Need some assistance is getting out to Vall.

[capi3101]

Howdy, all.

I'm going to be doing an entry soon for the Vall Exploration Challenge. Biggest problem I've got right now (as per my signature's salad bar) is that I've never been out towards Jool before. Now ordinarily, I'd just play it conservative and build a transfer stage that has double the amount of delta-V that it would take to get out there according to the delta-V maps (~14,000 m/s), but the challenge in this case has a mass limit that I'm adhering to, and the amount of payload mass I'm calculating is quite a good deal lower than I'd like it to be (just shy of fifty tonnes, but a I know I'll be hauling 35 tonnes of probe landers with me, that leaves precious little for the obligatory "manned lander with as many Kerbals aboard as you can muster" requirement. Especially if I want to bring along a 'hound for good measure.

So, Joolian veterans:

1) How much delta-V does a trip to Vall and back really take? 1915 for the Jool intercept, 2630 to orbit Jool at 150km with inbound aerobraking possible, 1970 for the Vall intercept, then 790 for a 15k Vall orbit - that's what the delta-V map says - for 7,305 total. Since I can aerobrake inbound, does that become 4675 instead? The trip back is also really getting me; I've read you can make it back to Kerbin with just 2800 or so.

2) How should I go about handling the transfer? I've heard you can aerobrake at Jool to put your orbit near Vall's; how much delta-V does that save?

There's too much variance in the numbers - I'm getting anywhere from 7500-14600 m/s; the lower it is, the more payload I can bring. So what exactly should I plan for? Any and all assistance is appreciated.

And before anyone says anything, I don't use Mechjeb and won't until I return a Kerbal from Eve. I do however use KER and Protractor, and I am aware of the aerobraking calculator website.

[700NitroXpress]

Well, does the lifter have weight requirements? because I have two kinds of options for you. One uses Ion engines, the other uses nuclear engines.

[700NitroXpress]

This lander can get a kerbal on and off any planet or moon, including Eve. Total mass, 38.23 tons. If you refuel it, it can be reused and it doesn't require much fuel to do so. Since this lander was designed for Eve, you can get rid of half the craft as far as the lower aerospike engines go. That cuts down on the weight. If you don't stage the craft, it should still be capable of getting of of Laythe and Tylo with no problem. To do this with more kerbals, you could use a probe body on the top and add four seats to it. Or a big metal plate and 6 - 8 seats and it should still work.

Then I would use this craft and take off the jet engines and asparagus the other engines as nuclear engines. I would have one on the large tank, and two on the last set of asparagus. That way, the rest will be slack tanks for fuel only and refueling of the lander.

Then I would attach that lander and transfer stage configuration to a lifter like this one that can easily lift over 200 tons into orbit with fuel left over for the Kerban escape burn.

The lifter is everything below the large decoupler next to the nuclear engines.

But that's just how I would do it. This last image is of my Papa Dragon ship and lander, it made it to Jool and landed on Laythe for the first test flight. Total weight 144.33 tons, lifter not included. It did not have enough fuel to get off of Laythe or return to Kerban, but it was just a limitation test flight.

Here is the result of the Papa Dragon

The next option is to do something like what I have in the second image. Make a lightweight lander and instead of using lots of delta V, use Ion engines. The amount of Ion engines and Xenongas on the lander shown had enough fuel to Orbit Jool and Laythe and have about 1/4 gas remaining. If you bring Xenongas in a 3:1 ratio of Gas to Engines you'll have enough for a trip around all of the moons. If your craft is larger than the one in the second image above, double the engines and solar arrays. Solar arrays gather less energy the farther out you get, like they should.

Here is my first orbit of Jool with the little lander craft and a fuel reading during the orbital burn to a Laythe intercept.

Here's the craft in action.

Edited November 9, 2013 by 700NitroXpress

[Tex_NL]

If you've never been to Jool before why not send a pathfinder first? The dV requirements for a small unmanned probe are identical to those of a megaton multipart ship. The most Kerbal solution to your dilemma is to just go for it and see what happens.

[capi3101]

Well, does the lifter have weight requirements? because I have two kinds of options for you. One uses Ion engines, the other uses nuclear engines.

No, there are no restrictions on the lifter (for once). Just the total mission payload - I don't play with Kethane, so I'm limited to a total mission payload of 320 tonnes. Sounds like a lot until you consider that the fuel to get out to Vall has to be included in that figure.

