What exactly IS an SSTO?

[Matuchkin]

Sure, a Single-Stage-To-Orbit vehicle is a vehicle that uses a single stage to get to orbit, as the acronym suggests. But to what extent should we push this definition? For example, do SRBs count as stages? If so, then the Space Shuttle and Ariane V are two-stage vehicles (not counting the payload), but then were the JATO-assisted C-130s used to evacuate Iranian hostages double-staged? How about JATO vehicles in general, that perform rocket-assisted take offs?

Edited September 26, 2016 by Matuchkin

[Guest]

Does not shed any hardware in order to get in orbit = SSTO

Boom.

[Superfluous J]

What @Aperture Science said. To be specific, if you get it into orbit, and then teleport it back to the launchpad and refilled it with fuel and only fuel, you could launch it back into orbit. Over and over. Forever.

14 hours ago, Matuchkin said:

do SRBs count as stages?

Yes

14 hours ago, Matuchkin said:

If so, then the Space Shuttle and Ariane V are two-stage vehicles

Yes.

14 hours ago, Matuchkin said:

(not counting the payload), but then were the JATO-assisted C-130s used to evacuate Iranian hostages double-staged? How about JATO vehicles in general, that perform rocket-assisted take offs?

I don't know enough about those specific JATOs, except I'm guessing they didn't go to orbit

But if you had a ship that used jets to assist in takeoff, and you carried them into orbit along with all other non-fuel hardware, then yes it's an SSTO.

(Note you could have any number of KSP-defined (hit the spacebar) "stages" so long as none of those caused a piece of the ship to fall off)

[Red Iron Crown]

Moved to Science & Spaceflight.

[Kryten]

In standard western reckoning, a vehicle with boosters and a core stage is a stage-and-a-half vehicle, meaning something like the R-7 that launches Soyuz isn't considered a proper SSTO. Ariane 5 and STS are incidentally two and a half stage vehicles; ariane 5 always has an upper stage, and shuttle needed it's OMS engines to actually reach orbit. In Russian reckoning, boosters are a complete stage and something like R-7 is a two stage vehicle.

[Red Iron Crown]

33 minutes ago, Kryten said:

In standard western reckoning, a vehicle with boosters and a core stage is a stage-and-a-half vehicle, meaning something like the R-7 that launches Soyuz isn't considered a proper SSTO. Ariane 5 and STS are incidentally two and a half stage vehicles; ariane 5 always has an upper stage, and shuttle needed it's OMS engines to actually reach orbit. In Russian reckoning, boosters are a complete stage and something like R-7 is a two stage vehicle.

It's my understanding that Soyuz uses an upper core stage, there hasn't been an orbital R-7 with a single stage core since the '60s. 

[Kryten]

Just now, Red Iron Crown said:

It's my understanding that Soyuz uses an upper core stage, there hasn't been an orbital R-7 with a single stage core since the '60s. 

That's what I get for posting right after waking up. I meant to put 'launched sputnik'.

[magnemoe]

Note that many first stages would be able to reach orbit if they only had an nose cone. 
It would be an true SSTO however pointless, no to very low cargo capacity.
For an SSTO to be useful you have to be able to land and reuse it. 
This would be easier with an two stage rocket where only the smaller upper stage reached orbit. 

[Nibb31]

Note that many modern launchers could be SSTO if they wanted to. They would just have a ridiculous payload and they wouldn't be coming back.

SSTO in itself is pointless. If it's reusability that you want, then you don't need "Single Stage to Orbit", you want "Whatever Stage(s) to Orbit and Back". If it's affordability that you want, you don't necessarily need reusability. If it's fast turnaround that you want, then it's payload integration that's the long pole.

ETA: Dammit @magnemoe, get out of my brain !

Edited September 27, 2016 by Nibb31

[todofwar]

I wonder if sci fi has led a generation of engineers astray here. We always talk about how science fiction inspires twch, and all the sci fi ships are SSTO VTOL crafts. I think people just sort of assume that's where we'll eventually end up. But until we find a loophole in the rocket equation staging just makes sense.

[Sereneti]

21 hours ago, Matuchkin said:

 If so, .... Space Shuttle ... are two-stage vehicles (not counting the payload),

no, a Space shuttle is a three-stage vehicle:

First stage - SRB; Second stage: Drop tank; third stage - the shutle itself.

[Nibb31]

18 minutes ago, Sereneti said:

no, a Space shuttle is a three-stage vehicle:

First stage - SRB; Second stage: Drop tank; third stage - the shutle itself.

The Space Shuttle was a bit of special case here. The second stage would have been the SSME, not the ET, so one could argue that the it brought most of the second stage to orbit (the engines are much more valuable than tankage).

