Posted on 12/08/2007 6:01:34 AM PST by AntiKev
MMT decide to try for a Sunday launch attempt for STS-122 The Mission Management Team (MMT) have concluded their meeting on flight rationale for proceeding with the launch of Shuttle Atlantis on STS-122, deciding to make a launch attempt on Sunday at 3:21pm Eastern, in a one minute launch window.
The main reason for waiting an extra day would be to finalize Flight Controller procedures for watching the tank closely during ascent, in the event of ECO (Engine Cut Off) sensors were deemed unreliable. The launch could be delayed longer if those procedures are not finalized.
(Excerpt) Read more at nasaspaceflight.com ...
Ping.
bookmark
LOL
I use the “we” because this program is funded by “we the people.” Even up here in Canada we’ve spent money on the shuttle and ISS programs (Canadarm I & II, as well as the OBSS). Also this mission will bring the European Columbus laboratory to the ISS. Marking the official start of European on-orbit participation (ignoring the Russians). This is truly an international mission.
Although I’m rather disappointed that they decided to push back the “US Core Complete” stage of ISS construction by delaying STS-119 into 2008. They could really use the extra power provided by those solar arrays right now.
I hope they can lift off tomorrow. I was disappointed they did not make it Thursday since they were on a roll with the other 3 launches this year. Was hoping for another one on time.
I’m surprised there has not been more coverage of this but perhaps I am not looking in the right places: I read that Rep Dave Weldon of FL has submitted legislation calling for the shuttle NOT to be shut down in 2010, but to keep flying til 2015. Not sure what to make of that idea.
Ling this candle BUMP!
so, it’s set for sunday ?
I’m all for anything that will get more money to NASA. But I think this might be barking up the wrong tree. This proposal is being met in the Space Industry with mixed feelings. If they can successfully increase NASA’s budget enough to keep the Shuttle flying with the required modifications AND continue on track with the Vision for Space Exploration. Then I will be happy. But historically this has not happened.
What I would be even happier with is extend the shuttle to 2012 and move IOC for Ares/Orion back to 2012 where it started. That would be the best and probably most politically pallatable solution.
Just checked my sources. Basically the MMT meets again in about 30 minutes (1PM EST) and will decide today whether or not to attempt a launch tomorrow. I’ll come with live coverage of the post-MMT press conference (provided there is one, but I assume there will be) later on in the day once I find out when it is.
Thank you... must be weather concerns.
No, weather is not the main concern. The Engine Cut-Off sensors in the External Tank are causing problems again. It’s an intermittent electrical failure. They’ve seen it before though, but don’t know what causes it. Usually they work properly during the second tanking, which is what they’ll figure out tomorrow.
Weather is only 30% chance to constrain launch as of the MMT yesterday.
The hydrogen sensors are way more than fuel guages. They have to work with liquid hydrogen, which is a harsh environment to begin with. Is this a science yet, or something of a rocket art?
Never said they were “just” fuel gauges. This is an issue that’s cropped up since RTF. They haven’t root caused it yet. It could be a manufacturing issue from a new batch of sensors.
The post-MMT press conference is currently scheduled for NET 5PM Eastern. I’ll keep you guys updated as it happens.
Eh, much ado ‘bout nothing. They never run those tanks dry. They always include an extra 700# of LiH to ensure rich MECO based on low oxidizer levels.
OTOH, if its the oxidizer sensors that are the one’s fritzing, that could be a problem (don’t want to be cavitating those pumps at 35,000 RPM). Bad.
They should just hover their fingers over the engine kill switch, and if the engines don’t cut off when they should just hit the button. How hard can it be?
They did something similar for Apollo 13 for the main engine burn around the backside of the moon.
That’s essentially the flight rationale. They never run the tanks dry (they can’t) and they always “waste” a little bit of propellant. But it would be disastrous if they do run a tank dry. Essentially the backup plan is to manually monitor propellant usage and back-calculate how much is left on the fly. Very worst case there will be an underspeed and they won’t be able to reach the ISS.
They know pretty much to the second when the engines should cut off (give or take). If they don’t by then, hit the switch (or button). I don’t think thats all that big of a deal. What probably is a big deal is the flight control software that is watching the 8 propellent sensors (two in float).
There are eight propellant depletion sensors. Four of them sense fuel depletion and four sense oxidizer depletion. The oxidizer depletion sensors are mounted in the external tank’s liquid oxygen feed line manifold downstream of the tank. The fuel depletion sensors are located in the liquid hydrogen tank. During prelaunch activities, the launch processing system tests each propellant depletion sensor. If any are found to be in a failed condition, the Launch Processing System sets a flag in the computer’s Space Shuttle Main Engie operational sequence logic that instructs the computer to ignore the output of the failed sensor or sensors.
