1. ## Parachute guidelines

Edit: check the second post for current info. Initial post left as is for posterity. Also, finally fixed the typo in the title!
Based on some experimentation, I've created some ball-park estimates of touchdown speed vs the mass fraction of parachutes equipped on a given lander. (using version 0.20)
-redacted-
I say "ball-park" since these experiments were all at Kerbin sea level, and extrapolated via the barometric pressure of the other planets given in the wiki, and does not factor in the differences in gravity. All test flights were taken to a 100km apoapsis (+/- 1km) and uncontrolled until touchdown. Not shown is the difference between standard and drogue 'chutes (though it is comparable to the difference between the Kerbin and Duna curves). Please point out any errors that you find. (kerbin data sample)

2. I had a bit more time today, so I've double-checked the data and corrected for the differences in gravity. Remember that drogue 'chutes are about 1/3 as effective as the other parachutes per unit mass. Note that the x-axis is logarithmic and spans from 1% to 100%.
-snip-
Sea-level and projections for other elevations (gravity and pressure), so those assume enough time in atmosphere to slow your lander down. I had to split it into two graphs in order to keep the finer detail though:

3. Quite nice This looks like another one for the Drawing Board.

4. Hm... "Mass fraction" of parachutes would be the mass of the parachutes divided by the mass of the vessel?

So, If my vessel weights 90 tons, I'd need 18 tons of parachutes to land on Duna? That would be like 180 MK-16...or 60 MK-16-XL.

Or the same for Kerbin, I'd need 3,6 tons of parachute, equalling 36 MK-16 or 12 MK-16-XL...

I have 7 MK-16-XL and 16 MK-25 parachutes on my Lander. Not quite sure about its mass at the moment (am on nightshift, can't look, but it was around 90 on the launchpad).

Not enough for Kerbin, I did need engines to assist.

Oh, well. There goes the idea of an all-parachute landing on Duna....

5. Oh, and I forgot!

Thanks a lot for your work! I've been looking for that kind of data for AGES now.

6. No problem I've seen the equation float around sometimes, but I think it's easier to look at a graph.
And yes, the mass fraction is referring to (mass of parachutes)/(payload mass plus parachutes). If you don't have any parachutes on a lander, you'd divide its mass by [one minus the mass fraction on the chart] to find the mass of parachutes to add. (e.g. a 90T lander would need an additional ~13T of parachutes to land at 6 m/s near Kerbin sea level) I'll try and include elevation at some point as well, but I think that might get messy.

7. Originally Posted by Tokay Gris
Oh, well. There goes the idea of an all-parachute landing on Duna....
I think thats the point of duna. Thats why curiosity/spirit/opportunity/ect couldn't use only parachutes.

8. I've seriously needed data like this ever since I considered landing on Duna in the first place. I wanted to number crunch but I didn't know how.
Thank you so much.

9. Originally Posted by jgkamat
I think thats the point of duna. Thats why curiosity/spirit/opportunity/ect couldn't use only parachutes.
I am not quite sure gravity doesn't play a role in this.

Landing velocity with a given mass and given number or parachutes (or fraction of parachute mass) must surely differ depending on gravity.

I will try that once my lander gets to Duna and see what happens if I reduce the number of parachutes....

Or maybe I have a misunderstanding here....

10. Amazing work!

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