How to get to Duna?

[LegitBro]

I've tried building a ship to do a return mission, but I just can't seem to get there. Main problem is it takes so much fuel to establish an orbit around Duna. anybody has any suggestions?

[G'th]

Aerobraking helps. The basic idea is to dip your Duna periapsis low into its atmosphere (though not too low) so that when you fly through it, it slows you down enough to establish orbit. It may not be perfectly circular or anything like that, but it'll save you a decent amount of fuel.

[Pecan]

Suggestions:

1. Ask questions in the Gameplay Questions and Tutorials section.

2. Use LV-N engines for fuel-efficient interplanetary transfer

3. Check alexmoon.github.io/ksp/ for WHEN to go - the planets must be aligned to do it efficiently.

4. Take absolutely everything you don't absolutely need off of absolutely every stage so that earlier ones don't have to push so much.

5. Make manoeuvres as early as possible in the flight for maximum effect at the cost of minimum deltaV.

6. Set your periapsis at 12-20km above Duna on approach to benefit from atmospheric aerobraking to supplement the fuel you burn.

7. Get captured into Duna's SOI then orbit - with aerobraking if possible - several times if that's what it takes.

8. Try to avoid hitting Ike.

[technion]

Why not show us your rocket?

The first question will be how efficiently it's designed. You may simply not be taking enough dv.

[LordCorwin]

I think you need about a minimum of 10500 m/s of delta-v to make a mission to Duna and back to Kerbin, assuming you follow an optimal path and good staging.

[Cerberus738]

Patience. You need to wait for the planets to line up before you transfer. Sometimes this means a 100 days. You'll end up burning all your dV away if you try and force your way into an intercept.

[Frank327]

It's all about good planning. Knowing how to calculate delta-v and reading delta-v maps gives you a guideline to design your landers. What you can learn about Duna:

1. You need some 1100m/s delta-v to get there from kerbin orbit.

2. You can use the atmosphere not just to slow down but to land if you've got enough parachutes (although using engines for a soft touchdown is a good idea). You can make sure you get into very low atmosphere (10km or less) by making precision burns far away from duna. They require almost no delta-v.

3. You need some 2000m/s delta-v to get back to kerbin.

Of course, knowing your phase angles is necessary to get these results, but with trial and error you can also find yourself the launch window you need. In the end, with these numbers I constructed this lander. All you need from the stages below that is to get it into kerbin orbit and you can do the return mission.

Funny thing is, it's actually overengineered. There's some 1000 spare delta-v in the final stage and also quite a bit in the earlier stage so you can afford mistakes.

Edited July 28, 2014 by Frank327

[Outo]

so here is my attempt and maybe i missed something because getting it to duna is where i fail at and sometimes i even fail to get it to orbit of kerbin

craft file.

https://www./folder/undefined/

image

http://www./view/en20q5eo23g483q/screenshot6.png

I would love advise to what i am doing wrong. This is built with the tech i have unlocked in .24 Science tree.

[Zwer.ch]

I would love advise to what i am doing wrong.

waaaaaaaaaaaaaaaaaaay to much payload for what do you need the fantastillion of RCS fuel you carry around?

If you compare your upper stage / lander section with Frank's lander in this post, differences are clear.

Keep it light and simple, carry only what you need to carry. Each ton you add to your lander equals a multiple tons in the lower stages.

Try out Kerbal Engineering Redux. It shows you all required details of your vessel, most importently the dV it can do.

[Seret]

waaaaaaaaaaaaaaaaaaay to much payload for what do you need the fantastillion of RCS fuel you carry around?

Probably about 10 times more LV-Ns than you need too. My interplanetary tugs have three engines, and are designed for Jool system return missions.

[NecroBones]

Probably about 10 times more LV-Ns than you need too. My interplanetary tugs have three engines, and are designed for Jool system return missions.

Yeah, I made the same mistake a long time ago. Lots of LVN engines will add way too much weight (particularly for a near target such as Duna), to the point where it might be better to use a chemical engine. It would be far better to use only two of them, or maybe four at the outside.

I just did a Duna trip again myself, and here's the design I went with for the transfer stage+lander (only 2 LVNs):

This is the entirety of what did the escape burn from Kerbin, and aerobraked into Duna's orbit. The lander portion has two drop-tanks. The lander would go down with parachutes, and an engine burn for a soft landing. After lifting off, it would dock with the tug again. So far it's managed to land on Duna, then Ike, and then Duna again (flag planting contract), and still has enough fuel to go home:

[NecroBones]

Suggestions:

1. Ask questions in the Gameplay Questions and Tutorials section.

2. Use LV-N engines for fuel-efficient interplanetary transfer

3. Check alexmoon.github.io/ksp/ for WHEN to go - the planets must be aligned to do it efficiently.

4. Take absolutely everything you don't absolutely need off of absolutely every stage so that earlier ones don't have to push so much.

