November 18, 2007
November has certainly been spacewalk month! And it's not over yet.
Tuesday Nov. 20 4 a.m. to 10:30 a.m. CST, NASA TV will broadcast live coverage as ISS Commander Peggy Whitson and Dan Tani conduct a 6.5-hour spacewalk to hook up fluid, electrical and data lines for the relocated mating adapter and Harmony module.
Thanksgiving weekend, Saturday, Nov. 24 from 4 a.m. to 10:30 a.m. CST, NASA TV will broadcast live coverage of Whitson and Tani again. This spacewalk will complete the hook up of the mating adapter and Harmony module to the station and leave them ready for the docking of Atlantis and delivery of the Columbus module, set to launch Dec. 6.
The STS-122 flight in December will feature at least 3 spacewalks by the shuttle crew to install and hook up Columbus, replace some nitrogen tanks, deploy some new experiment packages, and return a failed control moment gyro (CMG). A fourth spacewalk is under discussion involving the solar alpha rotary joint (SARJ) that has filings floating inside it.
Posted by m_dyson at 02:44 PM
November 09, 2007
Getting Ready for Moving Day
Today ISS station commander Peggy Whitson and flight engineer Yuri Malenchenko executed a 6 hour and 55 minute spacewalk to prepare the newly arrived Harmony module for a move next Wednesday from its current temporary location to its permanent home attached to the Destiny module. In the meantime, on Monday, the Pressureized Mating Adapter 2 (PMA-2) will be moved from its current location on the Destiny module to the Harmony Module. This complex dance will enable visiting spacecraft to dock with the station through the Harmony module and will free up the current location of Harmony for the delivery next month of the European Columbus module and later the Japanese Kibo module. These additions will substantially expand the usable volume of the station, making it much easier to perform scientific experiments.
On one of the upcoming shuttle missions, repairs must be made to the starboard SARJ unit, which controls the orientation of the starboard solar arrays, before full power becomes available, enabling a full spectrum of activities to take place. Considering all the work that remains to be done and the looming 2010 retirement of the shuttle, just about all the contingency time that was originally in the schedule as been used up.
Posted by allen.taylor at 01:53 PM
November 07, 2007
STS-120 Welcome Home
Discovery is on target to land at Kennedy Space Center at noon Central time today. It will fly over the U.S., and some of you may be able to see it. Check out the groundtrack: www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts120/news/landing.html
The crew is expected back in Houston no earlier than 4 p.m. on Thursday. The welcome home at Ellington air field (take Ellington exit off Route 45 South) is open to the public. Gates open at 3:30--no badge required. Kids welcome! I hope to see some of you there to show our support for the amazing work this crew performed in space during the past two weeks.
Posted by m_dyson at 12:01 PM
November 04, 2007
A Tearful Farewell
Yesterday's successful repair of the torn solar panel on the P6 truss rocketed the combined crew of the ISS and shuttle mission STS-120 to an emotional high that has not come down yet. Presented with an unprecedented challenge, the crew in orbit and the team on the ground combined to accomplish something that has never been done before in space: an unanticipated, unplanned-for repair of a major station component. If the repair had not been successful, it is quite possible that the station might never have been built out to its complete configuration. The crew is justifiably exultant.
Today, in a ceremony that showed just how much the crews of the ISS and STS-120 had bonded, there was a lot of emotion expressed and a lot of support all around. This is an experience that these people will never forget, and I am sure that they will all be close friends for life, based on what they have gone through together.
Clay Anderson was formally transferred to the STS-120 crew and Dan Tani was formally transferred to the ISS crew. At the end there were tears and a lot of hugging all around. Finally, the STS-120 crew floated into the shuttle and closed the hatch. Once the hatch was dogged tight, the ISS seemed strangely empty. The three ISS crew members were now knocking around in a space that had previously held ten. With the addition of the Harmony module, the ISS is bigger than ever. With a functioning P6 solar array, it will be ready for the next shuttle mission, which will carry the Columbus module.
