Two International Space Station (ISS) crew members successfully replaced a coolant pump in the ISS electrical system today, but there was no sign of the leak that led to this unprecedented ISS spacewalk.

Tom Marshburn and Chris Cassidy completed their tasks about an hour ahead of schedule today, finishing the spacewalk in 5.5 hours.  One objective of the spacewalk, successfully executed, was replacing an ammonia pump used to cool a solar array channel that provides electricity for the ISS.  There are eight channels, one for each solar array.   ISS crew members noticed “snowflakes” emanating from one of them on Thursday, signalling an ammonia leak.  That channel had shown signs of leaks in the past, origin unknown, but this time the amount was much greater.

NASA decided to conduct an emergency spacewalk not because the leak posed a threat to the space station or the astronauts, but because they hoped to spot the source of the leak while ammonia was still being released.  That part of the assignment was unrealized.   When Marshburn and Cassidy arrived at the site, there was no sign of an ammonia leak.  They replaced the pump because it was one obvious source of the problem, and when the new pump was activated, no leak was observed.  That might be a cause for celebration, but NASA officials stressed at a post-spacewalk news conference that it will be many weeks before they feel they are certain the new pump resolves the issue.

“We are happy.  We are very happy,” said ISS Deputy Program Manager Joel Montalbano about the overall success of the spacewalk. This is the first time in the “increment” ISS missions that a spacewalk has been planned and executed in such a short period of time.  The desire to view the leak as it was occurring, and the experience of Marshburn and Cassidy — who conducted two spacewalks together on a 2009 space shuttle mission, including working in this area of the ISS — drove the decision to move quickly.  Marshburn will be returning to Earth on Monday after almost 5 months on the space station, so today was a unique opportunity.

NASA will hold a press briefing at 4:00 pm ET (3:00 pm CT) today about the ammonia leak on the International Space Station (ISS).

The briefing will be broadcast on NASA TV.  ISS Program Manager Mike Suffredini and NASA Chief Flight Director Norm Knight will discuss plans for assessing and fixing the leak, which ISS crew members noticed yesterday.  A final decision on whether to conduct a spacewalk on Saturday is expected later today.

In a spacewalk characterized as unprecedented for the International Space Station (ISS), two U.S. astronauts will venture outside their home in space Saturday morning to see if they can find and fix a vexing ammonia leak in the ISS electrical power system.

Tom Marshburn has been preparing for his return to Earth on Monday after nearly 5 months in space.   NASA officials stressed today that there is no change to the plan for Marshburn and two other ISS crewmembers to come home on Monday, but first he gets another chance to do a spacewalk.

Marshburn and Chris Cassidy, who is part of a different set of ISS crewmembers that is remaining onboard the station, have already done two spacewalks together (on STS-127 in 2009) and worked in the area where they need to go tomorrow.  Their experience helped NASA officials decide that it was OK to go ahead with this spacewalk with less than 48 hours notice.  NASA chief flight director Norm Knight said that performing a spacewalk with so little advance planning is “precedent setting” for ISS missions (called “increments”), though perhaps not for space shuttle flights. 

ISS crewmembers observed “snowflakes” coming off one of the ISS solar array trusses yesterday that was quickly determined to be an ammonia leak in one of the eight power channels that provide electricity.  There is one power channel for each solar array.  Ammonia is used as a coolant.

This leak is in the vicinity of a previous leak that NASA was never able to identify so it is not known if something happened to increase that leak or if this is something unrelated.   ISS program manager Mike Suffredini stressed the difficulty of finding leaks, which may come from very tiny holes, perhaps caused by a Micrometeoroid Orbital Debris (MMOD) hit.  Or the leak may be from a seal in the pump.  They simply don’t know.  Marshburn and Cassidy will do a visual inspection and replace the pump.

The decision to do a spacewalk quickly was driven largely by the desire to observe the leak when a lot of ammonia is being released precisely so that the source can be identified.   The ammonia in the system is expected to be depleted in a day or so. 

