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Joined 11 months ago
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Cake day: January 2nd, 2024

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  • As you’re out hiking with your cat, a lettuce, and a vacuum cleaner, you come upon a river blocking the path. On the side of the river, there’s a boat that’s just big enough for you and one other passenger.

    The cat can’t be left alone with the lettuce.
    The vacuum can’t be left alone with the cat.

    How do you get everyone across?














  • “Arlington National Cemetery routinely hosts public wreath laying ceremonies at the Tomb of the Unknown Soldier for individuals and groups who submit requests in advance. ANC conducts nearly 3,000 such public ceremonies a year without incident. Participants in the August 26th ceremony and the subsequent Section 60 visit were made aware of federal laws, Army regulations, and DoD policies, which clearly prohibit political activities on cemetery grounds. An ANC employee who attempted to ensure adherence to these rules was abruptly pushed aside. Consistent with the decorum expected at ANC, this employee acted with professionalism and avoided further disruption. The incident was reported to the JBM-HH police department, but the employee subsequently decided not to press charges. Therefore, the Army considers this matter closed. This incident was unfortunate, and it is also unfortunate that the ANC employee and her professionalism has been unfairly attacked. ANC is a national shrine to the honored dead of the Armed Forces, and its dedicated staff will continue to ensure public ceremonies are conducted with the dignity and respect the nation’s fallen deserve.”

    https://www.npr.org/2024/08/29/nx-s1-5092087/trump-arlington-cemetery-altercation-video


  • When you heat hypergolic fuel up enough it will spontaneously ignite. It’s got its own oxidizer in it, essentially.

    Kinda. The RCS is fueled by two fluids that spontaneously combust when mixed: N2H4 and N2O4, aka hydrazine and nitrogen tetroxide (or dinitrogen tetraoxide).

    If the N2H4 gets hot enough, it will exothermically decompose into a large volume of hot gas. Its sometimes used as a monopropellant - squirt some of it onto a catalyst and direct the gas out a rocket nozzle, and you’ve got a simple, reliable thruster. Mixing it with N2O4 produces hotter gas, resulting in a thruster that gets about 35% higher fuel efficiency.

    Problems with the helium system could make hydrazine decomposition in the fuel lines more likely to happen. One of the ways the hydrazine is kept cool while its in the fuel lines is via high flow rate, but that requires the fuel tank to be pressurized by helium - clearing the fuel lines after thruster shutdown may also require helium. Low pressure could lead to lower flow rate and possibly cause cavitation (which can cause tiny spots of very high heat), which could in turn cause the hydrazine to decompose in the fuel lines/tank. At that point, mixing with N2O4 would be overkill - Starliner would already be destroyed before the oxygen started burning.