Duna Landing Help

[Weegee]

Currently in my world I have explored the Mun and Minmus. I kinda got bored, so I thought it would be cool to send a group of unmanned probes and rovers to Duna (and I even have a transfer window coming up! Yay!).

My current plan is to send 2 probes into orbit around Duna (One polar, one equatorial), land a rover at one or both poles, and one on normal terrain. And if I can figure out the logistics, I might send a probe and rover to Ike.

I'm fairly sure that I can manage getting everything there (probably in a huge stack sent up at once, I'm bad at docking) but I'm not sure how to go about the rovers. I have a design, but I have no idea how to get it down to the surface without damage. Any help figuring this out or pointing me to a good tutorial would be much appreciated.

Edited September 1, 2013 by Weegee

[lumpman2]

If you could put a picture of your rocket, that would help

But I think you could go for two rovers rather than one - it would be easier since you can balance it out. If the rovers are small, it's pretty likely that you could just stick a small mk16 chute directly on the top (use a separator for decouple from the bottom).

[Geschosskopf]

...I'm not sure how to go about the rovers. I have a design, but I have no idea how to get it down to the surface without damage. Any help figuring this out or pointing me to a good tutorial would be much appreciated.

Well, Duna has an atmosphere so you can use parachutes. Those can be used to at least make sure the rover lands rightside up. If the rover is light enough, you can even put enough parachutes on it to float down gently like on Kerbin.

To determine the number of parachutes you need, check out this great site with a KSP parachute calculator:

http://ksp.freeiz.com/

But the air is thin so to get the most use out of your parachutes, you need to come in low and flat. The atmosphere goes to about 41km so I like to start at 50km and do the deorbit burn to hit the ground about 1/4 to 1/3 of the way around the planet from where I am now. You can try deploying the chutes at 20km but they probably won't start to streamer until about 13-15km. Then you'll appear to go a very long way at what looks like a very low altitude going nearly parallel with the ground, gradually slowing down (you can help this firing retro rockets). And you should REALLY use rockets if you're still screaming along horizontally when you start seeing rocks on the ground, which tells you it's a good idea to decrease your horizontal velocity . After this, it's pretty much like anywhere else.

[SRV Ron]

Well, Duna has an atmosphere so you can use parachutes. Those can be used to at least make sure the rover lands rightside up. If the rover is light enough, you can even put enough parachutes on it to float down gently like on Kerbin.

To determine the number of parachutes you need, check out this great site with a KSP parachute calculator:

http://ksp.freeiz.com/

But the air is thin so to get the most use out of your parachutes, you need to come in low and flat. The atmosphere goes to about 41km so I like to start at 50km and do the deorbit burn to hit the ground about 1/4 to 1/3 of the way around the planet from where I am now. You can try deploying the chutes at 20km but they probably won't start to streamer until about 13-15km. Then you'll appear to go a very long way at what looks like a very low altitude going nearly parallel with the ground, gradually slowing down (you can help this firing retro rockets). And you should REALLY use rockets if you're still screaming along horizontally when you start seeing rocks on the ground, which tells you it's a good idea to decrease your horizontal velocity . After this, it's pretty much like anywhere else.

You do need to use retro to kill a lot of horizontal speed so the mains will open at 500 meters and a short burst to reduce vertical to under 4 m/sec. This experimental lander used three large capsule parachutes which slowed the descent to 11.5 m/sec.. Not quite enough for a safe landing.

I have safely set down 2 ton probes with a pair of radial parachutes with a burst from thrusters to reduce descent speed at the last second.

[Geschosskopf]

Here's a 15-to-18-ton lander on final approach using the low, flat landing profile described above. It has 2 drogues, 2 of the bluetip big round chutes and 8 radials. Per the calculator linked above, \tThis was enough for landing at 0m but the landing site ended up being 2500m, which made the parachutes much less effective. Still, they helped a lot.

As you can see from the smoke, the engines are burning hard because I'm trying to land in the lower spot ahead where it looks a little flatter, instead of on the hillside beyond.

I actually ended up about 2/3 of the way that hillside but fortunately on a relatively flat shoulder of it. Once the chutes fully opened, the thing floated down at like 15m/s so still needed a little thrust to make it a safe landing. But if I'd had more parachutes, I wouldn't have needed to use the engines so much. But this thing makes its own fuel and landed on Kethane so no big deal there .

