Slowing down on Duna?

[Frozen_Heart]

Hey.

I'm trying a Duna landing and return but my first attempt has ended with the crew stranded due to the parachute ripping off the capsule.

Is the atmosphere on Duna thick enough to use parachutes to slow or should I treat it like a Mun landing instead?

Edited August 12, 2014 by Frozen_Heart

[mike9606]

Hey.

I'm trying a Duna landing and return but my first attempt has ended with the crew stranded due to the parachute ripping off the capsule.

Is the atmosphere on Duna thick enough to use parachutes to slow or should I treat it like a Mun landing instead?

The parachutes could help a little bit, but you will need engines to land. Your not gojng to be able to land on parachutes alone due to Duna's atmosphere being extremely thin.

[Wanderfound]

Parachutes work on Duna, but the atmosphere is low and thin, so you need more of them and they'll deploy frighteningly late.

Slow down as much as you can before deployment (circularise a low orbit before descent, and come in at a very shallow angle to aerobrake on the way down), adjust the tweakables of your chutes to get them open as early as possible, use drogues before the main chute and be prepared to use a bit of thrust at the last moment before touchdown. And reinforce whatever you've attached the parachutes to: moar struts.

[Pecan]

Open the parachutes high so they have a bit more time to slow you down. A lot depends on your lander, of course - this is somewhat over-engineered, but reliable and reusable:

[Specialist290]

First, welcome to the forums!

Duna's atmosphere is quite thin compared to that of Kerbin's; as you can see here, it's as thin at "sea level" as Kerbin's atmosphere is around ~8km up. Parachutes certainly aren't useless as the extra drag will help slow down your craft to a more manageable speed, but you'll need a lot more of them to get the same effect as you would on Kerbin.

Typically, I tend to opt for a mix of standard and drogue 'chutes for Duna landings; drogues don't slow you down as much when they fully open, but they do so slightly higher than the main 'chutes do and help to smooth things out so that your mains don't tear off the craft due to the sudden deceleration. On top of that, for that last little stretch right before you touch down, I'd fire up my engines just enough to ensure you have a safe and soft landing; again, as Duna's atmosphere is rather thin, you'll probably be falling a bit faster on Duna than you would on Kerbin even with fully open 'chutes unless you brought a lot of them, which adds extra weight you don't strictly need.

[Frozen_Heart]

The parachutes could help a little bit, but you will need engines to land. Your not gojng to be able to land on parachutes alone due to Duna's atmosphere being extremely thin.

I'm struggling to get enough fuel in the rocket no matter how big I make it to even orbit and return. How can I get more range out of it if I have to burn all the way down?

[Xavven]

I encountered a lot of parachute shock issues as well on Duna and resolved it by setting my periapsis at around 10,000m instead, as opposed to intersecting the ground as I do on airless bodies like Mun. Duna's atmosphere is too thin to slow you down enough to the point that the chutes won't rip parts off your lander when it opens fully, yet ironically thick enough to rip parts off during said chute opening.

A 10,000m periapsis lets your lander skim the atmosphere, slowing with your chutes in semi-open (drogue) mode. By the time the craft descends below 10,000m automatically due to loss of orbital velocity, you will also be slow enough that the chute shock won't damage your lander. Chutes are definitely worth it to use, though. They will save you a lot of delta-v as well as orient your craft into landing position automatically, assuming you placed them ABOVE your center of mass (remember to account for fuel usage shifting your CoM).

[Xavven]

I'm struggling to get enough fuel in the rocket no matter how big I make it to even orbit and return. How can I get more range out of it if I have to burn all the way down?

Don't burn on the whole way down. Let the chutes do 95% of the work. When you're about 100m from touchdown, you'll probably still be going too fast, on the order of 15-30 m/s depending on your chute mass. You'll just barely throttle up enough to slow to 5 m/s for the touchdown. It barely uses any fuel at all that way

[Pecan]

I'm struggling to get enough fuel in the rocket no matter how big I make it to even orbit and return. How can I get more range out of it if I have to burn all the way down?

