Aerospike rebalance

[CaptainTurbomuffin]

Before we had RAPIERs, we only made SSTO spaceplanes with turbojets and an aerospike. Now, it's not an SSTO-engine. Many people claim that yes it is, because it's short, and it won't be smashed, but that's a far-fetched argument.

The good thing in an aerospike is that it produces relatively constant thrust and isp, making it useful for EVE landers. However, I'd like to make it a perfect spaceplane-engine.

The high atmospheric isp is useless, as there's nearly no atmospheric pressure on the altitudes where your jets flame-out. The good thing is that it offers a rather good efficiency even on orbit. Because on spaceplanes, you usually don't have many engine slots, but you have a large, heavy fuselage, high thrust is essential. What I would like: an aerospike, wich has nearly identical vacuum stats with the Poodle engine, but it's size 1. This would be awesome for spaceplanes. Maybe more mass, as aerospikes have high mass, not simply 1 ton...

But the best idea, is that due to its pointy shape, it should have minimal drag! With spaceplanes, regular rocket motors produce a HUGE percentage of your drag! If the aerospike had less drag, it would be awesome for spaceplanes again! But if the aerospike is same as the Poodle in vacuum, and a lot better than it in atmo, why should we even use the Poodle?

-Cheaper

-Lower-tech

-Can be stack attached

-When stack attached, it has less drag due to that fairing

-Aerospike having higher mass (so that they are not identical) (Low TWR)

-It's rocket style

But wait a second! The aerospike having more thrust, and less drag? It could be even more useful for those who bother abusing EVE! Jackpot

Conclusion:

-Aerospike having significantly less drag

-More mass, more thrust!!

(Note that this is a copy from my previous balance-thread, but due to the recommendation of an advisor, I'll post its major parts separately.)

---

Edit:

The point of it is to make the aerospike an engine ideal for EVE and spaceplanes.

For spaceplanes, a high vacuum Isp is necessary. In my suggestion, I didn't care about atm isp, I just state that it should have high vacuum isp. (A lower atm isp than this is necessary, or else it wouldn't make sense) Also, high thrust would also be useful.

To compensate this buff, the TWR is lowered, and you can't stack attach this, not to talk about gimbal (not having gimbal is a great nerf, but unrealistic). Aerospikes' downside is high mass -->low TWR. KSP aerospikes are having an excellent TWR, wich is inappropriate.

Also, these nerfs would also cause the aerospike to be used only as a first-stage rocket, giving even more use to Poodles.

For EVE, it would be excellent, wouldn't it? It would be a lot better for taking off, altough transporting it from KSC to EVE would be harder...

Edited September 22, 2015 by CaptainTurbomuffin

[Red Iron Crown]

Er, it's already one of the most efficient engines in the game in vacuum already, and it has a better TWR than its nearest competitors (the Poodle and Terrier) so I don't think it needs a buff that way. Lower drag and a bottom attachment node would be great, though.

[Frozen_Heart]

Er, it's already one of the most efficient engines in the game in vacuum already, and it has a better TWR than its nearest competitors (the Poodle and Terrier) so I don't think it needs a buff that way. Lower drag and a bottom attachment node would be great, though.

Aerospike is meant to be a launch engine though. Should have TWR closer to the LV-T30/45.

[Red Iron Crown]

Aerospike is meant to be a launch engine though. Should have TWR closer to the LV-T30/45.

It already has better TWR than the LVT-45 at all altitudes and within spitting distance of the LVT-30 at sea level (and beating it in vacuum) while being more efficient than either at all altitudes.

[Whirligig Girl]

Er, it's already one of the most efficient engines in the game in vacuum already, and it has a better TWR than its nearest competitors (the Poodle and Terrier) so I don't think it needs a buff that way. Lower drag and a bottom attachment node would be great, though.

280 is a high efficiency? Have you checked its current status because at this time it in very much far too inefficient. It does not even have a similar Isp for space and vacuum, which is kind of the main selling point of aerospikes. This means that it actually does WORSE on Eve than the Reliant or Swivel engine, when it should do significantly better.

The way I see it, the balance should be this: Not particularly amazing on Kerbin or Vacuum, but better than anything else on Eve.

[Red Iron Crown]

280 is a high efficiency? Have you checked its current status because at this time it in very much far too inefficient.

"One of the most efficient engines in the game in vacuum". For the record here are the numbers:

                   Isp                  TWR
Engine          SL     Vac          SL    Vac
Aerospike      290     340        15.65   18.35
Swivel         270     320        11.47   13.59
Reliant        280     300        16.36   17.53

It does not even have a similar Isp for space and vacuum, which is kind of the main selling point of aerospikes.

The point of an aerospike is it does not lose as much efficiency away from its ideal ambient pressure, which I think the game models reasonably well (being competitive with more specialized engines at both ASL and vacuum). An engine with more similar ASL and vacuum Isps is an engine optimized for sea level.

This means that it actually does WORSE on Eve than the Reliant or Swivel engine, when it should do significantly better.

Have you tried? The Isp curves aren't linear and have more points than just 1atm and 0atm, you might be surprised at how the engines perform at Eve pressures. The Reliant tapers to 0.001s of Isp by 7atm, the Swivel to 0.001s of Isp at 6atm, so each of them are near zero thrust at Eve's 5atm; meanwhile the Aerospike is chugging along at 230s at 5atm (and still at 170s by 10atm, if you care to Jool dive).

The way I see it, the balance should be this: Not particularly amazing on Kerbin or Vacuum, but better than anything else on Eve.

That is actually a fairly good description of the current balance (though the Mammoth very slightly edges it out on Eve).

[NathanKell]

I thought that "same Isp in Vac and sea level" myth was finally killed, but apparently not.

