Aerospike Nerfed too hard.

[Whirligig Girl]

290 in Kerbin Atmosphere, 330 in the Vacuum of Space. That's a huge difference! The whole point of the aerospike is that it is efficient at all altitudes, and it has failed in this variation! It is also supposed to be efficient anyway! I would suggest Isp of 335atm to 340vac, making it a little less efficient than the LV-909, like it originally was. It really should be built for Eve missions, right now it is way underspec'd for that mission.

Edited April 30, 2015 by GregroxMun

[Hcube]

Did you mean nerfed ?

[Azimech]

Yeah ... same goes for the basic jet engine. Not only does it provide a third less thrust when stationary, engine thrust drops off with altitude like it's a piston engine without a supercharger.

[Whirligig Girl]

Did you mean nerfed ?

I am not a smart man.

[NathanKell]

GregroxMun, I suggest you look up how altitude-compensating nozzles actually work.

They are not magic IWIN buttons that let you defeat the laws of physics. Your performance is always going to decrease, and quite sharply, as the ambient pressure increases. All an altitude-compensating nozzle does is let you have near (but not fully) optimal performance at that pressure. Want an example? Compare the toroidal aerospike J-2 derivative J-2T-250K to the SSME.

http://www.astronautix.com/engines/j2t250k.htm

http://en.wikipedia.org/wiki/Space_Shuttle_main_engine

1. A bell nozzle will always do better than an altitude-compensating nozzle at the bell's optimal altitude; however, for the same cycle efficiency and chamber pressure an altitude-compensating nozzle will do better at all other ambient pressures.

2. Chamber pressure matters as much or more than nozzle design in high-pressure situations. Squad seems to have taken this onboard, with the (SSME-lookalike) 3.75 booster having slightly better SL Isp than the 'spike (although worse vacuum Isp).

That said, I do think the 'spike's vacuum Isp is a bit low. It should be more comparable to the LV-909 and KR-2L.