Comment on China begins assembling its supercomputer in space
Umbrias@beehaw.org 3 weeks agoi highly doubt 10 years is even remotely close to breaking even on a rocket launch.
Comment on China begins assembling its supercomputer in space
Umbrias@beehaw.org 3 weeks agoi highly doubt 10 years is even remotely close to breaking even on a rocket launch.
TauZero@mander.xyz 3 weeks ago
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 or347/13.1 =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!
Umbrias@beehaw.org 3 weeks ago
Hm, that is unexpected. obviously that doesnt include the full manufacturing carbon cost of a rocket but it’s probably close enough anyway.