From: NASA Blogs
Posted: Monday, June 22, 2009
16 June 2009 Paul D. Tompkins
What a crazy week at NASA Ames. I really thought I'd be writing more (though some of you are probably wishing I'd write a little less when I actually get a chance to write)! But there's so much to write about!
Here we are finally, on launch week! NASA Ames has been really getting excited about flight missions, with Kepler, Pharmasat, and now LCROSS. Lately, the Center has been posting countdowns for each mission on the auditorium that most of the Center's employees drive by on their way off base. Let me tell you, as someone on the Flight Team, this really drives my adrenaline through the roof. To see that number get into the single digits, and now with only 2-3 days left! Each time I see this sign, I say to myself "hoooahh, let's go!"
Since our First Week Rehearsal, ending June 1, we've been pushing hard on improvements to make this mission go as smoothly as possible. Aside from our self-induced tests, there have been a lot of hoops to jump through to be approved to fly - for example, NASA Ames management, led by the Ames Office of Chief Engineer, has to sign us off on a process known as Certification of Flight Readiness, or CoFR (rhymes with "gopher"). We've spent quite a bit of time with the review team, proving that requirements are verified, ground software and hardware to support the mission are in place, and things like procedures, processes, and flight rules are all ready to go. Just like taking exams at the end of a semester, it's a worthwhile process, but that doesn't make it fun!
As everyone knows, LCROSS is sitting atop our Atlas V launch vehicle now, and our team at NASA Ames is waiting for its chance to launch. We are all anxious to get our mission started. We've trained for over a year, and now we're ready to prove ourselves. Due to the slip in the Space Shuttle launch to June 17 (for the latest information see http://www.nasa.gov/mission_pages/shuttle/main/index.html), our earliest date is now June 18, but only if the Space Shuttle decides they can't make June 17 later on Monday (or according to some, as late as Tuesday June 16). This is work in progress, so stay tuned while things get sorted out.
Our June 17 launch block has four days, each with three launch opportunities, for a total of 12 possible times we can launch. With Space Shuttle moving into June 17, that leaves us with 9 more shots in this block, before we have to slip to June 30. Here's the rub - not all launch blocks are created equally. This launch block is really good, the next one isn't as good. Here are the factors:
First, the engineering perspective. With each launch block, LCROSS alternates between performing a flyby of the moon over the North pole and South pole of the moon on Day 5 of the mission, in order to enter its Cruise Phase orbit that will ultimately intersect the Moon. The June 17 block has us flying over the South pole, which is far less expensive in terms of propellant. We end up having a lot more propellant to fight other problems that could occur, and that makes our mission less risky on this block. Our earlier block at June 2, and our next one starting June 30 involve North pole flyby, which is more expensive. Also, our June 17 block results in orbits that are far closer to the Earth at their furthest point (apogee) than for our June 30 block (570,000 km vs. 700,000 km). This means we can avoid re-orienting our spacecraft to communicate with Earth on our Medium Gain Antenna on this block. It means another propellant savings, and a less risky mission.
Second, what we're really all about - Science. Our impact geometry is excellent on this block. One of our criteria for a good impact is the angle at which we can feasibly impact the lunar surface. There's actually a strong dependence of this angle on launch date and time. For this block, our orbits enable impact angles of over 80 degrees, even though our requirement is for greater than only 65 degrees. This means we can impart more momentum into the lunar surface, and will be able to raise the lunar regolith "ejecta" cloud that much higher into the sunlight where we can analyze it for signs of water. Better for science.
One of the components of the LCROSS science campaign has ground-based observatories watching our impact from the ground. The LCROSS science team at NASA Ames has worked with several observatories in the continental US on this end of the mission. Sadly, as we slip later into this block, the observatories in the US begin to be too close to sunrise to "see" the impact. By the 20th, there may be too much sunlight at impact time in the US, outside of Hawaii, to get good observations here. So, there are consequences to moving later. Of course, our primary science observations, straight from LCROSS itself, are going to be great either way. If you have time, check out the LCROSS science briefing, scheduled for 6/16 at 9:00 AM Eastern. Tony Colaprete, our Principal Investigator, may address this issue in his talk. Our team will certainly make the best of what we have!
NASA has a difficult job balancing the priorities of missions competing for the same launch slot. Space Shuttle is also very important, and without knowing the constraints and pressures of STS-127, I am unqualified to judge the decision to slip LCROSS and LRO to June 18. Regardless of what happens, our Flight Team is anxious to get started, and will be ready when we're given the "GO".
Our hope is that we'll be allowed to take full advantage of this special opportunity we have over next few days to fly LCROSS to its fullest potential. The window is opening...wish us luck!
// end //