Impulse engines

[Mmmmyum]

Would using something like a mainsail as an impulse engine save any delta-v? I was messing around awhile back with the 3.75m KW Rocketry engine with 4000 KN of thrust, and a single pulse would push my craft to terminal velocity, then I'd wait till vertical speed dropped to zero before firing another pulse

Edited November 4, 2013 by Mmmmyum

[Artorp]

Interesting question but without checking the numbers I really doubt it, if your craft has enough TWR that a small burst would accelerate it to terminal velocity then you're wasting fuel dragging the heavy engine up. Using small bursts would mean you get the worst of both worlds, first you transcend terminal velocity where the drag slows you down, then you need to wait for your speed to slow which means more gravity drag; all the while you could be burning the excess fuel and obtain a gradually lighter vehicle.

[Kasuha]

Mainsail is useful for its enormous thrust, it has best TWR of all engines. On the other hand it is the third least efficient engine of all regarding fuel consumption.

Using it at pulse mode is no better than using it at low thrust - you're artificially lowering its TWR while you're not improving its efficiency.

In other words, if mainsail would get you to orbit in pulse mode, another engine would do the same task using less fuel.

Apart of that, whatever works for you is ok.

Edited November 4, 2013 by Kasuha

[Sirrobert]

No it would not. Thrust does not effect the deltaV you need in vaccum. It only affects burn time.

ISP is what you need if you want to save fuel

[jduchock]

^^ what he said...

check your ship to use high TWR (1.5+) and decent atmo ISP for the first 3500dV or so, then upper stages should use low TWR and High vacuum ISP to maximize the dV in a vaccum...(see nuclear engines)

[KvickFlygarn87]

Kashua: Actually the 48-7S has a higher TWR. However, the Mainsail has a higher thrust.

[Mmmmyum]

Well this is what I was messing around with

[UberFuber]

Well this is what I was messing around with

I can tell you, with nearly 100% confidence, that unless you modded your cockpit to have the mass of a couple hundred tons, you do not need 4 Mainsail engines. Just 1 is enough.

If you have problem getting into orbit, it's the issue with the amount of fuel you have (basically, not enough). For your rocket, I suggest having two stages. Lower stage use Mainsail, which is perfect at getting you out of the atmosphere, and the second stage using a rocket with very high Isp in vaccum (atomic engine should work best, considering its high Isp and the fact that you appeared to have a fairly light setup, so the low thrust shouldn't be a problem).

[Mmmmyum]

I can tell you, with nearly 100% confidence, that unless you modded your cockpit to have the mass of a couple hundred tons, you do not need 4 Mainsail engines. Just 1 is enough.

If you have problem getting into orbit, it's the issue with the amount of fuel you have (basically, not enough). For your rocket, I suggest having two stages. Lower stage use Mainsail, which is perfect at getting you out of the atmosphere, and the second stage using a rocket with very high Isp in vaccum (atomic engine should work best, considering its high Isp and the fact that you appeared to have a fairly light setup, so the low thrust shouldn't be a problem).

Lol I have no problem getting into orbit, and that's the biggest part from KW Rocketry. I was more messing around last night and that's what I came up with. I should mark this as answered