[AR] Re: Fw: Hydrogen / oxygen news
- From: Keith Henson <hkeithhenson@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Thu, 31 Oct 2013 08:43:22 -0800
On Wed, Oct 30, 2013 at 8:07 PM, Henry Spencer <henry@xxxxxxxxxxxxxxx> wrote:
> The bottom line is that for a rocket engine, no matter which number you
> pick, it's big.
Skylon C1 burns off 42 tons of hydrogen in the air breathing ascent
phase. Takes 694 seconds to do that or 62 kg/s. A kg of hydrogen
releases about 48 kWh or 0.173 GW-s/kg so 62kg/s would amount to 10.5
GW.
The rocket ascent to orbit burns the remaining 24 tons of hydrogen and
150 tons of LOX, like the SSME, way hydrogen rich to get the molecular
weight of the exhaust down and the velocity up. Only 16.6 tons burns
taking 295 seconds. That's 56.3 kg/s for an energy release rate of
9.7 GW. (The actual hydrogen flow is ~81 kg/s.)
The even more hypothetical laser powered version has about half the
takeoff mass (no LOX at all) so the air breathing ascent phase would
be ~5 GW. Acquiring the Skylon early, 240 second into the flight and
at 10,000 meters, allows ~20% augmentation of the thrust by preheating
the hydrogen.
The above burning phase uses ~80 kg/s of hydrogen with an exhaust
velocity of ~7.5 km/s. Accelerating 80 kg/s to 7500 m/s takes ~2.25
GW. Given nozzle efficiency and other loses, this is where the 3 GW
laser estimate comes from.
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