Why use the arospike

[Apature rocket science]

I want to know why people use the aro spike, personly I never use it but idont get why others use its just a rocket engine.

[Wanderfound]

For this:

[Overjay]

You see, specific impulses of aerospike in vacuum and atmosphere are almost equal. This fact makes it perfect for using in space planes and small multipurpose landers.

[astropapi1]

Eve ascent vehicles are where it shines like a diamond among clumps of coal. However, I've seen people using it for spaceplanes and small rockets too.

You just need to find a craft that will spend time in the atmosphere but won't be able to use jets.

[Wavechaser]

You won't say "it's just another rocket engine" if, if you take a look of its specific impulse. And compare it with LV T-45 and some other engines.

388s/390s (atsp/vacm), man!! 388s in ASL! That's almost as effective as LV-909/Rockomax Poodle/KR-2L in vaccum! I know it is kinda ugly and can't be attached in the bottom, but, hey, it's extremely fuel-effecient. In fact, it has the most ASL specific impulse among all the stock engines. Plus, 175kN of thrust is fairly a lot.

[Frank_G]

It is powerful, efficient and lightweight for a rocket engine. If you like, take a look at my Mission to Eve (Link in the signature) which makes extensive use of the aerospike engine. Its pretty much one of the best engines you can put on a heavy lander in my opinion.

[Xannari Ferrows]

It is fairly efficient, as it's specific impulses are balanced, so it is versatile.

On a space plane, it can be used for a gliding assist and landing assist.

On a rocket, it is typically used on landers, but can be used as a lightweight lifter.

On a rocket, I highly recommend the nuclear engine over all else as an upper stage.

[LABHOUSE]

I have used it for just aesthetic purposes before it was the last stage so the transit vehicle had to be upside down but still.

[Laie]

388s/390s (atsp/vacm), man!! [...] it's extremely fuel-effecient. In fact, it has the most ASL specific impulse among all the stock engines.

It also has a pretty underwhelming thrust-to-weight ratio, and the atmospheric ISP hardly ever matters (just look what happens to your engine's ISP during an ordinary launch). For most use cases, a lowly LV-T30 will serve you better. The aerospike really only shines if you try to get out of a deep, dense atmosphere; that is, Jool or Eve. Other than that, well, it looks sharp on spaceplanes.

[kujuman]

It also has a pretty underwhelming thrust-to-weight ratio, and the atmospheric ISP hardly ever matters (just look what happens to your engine's ISP during an ordinary launch). For most use cases, a lowly LV-T30 will serve you better. The aerospike really only shines if you try to get out of a deep, dense atmosphere; that is, Jool or Eve. Other than that, well, it looks sharp on spaceplanes.

I bet the aerospike would do nicely in some of the scaled-up Kerbin mods. Most of the time on lowly 600km radius Kerbin one's out of most of the atmosphere in maybe 20-30 seconds.

[Northstar1989]

I bet the aerospike would do nicely in some of the scaled-up Kerbin mods. Most of the time on lowly 600km radius Kerbin one's out of most of the atmosphere in maybe 20-30 seconds.

Indeed. The atmosphere is not only higher with Real Solar System- orbital velocity is a lot greater too. Which means, when running FAR (which will *drastically* increase your terminal velocity with an aerodynamically-shaped rocket: especially with any rocket large enough to make orbit in any of the RSS configs), you'll probably be wanting to start your gravity-turn fairly early: as you'll want to reduce the amount of velocity-change your upper stages will be responsible for...

What that means is, having an engine that operates well in the lower atmosphere is a MAJOR advantage with RSS. Especially with spaceplanes (though you don't have much hope of building a successful one in anything besides the 6.4x scale config- and even then you'll need a LOT of drop-tanks), as your lift-to-drag ratio tends to better with the smaller Angles of Attack you can maintain in the lower atmosphere (and you want all your thrust directed at the horizon- not being used to directly hold your spaceplane up...)

Regards,

Northstar

P.S. Aerospike engines also work extremely will with rockets that have a *VERY* low TWR (less than 1.10 on liftoff), as they tend to spend a lot more time in the lower atmosphere. So, if you're building some massive beast of a rocket using Procedural Parts fuel tanks...

Edited October 23, 2014 by Northstar1989

[Apature rocket science]

Thanks for clarifying that here's some rep

[Pecan]

You may like to look at tavert's Mass-optimal engine thread some time. It's a little out of date at the moment but the spreadsheet version is easy to update*.

In a lot of cases the aerospike (still) out-performs any other launch-engine for light to moderate payloads, as long as you ignore costs! If your optimisation of choice is for payload-ratio/mass-efficiency then you'll be throwing away a lot of stages (=expensive engines) but you want to get the most from them before you do; that's where the aerospike comes into its own. Getting into orbit from Eve is sufficiently difficult that mass-efficiency has to be your first priority, regardless of cost, which is why it's particularly popular for missions there.

