Eve Return

[Deadmanrunning]

Hi,

 

I am reasonably new to ksp. I won't attempt this in my career save until the patch but I was wondering :

 

Just what does it take to return from Eve?!

 

I have a KSP calculator app, the dV to return  from Eve is massive. Do you have to set up a mining station to refuel? Or maybe an orbiting nuke tug?

Edited September 24, 2016 by Deadmanrunning

[Aegolius13]

On 9/24/2016 at 10:50 AM, Deadmanrunning said:

Just what does it take to return from Eve?!

Not sure what you'd consider massive, but it's definitely bigger than Kerbin, owing to Eve's significantly stronger gravtiy.  AlexMoon's launch window planner says about 1,800 ejection delta v from a 100km Eve orbit; that sounds right to me.  

 

On 9/24/2016 at 10:50 AM, Deadmanrunning said:

Do you have to set up a mining station to refuel?

Mining is definitely an option on Gilly.  Since its gravity is practically non-existant, you can build a big honking mining ship without worrying much about thrust.  And with the close distance to the sun, it's easy to power the mining equipment.  

However, it's pretty expensive to send a mining ship Even from Gilly's orbit down to low Eve orbit.  Even more so if you can't aerobrake effectively (my Gilly mining ship can't, but it's probably possible to design one that can).

Mining on Eve itself is, uh, not recommended -- unless you're seeking a particular challenge. Or, if you're planning to land anyway, it can make sense to bring mining equipment but ditch it for the ascent.  

 

On 9/24/2016 at 10:50 AM, Deadmanrunning said:

Or maybe an orbiting nuke tug?

Eve is definitely expensive enough it may make sense to go nuclear (at least on the return trip).  You can do tugs, or just place nukes on the ship you're sending to and from Eve.  But if you have a very small payload, chemical may still come out ahead.  

 

Other thoughts:  Aerobraking will not help you LEAVE Eve, but it will make it cheaper to get there, and cheaper to get back to Kerbin.  So with aerobraking, you can put most of your fuel supply towards this particular burn.  However, Eve has a pretty unforgiving atmosphere, so a heat shield is recommended.  

What exactly are you planning on doing at Eve?  You can potentially save quite a bit of fuel by not getting all that close to the planet in the first place.  Of course, if you're aerobraking on the way in, at least your periapsis is going to be quite low.  

It should be manageable to get most any type of ship to Eve and back, but it takes some care in the design and staging.  I would call Eve (orbitally, at least) a medium-difficulty planet: harder than Duna, easier than Moho.  Jool is more complicated and generally more expensive, but gives you more options in terms of gravity assists or whatnot.

Happy to provide some more specific ideas to extend range, if you want to provide some more mission details and/or pics of the craft in question. 

EDIT: Think I got the wrong number of the launch window planner.  Also, my post was talking about returning from Eve Orbit... not Eve surface.

Edited September 26, 2016 by Aegolius13

[Foxster]

Assuming you want a manned return mission then one way to do it is to land a craft, do your surface walk and such and then launch it back to orbit, staging all but the capsule and a small engine/fuel combo on the way up. Then have a orbiting mothership meet this capsule, EVA over the crewman, return to Kerbin. 

You certainly don't want to try to have your lander achieve much more than making orbit, for instance trying to return to Kerbin would make your lander huge. 

[DrLicor]

take a look at this

[Warzouz]

It's around 7000m/s, (better to pack 8000m/s) with good ISP engines (ASL). The flight plan is VERY important (more than on Kerbin) for stability and efficiency. The ship design is also important I got very big delta-v differences. You must design a stable ship that will land AND ascent without flipping.

General mission is to rendez-vous at 100km with a small return ship.

But I find the hard part is not ascending : it's landing your ship without blowing everything (heat, flipping, losing control...).

6 hours ago, DrLicor said:

take a look at this

This is quite old. Now the recommended (comfortable) delta-V is 8000m/s and 3400 for Kerbin. Of course you could do with less (I did a Eve ascent with 6900 (iirc) and a Kerbin ascent with 2850m/s

 

Latest d-V Map is here

 

Edited September 26, 2016 by Warzouz

[DrLicor]

@Warzouz, i'm sorry, just took the first picture of google .

[Warzouz]

1 minute ago, DrLicor said:

@Warzouz, i'm sorry, just took the first picture of google .

Don't be sorry , be happy to have an up to date link

Edited September 26, 2016 by Warzouz

[Snark]

On 9/24/2016 at 10:50 AM, Deadmanrunning said:

Just what does it take to return from Eve?!

 

I have a KSP calculator app, the dV to return  from Eve is massive. Do you have to set up a mining station to refuel? Or maybe an orbiting nuke tug?

Returning from Eve orbit to Kerbin is not too bad.  It's a single burn that's around 1400 m/s if you hit a good launch window.

Returning from Eve surface to Eve orbit is an incredible bear, arguably the single hardest challenge you're likely to meet in the Kerbin system.  It's not just that you have to pack a metric crapload of dV (though you do)-- it's also that there are lots of other engineering constraints you have to simultaneously consider, as well.

