Advice for a maned mission to Dunna

[Nicholas Kerman]

So I was looking for advice for a manned mission to Dunna, I thought perhaps I could launch two stages. 1 the landing module that would dock with 2 the main part this would consist of a mobile processing lab fuel and engine anyway I am saying this to ask if I'm taking this game way to seriously and if their is an easy way to do a mission to do a mission to Dunna and return thank you!  

[Mastikator]

Yeah if you're bringing a mobile processing lab then it makes sense to have a detachable lander. Though, my advice would be to have 2 command modules on the landing craft, so that you get 2 sets of experiments. One loaded into each command module. One set is used in the mobile processing plant and another is brought home.

[Snark]

Moving to Gameplay Questions.

If I understand you correctly, you're planning on sending a Duna mission consisting of an orbiter and a lander.  The orbiter stays in orbit around Duna.  The lander goes down to the surface, then ascends and docks with the orbiter.  Yes?

That's a perfectly reasonable mission profile, and lots of folks do it that way, yes. 

In terms of engineering, going to Duna is not a lot harder than going to the Mun.  It doesn't need a huge amount more dV overall.  Duna has a higher escape velocity, which means you need more dV to get off it than ascending from the Mun... but on the other hand, Duna has aerobraking available, so landing is cheaper, which helps to balance that out.

My suggestion is to practice on the Mun first, get comfortable with it, make sure you can do the Mun easily and well.  Once you can do that, you're definitely ready for Duna.  Assuming that you're comfortable with the Mun already, things to know about going to Duna:

• Navigation is really important.  "Needs only a little more dV than going to the Mun" is true only if you hit a good launch window.  So plan accordingly; my favorite tool for this is http://ksp.olex.biz ... it'll tell you when to launch, in what direction, and how fast.
• Plan to aerobrake into orbit when you arrive at Duna, so you can save dV.  Design mission accordingly.  (Aerobraking is a lot easier at Duna than at Kerbin.)
• Lander should take advantage of Duna's atmosphere.  There are various ways to handle Duna landing.  My personal favorite:  Put on drogue chutes (you'll almost definitely need them), then a small number of parachutes (enough to slow you to a few dozen m/s, don't try to slow to a safe landing speed, you'd have to spam them), and use a brief burst of thrust from your engines just before touchdown to cushion the landing.
• Be aware that there's a big difference in atmosphere thickness with altitude.  Specifically, if you're relying on atmosphere to slow you down for landing, it's a whole lot harder in the highlands than the lowlands.  So you may find life easier if you try to land in the lowlands.
• If you're planning on including a mining vessel for refueling, plan on visiting Ike.  It's a lot friendlier than Duna for this.

 

[OhioBob]

Below are some rough numbers for your Δv budget.  Note that these can vary depending on the specifics of the launch window and your skill at performing the maneuvers efficiently.

Launch to Kerbin orbit:  3400 m/s
Trans-Duna injection:  1100 m/s
Duna orbit insertion:  600 m/s
Deorbit:  50 m/s
Landing:  100 m/s
Launch to Duna orbit:  1400 m/s
Rendezvous and docking:  150 m/s
Trans-Kerbin injection:  650 m/s

If you aerocapture at Duna, then you don't need the full 600 m/s for Duna orbit insertion, but it's not zero either.  Aerocapture will get you into some cockamamie orbit that will need to be refined to get into a nice stable orbit from which you can perform your landing.  You'll still need to budget something.  Landing is performed mostly with parachutes, as Snark described.  The 100 m/s budget is to perform a cushioning burn just before touchdown.  The budget for rendezvous and docking may or may not be needed depending on how the mission is designed.  I've budgeted nothing for your arrival back at Kerbin; it is assumed you'll perform a direct reentry.  If not, you'll have to budget something for either Kerbin orbit insertion, or refinement of your orbit following Kerbin aerocapture.

Let's assume we have a disposable launch vehicle that gives you the 3400 m/s needed to get to orbit and no more.  Therefore, your Duna vehicle must provide everything else, or about 4000 m/s.  That can easily be divided up into two stages.  I generally like to use one of two methods:

Stage 1 = 1100 m/s for trans-Duna injection + 600 m/s for Duna orbit insertion = 1700 m/s (less if aerocapture is performed)
Stage 2 = 50 m/s for deorbit + 100 m/s for landing + 1400 m/s for launch + 650 m/s for trans-Kerbin injection = 2200 m/s

or

Stage 1 = 1100 m/s for trans-Duna injection + 600 m/s for Duna orbit insertion + 650 m/s for trans-Kerbin injection = 2350 m/s (less if aerocapture is performed)
Stage 2 = 50 m/s for deorbit + 100 m/s for landing + 1400 m/s for launch + 150 m/s for rendezvous/docking = 1700 m/s

The first method is good for something like a simple 'plag a flag' mission.  You ditch stage 1 as soon as you reach Duna orbit and pack everything else you need into a single self-contained lander/return/reentry vehicle.  It a simple method that doesn't require any orbital rendezvous and docking.  Works well for a small-scale mission.

The second method is as you described, where the lander includes only what is needed to land and get back up to an orbiting mother vehicle.  This is good if you want to place some heavy components in orbit that don't need to go down to the surface, such as a science lab.  It is a bit more complex because of the need to perform a rendezvous and docking.  One of the questions here is whether you have one pod or two.  That is, is the lander pod separate from the return/reentry pod?  The Apollo moon missions used two pods, but you could do it with a single multi-function pod.  Just beware that if you abandon the orbiting module during landing that you include a probe core to control it while it is unmanned.

Note that in the second case, designing your vehicle to produce the correct Δv can be more challenging because of the complex staging.  For example, Stage 1 will perform TDI and DOI with a fully fuelled lander attached, while TKI will be performed with no lander, or a fuel-depleted lander.  You can't always trust what the Δv readouts say (assuming you're using KER or MechJeb).  You really need to think through all the staging steps, and it may be necessary to perform some of the Δv calculations by hand.

Note that it's possible to transfer some or all of the rendezvous/docking budget from the lander to the orbiter.  It is common practice to make the orbiting ship the passive vehicle and the ascending ship the active vehicle, but you don't have to do it that way.  For instance, if you don't want to pack RCS into your lander, you can always just have it attain a stable orbit and then have the mothership come get it.  Or you could have one ship perform rendezvous and docking, while the other performs any necessary plane change (assuming some launch error).  My budget includes 50 m/s (plus RCS) for rendezvous and docking, and 100 m/s for plane change (which is enough to perform up to about a 6-7 degree plane change).

I also recommend adding some Δv margin to play it safe.

 

Edited July 8, 2016 by OhioBob