Duna Mission: What's it take?

[grafdog1138]

Hello KSP Community!

So in the course of a science game of mine, I've become really, really tired of playing around in my own little corner of the solar system. I've built a Mun orbiting space station, landed a couple of times on the Mun, and flown more refueling probes to the Mun than I care to count. I want to go to Duna.

The question is, what does it take to get there? Manned or unmanned, I'm interested in both types of mission... but what does a typical Duna mission look like, and is it complicated?

Thanks in advance, I know y'all are an awesome community who'll respond in a helpful way.

Grafdog

[Rocket In My Pocket]

The most important thing when going to Duna or any other interplanetary destination is WHEN you go.

Besides that it's not terribly complicated, if you can get to the Mun/Minmus manned no problem, you should have an easy time sending a lightweight unmanned probe to Duna.

[Zeiss Ikon]

I've done a Duna flyby with single launch, using a single Mk. 1 Command Pod and a transfer stage consisting of two orange tanks and a Mainsail.  I don't recall what I had for a launcher under this, but I'm pretty sure it was a Mammoth engine -- possibly with some boosters added -- and did the job without an orbit insertion stage.

The problem with a flyby with intent to return the crew is that you're guaranteed to have a bad transfer window, either from Kerbin or from Duna, so you need to be prepared for a multi-year mission duration (if you play stock, that's not a big deal, but a life support mod will really complicate this) -- and this ship barely had the dV to use a gravity assist from Duna to get back to Kerbin (and was fortunate that Ike stayed out of the way).  I'd consider it pretty much the minimum crewed Duna mission.  In my case, the mission duration was around four years before reentry (of course, minimum even if you have the dV to capture and wait at Duna for a good window is close to three, so one extra year wasn't that bad).

[Ohm is Futile]

Duna is the easiest interplanetary target (well, I suppose Ike is kinda easier, but you get the idea...)
As others have pointed out, the transfer window is really important. In terms of dV, you can look at this map, it will give you a good idea of what it takes. Note that landing can be basically free using parachutes thanks to the atmosphere.

You can easily send a manned mission there and back, and that wouldn't require too much effort. You could send probes, but then you will need at least a couple of strong relays and you will probably want some less powerful ones to make a local network.

None of it is particularly complicated, you just need a bigger rocket to cover your fuel expenses due to the greater distance between Duna and Kerbin than Kerbin and the Mün.

I'd say you don't even need the mainsail unlocked. Skippers are probably alright if you plan your stages right and save mass wherever you can. It all depends on what you want to do around Duna. Do you want to science the hell out of it or do you just want to land, plant a flag and get what you can?

 

 

[Cunjo Carl]

@grafdog1138 What does it typically look like? It's funny, everyone here does things a little different, but we all get there in the end! As for how my trips look...

 

A much-more-massive-than-necessary rocket does a vertical launch at sunrise... any 'ol sunrise! Clusters of kickbacks and drop tanks peal off the thing as it screams straight up to interplanetary space. For a Duna trip, the core rocket would be composed of a skipper followed by a set of 3 terriers, the outer two staged on radial decouplers (everything tuned to TWR ~1.5). The top can just be a standard pointy pod. The craft would push just out into interplanetary space, and then I'd make a maneuver node (in solar orbit) with just enough prograde to put the craft onto Duna's orbit. By sliding the maneuver node around, you can find the time when the burn will put you into Duna's SOI (you can find your window).

Make the burn, and a couple weeks away from Duna, make a 'correction burn' manuever node to put you on course to whatever part of Duna you'd like to visit. For a first visit, I'd recommend having the periapsis at ~10km off Duna's surface. You know, the poles are nice to visit... bleak, all be.

I'd normally aerobrake using body lift from the rocket to maintain a ~7km altitude, but for a first trip I'd recommend just using the Skipper stage to bleed off extra speed in the upper atmosphere (down to 1000-2000m/s), and then use it to control a pleasant descent, finally dumping the thing a little ways off the ground.  The 3 terrier craft will be much more pleasant to land! My personal recommendation is to use the small landing gear over the medium landing legs, but that's just me. In any case, the outer two terriers can be put on 1.25m tanks topped with the big blue parachutes. Make sure to set them to open as high as possible in as low pressure as possible! While these parachutes won't slow you down enough on their own, a little kick from the engines just before landing will ensure you don't turn your trip into an extended impact test. Some extra reaction wheels really help at this stage. Just make sure to bring some extra batteries for them- best of luck and remember there's no shame in alt+F9 'till you can stick the landing!

