NASA’s transition from the Space Shuttle to the commercial crew vehicles will dramatically improve crew safety parameters relating to the transportation of astronauts to the International Space Station (ISS). However, preparing for the worst is a necessary requirement that is currently being evaluated by NASA, per presentations to the Aerospace Safety Advisory Panel (ASAP).
Loss Of Crew (LOC):
Recent mishaps relating to uncrewed Russian vehicles have resulted in the highly undesirable tags of Loss Of Vehicle (LOV) and Loss Of Mission (LOM).
However, by far the worst failures relate to the loss of human life during a mission, known as LOC (Loss Of Crew) – a tragedy suffered twice during the Space Shuttle Program era.
Although it could be deemed to be somewhat morbid, aerospace managers have to create a probability matrix to predict the LOV/C ratio for their vehicles, which also provides a guideline to portray how “safe” a vehicle is expected to be during its lifetime.
This subject was recently discussed at the latest ASAP meeting held at NASA HQ, with an overview provided by Justin Kerr, manager of the Spacecraft Office in the Commercial Crew Program (CCP).
“The LOC is loss of crew probability – how likely there will be loss of crew on a given mission. It is a top level metric that tells us how safe the system is overall. It is a theoretical number, evaluated by a probabilistic risk assessment,” noted the ASAP meeting minutes.
The overview first spoke of the Space Shuttle, which ended with a LOC ratio of “about 1 in 90”.
The LOC ratio became a battleground between the ASAP and Space Shuttle Program (SSP) management in 2009 when the former used it as part of its concerns over the Shuttle’s “safety” in briefings that discussed the potential extension of the Shuttle’s days.
Then-SSP manager John Shannon told the Shuttle workforce that the claims from the ASAP leader Admiral Joseph W. Dyer – that the Shuttle was “becoming more risky” – were “disturbing” and “not an accurate reflection of the program.”
Atlantis closed out the Shuttle Program with her STS-135 mission, completing a run of final missions that were considered to be extremely “clean”, as the fleet “finished strong”. However, by then the fleet’s fate was sealed, after last-gasp attempts to extend the Shuttle’s lifetime through to 2015 were denied.
The follow-on Constellation Program (CxP) was quick to boast how safe the crews of Orion – launching on the Ares I rocket – would be, while many observers claimed the numbers were far too optimistic.
“CxP had a goal of 10 times better (1 in 1000), based on a 2005 study, which at that time was thought to be possible and was consistent with the request from the Astronaut Office,” added the ASAP minutes.
“As the Constellation system design began and the program started looking at hazards and threats, in particular the very significant Micrometeoroid and Orbital Debris (MMOD) threat, they found that 1 in 1000 was going to be an impossible number to meet.”
The LOC ratio was greatly reduced after the initial bravado, with 1 in 270 – or 3 times better than Shuttle at end-of-life – the revised claim. The ASAP noted that at the time they were still skeptical of that figure but were told NASA felt it was the best they could come up with. In the end, the troubled CxP was canceled, making further evaluations irrelevant.
Interestingly, the ASAP minutes note that NASA kept the 1 in 270 LOC ratio in place for the initiation of the Commercial Crew Program “to keep an even playing field” – claiming commercial crew flights should be as safe as Constellation would have been.
Once again, that ambitious number was deemed to be unrealistic, with additional studies finally leading the CCP to conclude that the LOC number couldn’t be met, primarily because of MMOD hazard.
The dangers relating to MMOD are taken very seriously, given they are the third biggest threat to losing a vehicle during a mission – second only to launch and re-entry.
STS-125 would also see an increase in the concentration of MMOD, due to the region of Low Earth Orbit (LEO) Atlantis flew in for the majority of her mission.
The Program Requirements Control Board (PRCB) results – which took into account satellite breakups and a variety of other components evaluated to be in Atlantis’ orbital neighborhood – showed that the overall risk (LOV/C) scenario due to MMOD impact(s) to the Thermal Protect System (TPS) was 1 in 185, with an error factor of 1.35 based on MMOD distribution, velocity, and density uncertainties.
As noted, most of the risk was associated with impacts on the TPS and exposed areas such as the radiator panels, as opposed to the windows. In the end, Atlantis completed her mission successfully and without any MMOD related concerns.
The Commercial Crew vehicles will have less of a MMOD impact concern, not least due to their smaller sizes, but MMOD will remain as a major consideration for crew safety.
