ASAP discuss plans to deorbit the ISS via the use of two Progress ships

by Chris Bergin

Managers with the International Space Station Program have discussed their End Of Life (EOL) plans for the orbital outpost with NASA’s Aerospace Safety Advisory Panel (ASAP), citing a plan to use two Russian Progress vehicles to send the Station into a destructive re-entry. However, such an event may not occur until 2028.

ISS Advances:

Noted as a “positive meeting”, the ASAP heard from ISS Program manager Mike Suffredini, who has successfully seen the Station transition from assembly to utilization under his stewardship.

Utilization has always been an item of concern for NASA’s leadership, based on the need for the ISS to earn its way as the “National Laboratory”.

Such an effort was only going to become a reality after the intense period of ISS construction – itself a massive feat of engineering that will provide an extensive knowledge base for future large assembly tasks in space, such as the proposed Exploration Platform/Gateway, that would be constructed at the ISS.

However, it appears that the crew, at least on the US side of the Station, are now hitting their marks for the expected amount of science – sometimes known as “Payload Operations” – that is being conducted on the ISS.

“As far as research work on ISS, the average of the last several months for payload operations has been 37.1 hours per week on the US side. The mission requirement is 35 hours per week,” Mr Suffredini told the ASAP meeting. “While they are meeting the requirements overall based on the average, there is some variation week to week.”

The ISS also provides a huge database on the challenges of long-duration space flight on the human body, another key factor for the future ambitions of sending crews into deep space for many months at a time. On that subject, Mr Suffredini spoke of two areas of interest for the ISS crews.

“In the crew health area, we are tracking radiation exposure, and it has been below 24 millirad/day, which is the requirement. There is concern going forward for the 2013/2014 period because that is the solar maximum, and there could be additional radiation exposure issues,” added the meeting notes.

“Another thing that has come up in the past and is still a concern is the issue of ocular change (papilledema) that may be due to increased intracranial pressure, which has been showing up in some crew members. Some of the changes on orbit have not gone away when the affected crew return to a 1g environment.  This does not affect all crew, and it is actively being investigated.”

Also of ASAP interest is the safety of the vehicle itself, which was improved slightly via the addition of several Micro-Meteoroid and Orbital Debris (MMOD) shields during Monday’s Russian EVA-31.

Five of these MMOD panels were installed around a small diameter section of the Service Module (SM) “Zvezda” by the vastly experienced spacewalkers Gennady Padalka and Yuri Malenchenko, improving the protection on this part of the station.

The notes also discussed additional MMOD shielding that will be installed on future Soyuz vehicles, set to come on line in around 2014.

This is also relevant to the safety numbers for the ISS, due to the fact the Soyuz spend around six months on the Station, during which time they provide the role of a lifeboat, in the event of an evacuation being called during an emergency.

“Mr. Suffredini discussed the additional MMOD shielding for Soyuz. That is now beginning to be implemented, and is expected to be complete by 2014. The MMOD protection will change the LOC (Loss Of Crew) numbers in a positive direction. There are preliminary numbers for LOC, but not LOM (Loss Of Mission).

“The ASAP was supplied previous data that indicated that over a 10 year period, there could be up to a 32 percent chance of LOM. The actions being taken now will mitigate that risk somewhat, but it has not been quantified.”

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Ending The Life Of Station:

The ISS will eventually come to the end of its life cycle, although no date is currently set for when that day will come.

Numerous and 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, although the ASAP would like to hear more about the certification requirements relating to such extensions.

“Several meetings ago, there was a discussion about the potential extension of the life of the ISS from 2020 to 2028,” the ASAP meeting noted  “At that time, the ISS team said there were some systems on board that would need recertification to extend their lifetime into that period. The ASAP requests an update on this situation so that it can be tracked.

“While it is a future requirement, it would seem that early planning will prevent a “snowball” situation on certification requirements as the end of design life point approaches. Since it now appears that the leadership of the country is likely to extend the ISS lifetime beyond 2020, the ASAP would like to track this recertification activity so that should any re-design of a system be necessary there is adequate time to accomplish the work needed.”

When the time comes to end the life of the ISS, the Station will be deorbited for a destructive re-entry over a disposal corridor, allowing for a safe splashdown of hardware that are expected to survive re-entry.

Several proposals have been put forth for that sad day, some of which included the use of a European ATV vehicle.

However, it now appears that the use of the Russian resupply vehicle, Progress, would be used to deorbit the Station, plans that have to be drawn up way ahead of event, in order to accommodate an contingency EOL (End Of Life) for the ISS.

“With regard to the end-of-life (EOL) issues that have been discussed before – i.e. what would happen in either an off-nominal issue that would require ISS de-orbit or the nominal EOL de-orbit – additional work has been accomplished on these topics,” the ASAP notes continued.

“In the past, proposals for using Progress to provide impulse to de-orbit had been discussed. 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.”

“More work needs to be done on the modifications to Progress, and that work is going ahead. The ASAP notes that work is progressing in a positive direction. The Program still needs to report back on how it would deal with the off-nominal scenarios.

“The only formal recommendation is to obtain a revised estimate on the LOC and LOM numbers in light of the modifications that have already taken place and the ones that are forecast.”

The ASAP members called for NASA to provide them with the finalized EOL plan for the ISS.

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