the Centaur.
This plan represents less risk (the slow attitude change will be simpler to plan, test and execute than a TCM), and introduces less uncertainty into the prediction of our impact point (firing thrusters for very short durations adds a lot of uncertainty, while the separation springs in the LCROSS-Centaur interface mechanism are very repeatable). We’re fortunate to find ourselves in this situation, and we’ll take full advantage of it to ensure we impact on-target.
DOY 281 (October 8): TCM 10 (or not), Separation, Centaur Observation and Braking Burn
The last 24 hours of the mission, bridging DOY 281 and 281 (October 8 and 9), will be a flurry of activity. Here is the sequence of events. I’ve provided both UTC and Pacific Daylight Time references:
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