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Next ISS Crew Ready to Try 4-Orbit Rendezvous, But Pros and Cons Still Being Weighed

Marcia S. Smith
Posted: 17-Jan-2013
Updated: 17-Jan-2013 10:49 PM

The next International Space Station (ISS) crew is ready to try a four-orbit rendezvous instead of the usual two-day approach when it heads to the ISS in March, but NASA and its ISS partners are still weighing the pros and cons of the shortened trip.

In twin press conferences today, the NASA Johnson Space Center (JSC) officials who oversee ISS operations and the three-man crew of the next ISS mission discussed what is on tap for the next several months of ISS operations.

NASA astronaut Chris Cassidy and Russian cosmonauts Pavel Vinogradov and Alexander Misurkin are scheduled for launch on March 27, 2013.  During an afternoon press conference, Vinogradov, who will command the Soyuz spacecraft, responded to a question about whether the crew is ready to try the new four-orbit rendezvous approach -- already practiced by robotic Progress cargo spacecraft -- by saying he is confident it would be successful.  He said it really is not new, noting that shorter rendezvous trajectories were used in the U.S. Gemini program and in the early days of the Soviet Union's human spaceflight program when two spacecraft co-orbited.  The latter apparently is a reference to the Vostok program of the early 1960s where Vostok 3 and 4, launched one day apart, flew in a close co-orbit about four miles from each other.

Throughout the history of the Soviet and Russian space station programs, as well as ISS, however, two-day rendezvous trajectories for the Soyuz spacecraft are the norm.  The Soyuz spacecraft, in use since the 1960s, is cramped, however, and reducing the time needed to reach the ISS is desirable from some aspects of crew comfort.  

Earlier in the day, however, NASA's ISS program manager, Mike Suffredini, explained the overall pros and cons of the shorter transit time.

On the positive side, he said, the crews would spend less time in Soyuz, and the size of the ground operations crew would be reduced, saving money.   On the other hand, the crew would have to remain buckled in their seats for as many as 10 hours, from the time they get strapped in on the ground until they dock.  "Can they go stretch, can they use the facilities if necessary and ... [get] strapped back in" during that time, he asked.  More importantly, with a four-orbit rendezvous ground controllers would have to know in advance more precisely where the ISS would be at the time of launch.  Under the four-orbit rendezvous scenario,  "today If I do a debris avoidance maneuver I have to consider whether that impacts a flight in March," Suffredini said.  What needs to be decided from an operational standpoint, he explained, is the savings in time versus the impact of "flying the ISS day by day."   

There is agreement to try it once or twice to show that it is possible, he continued, but whether it will be a long term strategy remains to be seen, adding that the good news is that it is easy to transition from a four-orbit rendezvous to the traditional two-day rendezvous if needed.

Separately, Suffredini declined to provide any specifics on the cause of the engine failure on the last SpaceX flight to the ISS.  Although the mission was an overall success for NASA, delivering the Dragon spacecraft to ISS, one of the Falcon 9's nine engines failed during ascent and a secondary payload was not placed in the proper orbit.   SpaceX has not made the root cause of the failure public and Suffredini said that NASA is precluded from doing so because the information is proprietary.   He said the investigation is "not completely closed," but NASA was "deeply involved" in reviewing the anomaly.  While it is "hard to find the smoking gun," the failure appears to be related to amount of testing to which the engine was subjected prior to launch.  He said there are no reasons he knows of that the next launch will not take place on schedule on March 1, and the engines for that vehicle are all new, having been through acceptance testing only.


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