Shuttle astronauts pack for Wednesday's re-entry
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: February 18, 2008
The Atlantis astronauts are putting in a busy final day in space today, testing the shuttle's re-entry systems packing up loose gear and rigging the ship for landing Wednesday at the Kennedy Space Center. Forecasters are predicting good weather for the shuttle's return, but NASA plans to staff its backup landing site at Edwards Air Force Base, Calif., in a bid to get Atlantis down, on one coast or the other, before a U.S. Navy attempt to destroy a falling spy satellite.
It's not known when the shoot-down attempt will be made, but amateur satellite trackers monitoring the descent of the crippled NROL-21 satellite say a "notice to airmen," or NOTAM, issued by air traffic control in Honolulu Monday https://pilotweb.nas.faa.gov/distribution/center.html establishes a restricted zone west of Hawaii that NROL-21 will pass over around 10:30 p.m. EST Wednesday. But the NOTAM does not specify the reason for the restricted airspace and the subject line of an email alerting satellite trackers ended with a question mark.
(Editor's note: Interested readers can check the current location of NROL-21 (also known by its orbital designation USA 193) at the Heavens Above website.
Shortly after crew wakeup today, commander Steve Frick was asked to re-orient Atlantis, putting the ship's tail toward the sun to provide additional heating to four aft vernier thrusters that lost heater power late Monday due to a circuit failure. One of those thrusters, a left-firing jet on Atlantis' left-side aft rocket pod, dropped to 40 degrees overnight. prompting concern about possible freezing that could damage fuel lines. In a tail-toward-sun orientation, the thruster should stay warm enough to prevent any such damage.
Loss of the aft vernier thrusters will have no impact on the remainder of Atlantis' mission. Due to the redundancy built into the system, the shuttle can use various combinations of thrusters to operate normally in the event of failures.
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 failed heater circuit.
The primary RCS thrusters produce about 870 pounds of push in space while the vernier engines generate a thrust of just 24 pounds each. It's not clear what went wrong with the heater circuit Monday, but flight controllers suspect problems with a so-called "hybrid driver."
The astronauts were awakened around 12:45 a.m. by a recording of Monty Python's "Always Look on the Bright Side of Life" beamed up from mission control in Houston.
"Good morning, Atlantis. A special good morning to you, Steve," astronaut Shannon Lucid called from mission control.
"Good morning, Shannon," Frick replied. "And thanks very much to my wonderful wife Jennifer for that little touch of Monty Python in the morning. We get really busy up here, but it's easy to look at the bright side of life when you look out the window and see the Earth traveling beneath us once every 90 minutes. ... But even with that great view, I think we all believe the bright side of life is when we get home, hopefully tomorrow, and get to see our families."
Lucid then briefed Frick on the result of an overnight investigation into the thruster problem.
"The investigations that we had overnight indicate that a hybrid driver may have failed, resulting the loss of the heater power to the aft vernier thrusters," she said. "So the remainder of the mission will be conducted 'loss of verns.' The propellant margins support all the activities and all planned deorbit opportunities through end of mission plus two (days). Now, there is a potential to perform some unplanned maneuvers and attitude hold in the effort to maintain the aft vernier jets above their non operating limits."
"OK, Shannon, thanks a lot for those words," Frick said. "We kind of figured we'd be down verns from now on. But it's good to hear we don't have any power or prop concerns and I'm glad we have enough prop to fly those attitudes to keep the jets from being a turnaround concern."
He was referring to time lost from work that would be required to fix any fuel line damage after Atlantis returns to Earth. The shuttle's next flight is a high-profile mission in August to service the Hubble Space Telescope.
Here is an updated timeline of today's activity (in EST and mission elapsed time; includes revision M of the NASA television schedule):
EST........DD...HH...MM...EVENT 02/19/08 12:45 AM...11...10...00...Crew wakeup 03:45 AM...11...13...00...Cabin stow 05:10 AM...11...14...25...FCS checkout 06:20 AM...11...15...35...RCS hotfire 06:35 AM...11...15...50...PILOT landing practice 08:05 AM...11...17...20...Deorbit review 08:35 AM...11...17...50...PAO event 08:35 AM...11...17...50...Crew meal 09:35 AM...11...18...50...Cabin stow 12:30 PM...11...21...45...Launch/entry suit checkout 12:30 PM...11...21...45...Mission status briefing on NASA TV 12:45 PM...11...22...00...Ergometer stow 01:15 PM...11...22...30...Recumbent seat setup 01:25 PM...11...22...40...Laptop network teardown 01:35 PM...11...22...50...KU-band antenna stow 04:45 PM...12...02...00...Crew sleep begins 05:00 PM...12...02...15...Daily video highlights reel on NASA TV