How much dV for a Duna landing with chutes?

[Shmauck]

I want to land an outpost on Duna. The community dV map in this forum tells me that 1450 m/s of dV is required to touch down from a 60km orbit.

Q1: Is that the figure for a fully powered landing without chutes? 

I am planning to put about 1480 m/s on the outpost and to add 4 drogue chutes and 4 brake chutes for 18.6 tons of mass. And I wonder if that will be sufficient. My orbiter around Duna currently travels at 865 m/s in an 84 km orbit. 

 Q2: Is there a way to calculate this properly?

[Laie]

1450m/s is a suitable figure for launching into orbit on Duna. Duna's atmosphere is much thicker than Mars' and will slow you down a good deal. Landing with chutes will only require very little fuel for a soft touchdown, and possibly none at all. Assuming 300m/s for that purpose is positively generous.

As always, terminal velocity depends on how heavy and draggy your vessel is (a lump of iron falls faster than a sack of feathers). As a first approximation, expect to fall twice as fast as on Kerbin.

Make sure to tweak your chutes to toggle at low pressure and fully deploy at higher altitudes than you would on Kerbin. Also make sure to bring a drogue chute -- there's a decent chance that your main chute won't deploy in time because you're still going too fast, that's more common on Duna than on Kerbin. A single drogue makes all the difference in that case.

Remember that chutes are heavy and have diminishing returns. It's certainly worthwhile to bring one or two, but if you find yourself tiling the lander with chutes, have a good sharp look and ask yourself if 500kg of extra fuel won't be more useful than 500kg of chutes.

As for Queastion2: I'd need to look up the formula, but the inputs are available: The game tells you the effective diameter of your chutes (assume a circular disc), and you can look up the air pressure on Duna in the tracking station or (better) the Kerbal wiki. Finally your vessel weight in local gravity. From that you should be able to calculate the airspeed where drag equals weight.

Edited May 4, 2019 by Laie

[FloppyRocket]

My experience (which is small) is that Duna's atmosphere is weak and is only significant if you are landing at very low altitudes. Unless you're very good at selecting and landing at a specific location, I recommend you plan on a full rocket-powered landing.

[Aegolius13]

Question 1 - as @laie says, the 1450 m/s is for taking off, not landing.  When you're landing, drag works in your favor, so drag "losses" reduce your requirement rather than add to it, meaning the landing requiremnet should be a lot lower on a planet with an atmosphere.  By analogy, the map says it takes 3,400 m/s to take off from Kerbin, but you can land with nothing more than an initial deorbit burn.   Sounds like you should be more than fine with your current setup.

Question 2 - not really, since it's going to depend on the aerodynamic properties of each particular craft.  But at least in my experience, as long as you'd got a somewhat-draggy shape, and a chute or two, the delta-v requirement to land is always going to be pretty low.  The concern is probably more like "terminal velocity is 50 m/s higher if I skimp out on chutes, so I'll need to add 50 m/s to the landing burn" rather than "I'm going to have the burn the engines most of the way down to to have a chance."  

 

[Shmauck]

4 hours ago, Aegolius13 said:

Question 1 - By analogy, the map says it takes 3,400 m/s to take off from Kerbin, but you can land with nothing more than an initial deorbit burn.   Sounds like you should be more than fine with your current setup.

*facepalm* Oh yes, I should have seen that myself. 

Thank you guys!