How much dV do i need for a laythe trip

[Xaythe]

Heyo!

I need to know how much fuel and dV I'd need for a laythe trip and back to kerbin.

Thank you!

[bsalis]

There are lots of delta-V maps around to help figure this out.

My rough summary would be as follows, assuming aerobraking where available, and a regular rocket...

4500 to LKO

2200 to Jool (including inclination change)

300 for small maneuvers and power assisted parachute descent

2800 ascent to low Laythe orbit

1200 for return to Kerbin

600 contingency

Other important points worth remembering is that it is hard to land on, um, land with Laythe, because it is so easy to miss an island. So perhaps build a wide lander and test it out with water landings on kerbin first. Also, don't forget enough TWR for Laythe ascent.

[FREEFALL1984]

I agree with Bsalis But I like to add some jet engines on my descent stage so I could perform a precision landing since the few areas of land on laythe can be pretty bumpy so it might take a little jiggling until you can safely set down. but with a little clever design you can have a nice lander with 2km/s of vac DV from rockets and 5km/s of atm DV from jets and you can use the jets for a controlled targeted landing, perhaps with a little parachute assistance, then to assist the ascent. The alternative is to make a spaceplane, rule of thumb is if it can get to orbit on kerbin then it can get to orbit in laythe, finding somewhere to land might be more of a problem though

[Deadpangod3]

Basicly, it requires,

ALOT.

I speak from experience.

[KerikBalm]

This is a mission you should do "Apollo style"

Assuming you do it apollo style and use aerobraking: 9,000 m/s for your main ship, starting from the surface of Kerbin.

4500 m/s starting from LKO

And you also want a lander that can do 2800 m/s-> this is easy enough to acheive with a FL-T400 tank (remove some oxidizer), a lander can, a rapier engine, and some radial intakes + parachutes + landing legs. I suspect you could even do it with 1 can of jet fuel (partially filled), 1 turbojet, and 2 ion engines + radial xenon tanks+ electrical storage/generators in place of the rapier and rocket fuel tanks.

If you land your entire ship on laythe, then you need to spend an additional 2800 m/s to get it back into laythe orbit. Otherwise, with a small lander, you can effectively spend a fraction of that

I don't have mechjeb, or anything else, and I was recently contemplating a laythe trip with my rather well developed test payload for my SSTO.

I got out a spreadsheet, did the rocket equations (its meant as a Single stago from LKO to laythe orbit and back).

My payload had 5814 dV in the main stage (intentionally included a lot of dead weight for RP reasons/testing for career) on liquid fuel, and I figure its enough.

(Deadweight = that heavy Mk1-2 command pod+ hitchhiker container+ science lab, also a few tons devoted to ion engines that give it in theory another 3300 m/s)

LKO to escape + Jool SOI= 950+965 = 1915

I figured I'd use ~2000 dV to get there (~100 m/s in course corrections). Laythe is within Jool's SOI, all you need to do is get a very accurate trajectory, and aerobrake like crazy at laythe.

Then I had a SSTO lander that was easily capable of SSTO on Kerbin, so that was more than enough to get back to the "mothership"

For my return to Kerbin... I was not sure how much dV I needed, the transfer calculator wouldn't let me select Laythe to Kerbin, and the dV map isn't setup to show that (I won't go from laythe back to low jool orbit, then to jool escape.

I might try to add the dV for laythe escape (780) to the dv needed to go from jool escape to kerbin soi (965)= 1745

Then I figured.... what if I ask the transfer planner to calculate from jool's orbit to kerbin, and I just enter in a really high orbital altitude (laythe's orbital altitude)

So I'd spend 780 dV to get that point, then do the burn.

It told me 1600... and I know that will be lower if I do everything from within laythe's gravity well (Oberth and all) - granted I'd have to wait until laythe is in the right position, I think the transfer window is long enough for that.

Then of course, use the ions for a precision trajectory, and aerobrake at kerbin

So....

~4500 dV for the launcher to get the mission payload to orbit

~2000 dV to go directly to laythe and aerocapture with the Mothership+lander

~2800 dV for *only the lander* to get back to Laythe orbit

~780 dV for *only the mothership* to escape Laythe

~1600 dV for *only the mothership* to get back to Kerbin

4500 launcher dV

2800 Lander dV

4380 Mothership dV

As far as my Payload the SSTO delivered to LKO, it was 77.91 Tons

It would spend 2000 dV getting to Laythe, and drop the ~10 lander

At that point, it has 4900 dV remaining on its nukes - total nuke dV is thus 6900 dV, assuming it ditches the lander after spending 2,000 dV, if it keeps the lander the whole time as inert payload, its only 5815 dV on nukes.

The lander weighs 10.39 tons, and relies on its jets to do the heavy lifting, with emtpy jet fuel tanks, it has only 974 dV.... but I know it will reach over 2000 m/s in the upper atmosphere, so... that is fine.

Edited April 28, 2014 by KerikBalm