/sci/ - Science & Math

>>11950275
Personally I think that Virgin should’ve just used a liquid engine from the get-go. Alright I did some math and hear me out.

It takes 2.1 km/s to reach suborbit from the ground. Let’s say it’s 2.3 km/s to add some margin.

SpaceShipOne has a mass of 900 Kilograms (0.9 tons) without its motor. That’s pretty damn light. It’s 5x5 meters from Nose to Tail and Wing to Wing. It’s main body is a 1.5 meter cylinder.

Let’s say Virgin wanted to add a liquid fueled stage instead of their rubber engine. If they wanted to reuse their 1.5 meter wide cockpit diameter, then their tank would also be 1.5 meters wide and around 2-2.5 meters long. Remember, we don’t want it sticking out the back of the ship.

The closest thing we have to a tank that matches the diameter and length is the Falcon 1 stage 2. It was 1.678 X 2.7 meters, and held 3.348 tons of fuel at a mass of 0.45 tons. It also had a single engine with a mass of 0.052 tons.

For our version of SpaceShipOne we can use a 1.5X2.7 meter wide tank. This is small enough to be flush with the body and still give around half a meter of space between the tanks and the cockpit cabin. The back end of the tank would extend out to the same length as the wings, so it would need some form of either Thermal Protection System, or at least another aluminum shell.

A 1.5X2.7 meter tank has around 83.5% the volume of a 1.678X2.7 meter tank. This means it holds 2.73 tons of Kerolox fuel. Let’s be conservative and say that it uses the same mass as the F1S2 tank, but utilices a second engine (The “Kestrel” engine has a high ISP and a thrust of 52 kN. We’ll assume Virgin uses a Kestrel-like engine with 50 kN and an ISP of 300 seconds, with is very low). As this new tank has the same mass as F1S2, but has a new engine, it has a mass of 0.5 tons instead of 0.45 tons.

SpaceShipOne masses of 0.9 tons. With three people that’s 1.2 tons. Using the new tank, it has a mass of 1.7 tons.

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