The Shuttle crew has a few more tasks to perform before they can say that their job is done:
1. Undock from the ISS.
2. Perform a 360 degree fly-around of the station, paying special attention to how the P6 solar array looks.
3. Perform a final inspection of the shuttle’s heat protection system, to make sure that there is nothing that would prevent a successful reentry.
4. Stow the robot arm and close the payload bay doors.
5. Perform a deorbit burn.
6. Fly to a safe landing at the Kennedy Space Center.
7. Kiss the ground and reunite with loved ones.
Posted by allen.taylor at 10:37 PM
November 03, 2007
Repair a Success!
EVA Officer Dina Contella said there was "a lot of cheering going on in Mission Control" today as a result of the successful repair of the P6 solar array. The 7-hour and 19-minute spacewalk by Scott Parazynski and Doug Wheelock laced up the torn array so it could be fully extended.
As Parazynski arrived as far from the airlock as any spaceman has ever been, he described the damaged frayed wires as a "hairball." It became obvious that he had to cut wires, one of the most risky parts of the plan.
He first installed one of the "cuff links" to stabilize the blanket. Then he cut a hinge wire, and then a guide wire. Then the guide wire had to be retracted into a box. Ms. Contella said this was one time she held her breath because there was no video feed in Mission Control--she had to rely on Doug Wheelock, who was stationed at the box, to give a verbal report.
After the wire was retracted, Parazynski cut above the snag. He retrieved some of the pieces of the "hairball" for later inspection, and crimped the others. Then he installed the other 4 cufflinks, and headed back to the airlock.
I watached with fascination as Parzynski threaded the bulky wire through the grommets on the array blanket. The wire curled and snaked around and bounced off the blanket. I could hardly imagine doing that detailed work wearing those clumsy gloves! The blanket made an accordian-like motion, folding and unfolding and also billowing away and then coming back at Parazynski. He held it at bay with his trusty "hockey stick." He punched the "needle" end through and tugged on it to be sure it held. I had just read the newspaper article about the big annual quilting convention here in Houston, and thought that this solar "quilting" job should qualify for some sort of prize.
Parazynski did get a prize for his work: the team offered the former Olympic athelete a "Gold Medal" for Spacewalking. When asked if this spacewalk rated in the top ten of all time, Ms. Contella said that during her 12 years as an EVA officer, it was certainly her number one.
During the airlock ingress, a pair of needle-nose pliers in their book-like caddy, got away. Flight Director Derek Hassmann said the trajectory did not appear to pose a recontact risk to the station.
While the spacewalkers were in the airlock, the array was successfully extended. Mr. Suffredini said that despite the patchwork cufflinks on the array, "our baby is still beautiful to us." He said it was producing 217 amps, but was still "shunted," meaning that power was not flowing from the array to the station systems. Before they "unshunt" it, the flight team wants to do a few more tests to make sure there are no shorts caused by the damaged area. The array is structurally sound now, and can be rotated to track the sun. However, the power is not currently needed. The team fully expects to certify the array to be good through 2015, the expected lifetime of the station.
More Spacewalks Coming Soon
ISS program manager Mike Suffredini said, "The pace [of the assembly] is not going to slow down." He said EVA 5, the one that had originally been scheduled for this weekend, was now on tap for Friday, November 9. This spacewalk by Station Commander Peggy Whitson and Expedition crewmember Dan Tani, will get the PMA ready to be moved. The PMA will be moved on November 12 and attached to Harmony. Then on November 14, the stack of PMA and Harmony will be moved to the front of Destiny. More spacewalks are planned on November 20 and 24 to complete the activation of the Harmony module. This work needs to be completed before the shuttle arrives with the new Columbus module, currently scheduled for December 6. That date may be moved later, but Mr. Suffredini said that the station crew had made up some time in other areas so that it is still possible the launch date may not slip.
The starboard rotary joint (SARJ) repair is not scheduled yet. The spacewalk inspection that was preempted for the P6 repair will probably not be done. Instead, the ground team will analyze the samples the shuttle is bringing down next Wednesday and test some methods of removing this grit on a future space walk. The program has to find "up mass" on one of the future flights as well once they determine if parts need to be replaced. Mr. Suffridini expects this work may take more than one spacewalk.
