[Spaceships] Stats for RB545 Rocket Engines or Other Air Augmented Rockets

[scc]

OK the RB545 was the proposed rocket engine for the British HOTOL SSTO Spaceplane, but as it is apparently still classified I'm not expecting any specific, but rather more general rules.

The secret to how the RB545 was supposed to work is that it was an air augmented rocket, or an hybrid of (ram)jet and conventional rocket, meaning that it doesn't need to carry as much oxidizer.

Using a top speed to Mach 17 (Apparently to fastest a ramjet can go) it can reach a speed of 3.6 mps, out of the 5.6 needed for orbital velocity. Using a 2:1 oxidizer to fuel ratio I think that means I can get something into orbit with only 3.2 mps of delta-V, does this sound right?

[Anthony]

Originally Posted by scc

Using a top speed to Mach 17 (Apparently to fastest a ramjet can go) it can reach a speed of 3.6 mps, out of the 5.6 needed for orbital velocity. Using a 2:1 oxidizer to fuel ratio I think that means I can get something into orbit with only 3.2 mps of delta-V, does this sound right?

Well, you need 5.6 mps of delta-V -- just some of it is produced by an air-ram rather than a rocket, and the delta-V per tank is considerably higher (in a complicated and variable way, as effective Isp depends on intake velocity).

[RogerBW]

Originally Posted by scc

OK the RB545 was the proposed rocket engine for the British HOTOL SSTO Spaceplane, but as it is apparently still classified I'm not expecting any specific, but rather more general rules.

In strictly game terms, I'd probably build it as a combination of chemical rocket and jet engine systems.

For dV calculations, work out the vehicle's top speed on jets (p. 35), convert to mile/second, and subtract that from your rocket's dV requirement.

[Humabout]

You may also want to include fly in the direction of the spin of the earth by flying eastward*, and take into account how high you can fly, since it will reduce dv requirements for overcoming gravity drag, as well.

* This necessarily needs to be a great circle, so if you aren't launching from the equator, you'll need to fly there first. Also, if your destination is inclined, you're better off launching directly into that inclination, since orbital plane changes eat SO much delta-v.

[johndallman]

The RB545 is still classified, but the SABRE from the same designer is a civilian project and superior, at least in terms of concept. It's about the same thing in Spaceships terms.

[doctorevilbrain]

What is invlunation?

[johndallman]

Originally Posted by doctorevilbrain

What is invlunation?

A typo for inclination of the orbit.

[RyanW]

Originally Posted by Humabout

* This necessarily needs to be a great circle, so if you aren't launching from the equator, youll need to fly there first. Also, if your destination is inclined, you're better off launching directly unto that invlunation, since orbital plane changes eat SO much delta-v.

That's why the ISS is in the orbit it's in. The inclination is a close match for Baikonur's latitude, plus a little, since launches have to go slightly north to avoid violating Chinese airspace.

[Humabout]

Originally Posted by doctorevilbrain

What is invlunation?

It's Posting-From-My-Phone for "inclination".

Originally Posted by RyanW

That's why the ISS is in the orbit it's in. The inclination is a close match for Baikonur's latitude, plus a little, since launches have to go slightly north to avoid violating Chinese airspace.

Yup, the US got shafted on that one or we'd have put it at about 28.5 degrees inclination.