How much delta v to laythe with a spaceplane and FAR?

[peachoftree]

I'm building a spaceplane to laythe and was wondering with Ferram Aerospace installed how much rocket delta v do you need from LKO (130 km) to get to laythe land on it and take off. when I am in atmosphere I will be running on air breathing power so landing is not as much of a concern. Right now I have about 6500 m/s with full tanks.

Edited September 25, 2014 by peachoftree

[Taki117]

Might I suggest a dV map? That's going to tell you how much it's going to be to get there, as far as actually landing and taking off from Laythe, it really depends on how fast you are going in atmosphere. If you get going fast enough (I know far Tops out at Mach 4-ish) high enough you can circularize with only a fraction of the dV listed.

[peachoftree]

Ive seen that map before but don't know how to use it. do you add up every single value fron your destination and back because that gives me something like 7500 m/s I think thats much too high.

[Empiro]

Yes, you just add up the paths each way. The red arrows indicate where you can aerobrake to reduce the cost of going in one direction to nearly nothing.

Under FAR, it takes about 1000 m/s less to take off from Kerbin and Laythe. Also, the dV figures for air-breathing engines seem quite wonky in the game, though from a practical standpoint, they consume almost no fuel mass at all, and I almost never worry about liquid fuel. In addition, the use of air breathing engines reduces the dV to take off to about 1000 m/s in rocket mode (I assume you make it to about 25km at 1500 m/s with jet engines).

Edited September 25, 2014 by Empiro

[Taki117]

Ive seen that map before but don't know how to use it. do you add up every single value fron your destination and back because that gives me something like 7500 m/s I think thats much too high.

Yes, that's exactly how you use it (Don't forget to factor in any plane changes) Red arrows indicate aerobraking (Which is very useful because it significantly reduces the amount of dV needed) and if you are going to Laythe you don't even need to worry about getting into orbit before you land, just aerobrake to landing.

[peachoftree]

Sorry I worded my response badley. the part I dont understand is why there are areobraking arrows on the jool-dres-duna-kerbin transfers as you still need to burn at jool to lower your orbit to kerbin.

[pellinor]

Sorry I worded my response badley. the part I dont understand is why there are areobraking arrows on the jool-dres-duna-kerbin transfers as you still need to burn at jool to lower your orbit to kerbin.

Because you can aerobrake on your way back. So you first need to burn from LKO to a kerbin-jool transfer. Then you can aerobrake at jool into a Laythe transfer (the horizontal arrows), and then at Laythe into an orbit or a landing. On the way back you need to burn into a kerbin-jool transfer, and then can aerobrake at kerbin (following the vertical arrows).

[Empiro]

The part where you burn from Jool is calculated by the long chain of Laythe - Vall - Tylo - Bop - Pol - Escape - Jool Transfer. The map is Kerbin centric, so Jool Transfer means one part of your orbit touches Kerbin's, and the other part touches Jool's. To go from a Jool Transfer orbit to Kerbin orbit, you follow the arrows down, because you can aerobrake at Kerbin.

[KerikBalm]

There's also this map:

http://wiki.kerbalspaceprogram.com/w/images/7/73/KerbinDeltaVMap.png

But some of the values are a bit fudged - as you'll notice they are different between this map and the previously linked one. Plane changes, drag, etc add a lot of fudge factor.

The 2nd one is a bit easier to use, and a lot simpler, even if it is less precise.

From LKO:

950 (sufficient for edge of kerbin SOI) +

956 (gets you into Jool SOI) -> with just some minor course corrections, you can directly aerobrake at Laythe!

<2000 m/s to get to Laythe

The landing is essentually free (bring wings or a parachute)

Getting to orbit from laythe, the jets are essentially free (they have an effective ISP of something like 19,000 at high altitude, and 40,000 at mid altitude)

With far, you should only need another 200-300 m/s to get to orbit.

2200 (conservative) m/s to get to laythe from LKO, land, and get to laythe orbit.

The problem becomes finding out how much dV you need to get from low laythe orbit to Jool escape - the wiki's dV map doesn't help, as it routes you to low jool orbit first. As an approximation, take the dv from jool intercept to low jool orbirt, and from that subtract the dV to go from low jool orbit to laythe intercept.

2200+ 780 (laythe escape) + 2630-1600 = 4010 to get from LKO, to laythe and then escape jool.

Then you still need to get to kerbin intercept (and aerobrake from there), add another 956... 5,000 m/s, assuming proper aerobraking and use of jets (but not counting jets towards the dV) should get you to laythe and back.

Adding up the dV from the other ma gives a value of 5070 + whatever you need to get to low laythe orbit that jets can't provide (300 m/s is my estimate)...

I guess my rough estimates from the other map would have come up a few hundred m/s short... :/

[Laie]

As has been said often enough: ~2000m/s to get to Laythe.

Laythe has thinner air and lower gravity than Kerbin; the latter is by far more important, so any spaceplane that works on Kerbin can launch from Laythe on the same fuel budget or less. Usually less, much less even.

[Godot]

One should add that the transfer dVs between planets might vary considerably with the constellation of Kerbin to the target planet, that is, with the day and year of your start.

AlexMoons Launch Window Planner can help you a great deal with finding the right starting time and angle for a Jool transfer

http://alexmoon.github.io/ksp/

As you can see there, the needed dV between LKO and LJO can vary considerably .... from as low as 5 km/s (or even just 2 km/s with aerobraking) to more than 20 km/s, depending on time of start and length of flight you choose

Edited September 25, 2014 by Godot