The opportunity to discover the source of the leak coupled with the experience of these two ISS crew members were major factors in the decision to go ahead with the spacewalk tomorrow, Suffredini said.   It is not a matter of an emergency situation aboard the station.  The crew is in no danger from the leak and the ISS can operate with minimal impact using the other seven channels.   If the astronauts cannot identify the source of the leak and replacing the pump does not remedy the situation, the ISS can continue operating almost normally at least in the short term.   For the long term, operating with only seven instead of eight electrical channels could reduce the amount of research that can be conducted.   This is “not critical from a safety standpoint,” Suffredini said, but “if we have to live with this channel down for a long period of time” it will have an impact on research.   The main purpose of the ISS is to serve as a scientific research laboratory for experiments that need to be conducted in microgravity.

Marshburn and Cassidy are scheduled to open the hatch to exit the ISS at 8:15 am Eastern Daylight Time  (EDT) tomorrow morning (7:15 am Central Daylight Time).   During the 6 hour 15 minute spacewalk, they will inspect the area of the leak and replace the pump.   They then will inspect each other’s spacesuits for signs of ammonia contamination since NASA knows there is a lot of leaked ammonia in the area.   A 30-45 minute “bake out” period will ensue as a precaution to allow any unnoticed ammonia to evaporate.  They will then reenter the airlock and pressurize it to 5 pounds per square inch (psi) where another test will be conducted to ensure they are not bringing any ammonia into the station before full repressurization.

Marshburn, Russian cosmonaut Roman Romanenko and Canadian astronaut Chris Hadfield remain on schedule to return to Earth on Monday, May 13, in their Soyuz TMA-07M spacecraft.  Undocking is scheduled for 7:08 pm EDT, with landing at 10:31 pm EDT (8:31 am May 14 local time at the landing site in Kazakhstan).  They were launched on December 19, 2012.

NASA TV will cover tomorrow’s spacewalk beginning at 7:00 am EDT (6:00 am CDT).   It also will cover the landing on Monday, as detailed in NASA’s press release.

NASA reports that astronauts aboard the International Space Station (ISS) noticed a significant exterior ammonia leak beginning about 11:30 am Eastern Daylight Time (EDT) today.  The agency stresses that the astronauts are in no danger.

The crew noticed small white flakes floating away from a portion of one of the solar arrays where part of the cooling system is located.  Ammonia is used as a coolant for the power channels that provide electricity generated by the solar arrays.  Crew observations and images obtained from exterior cameras operated by ground controllers confirmed that it is in the same area where a leak was investigated during a November 2012 spacewalk. 

NASA said it is making plans to reroute other power channels to ensure full operation of the space station.   The leak rate is so high that a complete shutdown of that cooling loop might be required in the next 48 hours.

Russia’s Progress M-19M robotic cargo spacecraft successfully docked with the International Space Station (ISS) on schedule this morning even though one of the navigation antennas did not deploy.

Russian ground controllers sent a software patch to tell the spacecraft’s automated KURS docking system to ignore the lack of data that ordinarily would be provided by the ASF2 antenna.  It provides data on relative roll of the spacecraft when it is within 20 meters of the ISS.

The ISS crew was ready to use the manual TORU docking system if KURS failed, but it was not needed.  After Progress soft-docked with the ISS, ground controllers very slowly withdrew the docking probe, a process that enables the closing of latches that secure the spacecraft to the ISS — a hard dock.  During that process, ground controllers continually asked the ISS crew if they heard anything unusual that would indicate that the undeployed antenna was interfering with the docking mechanism.   The crew assured them that nothing sounded awry, but offered to go out on a spacewalk to visually inspect the area.  In the end, however, all was well.

NASA calls this Progress 51 because this is the 51st Progress cargo spacecraft to dock with the ISS.   The Progress program dates back to 1978, however, and there were many, many Progress flights to Soviet space stations before the ISS was built.  The Soviet Union launched six successful Salyut space stations beginning in 1971 followed by the modular Mir space station, which operated from 1986-2001.

The Progress spacecraft itself has been upgraded several times over the decades.   This is the 19th flight of the current version, hence its Russian designation of Progress M-19M.

Although Progress dockings have long since become routine, there are always risks.  A Progress spacecraft collided with the Mir space station in 1997 during a manual docking procedure.  It punctured one of Mir’s modules, creating an emergency situation when the space station began to depressurize.  Quick work by the Mir crew saved the space station, although that module (Spektr) was unusable for the remainder of Mir’s lifetime.  The accident occurred during a period of U.S.-Russian space cooperation where Russians flew on the U.S. space shuttle and American astronauts were included in Mir crews.  NASA astronaut Michael Foale was aboard Mir at the time.  A brief and compelling account of the accident is available on NASA’s history office website with links to additional material.

