Designing return vehicles

[Warzouz]

I'm working on return vehicle to bring back crew from my various stations

I came with

- Kerbin's moons : 300m/s

- Duna : 700m/s

- Eeloo, Eve, Dres : 2000m/s

- Jool's moons : 2500m/s

- Moho : 5000m/s

Do you agree with that ?

Further more : what are your return vehicle looks like ?

[The_Rocketeer]

I would have thought you could drastically cut back costs with slingshots anywhere that has a moon (except perhaps Gilly), but especially Jool. I have no personal evidence tho.

[Warzouz]

Slingshots/gravity assists are nice to get a kick. But I find that managing encounters is hard. I prefer adding some fuel; it's simpler

[Skorpychan]

Generally my return vehicles are the same nuclear space tugs I used to get there. I shuttle them back and forth, and just drag the lander back with me for simplicity's sake.

I'm tempted to set up a LKO station for actual return pods, though. Just hitchhiker cans, a probe core, and the re-entry gear needed.

[Warzouz]

I'm tempted to set up a LKO station for actual return pods, though. Just hitchhiker cans, a probe core, and the re-entry gear needed.

I tried that, it's not "efficient", sure you don't need re-entry stuuf, but you need more dV to capture and circularize. Ships are bulkier. All the returns I did like that ended in rescue mission in Kerbin SOI.

Now I dive straight to the atmosphere. The only brake I do is from Moho because speed is very high and even my airbrakes burn...

[Pax Kerbana]

I tried that, it's not "efficient", sure you don't need re-entry stuuf, but you need more dV to capture and circularize. Ships are bulkier. All the returns I did like that ended in rescue mission in Kerbin SOI.

Now I dive straight to the atmosphere. The only brake I do is from Moho because speed is very high and even my airbrakes burn...

I don't know about that. If you have a station with return pods, you don't need 'chutes, abalators, or decouplers. I've never had much luck doing a direct dive with much velocity so there is uncertainty with that approach. Deorbit from a station allows consistency, land right at KSP. Not to mention much more flexibility with mission ship design, layout, size, etc.

You need to perform a capture no matter what, even if it uses aerobraking. If you run out of fuel you doing a burn, as long as you reach an orbit around Kerbin, getting a refuel or rescue rendezvous is straight forward.

Really the big benefit isn't in direct dV savings, its in craft reuse. For every ship you reuse, that's one less that needs to lift off from Kerbin. Even without ISRU use, sending up a fuel top-off for the returned ship and station is easy, cheap, and straight forward.

[Kurld]

I generally design the return/re-entry vehicle as the first (last?) stage of any manned vessel I create. That vehicle is usually some variation on the NASA Apollo CSM concept. I don't bother to circularize at return. A periapse around 20 to 25km seems to allow plenty of time to bleed off speed and land, at least within Kerbin's SOI. I've had a few close shaves with mountain ranges, but what the hey? The little green guys seem to love the excitement. I have not returned anything from beyond Kerbin's SOI in any of the new versions.

[Warzouz]

I don't know about that. If you have a station with return pods, you don't need 'chutes, abalators, or decouplers. I've never had much luck doing a direct dive with much velocity so there is uncertainty with that approach. Deorbit from a station allows consistency, land right at KSP. Not to mention much more flexibility with mission ship design, layout, size, etc.

You need to perform a capture no matter what, even if it uses aerobraking. If you run out of fuel you doing a burn, as long as you reach an orbit around Kerbin, getting a refuel or rescue rendezvous is straight forward.

Really the big benefit isn't in direct dV savings, its in craft reuse. For every ship you reuse, that's one less that needs to lift off from Kerbin. Even without ISRU use, sending up a fuel top-off for the returned ship and station is easy, cheap, and straight forward.

I usually don't circularize return ships. I alway dive to the atmo with aribrake. The only exception is Moho, as the high speed is not compatible with my return vehicle (2 stackes landing can, a small heat shield, 2 airbraikes and chutes), so I brake to reasonable speed (down to 4500m/s) and, even I'm still on hyperbolic, I can dive into atmo.

Return vehicle that dive into atmo need less dV (sometime MUCH less). It also need less fuel to put it at target.

But your argument about ship reusability is very valid. If those "crew orbit to orbit transports" are reusable, they must be sigle stage. That maxes them very bulcky.

[cantab]

Those figures sound about right. They may be a bit high for the Joolian system - you can get from Laythe to Kerbin orbits for about 1100 m/s. They may be a bit low for Eeloo.

[Kobymaru]

I don't really have "return vehicles" anymore. I have reusable interplanetery Ships with enough fuel to get to the planet and back. If I wanna land, I strap a lander to it and leave it there before return.

The ships are launched unmanned, so to man the Ships I use a small SSTO that carries the Kerbals up there. After return, I pick them (and the science) up from the interplanetary ship in LKO.

I like using the SSTO's a lot because it's quick, cheap and safe.

[Champ]

I don't get the "circularise around kerbin wastes dv" argument.

If you use kerbin's atmo to lose any excessive speed, you need very little fuel to circularise (just a little burn at Ap to set back Pe above 70km). The fact that you don't have to bring airbreakes + chutes + heatshield all along the way certainly gains more dv that the little dv you will need to circularise around kerbin, no ?

[Warzouz]

Those figures sound about right. They may be a bit high for the Joolian system - you can get from Laythe to Kerbin orbits for about 1100 m/s. They may be a bit low for Eeloo.

Due to design constraints, I changed a little

- Kerbin's moons : 300m/s -> 500

- Duna : 700m/s -> 1000

- Eve, Dres : 2000 -> 1900m/s

- Eeloo : 2000 -> 2500

- Jool's moons : 2500m/s

- Moho : 5000m/s -> 5300m/s (mostly to slowdown before entering atmo, my return can only handle 4500m/s or airbrakes burn)

For Jool's moons, I calculated 2400 for laythe (worst case).

I don't know how to handle moons inclination (such as Bop). Do I count it ?

[Pax Kerbana]

I usually don't circularize return ships. I alway dive to the atmo with aribrake. The only exception is Moho, as the high speed is not compatible with my return vehicle (2 stackes landing can, a small heat shield, 2 airbraikes and chutes), so I brake to reasonable speed (down to 4500m/s) and, even I'm still on hyperbolic, I can dive into atmo.

Return vehicle that dive into atmo need less dV (sometime MUCH less). It also need less fuel to put it at target.

But your argument about ship reusability is very valid. If those "crew orbit to orbit transports" are reusable, they must be sigle stage. That maxes them very bulcky.

I need to work on direct entry I guess. I actually avoid aerobraking at Kerbin just because of how long it takes.. I'd rather burn at 70k and wait until the ship approaches the space center before deorbit.

You bring up a good point about fuel and I guess I should clarify that I try to only pack enough for a 1 1/2 way trip because I try to pick up a station contract and send that with a lander and a little extra fuel in advance of the Kerbalnauts. When the IPT is full and the station tanks run dry, time to go home.

Return pods are just a Mk1-2 pod, pancake tank, terrier, plus accessories. They're versatile enough to make a few rendezvous/crew transfers before running empty. I send them up on SRBs only so total expenditure is very cheap... plus the Kerbals love that upper atmosphere acceleration.