What kind of engines would you recommend for an SSTO?

[Brownhair2]

I mean, first thing that comes to mind is the RAPIER. But are there any engine combos what work better?

[icedown]

Take a look at some of the challenge threads.  There are several SSTO ones with some interesting designs and combinations.  Rapiers with NERVs are pretty common though

[bewing]

<insert RegEx's standard complaint that there are other vertical launching SSTOs besides spaceplanes>

It's not like there are a lot of options.

For the airbreathing phase: I find the Whiplash/NERV combo works approximately equally well as a Rapier/NERV. The Rapier actually goes a little too fast for me down in the atmosphere, and puts your nose at some pretty severe thermal risk as you climb through the 22km-40km danger zone. Since the Whiplash is lower tech, I think it is a very good option. I think it comes down to: Rapier = MK2 design, and Whiplash = MK1 -- which ends up making them equal choices (except that MK2 is prettier and reenters better, and MK1 is more fuel efficient). But part of that choice depends heavily on exactly how you design the nose (blunt vs. pointy) or if you can figure some other really clever way around the nose heating problem.

For the rocket phase: Part of the question is just how far up do you want your SSTO to fly? If all you want to do is get to LKO, do a little bit of docking, and then reenter -- then your rockets don't matter much because they won't be running all that long. So you either just use the Rapiers to go the rest of the way to LKO, or you slap on a couple Terriers to keep the weight down, or you use a Poodle or Skipper if you want to SSTO something big.

OTOH, if you want to fly your SSTO to Minmus or Duna, then you need 120kN to make any decent-sized SSTO climb and accelerate -- so NERV is your only fuel-efficient choice. You can't get a spaceplane orbital with a reasonable number of ion engines (which is your only available step up in Isp). Or, once again, you can use the Rapiers and hope that the weight savings balances out the bad Isp.

Edited June 16, 2016 by bewing

[mk1980]

in my experience, the whiplash & aerospike combo works very nicely for crew missions to low orbit. i'd even say it's superior to rapiers for that type of mission.

the main difference between whiplash and rapier is that the whiplash produces more thrust at low speeds and less thrust at high speeds - and the top speed and altitude is quite a lot worse than that of the rapier.

for a quick crew mission to LKO (ie. minimal payload) the higher "early" thrust of the whiplash allows for a more aggressive, steep ascent. this way you get to orbit almost as fast as a rocket. time is an important economic factor - if you spend 20 minutes on a mission using a plane and you could do the same mission with a rocket in 5 minutes, the rocket is probably more efficient overall (since you can earn A LOT more money in the saved time than whatever amount of funds you saved by using an SSTO) - unless you lift a very heavy payload or you send up crew (which you'd have to return to kerbin anyway, so the additonal "must reenter and land" problem of the plane is covered by that). so for small payloads, reduced mission time is more valuable than "absolute" fund efficiency (in my opionion)

other than that... well, i guess it's worth pointing out that SSTO planes with panther afterburner engines (+some early rocket engine such as a swivel or terrier) are possible. they aren't particularly good at anything, but you don't need to invest a whole lot of research points to unlock the tech, so they are a more or less viable alternative to rockets in the "mid game" for some mission types.

 

also, as bewing and icedown pointed out - if you plan to do more than just a little rendezvous & docking in LKO, adding a nuke or two into the mix can greatly increase your mobility in space.

[AeroGav]

Career mode, low tech -

Panther/Terrier   then Whiplash/Terrier

 

Science mode,  low kerbin orbit shuttle 

Rapier

 

Interplanetary,  Sandbox Mode

Rapier / NERV  

 

Interplanetary, Career Mode

Whiplash / NERV

 

The Whiplash / NERV choice depends on play style.  In terms of performance, the RAPIER's top end is preferable to the Whiplash's beefier midrange, because ultimately the first job of an airbreather is to get as high and fast as possible before engaging the closed cycle engine, this trumps all other considerations.  A well-designed low drag ship should still be able to bust the sound barrier despite the RAPIER's weaker subsonic thrust.

However, in career mode the Whiplash takes a ton less science points to unlock.   The other thing is that the Whiplash only costs 2000 Kredits, not much more than the Panther,  while the Rapier sets you back an eye watering 6000.      This means the Whiplash is cheap enough to throw away.   If you jettison the thing when it flames out, you can have 3000 delta V in low kerbin orbit - enough to make a return trip to Duna - because airbreathing engines weigh 2 tons each, their mass is the biggest limiter on what SSTO can acheive.

Note if you're planning to land an airplane on Duna, you'll be needing a lift rating of 1 per ton of vehicle weight - lots and lots of wing.

 

[Van Disaster]

Should point out that not all spaceplanes are SSTO either.

Panther/LV-Txx works, Panther/Thud also works if you don't want three 1.25 wide stacks, Panther ( any jet really )/LV-N+droppable rocket boosters for ascent stage is a nice combo mid-career. If you're going that way, strapping a couple of Junos to your plane and a couple more to the rocket boosters will get you a HOTOL spaceplane very early in the tech tree ( if somewhat costly in dropped parts... ). Juno/Spark works, believe it or not.

Is 20 mins in KSP *really* going to earn you more? I'd like examples of that.

Edited June 16, 2016 by Van Disaster

[Teilnehmer]

13 hours ago, bewing said:

The Rapier actually goes a little too fast for me down in the atmosphere, and puts your nose at some pretty severe thermal risk as you climb through the 22km-40km danger zone.

