[AR] Re: 500,000 tons

  • From: Keith Henson <hkeithhenson@xxxxxxxxx>
  • To: arocket@xxxxxxxxxxxxx
  • Date: Tue, 6 May 2014 08:50:30 -0700

On Tue, May 6, 2014 at 3:03 AM, Uwe Klein <uwe@xxxxxxxxxxxxxxxxxxx> wrote:

snip

> Ever looked at the carbon footprint for those PowerSats ;-?

The main carbon footprint is the natural gas used to make the
hydrogen.  To get a kg to GEO takes ~3.5 kg of hydrogen.  That takes 7
kg methane (the rest of the hydrogen come from water)

At 5 kg/kW, 35 kg of methane to get the parts for a kW up.

Combustion of methane releases about 55,000 kj/kg, or kwatt-seconds,
or 15.4 kWh.  The best combined cycle power plants deliver 60% of the
heat as electric power or 9.25 kWh/kg.

Thus burning the methane needed to put a kW of power satellite in GEO
would produce around 324 kWh.  The power satellite pays this energy
back at 24 kWh/day.  I.e., it would take about 13.5 days to pay back
the energy from methane used to lift the parts to GEO.

Given the energy going into the parts, it might double the payback
time.  They do have a carbon footprint, and it's going to be a
substantial one, between two and three shipload of LNG a week.  But
given how fast the power satellites displace LNG with electric power
from space, they seem to make a lot of sense.

Please check my number.

Keith

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