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Duna Mothership -- will this work as I intend?


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I have contracts to explore and land on Duna and Ike. I thought it would be amusing to try and do both at once, and I have access to the Rhino and Mammoth via experimental contracts, so I built a single huge ship to try and deliver a lander and a satellite to each in a single run. After a couple of launch attempts I got it on course for Duna, to arrive in about four months.

In the VAB it looked like this:

vab.jpg

 

The payload satellites/landers look like this:

payload.jpg

 

Each is pretty much a full-service job; all available science modules are on board, plenty of electricity, and the landers have RCS with a good bit of fuel.

Here's the mothership in flight, en route:

explorer.png

It looks rather majestic, if I say so myself. The main tank has about one-quarter of its fuel left, which will be important later.

Of course, it was only after getting this beast on its way that I thought to ask about whether what I had in mind was likely to work on the far end. The payload has two stacked landers and two satellites, one each for Duna and Ike. The idea is to get the satellites into polar orbits and the landers on the ground -- preferably in one piece. Functionally, all the pieces are there. But I've never been to Duna and don't really know what to expect as far as fuel requirements go. I based my design on Mun landings.

My flight plan: On approach to Duna, I want to release the two satellites. I'm pretty sure the two terriers can get them into their respective orbits without much trouble, and it reduces the mass the mothership needs to push around. The landers are more difficult. I don't know how fast I'm going to be going relative to my targets on the way in. They *might* be able to get into orbit and down to the surface under their own power unaided...but I don't think so. I'm thinking it might be best to use the remaining fuel in the main tank to get into Ike orbit with both landers attached. Assuming I can do that, the Ike lander should have no trouble getting down. That leaves the Duna lander, which will have to fall all the way to Duna and land under its own power. My main concern with this plan is that, while I know Duna has a thinner atmosphere and lower gravity than Kerbin, I don't know how that affects things. I have two radial parachutes, but no heat shield. I have a full fuel tank but it's not huge.

If I have spare fuel in the mothership to get out of Ike orbit and on course for Duna, that saves me some on the lander. Enough? Unsure. If I don't need to do mothership shenanigans, I'd like to leave what's left of it in Ike orbit for future use as a tanker (hence the docking ports).

A possible alternate plan: If the Ike lander can get from inbound to surface on its own, I could detach it when I detach the satellites and have all the mothership fuel to help the Duna lander get down.

So, first question is, is either plan feasible?

And second question: I'd *like* to follow up this mission with a manned one. But I'm concerned that by the time this mission arrives and I get to see how it works, Duna's orbital position will have fallen behind enough to make a second mission difficult. Do I need to launch my manned mission sooner?

 

Edited by Error_Sophius
Got Duna's moon mixed up with Kerbol's second planet.
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So you want to launch two satellites and two landers in a single mission and send one of each to Duna and Eve? Well... I suppose it is possible, depending on your skill, but it would be much more feasible to send a different mission to each planet. You'll spend a lot more fuel going from Kerbin to Duna to Eve with one ship than you would with sending smaller spacecraft on separate launches.

Landing on Eve is stupid easy, you won't need to use an engine at all unless you didn't put a parachute or the lander is excessively heavy. Taking off from Eve is... not easy, but since you're sending a probe right now, there's no need to worry about that. Also, if you didn't bring a heatshield on the Eva lander, it's not going to land 9/10 times. Eve's atmosphere is many times thicker than Kerbin's and you will experience more brutal heating effects for longer than you would on Kerbin.

Because Duna has an atmosphere, it takes less DeltaV to land on it than it does to land on the Mun. Your parachutes will help you, but you will want to tweak them to deploy as soon as possible (just not so high up that they burn up). Unless you went crazy  and brought upwards of a dozen chutes, you will need to use that rocket engine, but with the huge fuel tank you've gone with, you shouldn't run out of fuel. If you feel confident landing on the Mun, you should be ready for Duna. The planet's atmosphere is so thin that you shouldn't need a heatshield unless you come in at a crazy high speed, which won't happen as long as you insert the lander into orbit before landing.

One last suggestion regarding designing robotic landers for Duna/Eve; Make them as light as possible. The lighter they are, the less power you need to get them there, the easier they are to control, and the easier they are to land. If you give me a few hours I'll see if I can either dig up one of my Duna landers from an older version of KSP or build an example one for you if it turns out that I accidentally deleted my older installs.

/lecture

Edited by pTrevTrevs
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i think your landers should get the job done easily. they'd probably have enough fuel to not only land on ike/duna but also return to orbit and transfer back to kerbin.

the duna lander could have used some more parachutes (especially some drogue chutes) for a pure parachute landing. not sure if that will be possible - but a "semi powered" landing (ie do some retro burning to get to parachute safe speeds and to reduce the speed of the final touchdown) should work all right.

heat shields are generally not required for duna in my experience. the lander probably has enough heat resistance to survive direct aerocapture from transfer. using the same lander for ike is actually a bit overkill. Ike has pretty low gravity, so a terrier engine would have been more than enough. 

your safety margins are pretty large with the amount of fuel you brought along, so i think your mission will work as planned.

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Hrm. Assuming I can get one of them off the ground and back to kerbin, I might consider it...the Ike lander doesn't need its parachutes so it might even be able to land at home. I think I'd be more likely to use excess fuel to go biome hopping, though.

It is good to know that I likely have enough fuel to do what I initially intended; anything else is just gravy.

Still unsure about followup manned missions. Here's the flight path:

 

path.png

I'm a bit concerned that the position of the planets when it arrives will make a followup difficult -- kerbin might 'catch up' with duna by then, and going by the wiki Duna is best approached from behind if you want to avoid long transfers or large fuel costs.

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Yeah, you will have to wait some time for a follow up. In the screenshot above, it's already too late for the most efficient transfer. It may be more effective to launch more missions a few days prior to when you want them to depart for duna, and then schedule the transfer burns one orbit apart. 

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