How to pack enough parachutes?

[Spektyr]

Does anyone have a formula or cheat-sheet on parachute quantity per ton of spacecraft for the various atmosphere'd bodies in KSP?

Short of spending all the time and effort of launching something to Duna, for example, and finding out if it brought enough parachutes to land safely or not?

Of course there's always the option of just packing an insane amount of chutes, but that presents a whole series of problems itself. I'd much rather bring just enough, plus a couple extra "safety-margin" chutes, rather than plastering them over every exposed centimeter of hull or bringing along extra fuel just in case I need extra burn to get the m/s down to a safe landing speed. Surely there's some math to find this amount, but the end result should be a solution like "1.5 parachutes per ton of spacecraft on Duna" or something along those lines.

[42undead2]

I think 4-6 should be the max. If your lander needs anything more than that, you need to re-design.

[Xeldrak]

I usually go by gut-feeling when placing chutes. When landing on Duna however, its heavily recomended to use a combination of chutes and retro-rockets.

[EndlessWaves]

http://wiki.kerbalspaceprogram.com/wiki/Atmosphere

Although it's not that well written that page should contain most of the info you need.

[Daze]

I usually go by gut-feeling when placing chutes. When landing on Duna however, its heavily recomended to use a combination of chutes and retro-rockets.

Exactly, if your chutes don't brake you till ~5m/s you have to use a little burn during last meters

[Vanamonde]

I think 4-6 should be the max. If your lander needs anything more than that, you need to re-design.

The number of chutes you'd need depends on the mass of the ship and the atmosphere of the world. An arbitrary numerical limit doesn't make sense.

[Spektyr]

The number of chutes you'd need depends on the mass of the ship and the atmosphere of the world. An arbitrary numerical limit doesn't make sense.

Exactly.

http://wiki.kerbalspaceprogram.com/wiki/Atmosphere

Although it's not that well written that page should contain most of the info you need.

So all I need to do is combine the equations together, assume 500 drag, plug in all the numbers for Duna, assuming worst-case scenario of a high elevation landing, about 8-9m/s terminal velocity, and solve for mass. And that would give the maximum weight per parachute to safely land without engines, right?

[allmappedout]

If I'm not mistaken, the drag figure on the parachutes is also affected by the mass of the parachutes themselves, which is why there are two parachutes with 500 drag but they most definitely provide different values of drag.

[EndlessWaves]

assume 500 drag

No, because drag is a coefficient of mass so you only get 500 drag coefficient when your craft consist entirely of parachutes, otherwise your drag coefficient is weighted by mass.

I would solve the terminal velocity/atmospheric density equation to get the drag coefficient for your desired landing speed and from that you can then work out how much 0.2 drag mass you can have for the different parachutes.

For example if you need a drag coefficient of 100:

1x XL parachute is 500 drag coefficient & 0.3 mass.

500 * 0.3t = 150.

150 / max_mass = 100

max_mass = 150/100 = 1.5t

Payload = 1.5t - Parachute Mass = 1.2t

It would be marginally higher as you'd need to add the drag * mass from the other parts to the 150 figure but it's likely to be a good approximation for duna as you want a high drag coefficient and most parts tend to be very low.

[Tank Buddy]

I was looking for an answer, so here it is: http://ksp.freeiz.com/

Parachute calculator!

[cheeseit]

Nothing wrong with too many parachutes. Better to have them and not need them than need them and not have them. I typically test the crap out of anything I intend to land via chutes on Kerbin and only use half the chutes to simulate the lesser atmosphere.

[Procyon]

I was looking for an answer, so here it is: http://ksp.freeiz.com/

Parachute calculator!

This wa great, Loved the bit when you select Jool

[magnemoe]

Note that you can save weight by using braking rockets on larger landers, say you want to land an 20 ton ship on Kerbin, landing speed 4 m/s require 6.7 ton parachutes or 45 MK2-R using the calculator.

Now set speed to 10 m/s and you only need 6 MK2-R weighing 0.8 ton, the braking engines don't need to have TWR larger than 1 and not much dV, 100 m/s should be enough as you will only use them for some seconds. Yes you might also want to burn them some seconds around 500 meter to reduce the shock of opening the parachutes.

[Kasuha]

Yes you might also want to burn them some seconds around 500 meter to reduce the shock of opening the parachutes.

Drogues.

Every time you're landing anything bigger than just a pod, add some drogues. The DO help to prevent your ship breaking apart due to chute opening shock.

[magnemoe]

Drogues.

Every time you're landing anything bigger than just a pod, add some drogues. The DO help to prevent your ship breaking apart due to chute opening shock.

You are right, my 20 ton test reduced its speed from 150 to below 40 m/s, more fun using two radial parachutes and 160 in trust giving an twr of 0.8 I was able to land 20 ton using just 50 fuel.

Eve is a bit of an ***** as the atmosphere is very thick then the parachutes opens giving an far stronger shock than on Kerbin. You might want to open at least some of the standard parachutes far higher up.