Thanks to the "Space Multimedia" site, I have been able to watch yesterday's press conference. Now the big picture clears up.
First of all, I was very wrong in my statement in my earlier STS-122 status article that NASA will launch without working ECO sensors - well, kind off...
In fact, it is quite the opposite. As NASA's space shuttle program manager Wayne Hale stated the proposal is to require all four ECO sensors to work during launch preparations. Thus, the criteria has actually been tightened. Previously, only three good sensors were needed. Mr. Hale said that this plan came from the astronaut's office. This goes well together with a posting I read in the Flickr STS-122 group created by Armando Perdomo. There, someone from an astronauts family posted (excerpt):
Anyway, what I heard that is interesting is that NASA offered the astronauts to go "as is" - with 2 sensors. They declined. My thought is that they didn't decline out of fear of personal safety, but more of the consequences to NASA should something go wrong.This not only proves what great people the astronauts are, it fits well within the press briefing picture. Mr. Hale also explained the reasoning for the new launch commit criteria: previous experience showed that failed ECO sensors always worked on the second launch attempt. Nobody knows why. Mr. Hale actually said we saw "that they magically work".
Even if the cause is not know, one can assume that if the failure cause is the same as on previous missions, the sensors should behave the same. So seeing an additional failure on the next tanking would indicate that the failure cause is different. In this case, the launch will be scrubbed, as it would be an even less understood situation.
If the sensors work as expected during countdown, there is a good chance they will continue to function (based on previous experience). However, the problem was quite erratic and what was seen was different than before. This is the additional risk that NASA is accepting: the ECO sensor system may fail again during the launch. This is where new, still to be fully developed procedures kick in. They use new sensor instrumentation plus other systems to decide what to do in such a case. Here, some manual interaction may be required. NASA is actually reading itself to do the ascent without the ECO sensors.
So to sum it up: NASA requires 4 working sensors during countdown. If they don't work, launch will be scrubbed. After liftoff, loss of the ECO sensors will be acceptable due to new procedures. However, it is hoped that they will continue to work if they did during countdown.
The launch has been moved to Sunday to support creation of the new procedures. The launch window has been shrunk to one minute to provide as much spare fuel as possible. Both of these measures are to address a failure scenario which will hopefully not occur due to the four-sensor launch scrub requirement.
It is important to note that this plan is not final. The mission management team meeting did not find concurrence from everyone. So folks were sent back to think about the plan, gather more data, run more simulations, get a better grip on everything - and meet again today at 1pm ET. Today, the final decision will be made. Depending on the findings, we may end up with a totally different set of options. The time of the post MMT press conference has not been announced yet. I guess they now refrain from posting any time because we've seen that any prediction is at least inaccurate ;)
Let's assume NASA sticks with the plan. So what may happen? If there is a launch scrub on Sunday due to the ECO sensors, I guess it is mostly "game over" for the December launch window. If there is a scrub for weather reasons (more probable now due to the short one minute launch window), an additional launch attempt can be done on Monday. Chances of weather prohibiting launch are just around 30% for both days, so there is a fairly good chance that either of these attempts will succeed. If they don't, the oxygen and hydrogen tanks for the fuel cell system must be topped off. That requires a three-day stand-down. Interestingly it was said that this means the next possible launch attempt would be on Thursday (is my math wrong?). It was mentioned that they could also launch on Friday. The launch time will be approximately 25 minutes earlier for each attempt.
With a Sunday or Monday launch, the two-day mission extension to do the extra ISS solar array rotary joint spacewalk is still an option. For Thursday and Friday this seems not to look well. They intentionally didn't go into any specifics, but information I previously obtained tells me an extension would not be possible if launched late next week.
Finally, the commented that the overall shuttle launch schedule would not necessarily be affected if Atlantis' launch would need to be deferred to early January 2008. If, however, the sensor issue would really need to be troubleshooted, the whole launch schedule would probably be affected. And it was strongly expressed that all of this post-December launch scenarios are highly hypothetical and should not be considered real for the time being. I concur to this - let's solve today's problems today and look at further issues when they come up.
Even though I am in no position to judge, the plan presented seems to be very sound. I hope they will not find any hidden problems and can attempt for launch on Sunday. Let's keep our fingers crossed...
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