NASA Safety Panel call for crew risk mitigation via debut SLS mission
NASA’s Aerospace Safety Advisory Panel (ASAP) praised the Space Launch System (SLS) and Orion programs for making “considerable progress” during their latest meeting, but called for managers to ensure the debut SLS flight – known as Exploration Mission -1 (EM-1) – is heavily aimed at risk mitigation, ahead of the first crewed mission.
ASAP on SLS/Orion:
The ASAP met at the Marshall Space Flight Center (MSFC), under the chairmanship of Vice Admiral Joseph W. Dyer, USN (Ret.) – with the minutes of the meeting sent to NASA Administrator Charles Bolden in June.
The historically conservative body – known for raising flags on items such as Shuttle extension and elements of the commercial crew program – appear to be pleased with the opening development work on the Space Launch System, a program that is now into its first full year since being officially announced by NASA.
The ASAP meeting notes cite an update they received from Mr. Daniel Dumbacher, Deputy Associate Administrator for Exploration Systems at the Exploration Systems Development (ESD) Program, relayed to the ASAP via panel member Mr. John Frost.
“Mr. Frost observed that the program has made considerable progress; he summarized some of the accomplishments: Orion has completed acoustic and vibration testing; computer data flow has been exercised; and parachutes have been tested. First flight, using a Delta IV launcher, will occur in 2014. There have been many success stories and much activity,” the associated presentation noted.
A more valid update – per recent developments – was also cited, relating to the work conducted on SLS’ core stage via the Design Analysis Cycle (DAC) within the Program – as outlined in a recent article on this site. However, the ASAP report only made a passing reference, noting “the SLS core will be the most interesting part of the system. The program has moved forward there also.”
“Many new systems are being developed, and they will require the most attention,” the overview continued. “Ground systems are also making good progress. “The launch complex at Kennedy Space Center (KSC) is coming along nicely, and the mobile launcher is being modified.
“The ASAP will follow the ESD Program very closely over the years to come.”
The vague, yet positive, overview then entered into discussions on the opening flight of SLS and Orion, known as the EM-1 test flight – claiming the mission warranted the Panel’s attention.
EM-1 is an uncrewed Beyond-Earth Orbit (BEO) Demonstration flight, resulting in the debut of the Heavy Lift Launch Vehicle (HLV) in its 70mt Block 1 configuration. It is currently scheduled for December, 2017 – a date that continues to have a large amount of margin.
For the mission, SLS would launch Orion into an high-apogee orbit of 975 nmi at the insertion point, before the kick stage/ICPS (Interim Cryogenic Propulsion Stage) – a Delta Cryogenic Second Stage (DCSS) – would then conduct the Trans Lunar Injection (TLI) burn(s) to send Orion towards a date with the Moon.
The seven to 10 day mission would come to a conclusion with Orion parachuting to a splashdown in the Pacific Ocean, for what would be its second such return, following the Exploration Flight Test (EFT-1) demo in 2014.
“The EM-1 flight is currently planned as an uncrewed flight to validate the integrated system in flight,” noted the overview. “The ASAP has discussed the importance of such uncrewed flight to buy down risk and understand the integrated system’s performance in the real environment.”
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As is now standard, the first flight of a human-rated vehicle are uncrewed missions, aimed at validating the system before taking the larger risk of placing humans on board.
The most famous mission that broke that rule was STS-1. The 1981 debut mission of the Space Shuttle Program (SSP) saw John Young and Bob Crippen trust their lives to the flagship Columbia, an amazing feat of bravery, not least because the orbiter had no real launch abort system for the ascent, and only ejector seats – that may have killed the duo regardless – as their way to get off the orbiter during the ride uphill.
Thankfully Columbia conducted her mission safely, earning the respect of her crew, as noted in thanks by Mr. Crippen in a highly emotional speech in memorial of her loss during the entry of the STS-107 mission.
“For technical reasons, NASA did not do an uncrewed flight on the Shuttle Program,” noted Mr Frost. “NASA believed the Shuttle crew on the first flight represented substantial risk mitigation for the extended communications blackout during high-risk, hypersonic entry; however, NASA will probably not have a similar risk trade with ESD.”
The ASAP, however, do want to see NASA managers take full advantage of the EM-1 mission, to the point of treating it as a crewed mission – even if it requires slipping the mission past 2017.
“One issue that came up for discussion is what needs to be demonstrated on EM-1. The ASAP believes that it is important to demonstrate performance as much as practical, including Environmental Control and Life Support Systems (ECLSS). The more critical systems the test can exercise, the more confidence it will give the Agency to fly the first crewed test flight.
“The ASAP encouraged NASA to complete the plan as early as possible and maximize the fidelity of the flight system for the first full-up test. The ASAP was also concerned that NASA carefully weigh the utility of maintaining the schedule for the completion of the EM-1 flight if doing so adversely impacts the risk on the proposed (EM-2) crewed flight.
“Taking the time to do EM-1 right will maximize the safety of the crewed flight. The Panel requested future briefings on the requirements surrounding the EM-1 flight and the trade-offs related to schedule and future risk to the crewed flight.”
Unlike the Space Shuttle, Orion crews will have a Launch Abort System (LAS) to save them in the event of a serious failure with the SLS during ascent. In turn, such safety systems improve a key risk parameter is known as LOC (Loss Of Crew), a ratio that denotes the “probability” of losing a crew during a mission. Technically, this calculation is classed as the Probability Risk Assessment Number (PRAN)
For example, it was often cited that the Space Shuttle had a LOC ranging from of 1/78 in 1988, to 1/254 prior to the loss of Columbia. In other words, the aforementioned worse case probability of a mission ending in disaster was once in every 78 missions.
For the now-defunct Constellation Program (CxP), NASA managers initially published a LOC ratio of 1/2021 via the Exploration Systems Architecture Study (ESAS), a PRAN that was criticized at the time, based on Ares 1 being a new system, with no flight history. The number eventually came down during the development of the system.
For SLS and Orion, it appears NASA managers have avoided listing a PRAN for their projected LOC ratio. However, the ASAP note they wish to encourage the Program to move forward with the establishing of their safety numbers.
“The second topic was the probability of Loss of Crew (LOC) threshold requirement, which has been particularly important to the Panel. The number is a primary driver to the safety of the design and works hand in hand with other drivers, such as levels of redundancy, reliability, and hazard controls.
“The Panel is finding that NASA is proceeding on SLS with great alacrity, and decisions have already been made on architecture and other issues; however, the program has not yet established the final requirements for mission LOC. Ideally, on a large system such as this, one would try to establish requirements before starting the trade space decisions.
“The ASAP encourages getting those requirements established as soon as possible so as to inform subsequent design and operational trades. There are efforts underway to do that, and the Panel advises that it be accomplished sooner rather than later.”
As noted, the ASAP are looking for the LOC numbers not just for ascent, but for the entire missions – missions that are yet to be fully refined by the Agency, with leaders continuing to use the vague and somewhat monotonous “Asteroid in 2025s. Mars in 2030s” line.
However, the presentation noted that NASA managers have informed the ASAP that they should be able to provide such LOC numbers for up to EM-2 – currently a notional crewed mission around the Moon – with the Panel acknowledging the Agency may find in a year or two that “the number may have to be adjusted, as was done on Constellation”, but that “we need a target, and the target needs to be a reasonably challenging one.”
“We have an architecture now,” they added. “it is very important to set clear, firm requirements as early as possible to guide future decisions on safety factors, reliability, and redundancy.”
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