Planning a Jool-5-ish mission

[michal.don]

Hi guys,

as the title says, I'm planning a mission to Jool and his (hers?) five moons. I believe I'm comfortably capable of designing the landers for the moons, but I'm not sure about the mothership, and the overall mission flight path. Several possibilities came to my mind:

1 - Park the mothership outside of Tylo orbit, and add transfer stages to the landers, which then continue to their destinations and come back

2 - Start with the mothership in a high orbit, visit the outer moons, then move it to low orbit and visit the inner ones (possibly inner first and then move to higher orbit)

3 - Design the mothership so it can transfer from moon to moon and the landers go only to surface and back

4 - Park the mothership into an eliptical orbit with Pe around Laythe and Ap around Pol (which could be tricky because the moons could mess with my orbit).

I sent plenty of satelites and even a few crewed missions to the Joolian system, but only to visit a moon or two, so I never attempted anything this large. Which approach do you think is the best? How much delta-V should I pack for moving in the system? Is there another big problem or challenge that I didn't think of?

Thank you for sharing your experience,

Michal.don

[Zhetaan]

3 is the best, mass-wise.  1 requires you to pack transfer stages for five landers, which means you have to pack additional dV into the mothership to move the transfer stages.  2 is better, but if you're moving the mothership around anyway, why not just go all the way and use the mothership to move within the system?

Another possibility is to use an interplanetary tug to get everything to Jool, but then your 'mothership' is, in turn, an intraplanetary tug.  That way, you can, in essence, spiral in to the system (or out) carrying only the mass of what you need to visit the moons (are you discarding landers as you go?) and avoiding the essentially parasitic mass of your return vehicle.  Then you can return to the return vehicle and return to Kerbin.  Be sure to incorporate elements of 4, too--you want to encourage the moons to mess with your orbit, if the end result puts you where you want to be.  Free dV is the best dV.

Another option is a bit like 4: you come in with a low Pe to Jool, and as you capture, you toss away landers when your Ap is at the right orbit.  You can set this up as a multi-burn manoeuvre, going round Jool before burning for a lower Ap (and also to let the alignment favour a lander's transfer window), and it saves you the dV of having to raise and lower your landers' orbits to go wherever they need to go.  Then you only need them to pack the fuel to come back.

Edited June 14, 2016 by Zhetaan

[Wcmille]

Are you bringing an ISRU and Drill? How long are you there for? Does game time matter to you on this mission?

[Warzouz]

I did a mission like that back in beta 0.9. I chose a 500km orbit around Laythe (mostly because the view was beautiful). I had 6 landers (mostly of the same design. I assembled the station directly around Laythe from 13 different flights (6 or them were Orange tanks). I explore each moon 2 times (and had the capacity of doing it 4 times)

 

In 1.0, I used a different strategy and send a smaller space station, capable of moving from moon to moon, but I didn't complete the Jool 5.

 

[michal.don]

10 hours ago, Zhetaan said:

Another option is a bit like 4: you come in with a low Pe to Jool, and as you capture, you toss away landers when your Ap is at the right orbit.

Oh, that sounds like an interesting idea - I didn't think of that. That way the landers don't need to have the fuel for the journey to the moon, but They all eventually need to come a long way to a low orbit to meet the mothership, I need to find some numbers how much delta-v is needed from each moon. Thank you

3 hours ago, Wcmille said:

Are you bringing an ISRU and Drill? How long are you there for? Does game time matter to you on this mission?

Well, I am currently building some basic infrastructure in the Joolian system, so refueling is a possibility, on the other hand, I would like to fly the mission without having to refuel each ten minutes (so yes, game time is an issue, this also rules out a big ion ship that has LOTS of delta-v, but the burns are twenty minutes long). Regarding the mission time - this isn't such a big issue. I think I'll leave the Joolian system when a transfer window to Kerbin appears, which should give me enough time for the moon-hopping.

1 hour ago, Warzouz said:

I did a mission like that back in beta 0.9. I chose a 500km orbit around Laythe (mostly because the view was beautiful). I had 6 landers (mostly of the same design. I assembled the station directly around Laythe from 13 different flights (6 or them were Orange tanks). I explore each moon 2 times (and had the capacity of doing it 4 times)

Wow! This thing is beautiful

While I'm planning to build a proper infrastructure in the Joolian system later on, this time I'm looking for a more conservative mission profile - one ship (even though a bit larger than I'm used to) leaves LKO for Jool, does its mission, and one ship (presumably without the landers) leaves back home.

1 hour ago, Warzouz said:

In 1.0, I used a different strategy and send a smaller space station, capable of moving from moon to moon, but I didn't complete the Jool 5.

That looks like the sort of thing I'm going for. I'll read the whole article you wrote later today. It looks to provide me the answer to "in what type of vehicle wewill do this", but I'm still a bit unsure "HOW we will exactly do this"

Thanks a lot,

Michal.don

[Warzouz]

Anyway, this must be your bible

[cantab]

To be honest it completely depends on your designs and your piloting skills. But a few options to pick from for each moon - and they don't need to be the same for all of them.

Mothership in low orbit round the moon. This minimises delta-V needs for the lander, but it means hauling the mothership down to that low orbit then back to escape the moon.

Mothership in elliptical orbit round the moon. This saves delta-V needs for the mothership, but adds them to the lander, but the lander probably needs less fuel.

Mothership in orbit of a different moon. Even less delta-V spent by the mothership, even more by the lander.

