Space Shuttle Atlantis returned safely to Kennedy Space Center yesterday after completing STS-122 to the International Space Station which saw the delivery and installation of the ESA European Columbus science labaratory.

As Atlantis landed, Endeavor was already at the launch pad in preparation for STS-123, also to the ISS, which is penciled in to launch in just over three weeks time on the 11th of March. Endeavor will be carrying the pressurised section of the Japanese JAXA science module.

Just a quick reminder that Space Shuttle Atlantis is scheduled to lift off at 19:45GMT today. Best internet viewing is probably via the NASA TV main page now as the better Yahoo! stream seems to have gone away.

Direct link for NASA TV Update: I found the better quality video link for Yahoo! again.

Update: Atlantis launched successfully

NASA has scheduled the next launch attempt for STS-122 for Thursday 7th February at 19:47ZULU

Atlantis was first due to launch back at the beginning of December but a recurring fault with the ECO (Engine Cut Off) sensors in the main liquid hydrogen tank prevented this. If the ECO sensors became unavailable in flight, it could lead to a situation where the liquid oxygen could be depleted beyond safe limits potentially leading to a catastrophic failure of the SSME turbopumps. NASA traced the problem to the connector points on the side of the external tank. They then fabricated and fitted new connectors which means that the vehicle now stands read to fly this week.

Atlantis will be carrying the European Space Agency’s Columbus scientific module to the International Space Station.

I will be looking this week to find the best internet video feed source for NASA TV’s coverage of the launch and I will note it here when I do.

Just a quick update on the delayed launch of Space Shuttle Atlantis on STS-122.

NASA now believe they’ve isolated the ECO sensor fault to the connectors between the External Tank and the Orbiter. Their intention is to swap the connectors out at the pad and to try for a launch on the 24th of January. They hope to have the new connectors installed by next Thursday but the launch date is still a movable feast depending on how the work goes.

The launch date of US Space Shuttle Atlantis on mission STS-122 which had been put back to the 10th of January has slipped once more while remedial work is carried out on the external tank ECO sensors.

Atlantis’ original December launch date was scrubbed due to the simultaneous failure of two of the four ECO sensors during tanking.

As we explained before, the ECO (Engine Cut Off) sensors reside in the bottom of the liquid-hydrogen portion of the shuttle external tank. Their job is to detect the exhaustion of liquid hydrogen prior to it running out completely and signal the Space Shuttle Main Engines (SSMEs) to shut down. Normally, the Space Shuttle Main Engines would be commanded to shut down by the flight avionics with some liquid hydrogen to spare but should a fuel-line run dry at flight-power, the powerful turbopumps which force fuel and oxidiser through the engines would suddenly spin up beyond their rated rpm and fail catastrophically. Due to their proximity to vital systems such as APUs and avionics in the rear of the shuttle, the consequences of such a failure are not something NASA are willing to risk.

NASA appear to have now isolated the fault to the connections that lead from the External Tank carrying the ECO sensor signals. They intend to repair these connectors with the vehicle on the pad to make sure all of the sensors are functional for launch. No revised launch date has yet been set for STS-122

Such prudence with regard to safety is undoubtedly a good thing but it does raise an interesting problem for the remaining shuttle flights. The shuttles are due to be retired from service by mid-2010 (Atlantis is due to retire in mid-2008) which means that the ten remaining ISS construction missions will have to be flown at an average rate of one every 3 months, a rate which NASA has been unable to achieve in recent years. There is also a Hubble service mission scheduled for 2008 which, due to the different orbit and the inability to reach the safe-harbour of the ISS, will require a second Shuttle ready on the other pad for a contingency launch. It is planned that immediately after this flight, pad 39B will begin conversion for use with the new Ares I booster system which 39A is used for the remainder of the shuttle flights.

Personally, I’d be inclined to look at building Pad 39C which was projected but never constructed during the Apollo era, it would form the third pad in a row to the North of 39B and 39A which were themselves converted to shuttle use after the Apollo program. While 39C was never built, a short stub of crawler-way points toward it’s intended location from the dog-leg of 39B’s crawler-way. The construction of 39C would remove the constraint on Ares-I project testing as it is already intended that the VAB be fitted out to handle both Ares I and STS configurations at the same time during transition. The creation of 39C would also allow for more complex logistics when the Ares-V boosters come into service later. For the record, there were two further pads planned to the North of 39C but whether the VAB could ever need to service five vehicles at the same time seems unlikely.

I make the assumption that the construction of pads is a relatively insignificant cost in relation to the rest of the space program.

The next launch attempt of Space Shuttle Atlantis for STS-122 has been postponed until January 2008 due to faults with the ECO sensors in the Liquid Hydrogen fuel tank of the Space Shuttle System.

Launch had originally be scheduled for last Thursday but two of the four Engine Cut-Off Sensors in the liquid hydrogen section of the external tank failed to respond during fuelling. NASA requires that all four ECO sensors respond during tanking prior to launch. On Sunday’s launch attempt one of the four sensors failed to respond during tanking and the launch was scrubbed.

The postponement to the 10th of January is to allow time for engineering teams to evaluate the sensor problem and I’d also hazard a guess, to avoid any possible issues with the Shuttle’s annual ‘Y2K bug’. The bug is a potential issue with on-board computers when the calendar rolls over from one year to the next. This wouldn’t directly be a problem for a Shuttle launched in the next few days but it could perhaps become a problem if damage to the orbiter required an STS-3xx crew rescue mission.

The ECO sensor issue is a tricky one, they can’t risk them not working properly as a turbopump failure could lead to a ‘catastrophic’ engine failure. As I understand it, when the Space Shuttle Main Engine (SSME) turbopumps are at operating speed, fuel flow must be maintained for safe operation. A normal shutdown would be a controlled throttle-back of the engines so the turbopumps would spin down gradually. A sudden cutoff of the fuel would actually cause an rpm increase and failure (presumably uncontained) of the turbopump.

At a recent Mission Management team press briefing, they discussed the possibilities for fixing the ECO sensor issue. The MMT are optimistic that the fault lies in the avionics which are contained within the orbiter and can be accessed while on the pad. If, however, the fault lies at the sensors themselves within the base of the external tank, a roll-back to the vehicle assembly building may be required, perhaps even with the tank being demated from the stack. The MMT did mention that they had gained access to the tank while on the pad on a previous mission “a long time ago” but pointed out that it was a very difficult process involving removing an area of insulation foam, removing a panel of the tank and then putting it all back together again. The foam would then have to be re-applied in situ.

In the mean time, station life goes on. Progress M-62 is scheduled to launch to the ISS on the 23rd of December. The unmanned cargo vessel is expected to dock with the station on the 26th.