Making it (and back!) to Duna

[mabarry3]

So, I've been turning my sights lately on Duna as the next step in my KSP voyage, particularly one which will help me gain a lot of experience in terms of flying stuff since this will be my first interplanetary voyage. Would love to get some feedback from you lovely Kerballers if you're willing to answer questions, and I'm not sure how accurate the Wiki is lately on planetary data. Primarily curious if this ship seems capable of doing it:

Rocket:

Lander:

First of all, is that overkill/not enough? I'm trying to leave room for mess-ups since I'm still highly inexperienced at interplanetary movement. In addition, I was also considering trying to take down a rover with me to explore a bit, and curious if I would be able to fit that somewhere on my current lander if there's wiggle room in the DeltaV (However... that would also require me figuring out how to put a rover on a ship such that I can use it while there, then leave with it when I go as well... something I haven't figured out how to do yet), or if I should just assemble it with KIS/bring it on a separate trip. Also, I feel doubtful, but is that lander enough to get back to Kerbin? Or, at the very least, Dunian orbit so I can send a rescue.

In addition, are heatshields necessary for aerobraking in Duna's atmosphere? What is a proper aerobrake altitude anyway for Duna?

Is there anything else important to know about Duna?

P.S. I am aware that it's possible to go straight from an SOI intercept into a very elliptical orbit that has its periapsis below the atmosphere for aerobraking. I've been unable to do that thus far while tinkering with maneuver nodes from LKO, and all my intercepts have required an additional 1000+m/s dV burn once in Duna SOI to get into said elliptical orbit. Do I need to wait for an opening period or is there something I should know about doing my entire burn at once from LKO? Or any other tips in general on that matter.

Thanks for the help, everyone

Edited October 28, 2015 by mabarry3

[Superfluous J]

Just eyeing the rocket, lander, and dV stats I'd say it's got a pretty darn good shot, however you seem to have the staging wrong on the lander. Are you tossing the side boosters before igniting everything? I'd expect, with decouplers like that, to have 2dV readings. You should consider running fuel lines from them inward to the central core so when you toss them, the central core is still full. You don't need heat shields for aerobraking at KERBIN, so no, you don't need them for Duna

Don't bother with the rover. Assuming you don't break it deploying it, it'll flip in the first 5 minutes of using it. Also, it'll add even more mass to your vessel, requiring an even larger... everything.

The Lander is enough to get to Duna orbit, and probably home with the suggestion above. I see it has a docking port and no parachutes on the final stage, though, so I don't know what you'll do when you arrive back at Kerbin. Also, with that docking port I'd suggest leaving some fuel in orbit so you can, once you lift off and come back to space, you can top off the tanks for the journey home.

[mabarry3]

I can repack four of the chutes (the four that aren't discarded via being attached to the four Terriers on the side) once I use them the first time around, for use back on Kerbin. In all likelihood, I don't think I'll need nearly that many chutes but hey, I had them on my last (return-to-Kerbin) stage before just moving them to my Duna lander stage as well, since I could just repack after use. I do need to adjust the staging though, you're right - there's supposed to be the four Terrier decouplers on a separate stage from the Poodle in the middle. And I'll set those up with fuel lines now that you mention it.

[Snark]

Some observations:

Coming back home to Kerbin, you'll probably need a heatshield.

I'd say you can probably get by with just 4 legs on the lander; that will save you almost half a ton.

Be aware that it's hard to slow down enough for a safe landing on Duna using only parachutes, unless you pack on so many that their mass gets expensive. I usually aim t add just a few chutes, and use a burst of engine thrust just before landing to soften the impact to tolerable levels. Translation: consider ditching the four chutes above the Terriers. It will save you 1.2 tons, and you can make up for it with much less than that much fuel.

You may want to add a couple of the little radial drogue chutes for landing. Duna's atmosphere is thin enough that it can be tricky to slow down to safe speeds for activating parachutes. Drogues are safe to activate at double the speed, and can slow you down to where you can pop the main chutes.

