• 12 Posts
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Joined 2 years ago
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Cake day: June 9th, 2023

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  • Then you’d be surprised when you calculate the numbers!

    A Falcon 9 delivers 13100kg to LEO and has 395,700kg propellant in 1st stage and 92,670kg in 2nd stage. Propellant in both is LOX/RP-1. RP-1 is basically long chains of CH2, so together they burn as:

    3 O2 (3x32) + 2 CH2 (2x14) -> 2 CO2 (2x44) + 2 H2O (2x18)
    

    Which is 2*44/(2*44+2*18) = 71% CO2. Meaning each launch makes (395700+92670)*.71 = 347 tons CO2 or 347/13.1 = 26.5 tons of CO2 per ton to orbit. A lot of it is burned in space, but I’m guessing the exhaust gases don’t reach escape velocity so they all end up in the atmosphere anyway.

    As for how much a compute satellite weighs, there is a wider range of possibilities, since they don’t exist yet. This is China launching a test version of one, but it’s not yet an artifact optimized for compute per watt per kilogram that we’d imagine a supercomputer to be.

    I like to imagine something like a gaming PC strapped to a portable solar panel, a true cubesat :). On online shopping I currently see a fancy gaming PC at 12.7kg with 650W, and a 600W solar panel at 12.5kg. Strap them together with duct tape, and it’s 1000/(12.7+12.5)*600 = 24kW of compute power per ton to orbit.

    Something more real life is the ISS support truss. STS-119 delivered and installed S6 truss on the ISS. The 14,088kg payload included solar panels, batteries, and truss superstructure, supplying last 25% of station’s power, or 30kW. Say, double that to strap server-grade hardware and cooling on it. That’s 1000*30/(2*14088) = 1.1kW of compute per ton to orbit. A 500kg 1kW server is overkilling it, but we are being conservative here.

    In my past post I’ve calculated that fossil fuel electricity on Earth makes 296g CO2 per 1 kilowatthour (using gas turbine at 60% efficiency burning 891kJ/mol methane into 1 mol CO2: 1kJ/s * 3600s / 0.6 eff / (891kJ/mol) * 44g/mol = 296g, as is the case where I live).

    The CO2 payback time for a ton of duct taped gamer PC is 1000kg * 26.5kg CO2/kg / ( 24kW * 0.296kg/kW/hour) / (24*365) = 0.43 years. The CO2 payback time for a steel truss monstrosity is `1000kg * 26.5kg/kg / (1.1kW * 0.296kg/kW/hour) / (24*365) = 9.3 years.

    Hey, I was pretty close!





  • Yeah, with a Lagrange keyhole orbit past the Moon (which is what OP is asking about, not just plain escape velocity), you could park an Asteroid Belt asteroid in an orbit around the Earth. But it will be a high orbit. Not sure how low you could get it, I’m hoping a circular geostationary orbit is possible? But more likely something in the 300,000km range.

    Low orbit is out of the question. Maaaybe you could park the asteroid in a highly elliptical orbit where the perigee is inside the atmosphere. The drag will circularize it if the asteroid is small enough. But not so small or weak that it burns up or breaks up before that happens. And not so big that drag takes too long and the orbit wobble makes it hit the surface. In a low Earth orbit you now only have 8km/s delta-v to deal with.

    But to get the asteroid to gently touch the surface the way OP describes it, like some sort of skyhook? Is impossible short of a planet X or a rogue black hole passing even closer to the Earth than the Moon at the right moment. And whatever remains afterwards would be hard to call a surface: https://www.youtube.com/watch?v=kRlhlCWplqk



  • What about the “Protocol on Mines, Booby-Traps and Other Devices” that somebody linked above? Not sure if it’s the same as the “1996 Geneva Amendments” you mention, but both Ukraine and Russia are listed as signatories, and the language does seem to me to cover this exact situation:

    Article 7
    Prohibitions on the Use of booby-traps and other devices

    1. Without prejudice to the rules of international applicable in armed conflict relating to treachery and perfidy, it is prohibited in all circumstances to use booby-traps and other devices which are any way attached to or associated with:
      (a) internationally recognized protective emblems, signs or signals;

      (d) medical facilities, medical equipment, medical supplies or medical transportation;

    It says “medical supplies”, without reference to humanitarian aid, and clearly stressing in “any way associated with”. A “red cross” is also a recognized emblem. I can appreciate how “humanitarian aid” can be narrowly defined as medical supplies under direct control and chain-of-custody of the Red Cross Organization and doesn’t apply to random medkits. But I can’t see how this language above would not apply.

    Or is it the case that this would be a crime, committed during war, but not a war crime? How does that work? Does it have to be a violation of a specific Geneva Convention® version to count as a war crime, and not just any UN war-related convention?












  • NYC is using “Leading Pedestrian Interval” on most intersections. This feature has been installed about 10 years ago. When the cross traffic light has turned red and your (the car driver’s) traffic light is about to turn green, the pedestrian traffic light in the same direction turns green first. Your traffic light turns green a few seconds later, and the pedestrian light stays green. 15 seconds later, pedestrian light starts flashing red, and 30 seconds later both lights turn red at same time.

    This few second advanced-pedestrian-green protects pedestrians from collisions with cars by allowing the squishy road users to saturate the crosswalk before the cars trying to make a right/left turn get a go. Cars making a turn have to wait. When both lights used to change green at same time, the drivers making a turn had too much temptation to just gun it across an intersection before the pedestrians reached the middle of it. NYC has very many intersections and very many pedestrians. This caused many collisions and injuries.

    A 2019 city council law ammended the Administrative Code section 19-195 to clarify that bicyclists should use the advanced pedestrian green as well. This makes sense because bicyclists ride on the side of the road (in the right turn danger zone) and are in the squishy human category. NYPD hates bicyclists and ignores the law, pretending to “forget” it exists every time they write a citation violating it.