Kerbin to Eve

[Mordrehl]

Ok this is the deepest I've gotten in KSP and I've been playing it since 0.20ish ... 

Loving the patch, loving the mods I've grabbed ... but I think I'm doing something wrong

Now, found this website: https://www.dcl.hpi.uni-potsdam.de/home/feinbube/web/stealth/KSPDeltaVMap/

To low orbit - check

To Kerbin SOI - check

Intercept - yup, roughly

End up with a periapsis to Eve of 600km on intercept ... cost to even get an extemely eliptical orbit ... 2000+ m/s of dV yet all the charts I Iook at say it should be far less.   Should I be aiming for an intercept at the extreme edge of the Soi?   What relative speed are you cruising at when hitting Eve?

 

Detailed Mission Plan

Info

Delta-V

Accumulated

 

 

 To a low orbit around Kerbin.

3960 m/s

3960 m/s

 

To the edge of the influence of Kerbin.

1045 m/s

5005 m/s

 

To the orbital plane of Eve.

0 m/s

5005 m/s

 

 To an intercept trajectory of Eve.

99 m/s

5104 m/s

 

To an elliptical orbit around Eve.

88 m/s

5192 m/s

 

To a low orbit around Eve.

0 m/s

5192 m/s

 

 

 

 

 

 

 

 

 

[Foxster]

That's about right but probably cutting it fine. There's no need to build to exactly the numbers. Just over-engineer it a bit and allow for an extra 2000 dV or so. Better safe than sorry   

[KingPhantom]

little bit over engineer. but i aim directly for an Low Orbit High capture. on Eve its 100km. directly when i hit the SOI of eve i correct the inclanation and correct the PE to what i need. if i'm in a probe with raditors i try aerobreak. but comming from interplanetary will instantly kill you when you hit 89km....

 

other idea: aim for a small capture in a elliptical orbit. just burn at PE 100km enough for a capture.

then try to fix the PE at AP for a small aerobreak. redo that until you are slow enough. the problem of the high deltav is your speed relative to eve when comming from interplanetary

[Sharpy]

I don't see "Transfer window - check" on your list. The dV maps show dV for optimal transfer at optimal time. The delta-V requirements may go up by strides (I mean, from something like 800m/s up to 15,000!) if the transfer is not optimal - and great most of the extra expense accumulates on the capture burn.

Oh, also - periapsis of 600km? 0.1m/s mid-transfer will change that to 110km, just above the atmosphere - and Oberth effect is your friend here. It won't help a lot if the capture moment is anything but perfect, but it will help.

Edited November 16, 2016 by Sharpy

[Snark]

Moving to Gameplay Questions.

9 hours ago, Mordrehl said:

End up with a periapsis to Eve of 600km on intercept ... cost to even get an extemely eliptical orbit ... 2000+ m/s of dV yet all the charts I Iook at say it should be far less.

Two things, here.

First:  As @Sharpy points out, Oberth effect is your friend, here.  You always want your approach to any planet to be as low as possible, otherwise you're throwing away free dV.  So don't approach at 600 km; do it at 100 km or thereabouts.  Especially don't do this:

9 hours ago, Mordrehl said:

Should I be aiming for an intercept at the extreme edge of the Soi?

...that would be the worst possible thing you could do, and would waste scads of dV.  You want the precise exact opposite of that.

 

Second:  How much dV you need when coming in to Eve makes a big difference based on the transfer window.  Have you optimized that?  For a well-executed transfer window, you should only need ~1400 m/s to capture to a 100 km circular orbit, even if you don't use aerobraking at all.  Here's how to tell if your window is good:  it's good if your transfer-orbit Pe just "kisses" Eve's orbit, i.e. is tangent at the point of intercept.  It's bad if the paths cross like an X.

 

[Mordrehl]

6 hours ago, Sharpy said:

I don't see "Transfer window - check" on your list. The dV maps show dV for optimal transfer at optimal time. The delta-V requirements may go up by strides (I mean, from something like 800m/s up to 15,000!) if the transfer is not optimal - and great most of the extra expense accumulates on the capture burn.

Oh, also - periapsis of 600km? 0.1m/s mid-transfer will change that to 110km, just above the atmosphere - and Oberth effect is your friend here. It won't help a lot if the capture moment is anything but perfect, but it will help.

 

Yeah, the rig I sent wasn't optimized for an Aerobrake as I saw "88 m/s dV" from SOI to Elliptical orbit

 

7 hours ago, KingPhantom said:

little bit over engineer. but i aim directly for an Low Orbit High capture. on Eve its 100km. directly when i hit the SOI of eve i correct the inclanation and correct the PE to what i need. if i'm in a probe with raditors i try aerobreak. but comming from interplanetary will instantly kill you when you hit 89km....