That's Just. Not. How. It. Works.

Altitude-compensating nozzles are not magic fairy dust. All they do is lower (not even eliminate, just lower!) the penalty of using an engine at an altitude (i.e. ambient pressure) for which it was not optimized.

If you think it should provide the same Isp in vacuum and at sea level, I have a simple experiment for you. Make a compressed-air rocket motor (say, pump a soda bottle full of air). Now, measure how much thrust it provides in the air...and then measure it again underwater. That's about what we're talking about here.

You have to remember that what makes an engine produce less thrust (i.e. have a lower Isp) at sea level is not some magic "I hate you sea level!!!11one" force, but the pressure of air. No matter what your nozzle is, you're going to do remarkably better in vacuum than at sea level, because in vacuum there's 0 pascals of air pressure, and at sea level there's a hundred thousand pascals.

What this class of nozzle *does* do is eliminate the need for different engines at different altitudes. That means instead of needing a small bell at sea level (with relatively poor vacuum performance), and a large bell in vacuum (with utterly horrific sea-level performance), you get one nozzle that performs rather well at both. And so it does: the ingame Aerospike has better sea level Isp than most boosters, and better vac Isp than most upper stage engines.

[CaptainTurbomuffin]

Edited:

Er, it's already one of the most efficient engines in the game in vacuum already,

Nope.

and it has a better TWR than its nearest competitors (the Poodle and Terrier) so I don't think it needs a buff that way.

I talk about a nerf that way.

bottom attachment node would be great, though.

Not having one is a great way of nerfing and characterising.

better than anything else on Eve.

That's the main principle

                   Isp                  TWR
Engine          SL     Vac          SL    Vac
Aerospike      290     340        15.65   18.35
Swivel         270     320        11.47   13.59
Reliant        280     300        16.36   17.53

The point of an aerospike is being efficient, while being optimized for both vacuum and atm. usage. The downsige is its high mass --> low TWR

My rebalance is for making it excellent for spaceplanes, while remaining the best/getting better at EVE. With spaceplanes, you only use it in vacuum. Than it should be compared with other rocket engines you use with spaceplanes.

I thought that "same Isp in Vac and sea level" myth was finally killed, but apparently not.

That's Just. Not. How. It. Works.

Altitude-compensating nozzles are not magic fairy dust. All they do is lower (not even eliminate, just lower!) the penalty of using an engine at an altitude (i.e. ambient pressure) for which it was not optimized.

If you think it should provide the same Isp in vacuum and at sea level, I have a simple experiment for you. Make a compressed-air rocket motor (say, pump a soda bottle full of air). Now, measure how much thrust it provides in the air...and then measure it again underwater. That's about what we're talking about here.

You have to remember that what makes an engine produce less thrust (i.e. have a lower Isp) at sea level is not some magic "I hate you sea level!!!11one" force, but the pressure of air. No matter what your nozzle is, you're going to do remarkably better in vacuum than at sea level, because in vacuum there's 0 pascals of air pressure, and at sea level there's a hundred thousand pascals.

What this class of nozzle *does* do is eliminate the need for different engines at different altitudes. That means instead of needing a small bell at sea level (with relatively poor vacuum performance), and a large bell in vacuum (with utterly horrific sea-level performance), you get one nozzle that performs rather well at both. And so it does: the ingame Aerospike has better sea level Isp than most boosters, and better vac Isp than most upper stage engines.

In my suggestion, I didn't care about atm isp, I just state that it should have high vacuum isp. (A lower atm isp than this is necessary, or else it wouldn't make sense) But it should have enough atm. efficiency to be able to rock on EVE.

Edited September 22, 2015 by CaptainTurbomuffin

[Red Iron Crown]

Nope.

Your compelling counterargument has convinced me.

Care to back it up with numbers? The aerospike is currently more efficient in vacuum than all but four engines, only two of which are chemical rockets and all of which have worse TWR than the aerospike. It is literally "already one of the most efficient engines in the game in vacuum".

Edit: You should also read my response to Gregroxmun, it is already one of two engines that is worthwhile to use on Eve.

Edited September 22, 2015 by Red Iron Crown

[Val]

...

The high atmospheric isp is useless, as there's nearly no atmospheric pressure on the altitudes where your jets flame-out. The good thing is that it offers a rather good efficiency even on orbit.

...

Not all SSTOs in KSP have air-breathing engines.

While it's not very important for KSP game balance, I think it's an interesting anecdote, that some real life Aerospikes were also designed for non-airbreathing SSTOs (X-33 and VentureStar) and were considered for the Space Shuttle.

...

Aerospike engines have been studied for a number of years and are the baseline engines for many single-stage-to-orbit (SSTO) designs and were also a strong contender for the Space Shuttle Main Engine.

...

Source

[CaptainTurbomuffin]

Not all SSTOs in KSP have air-breathing engines.

While it's not very important for KSP game balance, I think it's an interesting anec...e, that some real life Aerospikes were also designed for non-airbreathing SSTOs (X-33 and VentureStar) and were considered for the Space Shuttle.

:rolleyes:Aham, that's what I frogot! I knew I frogot to mention something!

The aerospike would be even better for only-rocket SSTOs, as well as a central engine for asparagus rockets.

[Frozen_Heart]

Yeah Rocket SSTOs is pretty much all I would use the aerospike for. However I find the LV-T30 better as it has so much more thrust.

[CaptainTurbomuffin]

Yeah Rocket SSTOs is pretty much all I would use the aerospike for. However I find the LV-T30 better as it has so much more thrust.

Currently, the aerospike has nearly the best TWR. Based on my suggestion, it would have one of the lowest BUT its thrust would still remain high, so it would become even better than the LVT-T30!