how can i achieve retrograde orbit around sun?!

[idoporges]

took on a mission to put a satellite around the sun, realized the orbit is basically jool's orbit backwards
it just takes a ridiculous amount of dv i think im doing it wrong because this has a 270k reward on this it shouldnt me that hard.

what i've been doing so far - burning from kerbin orbit until my AP is touching jool's orbit, waiting until i reach AP then burning retrograde until orbiting the opposite direction (that takes almost 9000 dv!). i technically can complete this using ion engines but it would take FOREVER. how must i approach this?

Edited January 17, 2017 by idoporges

[Hodari]

Ion engines are probably going to be the way to go for that one.  You might also consider raising your Ap even higher than the final required orbit, doing the retrograde burn, and then dropping it back down and see if that would be more efficient, but either way, it's going to take a LOT of dV to do this one.  Just set up the maneuver, start your burn, turn on physics warp, and go afk for a while or watch youtube or something while waiting.  Might take a long time, but it's actually a pretty easy contract otherwise.

[DD_bwest]

how long do you have to complete it?   just wondering how much time you have for using gravity boosts or even heading to the far reaches of the suns SOI

 

either way this contract will take a large amount of deltav and a good amount of time

edit: also i would probably go nuclear, cause at that distance from the sun power isnt as easy to come by

Edited January 18, 2017 by DD_bwest

[Starman4308]

How I'd approach it with limited time:

Plot a trans-Jool slingshot (capture in front of Jool, eject behind Jool), burning at peri-Jool to take advantage of the Oberth effect and minimize delta-V expenditure to get a retrograde solar orbit.

If you've got MechJeb, just tell it to execute the burn, and go do something else for the duration. Without that, I'd have gone insane playing at 6.4x scale with my penchant for low-TWR vehicles.

With unlimited time:

Transfer to Eve, slingshot to Kerbin, back to Eve, back to Kerbin, out to Jool and near solar escape velocity (may take a second Jool slingshot, I don't know), reverse course at apohelion, use Jool slingshots to brake to target orbit. This sort of gravitational ping-pong, combined with a bi-elliptic transfer for the plane change, leads to very efficient but not particularly quick transfers.

[Superfluous J]

In my experience, any sun-retrograde contract is ridiculously underpriced for what they expect you to do. I'd never take a 3-star contract involving the Sun.

[Kryxal]

I tried to get science from a flyby of Laythe in a BTSM modded game once, and ended up in a retrograde orbit ... it was a major oops for me, but you could maybe try something like that?

[Streetwind]

1 hour ago, Kryxal said:

I tried to get science from a flyby of Laythe in a BTSM modded game once, and ended up in a retrograde orbit ... it was a major oops for me, but you could maybe try something like that?

I think you might have ended up in a retrograde Jool orbit, but definitely not in a retrograde Sun orbit. Getting gravity assist from all bodies in the solar system isn't enough to reverse you direction of travel around the Sun, so a Laythe flyby alone certainly won't do it.

@idoporges - try one Mk3 Liquid Fuel Fuselage Short, one 'Nerv' nuclear engine, and no more than 710 kg worth of additional stuff (probe core, power, reaction wheels). That gives you 9300 m/s dV with an initial TWR of 0.34 that climbs towards 1.1 as the burn progresses. Will still take quite a while to burn through it all, but that's about the most reasonable thing you're going to get. It also means you only have to push 18 tons out towards Jool's orbit, which is important in staying economical enough to actually turn a profit from the contract.

[Draalo]

If you are going with ion engines keep in mind that solarpaneels are pretty useless that far away from the sun.

 

You ll need a couple of RTG per ion engine combined with as much batteries as possible.

[Sharpy]

Yep, the "cheap" way is to make a "braking slingshot" with Oberth maneuver against Jool, go way beyond Eeloo orbit, there burn retrograde for the correct periapsis, then burn at that periapsis for the right orbit.

Before you do this though, check the time. And the contract deadline. 70 years is short.

Then there's the expensive way.

Make the minimal probe fulfilling your contract.