This spacewalk was an amazing success for the crew, the flight team, the international partners (the Canadians and Russians were especially thanked for contributing hardware, expertise, and crew time), and for everyone who dreams of one day living in space. We have proven that humans can solve the problems of a space utility and do complicated repairs with little preparation time. The knowledge and experience gained through this mission is ours to keep and apply to future activities in space.
Congratulations to the crew and flight control teams for a job fantastically done!
Posted by m_dyson at 04:35 PM
Anticipation and Preparation
Friday on the Internatonal Space Station has been a day of anticipation and preparation. As I write, spacewalkers Parazynski and Wheelock are in the Quest airlock, prebreathing pure oxygen prior to getting into their EVA spacesuits. Anticipation is high for what is probably the most hazardous EVA in history, and preparation has been done to the extent possible for an attempt to repair the torn solar array on the P6 truss. The exact nature of the problem is unknown, and thus what will be required to repair the damage is not well known either. Spacewalkers Parazynksi and Wheelock will attempt the repair, with Wheelock stationed at the base of the solar array and Parazynski attached to the OBSS on the end of the shuttle arm, held in the grasp of the station arm. The combined reach of the two arms along with Parazynski's own long reach will be enough to put the spacewalker in the vicinity of the two tears in the solar panel.
The major hazard stems from the fact that the solar array on the P6 truss is energized and producing electrical power. There is no way to turn it off before Parazynski starts the delicate operation of trying to repair the tears. There is definitely an electric shock hazard, but the crew has done everything possible to mitigate the hazard. They have covered all metal projections from Parazynski's spacesuit with insulating tape and have insulated his tools also. He may be called upon to cut one or more guide wires, however, and it is pretty hard to insulate the blades of a pair of wire cutters.
Probably the most hazardous aspect of the spacewalk is the fact that it is unanticipated. Up until now, every spacewalk ever attempted on the ISS has been practiced beforehand in the neutral bouyancy tank on Earth for many hours. The repair of the P6 solar array is uncharted territory. Parazynski will have to diagnose the problem on the spot, determine the best course of action, and then do it, all within the time constraints of the consumables in his spacesuit. Because of the hostility of the space environment, any EVA is risky. This one however, raises the risk to a new level. Success on this job will show that fifty years after the launch of Sputnik and 46 years after Alan Shepard became the first American in space, NASA still has the right stuff.
Posted by allen.taylor at 03:01 AM
November 01, 2007
EVA Difficulty Rated at 7.5
At Thursday's press conference, astronaut and veteran spacewalker Dave Wolf rated Saturday's planned EVA a 7.5 on a scale of difficulty from 1 to 10. He cited the fact that this spacewalk to repair the torn P6 solar array involved brand new procedures (which is why the EVA was delayed from Friday to Saturday, and may even yet be postponed to Sunday) in a dangerous environment.
The solar array blankets have no shut-off switch. Whenever the solar cells are exposed to the sun, they produce electricity. The space suits have metal fittings, and the astronauts carry metal tools. If any of these should come in contact with the cells: ZAP! the astronaut could be electrocuted. No one would estimate the potential effects because there are so many factors involved. But the number 100 volts was mentioned.
Another danger to Parazynski is that if he should have any damage to, or system failures of, his space suit, he may not be able to get to the safety of the airlock in time to avoid permanent injury. His suit carries a backup supply of oxygen that can make up for leaks for some period of time, but mission planners usually require spacewalkers to be able to execute an emergency return to the airlock within 30 minutes of a failure. Because of his location far out on the array, Parazynski would not be able to meet that time window. This is worrisome after the torn glove experienced earlier in the mission and on a previous flight and that Parazynski may be cutting guide wires whose sharp ends may bounce around and strike him when tension is released. Not to mention the danger of electrocution...
Astronaut Wolf was quick to downplay the danger, however, and warned the media against sensationalizing it. He said that it is the team's job to asses the risk and "mitigate" them. All tools are being covered in three layers of insulating tape, and the crew wrapped up in their best space mummy costumes. Cameras and crewmembers will be watching every move from every angle and be in constant communications.
