posted 09-07-2006 06:41 PM               

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NASA has set Space Shuttle Atlantis' launch for Friday, Sept. 8, at 10:41 a.m. CDT. Shuttle program managers made the lift-off decision after reviewing more detailed data on a problem associated with one of the spacecraft's electricity-producing fuel cells.

Mission managers will review an additional piece of analysis before the shuttle's external fuel tank is loaded at 12:45 a.m. CDT. Shuttle Program Manager Wayne Hale said he was confident the results of the analysis would support the launch decision.

Tuesday night as ground teams were preparing for a scheduled Wednesday launch attempt, a voltage spike in the motor of Atlantis’ fuel cell #1 coolant pump was observed during the activation of the shuttle's three fuel cells. The coolant pump circulates Freon through the fuel cell to prevent it from overheating during flights.

If Friday's launch is delayed, there could be another attempt Saturday at 10:15 a.m. CDT.

During Atlantis' mission, STS-115, astronauts will deliver and install the P3/P4 truss, a girder-like structure, with solar arrays that will double the International Space Station's power capability.

Atlantis' crew consists of Commander Brent Jett, Pilot Chris Ferguson and mission specialists Dan Burbank, Heide Stefanyshyn-Piper, Joe Tanner and Steve MacLean, a Canadian Space Agency astronaut.

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posted 09-08-2006 04:21 AM               

Mission managers are convening now to review the problem and decide if a launch at 10:41 a.m. CDT can continue as planned.

The sensor failed a routine pre-launch check, failing to read "dry" when engineers commanded it ignore its real status of "wet". The sensor protects the shuttle's main engines by triggering their shutdown in the event fuel runs unexpectedly low. The sensor is one of four inside the liquid hydrogen section of the external tank.

A similar failure occured during attempts to launch STS-114 in 2005. At that time, NASA decided it was acceptable to launch with 3 out of 4 ECO sensors functioning. It is not clear though, if the same conclusion can be made for Atlantis.

Tanking began late by about an hour due to the need by engineers to replace a faulty nitrogen purge control valve.

Weather remains at 70 percent "go" for launch, with the primary concern for rain within 20 miles of the Shuttle Landing Facility.

posted 09-08-2006 07:51 AM               

The astronauts are now taking their seats inside Atlantis. Once in place, the crew will begin powering up orbiter systems and getting the ship configured for launch.

At this time, NASA is still pressing forward with launch preparations. Mission managers are continuing to determine if they will consider launching with three working sensors or if it will be necessary to de-tank and try again tomorrow.

The decision hinges on whether NASA follows the rule exception devised after the STS-114 ECO failure — stand down for 24 hours and if the problem repeats itself tomorrow, then launch — or decides to amend the rule and fly as-is with 3 of 4 sensors operating.

posted 09-08-2006 09:53 AM               

From SPACE.com:

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NASA flight rules typically call for four working [Engine Cutoff or ECO] sensors in both the liquid oxygen and liquid hydrogen fuel tanks, but the regulations do have some leeway that would allow a Saturday launch. But that approval hinges on the results of additional sensor checks as engineers drain Atlantis’ external tank tonight and refill it early Saturday.

If all four sensors work fine, or if the problem occurs exactly as seen today, Atlantis could launch, NASA spokesperson June Malone told SPACE.com.

The rationale allowed NASA’s space shuttle Discovery to launch its STS-114 return to flight mission in July 2005 despite a 13-day delay due to a similar ECO sensor problem. The sensors, all tracked to a batch manufactured in 1996, were later replaced with new versions in future shuttle external tanks.

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Launch is now set for 10:14:49 a.m. CDT (1514:49 GMT) tomorrow, with weather forecasts offering an 80 percent chance of favorable flight conditions, NASA said.

NASA has only one remaining day – Sept. 9 – to launch Atlantis’ scrub-ridden mission to jump start ISS construction before settling into an extended delay to allow time for a Russian Soyuz mission to swap out station crewmembers. The next available launch attempt can occur no earlier than late September or early October, shuttle officials have said.

posted 09-08-2006 10:11 AM               

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Originally posted by ivorwilliams:
I don't mean to sound complacent but to the layman one would assume it makes NASA look like they just can't get their act together.

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We have seen the alternative twice before, and given the choice, I think everyone will agree that to err on the side of the launch commit criteria as they are written is anything but farcical.

posted 09-08-2006 12:14 PM               

I have to agree somewhat with Ivorwilliams, it does seem farcical that NASA has had this ECO sensor problem for years and they've done little to resolve it. There's an excellent article on the subject at www.aee.odu.edu/shuttlerepository/page.php?cat=6

Obviously crew & vehicle safety is priority 1, however, this is insane to scrub yet another critical launch due to one of the 4 ECO sensors showing an anomoly, AGAIN.

Yes, the shuttle is the most complicated spacecraft ever built, but the shuttle has been flying since 1981, so most of the hardware issues have been solved due to inflight data. The ECO problem has been an issue since they've been used in the ET in 1996, so why does it continue to be a persistant problem ?

Also remember, the ECO's are backup's, not primary MECO controllers, so what seems to be the problem if 1 of 4 aren't functioning ???

It's one thing if there was an issue like software, fuel cell, cracked fuel lines, ET foam, TPS tiles or other issues that weren't projected, but to constantly have problems with the ECO's is ridiculous.

What I'd like to know is if NASA is going to charge Martin the $650k that this scrub is going to cost. It makes NASA look like they're scared of their own shadow when they scrub over an issue like this. They're going so far overboard in the name of safety, that it's any wonder if they get to launch at all.

NASA is extremely competent at what they do, but if this is the criteria that's going be used to get to the moon, we'll all be very old people when we watch the next manned lunar landing.

Ray

posted 09-08-2006 12:34 PM               

Ray you are correct in stating that the ECO sensors are backups to the system. But what do you think would happen if they ignored the failed sensor, launched and the SME's came apart and destroyed the vehicle? They would be excoriated by the press, the politicians and the layman on the street.

NASA wrote this rule after STS-114 and if the sensor repeats this failed signature tomorrow, it will re-enforce what they expect is happening and be able to launch.

When someone asks you why can't NASA get their stuff together ask them how many appliances they have that are as old as those sensors and fuel cells on the stack?

These sensors were examined every which way prior to being installed in the tank. Sometimes things just fail. It's aggrivating but I'm more confident in THIS NASA than I was following the Columbia tragedy. They are doing everything possible to accomplish their mission and do it safely.

Besides Ray when we return to the Moon in the next decade, I'll be an AARP member anyway.

posted 09-08-2006 12:56 PM               

I'll be joining you as a member of AARP in another 10 years and I can't wait for the discounted dinners & movie tickets.

I'm not denegrating NASA or their mission rules and yes, they are the best minds in the country and they do a brilliant job with what they have. What I'm upset about is how the shuttle has flown without ECO's very successfully, so IMHO, this really isn't a safety issue, but a myopic microscopic issue that's causing the prevention of the flight. These ECO scrubs are costing millions of dollars that NASA doesn't have and it's taking away resources away from other projects.

The reason the ECO's were installed was to prevent SSME detonation in the event of fuel starvation during the boost phase. If LOX flow isn't cutoff before the liquid hydrogen to the SSME, it will cause the SSME to detonate, badly damaging or destroying the orbiter.