Best long range SSTO engines

[cebu516]

I know I know there's the NERVA engine but is there anything else? These NERVA engines are don't have enough thrust and can barely do 5 m/s gained per second.

[Vanamonde]

The Rapier engine saves weight because it can function both as a jet (requiring no oxidizer while in atmosphere) and as a rocket (once the air gets too thin). That being said, its thrust in jet mode is not terrifically high so many players still build with a combination of jet and rocket engines. 

[jimmymcgoochie]

The NERV might not have a lot of thrust, but it also has double the ISP of even the best liquid fuel/oxidiser engines so you’ll go further in the long run.

A good combination of engines for SSTOs is:

• RAPIERs in air-breathing mode for atmospheric flight- they might not be the most fuel-efficient, but they can produce a lot of thrust at higher speeds than any other air-breathing engine;
• “Dart” aerospikes for climbing towards orbit- not the most powerful, but very efficient both in atmosphere and vacuum;
• NERVs for orbital insertion and beyond- raw ISP gives it the edge over other engines even if it’s not very powerful and a bit on the heavy side.

It’s possible to do a liquid fuel only SSTO by only using RAPIERs and NERVs, but that’s not something I’ve ever done. If you’re doing a career or science mode game and haven’t unlocked those more high-tech engines, combining the Panther or Whiplash jets with the Reliant or Swivel rockets can make a decent SSTO if done right.

 

[magnemoe]

You need 800-1000 m/s getting from rapier atmospherically mode cutout to orbit. 
Would not go aerospikes unless you need them to take off, at rapier cutoff you are at 30 kilometer if you want more trust I would use pure vacuum optimized engines, I would fire the LV-N as soon as the rapiers start dropping in trust then you are already in vacuum. I say the question is is using an 3rd engine type worth it over using the rapiers in closed cycle. Remember you can shut them down as need for trust goes down. say you have 3 rapiers, first fire up LV-N, switch to closed mode a bit later, then kill center engine, then kill the two outer and fire up the center again, then finally shut that down. 
I say you probably need oxidizer for 4-500 m/s  for the rapier, a lot dependent on how you fly. Do not turn of your engines then Ap is above atmosphere and then have to do an high trust circulation but walk Ap ahead of you until you are in orbit. Real rockets don't do KSP style circulation burns for LEO  orbits, yes you looses some efficiency because not burning straight ahead but at 800 s ISP its not an big deal. 

[king of nowhere]

the best results for a long range spaceplane are achieved with a whiplash+nerv combo. the whiplash to accelerate in atmosphere, the nerv for space.

[Lt_Duckweed]

4 hours ago, king of nowhere said:

the best results for a long range spaceplane are achieved with a whiplash+nerv combo. the whiplash to accelerate in atmosphere, the nerv for space.

Rapier actually takes the win here,  the higher top speed means a better ratio of Nerv dry mass to overall wet mass (due to higher airbreathing speed meaning less nerv twr needed) and the fuel savings from shorter Nerv burn for the most part offset the lower isp of the Rapier vs the Whiplash in airbreathing mode.

Edited October 17, 2022 by Lt_Duckweed

[miklkit]

In my experience the Whiplash runs out of air too soon and I had to add a rocket engine to assist in getting to a higher altitude where the NERVs could work more efficiently.  Rapiers give a lower overall weight because of this.

[DeadJohn]

On 10/15/2022 at 1:27 PM, cebu516 said:

I know I know there's the NERVA engine but is there anything else? These NERVA engines are don't have enough thrust and can barely do 5 m/s gained per second.

If you're going to Mun and beyond, Rapier+NERV is often good because you'll get very high vacuum ISP after turning off the Rapiers. Once you're in orbit the NERV can do everything and your SSTO will be mostly liquid fuel. Only carry enough oxidizer for the Rapiers to provide a burst of extra TWR for getting out of the atmosphere, plus optional extra oxidizer if the NERVs can't provide enough TWR for Mun landings. The low acceleration of the NERV shouldn't be a big problem for other orbital maneuvering.

Whiplash+NERV+[maybe aerospike] can work but takes practice to get a good ascent profile that gives the NERVs enough time to circularize orbit. You may have to add an aerospike for more thrust which then makes a more complex 3-engine-type SSTO.

If you have the Making History expansion, Whiplash+Wolfhound is worth considering. The Wolfhound is the highest ISP LFO engine; still much lower than NERV but much higher thrust. Such an SSTO would use mostly LFO, with a little extra liquid-only for the Whiplashes.

Several mods add dual-mode engines as Rapier alternatives. Look at Near Future Aeronautics, OPT, Mk2 Stockalike Extension, Mk3 Stockalike Extension.

 

[magnemoe]

Now the question is why an long range SSTO? 
I launch them into LKO dock the a space station or something designed to operate in deep space. 
This is an Laythe base with its spaceplane on top. An tanker above that just topped off the tanks. 

Its an 3 stage rocket, chemical, an LV-N second stage cross feed to the tug with side mounted LV-N and the base who has enough fuel and oxidizer to land on Pol. 
Jool trip will be a bit more than an year. 
First stage will drop during the Jool injection burn, second at Tylo braking. Needed an intercept getting into Pol orbit but had another tug fueled so no issues. 
Also you might want kerbals to enjoy spin gravity during their trip. 

[king of nowhere]

23 minutes ago, magnemoe said:

Now the question is why an long range SSTO? 
I launch them into LKO dock the a space station or something designed to operate in deep space. 
This is an Laythe base with its spaceplane on top. An tanker above that just topped off the tanks. 

Its an 3 stage rocket, chemical, an LV-N second stage cross feed to the tug with side mounted LV-N and the base who has enough fuel and oxidizer to land on Pol. 
Jool trip will be a bit more than an year. 
First stage will drop during the Jool injection burn, second at Tylo braking. Needed an intercept getting into Pol orbit but had another tug fueled so no issues. 
Also you might want kerbals to enjoy spin gravity during their trip. 

yes, it is more efficient to use the ssto to bring to orbit a ship optimized for vacuum, but some people use ssto to everywhere for the challenge.