[*I'm playing with SSTOs (rockets that go to orbit and back without staging) at the moment so haven't bothered to update that spreadsheet myself. In the previous version of KSP (0.24.x) it was still true, however, that with staging for efficiency there were only three engines worth considering for almost any mission - LV-Ns, 48-7Ss or aerospikes. 909s were, except in a small exceptional set of circumstances, the 'wrong answer' every time.]

[AmpsterMan]

Going to move this to a more appropriate forum.

[EdFred]

As others said, it's all about Eve. And now that I think about it, it is the only place I use the aerospikes.

[Dispatcher]

My "rocket engine only" spaceplane uses aerospikes. I have no complaints about them.

[UmbralRaptor]

The high in-atmo Isp occasionally lets it give your craft a payload fraction advantage, and the high impact tolerance can be of use in landing. Before 0.24, it was arguably the highest performance lander engine, but with the extreme costs, meh Isp as a launcher engine, and Poodle buffed to almost the same TWR...

[juanml82]

It is powerful, efficient and lightweight for a rocket engine. If you like, take a look at my Mission to Eve (Link in the signature) which makes extensive use of the aerospike engine. Its pretty much one of the best engines you can put on a heavy lander in my opinion.

It's not lightweight, that's one of it's problems. The LV-909 is 1 ton lighter and clustered 48-7s usually beat the aerospike for light spacecraft.

It is useful, though, but it's sort of a niche engine. It's a must for a return from Eve surface. It can be useful in medium sized spaceplanes as you aren't likely to stack anything below it, it's efficient, short (so it won't collide with the runway on take off) and packs a decent thrust. However, LV-909s, nukes and 48-7s will often beat it in efficiency, so if you can push your Ap outside the atmosphere on air breathers or if your craft is light enough that you don't need the extra thrust, you shouldn't use the aerospike.

It does have a lot of clearance for landing gear so it can be useful in some lander designs where the low thrust of the 909 or the nukes won't be enough and the Poodle or the KR-L2 don't fit.

[KerikBalm]

I don't find it very useful.

For those that said spaceplanes:

By the time you light your rockets in Space planes, you are so high up, it might as well be vacuum ISP

For those that say Eve:

Its poor TWR means you need so many engines, that your dry weight increases so much that other engines are more efficient (48-7s clusters, LFBs, probably the buffed mainsails, etc).

It can't accept a stage below it, and its unique ISP properties are only useful deep in the atmosphere, that implies it should be used as part of a first stage- ie "Boosters" - but it has a pretty bad TWR, which is not what you want in boosters.

As a result, I buffed it on my install to have a TWR equal to the LV-T45.

[Oafman]

Its small size is a key factor. Full length rockets strapped to the back of spaceplanes look ugly; aerospikes look great.

[Wanderfound]

I don't find it very useful.

For those that said spaceplanes:

By the time you light your rockets in Space planes, you are so high up, it might as well be vacuum ISP

It ain't all about efficiency. Sure, by the time I need rocketry, I'm at 35,000m and Mach 5.5 and a wet sneeze can get me to orbit. But my spaceplanes have enough slack in their performance envelope that I don't need to sacrifice everything to efficiency. Aerospikes make good, high-efficiency orbital thrusters when I need them, but they also function well as atmospheric afterburners when I'm playing around. 4g thrust at treetop height is way fun, and there's something to be said for orbital burns that don't take ten minutes to do.

The 48-7's give better efficiency, but the 'spikes give better performance.

[Jouni]

The Aerospike is the engine of choice for small (1-kerbal) Eve landers. It could also be useful as a first-stage engine in ordinary rockets, but I never build small enough rockets to use it.

It's also a good lander/vacuum engine for situations, where the LV-909 is too small and the Poodle is too large. It has the same vacuum Isp as the other two engines, and a slightly higher TWR. I rarely use the Aerospike in this role, however, as I only the big non-nuclear vacuum engines in situations, where the engine has to fit inline in the stack.

[GoSlash27]

Yeah, what Pecan said.

When I go to design a rocket stage the first thing I do is plug the payload and desired DV into a spreadsheet to see which engine will yield the lowest total stage mass overall. A good deal of the time the aerospike comes out on top.

Best,

-Slashy

[lukeoftheaura]

It's useful for high in atmospheres, when you don't want a big rocket and jets won't work.

[EdFred]

For those that say Eve:

Its poor TWR means you need so many engines, that your dry weight increases so much that other engines are more efficient (48-7s clusters, LFBs, probably the buffed mainsails, etc).

My signature disagrees with you. The low profile of the 'spike allows for a lower CG Eve lander. A lower CG lander means when you go to land on Eve's surface - where it is near impossible to find a decent flat landing area - your rocket doesn't tip over. What's the point of an ascent vehicle that is laying on its side?

Edited October 23, 2014 by EdFred