What is the use of Aerospikes and some other engines

[Falkenherz]

Hi! I am slowly going up the tech tree in career mode and face a decision: Do I go for the nuclear engine or for the aerospike engine? While I know about the Nerva that it is best suited for transfer stages, I have no idea what the Aerospike could be good for.

So far, I found that

- for space travel, Sparky (light), Terrier (middle), Poodle (big) engines seem to be most efficient (pre-Nerv tech level)

- for launch, it depends on TWR in relation to the hallmark dV of 3500 with regards to the payload; right now I am content with Skipper engines (I usually use launch payloads to LKO of up to 30 tonnes).

I found some threads about engine efficiency, even a neat little webpage with a configurable engine chart but it is a bit weird to read for me. For spaceplanes, I use whiplash turbojets together with a Skipper for reasonable results.

So, where could the Aerospike fit in?

Edited May 26, 2015 by Falkenherz

[GoSlash27]

Hi! I am slowly going up the tech tree in career mode and face a decision: Do I go for the nuclear engine or for the aerospike engine? While I know about the Nerva that it is best suited for transfer stages, I have no idea what the Aerospike could be good for.

So far, I found that

- for space travel, Sparky (light), Terrier (middle), Poodle (big) engines seem to be most efficient (pre-Nerv tech level)

- for launch, it depends on TWR in relation to the hallmark dV of 3500 with regards to the payload; right now I am content with Skipper engines (I usually use launch payloads to LKO of up to 30 tonnes).

I found some threads about engine efficiency, even a neat little webpage with a configurable engine chart but it is a bit weird to read for me. For spaceplanes, I use whiplash turbojets together with a Skipper for reasonable results.

So, where could the Aerospike fit in?

Falkenherz,

The aerospike doesn't match the LV-909 or Poodle for vacuum operation, but it's not very far behind and pretty strong in- atmosphere. It would be useful for an SSTO lifter or (especially) a boost stage on Eve.

*edit* I missed the initial question.

I would go for the NERV before the Aerospike. Just remember that you really shouldn't use the Nerv unless you're going farther than Duna with a decent sized payload. Even then, it probably works out cheaper to use an LV-909 or Poodle.

Best,

-Slashy

Edited May 26, 2015 by GoSlash27

[Dilli]

It can be good for use on a lander, its relatively short and has a much higher thrust than the LV-909.

[Mister Dilsby]

Using two of them (in side-mounted nacelles) as main propulsion for a ship that launches two-stage horizontal from Kerbin and is meant for extended surface/atmospheric operations and SSTO on Duna. Acceptable TWR and of course good Isp at any altitude. Also, they look nice.

ETA: Not that it matters, but the above image is not canonical for my story. Note lack of Kerbfleet flag, this is sandbox

Edited May 26, 2015 by Kuzzter

[Falkenherz]

Falkenherz,

Just remember that you really shouldn't use the Nerv unless you're going farther than Duna with a decent sized payload. Even then, it probably works out cheaper to use an LV-909 or Poodle.

Best,

-Slashy

Wanted to soon build a transfer stage which couple to achieve efficient 0,5 TWR payloads with them (e.g. fuel payloads delivered from spaceplanes and delivered for extended landing operations). My current idea pre-Nerv is to have a 1440 payload-tank (then 2880) attached to a probe, with a LV-909 or Poodle and fuel for the required dV. Maybe I should stick to that version then?

Concerning the Aerospike, I understand now their best use is for operations on Duna and other atmospheric planets. Very helpful, thanks!

[Chaos_Klaus]

The thing about the Aerospike engine is that it doesn't loose so much thrust and efficiency when in high pressure atmospheres. This is especially true for flying on Eve, as the atmospheric pressure on the surface is so hight that most of the engines do not produce enough thrust.

The Nukes are the better choice in my opinion, as they are useful in more situations. They have double the efficiency of other vacuum rated engines (like the LV-909). They are heavy though and thus only make sense for larger craft with larger payloads. Also note that the LV-N only uses liquid fuel, so don't bring oxidizer!

[GoSlash27]

Wanted to soon build a transfer stage which couple to achieve efficient 0,5 TWR payloads with them (e.g. fuel payloads delivered from spaceplanes and delivered for extended landing operations). My current idea pre-Nerv is to have a 1440 payload-tank (then 2880) attached to a probe, with a LV-909 or Poodle and fuel for the required dV. Maybe I should stick to that version then?

Concerning the Aerospike, I understand now their best use is for operations on Duna and other atmospheric planets. Very helpful, thanks!

Falkenherz,

Again, it would depend on how far it's going and whether the added cost/ headaches associated with the LV-N outweigh the benefit.

