Are SSTOs' overpowered?

[Roflcopterkklol]

The biggest issue for large SSTO rockets will probably be slowing down to speeds where the parachutes can be safely deployed.

I launched my example rocket with FAR & DRE. The rocket had 1290 m/s of delta-v remaining in orbit, while the stock rocket had only around 50 m/s. Once I separated the payload, delta-v increased to 2114 m/s. Atmospheric reentry was not a problem, but I had to spend almost all remaining fuel to slow down, as the rocket was trying to hit ground at a supersonic speed.

Ehh there is a reason why i like the stock aero model.

[magnemoe]

I built a quick SSTO rocket for a heavy payload. It's a simple and practical design with no special tricks, apart from hiding some parts in the cargo bay.

http://jltsiren.kapsi.fi/ksp/0.90/ssto_rocket_1.jpeg

1030.1 tonnes on the launchpad with 126.6 tonnes of payload. It's also recoverable, especially if you're better at precision landings with stock aerodynamics than me. It looks much more aerodynamic than most rockets I fly in FAR, so something similar should work in 1.0 as well.

The KS-25x4 and the KR-2L are just too good for the stock Kerbin (and even more so with FAR), especially because the engine cluster doubles as highly durable landing gear. The only reason I build staged rockets is that I like dropping huge boosters.

Practical design, I guess you don't use cross feed on that but rather let the good vacuum performance of core do its work, and yes it might work in 1.0 too, the engines works as decent heatshields with deadly reentry. With an standard design you can use the same landing profile each time.

- - - Updated - - -

The biggest issue for large SSTO rockets will probably be slowing down to speeds where the parachutes can be safely deployed.

I launched my example rocket with FAR & DRE. The rocket had 1290 m/s of delta-v remaining in orbit, while the stock rocket had only around 50 m/s. Once I separated the payload, delta-v increased to 2114 m/s. Atmospheric reentry was not a problem, but I had to spend almost all remaining fuel to slow down, as the rocket was trying to hit ground at a supersonic speed.

Unless your flight profile and design is like an ICBM warhead you will not be at supersonic speed then landing in real life, look at real life reentry profiles of pods and shuttles.

Remember that your rocket is mostly empty tanks and not very aerodynamic then coming in ass first. Falcon 9 return missions might be an good example, no the max speed is not orbital but it should not affect sea level speed much.

[Jouni]

Unless your flight profile and design is like an ICBM warhead you will not be at supersonic speed then landing in real life, look at real life reentry profiles of pods and shuttles.

Remember that your rocket is mostly empty tanks and not very aerodynamic then coming in ass first. Falcon 9 return missions might be an good example, no the max speed is not orbital but it should not affect sea level speed much.

You're missing something important: the rocket is really heavy. Its dry mass is over 150 tonnes (2x more than the Shuttle on reentry), while the cross section is only around 45 m^2 (5.5x less than the wing area of the Shuttle). Once something like that loses enough speed that it's no longer even pretending to be in orbit, it's going to fall quickly through Kerbin's shallow atmosphere and hit ground well past terminal velocity.

Edit: I also forgot one important thing: there was around 100 tonnes of fuel left in the rocket. In a shallow uncontrolled reentry (95x45 km orbit), the rocket hit ground at around 430 m/s at 400 m above sea level. The terminal velocity was around 330 m/s just before the impact.

Edited February 26, 2015 by Jouni

[rkman]

SSTO is going to lift jack squat compared to a multistage rocket.

Imo the fact that a basic run-off-the-mill jet plane can get into LKO at all shows that planes/jets/winged-ssto's are OP.

[magnemoe]

You're missing something important: the rocket is really heavy. Its dry mass is over 150 tonnes (2x more than the Shuttle on reentry), while the cross section is only around 45 m^2 (5.5x less than the wing area of the Shuttle). Once something like that loses enough speed that it's no longer even pretending to be in orbit, it's going to fall quickly through Kerbin's shallow atmosphere and hit ground well past terminal velocity.

Edit: I also forgot one important thing: there was around 100 tonnes of fuel left in the rocket. In a shallow uncontrolled reentry (95x45 km orbit), the rocket hit ground at around 430 m/s at 400 m above sea level. The terminal velocity was around 330 m/s just before the impact.

Ok I see, braking parachutes sounds like an good idea, no wind on Kerbin so they works very well, might be an idea to set them to open early too like you do with normal ones on Duna so they get longer time braking.

[InterCity]

Imo the fact that a basic run-off-the-mill jet plane can get into LKO at all shows that planes/jets/winged-ssto's are OP.

It's due to stock aerodynamics. Try using FAR and it won't work anymore.

Anyway, have you ever tried to get a full orange tank to LKO with a SSTO in stock aerodynamics? Unless your PC is top-class, it's outright impossible. It takes much more effort than a similar rocket. For example, you'll have to balance it and also add A LOT of jets, because otherwise you'll just roll out of the runway at barely 100 m/s.

