Eve return vehicle - hard numbers

[Guest]

I've done some searching around but have yet to find an answer that was specific. I'm curious if anyone can provide some specific numbers on an Eve return vehicle. More specifically, is there a minimum TWR I should be aiming for?

My current, untested return vehicle masses some 15 tons and uses two turbofans as the first stage, each with four intakes and a single mark 1 fuel tank, having a total TWR of @ 2.5. The second and third stages consist of pure rocket parts with a combined delta-V of @ 4,400 with a TWR of or greater than 1.75. My thinking is that the vehicle will use the turbofans to ascend as far out of the atmosphere as possible before igniting the rocket staging to get into a low orbit (and my action groups are set up to support this). From there I can bring in another vehicle for rendezvous and rescuing the crew (this one is purely for getting into orbit, nothing beyond that).

Has anyone else had success with the turbojets? What TWR did you have at ground level? How much fuel did you need?

Edited August 21, 2013 by regex

[oktupol]

Jet engines don't work on eve, only on Kerbin and Laythe! I used Aerospikes for my return vessel because of their high ISP, especially in Eve's very dense atmosphere. But I haven't been there since 0.18 so I don't know how much fuel you need...

[TheDarkStar]

First, your idea won't work because jet engines won't work on Eve. Second, you need a TWR > 1.7. Third, ascent from sea level is about 11500 m/s, and ascent from the highest mountains is about 7000 m/s, so you'll need good rocket.

[Guest]

First, your idea won't work because jet engines won't work on Eve. Second, you need a TWR > 1.7. Third, ascent from sea level is about 11500 m/s, and ascent from the highest mountains is about 7000 m/s, so you'll need good rocket.

Thanks, probably should have checked the wiki about the jet engines. Too bad... vOv

[tavert]

More like 7500-8000 m/s from the highest mountain. And this number goes up if your TWR is not very good. Divide your TWR on Kerbin by 1.7 and that's what it'll feel like. Unless you have efficient Kerbin ascent vehicles that have TWR of only 1.2, I wouldn't try ascending from Eve with a TWR below 2 (relative to Kerbin). More like 2.5 at the start of each stage, and hitting terminal velocity just before the end of each stage will reduce the delta-V you need, though you'll need more engines to get a higher TWR which will reduce the delta-V capacity of your design.

For future reference when you're using jet engines on Kerbin or Laythe, the turbojets only generate half their rated thrust when stationary. So if you're looking at TWR from MechJeb or Engineer, you'll need to divide by 2 to get the 0-velocity actual TWR.

[Guest]

For future reference when you're using jet engines on Kerbin or Laythe, the turbojets only generate half their rated thrust when stationary. So if you're looking at TWR from MechJeb or Engineer, you'll need to divide by 2 to get the 0-velocity actual TWR.

That's helpful, thanks!

[maccollo]

If you're looking for an engine to replace your turbofans the 48-7S is probably the best suited.

It has terrific thrust to weight ratio, and it's small size allows you allows you to ditch excess weight very quickly with asparagus staging.

If you use the command chair as the only part for the final stage besides fuel and engine you can get an assent craft that weights around 10 tons.

Here's a craft I made. It weights 12 tons with the parachutes, 11 tons without.

[Sirine]

Check my signature... you only need 3340 fuel.