True or False, Is Eficency Better Than High Thrust?

[Titan Space Agency]

This is my second true or false, My first one got good feedback so i decided to do a second:).

In this experrement I used kerbal enginer to get the data. I took the rockomax tank that was a 4th of the orange tank and put the logical engines for injection burns on it to see what the delta-V was, here is my data, it will be in order of least thrust to greatest thrust.

LV-N Thrust:60.0 KN Delta-V:8963 m/s

Rockomax 24-77x4 Thrust:80.0 KN Delta-V:4909 m/s

Aerospike Thrust:175.0 KN Delta-V:4971 m/s

LV-T45 Thrust:200.0 KN Delta-V:4716 m/s

LV-T30 Thrust:215.0 KN Delta-V:4948

Poodle Thrust:220.0 KN Delta-V:4203

Skipper Thrust:650.0 KN Delta-V:3083

As you see the LV-N has the highest eficency but least thrust. The Aerospike had the most delta-V, but it was just 30 m/s over the LV-T30 witch had 4948 m/s of delta-V. I say you should through out your Poodle engines and replace them with LV-T30 because they have nearly the same thrust, but the LV-T30 has nearly 500 more m/s of delta-V than the poodle. Tell me witch is the best injection burn stage based off of this chart.

[Themohawkninja]

Efficiency will technically always be better, but for the sake of orbital injection, you will need to balance enough thrust to get into orbit, with enough fuel to get into orbit withou adding too much weight in the form of engines.

[Xeldrak]

Well, it depends on the sitiuation. What do you want to inject into?

For trans münar injections I tend to use a skipper or a poodle. A skipper has the best looks and the high thrust simple make the burn less tedious. A poodle is also awesome if you want to land on it, because it's short. From an engineering point of view, a LV-T30 on a large tank tend to create a wobble-point, so I try to stick to engines that fit the tank they are attached to.

[Gus]

The LV-N is always the best choice except where time is an issue (or you're in a dense atmosphere). The LV-N does things slowly and efficiently. However, during launch, every second you spend not yet in orbit is one more second that the planet is dragging you down. Slow won't do. You need all the power your ship can handle to get into orbit as quickly as possible to stop this bleeding loss of delta-v. Thats where the less efficient but more powerful rockets come in. Usually I go for Mainsails on launch, but on lighter craft without much fuel to burn, the medium thrust/medium efficiency engines are probably the better choice.

Edited August 3, 2013 by Gus

[Bunsen]

Like almost every true/false question, the answer is "definitely maybe." Long burns are sometimes inherently inefficient, whether due to gravity losses (as Gus pointed out) or the Oberth effect (where your optimal efficiency is only available at periapsis, but much of your burn happens at higher altitide because it takes so long -- this happens a lot with interplanetary transfer burns). And there's always human impatience, which is why we don't do all our orbital maneuvering with ion engines.

As for the uselessness of the Poodle, you should take a look at what happens when you put some more payload mass on top of that tank. When the engine accounts for much of the stage's dry mass, engine mass has a huge influence on delta-v and the light engines look great (that's why the 24-77s look so good in your list -- they're light as hell, despite having crap I_sp). But when there's a bunch of payload also, the engine mass has a smaller impact and the Poodle's high I_sp often wins out over the T30's low mass -- and the 24-77s will look utterly terrible.