To send the Kitchen Sink to Duna or not?

[turmith]

Trying to set up a foothold on duna.

Due to the long periods of time between Duna launch windows; I came up with the idea that i could do it in 2 launches mainly due to lifting limitations i currently have in carrer. These 2 launches would assemble in Minmus orbit. This final rocket would contain 1 survey sattelite, 4 communication relay satelites, lander module, a Science lab, Mining Rig, transport tug, and a orbital fuel depot, Essentially the kitchen sink of rockets. I'd refuel said rocket in Minmus orbit(from existing ISRU setup) and then launch for Duna at the appropriate time. Mid-transfer i'd uncouple the survey scanner and it would boost it'self into a polar orbit and then shortly after the 4 communication relays would uncouple and boost themselves into orbit as well. Mining Rig would head to Ike with the tug following into Ike orbit and the Fueldepot(orange tank)/Science Lab would orbit around duna to facilitate refuling lander which would land on duna.

The question is, does it make sense to do this as 1 mammoth rocket, or do i do seperate launches from Kerbin/Minmus. I'm in career and cost efficiency/time efficiency are my two most important critera.

Opinions?

Thanks,

Turmith

[Vanamonde]

Making the trip in one transit simplifies things from an organizational standpoint, but isn't really much of a fuel savings since you're moving the same mass whether as multiple ships or one. However, the difference in starting out from Minmus rather than Kerbin is so small that there's no advantage to stopping to refuel at Minmus on the way out. 

[turmith]

I figured there would be some cost savings in having not to lift the fuel needed for the trip from Kerbin to orbit. I figured that'd be the most expensive part of the trip and where I could get the biggest savings. Does it then make more sense to transport fuel in from minmus and refuel in orbit over Kerbin then start for Duna?

[Capt. Hunt]

in that case, considering the effort to set up ISRU on Minmus and then mine and refine all the ore, it would probably be cheaper in the long run to launch the fuel from Kerbin.  The Delta-V saved by taking the fuel down the well instead of up it is not going to offset the funds and time cost of the Minmus operation.

Edited April 4, 2017 by Capt. Hunt

[Kryxal]

As I read it, the Minmus setup's already there, but a Duna transfer isn't going to take much more delta-v than going to Minmus.  Honestly, I'd think that multiple launches would be fine, easier to just do the burns in a row and they'll naturally arrive somewhat spread out.

[bewing]

There's a 900 m/s dV bonus in starting from Minmus rather than LKO, if you time things properly and do an Oberth dive. 900 isn't huge, but it's nothing to sneeze at, either.

[wumpus]

I know what I am suggesting for the Falcon Heavy now!

[Aegolius13]

8 hours ago, bewing said:

There's a 900 m/s dV bonus in starting from Minmus rather than LKO, if you time things properly and do an Oberth dive. 900 isn't huge, but it's nothing to sneeze at, either.

But it only takes a little over 1000 m/s to eject to Duna in an ideal launch window.   And it takes over 900 just to get to Minmus, plus the delta-v to circularize.  So I think the best plan here is just to burn straight to Duna.

I do like using the moons as refueling points for longer interplanetary trips, but Duna does not seem worth it, at least in a good launch window. 

 

 

[Wanderfound]

How are your SSTO abilities? It's possible to put all of that into orbit for peanuts if you start with reusable lifters...

RAPIERs etc make it a lot easier, but it is possible to pull similar tricks with Whiplashes and conventional rocket motors. Cargo for about √100/ton, bulk fuel for even less.

[turmith]

15 hours ago, Wanderfound said:

How are your SSTO abilities? It's possible to put all of that into orbit for peanuts if you start with reusable lifters...

RAPIERs etc make it a lot easier, but it is possible to pull similar tricks with Whiplashes and conventional rocket motors. Cargo for about √100/ton, bulk fuel for even less.

It's an interesting idea, but i've not invested in that part of the tech tree :-(

I'm going to look at doing seprate launches closely spaced together with a refuel in orbit of Kerbin for the larger items(miner,science lab, etc.) to minimize the caust of the Kerbin launch.

The kitchen sink was a really cool idea I had for an all in one planetary footprint system. But i'm not convinced there's significant cost savings because of the cost of larger Rocket Motors(Mainsails and skippers mainly) that i'd need to launch larger masses off of Kerbin. Plus cost of the Nerv's needed to move the thing out of Kerbin system once it was assembled.

I'll build each system and then compare costs and then post back here on what i've found.

 

[Freshmeat]

My experience has been the bigger the rocket, the less cost per ton of payload. So send off the kitchen sink, if your setup can handle the frame rates.

I am in the process of a Jool expedition with the same framework as you describe, and given that you have ISRU setup I would use it: It means that you can send the entire craft with just enough fuel to get to Minmus. While you only need 1000 dV for an ejection burn, you also need capture and circulariztion burns, and probably power assist for your descent. Every ton of fuel gotten from Minmus saves on your booster, cutting the cost of the launch.

The Oberth dive is tricky, though. I have calculated ephemeries to figure out when to eject from Minmus, but I still don't get the full savings from the dive. Part of the problem is that Minmus is inclined to your launch orbit, so it might be necessary to start out with a high periapsis, adjust inclination, and then lower periapsis for full effect. The savings might not be phenomenal, but part of the fun in KSP is setting up and executing complicated maneuvers.