[Superfluous J]

Aha. I thought those four side tanks were going to be tossed when they ran out of fuel on the ascent from Duna.

If you're careful on the way home you don't need a heat shield. Just aerobrake enough to get captured, then again enough to get your periapsis down between Mun and Minmus, and then a final one to actually get captured. This won't work of course if your relative speed to Kerbin is something crazy but if you do a good Hohmann transfer you should only have to bleed off a few hundred m/s to ensure a capture. Quicksave before aerobraking and try some altitudes, but I expect 45 will get you captured without blowing up your ship.

Regarding how to get there most efficiently, I highly recommend both the PreciseNode and Transfer Planner mods. For aerobraking/capture I also highly recommend Trajectories. It's extremely hard to describe in general terms how to correctly perform the burns. I suggest you look up some "how to perform an interplanetary transfer" videos on YouTube.

[mabarry3]

I have a heatshield on what would be coming back to Kerbin (Heat shield, cargo bay, command pod, docking port from bottom to top), but I may apparently need to take it in low Duna orbit rather than planning a full return trip and send over a rescue tug behind it to sit in Duna orbit until the lander is ready to go.

I had heard Drogue chutes were practically useless in Duna due to the low drag, are they definitely worth it in terms of dV savings?

[Mastikator]

Use airbrakes for aerobreak. They are immensely effective and weigh very little.

[Snark]

Some more thoughts:

- You could probably not just reduce from 8 to 4 legs, but go down to the next-smaller legs. That'll save another couple of hundred kilograms.

- Suggest rearranging your struts. The most stress you'll have to deal with is the impact of landing, and if you think about it, that will be shock that's directed upward. Your existing struts won't help much with that. Suggest getting rid of the 8 horizontal struts that you now have, and replace with 4 "radial" struts, each of which goes from one of the outrigger fuel tanks up to near the apex of the command module. This will save you another 200 kg (four struts instead of eight), and will likely do a better job of impact resistance.

- Is there a particular reason you're using the radial decouplers that hold the outriggers way out from the central body? I think you ought to be stable enough-- you've got plenty of mass down below, and you have the legs mounted on the radial tanks. You could use the "standard" radial decouplers instead, will save another 100 kg, and be mechanically stronger (less breaking torque from shock transmitted up the legs on landing, due to shorter lever arm). Doing this will also reduce the angular moment of your craft, which means it will be more nimble rotating on its reaction wheels.

- If you're putting heat shields on, consider adjusting the amount of ablator in them (say, down to 50%). Will save a fair amount of mass, and in my experience I almost never need more than half of a load.

- Per 5thHorseman's suggestion, add fuel lines leading inwards. However, I'd suggest doing asparagus staging for takeoff. See the wiki article I just linked for details, but basically this will involve doing two things: 1. setting the fuel lines appropriately, and 2. tinkering with the staging UI so that the external tanks are dropped in two pairs instead of all four at once. This will allow your ship to launch on all 5 engines, use up all the fuel in 2 of the tanks, drop those two (with their engines), use up all the fuel in the next 2 tanks, drop those two (with their engines), then continue on with the last (central) engine.

One more comment about Duna: be aware that it has both lowlands (near zero elevation), and extensive areas of highlands (large plateaus at elevations over 5000 m). This makes a huge difference to the landing experience, particularly if you're relying on parachutes, since Duna's atmosphere drops off more rapidly with altitude than Kerbin's does. I'm not telling you this in order to advocate for one or the the other (they both have their advantages and disadvantages), just be aware of the difference. If you get to Duna, and try to land, and are having a hard time and keep failing, try landing somewhere at a different elevation to see if you have better luck with that.

By the way, if your goal is to maximize science, then landing in multiple biomes can boost your returns. For example, if you can leave enough fuel orbiting in the big orange tank when you go down to land, you could land, take off, dock, refill, and repeat. Not sure if you have enough fuel for that.

- - - Updated - - -

I had heard Drogue chutes were practically useless in Duna due to the low drag, are they definitely worth it in terms of dV savings?

On the contrary, I would contend that Duna is the poster child for drogue chutes. It's just about the only place I use them.

