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How to get ready for interplanetary missions ?


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Hellooow everyone !

Today I come up with a weird question :

Okay, so I wish to start exploring other planets in the game now, but I like  to do things properly and well, because the most amazing part of the gameto me is when excrements works and you succeed in actually going somewhere.
My first target will obviously be Duna and I have this program idea, that's kind of inspired by the Mars Semi-direct Mission, with a hab module, a Duna Ascent Vehicle and a Kerbin Return Vehicle.

Now I know Duna has a different atmosphere and gravity pull than Kerbin... So how do I test properly my crafts ? How am I going to know if they'll actually work waaaay over there ?
That's the kind of mission I don't want to have to restart from the beginning if something doesn't work..
I mean, I enjoy problems that are interesting and spectacular, like when everything goes south or when you forgot a step and the result is just too funny to be reverted etc... Not the annoying stuff that makes you start again 60 times and takes you 7hours to get right.


So yeah, thanks in advance for all the help and have a nice Odyssey :confused:

Edited by Smalish
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First of all: Check a DeltaV map

600px-KerbinDeltaVMap.png

As you can see, getting to Duna is actually surprisingly cheap. The gravity is .3G. Mun gravity is .16, so half that of Duna.

As a lander, I would advise a 2 stage lander, in the likes of the Apollo program (also, don't land the entire rocket like you can on the Mun). Build your rocket in steps. First the ascent stage of the lander. Note how heavy this is, now build a lander capable of landing this. Note how heavy this contraption is, now build a stage capable of getting all that back to Kerbin. Note how heavy that is, now build a stage capable of getting all that to Duna (don't forget something that can come back home with Kerbin Reentry. So put a heatshield on your command pod.)

Note that the transfer numbers are based on optimal numbers. So transfer windows. There are several helpful tools to help you with this. MJ can automatically plot a transfer for you, but there are also web based calculators that do the same thing, but leave you to plot the actual manouver (they just tell you when and in what direction).

And don't forget Ike. If you're there, you might as well visit Ike (this can be a really tiny lander)

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Well, if you're into calculations and all that I would suggest heading over to the Wiki and looking up Duna, then doing all the math required.
If you are more like me and like planning and playing but not calculating things then I suggest getting Kerbal Engineer (this gives you dV readouts even for complex staging) Transfer Window Planner (this will provide you with travel duration, dV requirements with and without aerobraking etc) and either Hyper Edit or Kerbal Construction Time to simulate going to Duna, landing, lifting of etc. Note that Hyper Edit is in fact pretty much cheating and if you forget to revert you will have kerbals stuck wherever you left them since everything you do with tha is actually happening.
I would reccomend Kerbal Construction Time, since that provides you with a Sim Only option where you won't have all the actual construction time but it provides you with the option to simulate key parts of the mission (such as landing, lifting off and transfer burns) in a simulation enviroment (meaning you don't risk killing anyone because everything get's reverted automatically) and also at a certain cost, which I think is actually kind of neat since money is never a real problem in KSP anyways
 

Edited by TheXRuler
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Thanks for your answers ! I'll try this all as soon as I get to play again.

To me Transfer Window planner looks really useful in order to be sure about the travel in itself... But yeah, landing and all will be more of a story of Delta-v. I like doing calculations so it's alright haha, but the mods you suggested will surely comein handy. on the other hand thanks for the map Sir-Robert, it's really nice. As for Ike, I'll probably get to it later, I'm planning the missions in advance !

The first one is supposed to send 4 kerbals on the surface of Duna for a year to establish a permanant base and explore the surroundings until the next best window to depart the planet and go back home.

For that it's going to be a three launches operation over two years I guess.
First I'll send the unmanned Duna Ascent Vehicle to Duna's surface, then, an unmanned Habitation Module to Duna's surface as well. It holds all the stuff needed to mine ore and make fuel, in order to refill the DAV. 
Then the Kerbin Return Vehicle is launched to Duna's orbit, it holds a pod with the crew that then detaches and joins the Hab at the surface, it will be equipped with deployable airbags and probably some landing engines.
At the end of the mission, when the DAV is refuelled and ready,the crew uses it to climb back into orbit and dock with the KRV... And back to mommys I suppose ?
Because the pod (which is the upper stage that's left of the DAV) in intself doesn't have engines to be lighter, I plan on deorbiting the entire vehicle, and then detach before entering the atmosphere.

What do you think of this ? Seems feasible ?