5. Make manoeuvres as early as possible in the flight for maximum effect at the cost of minimum deltaV.

6. Set your periapsis at 12-20km above Duna on approach to benefit from atmospheric aerobraking to supplement the fuel you burn.

7. Get captured into Duna's SOI then orbit - with aerobraking if possible - several times if that's what it takes.

8. Try to avoid hitting Ike.

This is very good.

I also want to add-- Right after entering the SOI, while still out on its edge, you can do a relatively cheap correction burn here using the "radial" maneuver handles, to fine-tune the periapsis altitude for the aerobraking. I like to do it here, because it's after the SOI transition (where you'll lose some precision if you do it before entering, and probably need to adjust again anyway), but still far enough out not to cost too much fuel. The most fuel-efficient option, of course, is to get it as precise as you can from much further away, and only do a small fine-tuning maneuver here.

If you do the aerobraking well, you may not need to use any fuel at periapsis at all, and let the atmosphere do all of the work. Often you'll need to burn at least a little though. It's OK to do the aerobraking over multiple orbits, as long as you don't swing into Ike, or stay on an escape trajectory.

Then, swing around to the apoapsis side, and burn prograde to raise your periapsis back out of the atmosphere, if you're satisfied with the orbit's altitude. Remember to use only prograde and retrograde burns to change PE and AP altitudes (the radial burn earlier is the exception, because you're approaching on a hyperbolic escape trajectory).

[DeepSpaceDutch]

Suggestions:

1. Ask questions in the Gameplay Questions and Tutorials section.

2. Use LV-N engines for fuel-efficient interplanetary transfer

3. Check alexmoon.github.io/ksp/ for WHEN to go - the planets must be aligned to do it efficiently.

4. Take absolutely everything you don't absolutely need off of absolutely every stage so that earlier ones don't have to push so much.

5. Make manoeuvres as early as possible in the flight for maximum effect at the cost of minimum deltaV.

6. Set your periapsis at 12-20km above Duna on approach to benefit from atmospheric aerobraking to supplement the fuel you burn.

7. Get captured into Duna's SOI then orbit - with aerobraking if possible - several times if that's what it takes.

8. Try to avoid hitting Ike.

Great suggestions! Although for point 3 I would suggest http://ksp.olex.biz/, for beginning players it's much easier!

[tjsnh]

Some random thoughts:

I use two basic mission profiles for landers to other planets/moons : Monolithic, and target-orbit transfer.

For the monolithic mission, the lander is capable of the return trip to Kerbin all on it's own.

I use disposable LV-N boosters to get to the target - in fact, once I'm out of Kerbin's SOI on launch I dont use anything but nuclear engines while in space. Once at target, wait until you're at Aps and burn retrograde like a mofo to establish an orbit, and get in close from there - you know the routine. Landing on duna makes monolithic easier because you can attach 32425256 parachutes to land big monstrosities with only a small amount of burn needed to slow down before impact.

My monolithic landers are usually the 1-or-2 man lander can, with four "pods" radially attached containing fuel tanks and LVN boosters, with the small size solid fuel boosters below them to get back into space. Science lab stuff can be attached to your solids, just "take science" and transfer the data to your command pod before launch - saves weight on the return trip.

For the target-orbit linkup profile, I have a "return ship" - which is usually a 1 man capsule with a couple of fuel tanks and a single nuclear engine. Then a lander, which only needs to have enough oomph to get back into orbit from the target body, which cuts back on weight significantly and makes design easier. One common misconception/assumption - your lander does NOT have to actually "dock" with your return ship once you get it back into space .. I rarely bother .. just get within 1km and eva your kerbal back to the return ship, and don't forget to "take science" from your lander so you dont lose your surface samples and all that. I'm not at my home PC but I can post a couple example pics when I get home of each mission profile.

The TLDR: use LV-N engines for interplanetary transfers and retro-burns to slow down for orbit, try for light weight when possible.

[LethalDose]

I think you need about a minimum of 10500 m/s of delta-v to make a mission to Duna and back to Kerbin, assuming you follow an optimal path and good staging.

That's very high for a minimum dV to Duna. After the 5.5 km/s of dV to get from the launch pad to a Duna transfer orbit, you can get captured by Duna, circularize, escape Duna, and return to Kerbin for less than an additional 1.5 km/s dv, making the minimum for the whole trip for under 7 km/s of total dV, which is 2/3 your minimum. Obviously you can take more for safety, but 50% is pretty excessive.

Unless you're talking about a surface mission, in which case ~ 10 km/s is about what you need, but the OP was talking about having difficulty just getting to Duna and establishing an orbit.