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firerider521

On Parachutes and Duna

Question

I've been thinking of landing on Duna for some time, and I've come across a certain conundrum: Parachutes. I've been testing all of my parachute layouts on Kerbin, which is a terrible idea, but some of my designs simply rip apart the space craft. I know that Duna's atmosphere is tiny, so there may or may not be anything to worry about, but...

Is there a way to number crunch the optimum number of parachutes? Also, I've looked at the wiki, and it says that the parachutes take 0.9 atm of pressure to deploy(http://http://wiki.kerbalspaceprogram.com/wiki/Parachute), so parachutes technically wouldn't fully deploy at all. Is it just that Squad set the deployment height to how-many-meters and the wiki got the approximate pressure from that? Halp!

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From experience, all parachutes deploy at pre-set altitude above the surface.

Regular chutes at 500m and drogues at 2.5km

Don't know about semi-deployed altitudes though

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I'm afraid I can't be much help in regards to Duna (have yet to leave Kerbin's local system, save for a rogue satellite that escaped into Kerbol orbit on accident -- was trying to put it into orbit using only solid boosters, just 'cuz), but when I was testing a heavy lander design on Kerbin (in my defense, its purpose was to visit Mun and Minmus and then return to Kerbin) I found it ripping itself apart when the chutes deployed; I fixed it by adding a few drogue chutes, which slowed it down enough that the g-forces when the main chutes deployed no longer ripped it asunder.

Also, chute placement matters. When I had most of the chutes on the radially-mounted fuel tanks, they'd just rip right off; when I moved the bulk of the chutes to main central tank, though, it was much more rigid.

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From experience, all parachutes deploy at pre-set altitude above the surface.

Regular chutes at 500m and drogues at 2.5km

Don't know about semi-deployed altitudes though

I know about semi-deployed altitudes, they actually ARE based on atmospheric pressure. I also knew the preset altitudes for KERBIN, not for other planets, but I didn't know that it was pre-set for every planet, thanks. What I'm looking for is a way to make a parachute configuration that doesn't blow apart, but creates as much drag as possible.

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Test it on Kerbin. My rule of thumb : when your lander hits the ground at <3.5 m/s then you can land on Duna at < 12 m/s. To prevent ripping apart, add one or two drogues. they fully open higher, so when your main chutes open. you will have much less speed.

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I've done a successful landing on Duna with a fifteen-tonne lander using three Mk16s. You do need to apply some thrust on your descent stage to get it slowed down; not generally as much as you would for a Mun landing, though.

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Test it on Kerbin. My rule of thumb : when your lander hits the ground at <3.5 m/s then you can land on Duna at < 12 m/s. To prevent ripping apart, add one or two drogues. they fully open higher, so when your main chutes open. you will have much less speed.

Funny enough that you mention drogue parachutes. One time, I tested a model on Kerbin with 3 drogue parachutes and 2 XL parachutes instead of just 3 XL parachutes, and it ripped apart at 2500m. However, when I used 3 XL parachutes, it was fine. I'm pretty sure that it had something to do with the added weight of the adapters.

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You may want to do a powered landing as well as rely on the parachutes, or else consider adding struts to the parachute, connecting it more securely to the main craft.

Or in Jeb's language: MOAR BOOSTERS! MOAR STRUTS! :P

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When I build my Duna ships, I test them on Kerbin and keep adding parachutes until they fall at about 3m/s or less. I find that this brings them down on Duna at about 10m/s, which is roughly the maximum speed that you can land anywhere without taking damage. You can land on Duna using chutes alone, but I find that the chutes rip off if I open them while going faster than 300m/s. So what I do is come in at as shallow a descent angle as possible, then when I'm approaching the ground I use engines to get my speed down to 300m/s, then pop the chutes and shut he engines off, floating the rest of the way on the chutes.

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Is there a way to number crunch the optimum number of parachutes?

There's a python module for that. It has functions to compute the landing speed given a number of parachutes, the number of parachutes you need to achieve a given speed, or a recommendation for how much fuel versus parachutes to bring along for a powered landing with parachutes. That last one assumes you're a better-than-optimal pilot, so err on the side if more fuel or more parachutes.

