Space Station Suffers Lengthy Computer Woes; Huge Truss Installed
Space Shuttle Atlantis Insulation Problem Fixed
A minor heat insulation problem with Space Shuttle Atlantis was fixed, but a significant computer problem with the International Space Station (ISS) for a time defied repeated attempts to resolve it, as the shuttle and space station remained joined together in orbit about 250 miles above Earth.
Finally, by using a “jumper cable” to bypass a faulty secondary power switch, crew members managed to get all six computers back up, although troubleshooting continued since the root cause of the problem still is unknown.
And later, four computers were operative while the other two were down.
The computer problems never were so threatening as to force evacuation of the space station and leave it floating abandoned in space, Mike Suffredini, the ISS program manager, said.
He added that that safety of the crew aboard the ISS already was ensured, even while some computers were shut down, and attitude control and stability of the space station was sure to be attained, one way or another. “The crew is absolutely not at risk,” he said.
If there were a problem, all three Expedition 15 ISS crew members could have exited the space station in a Soyuz space vehicle, using it as a life raft for a quick return trip to Earth.
There is a potential for an earlier launch of a Russian Progress cargo ship, which would blast off on a mission to the space station on July 23 instead of the earlier-planned Aug. 8. It could help maintain the ISS attitude, as propulsion systems on Atlantis now can do.
Those ISS computer problems helped NASA decide to extend the STS-117 Atlantis mission by two days, to a total of 13 days, with a return to Earth set for 1:52 p.m. ET Thursday at Kennedy Space Center.
Flight controllers at Mission Control Houston told the Atlantis crew that the orbiter vehicle was cleared for reentry and landing, after minute inspection of heat shields on the orbiter showed no damage.
Ever since Space Shuttle Columbia and its crew were lost in 2003 because of undetected damage to the heat shield on the leading edge of a wing, with blistering heat of re-entry blasting inside the wing and causing structural failure, NASA has ordered careful, multiple inspections of each orbiter vehicle after it reaches orbit, and then after undocking, prior to reentry.
While the ISS has three computers (including two backups) to control the station attitude and orbital altitude, and vital systems such as oxygen and air purification, all three computers handled by Russian ground control went down.
Some computer capability in the service module was recovered for a while. At one point, Russians attempted a computer restart, but they “were not successful,” Suffredini said. Finally, Russian flight controllers shut down the computers as troubleshooting efforts continued. “We did not get an attitude control computer up … for long,” he explained.
Suffredini rejected speculation that has arisen that the computer problems may force abandonment of the multi-billion dollar space station.
“There is no one in this agency or in the Russian space agency [who] thinks this [ISS] vehicle is at risk of being lost,” Suffredini said in a news briefing Friday. “I have no plans to de-man this space station … I am not remotely concerned right now [about] a scenario like that.”
Even if a decision were made to pull all personnel off the space station, it could be re-manned at some later point, Suffredini said.
For the time being, the space station attitude is controlled by Control Moment Gyroscope (CMG) assets, Suffredini said. “The CMG are plenty adequate to hold the attitude of the” ISS, he said. And that can continue until something jars the space station — in this case, the jolt of Atlantis undocking from the space station tomorrow to prepare for departure.
The STS-117 crew is scheduled to exit the station today before the hatches close at 6:23 p.m. ET, and then Atlantis is slated to undock at 10:42 a.m. ET tomorrow.
However, mission managers may decide to add a day of docked operations for STS-117 if the Russian navigation computers do not perform adequately during a test of Russian attitude control capabilities this morning.
Undocking of a space shuttle moving away from the space station can overwhelm its gyros, but there are ways to compensate, perhaps by using gear on the Soyuz spaceship that also is docked with the ISS.
While the ailing computers control such life support hardware as oxygen providers and systems that scrub carbon dioxide from the air, there were no threats of problems with cabin air.
Even when the computers go down, “we are in a very good position” as far as life support systems on the space station, Suffredini said.
Further, in addition to the Russian oxygen generating system, a new U.S. oxygen generator was activated, as planned earlier. That’s not because of the computer problems, though, because there is no problem providing adequate oxygen for the crew, Suffredini reported.
