Interplanetary Slingshot-Tug Concept

[Neici]

Hi dear rocket-sience colleagues

Today i thought of a intersting concept for accelerating sience crafts into interplanetary trajectories.

Concept principle:

You have a SST(SlingShotTug) in your LKO.

After you have launched, rendez-voused and docked your craft with the tug you will burn prograde into a direct trajectory to your target. Duna for example. So you have a trajectory that leads direct into dunas SOI and you are still around 100km over kerbin.

Undock now your craft from the tug and let it fly. Change to the SST immediately, turn it around and burn retrograde. Reaccomplish LKO.

The SST is ready for further use.

Pros:

+ Reusable interplanetary tug that stays at Kerbin.(Less part costs for economics)

+ You don't have to Launch new Tugs befor every launch.

+ You may save some gametime(gaming time not ingame) if you launch several crafts to other planets

+ No interplanetary debris, or at least less if you count your crashed craft

Kons:

- It wastes some fuel because of spending the delta v for the trajectory one time and for returning the tug into LKO a second time.

- You have to set up a accurate and direct trajectory.

- Not recommendable for a journey further than dres.

My thoughts:

- Pro 1 speaks for it self

- Pro 2 is realated to 1. You also don't have to build big launchers to bring a interplanetary stage into orbit.

- The game time you save is: Pro 2 and you can designe a SST that can launch more than one craft without refueling. You only have to rendez-vous a new craft with the tug. So minus refueling launches. But plus the time you need to refuel it later and bringing it back to LKO after use.

- Pro 4 speaks for it self

- Yes you waste fuel, but it is much less than used for launching your craft. Because you have less fuel and no payload to slow down again.

- The last two Kons are related. Accurate trajcetories out of a SOI into an other one can be difficult because of KSPs shakeing orbital lines.

But it is allowed to bring some sort of trajectory ajustment device in your payload.

My thought example:

SST = a half Tank (18t) + 4 LV-N

Payload 1 = 25t

Payload 2 = 10t

Duna delta v = 1100 m/s

start SST + Payload 1 delta V = 2820 m/s

slingshot burn time = 54s

remaining delta V without Payload = 3093 m/S (1100m/s will be used to return to LKO)

Delta V left with payload 2 (SST + Payload 2) = 1149.7m/s

So in theorie it would be able to launch a second payload with 10t to duna but not to reaccomplish LKO again.

Well with only 2 LV-N it could have enough delta v to bring 2 payloads (20t and 10t) to duna without leaving Kerbin.

But needs as twice as long to burn => gets on a higher orbit after slowing down => wastes more fuel to lower orbit.

It's all a matter of designing. As more crafts the SST should launch without refuelling as more fuel gets wasted.

You can design a SST for almost every payload and for any Planet it should get.But this i leave to to you as spacecraft engeneer. ^^

Tell me what you think about this concept!

PS: It would also be a cool challenge to land a lander on duna, but you are not allowed to use any thrust generating part at the outside of the SOI of Kerbin.

Neici

[Tw1]

Perhaps you could shave of a little Delta V by just lowering the periapsis to Munar orbit, then tweaking for a reverse gravity assist. Then, more tweaking, an aerobrake and circularisation burn, you could return to LKO.

[rodion]

The launches you might save in conventional interplanetary stages from this scheme seem to be likely to be canceled out by the refueling schedule such a system would require. Remember, it's always possible to return your normal IP stages to orbit and refuel and reuse them for future launches, so long as they are robotic and can function autonomously away from the payload. The main way I can see this benefiting anyone is that if you have to launch a large number of separate craft in a relatively small launch window, a small fleet of these with frequent refueling trips would probably be able to serve any number of Kerbin escapes. I don't know what kind of space program would be so busy to require that many launches, though.

[Neici]

Tw1: Well i think it would be luck if you get a encounter for a munar reverse assist. Or at least time consuming.

But your aerobrake suggestion could be a nice idea. Just burn as much you need to not leave the SOI. From there you can time warp, lower your periapsis into the atmosphere, do a aerobrake and recircularise.

rodion: Well yes, but you could design you SST to support more shots than one. So you would need less refuel launches.

it would be less effective for the SST but you would require a lot less fuel than launching a refuel mission.

Thanks!

Edited October 1, 2013 by Neici