Amount of Delta-V for a Duna-And-Back mission

[Elowiny]

As the title says, how much Delta-V is required for a Duna-and-back mission with one kerbal ? Because I can land on nearly any body but I can't come back... How much delta-v should the rocket have to land on Duna, and how much to get back to Kerbin? I know Delta-V maps exist but I prefer asking to be sure. Also, I'm using a rocket, not a plane. Thanks for any answer!

Edited January 2, 2016 by Elowiny

[Alpha188]

For my missions 8k ∆V are usually enough, but it can change quite a bit and if you feel like you are a very good pilot. If it's your first time I'd go with 10k just to be sure, so that you can make some mistakes and still manage to get the brave Kerbal back home.

The best way to reduce the ∆V needed is (of course you have to wait for a proper launch window) to aerobrake both at Duna and Kerbin. Aerobraking at Duna is kinda difficult because if you have a really big vessel (not really your case) the atmosphere may not be thick enough to slow you down, but on the other hand expect to get really hot when trying to slow down at Kerbin (you can split the reentry in multiple passes so you need to deep in the atmosphere less and also heat up less).

Sorry for my bad english, and I hope you'll be able to get a orange surface sample back to Kerbin!  

[wibou7]

10k is probably enough... But if you want a tips, the best way to make sure to make it back is to always send 2 spacecrafts on each mission : your usual transfer-lander craft AND a second craft composed of a probe core and the largest tank of fuel you can lift.

A single orange tank of fuel is usually enough to get you back from any Kerbol's body (unless your return stage is too big but that's another story). Better yet, if you use that tank to dump the excess fuel on any spacecraft visiting that body, you will have an emergency refuel station in case your future missions go wrong.

[Evanitis]

I just wanted to add that the Kerbin - Duna transfer is the prefect opportunity to learn the basics of the slingshot manuver (if you didn't already). It can save thousands of dV. It's not an exact science (well, not for me anyways), but I always managed to get from LKO to LDO by using less than 1000 m/s (that includes patient aerobraking until I can circularize with a minimal burn).

Thanks to Ike, gravity assisting works on the way back too.

I'm not a super efficient KSP-and-math-expert, but I bet the absolute minimum dV required is a surprizingly low number - not much more than the two takeoffs from the planets cost. It would be a fun challenge to figure out..

Edited January 2, 2016 by Evanitis

[Snark]

Welcome to the forums!

Going to Duna's a great mission, very educational.    It introduces a lot of new challenges for you to learn, and is great practice for going to the rest of the solar system.

To answer your specific question about dV:  You'll need approximately the following (these numbers are the bare minimum, you should add safety margin):

• Transfer from Kerbin LKO to Duna:  1050 m/s (with a good transfer window)
• Duna arrival:  zero (use aerobraking)
• Duna landing:  ~50 m/s (descend on parachutes, use brief burst of retro-thrust on landing)
• Return to Duna orbit:  1400 m/s
• Transfer back to Kerbin:  600 m/s (with a good transfer window)
• Kerbin arrival:  zero (use aerobraking)

So if you're starting from Kerbin LKO and use ideal transfer windows, you're looking at a bare minimum budget of 3100 m/s of dV.  Add plenty of padding to that if it's your first try. 

 

Here are some questions you're likely to have:

 

How do I transfer between Kerbin and Duna? (dV amount, launch window)

My favorite tool is http://ksp.olex.biz .  Very simple and intuitive to use; just tell it your origin and destination planets, and the height of your parking orbit, and it tells you exactly how much dV you need, with simple graphics showing when to launch.  You can use it to see for yourself, but you'll need around 1050 m/s to go from LKO to Duna, and around 600 m/s to go from Dunar orbit back to Kerbin.

It's really worth trying to hit a good orbit window.  It will greatly reduce not only the dV you need to get there, but also the speed you're going on arrival (making reentry easier).

 

What should my mission design look like?  Direct lander?  Leave transfer stage in orbit?  Use an airplane?

There are a lot of ways to go to Duna, and trying them out is one of the fun parts of KSP. However, if you're new to KSP and just trying your first interplanetary mission, I'd recommend a direct lander (i.e. you go to Duna, directly land, then take off and go back to Kerbin).  It's the simplest mission to design and fly.

 

What should my approach look like on Duna arrival?

For a direct landing, set your Duna periapsis to around 15 km as you approach, and you're pretty much guaranteed to get captured and go down to the surface.

(If you were going to be leaving the transfer stage parked in orbit, then aerobraking gets a lot more finicky, because there's a razor-thin margin for error-- on Duna, the difference between "too much aerobraking, go down to the surface" and "not enough aerobraking, go flying off into space" can be only a few hundred meters of altitude.  But for a direct landing such as I'm suggesting, it's a lot easier, since you only need to worry about "low enough" and not "...but not 500 meters too low.")

 

What should my lander look like?

Make sure it has the following:

1. Heat shield for aerobraking on arrival.  Duna reentry heating is fairly forgiving, you may be able to manage without a heat shield.  But having one doesn't hurt, especially if you're new and want to hedge your bets.  And in any case, you'll definitely be wanting a heat shield when you arrive back at Kerbin.
2. Drogue chutes.  Duna's atmosphere is thin, and it can be hard to slow down enough (before impact) to deploy regular parachutes.  Drogue chutes are great for slowing you down.  You don't need a lot of 'em, just a couple should do.
3. A few parachutes.  It may be tempting to say to yourself "I've heard Duna's atmosphere is really thin, I'd better pack on lots and lots of parachutes to slow down."  I'd recommend against this approach (details below)-- just put a few parachutes on.
4. A bare minimum of 2000 m/s dV remaining when landed if you're going home to Kerbin.  It takes at least 1400 m/s to get to Duna orbit, then another 600 m/s to get home to Kerbin.  That's the absolute best possible case, where you have an ideal launch profile and a perfect launch window, which of course hardly ever happens.  So I'd recommend adding at least a few hundred m/s as a safety margin.  2500 m/s would be a nice amount to have.  3000 m/s would be really safe, if you're paranoid. 

Why only a few parachutes?  Well, parachutes are heavy.  If you pack on enough parachutes to reduce to a safe landing speed, you'll have so many of them that your lander will be heavy.  So a better way (IMHO) is to add just a few parachutes, enough to reduce your speed to a few dozen m/s but no lower than that.  Then you can fire a very brief burst of your rockets to slow down to a safe landing speed just a second or two before impact.  (It's how NASA does it on Mars!)  The fuel you spend for that brief burst will be a lot lighter than the mass of extra parachutes you would have needed.

 

What should my approach look like when I return to Kerbin?

Assuming that you used a good transfer window for departing Duna, then arriving back at Kerbin is pretty much the same as arriving back from Mun or Minmus; it's only 100 m/s or so faster.  So if you can design a craft that can reenter after visiting Minmus, you can do this.

Note that if your transfer window from Duna is less good, then you could be arriving quite a bit faster.

Edited January 2, 2016 by Snark

[Elowiny]

1 hour ago, Snark said:

-snip long text-

Thanks! I'll use that when I try to return from the red planet. I might even post it in mission reports, but I'm not sure about that.

[Aethon]

 

 

This may help.

Swash's Delta-V Map - KSP 1.0.5