Next stop: Duna

[Yuming]

I've been to the mun, minmus, and sent one way landers and rovers to Eve and Duna. I figure my next step is to make a manned, round trip expedition to Duna. I've tested a lander on Kerbin that can make a parachuted decent, land, take off, achieve orbit, and escape kerbins sphere of influence, and since Duna's atmosphere is thinner, I believe it will have no trouble coming home. The problem is, my existing launcher and interplanetary stage designed for small rovers just won't cut it with the extra weight. If you guys could give me tips and examples of good round trip Duna mission vehicles, I would greatly appreciate it.

[hound392]

I've not yet played the game but i've watched various let's plays and tutorials(by this i mean 100+) i would suggest that you use jet engines as boosters(they can be used) which will very effectively with a minuscule amount of fuel get you up to about 13000 ft without using any main fuel, After this you could swap to Liquid fuel boosters(stage all boosters in asparagus staging to enhance effectiveness to max) Once you are then out of the atmosphere and in orbit you could use the fuel you have(give yourself a decent amount and aspargus stage all your fuel tanks to your PRIMARY engine in the centre) then you can break free of the orbit of kerbin and use all the fuel you didn't need to use getting into orbit to get yourself to Duna. and then just have a Normal Lander probe/manned vehichle. Also if your running out of space in the VAB you can detatch sections and put them to the side and build the required parts and then re-attatch the other parts and although it will go through the ground of the VAB it will automatically fix itself on the LaunchPad.

Hope it helped.

[ThePsuedoMonkey]

I think a good way to drop some weight is to make your Duna touchdown vehicle a glider, which could also help out your Duna liftoff stage. If you want to go that route, then check out the FireSpitter mod too since it adds lots of aircraft parts. The gravity of Duna is about 1/3 of Kerbin, so I think 2500 deltaV should be a decent target for its liftoff stage. Your final transfer stage will probably be easiest to design around if it's ion-based, but Duna's atmosphere is thin enough that an LV-N isn't useless and some of the tiny radial rockomax thrusters would pair well with that since they have a great TWR. Using moons to slingshot is a great way to conserve fuel too, and both planets have a decent-sized one to use for that.

[capi3101]

Working on a round-trip manned Duna mission myself at the moment. I'd suggest docking; stick a docking port on your lander and boost a corresponding unmanned transfer module into orbit to rendezvous with it. You should still be able to use the same boosters you've got if you don't try to lift it all into orbit all at once.

Would love to see a pic of your lander; I have yet to build one that will achieve Kerbin orbit all on its own.

[Jason Patterson]

A return trip from Duna is the lowest delta-v interplanetary mission you can do; it's a great place to start. The biggest challenge for most KSP players is getting the idea that minimal designs are almost always best, and that's the case here. If you've built a ship that can get to Duna, you've almost surely got one that can get back home.

Things to keep in mind:

- Every kilo you can shave off of upper stages winds up saving 7-10 times more mass from the stage below (and that total mass saved saves another 7-10 times as much from lower stages and so on.) So keep your return stage as minimal as humanly possible if you're having trouble getting your vehicle into orbit.

If you're reasonably good at launches and getting from place to place in the solar system, then you can get from Duna's surface to Kerbin's with a vehicle that masses 4 tons. (Command Pod Mk1 - parachute - ASAS module - FL-T400 fuel tank - LV-909 engine - ladder - LT-2 landing struts x 3. Go with LT-1 legs if you are good with landings, but the difference is small for the additional ruggedness that LT-2 gives.)

Add an interplanetary transfer stage to this by attaching a pair of FL-T400 fuel tanks on radial decouplers with fuel lines. Done cleanly, you'd have ~1500m/s to get to Duna, ~900 m/s for slowing down at Duna (to assist your parachute and keep it from ripping off), ~1300 m/s to get back into orbit around Duna, and ~1300 m/s to get back to Kerbin. There is slop in all of this, and if you aerobrake properly at Duna, you could move the 900 m/s to any other part of the deal.

Total mass for a vehicle to get from LKO to Duna's surface and back - 8.6 tons. I'm reasonably sure that you can get that into orbit. (This could definitely be shaved down further, for all of the minimalists who are thinking, "Oh yeah, well I did it in 4 tons!" This is a reasonable design with a fair amount of excess delta-v.)

Note: If you want to add some wiggle room to the mission, change the fuel tank for the return vehicle to an FL-T800. That will add a couple of tons to the vehicle, but it also gives you another 600 m/s to play with. If you do this, you could also use an X200-8 fuel tank, which will give the same fuel load with a broader base, but it will look weird.

- Good staging adds small but significant amounts of delta-v to virtually any design. If you aren't using asparagus staging, you should seriously consider doing so. Some people don't like the look and refuse to do it, but it's impossible to beat in the current version of the game.

- Because Duna's atmosphere is thin, you want to try to land at the lowest altitude possible to maximize drag on your landing. Even with that, your landing can be pretty hairy. Be sure to add struts from your command module to the parachute, because it's going to deploy when you're going 400 m/s or faster, most likely. Also add struts from the command module to the ASAS and between the fuel tank and ASAS, because they really like to break at that point. I like the large, dark brown feature that crosses the equator for a landing site. It's flat and at the datum altitude, so landings are relatively easy.

- Duna's atmosphere is so thin that your launch profile will be closer to launching from a vacuum planet than from Kerbin. You can start turning immediately, and go completely horizontal by the time you get to 5-10km. This will save you a substantial amount of delta-v from gravity drag.

ETA:

I forgot to mention that you will want to set up your parachute to activate via an action group. You can deploy it the first time using staging, but the second time, once you've repacked it at Duna, can't be done in staging, so you need the action group or you're going to make a hole in the ground on your return (though a powered landing on returning to Kerbin is a real possibility, believe it or not.)

ETA some more: Another possibility is switching to an LV-N engine for the lander. I don't think it's a great choice here, however, since it will require you to build out the landing legs and add an additional ladder, plus the engine itself is much more massive than the LV-909. Swapping the engines out and making necessary changes to the landing gear and such got me something like 1000 m/s extra delta-v but it requires about 3 tons more mass and looks clunky. For a longer range trip, like a Moho or Dres return vehicle, it would be a much more viable option.

Edited April 21, 2013 by Jason Patterson
Subtraction is not my friend.

[CalculusWarrior]

I agree with Jason; asparagus staging really helps out when launching heavy stages. I tend to use one massive rocket for all my heavy lifting needs.

The size of your vehicle all depends on how many Kerbal you want to send to the Red Planet, as the three-man cockpit weighs four times as much as the basic one-man capsule.

For your interplanetary transfer stage, use the nuclear engines, as those have amazing efficiency that will get you to Dina with fuel to spare. My favorite strategy is to make a transfer stage from one of the large grey tanks and surround it with nuclear rockets. It probably has too much delta-v for a trip to Duna though, you may want to downsize that design a bit.

If you want a good delta-v guide, check out this site: ksp.olex.biz It is a great guide for calculating when you'll need to burn and how much delta-v you'll need to expend to get there (and back). In order to find out how much delta-v your rocket actually has, I suggest downloading the Kerbal Engineer (http://kerbalspaceprogram.com/0-18-1-kerbal-engineer-redux-v0-5/ ) It has all the information windows of Mechjeb, minus the sour reputation!

If you want to remain mod-free, then try scaling up your rover interplanetary rocket: add more engines and fuel tanks. You could also add a docking port, so that your lander could detach when you arrive in Duna orbit, then reconnect after they've performed their mission. This allows for much smaller lander designs, and I find it feels a lot cooler

Hope this helps!