Without drogues, you'll probably have to burn up lots of fuel trying to get down to a low enough speed that you can safely pop your main chutes. A couple of the little radial chutes will have a mass of only 0.15 tons, well worth the investment IMHO. Just to run some rough numbers: I don't know how much mass you have squirreled away in that service bay, but I'd put your lander mass at 25+ tons with full tanks, even with the previously-suggested optimizations. Drogue chutes will save you ~250 m/s of dV, and with Terrier engines that would translate to around 2 tons of fuel for a 25-ton ship. Pretty good return on investment, I'd say.

[mabarry3]

Struts: I didn't think of it like that. I just typically kept two attachment points per radial fuel tank, one on the top and bottom of the fuel tank, attached to the item in the center of the stack. The strut image in that picture was a bit of a test but I'll stick with what you've said then.

Radial decouplers: I actually already switched those. I thought I had the normal ones when I posted this but noticed it shortly thereafter.

The main rocket already is asparagus staged, but I'll have to see how much fuel I have left once I get there. I may try to drop down into multiple biomes. In my cargo bay is basically 3 of every science-gaining unit with the exception of having a "mere" 1 Science Jr. in the middle of it.

As far as mass/deltaV savings... Hmm, not bad. Didn't think drogue parachutes did much anywhere, especially not in thin atmospheres. That's significantly better than I thought.

While we're on the topic of saving mass, what about Rockomax Brand Decouplers? I've had some stability issues in the past in using parts that don't "fit" the stack below them but I don't know if that warrants the extra .35t per switch from a normal to a Rockomax. I have two on the rocket which could be another potential .7.

[Snark]

Struts: I didn't think of it like that. I just typically kept two attachment points per radial fuel tank, one on the top and bottom of the fuel tank, attached to the item in the center of the stack. The strut image in that picture was a bit of a test but I'll stick with what you've said then.

One thing to be aware of with struts: their mass is always attached to the first node you lay down when you place them. Therefore, any time you're attaching a strut between a radial booster and the central body of the rocket, always start the struts from the outside booster, not from the central body. That way you'll drop the strut's mass when you drop the booster, instead of having it stick around.

The main rocket already is asparagus staged, but I'll have to see how much fuel I have left once I get there.

But it's still worth asparagus-staging the lander itself. dV is dV.

In my cargo bay is basically 3 of every science-gaining unit with the exception of having a "mere" 1 Science Jr. in the middle of it.

And some batteries, right? You'll want a lot more electricity storage than the command pod holds, if you want to be able to transmit science. (Yes, it's better to bring it back than to transmit. But you can transmit, and then do another science grab to bring back with you. That way you can get a decent chunk of the tech benefit back home, before you actually bring your ship back.)

Also: Reason for having 3 of every science experiment? That sounds kinda expensive. You're aware that you can re-use them, right? After you get science from them, send an EVA kerbal out to take the science out of the instrument, and then go back to the command pod (which stores the science result in the pod). This leaves the instrument empty and available to take another science reading. Make sure that you have a scientist along, since they're the only ones who can reset the Science Jr. and the goo canister to let them be used multiple times.

You're familiar with the ability of science instruments to get different readings for different situations, yes? e.g. the thermometer gets one reading for "space high over", one for "space near", one for "upper atmosphere", one for "flying" (per biome!), one for landed (per biome). Different science instruments get per-biome results for different situations, so it's good to be familiar with that so you can squeeze out every last drop of science from your visit.

As far as mass/deltaV savings... Hmm, not bad. Didn't think drogue parachutes did much anywhere, especially not in thin atmospheres. That's significantly better than I thought.

Here's the deal. "Regular" chutes can't be opened until you're down around 250 m/s; if you're much faster than that, they get ripped off. Drogues' safe deployment speed is about double.

On Kerbin, that's usually not an issue-- most ships have terminal velocity under 250 m/s, so they slow down naturally to safe parachute speeds as they approach the ground. (Unless they're big and heavy, or very streamlined... but then you can use airbrakes to help.)

