How many more chutes for Duna compared to Kerbin?

[ROXunreal]

My question is pretty much summed up in the title.

Wiki says 2.5 times more but I'm unsure if this is based on old data, as they've recently changed the atmosphere.

I put three times more chutes on my lander as well as a large drogue chute and am wondering if this will be enough, I don't plan to use engines.

[Sharpy]

If your landing vehicle is simultaneously your ascent vehicle, one or two chutes total. Instead of packing more chutes, perform a powered landing - ignite the engine a moment before touchdown, throttling it so that TWR is around 0.95-0.98 - relieved of majority of payload mass, the one chute will neatly arrest the descent. And the fuel mass will probably be less than the extra chute mass.

Otherwise, if you don't plan powered landing - rule of thumb: if it lands on Kerbin at 3.5-4m/s, it will land on Duna at 15-20m/s. Adapt your lander on Kerbin until it can withstand a 15-20m/s impact, then add chutes till it slows to 3.5-4 m/s.

Edited December 30, 2016 by Sharpy

[ROXunreal]

Thanks! there will be no ascent, it's just a lander with a rover.

[Sharpy]

Then ruggedized wheels have a very good impact tolerance. Land your rover wheels down, and it will be fine.

[KevinW42]

Also, be sure to pack a drogue chute to make sure your main chute has enough time to deploy.

[Carl]

Even on Kerbin thats not a bad idea IMO. More for the extra slowdown before they fully deploy but still, my tourist orbiter would probably smash into the terrain before it bled off enough velocity for the main chutes without the pair of drouges, they strip enough for the mains to come out well above the drogue's 2.5k fully open altitude.

[Sharpy]

Drogue is a good idea, also definitely reset the open altitude of the chute to at least 2km, and pressure to minimum. The thin air makes the chutes act way slower than on Kerbin. You can open them at higher speed, but they bleed the speed way slower; fully deployed at 1km it's quite likely not to slow you fully before the ground.

Also, aim for Midland Sea, or craters - lowest altitude, densest air. Avoid polar caps, they are regularly 5km or more above '0'.

[Wanderfound]

Alternately: forget the chutes, use wings, airbrakes and vernors.

Doesn't need to be a spaceplane; anything with sufficient drag and lift will do. A disposable glider style thing.

For show-off value, replace the Vernors with Sepratrons.

Edited December 31, 2016 by Wanderfound

[Nich]

Chutes get excessive on Duna, I agree with powered landings.  Seperatrons with tweaked .95-1 twr are nice. As an alternative some experimentation with a crumple zone (cubic octagial struts) can absorb 40-50 m/s

[Carl]

With 2.5m parts chutes get excessive on kerbin too.

[Nich]

On 1/3/2017 at 1:40 PM, Carl said:

With 2.5m parts chutes get excessive on kerbin too.

If you are talking about part count I will agree, otherwise you have to split hairs and it would be that same ratios for 1.25m parts.

I have not done the math but it feels like parachutes weight more after about 20 m/s (terminal full deployment) if you don't have to add an engine or 5 m/s if you have to add an engine specifically for landing.  To be fair I have never really played with seperitrons.

I am guessing @GoSlash27 has a spread sheet for this

 

[Snark]

Moving this question about gameplay to Gameplay Questions. 

My own answer to the question of "how many more chutes on Duna compared to Kerbin" is... no extra parachutes.  In fact, I usually put fewer chutes on.

Rationale?  It comes down to the diminishing-returns thing that folks have already alluded to:  I use only a bare minimum of chutes on Duna, and then do a powered landing.

Why?  Because getting the terminal velocity down to, say, ~30-40 m/s requires only a very tiny bare minimum of parachutes.  So, why bother putting on more?  Slowing just 30-40 m/s right at landing time, using engines, takes only a tiny amount of fuel, and the chutes needed to slow much more than 30-40 m/s will almost certainly weigh more than the fuel expended.  So I don't bother.

Why don't I do this on Kerbin, too?  Well, aside from chutes being much more effective on Kerbin, there's also the matter that my landing vehicles on Kerbin very often don't have engines on them (or, if they do, they're really low TWR vac engines that wouldn't help  much with a Kerbin landing).  So I need to land on chutes alone.

[Fearless Son]

@Snark's advice is good.  Some chutes will certainly help at reducing the total delta-v requirements of landing on Duna, but to land on only chutes would require so many chutes that the mass of them would offset the delta-v advantage gained by using them.  

Drogue chutes have been mentioned as a good idea and I fully endorse them.  The thin atmosphere will not slow your craft nearly as much as Kerbin, and if you do not do something to slow down before deploying the main chutes you will be going too fast for them to safely deploy before you hit the surface.  They will be a big help.  

But like Snark said, you should do a semi-powered landing.  Let the chutes slow you, then use an engine on low-throttle to slow the descent before touchdown.  Now, this landing does not require much power, so you can get away with some tiny engines and only a little fuel.  I often use these same engines to conduct my de-orbital burn, especially if I am landing a rover or the like.  Since the trip is one-way, I do not have to worry about having enough fuel to get back to orbit.  

Think of it as a "sky crane" style landing.