You can jet pack on Duna, but only barely. Pop on out, enjoy the fresh rarefied air! Plant some flags, sing some songs... sure maybe do some science.

For the trip back, I am once again a fan of the vertical launch. If you just nip yourself outside Duna's SOI, you don't need to worry about what direction you're flying. Just use the same make a node and move it technique from before. For the trip back in to Kerbin... everyone has their own tricks for reentry. I'm a fan of heat shields with their ablator removed, but you'll find all sorts of ways.

And that's about that! So. Brass tacks, what's it take?

 

Traveling to Duna becomes "easily" possible once you get access to the science nodes that cost 45-science as well as the following 90-science nodes: kickback+skipper (heavy rocketry), fuel cross feed (fuel systems), the mini solar panel (electrics), and the big parachutes + medium legs (landing). I put easily in quotes because no matter what, everything is harrowing the first time you do it in KSP.... That's the fun! The mission will be easier if you have the next tech level higher in each of these, but I wouldn't consider it a necessity. For facilities, I consider the following to be a good point: Launchpad level 3, VAB level 2, Tracking station level 2 and Mission control level 2. It's totally possible with lower upgrades, but this is the point where you won't be fighting the system.

 

I hope that's enough to get your brain tinkering! If you happen to want more specific information, it'd be handy if you let us know what kinda tech level you're at, and send us a snap shot of one of your ships. so we can get a feel for your building style. Best of luck, and let us know how it goes!

Edited June 6, 2017 by Cunjo Carl

[Zhetaan]

Timing is important, but one you know the correct time, getting it is as trivial as hitting the time warp button:  obviously, you have to know when to stop the warp, too, but there are enough tools for that and others have covered that far better here.

An uncrewed Duna rover that stays there will be far different from a crewed land-and-return, but if you've landed on the Mun (and returned) and you want a dead-simple Duna mission, take your existing Mun lander, add parachutes and a heat shield, and give it a bigger transfer stage.  About one thousand metres per second more delta-V should do it.  Just by glancing at the map, I can tell you that Duna requires about 1500 m/s more than the Mun for a one-way trip, but because you can aerobrake both going to Duna and coming to Kerbin, you don't really need to take that much.

Depending on your configuration, you may need to get more powerful engines, but Duna's gravity is only twice the Mun's and most Mun landers have better than 2 thrust-to-weight (respective to Mun gravity; that won't even tip over on Kerbin), so unless you're right at the edge of that value, you probably don't need to bother.  You may also need to use engines to soften the landing; parachutes are nice but Duna's atmosphere almost isn't there; keep that in mind so you don't crash.

It is interesting to note that (albeit only with very careful flying) the stock Kerbal X can get to (but not back from) Duna.  You can use that for some ideas if you like, though I will warn you that the Kerbal X has some problems with it (all the stock craft do; part of the challenge is tweaking them so they work better).

I'll grant that it will not be the prettiest of missions, but unless you're playing with a life support mod, you can stand to keep your Kerbals in a can.  If you want to visit Duna, the best piece of advice I can give you is to build a rocket that is enough to do the job and just go.  Don't let it get bogged down in development hell by trying to design the do-absolutely-everything Duna mission.  For Kerbals, time is cheap.  For Kerbals in Science Mode, so are rockets.  You aren't planning on visiting Duna only once, are you?  And if you mess something up, so what?  Deal with it and make the mission succeed anyway--you'll have more fun that way.  If that's not possible, then fix it and do it again; you'll still have more fun doing that than spending the next six months in the VAB.

[Starman4308]

I'll point out that @Cunjo Carl's strategy wastes a fair chunk of delta-V by splitting the Duna transfer into two burns, one outside Kerbin's SOI. The Oberth effect is your friend, which means you can get that Duna transfer energy for less delta-V if you do it in LKO. It's probably a bit simpler for finding the appropriate transfer window, but there are mods (and tools) for that.