However, on Duna, the air is so thin that there's an excellent chance you'll still be going well over 250 m/s when you hit the ground, which means you never have an opportunity to open your parachutes at all.

Of course, you can fire your engines to slow down enough to use your parachutes... but that costs a lot of fuel. Let's say you get to the point where you're going 500 m/s and getting dangerously close to the ground. At this point, you have two choices: 1. Fire your engines to reduce your speed by ~250 m/s so you can pop your main chutes, or 2. Open your drogue chutes and let them slow you down by 250 m/s so you can pop your main chutes.

#2 gets my vote, but of course that only works if you have drogue chutes.

By the way: the other thing you should do, before launch, is adjust the fully-open altitude of your chutes from the defaults-- e.g. boost your main chutes from their default 1000-meter altitude up to at least 2000 meters, and similar increase for any drogues. Chutes take a longer time to slow you down in Duna's thin atmosphere, you want to give them more time to work.

While we're on the topic of saving mass, what about Rockomax Brand Decouplers? I've had some stability issues in the past in using parts that don't "fit" the stack below them but I don't know if that warrants the extra .35t per switch from a normal to a Rockomax. I have two on the rocket which could be another potential .7.

As long as they're on the main rocket and not the lander itself, I wouldn't worry about it. The rocket's so massive that the decouplers are a pretty small fraction of it, so you're not losing much. If you tried to hack it with a smaller decoupler, you'd end up with something so floppy that you'd need struts to make up for it, which would largely cancel out the mass benefit of using the smaller decouplers.

[Zophos]

I'll second the recommendation for airbrakes - they're lower mass even than drogues, and you can deploy them in space and use them all the way down. I have a small science lander on my current Duna mission, with two airbrakes and four radial parachutes. Uses no fuel to land other than a deorbit burn to put periapsis in the atmosphere.

[Vegvisir]

I'm setting sights on Duna and/or Eve for my next unmanned mission in Career. This thread is helpful

[mabarry3]

I'm setting sights on Duna and/or Eve for my next unmanned mission in Career. This thread is helpful

As long as you're not planning on landing on Eve any time soon but yes, this has been very helpful. Thanks again to everyone!

I'll second the recommendation for airbrakes - they're lower mass even than drogues, and you can deploy them in space and use them all the way down. I have a small science lander on my current Duna mission, with two airbrakes and four radial parachutes. Uses no fuel to land other than a deorbit burn to put periapsis in the atmosphere.

I added two airbrakes, so currently using 2 airbrakes, 2 drogue chutes, 2 normal chutes.

One thing to be aware of with struts: their mass is always attached to the first node you lay down when you place them. Therefore, any time you're attaching a strut between a radial booster and the central body of the rocket, always start the struts from the outside booster, not from the central body. That way you'll drop the strut's mass when you drop the booster, instead of having it stick around.

Nice. I switched the location around on the struts - had no clue.

And some batteries, right? You'll want a lot more electricity storage than the command pod holds, if you want to be able to transmit science. (Yes, it's better to bring it back than to transmit. But you can transmit, and then do another science grab to bring back with you. That way you can get a decent chunk of the tech benefit back home, before you actually bring your ship back.)

Yes, I have two 400-charge batteries, which is also plenty to run the torque wheel on the way there.

Also: Reason for having 3 of every science experiment? That sounds kinda expensive. You're aware that you can re-use them, right? After you get science from them, send an EVA kerbal out to take the science out of the instrument, and then go back to the command pod (which stores the science result in the pod). This leaves the instrument empty and available to take another science reading. Make sure that you have a scientist along, since they're the only ones who can reset the Science Jr. and the goo canister to let them be used multiple times.

You're familiar with the ability of science instruments to get different readings for different situations, yes? e.g. the thermometer gets one reading for "space high over", one for "space near", one for "upper atmosphere", one for "flying" (per biome!), one for landed (per biome). Different science instruments get per-biome results for different situations, so it's good to be familiar with that so you can squeeze out every last drop of science from your visit.

