Accidental Duna Colony

[Ehco Corrallo]

So...

I think you all know the premise: "It wasn't supposed to be a colony."

Well, in my desperation to land something on Duna, I sent a one way mission, and landed it on the surface. I feel obligated to get my crew of the surface because I've already killed three similar crews in botched capture burns (I failed to capture around Duna because I designed a terrible ship, and the kerbonauts were flung into frigid, interplanetary space). Considering I managed to save Jeb, Bill, and Bob from a horribly protracted death, and I actually have a chance to bring them home, I figure I should send a rescue party. 

I barely managed to get a one way mission down to the surface however, and though I designed a perfectly functional interplanetary shuttle for transport, I'm still not sure how to manage the landing. 

Here's where things stand: 

I'm playing in stock sandbox mode. I know how to fly interplanetary missions and build launch vehicles. Landers are not my forte. 

Three kerbals are stranded in a Mk 1-2 Command Pod. They're landed well below the equator. That's the entirety of my assets on the Dunatian surface. 

The biggest issue I've found in ship design is crew capacity. I haven't been having trouble building something simultaneously light enough to reach Duna and big enough to carry three crew and a pilot for the trip out. 

Any advice as to procedure, Duna landings, and actual plausibility would be greatly appreciated (and I don't use the word appreciated lightly, least of all in bold font).

I've been thinking of getting a rover down to the surface to help with transport in case the landing sites of the postulated rescue ship and the stranded lander are too far apart. Is this a necessary step?

Are wings a good way of landing a ship on Duna? They didn't seem to help my shuttle (I sent a shuttle mission, but after numerous failed landings and quickloads, I abandoned the mission, and flew back to Kerbin. The shuttle is now stuck in retrograde orbit around Kerbin).  

TL;DR: The original three are trapped on the surface of Duna with no provisions for return. How do I bring them home?

[juanml82]

Winged craft, IMHO, aren't a good idea in Duna - you can't maneuver well because the air is thin, horizontal landings tend to end up in wings getting torn (you can't easily brake and the terrain is mostly rolling).

I'd say:

Forget light. Use larger, probably Aspargused, boosters to put your ship in LKO. You may want to use a nuclear tug for the interplanetary legs of the journey.

You may be able to aerocapture at Duna, but don't count on it, bring 1,000 dv to capture by firing your engines

Use a heavier lander with aerospikes. It can either be a skycrane for your rover, or the lander itself can double as a rover. Use drogue chutes to help slow down, but keep in mind regular chutes are unlikely to deploy in time, so you'll need to make a powered landing

Consider using ISRU, either by having a mining rig in your (even heavier) lander or by landing a mining/tanker ship in Ike. You can do without it, but it maybe a good idea.

[Ehco Corrallo]

Thank you so much. This was exactly what I was looking for. 

[Snark]

Be aware of mass.  The Mk1-2 command pod is terrible.  It's crazy stupid heavy.  4 tons for 3 kerbals is ridiculous.  For comparison, a Mk1 command pod with a Mk1 crew cabin is less than half the mass (not to mention a more streamlined profile), therefore a lot easier to to get back to orbit from Duna.

For example:  Mk1 command pod, Mk1 crew cabin under that, small fuel tank with Terrier under that.  Some radial asparagused tanks around it, both for the extra dV and to widen your stance so that you don't topple over.  Enough Terriers on the radial tanks to give you a reasonable Duna TWR.  (Duna's atmosphere is thin enough that Terriers give pretty reasonable performance even on the surface.)

For Duna landers:  Landing with wings is a challenge.  I've done it, it's not for the faint of heart, probably easier to go with a conventional lander.

Make sure you have some drogue chutes on the lander (don't need many, just a couple will do)-- it can be hard to slow down to safe deploy speeds for regular chutes on Duna.

