Returning from Eeloo?

[627]

I recently took my whole space center on a class trip to dres. This is the school bus:

And we even did some science, not just astronaut training. Two science bombs and a satellite came with us:

Here we are at Dres, but herding all those kerbals for a class foto is hard.

Ok, enough eye candy, here comes the problem. The return.

From Dres, I ended in the kerbal system with around 4k m/s, way too fast for a safe aerocapture. I thought that heat shield will help and those outer tanks/engines will just explode like it does on my ION probes on eve.

Well, they did explode but the rest of the ship, too. The end was a catastrophic failure, everyone dead and the game was more or less game over. I cheated some fuel on the empty tanks and I needed around 2000m/s or so to brake enough for not exploding in the atmosphere but get captured.

So here's my question, I plan my next class trip to Eeloo. I wasn't there since 0.90 so it's time. Getting there shouldn't be that big of a problem and maybe this time I'll take some mining stuff with me, just to be sure.

But how to come back? How fast will I be when I came back from there? And how to brake without carrying an insane amount of fuel there and back?

Is there a way with some gravity assists or with a pit stop at another planet? Or do I only need to drop the engine pods and that Heatshield will do it? Are stacked Heatshields a thing?

[DeMatt]

That's a very stylish design you've got for that Dres ship. But I think you need to start thinking in terms of a multipart mission, instead of an all-in-one:

1. Kerbin SSTO (or even just a big conventional rocket): Takes kerbonauts from KSC to low Kerbin orbit. Does not travel to Eeloo.
   
2. Interplanetary carrier: Takes kerbonauts from LKO to low Eeloo orbit, carrying satellites and landers as necessary.
   
3. Eeloo personnel lander: Takes kerbonauts from low Eeloo orbit to surface. May also ferry fuel from the miner, if you trust your piloting.
   
4. Eeloo miner: ISRU facilities.

I'd also think about switching over to LV-N engines and using the Mk3 Liquid Fuel fuselages. Poodles are efficient, but LV-N's are better - and on a voyage of this magnitude efficiency counts.

You can try for gravity assists, but because they require you to transfer to other planets before you head for Kerbin, they will extend your travel time by a lot.

[Evanitis]

they require you to transfer to other planets before you head for Kerbin

They do? What's the matter with the Mun? It has gravity, so it can slow you down on the way home.

[627]

oops, my fault.

This is the whole dres rocket:

The Lander/Return vehicle is only used in dres orbit. That thing has around 3200m/s delta-v So I thought that's enough for one landing and returning to kerbin. And it was!

Just not enough for the insane braking I had to do.

I think I won't have problems getting to eeloo and back. Just stopping at the end is my problem. Well not stopping but not exploding

[TheXRuler]

I once had a similar problem when I was aerobraking at Duna after an extremely aggressive ~85 day transfer (life support on my duna mission was running out so I spent I think around 14km/s to get there ASAP). I was arriving hitting Duna's atmosphere at ~8km/s and either not slowing down enough or burning up. The problem was I did not have enough dV to slow down after a small aerobraking manouvre, so what I ended up doing was a massive braking burn, like 85% of my remaining fuel, timed so that I hit the atmosphere at the end of the burn. By doing that I managed to slow down enough so that I could aerobrake properly. Also, due to the oberth effect, and me going very fast at the time of the burn, I managed to loose a substantial amount of speed before reentering. Of course this technique is not very viable if you only have a small amount of fuel left.

A gravity assist with the Mun to slow you down relative to kerbin might be possible, although it will only have a rather small effect, due to your high relative velocity and the low gravity of the Mun. It might however be worth it to get a gravity assist from the Mun to put you on the correct reentry orbit, and thereby maybe saving some fuel for the initial braking.

Also, if you didn't do that anyway you might try aerocapturing into an eccentric Kerbin orbit, then slowly lowering yourself ever farther instead of trying to loose 4km/s at once. Kerbins escape velocity is about 3.4km/s so you really don't have to be very aggressive for your first approach.

[Jouni]

This is what my standard Kerbin return looks like these days:

A good encounter is essential. If your inclination is 0 degrees and your apoapsis/periapsis barely touches Kerbin's orbit, you should never have to lose more than about 1200 m/s during the first aerobraking pass. This guarantees capture, and the rest of the speed can be bled off during subsequent passes.

Ship design is also important. Small radially attached parts are usually the first ones to explode, so you should avoid exposing them to the airflow. Placing them behind an oversized heat shield in the return capsule is a good idea. Engines, radiators, and large fuel tanks withstand reentry heat quite well.

Even a small burn can make the difference between capture and destruction. Reentry heating is proportional to v^3, while drag is proportional to v^2, so the burn should ideally be made just before the heating gets serious.

[Sharpy]

They do? What's the matter with the Mun? It has gravity, so it can slow you down on the way home.