…or if you can figure some other really clever way around the nose heating problem.

I place a Communotron-16 antenna in front of a cabin. It shares the heating between itself and the cabin so the craft can survive higher speeds in atmosphere.

In orbit:

Spoiler

 

Edited June 16, 2016 by Teilnehmer

[xendelaar]

2 hours ago, Teilnehmer said:

I place a Communotron-16 antenna in front of a cabin. It shares the heating between itself and the cabin so the craft can survive higher speeds in atmosphere.

 

Interesting idea.  How much faster does this allow you to go (roughly) compared to a ship without an antenna?

[bewing]

About 250 m/s.

[panzer1b]

While i dont design SSTOs as much as i used to, in the current game there are pretty much three engines that make any sense to have on a SSTO (in terms of raw efficiency).

 

Rapier:  Self-explanatory, it has both jet and rocket in one, so you can potentially get a rather efficient design as its lighter then a jet+rocket combo such as aerospike+turboramjet.  That said, it comes with 2 major downsides.  It has lousy rocket ISP, a big problem if you want the SSTO to go past LKO, for mun/minmus id rather have a lv-909 or something which has better ISP even if it means heavier total engine mass.  Also, it requires very tricky thermal design to keep the nose/wings from melting on ascent.  Since the rapier flies very very fast in the dangerous area between 20-40km, you will fry if you are not careful.  Personally ive found a higher ejection angle solves this with most craft (trade altitude for speed, less fuel efficient, but there is only so fast you can go before your craft vaporizes itself with heating at 100%).  Finally, it is fairly bad for landing and takeoff (especially if you are trying to fly 50t on a single rapier), given its anemic TWR when flying very slowly.

Turboramjet:  Its better then the rapier if you want to spend alot of time in atmo because it uses less fuel and is way better at low altitudes/low speeds.  The downside to it is that it is less efficient hands down compared to the rapier for pure ascent (even if you never use the rapier's rocket mode).  I have personally used them both for fun and with nukes (both use LF only), so they are solid choices (especially if you play career and dont have rapier yet), but generally speaking rapiers are just easier to work with and give you better performance.

Nuke:  If you want to go anywhere past minmus with your SSTO (discounting ISRU) you NEED to have one or more nukes on your craft.  Personally my best nuke/rapier combo (in 1.0.5) managed to get over 7000 dV in LKO and i managed to go to laythe, pol, and bop (including landing on all of these) and then returning to kerbin without any form of refueling.  While it doesnt really make alot of sense to make SSTAs (single stage to anywhere) given that its more viable to have a separate interplanetary ring or whatnot where a shorter range SSTO docks to, knock yourself out, afterall, ive spent alot of time in KSP making these things!

 

 

Now there are always other engine options depending on situation (for example a Eve SSTO will need to use aerospikes/new shuttle engine/ks25x4), but in general these 3 will do you well with most builds.  Also, worth noting is that the jumo jet engine coupled with a 48-7s will make a very good micro-SSTO, although i do not build things that small and thus dont really have experience with those engines.  If you want stuff thats below 5t, then those 2 engines work well (you can also use a lv-909 instead of the 48-7s but it depends on how much thrust you need).

[cantab]

I'll just add that if it's a VTOL, Panthers make great lift engines in afterburning mode, more TWR than other jets and much more fuel efficient than rockets.

[mk1980]

17 hours ago, Van Disaster said:

Should point out that not all spaceplanes are SSTO either.

Panther/LV-Txx works, Panther/Thud also works if you don't want three 1.25 wide stacks, Panther ( any jet really )/LV-N+droppable rocket boosters for ascent stage is a nice combo mid-career. If you're going that way, strapping a couple of Junos to your plane and a couple more to the rocket boosters will get you a HOTOL spaceplane very early in the tech tree ( if somewhat costly in dropped parts... ). Juno/Spark works, believe it or not.

Is 20 mins in KSP *really* going to earn you more? I'd like examples of that.

ok this is off topic, but in my experience there is always some satellite contract, orbital rescue or station/outpost contract available. some of them may not be doable in 20 minutes from start to cash-in, but they still earn you more "cash per minute playtime" than what you save by using an SSTO to deploy some minor cargo (satellite, probe, station modules etc. - basically anything that isn't "large amount of fuel/ore")

of course that also depends on how efficient you are at making rockets. if your rockets are too expensive for what they do, the time saving may not be worth the extra cost.

simple satellite contracts in the kerbin SOI are perfectly doable within 10 minutes or so, and even on harder settings they can easily earn you like 50k funds. the advance payment already covers more than the cost of the rocket+satellite and the reward is pure profit.

 

 

[jarmund]

Presumptions:

1. You're asking about winged crafts that launch horizontally.

2. Your destination is a 100x100 orbit or lower.

3. You're using an MK2-based design

 

In that case there are multiple options. Personally I'm a big fan of RAPIERs combined with LV-Ns, but that's mostly because I tend to use my SSTOs further than just a 100x100 O. The nuke, despite the massive weight increase, allows me to go a lot further with proper planning and piloting. If I'm just shuttling things to orbit, then RAPIERs work fine on their own. Alternatively, when I'm working lower in the tech tree, Whiplash + Terrier is also a decent combination, but somewhat harder to fly.