Kethane efficiency?

[Jas1126]

Hello, I was just testing a use for Kethane and I'm rather confused. Side note: I've rarely ever used this mod for anything.

I had a low burning engine (See below) and a tank full of Kethane (8k). It took the entire 8k tank of Kethane just to encounter Eeloo. Is that correct or am I not using this properly? I had MechJeb do the encounter just to see how well 8k of Kethane could do. I used the large converter and it had a cooling efficiency of around 83%. I was converting while in flight and my electrical charge was sufficient. The flight started at 850km of Kerbin orbit.

Is there any way to improve upon this?

Ship Information:

Edited May 9, 2014 by Jas1126

[shynung]

My first advice? Start from a lower orbit; the Oberth effect will help conserve fuel. Personally, I usually start transfer burns at between 80-100 km in Kerbin orbit. It does not matter how elliptical/circular the starting orbit is, what matters is to do the burn at the lowest altitude possible.

Also, I'd suggest using a different engine. I somewhat recall that KW Rocketry has one with 410 seconds of I_SP. Use those instead.

P.S. This advice also works on non-Kethane ships. The principle is the same.

P.P.S Here's a good read on the subject.

Edited May 11, 2014 by shynung

[Deathsoul097]

Yeah, you'll want to use an engine with better ISP than the WildCat V, along with starting from a lower orbit if possible, and yes, TWR will go through the floor, but there are some pretty good and balanced NERVAs from Lack's SXT pack, if you wanted something that is a well rounded big brother to the LV-N. Also, I advise you try to and send the tank to Eeloo without Kethane, and mine it when you get there. Also, it will benefit you to set up a fuel depot, with kethane storage, and conversion units, and just dock and refuel from it. Fact is, while kethane itself is just as efficient as LF/O before and after conversion, you are also having to carry the conversion equipment, along with what you need to power it. That means a lot of extra dead weight, and that really cuts into your DV.

[Jas1126]

My first advice? Start from a lower orbit; the Oberth effect will help conserve fuel. Personally, I usually start transfer burns at between 80-100 km in Kerbin orbit. It does not matter how elliptical/circular the starting orbit is, what matters is to do the burn at the lowest altitude possible.

Also, I'd suggest using a different engine. I somewhat recall that KW Rocketry has one with 410 seconds of I_SP. Use those instead.

P.S. This advice also works on non-Kethane ships. The principle is the same.

P.P.S Here's a good read on the subject.

I normally start with a much lower orbit but time warp required I be at 800+ so that I wouldn't be waiting an extreme amount of time for the 176 day window to open. I understand that there are far more efficient engines but to take the entire 8k tank just to encounter? That seems a bit off considering that MechJeb waited for the prime launch time.

Funny enough, I got there last night and found out that it has more Kethane than I'll ever need. I plan to build a massive operation there. Thanks for the advice.

Edited May 11, 2014 by Jas1126

[shynung]

I normally start with a much lower orbit but time warp required I be at 800+ so that I wouldn't be waiting an extreme amount of time for the 176 day window to open. I understand that there are far more efficient engines but to take the entire 8k tank just to encounter? That seems a bit off considering that MechJeb waited for the prime launch time.

Funny enough, I got there last night and found out that it has more Kethane than I'll ever need. I plan to build a massive operation there. Thanks for the advice.

If I were you, I'd stay at 800+ km until launch window appears, then lower the periapsis below 80 km. Then, I'd burn at periapsis.

Or, go to the tracking station, and time-warp from there. No minimum orbit limits, so you could stay at the 80 km orbit.

Good luck with your mission!

Edited May 11, 2014 by shynung
confused apoapsis and periapsis

[Jouni]

The difference between an 800 km orbit and an 80 km orbit is negligible for an Eeloo launch, usually less than 1% of the delta-v requirements of the transfer.

The 8000-unit kethane tank is basically a lightweight version of the X200-32 fuel tank. It has enough fuel to get a small ship to Eeloo, but that's it.

Edited May 11, 2014 by Jouni

[Jas1126]

Or, go to the tracking station, and time-warp from there. No minimum orbit limits, so you could stay at the 80 km orbit.

Doh! That should have been obvious. XD Thanks.

[shynung]

The difference between an 800 km orbit and an 80 km orbit is negligible for an Eeloo launch, usually less than 1% of the delta-v requirements of the transfer.

It is? Pardon my ignorance; I have never sent a mission to Eeloo before.

[Jouni]

An 800 km orbit over Kerbin is only about twice as high as an 80 km orbit. If the escape burn is roughly between the orbital velocities at the two orbits, the effect of such small differences in altitude is negligible.