During main engine thrusting, the computer constantly computes the instantaneous mass of the vehicle, which constantly decreases due to propellant usage from the external tank. When the computed vehicle mass matches a predetermined initialized-loaded value, the computer arms the propellant depletion sensors. After this time, if any two of the good fuel depletion sensors (those not flagged before launch) or any two of the good oxidizer depletion sensors indicate a dry condition, the computers command main engine cutoff. This type of MECO is a backup to the nominal MECO, which is based on vehicle velocity. The oxidizer sensors sense propellant depletion before the fuel sensors to ensure that all depletion cutoffs are fuel-rich since an oxidizer-rich cutoff can cause burning and severe erosion of engine components. To ensure that the oxidizer sensors sense depletion first, a plus 700-pound bias is included in the amount of liquid hydrogen loaded in the external tank. This amount is in excess of that dictated by the 6-1 ratio of oxidizer to fuel. The position of the oxidizer propellant depletion sensors allows the maximum amount of oxidizer to be consumed in the engines and allows sufficient time to cut off the engines before the oxidizer turbopumps cavitate (run dry).
So like I said, much ado ‘bout nothing. Just take the stinkin’ LiH sensors out of the loop and run a nominal MECO (with oxidizer sensor backup).
Worst case situation is a bit of overspeed. Which they can bleed off by swinging around the moon and hook up with the ISS with time to spare.
Worst case situation is a bit of overspeed. Which they can bleed off by swinging around the moon and hook up with the ISS with time to spare.
Didn't know they had Lithium Hydride on board. I assume you mean liquid oxygen (abbreviated LH2). It's much ado about nothing until an off-nominal shutdown blows one of the SSMEs apart in the orbiter aft. In any case they would NEVER EVER have enough velocity to get anywhere near the moon. If the worst case was overspeed then they would have no problem, but the worst case is actually an underspeed or even a premature engine shutdown in which case we're talking abort to orbit or abort once around, immediately LOM. Possibly LOV and even LOVC. You're poo-pooing this situation as if it's nothing. Spaceflight is NOT routine no matter how easy the professionals make it look. These are still very experimental vehicles. The idea is to make the system as safe as possible. In other notes, the post-MMT briefing has started. Wayne Hale has announced they will attempt to launch tomorrow (as expected). ANY ECO sensor issues (be they LH2 or LOX) will be grounds for a scrub. The Launch Commit Criteria have been changed to only allow for FOUR good ECO sensors, previously they could launch with 3 of 4 working.
Forecast is only 20% no go, i.e. 80% go.
Wayne Hale describing the operation of the ECO sensors. Basically when wet and cold they indicate ~3V and higher when dry. But at open circuit voltage (~13.5V) they go back wet. Meaning that the sensors fail “wet” as opposed to dry. This is the key issue. If all four sensors fail wet, then the tank will run dry while combustion is ongoing. There are more safeguards but this would mean one layer of protection is gone.
Tanking coverage begins tomorrow morning at 6AM. See you all then.
Sounds good.
Wow! A Sunday launch?! Cool! I’ve been missing these threads since returning back to work.
Sunday, December 9, 2007, 3:21 p.m. EST
Be here early.
thanks!
:) See you then!
I hope I can get home from church in (west coast) time...:)
Well at least the Bears are not playing..
Ping the list again Kevin. They’re done for the day. An ECO sensor failed during tanking at about 630 this morning.
We’re going to come back and do this again in January most probably. They’re in the process of de-tanking.
MMT is meeting right now. The team is into a 24 hour scrub turnaround. After tomorrow they have to replenish the orbiter cryogenics in order to preserve the 11 + 2 + 2 day mission profile.
Shuttle Launch Off Until January
By MARCIA DUNN
The Associated Press
Sunday, December 9, 2007; 9:39 AM
Glad I checked in...
They can put the cargo on a later ship.
Not really. Theoretically possible, but not palatable for the Euros. This launch is now NET 2 Jan 2008.
The Shuttle may be totaled. Off to the junkyard with it.
Weldon is grasping at straws. Atlantis is scheduled to have its final flight next August and then it becomes a parts supply for the Discovery and Endeavour shuttles. I don’t know that these birds have another seven years in them without another catastrophic loss.
In order to fly past 2010 they need to have a whole bunch of money poured into them. As a result of the Columbia Accident Investigation Board. Congress has (in the past) not been willing to release these funds in favour of social welfare projects “for the children.” What is more “for the children” than expanding the species beyond this planet?
I also am eager to see the shuttle retired ASAP, though I will sure miss it after nearly 30 years! You are right though. It just is not safe and I will be relieved when astronauts are flying a less dangerous vehicle. Problem though is if the next generation vehicles are not ready for a few years then we are looking at a gap in American space flight. And if an anti space president like Obama (gasp!) is in the White House, NASA could be in big trouble.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.