Separate support vessel in low orbit round the moon while the mothership is in a different orbit. It could be a simple fuel depot, or a full-on orbiter spacecraft for the lander to dock with. I think that overall this would probably minimise fuel needs, but adds a layer of complexity.

Forget separate motherships and landers, just land the whole dang thing everywhere and use ISRU to fuel up Might want some expendable boosters for Tylo.

Edited June 14, 2016 by cantab

[michal.don]

5 hours ago, Warzouz said:

Anyway, this must be your bible

Great, like I don't have enough delta-v maps on my wall already  Just kidding, this will be extremely helpful, thank you.

 

18 minutes ago, cantab said:

But a few options to pick from for each moon - and they don't need to be the same for all of them.

Yeah, It seems that almost everbody thinks it will be best to bring the mothership to each of the moons, so that will probably be the way I'll fly the thing (maybe with the exception of Pol - the delta-v to get there isn't much and the gravity is very low, so maybe I'll visit it from another moons orbit). Another thing came to my mind - it could be on a quite tight time budget, but why bother getting the mothership to orbit? I could just get i to low fly-by, detach the lander a few hours prior to the periapsis, and go ahead for landng. Then I'll do the flag-planting and science on the surface, and take off to meet the ship when it closes in. I think it shouldn't be a big problem on the lower gravity moons (of course I won't be doing that on Laythe and Tylo, I'm not that crazy  ). Do you think it's a viable option, or the savings of delta-v aren't worth the nerve-wrecking manouvers and possibility to be forever stranded far away from home?

Thanks,

Michal.don

[Ozymandias_the_Goat]

as @Zhetaan said, I would recommended using Tylo for a gravity assist to slow down. Then, at Pe jettison the lander and land it on Tylo. After that, fly an ascent stage to Rendezvous with the Mothership now in Jool orbit. You could also park in Orbit around Tylo, and make that your "base of operations" . This vid might help:  

 

Jool part starts at 2:35. It's a bit fast.

[Zhetaan]

43 minutes ago, michal.don said:

Another thing came to my mind - it could be on a quite tight time budget, but why bother getting the mothership to orbit? I could just get i to low fly-by, detach the lander a few hours prior to the periapsis, and go ahead for landng. Then I'll do the flag-planting and science on the surface, and take off to meet the ship when it closes in. Do you think it's a viable option, or the savings of delta-v aren't worth the nerve-wrecking manouvers and possibility to be forever stranded far away from home?

I'm not certain I understand your idea here.  If my interpretation is correct, then it won't work very well.  Your mothership and lander will both fall towards your target body.  Being at the same height for the entire fall, they each will gain the same amount of speed and will arrive at the same time.  The mothership will then begin its escape; the lander needs to slow down to approach, land, take off again, rendezvous, and match velocities with the mothership.  By this time, the mothership is gone.  If you undock a few hours out from Pe, you can gain some time by burning to increase speed, but that is countered by needing to burn again to shed that speed once you reach your target.  Total time saved will be measured in minutes, at best.

That being said, it is possible to do something like what you want.  The idea is essentially an exaggeration of orbital error:  if you launch two ships from Kerbin to Jool within five minutes of one another, their arrival times can be days apart.  A miniscule amount of that has to do with optimising the transfer window, but the bulk of it has to do with error in the burn.  Miscalculate your direction by an arcsecond, or hit the MECO button a tenth of a second off, and you might not even get the encounter; hence mid-course corrections on most interplanetary transfers.  It can be very sensitive; for an example, launch one ship to Jool and after the burn and decouple something from it at near-zero force.  The .01 metres per second of drift isn't much but it adds up to a lot of metres over the roughly twenty-five million seconds it takes to get to Jool.

Provided you undock your lander and give it the push it needs to be sure it arrives first, you can certainly pull this off if you give yourself enough time for the error to build up.  The point of entering a moon's SoI is not enough time.  On the other hand, I'm not certain whether you're doing this for the official Jool-5 challenge; if so, be sure that sending what amounts to a flotilla is not against the rules.

[michal.don]

12 hours ago, Zhetaan said:

 If my interpretation is correct, then it won't work very well

Yes, you got my idea. And you're right, it might not be the best one. The burns to get there comfortably first would probably need to be quite costly, so it's pointless.

Thank you all for your answers,

Michal.don

[ElWanderer]

My approach (pre-v1.0) was to take two landers and a nuclear tug. Lander one was a spaceplane to visit Laythe. The second had two stages: Tylo descent and Tylo ascent. The ascent stage was then used to land on all the other moons. For Pol and Bop, the lander was short-fueled (Tylo ascent is about 2750m/s, Vall is about 2400m/s in total, the others you only need 600m/s each) so that the tug used less fuel moving them about. I parked the mothership inside of Tylo's orbit, but had to go into Tylo orbit to rendezvous with and refuel the tug after over-estimating the delta-v that the tug had when carrying the full lander stack.

If you leave anything in a highly-elliptical Jool orbit, bear in mind you'll need to keep checking for encounters and make course corrections as necessary to avoid collisions/getting flung out of the system.

[michal.don]

Thank you all very much.

The mission is now under way, the ship is fully fueled and waiting in a LKO. It is a monstrosity, probably the biggest and most expensive thing I've ever launched.

It's probably a bit over-engineered, but this is my first mission of such size, and better be safe than sorry.

Michal.don