Building and flying a Duna mission.

[Dizzle]

Hey guys. This is something that's been bugging me for a long time, and I figured I should finally make an effort to get it down. It seems like no matter what, I have a really hard time getting kerbals to Duna and back. Here's what I want to know:

-How much delta-V should a lander have to be able to land anywhere on the planet and return to Kerbin? This is probably the most important.

-How low should I aim to aerobrake?

-At what speed should I be entering Duna's SOI? Sometimes I seem to come in at around 1km/s or less, and sometimes it's upwards of 3km/s. Why?

-What is the usefulness of drogue chutes? I know to use them in conjunction with engines, but they don't even seem to deploy until a ridiculously low altitude.

-Anything important I'm missing? Usually I wait for KAC's transfer window, adjust so the periapsis is about 11km, and land wherever I end up. Usually I don't have enough delta-V to return.

Thanks for any help.

Edited December 24, 2014 by Dizzle

[The_Rocketeer]

-What is the usefulness of drogue chutes? I know to use them in conjunction with engines, but they don't even seem to deploy until a ridiculously low altitude.

I read something about this in another post. For some reason chute deployment on Duna is currently (v0.9) based on datum surface level (basically 0 altitude, for planets with oceans this is at sea level) and not being modified for surface elevation. So, if you're landing on a mountain and the chutes are set to 500m, you could well never have your chutes open at all.

[Anquietas314]

-How much delta-V should a lander have to be able to land anywhere on the planet and return to Kerbin? This is probably the most important.

It's been far too long since I've been to duna to remember exactly, but I would estimate it at perhaps 10-12km/s total at launch.

-How low should I aim to aerobrake?

Low. About 11km periapsis ought to bring you into an elliptical orbit. Be careful though - much lower and you'll be dragged down, much higher and it won't have any effect.

-At what speed should I be entering Duna's SOI? Sometimes I seem to come in at around 1km/s or less, and sometimes it's upwards of 3km/s. Why?

Use a transfer window planner like http://alexmoon.github.io/ksp/ to choose when to go. A suboptimal transfer is probably your issue there.

-What is the usefulness of drogue chutes? I know to use them in conjunction with engines, but they don't even seem to deploy until a ridiculously low altitude.

These probably won't help much with Duna, but they're mostly for slowing very large ships down before activating the main chutes - they were added to help solve a problem where the shock of opening the chute will rip large ships apart.

-Anything important I'm missing? Usually I wait for KAC's transfer window, adjust so the periapsis is about 11km, and land wherever I end up. Usually I don't have enough delta-V to return..

KAC can be quite inaccurate as to when the optimal time to transfer is. The "model" setting will produce better results on average but it's not perfect. Like Kerbin, your ascent from Duna's surface will impact how much deltaV you need, but to a lesser degree than Kerbin.

[Anquietas314]

I read something about this in another post. For some reason chute deployment on Duna is currently (v0.9) based on datum surface level (basically 0 altitude, for planets with oceans this is at sea level) and not being modified for surface elevation. So, if you're landing on a mountain and the chutes are set to 500m, you could well never have your chutes open at all.

I would check this ingame. Way back when Duna was added parachutes worked just fine on Duna - they were very risky due to the thin atmosphere, but they did work.

[lirg03]

I would check this ingame. Way back when Duna was added parachutes worked just fine on Duna - they were very risky due to the thin atmosphere, but they did work.

I have landed on Duna in 0.25, and the parachutes did work as intended. Proof:

[Anquietas314]

I have landed on Duna in 0.25, and the parachutes did work as intended. Proof:

http://i.imgur.com/U5xKbML.png

You know KER and KAC are both updated for 0.90 right?

[lirg03]

You know KER and KAC are both updated for 0.90 right?

Yes, the above pic is from 0.25. But I don't expect the behavior of parachutes on Duna suddenly change in 0.90.

[lirg03]

-How much delta-V should a lander have to be able to land anywhere on the planet and return to Kerbin? This is probably the most important.

I often use this pic http://wiki.kerbalspaceprogram.com/wiki/File:KerbinDeltaVMap.png as a reference of how much dV I need for a particular lander. If you plan to design a dockable lander that will be separated from mothership, land, and fly back to dock with the mothership, then I think a lander with parachutes with 1600~2000 m/s dV should be enough.

-How low should I aim to aerobrake?

This http://alterbaron.github.io/ksp_aerocalc/ should help you to plan aerobraking maneuvers.

-At what speed should I be entering Duna's SOI? Sometimes I seem to come in at around 1km/s or less, and sometimes it's upwards of 3km/s. Why?

That depends on how you do the interplanetary transfer. With the above calculator, it will be easier to setup aerobraking even if you are coming in with different speeds.

-What is the usefulness of drogue chutes? I know to use them in conjunction with engines, but they don't even seem to deploy until a ridiculously low altitude.

Parachutes and drogue chutes have a min atmo density for partially opening. They will fully open 500m and 2500m above surface with default setting respectively. Duna atmosphere is very thin, so you may approaching ground very fast before the chutes open. Try to aim for 'valley' for better result.

-Anything important I'm missing? Usually I wait for KAC's transfer window, adjust so the periapsis is about 11km, and land wherever I end up. Usually I don't have enough delta-V to return.

KAC's transfer window is usually good enough that you don't need too much more dV than the 'optimal' ones. http://alexmoon.github.io/ksp/ gives much better transfer windows.

[The_Rocketeer]

I would check this ingame. Way back when Duna was added parachutes worked just fine on Duna - they were very risky due to the thin atmosphere, but they did work.

This thread is the one I was reading. It was reported and confirmed by Alpheratz. I haven't personally verified it.

[Anquietas314]

This thread is the one I was reading. It was reported and confirmed by Alpheratz. I haven't personally verified it.

Hmm. I'll see what happens on my end. Should be a fun experiment / revisit of old memories

[MrCynical]

-What is the usefulness of drogue chutes? I know to use them in conjunction with engines, but they don't even seem to deploy until a ridiculously low altitude.

Using the tweakable settings for parachutes can really help you out here. You can raise the altitude for deployment up to 5000m and down to 0.01 minimum pressure. Which isn't a bad combination of settings if you're coming down over the highlands of Duna. Still will probably need a short burst from the engine at landing to get down to a safe speed, especially on high ground.

[Scarecrow88]

The last time I went to Duna, I used the lander I had originally built to go to Mun. The only change I made was to add a few chutes, which meant that I used hardly any fuel to land, and had almost full tanks for my return to orbit.

[SRV Ron]

I was able to land this probe with a single chute at high altitude in 0.90 Beta. Just a small burn prior to touchdown ensures a safe landing. So, even though the probe is on its side as it has no landing gear, it is still fully operational.

The ship on the left was sent to Duna.

Entering aerobraking

Under main chute

Safely landed.

[Dizzle]

Thanks for all the advice guys, it helps a lot.