Doing the Jool 5 challenge with deadly re-entry and lathe aerobrake

[sedativechunk]

I've been planning in my head how to do the Jool 5 challenge on these forums. In fact, I've paid several visits to Jool already and my last mission I successfully visited two moons in one trip. I was thinking of taking on all 5 moons with deadly re-entry. I've already used it and Jool itself is far enough from Kerbol to not develop heat as far as aerobraking on Jool. The real challenge is with Laythe! I wanted to see if anyone here has gone to Laythe (or done the Jool 5) with deadly reentry.

I've lost two ships with deadly reentry attempting aerobraking on Laythe. For one reason or another, I'm always coming in stupidly fast when I visit Laythe (I'm talking velocitys of 5,000+ m/s). If I go JUST to laythe, I can manage to land and return from Laythe by burning retrograde, but to do the Jool 5 challenge, bringing all the extra cargo along and additional laythe lander (which is the lightest SSTO I've ever built with jet engines), I don't see it being a viable option for me to burn all the fuel to get in orbit. IT would take too long and too much fuel.

Has anyone aerobraked a huge vessel around Laythe with deadly re-entry? Furthermore what kind of velocities do you all have coming into Laythe? Every time I visit I end up having to burn fuel for 25+ minutes shedding off thousands of m/s of Delta V. Laythe is hard to get to and tricky to orbit. Even if i was cable to implement heat shield(s) on my entire ride to Jool, the velocities are too high, the heat shields would get too hot and/or the kerbals would experience too much g force. Any thoughts how how to approach this?

For now, I'm thinking I'm going to attempt the challenge without deadly re-entry first, but it will be llooooong mission so I wanted to revisit the idea of using the deadly reentry mod again!

[Taki117]

Might I suggest using Tylo for a gravity assist? I know it sounds wiered but if you aero break around Jool, and then set youself up to come in ahead of Tylo that will change your orbit, and maybe then you can aero brake at Laythe. Also, instead of trying to aero brake your whole ship why not detach just the lay the craft and aero brake that?

[Kryxal]

I wonder, what sort of angle are you coming in on Laythe at? For a direct approach, the logical solution seems to me to be to come in with your periapsis on Laythe's orbit, and fiddle with transit times to catch Laythe there. That would let you effectively knock off a good 3 km/s effectively.

[Yakky]

Another way to lose some speed when arriving at the Jool system, at least in theory, is to do the opposite of a gravity assist: a gravity deceleration. Set up your arrival encounter to take you very close to Tylo in the retrograde direction (the opposite direction to its orbit around Jool). Passing close by Tylo in the reverse direction will bleed some speed off your vessel.

The challenge with this is that it will probably result in you orbiting Jool in a direction opposite to all the moons. But this may not be a big problem if you can get yourself flung far out into the outer reaches of the Jool system via a highly elliptical orbit. At the apoapsis of your highly elliptical orbit, when you have very little velocity, a small correction burn would turn you around and set you up in the proper direction again. Then you could use a couple small gravity assists to get you where you wanted to go.

This is all in theory. I've never done it. In theory you could shed more than 2000 m/s this way, but in practice I have no idea how much you could actually shed. Hopefully you could lose enough speed that an aerobraking maneuver would then be survivable afterward.

Another option is to carefully align your arrival so that you can take advantage of two aerobrakings, one in Jool's atmosphere and the other in Laythe's. That way you don't need to lose as much delta-v in either one and the forces on your spacecraft will be lower. But lining that up will be tricky.

Edited October 16, 2014 by Yakky

[xtoro]

Another way to lose some speed when arriving at the Jool system, at least in theory, is to do the opposite of a gravity assist: a gravity deceleration. Set up your arrival encounter to take you very close to Tylo in the retrograde direction (the opposite direction to its orbit around Jool). Passing close by Tylo in the reverse direction will bleed some speed off your vessel.

The challenge with this is that it will probably result in you orbiting Jool in a direction opposite to all the moons. But this may not be a big problem if you can get yourself flung far out into the outer reaches of the Jool system via a highly elliptical orbit. At the apoapsis of your highly elliptical orbit, when you have very little velocity, a small correction burn would turn you around and set you up in the proper direction again. Then you could use a couple small gravity assists to get you where you wanted to go.

This is all in theory. I've never done it. In theory you could shed more than 2000 m/s this way, but in practice I have no idea how much you could actually shed. Hopefully you could lose enough speed that an aerobraking maneuver would then be survivable afterward.

Another option is to carefully align your arrival so that you can take advantage of two aerobrakings, one in Jool's atmosphere and the other in Laythe's. That way you don't need to lose as much delta-v in either one and the forces on your spacecraft will be lower. But lining that up will be tricky.

Thanks a lot man.... now I have to start a new flight just to try this out and see if it works lol

[Jouni]

This is what your Jool approach should look like:

First get your orbital inclination roughly the same as Laythe's. Then lower your Jool periapsis to the same level as Laythe, while orbiting in the same direction. This makes you approach Laythe from retrograde. Finally get an encounter with Laythe. Tweaking both radial and prograde of the maneuver node will keep your Jool periapsis the same, while changing the time of closest approach.

I tried this with a not-so-optimal transfer to Jool. My highest surface speed during aerobraking was slightly under 2900 m/s, which is clearly survivable.

[technion]

I did the Jool 5 with DRE, and ended up doing a direct capture to Tylo. It only took around 1100dv to capture there.