Don't overburden your lander with parachutes.  Duna's atmosphere is thin enough that if you try to pack on enough chutes to slow it to a safe landing speed, you'll be wasting way too much mass on chutes.  Rather, just give your lander a relatively small handful of chutes, enough to slow it down to something sane like 20 or 30 m/s.  Then use a brief blip of retro-thrust to slow down right before impact.  It only needs a smidgeon of fuel to slow you by 20 m/s, and the amount of fuel you use will be more than paid for by the savings in parachute mass.  Suggestion:  Attach your chutes to the first stage you'll be jettisoning on ascent, so that you don't waste too much fuel lugging them all the way back to orbit.

If your design/piloting skills are such that getting a lander to Duna surface is marginal, then it may be worth considering not to try to build a Duna rescue lander that will take the crew all the way back to Kerbin-- it's good enough just to get them to Duna orbit.  Then you could have a second craft that's just an orbiter, for the trip home.  Rendezvous in orbit.

 

[KerikBalm]

You don't need to carry something "big enough to carry three crew and a pilot for the trip out".

Stick a probe core on there, and only have crew space for 3... this can be done for less than 2 tons... as in my Eve ascent vehicle (last stage here):

You haven't specified the elevation that your crew is at... but I do like winged vehicles.

This is my winged Duna lander:

The wings are to guide it to its landing site, not to perform a horizontal landing. It glides well enough (I'm landing in the lowlands below 1km) to be on a flight path pretty much right over my surface base... at which point I pop the drogue chutes, and then shortly thereafter, the main chutes, and use the engine to land(and launch) vertically.

Its on the right there... the thing with the 2 gigantors in the middle is my surface habitat/lab (the plane in the center uses modded parts to fly using only electric charge... the far left is an ISRU miner&tanker... there's no ore in my game there, so it needs to take suborbital hops to go get more fuel)

Edited December 10, 2015 by KerikBalm

[Ehco Corrallo]

I have to say thank you again. I didn't expect to get so this much feedback, and I'm incredibly grateful that you took time out of your lives to remedy a badly planned mission. 

I agree, the Mk 1-2 Command Pod is awful. I'm planning on using a Mk 1 Pod/Mk1 Crew Cabin combo to get them back, and I'll probably have a ship in orbit to rendezvous with. Is the hitchhiker pod mass efficient enough to bother with for three kerbals, or would the Mk1 Combo be better? I'll ditch the wing idea, but I'll probably throw on some canards or something. 

I think my mistake with previous rescue attempts is that I approached Duna as though it were Kerbin or Eve: enter atmosphere, pop chutes, wait.  

I might look into dropships as well. Having a more mobile lander or one capable of deploying a rover would be really helpful.

I'm also thinking of using airbrakes in lieu of extra drogues.

 

Edited December 10, 2015 by Ehco Corrallo
Forgot about airbrakes.

[KerikBalm]

Well the hitchhiker used to be pretty mass efficient... but now the Mk2 crew cabin beats it... and the mk1 crew cabin is darn good too.

That Duna lander of mine is over built - I wanted it to be able to undock from an equatorial orbit, land at the poles, and then redock with the station orbiting in an equatorial orbit.... it could almost go to orbit, de orbit, and then go to orbit again on one load of fuel... although the slower and more efficient way is to raise apoapsis and do a plane change at apoapsis... or using Ike to do it. - and the lander uses the unneccessarily heavy mk1-2 command pod... I did it for "looks"/"style", and because with my experience... its not so hard to get stuff to duna that I can afford to be purposefully inefficient

For an eve lander though... that is still challenging and I try to optimize as much as possible without getting exploity. I didn't want to overbuild things and waste mass on more "stylish" accomodations... the pod (on duna you could get away with a lander can)+mk1 crew cabin is about the most mass efficient transport for 3 kerbals... I didn't use the lander can for eve because its draggier and less heat tolerant... and heat tolerance matters even during eve ascent.

