The latest meeting of NASA’s Aerospace Safety Advisory Panel (ASAP) was briefed on an updated action plan pertaining to the End Of Life (EOL) scenario for the International Space Station (ISS). The plan for a destructive deorbit of the Station is required in the event of a serious contingency resulting in the evacuation of the crew.
The orbital outpost is currently set to continue flying until at least 2020, although ongoing studies are being used to evaluate how long the ISS can continue to perform its duties, especially from the standpoint of the hardware’s long-term health.
At present, it is hoped the ISS could continue to operate until at least 2028, pending political and international agreement on the operational requirements and running costs.
Providing the ISS continues to be mechanically healthy, opting against an extension would be close to unthinkable.
The Station took decades and billions of dollars to assemble, providing the Space Shuttle fleet with their final major role ahead of retirement – completing assembly and allowing for the transition to the utilization phase.
With the ISS permanently crewed by up to six international expedition members, resupply ships from Russia, Europe and Japan take it in turns to restock the Station with vital supplies, while the Russian Soyuz provides the task of crew rotations.
This fleet of “Visiting Vehicles” has since been joined by the first commercial spacecraft from the United States, with SpaceX’s Dragon currently preparing for its fourth visit during CRS-3 (SpX-3) at the end of this year. Orbital’s Cygnus spacecraft is also expected to make its first trip to the ISS this summer, ahead of initiating its Commercial Resupply Services contract obligations.
Commercial space companies are also primed to remove the United States’ dependence on the Russian Soyuz as a means of lofting NASA astronauts to the Station.
America’s domestic launch and crew transportation capability was lost when Atlantis closed out the Space Shuttle Program (SSP) at the conclusion of STS-135. And, with the aborted Constellation Program (CxP) failing to allow Orion to take up the role before the middle of this decade, NASA created the Commercial Crew Program (CCP).
With hundreds of millions of NASA dollars aiding the development of three commercial spacecraft options, the first “United States Crew Vehicle” (USCV-1) flight is currently manifested for late 2017.
Should the ISS be abandoned in 2020, no more than six USCV missions will have taken place – with the final flight (USCV-6) supporting the last Expedition to iconic laboratory – per the latest long-term manifest available on L2.
However, the death of the ISS isn’t restricted to hardware health or political meddling, it also has to deal with the inherent risks of flying in space, which forever threaten a contingency scenario.
While the Station is protected against major contingencies via teams of expert engineers on the ground, along with techniques in space – such as the Debris Avoidance Manuever (DAM) that allows the ISS to move out of the way of space debris – NASA managers always have to consider the worst case scenarios.
Almost all contingency events should still result in the crew surviving, with two Soyuz spacecraft ready to provide the role of lifeboats in the event of an evacuation being called. However, a painful decision would then be required over the fate of the Station itself.
ISS Program manager Mike Suffredini recently briefed the ASAP on such plans at the Marshall Space Flight Center (MSFC), describing the latest evaluations on what would be an EOL scenario for the Station.
“NASA now has a plan so that in the event the Station must be evacuated, there will be a 14-day period in which to make a decision on whether or not to bring the ISS down. The Program is setting the contingency plan in place, although there is still a lot of work to be done,” noted the minutes from the meeting.
Previous plans have noted that NASA’s initial response would be to plan to raise the Station’s orbit, buying them potentially years to work out what to do with the abandoned spacecraft – hypothetically allowing for a potential repair or some form of orbital salvage operation.
However, based on the scenario where the ISS was dying, a controlled deborbit plan is preferred, aided by two final Visiting Vehicles.
“They will have 180 days to get down to deorbit altitude. This would give them time to get two Russian Progress vehicles launched to autonomously dock, autonomously transfer propellant to the Service Module, and to provide propulsion to deorbit. This would provide a good, safe, controlled deorbit.”
Although the disposal corridor over an uninhabited ocean expanse would be refined nearer the time, the deorbit and destructive re-entry of the Station would be by far the largest man-made object to make the fiery plunge back to Earth. A large amount of hardware would likely survive re-entry.
The use of two Progress vehicles is also the current method of execution for the Station per its natural EOL.
“In the past, proposals for using Progress to provide impulse to de-orbit had been discussed,” noted a previous ISS Program overview to the ASAP. “The Program is developing plans for a single Progress, which would be used for off-nominal EOL; for the planned EOL, there would be two Progress vehicles that would provide more impulse and better targeting to hit the impact point.”
The ASAP noted they are “very pleased” with the progress being made on the EOL scenarios.
“The ASAP raised this issue two or three years ago as the kind of thing to think about ahead of time,” added the minutes. “At that time, the general thinking was that the response would be to boost the orbit to get the Station higher; however, after all the analysis was done, it was determined that what will actually be needed is the opposite.
“The ASAP is pleased that all of this work has been done in advance.”
(Images via L2 and NASA).
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