Duna, Parachutes and You

[DChurchill]

My only successful mission to Duna is a very small landed probe which consisted of a Probodobodyne OKTO, an OSCAR-B fuel tank with 4 Rockomax 24-77 radial engines, 4 Micro Struts, a PB-NUK RTG, and two Mk-2-R parachutes. Turns out the engines were pretty much useless, and the chutes were enough to set it down at around .8 tons.

I'm planning a small rover mission, a la Spirit/Opportunity, with a small lander that I can detach the rover from. My question is: how do parachutes perform with heavier payloads on Duna? Do I need to plan for descent engines?

I figured I'd get some advice first. Duna is pretty far for trial and error.

[7499275]

Duna's atmosphere is thinner then Kerbin's so depending on the payload I would have engines to slow down near touch down but chutes for the main part of the decent

[Jacob01]

I managed to do it fine with just parachutes, although I think it might depend on where you land due to height differences. Thing is, on Duna, even when the parachutes are fully opens, it take a while to get the speed down enough to land safely. If you are using a similar Skycrane to what is on the stock rover, just put a small parachute on top, and use the engines if needed.

[regex]

I successfully landed a ~16-ton craft on Duna twice using only four of the radial parachutes for braking. It bounced on its legs and landed sideways though, so you'll still need controls, but parachutes are great for braking.

[Dedjal]

6 parachutes will not stop your 50 ton research rover from becoming a scrapyard. Not even with itsybitsy thrusters on full throttle. Or maybe they will... I just know that the ground showed up way earlier than expected. Note to self, Deploy 'chutes at 20k meters.

[firerider521]

Here, take this!

http://forum.kerbalspaceprogram.com/showthread.php/31405-Parachute-guidlines

Credit to ThePseudoMonkey for originally posting this. It's very useful.

[Pulstar]

It really depends on the altitude you will be landing at and how heavy the landing craft is. Surface pressure on Duna is about 10 times lower at "sea level" (0m) than on Kerbin, this means far less drag and thus parachutes are less effective. However the gravity is about four times lower which lessens the negative effect of the thin Duna atmosphere on parachutes. In general though aim for the low lands since they have the highest pressure and thus parachutes are more effective there, the darker areas of the surface (marias probably, but what do I know of dunar geology) are the lowest ones. You also want to be coming in at a shallow angle so that the parachutes have enough time to slow you down as much as they can (also so that the forces when they deploy don't tear the lander apart, although strutting the parachutes to the rest of the craft helps with that).

Either way in my experience, even with heavy landers, you can slow down the craft to about 30 m/s at least just using the parachutes. Usually it's just below 20 m/s for me, sometimes less. Few manage to slow down below 10 m/s although I did see it happen. Overall landing with just parachutes is doable for lighter and more sturdy craft (landing legs tend to break anywhere between 5 to 10 m/s landing speed depending on the leg type) but there are diminishing returns to adding more parachutes. The simpler solution to just adding enough parachutes for that to work is to just add a descent engine for the last 500>meters to assist them in slowing down the lander.

You want fairly high thrust (for Duna, which is anywhere between 0.5 to 1.0 Kerbin TWR IMO) and just enough fuel for about 5 seconds of burning. That may not seem like much but the truth is the parachutes will kill all horizontal velocity, so you'll be falling straight down thus steering is not an issue, and you can focus just on pressing shift and ctrl while watching your velocity and nothing else. Just remember that it's called a suicide burn for a reason, so wait until you are close enough to the ground or the tanks will go dry before you are safely on the surface. That's why you need good thrust, to decelerate fast as close to the ground as possible and thus save on the needed fuel (since the parachutes did most the work). Still I find landing on the razor's edge so to speak quite fun.

Edited June 17, 2013 by Pulstar

[SDIR]

Also, for landing having an ASAS module helps to keep the probe from tipping over during landing if you come in too fast or slow.

[MBobrik]

Duna's atmosphere is thinner, but it has a lower gravity that partially cancels that out. I did the math and the result was quite shocking to me. You need only 50 % more chutes to land at the same speed at sea level as on Kerbin ! The major difference however is, that Duna has got far more highlands than Kerbin, and Duna's atmosphere thins ou much faster with height than Kerbin's.

So, either find a nice deep crater to aerobrake into, and land with 1.5 x more chutes normally, or add 3 x chutes, or do a powered landing to reduce the last ~20-30 m/s excess speed the chutes left you with.

[DChurchill]

I'm coming in at 1.64 tons with a Mk16-XL chute. Lander carcass and rover. 4.7 m/s touchdown at KSC. Nothing broke at touchdown.

I'm thinking of adding an RCS quadrant at each corner with 1 or 2 roundified tanks each. Something about zero control at re-entry makes me queasy.

Edited June 18, 2013 by DChurchill

[alacrity]

My latest Duna project

around 127 tonnes (depending on fuel at the time). I used a Rockomax skipper engine under the center stack to bring it out of orbit. two advantages, empties the on board fuel before impact and the engine itself get tossed before landing, after the chutes open.

As you can see even with the engine breaking and 4 geodex and one inflateable balloon, the chutes need was... extensive. A combination of large drogues and many msaller chutes spaced over the whole structure.

Failures included...

1) Too many chutes at the ends with out supporting the cross conectors. Ripped itself apart as the different stages decelled and seperated.

2) Smaller engine for decel... Not enough delta-v to get the structure slowed to a manageable point... could have built the thing out of chutes and still died

3) Chutes alone... one word... Crater

The simple thing to remember about Duna... Chutes open later and work less, while the ground comes sooner. Best thing to do for design is combine chutes with engines and do a power assisted soft landing. RCS fuel won't cut it... you need controllable liquid fuel rig. Have it around till the chutes actually open and get the ship to around 100m/s before they do. Heavier the ship the slower you want to be going when the chutes open.

The other option I am looking at is going over to gliders and winged lift vehikles. Not sure about it but gonna give it a shot.

Alacrity Fitz

[DChurchill]

That's a lot more than 1.64 tons, I'm guessing.

[DChurchill]

Made it, if anyone is interested. Touched down at about 4.8 m/s.

[AmpsterMan]

Nice dude. Liked your lander, I personally prefer to use the drogue chutes and engines, but that's just me.

[DChurchill]

Thanks. I was trying to see how minimalist I could get. I've got a bigger and faster rover waiting in the wings which will need descent engines. Might leave that for Eve, though. I think I want to do an Apollo style Duna landing for my first extra-Kerbin landing with live kerbals.

[MBobrik]

Made it, if anyone is interested. Touched down at about 4.8 m/s.

Landed 2 pieces at once.

One landed at 4.2 m/s though it was designed to land at 5m/s

the other was designed to land at 7 m/s and landed just fine separately w/o any control

.

[Uberick]

I find the parachutes more useful for guiding the descent and descelerating vessels to under 100 m/s than for actually landing. For small probes and rovers they seem to work, but for any manned vessels I have to throw on so many parachutes to do a pure parachute landing that it starts to get crazy. A single small engine can usually do the work of a dozen parachutes, and saves on part count.

If you are planning on using just parachutes though, try to aim for one of the craters to give yourself more altitude to slow down. It might seem small but a km or two makes a big difference for parachutes!