Lesson learned: almost all of Duna is at least 2000-3000m high, so plan your parachutes accordingly. And expect to land on a fair amount of slope so be sure your landing gear can handle it.

But anyway, Duna landings aren't so hard as they are disconcerting. If you've never done one before, you'll be a bit anxious from the unfamiliar long time spent going fast, flat, and fairly low. But just roll with it, burn as you think necessary to kill horizontal speed, and let your parachutes do what they can. Once the chutes fully open, it's just like anywhere else. Either you've got enough chutes that you can let it float, or you just have to give it a little help with thrust, like with landing on a very low-gravity world.

Edited September 1, 2013 by Geschosskopf

[Weegee]

Very good advice. Knowing me I'll somehow screw it up, but that's the fun in the game, isn't it?

Thank you all for helping.

[Moar Boosters]

Duna is quite hard to land on due to the thin nature of it's atmosphere. There's a reason we've lost so many probes and landers in real life!

You go really fast at really low altitutes. The atmosphere above 10,000m does very little to slow your speed, and most of the terrrain is around 3-4k in height so it leaves you with a very margin for error. Landing site is important too. There are some deep valleys which have lower altitude but are quite hard to aim for, but there are also the giant dark bits which are lower altitude. I'm not sure if they're supposed to be dry seas or giant impact craters, but whatever the are they're the easiest place to land.

An alternative to Geschosskopf's technique is to pretty much treat it like a Mun landing but with a few chutes to help on your vertical decent. Do your deorbit burn, kill a lot of your horizontal speed and then open the chutes to decent vertically doing another little burn to break just before you hit the ground. Geschosskopf's technique is much more efficient, but harder to pull off and will probably result in a few "high speed" landings before you get it right. I'm currently trying to land my spaceplane there, so I know all about high speed landings.

[Geschosskopf]

I'm currently trying to land my spaceplane there, so I know all about high speed landings.

Oh geez, I feel your pain . I had a nice kethane jet that few great on Duna, but this was more due to thrust than lift. It could drop down from orbit, catch enough air to function, and then fly around anywhere it wanted to just fine, but COULD NOT LAND SAFELY. The slowest it could go forward while still keeping the vertical velocity below -10m/s was 80m/s. Given that most of Duna is quite hilly, the gravity is so low that wheel brakes don't do much good (especially with lift fighting traction), and the air is so thin that airbrakes don't do much, either, this was a recipe for disaster. I tried parachutes but it was too heavy to float down and putting a drag chute on the tail tended to make it lawndart. So I gave up on that and made an ultra-slow, ultra-high-lift STOL biplane, which I could touch down at 30m/s. It still rolls (mostly bounces) about 500m before it stops but it's slow enough and tough enough not to break doing it. But this caused major problems getting it off the ground at Kerbin. Flying Duna is a bitch .

But anyway, back to landers, your more vertical approach is also quite doable. You have to kill off the same amount of velocity either way so the question is how you share the workload between engines and parachutes, which is more a function of how big your ship is and what you want to do with it after you land. The more parachutes you have, the less fuel you burn on descent, which means the more you have to get back into orbit with, if that's the plan. This favors the low, flat approach. OTOH, if you're just dropping a probe rover, you don't need to save fuel for ascent so parachutes aren't as important and you can come in steeper.

Besides, parachutes are heavy and you need lots of them to do much good on Duna, so you pretty soon start running into diminishing returns. Just from playing with the parachute calculator, it looks like about 20 tons is the practical upper limit for a returnable lander that can get any real fuel savings from parachutes. Beyond that, you're going to be doing most of your braking with the engines anyway.

[Moar Boosters]

Here is the publicity shot for my DunaVentura single stage aircraft.

Unfortunately it doesn't show the truth behind my landing. There's supposed to be an engine there and quite a lot more wing.

The first touchdown was perfect, unfortunately I was catapulted back into the air and then came down on my tail. This was just a prototype which wasn't even supposed to leave LKO so I'm hopeful a further modified version will be able to nail the landing. It's got enough lift to fly on Duna, but I'm trying to do a single stage return craft..... so it doesn't really have the delta V budget to do any powered flying on the descent to Duna, it needs to save everything for the journey home.

Edited September 1, 2013 by Moar Boosters