Slash Boxes

SoylentNews is people

posted by Fnord666 on Sunday January 14 2018, @06:53PM   Printer-friendly
from the space-is-risky dept.

Safety panel raises concerns about Falcon 9 pressure vessel for commercial crew missions

An independent safety panel recommended NASA not certify SpaceX's commercial crew system until the agency better understands the behavior of pressure vessels linked to a Falcon 9 failure in 2016. That recommendation was one of the stronger items in the annual report of the Aerospace Safety Advisory Panel (ASAP) released by NASA Jan. 11, which found that NASA was generally managing risk well on its various programs.

The report devoted a section to the composite overwrapped pressure vessels (COPVs) used to store helium in the second stage propellant tanks of the Falcon 9. The investigation into the September 2016 pad explosion that destroyed a Falcon 9 while being prepared for a static-fire test concluded that liquid oxygen in the tank got trapped between the COPV overwrap and liner and then ignited through friction or other mechanisms.

SpaceX has since changed its loading processes to avoid exposing the COPVs to similar conditions, but also agreed with NASA to redesign the COPV to reduce the risk for crewed launches. NASA has since started a "rigorous test program" to understand how the redesigned COPV behaves when exposed to liquid oxygen, the report stated. ASAP argued that completing those tests is essential before NASA can allow its astronauts to launch on the Falcon 9. "In our opinion, adequate understanding of the COPV behavior in cryogenic oxygen is an absolutely essential precursor to potential certification for human space flight," the report stated, a sentence italicized for emphasis in the report.

[...] The report raised issues in general about the commercial crew program, including concerns that neither Boeing nor SpaceX, the two companies developing vehicles to transport NASA astronauts to and from the International Space Station, will meet a requirement of no greater than a 1-in-270 "loss of crew" (LOC) risk of an accident that causes death or serious injury to a crewmember. That includes, the report stated, a risk of no more than 1 in 500 for launch and reentry.

Both programs are likely to be delayed:

Boeing, SpaceX have razor-thin margins to fly crew missions in 2018

Original Submission

This discussion has been archived. No new comments can be posted.
Display Options Threshold/Breakthrough Mark All as Read Mark All as Unread
The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.
  • (Score: 2, Troll) by khallow on Sunday January 14 2018, @08:51PM (3 children)

    by khallow (3766) Subscriber Badge on Sunday January 14 2018, @08:51PM (#622267) Journal
    I don't buy that you care, but if you do, feel free to give it your best shot. I'll note that NASA played this game with both the Space Shuttle and Constellation programs over the decades. The latter was particularly egregious since they started with a consideration of various competing launch platforms and systematically ignored [] the risks of the favored approach (using a Shuttle-based stack) while specifying that competing approaches had to meet a very high standard. They then hid all those games in an appendix which wasn't released publicly for several years due to alleged NDA restrictions.

    For example:

    Probably the most egregious of the flaws I saw was the exception given in the “ground rules and assumptions” to the Stick concepts. Now, as I’ve discussed before on this blog, tweaking assumptions to make sure that “the right answer” looks favorable is standard fare for trade studies. Now, this isn’t always a case of deliberate larceny. Many times honest engineers can have an opinion about the best route, and when the numbers don’t come out quite they way they expected, they go back and try and see if they “made a mistake” in their assumptions. That said, typically when a honest person is unintentionally massaging the assumptions–or when a dishonest but competent person is intentionally gaming the assumptions–they aren’t as blatant as this (found on page 28, my emphasis added):

    Max dynamic pressure = 800 psf (undispersed), except for certain In-line Crew (ILC) configuration-Solid Rocket Motor (SRM)-In-line cases where the limit was raised to 1,000 psf due to very high accelerations early in the ascent profile.

    Max dynamic pressure = 1000 psf (dispersed), except for certain ILC-SRM-In-line cases where the limit was raised to 1,200 psf due to very high accelerations early in the ascent profile.

    Dynamic pressure (or “q”) is the component of total pressure due to fluid kinetic energy, ie in this case it is pressure felt by trying to shove a high speed rocket through the air. Dynamic pressure is proportional to the air density and the square of the vehicle’s velocity. The maximum dynamic pressure (“max-q”) is an important factor for designing manned launch vehicles, and there are legitimate safety reasons for wanting to keep max-q within reasonable levels. Higher max-q can rapidly drive up the required thrust of an LAS, it drives up the structural stress, especially bending loads, and in the case of a controls problem could lead to tumbling and rapid failure of the stack.

    So, what is it about an SRM-based vehicle that makes it safer to fly at higher max-q? Why do they get an exception, when no other approaches do? To me, the fact that an exception was given only to “ILC-SRM In-line” (aka variants on der Griffenshaft) is what really marks this as an amateur job of assumptions gaming. A clever assumptions gamer would’ve just upped the max-q value for everyone. After all, even though no other alternatives come anywhere close to needing an exception, at least by giving some technobabble excuse like “on further analysis we found that the original GR&A numbers were too conservative” it looks like you’re being honest.

    So now we see the same game being played with commercial launch vendors. It's worth noting here that there probably won't be enough launches of the SLS (assuming it launches at all) to get an estimate of the LOC (loss of crew) within an order of magnitude of 1 in 500. In other words, the precision of the estimate of LOC will be plus or minus 2% due to the low launch frequency of the family of vehicles. But this game will be played right up to the moment when they actually do lose a crew.

    Starting Score:    1  point
    Moderation   +1  
       Troll=1, Interesting=1, Underrated=1, Total=3
    Extra 'Troll' Modifier   0  

    Total Score:   2  
  • (Score: 3, Touché) by mhajicek on Sunday January 14 2018, @09:18PM (2 children)

    by mhajicek (51) on Sunday January 14 2018, @09:18PM (#622271)

    I predict that the SLS will have a total loss of crew rate of 0% or 100%. If it fails, it's most likely to fail on the first launch and then never be used again. The other two launches before EOL of the program are far less likely to fail.

    The spacelike surfaces of time foliations can have a cusp at the surface of discontinuity. - P. Hajicek
    • (Score: 1) by khallow on Monday January 15 2018, @12:49AM (1 child)

      by khallow (3766) Subscriber Badge on Monday January 15 2018, @12:49AM (#622338) Journal
      Depends whether the first launch is manned or not. That's still up in the air.
      • (Score: 3, Funny) by mhajicek on Monday January 15 2018, @03:35AM

        by mhajicek (51) on Monday January 15 2018, @03:35AM (#622403)

        Bah dum pish!

        The spacelike surfaces of time foliations can have a cusp at the surface of discontinuity. - P. Hajicek