The other thing about wings... one of the problems with duna's thin atmosphere is that unless you come in very shallow, you don't slow down in time ot use your chutes/your chutes don't do enough... Wings are always deployed, and coming in with a 30 degree AoA with wings is a good way to make sure you have plenty of time to deploy chutes. Airbrakes could probably work too... I'm not sure which is more mass efficient (although winged vehicles as a payload are a pain to launch... airbrakes don't cause that problem)... they have a low heat tolerance, but that shouldn't be much of an issue on duna. But even just small canards/small delta wings should be enough to help control reentry trajectory, and to give you a better margin for chute deployment - as I said... that duna lander I posted was over built... part of it was that I just wanted a really wide base so that it wouldn't tip over. The wings were more mass efficient (and less draggy) than using girder or I-beam segments... once I had my X of wings to put landing struts on for a wide base... it was just 1 more set of wings and some control surfaces to make it a functional glider.

I have also done plenty of duna landers without aerudynamic control surfaces/wings... they aren't needed, but they can be convenient if their mass penalty isn't causing you a problem, or messing up the aerodynamics when you try to launch it.

Edited December 10, 2015 by KerikBalm

[Snark]

2 hours ago, Ehco Corrallo said:

I agree, the Mk 1-2 Command Pod is awful. I'm planning on using a Mk 1 Pod/Mk1 Crew Cabin combo to get them back, and I'll probably have a ship in orbit to rendezvous with. Is the hitchhiker pod mass efficient enough to bother with for three kerbals, or would the Mk1 Combo be better?

...

I'm also thinking of using airbrakes in lieu of extra drogues.

The hitchhiker is 2.5 tons; a Mk1 command pod plus Mk1 crew cabin is 1.8 tons.  700 kg is nothing to sneeze at, plus there's the form factor to consider (1.25m versus 2.5m).  I'd lean towards the skinny option.  Hitchhiker can still be useful, but mainly for big ships / stations where you have a 2.5m stack anyway, and the mass of the hitchhiker is small compared to the overall ship mass.

Airbrakes have their place; for one thing you can use them at very high speeds, whereas drogues top out at around 500 m/s.  However, in that crucial range between 500 m/s (where you can use drogues) down to 250 m/s (where you can use regular chutes), drogues are considerably more effective.  They're also a lot easier to design around than airbrakes are (not so bulky, you can slap 'em on pretty much anywhere).

Personally, I'd go with drogues for Duna, but by all means try out the airbrakes if you prefer. 

Another suggestion:  use body lift as much as you can, that will help you slow down until you get to parachute speed.  In other words, as soon as you've slowed down enough that you don't have to worry about getting fried, rotate your craft so that instead of pointing perfectly retrograde, it's tipped at about a 30 degree angle so that the incoming air is deflected downward, generating lift.  (You don't have to have wings for this-- just the side of a cylindrical rocket can generate a surprising amount of lift.)  This will help keep you from losing altitude too quickly while you're aerobraking, so that you have a longer opportunity to bleed off speed.  (Here's where some stubby wings could actually help-- they generate lift, unlike airbrakes.)

[Ehco Corrallo]

I was think of using airbrakes to slow down enough to deploy the drogues. I could use few parachutes because of the brakes (I'll check the mass difference between drogues and airbrakes) and actually slow down while in high atmosphere at high speed. The last few landers I've tested weren't able to slow down soon for parachutes to be 100% efficient. If I use airbrakes I can slow down earlier, deploy the drogue earlier, and make the most of the drag. It's actually a good thing that airbrakes aren't always on, at least in this case it might be: I can use them to get a better degree of control on entry. 

Who knows, maybe this is just a huge rationalization and I just want to use them. I feel guilty that I haven't used the airbrakes a whole lot, even though they're one of my favorite parts.

I had a revelation about the crew compartment. I'm pretty sure I can use a Service Bay and rotate three EAS-1 seats inside of it, and send my crew into space Martian-style. The Service Bay has a nice flat profile, ideal for generating large amounts of drag and landing on hills. My two biggest enemies in landing on Duna have been, incidentally, a lack of drag, and hills. 