Spoiler

I'm pretty sure there's at least one more mod I can't remember the name of, which would make an even three for the "mods for that" link set.

To transfer to Duna, you need enough orbital energy to kick yourself out of Kerbin orbit and raise your apoapsis to Duna intercept. By doing it all at once, you're starting the Duna intercept "burn" with the velocity of Kerbin around Kerbol, plus the velocity of your LKO parking orbit, plus the velocity of Kerbin ejection. By splitting it up, you lose all the velocity you had in LKO, plus the velocity of Kerbin ejection.

[grafdog1138]

Hmmm, well this certainly gives me a lot to chew on! I think I'm gonna follow the general advice of this discussion and just try some stuff. I think that all the numbers in this game are scaring me off the "just build a friggen big rocket and shoot it off" approach, but its looking like everyone does that, so that's good enough for me!

I'm also thinking about getting a mod or two. I wanted to play vanilla for as long as possible, but these fancy dV calculators and such are too tempting!

[MiffedStarfish]

Keep it simple, Duna is just like going from the Mun to Minmus, on a much larger scale. 

[Ohm is Futile]

1 hour ago, grafdog1138 said:

Hmmm, well this certainly gives me a lot to chew on! I think I'm gonna follow the general advice of this discussion and just try some stuff. I think that all the numbers in this game are scaring me off the "just build a friggen big rocket and shoot it off" approach, but its looking like everyone does that, so that's good enough for me!

I'm also thinking about getting a mod or two. I wanted to play vanilla for as long as possible, but these fancy dV calculators and such are too tempting!

Well, Duna is close enough that you can pretty much throw something together as long as you respect some rules of thumb to make it strong enough. It will be over-engineered and more expensive than it needs, but it will do the job.

That said, I am a sucker for tools such as dV calculators and launch window planners. Basically, anything that takes the guesswork out of the equation and I wouldn't say it's perfect for new players, but it can take a lot of frustration out of the process especially with interplanetary trips as those involve a lot more time both designing and flying. It also makes it easy to underestimate interplanetary trips as all the numbers those tools put out are the most efficient ones and most people including myself end up wasting a certain amount of fuel to a number of factors. Then again, at least you get a ballpark idea of what your rockets can do. So, it's up to you really.

[Spricigo]

29 minutes ago, grafdog1138 said:

I'm also thinking about getting a mod or two. I wanted to play vanilla for as long as possible, but these fancy dV calculators and such are too tempting!

Start with a simple one, Basic DeltaV just make the calculations for deltaV, TWR, burn time, Isp, mass and thrust and display it next to the staging sequence in the VAB/SPH. It really only automatize calculation you may do it yourself or with an online tool, it barely change anything.

OTOH you may be more comfortable with using out off game aids, like a transfer planner .

 

Back to the topic at hand, that is how I do Duna:

-Setup the CommNet, 2 satellite with RA-2 around Duna, 3 with HG-5 around Duna and 4 with HG-5 around Ike

-Send the vessels to collect the science, usually a lander* for Duna and a lander for Ike. The one for Ike usually is good enough for the science in orbit.

-Send tanker to refuel

-Send interplanetary crew vehicle transfer vehicle, mostly to bring back the rescuees. Reusable

-Send crew landers, rover and orbital vehicles for the rescue mission that appear.

-Send the mining/refining/refuelling base.

At this point my infrastructure is setup, I refine it as new technology is available and add some redundancy. 

Notice that, since you are playing in science mode, most of what I bring to Duna (or any other place) will have little or no use for you. I suggest to bring a good lander, capable of exploring 2-3 biomes at time and refuel in orbit (when you are done with Duna It will be good enough to explore Ike also) some fuel in orbit and a return vehicle (that can be the lander itself after drooping the, now unnecessary, science equipment).

Also notice that if you manage to explore Duna, you will also be able to explore Gily (its even easier IMHO), and the lander design used in Duna don't need much adaptation to also work in Eeloo, Dres, Moho, Vall, Bop and Pol, granted reaching those destination is a bit more of a issue.

 

*I have no shame.