The matter with Mun is that it's small, and as result the boost/braking it gives is lousy. Sure it's good for the final capture, but it will give you maybe 200m/s of savings.

[cantab]

But how to come back? How fast will I be when I came back from there? And how to brake without carrying an insane amount of fuel there and back?

Is there a way with some gravity assists or with a pit stop at another planet? Or do I only need to drop the engine pods and that Heatshield will do it? Are stacked Heatshields a thing?

The speed you'll come back with is about the same as the speed you leave with after finishing your Kerbin departure burn, which is the same as your LKO orbital speed plus your burn delta-V. That's going to be at about 4000-4500 m/s.

Anyway three ways to slow down:

Powered captures are simple and reliable but of course fuel-hungry. If you carry equipment to mine at Eeloo this could work well.

Aerobraking costs no fuel, but is of course dangerous. Do keep in mind your initial aerobrake needs only get you into a closed Kerbin orbit, you don't have to go right into LKO on the first pass.

Gravity assists cost next to no fuel and are safe, but tricky to set up. You can use Eve or Kerbin itself for this, and what you want is the assist to put you into a more circular orbit round the Sun that crosses Kerbin's orbit at a shallow angle or just touches it, and preferably secures you a Kerbin encounter again after a small number of orbits round the Sun. Then your second Kerbin encounter will be at lower speeds permitting an easier powered capture or safer aerobrake. For gravity assist work I always recommend Precise Node.

[AaronLS]

I'm with Jouni. Don't try to do it all in one oass. Don't dip so deep into atmosphere, but burn at periapsis. You'll get a better oberth effect than a regular burn above 70km.

This is not much help now, but I use real chutes mod so can configure chutes to deploy at any altitude. Deploying one or two of them above 60km even at high speeds is usually safe. I'll have an action group configured to cut them once I'm happy with the amount of speed I've lost, just so I can continue downrange and properly descend near space center.

[Geschosskopf]

But how to come back? How fast will I be when I came back from there? And how to brake without carrying an insane amount of fuel there and back?

Is there a way with some gravity assists or with a pit stop at another planet? Or do I only need to drop the engine pods and that Heatshield will do it? Are stacked Heatshields a thing?

You have several options ranging from flat-out cheating to getting artistic.

1. Turn Down Reentry Heat

This can be done in existing games by editing the save file. Up near the top is a section called Difficulty and one of the last lines in it is reentry heat. Given that the atmospheres of other planets are borked at present, with way too much density way too high (so they're effectively oceans, not atmospheres), this is actually just compensating for a bug, not wimping out, so don't feel bad about it. 20-30% is probably about all you really want. Problem is, Kerbin's atmosphere actually does act like an atmosphere instead of an ocean, so such a low setting makes Kerbin reentries a doddle, at least at low speeds like from Minmus/Duna. From Eeloo, maybe this would still be a problem.

2. Turn Off Reentry Heat Via Debug Menu

Check the box that says "Ignore maxTemp". At least until you're done with this ship.

3. Get Crazy with Heatshields

Stacked heatshields are indeed a thing, as is making a huge, unwieldy, laggy construction wide enough to cover a wide ship. This is of course combined with airbrakes. All this is hugely silly IMHO (especially the airbrakes) and just points up the flaws in the game. So this strategy is just another workaround no more or less "cheaty" than using a lower heat setting.

4. Gravity Braking

Make retrograde flyby passes on 1 or more planets between Eeloo and Kerbin (so you leave Eeloo when the window for one of those planets comes up, not on the Kerbin window). There's probably a way to plan this all out perfectly in advance so you can just bounce straight to Kerbin but I have no idea how to do that. If you don't, either, then what will happen is you'll get kicked into a solar orbit with a Pe somewhere in the vicinity of Kerbin's orbit (hopefully no lower or you haven't helped yourself) and an Ap near the planet you flew by, instead of all the way out at Eeloo (which means you'll hit Kerbin slower). Then you'll have to wait a while (possibly quite a long time) and burn some to hit Kerbin from there or do another braking pass at another planet closer in. And once you're in Kerbin's SOI, do a final braking pass off Mun if you have the chance.

5. Do it Like Moho

Leave Eeloo at one of its nodes with Kerbin's orbit and burn so your Pe is on Kerbin's orbit and you do NOT have a Kerbin encounter. When you get to this Pe, burn retrograde to pull your Ap down to the vicinity of Duna's orbit, which will make you hit Kerbin at about the same speed as coming home from Duna, which really isn't any worse than coming home from Minmus. Then just wait several orbits (which will be longer than Kerbin's year) and/or tweak as necessary until you get an encounter.

6. A Combination of #4 and #5)

This is probably the what will end up happening if you try #4 by itself.

That that every option that doesn't involve flat-out cheating is going to require rather more dV for the return trip than you're used to due to having to burn off some of your speed, maneuvering for braking passes, and/or lugging an immense heatshield around.