Russia’s RIA Novosti is quoting Russian space officials as saying that the docking of Progress M-19M will proceed on schedule tomorrow morning Eastern Daylight Time (EDT) even though its navigation antenna did not deploy.

The robotic cargo spacecraft was launched yesterday from the Baikonur Cosmodrome.  Once on orbit, one of the antennas for its KURS navigation system used to bring it in for docking with the International Space Station (ISS) failed to deploy, however.  The spacecraft is continuing on its 2-day rendezvous course to meet up with ISS tomorrow morning, Friday, April 26.   The nominal schedule calls for docking at 8:26 am EDT.  NASA TV will provide live coverage beginning at 6:30 am EDT.

RIA Novosti reported that ground controllers will continue to try to get the antenna to deploy, but quoted a spokesman for the Russian space enterprise Energia as saying “Even if we fail, the problem with the antenna should not hamper the docking.”  The ISS crew will be instructed to conduct a manual docking instead of an automated docking if the antenna remains undeployed.

NASA’s new asteroid retrieval mission has not won over two influential voices in space policy debates.  Cornell University’s Steve Squyres and George Washington University’s Scott Pace told the National Research Council (NRC) on Monday that it is not necessarily the best next step for the U.S. human spaceflight program.

The NRC’s Committee on Human Spaceflight met Monday and Tuesday in Washington, DC.  The committee is tasked with describing the value proposition of the human spaceflight program – what do taxpayers see as its value for the money spent – and providing advice on future planning for that program.  Among the topics discussed was NASA’s new asteroid retrieval strategy to capture an asteroid, redirect it into a retrograde lunar orbit, and send astronauts to retrieve a sample.

Squyres chairs the NASA Advisory Council (NAC) and is perhaps best known as the principal investigator for the twin Mars rovers Spirit and Opportunity.  He also chaired the NRC’s 2011 Decadal Survey for planetary science.   In addition to talking about NAC’s view of NASA’s human exploration program, he shared his personal views on topics NAC had not yet considered, including the new asteroid retrieval strategy.

His personal recommendation is that NASA not attempt to sell the asteroid retrieval mission either on the basis of exploring asteroids or that it is a more effective way to satisfy President Obama’s goal of using an asteroid mission as a step towards Mars.  Quoting the President’s April 15, 2010 speech at Kennedy Space Center, Squyres reminded the committee that the President’s goal was to build “new spacecraft designed for long journeys … beyond the Moon into deep space,” which is not what the new strategy entails.  He agrees that understanding asteroids is an important scientific goal, but not one that requires humans on-site.   Humans and robots work effectively together in exploring complex environments like Mars where Earth-bound scientists cannot anticipate the many surprises that lie ahead. Comparatively straightforward environments like that of an asteroid can be effectively explored with robotic spacecraft alone, he believes.

Squyres does, however, support the idea of sending astronauts into cis-lunar space for longer periods of time than during the Apollo era, such as the 22-day mission envisioned for the asteroid retrieval mission.   In his view, that is worth doing whether or not an asteroid has been redirected there.  His major concern personally, which he said also has been expressed by NAC, is that “NASA needs a compelling and clearly articulated goal for future human spaceflight that is consistent with its budget.”

Pace strongly supported a robust U.S. human spaceflight program, but not the asteroid mission as a step towards Mars.   He said he is “hard pressed to run into anybody who thinks that going to an asteroid is the right way primarily to go to Mars.”  He believes that the Obama Administration made a decision “not to do anything the prior Administration was doing” in space, and that is how the asteroid idea emerged despite broad bipartisan and international support for returning to the Moon as laid out in President George W. Bush’s Vision for Space Exploration.  Pace was a high ranking NASA official in the Bush Administration.

Asked what would happen if the United States abandoned human spaceflight entirely, Pace said it would diminish U.S. influence on the global stage in discussions about space issues such as orbital debris and sustainability.  “We will have made ourselves irrelevant to a lot of discussions,” adding that he sees some of that reduced influence already with the U.S. decision to withdraw from cooperation with Europe in the robotic ExoMars missions.   “Countries are not upset at us. They simply think we’re irrelevant….I can’t think of [anything] that is … more dangerous or serious for a great power than to be considered irrelevant.”