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Thread: SpaceX

  1. #2161
    Join Date
    Feb 2011
    Posts
    653
    At Cocoa, I spy an inverted dome between the cargo and propulsion modules. Lower dome, waiting for the thrust structure?

    Omar Izquierdo ✈ @izqomar
    And since Im probably the only person on earth that hasnt posted pics of the east coast #SpaceX Starship, heres my entry

    IMG_20190714_131022.jpg

    https://twitter.com/izqomar/status/1150417690357579776

  2. #2162
    Join Date
    Feb 2011
    Posts
    653
    This is about the explosion during a Crew Dragon thruster test.

    SpaceFlight Insider @SpaceflightIns
    SpaceX has a teleconference set for later today. Most agencies / companies give a couple days notice @SpaceX gave less than 3 hours. Topic is explosion of their @CommercialCrew offering @CrewDragon2

    https://twitter.com/SpaceflightIns/s...25006663897088

    SpaceX press release

    4 titanium valves need to be replaced by burst discs.

    On Saturday, April 20, 2019 at 18:13 UTC, SpaceX conducted a series of static fire engine tests of the Crew Dragon In-Flight Abort test vehicle on a test stand at SpaceXs Landing Zone 1, Cape Canaveral Air Force Station in Florida.

    Crew Dragons design includes two distinct propulsion systems a low-pressure bi-propellant propulsion system with sixteen Draco thrusters for on-orbit maneuvering, and a high-pressure bi-propellant propulsion system with eight SuperDraco thrusters for use only in the event of a launch escape. After the vehicles successful demonstration mission to and from the International Space Station in March 2019, SpaceX performed additional tests of the vehicles propulsion systems to ensure functionality and detect any system-level issues prior to a planned In-Flight Abort test.

    The initial tests of twelve Draco thrusters on the vehicle completed successfully, but the initiation of the final test of eight SuperDraco thrusters resulted in destruction of the vehicle. In accordance with pre-established safety protocols, the test area was clear and the team monitored winds and other factors to ensure public health and safety.

    Following the anomaly, SpaceX convened an Accident Investigation Team that included officials from the National Aeronautics and Space Administration (NASA), and observers from the Federal Aviation Administration (FAA) and the National Transportation Safety Board (NTSB), and began the systematic work on a comprehensive fault tree to determine probable cause. SpaceX also worked closely with the U.S. Air Force (USAF) to secure the test site, and collect and clean debris as part of the investigation. The site was operational prior to SpaceXs Falcon Heavy launch of STP-2 and landing of two first stage side boosters at Landing Zones 1 and 2 on June 25, 2019.

    Initial data reviews indicated that the anomaly occurred approximately 100 milliseconds prior to ignition of Crew Dragons eight SuperDraco thrusters and during pressurization of the vehicles propulsion systems. Evidence shows that a leaking component allowed liquid oxidizer nitrogen tetroxide (NTO) to enter high-pressure helium tubes during ground processing. A slug of this NTO was driven through a helium check valve at high speed during rapid initialization of the launch escape system, resulting in structural failure within the check valve. The failure of the titanium component in a high-pressure NTO environment was sufficient to cause ignition of the check valve and led to an explosion.

    In order to understand the exact scenario, and characterize the flammability of the check valves titanium internal components and NTO, as well as other material used within the system, the accident investigation team performed a series of tests at SpaceXs rocket development facility in McGregor, Texas. Debris collected from the test site in Florida, which identified burning within the check valve, informed the tests in Texas. Additionally, the SuperDraco thrusters recovered from the test site remained intact, underscoring their reliability.

    It is worth noting that the reaction between titanium and NTO at high pressure was not expected. Titanium has been used safely over many decades and on many spacecraft from all around the world. Even so, the static fire test and anomaly provided a wealth of data. Lessons learned from the test and others in our comprehensive test campaign will lead to further improvements in the safety and reliability of SpaceXs flight vehicles.

    SpaceX has already initiated several actions, such as eliminating any flow path within the launch escape system for liquid propellant to enter the gaseous pressurization system. Instead of check valves, which typically allow liquid to flow in only one direction, burst disks, which seal completely until opened by high pressure, will mitigate the risk entirely. Thorough testing and analysis of these mitigations has already begun in close coordination with NASA, and will be completed well in advance of future flights.

    With multiple Crew Dragon vehicles in various stages of production and testing, SpaceX has shifted the spacecraft assignments forward to stay on track for Commercial Crew Program flights. The Crew Dragon spacecraft originally assigned to SpaceXs second demonstration mission to the International Space Station (Demo-2) will carry out the companys In-Flight Abort test, and the spacecraft originally assigned to the first operational mission (Crew-1) will launch as part of Demo-2.

  3. #2163
    Join Date
    Jun 2015
    Location
    Houston
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    1,121
    Reaction between NTO and Titanium? I guess stainless steel was used in prior operations. Doesn't make sense to me either.

  4. #2164
    Join Date
    Sep 2003
    Location
    The beautiful north coast (Ohio)
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    48,925
    Very interesting. Just out of curiosity, I did some googling of titanium and NTO, to see if I could find anything about reactions, and what I found would not seem to indicate a problem.

    NASA technical note from 1968 "STRESS-CORROSION CRACKING OF Ti-bA1-4V TITANIUM ALLOY IN NITROGEN TETROXIDE"
    Stress corrosion cracking would be expected on long term exposure. I also don't know if this is the same titanium alloy.

    "An Experimental Investigation of Chemical Reaction between propellant tank material and rocket fuels or oxidizers....", NASA Technical note from 1963

    On page 11 (PDF page 13) they found no ignition or chemical reaction between NTO and titanium after a simulated impact.
    At night the stars put on a show for free (Carole King)

    All moderation in purple - The rules

  5. #2165
    Join Date
    Feb 2011
    Posts
    653
    The conversation seems to center around a titanium check valve leaking NTO into a helium pressurization line during the fill. When pressurization of the NTO tank was commanded, this slug of NTO was driven back into the titanium check valve by helium at very high pressure, causing the valve to ignite.

    Weird.

    And they say this was confirmed at their McGregor, Texas test site, which has a "boom pit" for testing such things.

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