Also, since the SSMEs were started on the ground, it would be considered a 2.5 stage vehicle.

It's just semantics and really isn't very important.

[magnemoe]

21 minutes ago, Nibb31 said:

The Space Shuttle was a bit of special case here. The second stage would have been the SSME, not the ET, so one could argue that the it brought most of the second stage to orbit (the engines are much more valuable than tankage).

Also, since the SSMEs were started on the ground, it would be considered a 2.5 stage vehicle.

It's just semantics and really isn't very important.

However I think the half stage for SRB is more suiting for the smaller ones who mostly give TWR than the large ones who weight more than the rest of the rocket. 

[Kryten]

1 hour ago, Sereneti said:

no, a Space shuttle is a three-stage vehicle:

First stage - SRB; Second stage: Drop tank; third stage - the shutle itself.

The definitions are a little fuzzy, but if what you drop doesn't contain an engine not many people will call it a stage. I don't of anyone who lists Briz-M and it's auxiliary tank as two stages, for example.

[Superfluous J]

3 minutes ago, Kryten said:

The definitions are a little fuzzy, but if what you drop doesn't contain an engine not many people will call it a stage.

I'm pretty sure every single person on this forum who has ever made an SSTO would call shenanigans on someone who made an "SSTO" that dropped its fuel tanks as they emptied.

[Nibb31]

47 minutes ago, 5thHorseman said:

I'm pretty sure every single person on this forum who has ever made an SSTO would call shenanigans on someone who made an "SSTO" that dropped its fuel tanks as they emptied.

Who cares what your vehicle is called as long as it meets requirements. SSTO is a meaningless badge that is only valued by a couple of KSP players.

[DerekL1963]

20 minutes ago, Nibb31 said:

Who cares what your vehicle is called as long as it meets requirements. SSTO is a meaningless badge that is only valued by a couple of KSP players.

No, there's a lot of people out in the real world who badly want SSTO as well.

[Gaarst]

1 minute ago, DerekL1963 said:

No, there's a lot of people out in the real world who badly want SSTO as well.

No one cares about SSTOs. As other have said, reusable SSTOs is the thing.

 

[wumpus]

Basically a design based on confusing cause and effect.  Nearly all "magical" high efficiency rockets are SSTO, so the idea is to build an SSTO to somehow get that high efficiency.  The other consideration are logistics issues, it *should* be somewhat cheaper to get an SSTO.  That said, you better not have the issues of refurbishing the shuttle or you will never get the costs down to flying a falcon9 on a reused booster (even with a new first stage).

SSTOs are likely to make sense with ISPs>>400s (or similar tech), or on planets with lower gravity wells than Earth.  On Earth they are a sign of someone who doesn't know the first thing of rocket science.

[magnemoe]

1 hour ago, wumpus said:

Basically a design based on confusing cause and effect.  Nearly all "magical" high efficiency rockets are SSTO, so the idea is to build an SSTO to somehow get that high efficiency.  The other consideration are logistics issues, it *should* be somewhat cheaper to get an SSTO.  That said, you better not have the issues of refurbishing the shuttle or you will never get the costs down to flying a falcon9 on a reused booster (even with a new first stage).

SSTOs are likely to make sense with ISPs>>400s (or similar tech), or on planets with lower gravity wells than Earth.  On Earth they are a sign of someone who doesn't know the first thing of rocket science.

Yes, KSP is not real world, In KSP you only need a bit over 3 km/s to reach orbit not 9 km/s. its also not efficient to reuse first stages leaving ssto 
Note that falcon 9 first stage reaches 2 km/s before doing an burn back and return to pad that is while lifting an 100 ton second stage+ fairing and payload, 
the x15 suborbital space plane would be orbit capable on kerbin, 

 

 

[kerbiloid]

SSTO are for game worlds where your orbital speed is less than ISP.

Edited September 28, 2016 by kerbiloid

[razark]

50 minutes ago, kerbiloid said:

SSTO are for game worlds

We've flown a half-dozen (or more, depending on how you count) manned SSTOs in real life.

 

(Of course, it took a Saturn V to deliver each of them to their launch sites...)

[kerbiloid]

17 minutes ago, razark said:

We've flown a half-dozen (or more, depending on how you count) manned SSTOs in real life.

If you mean Atlas, it was S-with-a-halfSTO. It dropped a significant part of construction.

[razark]

2 minutes ago, kerbiloid said:

If you mean Atlas, it was S-with-a-halfSTO. It dropped a significant part of construction.

Did you read the fine print?

[kerbiloid]

9 minutes ago, razark said:

Did you read the fine print?

Ah, the small font ? Lunar module upper stage. And this is exactly what I'd meant: lunar orbital speed is 1.6 km/s, while ISP(*g) ~ 2.8.