Create a subassembly "booster" comprising of Dawn, Oscar B, two small xenon tanks. Bundle these boosters into at least 6 stages, though 15 is not overkill - it's gonna be an awful pancake, so you may want to autostrut it some.. Add a fuel cell battery to every 4th stage or so (one battery can run about 4 Dawns). Make sure to set fuel priority and crossfeed right, so that it behaves as asparagus.

Make a "booster" of LV-N and two or three Mk1 LF fuselages. Again, bundle that into some 4 stages (say, central + 3 radial pairs). Attach below the ion asparagus.

Pack that up in a fairing. Make a launcher of Mammoths, with enough spare delta-V to be able to give it a good boost towards Jool. Probably 5 Mammoths, each with 2 Kerbodyne tanks, again, asparagus staged. Possibly attach some Vectors to the Mammoths if your TWR falls short.

Launch, Hohmann to Jool, then Oberth maneuver into retrograde orbit. Keep observing fuel levels, dropping empty stages as needed. Get to the correct orbit through straightforward techniques and obscene delta-V expenditure.

[Kryxal]

8 hours ago, Streetwind said:

I think you might have ended up in a retrograde Jool orbit, but definitely not in a retrograde Sun orbit. Getting gravity assist from all bodies in the solar system isn't enough to reverse you direction of travel around the Sun, so a Laythe flyby alone certainly won't do it.

No, it was definitely retrograde Sun ... after all, it was a Laythe gravity assist OF a Jool gravity assist, and it was a royal pain trying to get that craft back to Kerbin in a survivable manner.

[idoporges]

thanks for the advice guys! i sent a science mission to minmus to unlock the nerv. gonna try oberthing into jool break and try to get rid of this contract.

to those who said not to use solar panels and use the bluetonium instead - this thing is way too expensive for this contract.

iv'e only ever tried gravity assists when i happened to notice an easy opportunity, gonna be hard. learning cliff here i come (again)!

Edited January 18, 2017 by idoporges

[CodaThePortalmaster]

I don't know why your trying to do it going prograde... anyways, just launch BACKWARDS from the KSC and once your in orbit burn retrograde at your farthest point from the sun until you achieve escape velocity, should be cheaper in delta v to do this too.

[Kryxal]

It may be expensive, but you're going to find a lack of power because it's so far out.  Honestly, I'd just push your apoapsis as high as you can afford time-wise and make the plane change WAY up there...

[idoporges]

46 minutes ago, CodaThePortalmaster said:

I don't know why your trying to do it going prograde... anyways, just launch BACKWARDS from the KSC and once your in orbit burn retrograde at your farthest point from the sun until you achieve escape velocity, should be cheaper in delta v to do this too.

no idea why i didnt do that....

i did say i thought i was missing something 

update: oh that comment below... my brain's not working today

Edited January 18, 2017 by idoporges

[Ohm is Futile]

27 minutes ago, CodaThePortalmaster said:

I don't know why your trying to do it going prograde... anyways, just launch BACKWARDS from the KSC and once your in orbit burn retrograde at your farthest point from the sun until you achieve escape velocity, should be cheaper in delta v to do this too.

Maybe your joke was wasted on me. If so, disregard the next part:

Spoiler

Doesn't matter which way you launch from the KSC, the issue with the orbit is that it is retrograde relative to the sun. Kerbin is going prograde, no matter how you launch you will escape in a prograde orbit. The only difference you can make is the size of your orbit once you escape Kerbin*. The part that works with this advice is burning retrograde at your farthest point, but not until you reach escape velocity, because you never will unless you use mods or the game glitches. You burn retrograde until your orbit goes in the other direction.

Given Kerbin orbits its star at over 9000m/s you will need at least 18 000m/s to reach an orbit in the opposite direction.

* If you escape Kerbin in its prograde direction, you will end up with a higher apoapsis and a slower orbit. If you escape in its retrograde, you will escape with a periapsis lower than Kerbin's. However, no matter which way you launch and which way you escape, you will be on a prograde trajectory.