If you've never been to Jool before why not send a pathfinder first? The dV requirements for a small unmanned probe are identical to those of a megaton multipart ship. The most Kerbal solution to your dilemma is to just go for it and see what happens.

I happened to do this last night in a different save game - I set up a craft that would deliver six satellites to Jool, with the intent that each satellite would then make its way to one of Jool's moons (except for one, which would remain in Jool's orbit). The original craft would then plunge into Jool's atmosphere. My first real try at using Protractor. I think I mucked it up - burned with theta and adjusted phi at zero along the prograde until the closest pass number for Jool started going back up again, then killed it - my apoapsis at that time was somewhere in the neighborhood of Dres's orbit, with no Jool encounter indicated at all...

I do understand that the most Kerbal solution is to just go for it; I'd still like a target range of figures that doesn't vary by over 7,000 m/s.

[700NitroXpress]

I'm actually doing this challenge right now since I checked it out after you're post. 320 tons is gravy, my mothership is on the way, apollo setup. I don't use any mods at all and no 3rd party information either, so this is fun. My Leviathan lifter unit can get everything into orbit as long as it doesn't exceed 250 tons because then structural stability becomes an issue.

[capi3101]

And that's helpful to me...........how?

My apologies for the 'tude; it's been a rough day.

[700NitroXpress]

And that's helpful to me...........how?

Well, I posted pictures of some of my other ship above and I'm using the lifter attached to the Papa Dragon. I explained my thought process of how I would do it with a combination of those ship ideas and that's the inspiration I'm using for my craft.

So here's some "help" for the challenge.

1. First build an extremely lightweight lander unit for your crew. Make sure it has enough power to to fly well on Kerban, if it achieves orbit than you're good to go. Vall has roughly the same gravity as Moho, so about double the gravity of Mun. If you test your lander on Mun and you can land, take off, get back to Kerban, with just the lander alone after you transfer it to the Mun, then that should be a good benchmark. You can build landers like this with the really small engines, and the 180 liquid fuel tanks and a command seat on top of the lightest probe core.

2. If you plan on doing apollo style with the lander, don't put any RCS on the lander to save on weight. Instead put only a 750 RCS tank on the main ship at maximum. Dock the main ship to the lander with the RCS. Or don't dock at all and space walk instead. You shouldn't take an extra lander back with you, it's just dead weight.

3. I used 3 nuclear engines total to get my craft from Kerban to Jool. One of the double long grey tanks and the other two were on the thin long tanks that were placed on the side. I then used the slack tank asparagus staging method that is in the lifter in the images above, to stage the slack tanks that were feeding the nuclear engines. The 3 engines were capable of pushing a 150 ton craft from Kerban to Jool with 5030 units of liquid fuel. One 1440 tank, one 720 tank, and 8 * 360 tanks. So there's an idea of fuel consumption for the engines I had and the total weight they were pushing. That's a one way trip fuel load, so you double that and add about 720 more and there's a round trip. 10,780 units of delta V to make a round trip to Vall and back to Kerban, with perfect orbits and landings, for a 150 ton, initial weight craft.

Hope this is helpful to you.

Edited November 9, 2013 by 700NitroXpress

[Kasuha]

1) How much delta-V does a trip to Vall and back really take? 1915 for the Jool intercept, 2630 to orbit Jool at 150km with inbound aerobraking possible, 1970 for the Vall intercept, then 790 for a 15k Vall orbit - that's what the delta-V map says - for 7,305 total. Since I can aerobrake inbound, does that become 4675 instead? The trip back is also really getting me; I've read you can make it back to Kerbin with just 2800 or so.

2) How should I go about handling the transfer? I've heard you can aerobrake at Jool to put your orbit near Vall's; how much delta-V does that save?

I won't tell you exact dv because it varies a lot but you can get some estimates from dv maps.

Aerobraking in Jool's atmosphere is not optimum approach, there are at least two options which are better.

Option 1: aerobrake in Laythe's atmosphere to get your PE at Laythe's level and AP at Vall's level. No significant dv over the Jool intercept needed, except for corrections and then circularizing at Vall

Option 2: gravitational slingshot from Tylo getting AP on Tylo's level and PE at Vall's level. Again no significant dv over intercept and circularizing.

In both cases you may need to wait a few orbits to get Vall intercept and you may need to perform some small corrections to get it happen soon enough.

I'm not sure which of the two is better but I believe either is better than aerobraking on Jool and then pulling up to Vall. The slingshot may be easier to prepare in advance, aerobraking is always tricky.

Edited November 9, 2013 by Kasuha