Ion return from Eve?

[recursive_mouse]

Hi guys, I have zero experience with ion thrusters, need advice from expert. 

 

Recently I strapped a stock mining SSTO (extreme offset) could reliably takeoff from Eve surface, obtain 90-120 low Eve orbit, with some kinda excess. Then like any Kerbal, I want to do the most meaningless activity once in my lifetime, SSTO to Eve surface -- without left a single penny in orbit, then return to Kerbin wholesome. Or at least know it's doable. 

After rigorous weight shaving, now have 1,425 m/s ion delta v on top of what needed to obtain orbit,

TWR 0.01,

split in 1 day burn, 

only works when sunlit. 

 

Even a pair of wing is shaved off, but adjust incidence somehow it retains similar stall speed and drag profile. I'm yet to test it for Eve orbit, because Kraken attacked my ship last time I ordered Kerbal to get out service bay.

Now, suppose it works like intended,  and 1425 m/s ion delta v left at 90-120 orbit, 25.227 inclination. 

Is there any possiblility for a feeble ion spaceplane return from Eve to Kerbin aerocapture? I have high altitude parachutes called cargo bay doors so safe reentry will be easy(kinda). 

The mission planner window shows absolute minimum of 1354 m/s dv. Dunno if its doable for ion. And ejection burns have to be done entirely when sunlit. From what I understand, ions benefits none from Oberth effect and their dv quality is inferior. 

 

Link to the non-ion version of Eve climber:

 

The yet-to-be-tested ion version:

Edited June 9, 2018 by recursive_mouse

[recursive_mouse]

Time is no constraint here. Could I spend 200 burns for a high elliptical orbit and wait for the right moment? Should I take precaution with some orbital parameters, like avoid certain range of period time?

[Xd the great]

Well, burn prograde until you are at the edge of the SOI of eve. Literally the edge. Yhe burn and get home.

Or even better, burn prograde until you are in an almost identical orbit with kerbin and timewrap until you slam into irs SOI. Used to do that as a noob.

Do keep in mind that you will need more delta V to pull this off

[Laie]

First off, you can periapsis-kick however often you like (or need to) in arbitrarily small increments, until AP reaches the edge of the SOI. But then, for a halfways dV-efficient transfer your last kick has to provide for all the remaining dV, all in one kick. That's where I see a problem. If that burn is going to last longer than a couple of minutes, you'll have a problem , both with planning and with needing more (possibly much more) dV than with a standard maneuver.

I haven't checked, but 1400m/s doesn't leave much headroom, does it? Would it even suffice if you could do an instantaneous burn?

[recursive_mouse]

Thanks for answers, notes taken!

Will try a Mammoth design( save 0.3% dry weight ) to gain more room for dv and thrust. 

[Snark]

On 6/9/2018 at 12:08 AM, recursive_mouse said:

After rigorous weight shaving, now have 1,425 m/s ion delta v on top of what needed to obtain orbit

The absolute bare minimum dV to get from low Eve orbit to Kerbin, assuming a perfect transfer window, is nearly 1400 m/s-- and that leaves zero headroom, and allows for no inefficiency whatsoever.  You're shaving it awfully thin, there.

I gotta say that 1425 m/s sounds awfully low for dV on an ion-powered craft.  That's what you'd get for putting a single PB-X150 tank on a 2-ton craft.  That tank is only 0.1 tons-- can you not add a second xenon tank and nearly double the ion dV?  Would make the return trip a slam dunk, and also give you a bit of leeway when climbing from the surface (i.e. you could squeeze out a bit of ion dV if your lifter doesn't quite make it to Eve orbit).

[recursive_mouse]

55 minutes ago, Snark said:

The absolute bare minimum dV to get from low Eve orbit to Kerbin, assuming a perfect transfer window, is nearly 1400 m/s-- and that leaves zero headroom, and allows for no inefficiency whatsoever.  You're shaving it awfully thin, there.

I gotta say that 1425 m/s sounds awfully low for dV on an ion-powered craft.  That's what you'd get for putting a single PB-X150 tank on a 2-ton craft.  That tank is only 0.1 tons-- can you not add a second xenon tank and nearly double the ion dV?  Would make the return trip a slam dunk, and also give you a bit of leeway when climbing from the surface (i.e. you could squeeze out a bit of ion dV if your lifter doesn't quite make it to Eve orbit).

The craft taken off from Eve, suppose return to Kerbin 100%. 52 tons from just empty fuel tank

Now modified to 1,559 m/s delta-vs total... split to:

1285 dv for edge SOI,

180 dv for 3 minutes ejection kick, 

70 dv ion correction. 

Battery bank 3050, Ion x 2, outputting 2.5 dv per minute. 

 

Dunno if doable from 26 inclination low Eve orbit  fingers crossed

 

[Snark]

Ah, okay.  Returning the whole thing, and using ions for kicking the orbit.

You've got *way* more patience than me.

So. If you were in a 90 km circular orbit, the max dV you can add with periapsis kicking (without actually escaping) is just over 1300 m/s.  The dV needed from such an orbit to go back to Kerbin is about 1400 m/s. 

So, the good news is that you can get great Oberth benefit,  even with ions. Using periapsis kicking, you can do all but 100 m/s of your burn (actually, closer to 50) right at 90 km, nice and efficiently.  So your final ejection burn is small, well under 100 m/s, meaning you don't lose much even if you don't get much Oberth.

The bad news is that you're really gonna have to ace the navigation.  It's going to take many weeks of periapsis kicking,  so you'll have to work out, long before your launch window, not only what longitude to place your periapsis, but also to make sure that you reach periapsis right when Eve and Kerbin are in the right places to do the ejection burn. That's gonna be a challenge!

[Kryxal]

Assuming you're in a prograde orbit, you're going to be doing your ejection burn on the dark side of Eve ... but you can do all the setup burns weeks in advance, so you have light to work with.

[recursive_mouse]

Thanks for everyone. Somehow pushed dv-budget to 1606-1626 (167 from LV-N). While trippled Ion output.

Did a pure speculation run via F12 infinite propellent, after stable 25 inclination 90-136 LEO obtained in one go. 

 

 

1. spent 1318 to edge of SOI (simulated by a single 5 minutes rocket burn)

Also boosted PE to 136. This is a mistake but it could actually help stock warp and save liquid fuel.

~ 300 remaining

 

2. spent 123 for ejection at next optimal Eve position. put AP just beyond Kerbin orbit, and AN dead on. 

~ 177 remaining

 

3. waited 9 yrs plus 147 days the first reasonably close approach to appear. 

 

4. plotted 152m/s single burn on collision course (Kerbin PE 19km). 

Should take 9-10 hours. Simulated by rocket burn 5 hours prior and after. 

Actually saved 0.1 dv this way.

~ 25 remaining.

 

5. T+10yrs 32d. Somehow startled by SSTO arrived for exact 19km PE

Used last potion to boost radial 40km.

0 remaing, orbital speed 3500m/s at 40km altitude. 

 

 

6. After 10yrs of Eve take off, survive Kerbin reentry.

Max temperature 2398K, max load 10.51g. Tumbly-wobbly and safe inverted landing. 

Actually after quite easy reentry, smashed many times at touch down. Found out nose gear is overloading main gear. Retract nose gear then safe landed. 

 

 

Now the only question is, to raise the orbit, will 200 of 2-min Ion burn as dv-effecient as single 5-min rocket burn? And exactly how long it takes? 

 

 

Edited June 13, 2018 by recursive_mouse