I can accomplish an awful lot with the plain old LV-909, so I tend to not resort to the LV-N unless I really don't have a choice.

Still and all.. the LV-N has more opportunities to be useful than the aerospike.

Best,

-Slashy

[A_name]

At what point does the Nerva begin being useful? The largest craft I've built so far was to capture an asteroid. Don't remember the weight but it was made of 2 orange tank's worth of fuel, a capsule and a claw. I thought, well this is pretty heavy, for sure the Nerva will be useful here. Nope. KER showed more delat v using a poodle. What kind of payload do I need to make the Nerv worthwhile?

[GoSlash27]

A-Name,

The short version:

Where required acceleration is under .5G

and

DV requirement is over 2kM/ sec

and

payload is at least 7 tonnes

This is the range where an LV-N will yield a lighter stage than an LV-909.

It will still be more expensive and troublesome, though.

In any case with a substantial payload where you need more than about 4km/ sec DV, the LV-N will be your best bet because it's really the only option you've got. 4kM/sec represents a *huge* DV requirement.

Best,

-Slashy

[ElWanderer]

At what point does the Nerva begin being useful? The largest craft I've built so far was to capture an asteroid. Don't remember the weight but it was made of 2 orange tank's worth of fuel, a capsule and a claw. I thought, well this is pretty heavy, for sure the Nerva will be useful here. Nope. KER showed more delat v using a poodle. What kind of payload do I need to make the Nerv worthwhile?

It's more awkward now the nuclear engines don't use oxidiser. Simply swapping one in for another engine won't show it in its best light unless you also change the tanks.

Anyway, this sounds like a question that could be answered by the awesome engine comparison http://forum.kerbalspaceprogram.com/threads/121565-Optimal-engine-charts-for-1-0-2 thread in the General KSP Discussion forum.

[Endersmens]

Yeah, I was working on a duna transfer stage (I usually do my Duna missions with a three module ship. Transfer Stage>Main Module (with lab and utilities)>Lander)

using LV-909's, I got 4,100 m/s of Delta-V. Using Nerv's, I got 3,900 Delta-V. I chose the Nerv configuration.

Why would I give up 200 m/s? Cause the Nerv config weighs significantly less due to the tanks not having oxidizer. Makes the whole craft lighter, and I think with the added weight of the rest of the module, the Nerv will outperform.

Anywho, Aerospike pretty much is the go-to for anything Eve.

[moogoob]

It's a good engine but keep in mind that it can't gimbal. The Aerospike is very useful in certain situations - I use it in a rocketplane (put it on a small plane and you can go stupid fast in seconds and it doesn't run out of fuel too quickly) design or two, and as a main engine on my Mk2 shuttle which fires from launch alongside and drawing fuel from the boosters.

Alongside the Thud it's one of the best heavy-thrust lander engines, and much much better in atmospheres.

[Chaos_Klaus]

Yes, comparing the Nerva to other engines is tricky, because you need to use extra liquid fuel instead of the oxidizer to compare correctly.

[GoSlash27]

Yeah, I was working on a duna transfer stage (I usually do my Duna missions with a three module ship. Transfer Stage>Main Module (with lab and utilities)>Lander)

using LV-909's, I got 4,100 m/s of Delta-V. Using Nerv's, I got 3,900 Delta-V. I chose the Nerv configuration.

Why would I give up 200 m/s? Cause the Nerv config weighs significantly less due to the tanks not having oxidizer. Makes the whole craft lighter, and I think with the added weight of the rest of the module, the Nerv will outperform.

Anywho, Aerospike pretty much is the go-to for anything Eve.

Endersmens,

You have to check that to be sure.

Remember that the Nerv weighs 2 1/2 tonnes more than the LV-909 and that's not counting the wing sections to keep it from overheating.

A proper apples/ apples comparison is difficult to do using KER. All it really says is how much DV you have when you swap engines, and it may be misleading, depending on the situation.

The question isn't "which engine will give me the most DV" when designing a stage, it's "which engine, when combined with everything it needs, will give me the necessary DV and t/w with the least mass and cost". This is a question that KER can't answer. We rely on mathematical analysis for that.

Meithan is working on an awesome webapp for it. I have ginned up a spreadsheet based on the principles I discuss here.

Best,

-Slashy

[A_name]

Thanks for the replies.

Anyway, this sounds like a question that could be answered by the awesome engine comparison http://forum.kerbalspaceprogram.com/threads/121565-Optimal-engine-charts-for-1-0-2 thread in the General KSP Discussion forum.