Edited by Smalish
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Sounds very feasible. The addition of the mining operations is going to save some effort. For example, you could probably refuel your transfer stage to go home (if you have the means to transport fuel to orbit).

You also won't have to worry about having enough fuel on your lander for a side excursion if you are going to mine new fuel. Of course, you'll need to ship the mining equipment, but once it has arrived, it will be very useful.

As for the pod returning to Kerbin, that is indeed the easiest solution. Just remember to bring a big heatshield

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The other advantage in starting with going to Duna (imho, in your first career, assuming you are playing without mods) is that Ike is there as a backup destination if you discover that your build isn't quite capable of doing everything you expected to do on Duna. Ike is incredibly (a touch too incredibly, perhaps) close to Duna, with less gravity and a decent number of biomes, so you can still consider your mission a "success" if you end up doing your science there instead of Duna.  In fact, I didn't put people down on Duna until at least my third mission to the system.

So... if you're basically eyeballing and guesstimating/SWAGging your way around the Kerbin system, and you find yourself returning to Kerbin from the Mun with a decent amount of fuel still left in your tanks, then you're basically already able to do a round trip plus landing on Ike.

What kills on Duna is the atmosphere. It isn't thick enough to rely on for landing, but it isn't thin enough to do a grazing low-level pass for a low-TWR landing. You need parachutes, but if the terrain isn't low enough your parachutes will never deploy due to insufficient pressure. Alt-F5 is a must.

So what would I say would be the best simple bits of advice to be confident about going to Duna for your first interplanetary trip?

- have a return capsule that'll get you back in any event. The Transfer Window Planner will tell you what your dv needs are. They aren't much from Duna.
- have several drogue and main chutes on your lander, and be ready to use engines to slow down to deployable speeds (and to kill the last few m/s down to landing speed).

Finally, as for testing, I'd say you don't really need to: being at the surface of Duna is very much like being at high altitude over Kerbin. So if you have an upper stage able to get to orbit from about 12-15km above Kerbin (on a normal ascent profile), then that same upper stage will get you from the surface to orbit on Duna. Minimum delta-v and TWR requirements to do those two things are actually very similar, even though most people will tend to have a higher TWR for their Kerbin upper stage.

 

edit: after reading your reply in this thread: if you have a mining craft that works for the Mun, send a copy to Ike. As long as you don't land on a very resource-poor spot, your Ike miner will be perfectly able to provide all of your Duna-orbit and return requirements.

Edited by Plusck
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Awesome ! I'll think I'll start exploring Ike woth probes and rovers as well then !

The next mission will be similar except it'll consist on landing mining equipment on Ike and/or having some mobile mining equipment on Duna's surface.

Of course if anything goes wrong, I can get the entire crew into orbit with the Ascent Vehicle and rendez-vous/docking with the Return Vehicle within a day or less. The KRV has a built-in habitat module in which they can stay until the next good enough return window !

I'll post pictures when I'll get to the game I think, maybe making a shortvideo montage of the mission could be fun too.

Also : "So if you have an upper stage able to get to orbit from about 12-15km above Kerbin (on a normal ascent profile), then that same upper stage will get you from the surface to orbit on Duna." will be useful too, in case I'm not sure with my calculations, I'll still have that as back-up.

Thanks alot !

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11 hours ago, Plusck said:

- have several drogue and main chutes on your lander, and be ready to use engines to slow down to deployable speeds (and to kill the last few m/s down to landing speed)

Just to add on to this:  if you can arrange your Duna lander to have some lift capability, that'll help you to bleed off enough speed that you can pop your drogues before faceplanting.  The atmosphere's really thin, it's not out of the question to still be going over 500 m/s when you get down to the surface.

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Some tuts & links :

Now you have some readings ;-)

 

Fly safe

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2 hours ago, Smalish said:

Like some AIRBRAKES ? I can arrange this surely !

Actually, no, not airbrakes.

That is to say, they're not bad, you can put some on if you want... but all they can do is try to slow you down, they can't give you lift.

I mean lift as in wings and control surfaces.  The problem with Duna is that the atmosphere is really shallow-- if you're heading downward at a steep angle, you simply don't have time to slow down before you faceplant.  So the key is to try to keep moving sideways through atmosphere for a really long time without losing too much altitude, so you can bleed off lots of speed.  And the only way to slow down without dropping like a rock is to have some lift.

You don't have to have aero lifting surfaces for a Duna lander, you can design one without 'em.  It's just a handy design option to consider, is all.

Edited by Snark
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