 

other idea: aim for a small capture in a elliptical orbit. just burn at PE 100km enough for a capture.

then try to fix the PE at AP for a small aerobreak. redo that until you are slow enough. the problem of the high deltav is your speed relative to eve when comming from interplanetary

 

My downfall is probably relying on Mechjeb ...  used the porkchop selection but from memory I don't think I chose the lowest dV for the transfer.     It's also possible I messed up my approach angle when I adjusted the closest approach distance mid-transfer.    From memory (at work) ... I think my approach was fairly sharp come to think of it.      What I was driving at in my original post is this

 

 

3400 dV to Kerbin LO

1380 dV for Eve transfer (950+430)

then if I'm reading that right, now that I'm in the Eve SOI under ideal circumstances it should be roughly 80 m/s dV to establish an elliptical orbit (AP near SOI)?   

[KingPhantom]

20 minutes ago, Mordrehl said:

My downfall is probably relying on Mechjeb ...  used the porkchop selection but from memory I don't think I chose the lowest dV for the transfer.     It's also possible I messed up my approach angle when I adjusted the closest approach distance mid-transfer.    From memory (at work) ... I think my approach was fairly sharp come to think of it.      What I was driving at in my original post is this

 

 

3400 dV to Kerbin LO

1380 dV for Eve transfer (950+430)

then if I'm reading that right, now that I'm in the Eve SOI under ideal circumstances it should be roughly 80 m/s dV to establish an elliptical orbit (AP near SOI)?   

First: The Map is from 1.1.3. I hope there will a 1.2.1 update soon. But i dont think that the values will be different that much.

Your calculation is wrong.

3400 for Kerbin LO

950 for Edge of SOI from Kerbin

430 for Inclanation change to Eve

90 for Intercept with Eve (PE near to Low Orbit)

 

When you are at 100km you barely need 80 to do an Elliptical Orbit to the SOI Edge (like in the legend of the map)

Then you can use aerobreak without exploding (with a littlebit of trial and error and dont dig to deep into the atmosphere... just step by step. When you will be slow enough you can risk more. In the end you can make a Low Orbit witout that much DeltaV.

When you dont use Aerobreaking the LO is 1330...

 

So the DeltaV needed without Aerobreaking: 6280

[Mordrehl]

Just now, KingPhantom said:

 

So the DeltaV needed without Aerobreaking: 6280

 

I wasn't including Kerbin LO etc ... I was looking at just what is needed once you hit Eve SOI ... based on these numbers I'm pretty sure my angle of approach was way off.  At 600km PE it was going to be 3240 m/s to circularize.   Clearly I was coming in too hot .     And I'm guessing that was due to me fiddling with the closest approach manuever (MJ) mid transfer without heeding the angle that had me rushing by Eve to the point gravity wasn't slowing me down

When I get home guess I'll sandbox and quicksave before hitting SOI and play with the approach angle.     

[KingPhantom]

14 minutes ago, Mordrehl said:

When I get home guess I'll sandbox and quicksave before hitting SOI and play with the approach angle.     

i do it directly after i'm in SOI. i dont trust the SOI-changes 100%...

Edited November 16, 2016 by KingPhantom

[Aegolius13]

For what it's worth, I think it's gotten a little cheaper to get to LKO, provided you have decent aerodynamics and TWR.  I've mostly been seeing around 3,000 m/s to get to an 80km orbit.

[Mordrehl]

So after some sandbox testing seems I was trying to brute force the Eve intercept and coming in so hot that gravity just shrugged and said "see ya"

Few test runs and closest approach of 100-150 km to Eve on a shallow approach that then slingshots me around Eve back towards direction I entered and burn to get an eliptical orbit to edge of SOI is 100-400 dV m/s depending on the angle ... much better.   Thanks all.

[crackerbal]

On 16/11/2016 at 8:52 AM, KingPhantom said:

 comming from interplanetary will instantly kill you when you hit 89km....

 

other idea: aim for a small capture in a elliptical orbit. just burn at PE 100km enough for a capture.

then try to fix the PE at AP for a small aerobreak. redo that until you are slow enough. the problem of the high deltav is your speed relative to eve when comming from interplanetary

actually with a basic mk2 ssto i was able to aerocapture on around 75-80km, the deeper was 72km and i burn out ( the mk2 cockpit isn't great for this ),

Edited November 19, 2016 by crackerbal