As sleuthing scientists and engineers in Russia, and at NASA, attempt to identify the culprit causing the computer glitches, some suspected the issue might relate to a new solar array electrical power source. Atlantis crew members in an earlier spacewalk attached and deployed the array on the Starboard S3/S4 truss attached to the steadily-growing space station.
There might have been arcing when a power line from the new solar array was connected to a line on the space station.
In a sense, Suffredini said, it is unsurprising that NASA at times might encounter ISS computer problems, as a routine reality in operating the space station. There are some 60 to 70 computers with perhaps something on the order of 4 million lines of computer code, he noted, and “all of them are exposed to the radiation of space.”
It is to be expected that there will be a problem with a computer, he said. What departs from the norm here, however, is to lose an entire line of computers simultaneously.
Even so, the problems haven’t caused NASA to veer from its stated goal of completing the space station construction and retiring the space shuttle fleet by 2010, Suffredini indicated, and there has been no change in the manifest of future planned space shuttle flights.
The shuttle flights schedule was thrown off this year when the external fuel tank on Atlantis was damaged extensively by a violent hail storm, requiring repairs of thousands of dings in foam insulation on the tank that forced postponement of a planned March 15 liftoff to June 8. That setback cut the number of shuttle liftoffs to four from an earlier- planned five this year.
Space Station Work
Even as the computer problems were playing out, work continued during spacewalks.
First, the Atlantis orbiter vehicle that appeared to launch smoothly arrived in orbit with a thermal blanket pushed out of place or torn. (Please see Space & Missile Defense Report, Monday, June 11, 2007, page 1.)
In a spacewalk Friday, Mission Specialist Danny Olivas, riding a robotic arm, tucked in the blanket and then stapled it in place. As he began work, mission control told him that test results just showed a high confidence that the repair would work as intended to shield the shuttle from the blistering heat of reentry, when the spacecraft returns to Earth.
He poked repeatedly at the blanket with gloved fingers in his space suit, tucking in the loose blanket at its edges. Then he came to the apparently torn bit of fabric jutting out from the orbiter vehicle that prompted his spacewalk repairs. He used one and then two fingers to jab the protruding fabric back into place. Later, Olivas used pins, each with a ring of metal on the blunt end, to hold the blanket firmly in place.
Meanwhile, Mission Specialist Jim Reilly conducted a simultaneous extra vehicular activity, venturing out of the space station to install a hydrogen vent on the ISS Destiny Laboratory. The vent is for a new oxygen generation system.
Then he and Olivas took on a job that typically can require some muscle. They went to the top of the ISS Port (P6) truss to assist in retraction of an old solar array.
A future shuttle crew will relocate the P6 to the end of the Port 5 truss.
Then, yesterday, yet another spacewalk occurred, a fourth extravehicular activity that was added to the three planned earlier, providing extra time outside the spaceships to offset time lost on the heat blanket repair.
During the 6-hour, 29-minute orbital stroll, Mission Specialists Patrick Forrester and Steven Swanson performed tasks to activate the new truss segment and completed work that will help future spacewalkers.
Forrester and Swanson prepared the Starboard 3 and 4 (S3/S4) truss segment for operation.
The S3/S4 was installed onto the station a week ago. Most of the S3/S4 work centered on activating the Solar Alpha Rotary Joint (SARJ), which will allow the S3/S4 solar arrays to track the sun as the arrays generate electric power for the space station.
The get-ahead tasks included the installation of a computer network cable onto the Unity module and the removal of a Global Positioning System antenna. The two astronauts also finished the installation of a piece of debris shielding on the Destiny laboratory.
Mission Specialist Jim Reilly coordinated the spacewalk and Pilot Lee Archambault operated the robot arm. Earlier, Forrester and Swanson had conducted the STS-117 Mission second spacewalk. Reilly and Mission Specialist Danny Olivas conducted the other two.
New Commercial Space Pacts
Separately, through three new Space Act agreements, NASA is expanding cooperation with companies interested in commercializing access to space, transporting goods and people to low Earth orbit.NASA signed nonreimbursable Space Act agreements, which do not provide any government funding to the companies, with SpaceDev of Poway, Calif., SPACEHAB of Houston, and Constellation Services International (CSI) of Laguna Woods, Calif. The pacts establish milestones and objective criteria by which the companies can gauge their progress in developing orbital cargo transportation capabilities.