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Parachutes work very well on Duna, though of not quite as well as Kerbin, so don't rely on purely Kerbin testing - over design your Duna lander.

For placement you ideally want the parachutes to be connected to the heavy core of your ship, such as a fuel tank... if they're connected to (for example) some light module at the top, as soon as they kick in that module is going to brake hard, and if there's several tons hanging off the bottom of it the stress on the joins will just rip them away. If you break your heaviest part (or parts) hopefully all the smaller items should survive the deceleration.

Of course with parachutes this often isn't possible placement wise, so you need to address the problem in two other ways.. firstly, re-enforce likely break points with struts and secondly don't allow your ship to decelerate too hard. Before hitting Duna's atmosphere I usually make sure I've shaved my speed down to under 700m/s with engines and then just leave them on very low thrust maintaining this kind of velocity. When parachutes kick in the force isn't going to be quite so rough. The high altitude parachutes are also your friend here... they drag for a good long time before opening, and can shave a lot off your speed before they even put much of a force on your ship. By having both high and low altitude parachutes you split the deceleration into two parts as well, rather than have everything open at once and shave off huge speed instantly, ripping you apart.

You will probably find that although parachutes save massive amounts of fuel, they won't be enough to land delicate loads slowly enough on Duna (I find they usually leave me 12-20m/s) so be ready for a quick final burst of your engines before touch down.

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Formula you need is the first one on http://en.wikipedia.org/wiki/Terminal_velocity

will give you the formula and how to calculate rho in ksp,

I was doing this exact thing last night. Dropping parachute landers over various kerbin altitudes, noting the touch down speed and solving for A which is the only value I don't know how to calculate.

Now that I have that it is time to see if it works on duna

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I find that one drogue parashute works best, but I did not try to get heavy things to duna. This worked very well, to give you an example:

KzVlP3ul.jpg

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What happens is all your big chutes deploy at once, stopping your craft at such a high speed it breaks. Add a couple drough chutes, let those slow you down, then deploy main chutes. Also, a small, light lander helps.

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Well, I landed a several ton heavy rover on Duna - as the others allready said, drogue shutes are key. However I also used retro-rockets - they are useful for landing a heavy payload and to break your ship shortly before you main parashutes deploy fully, so it doesn't ge ripped apart.

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Reading this made me think, Can you not 'stage' the chutes? deploy one, then one more, then one more, to give a more gradual reduction in speed???

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Thank you guys so much.

Sadly, I don't know how to use a python script(and the drogue chute value is wrong, 170 not 100). But I now have plenty of tips to calculate my parachute touchdown!

Like I said, though, I tested a lander with 3 drogue parachutes attached to the main body on Kerbin, and it fell apart. However, it did not fall apart when I used an XL parachute instead. I think that it actually has to do with weight. I realize that I have to do a powered landing as well. Thankfully, the nuclear engines retain most of their Isp in the thin atmosphere of Duna.

I should try to lighten my lander as well.

Also, more struts. :P

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Reading this made me think, Can you not 'stage' the chutes? deploy one, then one more, then one more, to give a more gradual reduction in speed???

It's possible.

gYa7AD2.jpg

It does need a meticulous staging arrangement though, depends on how you want it to work.

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It does need a meticulous staging arrangement though, depends on how you want it to work.

Question. What are the six unconnected mainsails good for ?

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What on earth is that thing?
me thinks that's a submarine :) correct?

Yes it is - an immobile one though.

Along with infinifuel, it's used to go deep into the ocean and take measurements with the on-board instruments. That particular one is designed for Eve.

And speaking of Eve and parachutes, it's enough to give me the softest splashdown as possible on Eve (rated <5 m/s on Kerbin tests with 12 more chutes). Oh - and it's a perfect demonstrator of multi-staged parachute setup, to prevent the craft from getting ripped apart on landing. :)

Also, as for Duna, a handful chutes + powered landing is enough, given the thickness of its atmosphere. Easy come, easy go.

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I set up my staging so my last engine slows me down even as low as 8000m. My pre-chutes are out for sure, then I kill the thrust, dump the engine and lower the landing gear. There is normally enough side movement to avoid landing on the engine.

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