On orbit TPS inspections, specific to MMOD impacts, are also playing into the considerations between the setting of a LOC ratio of 1 in 270 and 1 in 200, note the ASAP.
“NASA has a made commitment to find other operational control mechanisms that will make up the gap between 1 in 200 and 1 in 270,” added the ASAP minutes.
“The kinds of things that can be done on orbit include: inspection by ExtraVehicular Activity (EVA) or robotic arm, docking procedures and location of docking port, and reducing time on orbit.”
However, the ASAP cautioned that some of those operational constraints, such as EVA inspection, carry their own risk.
“NASA needs to be careful as it picks what the controls will be and to be smart about how to make up the gap. Bottom line, there is still a 1 in 270 requirement; some of that has been allocated to the contractors and some to the Program.
“The Panel believes NASA is moving forward in an orderly and well-thought-through process.”
The time is fast approaching where the Commercial Crew vehicles will start launching people to the International Space Station.
The first two missions will come after uncrewed test flights to the orbital outpost, followed by a crewed demo flight, prior to the first contracted crew rotation mission known as USCV-1 (US Crew Vehicle -1).
Based on the current projections, NASA’s Flight Planning Integration Panel (FPIP) team installed projected dates (L2) for the historic test flights of both Dragon 2 and CST-100.
For Boeing, its CST-100 will first launch on an uncrewed test flight to the Station via the “Boe-OFT” mission in Apr, 2017 – on a 30 days mission, ending with a parachute assisted return.
Should all go to plan, the second mission will involve a crew – yet to be selected – on a mission designated “Boe-CFT”, launching in July, 2017, on a 14 day mission to the ISS.
The FPIP dates show SpaceX to be the most advanced in the Commercial Crew path, with their projected test flight dates currently set to win the honor of being the first Commercial Crew vehicle to arrive at the orbital outpost.
That first Dragon 2 mission, designated “SpX-DM1”, has a December, 2016 launch date, ahead of a 30 day mission – most of which will be docked to the ISS – ending with a parachute assisted landing in the Pacific ocean.
This would be followed by “SpX-DM2”, a crewed flight, launching in April of 2017, on a 14-day mission. This would mark the first time astronauts have launched from American soil on a US built spacecraft since Atlantis’ STS-135 mission in 2011.
Just a few days ago, the CCP ordered that first crew rotation mission (USCV-1) from Boeing. SpaceX is expected to receive its first order later this year, with the determination of which company will fly its mission to the station first to be made at a later time.
While both of these vehicles are expected to be extremely safe by nature, especially when compared to Shuttle, there will always be a risk to human life during a crewed space flight.
The ASAP discussed the procedures involved, should that worst case scenario materialize during a commercial crew mission, with panel member Dr. George Nield providing an update based on information provided by Rick Gavin, Federal Aviation Administration (FAA) Liaison/Range Safety in the CCP.
“One of the key interests is: What happens in the event of a mishap?” noted the ASAP minutes. “Efforts have been devoted to focusing on this topic. One of the most interesting parts of the presentation was the review of the current law.”
The discussion pointed to the NASA Authorization Act of 2005, which covered the loss of the ISS or its operational viability, the loss of any American space vehicle carrying humans that is owned by the Federal government or that is being used under government contract, or the loss of a crew member or passenger in any of those types of space vehicles.
Such a tragedy would require a Presidential Commission to investigate the incident, prompting the ASAP to call for a baseline plan to put into place. That plan is now being worked on via a document entitled “Mishap Preparedness and Contingency Plan for the Commercial Crew Program”.
Speaking of a couple of the key matrices, the document is evaluating who has the search and recovery responsibilities by mission phase – whether it is the contractor, NASA, Department of Defense (DoD), FAA, or the National Transportation Safety Board (NTSB) during pre-launch, ascent, on orbit, descent, and landing, along with identifying the lead investigator organization – be it the contractor, NASA, the Presidential Commission, FAA, or NTSB.
The ASAP noted that the entire document was expected to be complete and baselined by the end of May. The panel also said it was “heartening” to see that NASA is looking to being prepared, but that there there are a number of situations that need to be “fleshed out” to fill some voids.
The ASAP will continue to observe these to ensure that they have a thorough plan.
(Images: via NASA, SpaceX, Boeing and L2’s SpaceX and CST-100 Sections, including renderings created by L2 Artist Nathan Koga – Click here for full resolution F9, F9-R, FH, Dragon 2, BFR and MCT renderings and more – with those not official SpaceX images.)
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