I'm figuring I'll launch the lander inside of the cargo bay of a nuclear mothership and decouple it from the mothership when I reach Duna so I can land and pick up the crew. After that, I'll rendezvous the lander with the mothership and head home. I don't think I'll try landing the main ship; I'll send up a ship to bring the crew down from LKO. I don't have to bother about heat shields and radiators that way. 

As always, thank you for taking the time to hash this out. 

[Ehco Corrallo]

Well, a bugged out "resume saved" button just remedied the problem. I was forced to delete the troublesome save. Jeb, Bill, Bob, the lander, and my problem are completely gone. Forever (a long time).  

You're invaluable advice however, is immortal. In honor of my poor, poor savegame I'm going to go to Duna again, but correctly this time. 

Thanks for the support!

Ehco

 

[Snark]

19 hours ago, Ehco Corrallo said:

I was think of using airbrakes to slow down enough to deploy the drogues. I could use few parachutes because of the brakes (I'll check the mass difference between drogues and airbrakes) and actually slow down while in high atmosphere at high speed. The last few landers I've tested weren't able to slow down soon for parachutes to be 100% efficient. If I use airbrakes I can slow down earlier, deploy the drogue earlier, and make the most of the drag. It's actually a good thing that airbrakes aren't always on, at least in this case it might be: I can use them to get a better degree of control on entry. 

Who knows, maybe this is just a huge rationalization and I just want to use them. I feel guilty that I haven't used the airbrakes a whole lot, even though they're one of my favorite parts.

I had a revelation about the crew compartment. I'm pretty sure I can use a Service Bay and rotate three EAS-1 seats inside of it, and send my crew into space Martian-style. The Service Bay has a nice flat profile, ideal for generating large amounts of drag and landing on hills. My two biggest enemies in landing on Duna have been, incidentally, a lack of drag, and hills. 

A few observations:

• As long as you make good use of body lift and don't set your approach angle too steeply, you should have no problem slowing down to drogue speeds; you really don't need airbrakes for that.  By all means use 'em if you want, I just think you don't need them.
• Airbrakes are indeed cool, and the fact that you can turn them on/off is a major attraction.  I like using them myself, I just don't use them on Duna because I find that drogues are both necessary and sufficient.
• If you do use a service bay with command chairs:  be very, very careful if you do that.  Service bays can behave oddly (e.g. shake your ship to pieces) if anything clips them from the inside.  Make sure none of your command chairs (or the kerbals sitting in them) come close to touching any of the interior surfaces of the service bay.  Also, I'm not sure how much protection the kerbals will get from overheating-- I think things in a service bay heat up to the same temperature as the bay itself, and spacesuited kerbals have a pretty low temperature tolerance these days.  I'm not flat-out saying it won't work, just be aware that it's a potential issue, and you may want to try doing a sandbox test run first to make sure they'll be okay.

Duna is indeed hilly.  I find that it's not too much of a problem for "traditional" landers that come down vertically on parachutes-- just make sure the lander is low and squat so it doesn't tip.  Where the Duna hills become a royal pain in the fundament is if you're trying to land a plane.  Finding somewhere flat enough to land is a real chore.

[Ehco Corrallo]

I've ran a test with Hyperedit, and the airbrakes worked really well. They helped keep the lander stable too. The only glitch was when the lander tipped over. It landed fine otherwise.

I'm thinking of bringing a Mk16 chute for the very final decent. It'll make things that much more fuel efficient. 

10 minutes ago, Snark said:

you may want to try doing a sandbox test run first to make sure they'll be okay.

I'm playing in sandbox. I'm just not very good at designs. You've helped me immensely. I might actually manage a proper Duna mission now.  

Edited December 11, 2015 by Ehco Corrallo
Amplified gratitude.