Comment on China begins assembling its supercomputer in space
TauZero@mander.xyz 2 weeks agoA solar-powered computer in space could recoup the CO2 cost of its launch fuel over its lifecycle (say 10 years?) when compared to coal-fueled electricity on the ground. After that it’s free. Of course, you’d benefit more by filling up every available spot on the ground with solar arrays first! But you will eventually run out, or you might not want to do that.
Umbrias@beehaw.org 2 weeks ago
i highly doubt 10 years is even remotely close to breaking even on a rocket launch.
TauZero@mander.xyz 2 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 2 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.