Veteran spacewalker Scott Parazynski will be the man in the "hot" zone on the end of the robotic arm. The station arm is not long enough to reach out to the section of the array that is damaged, about 50 feet from the mast box. So the arm is being extended using a piece of equipment borrowed from the space shuttle, the orbiter boom sensor system (OBSS).
The OBSS is designed to extend the shuttle arm so it can inspect the tiles under the belly. The station arm will grab the OBSS out of the shuttle bay, then hand it to the shuttle arm for safekeeping while the station arm trundles down to the end of its track on the port side. Then the shuttle arm will hand the boom back to it, and Parazynski will hop on for what is sure to be the ride of a lifetime with Dan Tani at the controls.
Fellow spacewalker Doug "Wheels" Wheelock will position himself at the base of the array as a lookout. His primary task is to make sure that arm does not become a lightning rod and that his partner is warned to get out of the way if the array should bounce up and down or if something comes loose. Those of us who have ridden the air-bearing chair at Space Center Houston know just how easy it is to impart unwanted motions to objects in freefall.
The repair will place what engineers are calling a "cufflink" on the array. This will keep the torn section folded and prevent further tearing. With the array repaired, the station will have all the power it needs at least until the spring. By then, some other brave spacewalkers will have tackled the repair of the starboard SARJ.
If the repair is not successful or not completed on Saturday (the suit limit is 7 hours), NASA will decide whether or not to do another spacewalk on this mission. They are really hoping they won't have to face this question because the schedule tradeoffs are very complicated. Assuming the repair is successful Saturday, then the shuttle will land at KSC on Wednesday.
Posted by m_dyson at 04:04 PM
Power is the priority. So Thursday's spacewalk, that had originally been to check out a new shuttle tile repair method (something called T-RAD) and then changed to a check of the starboard SARJ, is now going to be a repair of the P6 array. But Mission Control needed time to work out the procedures, and the crew needs time to go over them. So the spacewalk has been postponed until Friday at the earliest.
The array is working at 97 percent power. Because the thin solar blanket has a tear in it, it has been locked in place, and is not fully extended. (Ironically, this is the side that has a working SARJ.) The concern is that the stress/flexing induced by rotating the array could increase the damage. One option I heard discussed is to fold that section shut, and then extend the array. It will be interesting to see what the repair entails.
The starboard SARJ repair has been postponed to an unspecified date--meaning it will not be done by the STS-120 crew. As ISS Program Manager Mike Suffredini noted before, the power loss from not being able to rotate the starboard arrays is not an issue until next spring. It is more important to get the P6 array repaired.
Hopefully, the repair can be completed on Friday. If so, the shuttle will undock on Monday and land Wednesday. If not, another spacewalk may be added, presumably on Sunday.
The spacewalk that had been planned by the station crew (to disconnect the PMA in preparation for moving Harmony to its permanent location) for Friday, and then postponed to Saturday, is being moved to after the shuttle leaves. If another spacewalk is required for P6, then the shuttle will probably leave on Wednesday and land Friday. What this means to the timeline for the STS-122 in December is not yet clear. That flight has already been postponed from December 6 to 7.
The space station is the first to use a distributed power system: with the arrays on a truss providing power to multiple modules. In this sense, it is the first space "utility" ever built. So there is a definite silver lining to the problems we've encountered with this first system. We now know what to expect in terms of lifetime degradation of the arrays. We know it is difficult to fold up and move older arrays. They tend to tear when redeployed. We also now have a way for our spacewalking repairmen to coax arrays into their boxes, and are working right now on a way to fix a tear and clean out a clogged joint. With these skills neatly tucked into our space utility plans, we can be much more confident in building a future space solar power station to provide electricity to Earth.
So let's hope for no more torn gloves or arrays, and that all goes smoothly on Friday. But if it doesn't go as planned, we will still have learned some valuable lessons that will benefit us all in the future.
Posted by m_dyson at 01:20 AM