But if you do succeed in making a really good spaceplane, then it's unbeatable by a rocket.

TL; DR: I wouldn't say that Spaceplanes are OP. Compared to rockets, they require too much effort.

[Jouni]

It's due to stock aerodynamics. Try using FAR and it won't work anymore.

FAR allows many silly things, even if it nerfs the jets a bit. Some time ago, I was testing this Laythe lander with FAR and DRE. I launched it on top of a rocket to LKO, deorbited under its own power, landed near KSC, and returned back to orbit.

Anyway, have you ever tried to get a full orange tank to LKO with a SSTO in stock aerodynamics? Unless your PC is top-class, it's outright impossible. It takes much more effort than a similar rocket. For example, you'll have to balance it and also add A LOT of jets, because otherwise you'll just roll out of the runway at barely 100 m/s.

It takes a lot of effort, because you choose to use wings and other aesthetic elements that make designing and flying the ship much harder. Try without any wings, and jet-powered SSTOs become much easier, even with a minimal number of intakes.

(Of course, SSTO rockets are also SSTOs, and I just demonstrated a simple recoverable one that can deliver 1.5 S3-14400 fuel tanks to orbit in both stock and FAR&DRE.)

But if you do succeed in making a really good spaceplane, then it's unbeatable by a rocket.

Except by jet-powered rockets, which are much easier to build. If you choose to airhog, their payload fractions are generally a bit higher than stock spaceplanes'.

[Krakis]

It will be fun to see what the new changes will bring. IMHO the current turbojets are over powered and way too fuel efficient, using them on an SSTO is what makes them OP. Here is my [sTOCK] SSTO drone I use for refueling in .90. I do not have to switch from the turbojets until 40Km and am moving about 2300 m/s.

Krakis

[UmbralRaptor]

Anerobic SSTOs have significantly (about 1/3) less payload than their multistage counerparts, which does a good deal to balance any increase in recoverability.

Jet engines need a nerfbat, though. 70% payload fraction is just silly.

[r_rolo1]

Ok, it looks that there are some very different lines of answers regarding SSTO being OP ( besides the fact that a lot of people don't know that SSTO = Single Stage To Orbit and not spaceplane ):

a) Jets are OP , so SSTO are OP. Well, aside the wrong assumption that all SSTO have jets, this is actually correct. But remember that jets are what they are because they were designed to make planes work on the stock atmo, so they need to be absurdly powerful ( even after they have being cut out from the first versions, where you actually could go to Kerbin escape velocity on jets ). So, I would be VERY surprised if the gets would not get a nerfhammer with the new stock atmo. Will it be enough ? Maybe we can actually see the new atmo this Friday on Squadcast, as we were supposed to have seen last week, and take our own conclusions ... :/

Kerbin, because it is far smaller than Earth, has smaller orbital velocities, thus SSTO are far more viable and easier to do than in RL. 100% in agreement on that, and there is not much it can be done about that if you want to have minimally realistic engines and 1 atm atmo in a 600 km Kerbin. In other words , we have to eat this one up.

c) SSTO are hard to design, tune, fly and it is hard to scale them up to big loads. True, but half of that is because this game was built under the presumption that you're launching rockets to space, that you'll never never need to fly more than one at the time and that you'll not have prolonged burns or anything that needs more than instantaneous actions by the player. That is why anything that is not launching rockets to space one at the time and make less than 1 min burns up there is insanely grating ( rovers and boats? Prepare to stay some hours holding the W key Juggling more than 2 ships in the sky? I hope you have a notebook or a mod that allows bookmarking stuff :/ ) and jet based SSTO also suffer from a lack of air related tools ( say the lack of a auto altitude stabilizer, that is a common feature of flight simulators ( and RL auto pilots ) or the hacky "fix" they did to SAS some patches ago , that creates situations where the SAS will not hold a attitude in spite of the ship having enough control authority to do so ). In other words , making jet based SSTO is doing stuff that the game is ill equiped to deal with, thus it is harder to pull out ... This being a balancing factor is simply idiotic , though.

[Renegrade]

Ok, it looks that there are some very different lines of answers regarding SSTO being OP ( besides the fact that a lot of people don't know that SSTO = Single Stage To Orbit and not spaceplane ):

Don't worry, several of us do know; I do, Jouni posted an SSTO rocket just above, plus I saw a couple of others.

Unfortunately a good percentage of the community thinks SSTO=spaceplane (when quite clearly you can build rocket SSTOs, or multi-stage spaceplanes. Droptanks are kinda fun ). It's as bad as the SAS=reaction wheel thing~

Kerbin, because it is far smaller than Earth, has smaller orbital velocities, thus SSTO are far more viable and easier to do than in RL. 100% in agreement on that, and there is not much it can be done about that if you want to have minimally realistic engines and 1 atm atmo in a 600 km Kerbin. In other words , we have to eat this one up.