Here are the things you need to contend with at Eve, that you don't have to deal with anywhere else and are therefore likely not used to:

• Need a lot of dV.  It takes more than twice the dV to get to Eve orbit from the surface as it does from Kerbin.
• Need a really high TWR.  Eve has by far the strongest gravity anywhere in the solar system, which means you need a much higher TWR than anywhere else.  And its thick atmosphere means you need to climb straight up for a long time before you can start a gravity turn, which means your engines will be directly fighting that gravity for a much longer time than anywhere else.
• Very limited engine selection due to atmospheric Isp.  Engines get worse efficiency and lower thrust in atmosphere, compared with vacuum.  Eve's surface pressure of 5 atmospheres is really punishing for that.  It means that you really have to pay attention to your engines' atmospheric Isp, and pick ones that have a good curve.
• Streamlining really matters.  You're going to be slogging through thick atmospheric soup a long, long time on the way up.  It's not like Kerbin, where you're in mostly-vacuum as soon as you're 10 km up, which happens within a minute of launch.  So your ascent stage has to be seriously sleek.
• You have to care about terminal velocity on ascent.  This makes piloting much trickier, because you have to worry about going too fast too soon.  The ideal ascent speed (at least, during the vertical-climb part) is where your upward speed matches terminal velocity.  In practice, you don't have to worry about that anywhere other than Eve, because pressure drops so fast compared with altitude that terminal velocity rises far faster than your rocket's speed does.  For example, on Kerbin, unless you have a really unreasonably high TWR, or a really draggy design, it's basically impossible for you to "catch up" with your terminal velocity, so the right answer is pretty much always to just floor it at maximum throttle and go as fast as you can as soon as you can, in order to minimize gravity losses.  That's not the case on Eve.  You need to climb ~20 km before you can do a gravity turn, and during that climb, you really have to be careful not to go too fast or you'll waste fuel on drag... but don't go too slow or you'll waste fuel on gravity loss.  (Doesn't help that you don't actually know exactly what your ship's terminal velocity is, since it depends on your shape, and changes with your altitude.)  It means that piloting during ascent requires careful control of the throttle, in a way that nowhere else does.
• Your lander has to be really structurally sound.  Landing a super-heavy craft under high gravity is no joke. The mechanical shock of landing big, high-inertia things has a tendency to snap part connections, rip struts loose, cause the whole shebang to collapse like a jumble of jackstraws.  It needs to be sturdy.  Your Eve lander is going to be far larger than anything you're likely to need to land anywhere else (we're talking 60+ tons, minimum, for a crewed lander-- much bigger if you don't have it dialed in just right), and it's going to be landing under far higher gravity than anywhere else.

General advice for building an Eve lander that can ascend to orbit:

• Make it streamlined.
• Give it really high TWR (you want ~2 times Eve gravity for the first 20 km of ascent, which means you need ~33 m/s² of acceleration).
• Pick your engine carefully for high atmospheric thrust.  Mammoth works well.  So does Vector.  Aerospike can work, but their TWR's not as good.
• Don't bring anything along on the ascent that you don't absolutely have to.  For example, don't even think about trying to build something that can ascend from Eve's surface and then go home to Kerbin-- just get to orbit, then rendezvous with a parked return ship, as others have suggested.  If you have a bunch of parachutes or similar paraphernalia that you used during descent but don't need during ascent... consider mounting them on decouplers that you can blow once you've landed, so that you're not lugging that dead weight on the way up.
• Has to be very sturdy, to withstand the shock of landing.
• F5 is your friend. 

[Deadmanrunning]

Thanks so much guys!!

I am happy to hear that it will take lots of fiddling and planning to do. My new career goal may be to recover a purple surface sample. A boss battle of sorts. 

 

The Gilly mining station sounds super cool!

[foamyesque]

I would strongly recommend HyperEdit testing of your lander and return-to-orbit process, because you will get it wrong and reflying the rest of the mission to put a big lander into a low Eve orbit sucks.

One constraint I've not seen mentioned yet is heat; Eve will punish you with it both on entry and on ascent. The high gravity means orbits are fast, and the thick atmosphere means you'll be going fast in noticeable air. It's very easy on Eve ascent, as your vehicle lightens and you get out of the soup, to find yourself with way more TWR than you need. Normally that'd just cut your gravity losses, but if you succumb to that temptation you'll probably overheat your nosecones somewhere around 60km.

Likewise, on entry, you're coming in from 3km/s+ with a heavy machine, so you need a. lots of drag to slow down or b. excellent thermal protection or c. both. The inflateable heat shield is often used in tandem with airbrakes in order to keep your orientation correct during the descent, but personally I prefer a winged approach. You get a lot more control over your landing site in that way, which can be important if you're planning to use ISRU refuelling to execute your RTO. Doing so (and leaving the ISRU unit behind on the surface) allows you to send a lot less weight to Eve, since the ISRU setup will weigh much less than the fuel it generates for even the smallest crew-return missions.

As mentioned, leave a return-to-Kerbin setup in Eve orbit. That can be a refuel tank for your upper Eve stage, a totally separate mothership, whatever, but Eve return-to-orbit is nasty enough as it stands that you don't want to take anything at all to orbit you don't absolutely have to.

[Deadmanrunning]

4 hours ago, foamyesque said:

I would strongly recommend HyperEdit testing of your lander and return-to-orbit process, because you will get it wrong and reflying the rest of the mission to put a big lander into a low Eve orbit sucks.

I am on console so not an option

Edited September 27, 2016 by Deadmanrunning