Apart from the parachutes that lander in my post above has a Duna TWR of 3.87 and 2,895m/s vacuum deltaV. Technically, it has 200-odd m/s more than needed to burn all the way down and back up again, but I've never had to because the parachutes cut the requirement so much anyway.

[Master Tao]

Something no one else has mentioned: set your parachutes to deploy at slightly different altitudes when you tweak them to open higher. So if you have four parachutes, you might set them to deploy at 1200m, 1100m, 1000m, and 900m.

[Laie]

Something no one else has mentioned: set your parachutes to deploy at slightly different altitudes when you tweak them to open higher. So if you have four parachutes, you might set them to deploy at 1200m, 1100m, 1000m, and 900m.

THIS.

However, it's not a panacea -- depending on craft and circumstances, it may not be enough. In my experience, drogue chutes work where even the most tricked-out staggering schemes fail. I don't need them often, but boy am I glad that they exist.

[Xavven]

THIS.

... In my experience, drogue chutes work where even the most tricked-out staggering schemes fail. I don't need them often, but boy am I glad that they exist.

Agreed. You can even ditch the regular chutes and just use 1 or 2 drogues. They have lower drag in their fully open state and thus are less likely to damage your craft, and they'll go semi-open at lower pressures (higher altitudes). You're going to have to use your rockets at the last 100m to slow down to landing speed either way. I found these work very well for Duna.

[Eric S]

It is possible to land on Duna parachute only, but I don't recommend it as you'll need the equivalent of a pre-0.24 radial parachute per ton of craft, and you'll probably need less mass total if you take a little more fuel and quite a bit less mass in parachutes assuming you don't fire up the engine until the parachutes are fully deployed (ideally, you want to do a suicide burn).

As has been pointed out, you want your periapsis to be as high as possible without leaving the atmosphere again (even that may be acceptable) as doing so will maximize the amount of time the atmosphere has to slow you down.

Also, (and the above advice may make this more difficult), you want to make sure that you're landing in an area where the surface elevation is low so that you have more time with your parachutes fully deployed.

[Laie]

drogues [...] have lower drag in their fully open state

In KSP physics, any "drag" value is multiplied by mass. So the 200kg/170drag drogues have twice as much drag as the 100kg/170drag Mk16 (the small one that fits a one-man pod). Likewise, two radial chutes have as much drag as a single Mk16-XL, and for the same reason.

However, when you need a drogue, you should pick the genuine article -- they work better at the task than any other. I guess that is because their semi-deployed drag is higher than the others (but then again, just from looking at the changes in airspeed, it doesn't seem to make much of a difference either way). So I can't tell you why they work, but I assure you that they do.

Spreading the word: http://forum.kerbalspaceprogram.com/threads/31405-Parachute-guidelines

[Rhomphaia]

In KSP physics, any "drag" value is multiplied by mass. So the 200kg/170drag drogues have twice as much drag as the 100kg/170drag Mk16 (the small one that fits a one-man pod). Likewise, two radial chutes have as much drag as a single Mk16-XL, and for the same reason.

Mk16 is 500 drag, just like the MK16-XL and Mk2-R So a drogue still has less drag when you take mass into account.

[Frozen_Heart]

Thanks for all the replies guys. Going to have another attempt at it and see how things go.

[moogoob]

Was looking for a thread like this. Good tips. My second time attempting Duna. Came in shallow correctly, did a bit of chute staggering too. Brought like twelve of the radial chutes for a 2-kerbal lander; it was comical looking. Good to know that I should just save the weight next time.

[SRV Ron]

In addition to coming in at as shallow an angle as possible, try to land in a valley where the atmosphere is a bit thicker. You will still need to use engines to reduce descent speed to a safe level at the last 100 meters

[EdFred]

I never land under power on Duna. Drogue chutes and radial chutes slow my craft down enough that I'm under 12m/s on touchdown. Oh, and use the beefed up landing legs. I also have the radials open at 1000m and 1500m instead of 500m