Well, if you wanted to duplicate an Earth-like experience, without scaling, you could just bring the nerf bat to the Isp numbers and beat them viciously. The interplanetary values are low compared to Earth as well, so you could just saw off half-ish of the Isp. (KIDS uses values of 0.39 and 0.45 for FAR stock world -> real world, 0.45 includes a tweak to account for the poor mass ratio of KSP tanks)

Delta-v numbers wouldn't change, but attaining them would require more Earth-like rockets (ignoring the very high fuel density)...

[r_rolo1]

Don't worry, several of us do know; I do, Jouni posted an SSTO rocket just above, plus I saw a couple of others.

Unfortunately a good percentage of the community thinks SSTO=spaceplane (when quite clearly you can build rocket SSTOs, or multi-stage spaceplanes. Droptanks are kinda fun ). It's as bad as the SAS=reaction wheel thing~

I know that I'm just venting about the bad usage of the term SSTO. Even yesterday someone posted a challenge where the OP forbid rockets, but allowed SSTO and RAPIERs ... and when someone pointed out that this was contradictory , the answer was "SSTO's run on RAPIER's" :| ( bold is not mine, btw ) . Here is even worse, because there is a lot of people discussing if SSTO are OP without knowing what a SSTO actually is ...

Well, if you wanted to duplicate an Earth-like experience, without scaling, you could just bring the nerf bat to the Isp numbers and beat them viciously. The interplanetary values are low compared to Earth as well, so you could just saw off half-ish of the Isp. (KIDS uses values of 0.39 and 0.45 for FAR stock world -> real world, 0.45 includes a tweak to account for the poor mass ratio of KSP tanks)

Delta-v numbers wouldn't change, but attaining them would require more Earth-like rockets (ignoring the very high fuel density)...

That was my point, even if somewhat hidden. If you are working in a 1/11 scale and insist on having engines of a 1/1 scale, the engines will do stuff that they can't do / is hard to pull with in 1/1, and easy SSTO is one of them. And it is not like SQUAD did not tuned down engines before from their RL values because they were OP in the context of the game ... RIP 0.15 aerospike, for a quick example

[Renegrade]

That was my point, even if somewhat hidden. If you are working in a 1/11 scale and insist on having engines of a 1/1 scale, the engines will do stuff that they can't do / is hard to pull with in 1/1, and easy SSTO is one of them. And it is not like SQUAD did not tuned down engines before from their RL values because they were OP in the context of the game ... RIP 0.15 aerospike, for a quick example

Yep.

Anyhow, re: the aerospike - I hope they manage to straighten that out. It went from the god engine to the godawful engine :/

PB-ION (0.23)      2.000 (  0.204g) (SP=41.24)
PB-ION (HN)        4.167 (  0.425g) (SP=85.93)
Vernor           150.000 ( 15.291g) (SP=103.11)
LV-N              26.667 (  2.718g) (SP=104.75)
PB-ION             8.000 (  0.815g) (SP=164.98)
LV1              133.333 ( 13.592g) (SP=189.85)
LV-909           100.000 ( 10.194g) (SP=191.49)
48-7S (HN)       120.000 ( 12.232g) (SP=194.44)
Poodle           110.000 ( 11.213g) (SP=210.64)
[B][COLOR="#FF0000"]Aerospike        116.667 ( 11.893g) (SP=223.40)[/COLOR][/B]
MK55R            133.333 ( 13.592g) (SP=235.68)
O-10             222.222 ( 22.653g) (SP=240.04)
LV-T45           133.333 ( 13.592g) (SP=242.23)
BACC             210.000 ( 21.407g) (SP=257.77)
S1 SRB-KD25K     216.667 ( 22.086g) (SP=265.96)
LV-T30           172.000 ( 17.533g) (SP=312.47)
24-77            222.222 ( 22.653g) (SP=327.33)
48-7S (0.21)     200.000 ( 20.387g) (SP=343.70)
Skipper          216.667 ( 22.086g) (SP=393.62)
Mainsail         250.000 ( 25.484g) (SP=441.90)
[B][COLOR="#FF0000"]Aerospike (.18)  250.000 ( 25.484g) (SP=478.73)[/COLOR][/B]
48-7S            300.000 ( 30.581g) (SP=515.55)
LFB KR-1x2       333.333 ( 33.979g) (SP=556.47)
S3 KS-25x4       328.205 ( 33.456g) (SP=580.14)
RT-10            500.000 ( 50.968g) (SP=589.20)
Sepratron       1440.000 (146.789g) (SP=707.04)
KR-2L            384.615 ( 39.206g) (SP=717.62)

It used to keep company with the (current) 48-7S and Mainsail in many ways.. Given that we have the thrust/isp relationship straightened out in '1.0', it would be nice if it could fit itself in around the T30's level so we have something with some good kick to lift us off Eve~

[TokiTech]

With adding many intakes to your spacecraft you can make it able to reach almost orbital speed at about 35 km high while using very low amount fuel compared to rockets. If this can happen in reality why they are stil using rockets to put small payloads or astronauts into orbit.

