Friday, June 17, 2011

Rotovator assisted Aerial Propellant Transfer

In my post Aerial Propellant Transfer I concluded that with APT each flight could costs as little as "$1.5 million per flight plus the operators profit. Which comes to $75,000/tonne or $75/kg payload".

But by combining APT with hypersonic rotovators we can substantially improve even on that $75/tonne. Using a 600km long tether we can get the maximum velocity required from the orbiter spaceplane from orbital velocity of 7900m/s down to 4030m/s, a reduction in the required delta V of 3870m/s. We still have the ability to transfer 340 tonnes of propellant to the spaceplane from a tanker at 12,000meters, and because we've gone with APT rather than using the A380 (or similar aircraft) as a booster for air launch, we won't have the compatibility problems that would certainly have occurred in trying to mate a different spaceplane to the booster.

In my previous example post refueling the spaceplane needed a delta V of 8400m/s, by knocking 3870m/s off that requirement delta V comes down to 4530m/s, now we still separate from refueling with 340 tonnes of propellant, and our rocket engines are still H2/O2 with an exhaust velocity of 4500m/s so using the rocket equation a mass ratio of 2.75 gets us a delta V of 1.011 times exhaust velocity, ie. 4500 x 1.011 = 4550m/s. total mass to orbit is 1/2.75 of total separation mass which is 340/1.75 = 194.2tonnes, because total mass at separation has increased (from 400 tonnes to 534.2tonnes (33.6%) the unladen mass of the spaceplane will also have increased, working on a 33.6% increase, unladen mass goes from 40 to 53.4 tonnes, and payload increases from 20 to 140 tonnes. While we will have to increase the engine power of the spaceplane by 33%, the time those engines fire will also be reduced, the tanker requirements are unchanged ($500,000) allowing an increase of 33.6% in orbiter costs (servicing and capital) takes that to 1,336,000 total 1,836,000 divided by 140 tonnes brings cost/kg down to about $13.10, with rotovator energy costs of around $2.50/kg (the rotovator uses electric propulsion to maintain momentum, accelerating 1kg of payload by 4km/s 0.1kg of propellant is expelled at 40km/s, using E=1/2MV^2 that's 80 million joules or 22.2 KWh, at $0.1/KWh thats $2.22/kg of payload plus energy loses) totaling $15.60 plus the servicing and capital cost of the rotovator(?)

No comments:

Post a Comment