Back to newsletter listDate:
Mon, February 18, 2008 06:35:26 PMFrom:
CBS Space News
Subject:
630p 2/18 Update: Steering jet heater problem under study; not considered safety issue
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CBS NEWS STS-122 STATUS REPORT: 88
Posted: 06:25 PM, 2/18/08
By William Harwood
CBS News Space Analyst
Changes and additions:
SR-85 (02/18/08): Shuttle crew begins final heat shield inspection
SR-86 (02/18/08): C-O-R-R-E-C-T-I-O-N: Landing strategy news conference Tuesday (fixing time, adding dropped day)
SR-87 (02/18/08): Adding quotes and details from flight director's briefing
SR-88 (02/18/08): Flight controllers troubleshoot vernier thruster heater failures
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6:25 PM, 2/18/08, Update: Engineers troubleshoot vernier thruster heater glitch
Engineers are troubleshooting problems with heaters used by four of the shuttle Atlantis' aft steering thrusters. Flight controllers noticed problems with one aft vernier thruster - L5L - around 4:30 p.m., at the end of the crew's day. Shortly thereafter, controllers saw similar symptoms with the heaters of three other aft vernier jets. Officials said the problem was not considered a safety issue and the crew will get up as planned around 12:45 a.m. Tuesday to rig the ship for landing Wednesday.
"The propulsion officer a little over an hour ago noticed a sign that one of those heaters was failing," said NASA mission control commentator Pat Ryan. "Subsequently, heaters for all four of those aft vernier jets have either failed or appear to be failing. It's not an issue for crew safety and, in fact, the team has made the determination that they will not call up any further instructions to the crew, they don't want to disturb them. But the teams will continue working, different disciplines are consulting with one another, trying to run down a cause for these heater failures.
"One late call to the crew, that is to say just after their sleep period (began), was to have commander Steve Frick throw the switch on the flight deck that would cycle those heaters and the propulsion officer has reported no joy in recovering the heaters in that fashion. The heater temperatures are still well above the level where they would pose any threat to that system. But they will be watched overnight by members of the planning team as they work through changes to the upcoming day on orbit for Steve Frick and his six shuttle crewmates."
Space shuttles are equipped with two large orbital maneuvering system - OMS - rocket engines in two pods at the back of the ship that are used to make major orbit changes, including the rocket firing needed to drop the ship back into the atmosphere at the end of a mission.
For smaller changes and adjustments to a shuttle's orientation, 14 reaction control system, or RCS, jets are mounted in the nose, along with two smaller vernier engines. Another 12 primary RCS jets, and two vernier thrusters, are mounted in each aft OMS pod and it is those four aft vernier jets that are affected by the heater problems under discussion in mission control.
The primary RCS thrusters produce about 870 pounds of push in space while the vernier engines generate a thrust of just 24 pounds each. Due to the redundancy built into the system, the shuttle can use various combinations of thrusters to operate normally in the event of failures.
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Quick-Launch Web Links:
CBS News STS-122 Status Reports:
http://www.cbsnews.com/network/news/space/current.html
CBS News STS-122 Quick-Look Page:
http://www.cbsnews.com/network/news/space/currentglance.html
NASA Shuttle Web: http://spaceflight.nasa.gov/shuttle/index.html
NASA Station Web: http://spaceflight.nasa.gov/station/index.html
Spaceflight Now: http://spaceflightnow.com/index.html
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