Your second paragraph was the primary reason I had 3 of each. The reason was so I could capture as many as possible while de-orbiting/re-orbiting. It's somewhat difficult to EVA from "flying over Midlands" or "In Duna's upper atmosphere" (though I might be able to pull off an upper atmosphere grab) and collect science modules, and impossible to EVA during a flight to collect it. So, if I went over multiple biomes on the way down or up, and I wasn't too focusing on not getting blown up, I could open up the bay real quick and have options to choose from regarding what was still an unused module. But, I dropped the module number to 2 because I just now realized I could set an action group to log one group's data over one biome/situation, and a second action group to log the other group's data over a biome/situation, which saves me valuable time in trying to collect as much as possible. So I could probably pull off an "upper atmosphere" grab which allows me to drop it down to 2 in hopes that I can collect two different biomes while "in flight" above them.

As long as they're on the main rocket and not the lander itself, I wouldn't worry about it. The rocket's so massive that the decouplers are a pretty small fraction of it, so you're not losing much. If you tried to hack it with a smaller decoupler, you'd end up with something so floppy that you'd need struts to make up for it, which would largely cancel out the mass benefit of using the smaller decouplers.

Okay, I'll keep that in mind. I was on the fence about using it or not using it, but was noticing some stability issues arising from smaller decouplers, and had assumed the weight increase was worth the part about not having my rocket spinning around its decoupler.

Side question about transmitters: I was going to use the Communotron 16 because of the 0.05 weight, but does that work outside of Kerbin's SOI or at another planet? I could use the 88-88 but no reason to if that's unnecessary extra weight.

Edited October 27, 2015 by mabarry3
Removing accidental additional code

[Snark]

As long as you're not planning on landing on Eve any time soon

Actually, landing on Eve is trivially easy. It's easier than Duna, probably the easiest place in the solar system outside of Kerbin's moons.

It's taking off again that's the hard part.

I added two airbrakes, so currently using 2 airbrakes, 2 drogue chutes, 2 normal chutes.

Be aware that the airbrakes and drogue chutes will be useless for slowing your speed below several dozen meters per second. May be worth going up to 4 normal chutes (by which I mean the radially-attached ones), like you had on the command pod to begin with.

Your second paragraph was the primary reason I had 3 of each. The reason was so I could capture as many as possible while de-orbiting/re-orbiting. It's somewhat difficult to EVA from "flying over Midlands" or "In Duna's upper atmosphere" (though I might be able to pull off an upper atmosphere grab) and collect science modules, and impossible to EVA during a flight to collect it. So, if I went over multiple biomes on the way down or up, and I wasn't too focusing on not getting blown up, I could open up the bay real quick and have options to choose from regarding what was still an unused module. But, I dropped the module number to 2 because I just now realized I could set an action group to log one group's data over one biome/situation, and a second action group to log the other group's data over a biome/situation, which saves me valuable time in trying to collect as much as possible. So I could probably pull off an "upper atmosphere" grab which allows me to drop it down to 2 in hopes that I can collect two different biomes while "in flight" above them.

Makes sense. I generally don't bother with that on Duna, since its "in flight" altitude is very low, and the atmosphere is so thin that by the time I get down to "flying" altitude instead of "upper atmosphere", I'm generally descending at a fairly steep angle (unless I'm landing a spaceplane).

This means that the horizontal distance traveled while "flying" is quite short, so it's pretty rare for me to touch two biomes via "flying" on one landing.

Going EVA to recover science from instruments is quite easy in "upper atmosphere", as long as you're holding on to a ladder the whole time (want to be careful about letting go and flying, since your kerbal is much draggier than the ship and you can get swept away easily). It's especially easy if the instruments are mounted just outside the command pod door, so the kerbal can hop out, grab science, and hop back in again in just a couple of seconds.

My usual pattern for science recovery (to minimize the number of copies of instruments I need to carry):

1. Gather everything in space, before entering atmosphere to land the ship.

2. In upper atmosphere, hop out briefly to grab the science.

3. Acquire science while "flying", but don't try to recover from the instruments.

4. Land. Recover the "flying" science. Do "landed" measurements and retrieve those.

5. If by some chance I did cross biome boundaries while "flying", I got at most two. One of them I got during the descent, and retrieved the science from the instruments after landing. The other I can acquire during ascent, and retrieve from the instruments after achieving orbit.