The game is originally meant for education purpose i think, from that i understand why parts can be overpower and Kerbal world is smaller etc. Alternatively there are balancing mods to make things little more realistic interesting.

[LethalDose]

With adding many intakes to your spacecraft you can make it able to reach almost orbital speed at about 35 km high while using very low amount fuel compared to rockets. If this can happen in reality why they are stil using rockets to put small payloads or astronauts into orbit.

They're trying to do exactly that with Reaction Engines Ltd's Skylon and Virgin's SpaceCraftTwo.

[Frozen_Heart]

If they manage to solve the intake spam issue and the jet engine ISP issue then SSTOs will become much more difficult to build.

I'm glad its not real life difficulty though like some people seem to want. That would make SSTOs all but impossible and prohibit launching anything but tiny probes anywhere. Not my idea of fun.

[Commander Jebidiah]

The biggest issue for large SSTO rockets will probably be slowing down to speeds where the parachutes can be safely deployed.

I launched my example rocket with FAR & DRE. The rocket had 1290 m/s of delta-v remaining in orbit, while the stock rocket had only around 50 m/s. Once I separated the payload, delta-v increased to 2114 m/s. Atmospheric reentry was not a problem, but I had to spend almost all remaining fuel to slow down, as the rocket was trying to hit ground at a supersonic speed.

Flew ksos shuttle and upon returning it hit the ocean at mach 1 and this was with near.

[LethalDose]

If they manage to solve the intake spam issue and the jet engine ISP issue then SSTOs will become much more difficult to build.

Well, since they're improving the aero model and tracking coverage, there may be a chance for them to revisit air intake logic in terms of overlapping intakes.

But this is Squad we're talking about, so who knows what they'll do.

[Pecan]

... besides the fact that a lot of people don't know that SSTO = Single Stage To Orbit and not spaceplane ...

And even worse, there are some people who think SSTO = spaceplane to Eeloo, or somewhere. The concepts of "single stage" and "to orbit" must be more difficult than they look ^^.

[Renegrade]

I'm glad its not real life difficulty though like some people seem to want. That would make SSTOs all but impossible and prohibit launching anything but tiny probes anywhere. Not my idea of fun.

You can have rocket-powered SSTO with the thick, sludgy stock atmosphere, so you can easily have a jet-powered SSTO in the thinner, more realistic atmosphere without spamming intakes.

As an example:

Behold the basic-jet powered SSTO in FAR. Capable of putting about three tons in orbit under FAR (two tons of cockpit, LS, and HN-batteries, one ton of fuel, and a fair deal of RCS..), it uses the (stock values) jet engines to carry it about a third of the way to orbit, and a T45 to carry it the rest of the way to orbit.

The ascent profile takes it up in a thirty degree climb, and it cuts over to rockets between 15 and 20km (that's about 45,000 to 60,000 feet in obsolete/legacy units).

That's about a 40% payload fraction. I threw this together in like 15-30 minutes and I'm by no means any sort of spaceplane expert (I don't even like making supersonic planes at all).

And even worse, there are some people who think SSTO = spaceplane to Eeloo, or somewhere. The concepts of "single stage" and "to orbit" must be more difficult than they look ^^.

Well, Eeloo orbit is technically still orbit.. just not the right one as per normal conventions

[hazard-ish]

Yes, I agree that SSTOs are overpowered. I would highly recommend checking out 'MrOverfloater' if you haven't already. I have taken a several tonne cargo to Minmus using an SSTO too on my channel and am planning on going to the Sarnus system and back in one soon.

However, as has been discussed previously here, building a nice looking and well flying SSTO is hard and from my experience SSTO missions are harder than standard rocket ones.

[LABHOUSE]

Real life has more expensive parts (and a larger bugget, but still) , and a higher delta-v to orbit, and no part clipping, and no intake spamming, and less powerful engines and intakes, and it need to be bigger for people.

[Crow Titanium]

After many attempts, I finally have a decent, heavy-lift SSTO - it uses the super-large cargo bay, flies great, stalls at under 30m/s when empty. I'll post a craft file if I can...

[The Yellow Dart]

I'd chalk it up mainly to overpowered jet engines. The number of RL planes with a thrust to weight greater than 1 is pretty small yet in KSP the vast majority of them have T/W higher than 1. Additionally, the lack, thus far, of atmospheric heating or a need for precoolers explains the high speeds and high altitudes that can be achieved.