If only I could understand these things

[arq]

Go for the LV-N. It is the best for moving heavy payloads around in space. The aerospike is mainly a strong contender for Eve launches. The LV-T30/45 are usually preferable over the aerospike in the 1.5m category, because of the higher TWR of the 30 and the gimbal of the 45. The strength of the aerospike is that it retains thrust/ISP at much higher pressures than other rockets. However, only the bottom 5km or so of Kerbin's atmosphere is really thick enough for the aerospike to be any better than the other engines, and you don't spend very long there when launching.

As mentioned, the exception is Eve (or Jool, if you have some reason to be deep there), which has a much denser atmosphere that renders most engines exceedingly weak. The aerospike has the best ISP (and maybe TWR? I'd have to look closer) in the lower Eve atmosphere by quite a bit.

Many people also like the aerospike for its short profile that looks good on spaceplanes. However, from a performance standpoint the T30 is usually preferable (if you don't need the gimbal), since it is both lighter and more powerful (which can offset some of the ISP loss). The LV-909 also works well in this capacity, if less thrust is needed.

[ajburges]

The other complication from the new nuke implementation is that you can no longer pool fuel and fuel payload together. You need to calculate them separately.

Every lander mission I do is an orbit rendezvous approach. This allows me more landings per ton. With conventional drive engines, I give the CSM a ludicrous dV and make landings until I approach dV amount required for mission return. With nukes though, I need to account CSM dV separately from lander fuel. (Unless I loose my mind and make a nuclear lander)

I believe nukes are more useful than aerospikes. That node does have other stuff than the aerospikes though. Also, you want Mk3 parts to make the most of nukes. (to optimize dry mass of your nuclear craft)

[Dispatcher]

I made an SSTO spaceplane (which launched horizontally from the runway) using ONLY rocket engines; no jets and this was before the Rapier was introduced. The rocket engines? Aerospikes. I didn't succeed with other engines (yeah, yeah, probably my lack of design and piloting skills). My biggest beef with the spikes is that they do not stack.

I also made a (vertical) ship which lands on Laythe and returns to Kerbin. It uses jets and aerospikes. (Edit: that was the lander; O to O were NERVAs).

It may be a niche product, but for those times it works well.

[jarmund]

Personally I love the aerospike. Good TWR, and decent Isp, so when the LV-909 lacks in power for my lander, I go for the aerospike.

It is currently in use on the lander of my Dres-expedition. It's very low profile makes it easy to build wide instead of tall.

[GoSlash27]

Thanks for the replies.

If only I could understand these things

A_Name,

You should let them know you don't understand the charts. They'll be happy to help explain it. It might also give them ideas on how to make the charts more user friendly.

Best,

-Slashy

[luizopiloto]

any return vehicle that will bring stuff back from Eve or Laythe will performs better with Aerospikes...

[juanml82]

As for the OP, I'd go for the Nervs. The aerospikes are sort of a niche engine. There are situations in which they are the best (or only) suitable engine, but outside those, they are hampered by their weight, their lack of gimbal and because you can't stack anything below them.

The Nervs, OTOH, are the go to engine for interplanetary travels and for moving around heavy payloads. Use them with MK3 liquid fuel tanks or use a very useful "mod" (really, a module manager patch) which allows you to switch any/most tanks from fuel&oxidizer to fuel only. Unfortunately, I don't remember how that thread was named, so I can't help you look for it.

[mikeb30165]

- - - Updated - - -

At what point does the Nerva begin being useful? The largest craft I've built so far was to capture an asteroid. Don't remember the weight but it was made of 2 orange tank's worth of fuel, a capsule and a claw. I thought, well this is pretty heavy, for sure the Nerva will be useful here. Nope. KER showed more delat v using a poodle. What kind of payload do I need to make the Nerv worthwhile?

The KER result is because the Nukes only need Liquid fuel now; the Oxidiser is just dead-weight.

- - - Updated - - -

Endersmens,

You have to check that to be sure.

Remember that the Nerv weighs 2 1/2 tonnes more than the LV-909 and that's not counting the wing sections to keep it from overheating.

A proper apples/ apples comparison is difficult to do using KER. All it really says is how much DV you have when you swap engines, and it may be misleading, depending on the situation.

The question isn't "which engine will give me the most DV" when designing a stage, it's "which engine, when combined with everything it needs, will give me the necessary DV and t/w with the least mass and cost". This is a question that KER can't answer. We rely on mathematical analysis for that.

Meithan is working on an awesome webapp for it. I have ginned up a spreadsheet based on the principles I discuss here.

Best,

-Slashy

Wing sections to keep Nervs from overheating? Since 1.02 rebalanced thier heat production, I've not had to use that trick - even for long Jool burns. The biggest irritation with the Nervs is lack of choice regarding liquid-fuel only tanks, but apart from that (IMHO) they are still the natural choice for inter-planetary missions.