How much Dv to orbit from the top of EVE's atmosphere?

[Motokid600]

Im planning a land a return from EVE for the very first time in career mode. My goal is to simply get a surface sample back to Kerbin. Now im not in it for the challenge of building a 500 part, lag-fest lander. Instead im going about it the practical way. Air balloons via HL Airships. So.. from the top of EVE's atmosphere ( As high as I can get anyway.. ). How much Dv would a rocket need to reach orbit? And.. at this point would it make more sense for the same rocket to be the return vessel as well? ( if the Dv gain from balloons is enough ) Or.. even with balloons should I still have the craft rendezvous with an orbiter?

And one more thing that comes to mind... is it possible to return TWO surface samples? Im going to try and land on a beach in order to get both the ground and ocean sample.

Edited February 22, 2014 by Motokid600

[Taki117]

Here's a couple of dV Maps to help you out.

http://i.imgur.com/IV8rzue.png

http://i.imgur.com/UUU8yCk.png

Now, that being said unless you are also travelling laterally you aren't going to be getting to orbital velocity with the balloons alone, and it's always a good idea to rendezvous with an orbiting mother ship to cut down on lander weight (Though it is Eve...but then again you are using ballons)

Yes, it is entirely possible to return two samples if they are of different biomes, you don't even need a second capsule. You can also return multiple EVA reports from separate biomes as well.

[Motokid600]

Thanks. I figured if I could launch from the top of the atmosphere that would save me SO MUCH that it'd just be easier to then go home with the same craft. But either way on that one.. How much Dv do you figure I can save launching from 80km ( Is what im hoping for )? I know no horizontal velocity, but not having to power though that soup of an atmosphere has to count for something.

Oh.. big thing I forgot to mention. Im using FAR. So that may hurt the altitude I can float up too... idk.

Edited February 21, 2014 by Motokid600

[Taki117]

IT changes the density of the air, I Don't know how the Hooligan Labs works, but you should be able to get going sooner with FAR, the issue you are going to have is getting enough vertical altitude so that you can get enough horizontal speed before hitting the atmosphere again. If you apply some horizontal thrust as your using the balloons to carry you up you should be fine. but I would ditch the balloons once they are no longer useful, this way you can cut down on some weight. The key here is to build up horizontal velocity as you increase your altitude.

[Motokid600]

Hmm.. I suppose I will try and incorporate an engine that can boost me sideways during ascent. But basically all I planned was doing is floating a rocket up as far as these balloons can take me ( still working on which ones to use ) and then treating it as any other launch.. but from the top of the atmosphere. Soon as the vertical speeds drops with the balloon ill detach it and fire engines maybe only pitching over to 10 degrees then accordingly as speed increases. The air should be thin so Im hoping a high TWR can do the trick. Which brings me to another question. .. Whats a good TWR for Eve? I use 1.3 for Kerbin and that keeps the rocket nice and close to the prograde marker.

And then I need to know.. what Dv number should I shoot for when designing this thing? Id like to keep it SSTO to keep my part count down, but idk about that.

[KerikBalm]

Simple math would say that your weight is 70% more on eve, due to the higher gravity, and a 1.3:1 ratio on kerbin wouldn't be sufficient for liftoff on EVE.

Your thrust would be the same, but your weight would be 1.7x and 1.3/1.7 <1, not enough for a vertical ascent, and since you're at the top of the atmosphere, you can't use wings to help.I suppose it would still be possible.... get going really fast in the upper atmosphere, but in this case you'd be thrusting nearly horizontally.

Of course, the gravity will be a little bit less at the top of the atmosphere than at the surface...

I'd say take your 1.3:1 TWR and multiply it by 1.6 to get 2.08 - although I haven't done any eve ascent yet, I'm just doing simple reasoning here.

[technion]

Having built sea level rockets before.. I know that once I hit 23km and start a gravity turn, you're basically looking at four of those FL-T200 tanks sitting around a middle one, with 47-8S's on each - with an FL-T100 staged on top of all of it - to hit orbit.

[Motokid600]

That TWR sounds good ill shoot for that thanks Kerik. Now I'm using modular fuel tanks so I'm going for a simple serial stage rocket. It will be tall, but thats what I got the SpaceX lander legs for so that I'm not worried about. I just need a Dv number so that I can begin construction. If its 12k from sea level what do you figured it'd be from the top of the atmosphere?

[Taki117]

Rough guess, but I'd say about half that. So 6-8 km/s, any remaining fuel can be transferred to your mothership for the retun trip.

[Xavven]

The wiki provides a nice delta-v chart for different starting altitudes up to 7,540m. This is assuming using rocket power from the ground:

Altitude (m)	 Delta-V Required (m/s)
0	 11,282
1000	 10,731
2000	 10,219
3000	 9,743
4000	 9,300
5000	 8,888
6000	 8,507
7000	 8,150
7540	 7,968

You're using balloons, so your delta-v requirement will be far less. I'm not able to access my game at the moment, but look at a craft in low Eve orbit and check its orbital velocity. That's how much horizontal delta-v you'll need at minimum. You'll have to add in extra to counter gravity drag. I don't know of a way to calculate that, so what I'd do is figure it out experimentally. Run some tests from Kerbin using unmanned orbital airships with the same payload you're going to use on Eve. Make sure you consider the difference in atmospheric pressure:

Altitude	Eve	Kerbin
0	5	1
1000	4.33439	0.81873
10000	1.19826	0.13534
20000	0.28716	0.01832
30000	0.06882	0.00248
40000	0.01649	0.00034
50000	0.00395	0.00005
60000	0.00095	0.00001
70000	0.00023	0.00000
80000	0.00005	0.00000

Maybe multiply the required delta-v on Kerbin by some arbitrary number, like 1.7, or by the ratio of orbital velocity on Kerbin vs Eve, and then pad your number by 1,000 delta-v and try it out. Sounds like a pretty Kerbal way to do it, actually

[Motokid600]

Thanks Xavven that's a GREAT way to do it. And ty everyone else. Im going to get started on this monstrosity. .. Im almost more exited to build the rocket that's gonna get this rocket to Eve lol.