That pattern only requires one of each instrument (though in practice I generally have two goo canisters, to balance the mass).

Edited October 30, 2015 by Snark

[mabarry3]

So, is drogue vs. airbrakes mostly a personal preference where you choose one to get you below chute deployment speed but there's no point in packing both drogue and airbrakes?

As far as science goes... I guess I like having a little wiggle-room right now in case I mess something up. Extra dV, extra science modules for if I miss something or can't make it down to recover, etc. I may (most likely) change that once I get into a better pattern (since this would be my first attempt at actually recovering a significant amount of things and all that), but for this first attempt I'll try to keep it down to a set of two just so if I mess up and don't capture everything I need to, I have a second set that can do the job. Your pattern seems to be better than mine and makes more sense though for sure.

Also Snark, it appears you had a bit of a code malfunction at the end of your last message, you may want to double check the end there.

[mabarry3]

And my ships are on their way to Duna!

I decided to send a second one behind it for safety and bonus science reasons, creatively called the "Floating Fuel Tank", which should get to low Duna orbit with something around 2500-3000 units of liquid fuel left, meaning I should have enough fuel available to add to the lander to visit a few different biomes and possibly even Ike, or I may go straight from Duna to Ike and ignore other biomes for now, trying to sneak some more science in where there's no atmosphere and lower gravity.

Do you guys know where screenshots from the F1 function are stored? I can do shift + Prt Sc but that causes my engines to fire, making it annoying because I have to F5, screenshot, F9 to not mess anything up

I'll let you guys know how it's going

Thanks (massively) for all the help! First interplanetary launch, check... now I just need to not get myself blown up!

Edited October 28, 2015 by mabarry3

[technion]

Do you guys know where screenshots from the F1 function are stored? I can do shift + Prt Sc but that causes my engines to fire, making it annoying because I have to F5, screenshot, F9 to not mess anything up

Check C:\Program Files (x86)\Steam\steamapps\common\Kerbal Space Program\Screenshots.

[The Optimist]

your rocket is too damn big

[mabarry3]

your rocket is too damn big

I never said I didn't overbuild.

[Snark]

So, is drogue vs. airbrakes mostly a personal preference where you choose one to get you below chute deployment speed but there's no point in packing both drogue and airbrakes?

They're not quite the same. Compared with drogues, airbrakes can be used at much higher speeds, but are less effective at slowing you down a lot in the under-500m/s range.

For example, you can use airbrakes as a reentry aid; depending on circumstances, they can even be an alternative to using a heatshield.

Drogues are pretty specialized. The only thing they're good for is getting you from 500 m/s down to 250 m/s. Faster than 500, you can't deploy them. Slower than 250, you don't need them because regular chutes work much better. But within that range, they work really well; much better, kilogram for kilogram, than airbrakes.

On Kerbin, this rarely comes up. Lots of craft have a terminal velocity under 250 m/s and get along just fine with regular chutes and nothing else. And for craft that do fall faster than 250, it's usually not much more, and airbrakes are good enough to get the speed down to 250 before you go splat.

However, there's one place where drogues become useful, and that's Duna. The air is thin enough that you can easily be going around 500 m/s when you get low, and you likely don't have much time to slow down. Airbrakes may have trouble keeping up with that, particularly if the craft is a bit massy. Drogues can come in really handy there.

- - - Updated - - -

And my ships are on their way to Duna!

...

Do you guys know where screenshots from the F1 function are stored? I can do shift + Prt Sc but that causes my engines to fire, making it annoying because I have to F5, screenshot, F9 to not mess anything up

I'll let you guys know how it's going:)

Congratulations! Bon voyage.

Screenshots are where technion said. FYI, in case you don't already know, you can hit F2 to toggle all of the UI on/off, which can be useful for removing clutter when taking a screenshot.