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If you've been reading the news lately, you've probably been reading about Skylon and it being Single Stage To Orbit (SSTO).

I've had a think back and to the best of my knowledge humanity has always used multi-stage rockets. Am I wrong? Has humanity ever launched to Earth orbit carrying the initial stage?

I'm not sure what the technical definition of a "stage" is but I take it to mean jettisoning anything other than propellant - so engines, tanks, etc.

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    $\begingroup$ Offhand, I can think of SCORE/Atlas 10B which orbited with no upper stage. $\endgroup$
    – 2012rcampion
    Nov 4, 2015 at 6:18
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    $\begingroup$ The Atlas-B did drop the booster engines ("stage-and-a-half" configuration), so I'm not sure if that qualifies. $\endgroup$
    – Brian Lynch
    Nov 4, 2015 at 7:27
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    $\begingroup$ @Brian Thanks, I had forgotten about the boosters. If I remember correctly though, it basically just drops off the engines and a couple meters of fairing, so it would count as "carrying the initial stage" although not "single stage to orbit." $\endgroup$
    – 2012rcampion
    Nov 4, 2015 at 10:18
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    $\begingroup$ Yes, I think it is basically 99% SSTO but the term "stage-and-a-half" is a pretty fair assessment -- a true single-stage solution doesn't jettison any parts. It would be interesting to know if the Atlas-B would be capable of reaching a decently stable orbit while keeping those parts, even without any payload. $\endgroup$
    – Brian Lynch
    Nov 4, 2015 at 11:19
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    $\begingroup$ By the way, the lack of SSTO is not because "we can't do it", but because it would be impractical - significantly higher cost for tiny payload. $\endgroup$
    – SF.
    Nov 4, 2015 at 12:37

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Yes, technically humans have launched to orbit with a single stage -- the Apollo lunar excursion modules launched from the Moon's surface to lunar orbit using a single stage.

As for Earth orbit, there have not been any true single-stage-to-orbit launches since the vehicle should not jettison any components to be considered true SSTO. However, both the Atlas-B and Space Shuttle did carry the first stage to orbit in some sense (sometimes referred to as "stage-and-a-half" configuration). The Atlas-B is definitely the closest to SSTO since it only jettisoned booster engines (not entire stages or strap-on boosters). The Space Shuttle Orbiter contributes its main engines to the entire flight so you could definitely say it is part of the first stage and of course makes it to orbit.

Note: the Atlas-B was pointed out by 2012rcampion and Mark Adler, the Space Shuttle was pointed out by Organic Marble.

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    $\begingroup$ Technically, you have answered the question asked. But I did mean Earth... You get a vote up for such a great answer. $\endgroup$
    – Coomie
    Nov 5, 2015 at 1:22
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    $\begingroup$ I figured that's what you meant but couldn't resist mentioning the LEM. Doesn't seem like there have been any true SSTO flights, but you do ask if we've ever launched a vehicle carrying the first stage into orbit and arguably the Atlas-B and STS both do that even though components are jettisoned as well. $\endgroup$
    – Brian Lynch
    Nov 5, 2015 at 1:54
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    $\begingroup$ Even working with that extremely loose definition, the Shuttle wasn't an SSTO. The main engines were only used until the external tank was jettisoned, at which point the orbiter was still on an extremely long suborbital arc. The last 100 m/s of acceleration was contributed by the OMS pods. The Shuttle carried components that contributed thrust at liftoff all the way to orbit, but they became dead weight beforehand. The boosters and external tank could be called half-stages, but there's really no way to say the same thing about the OMS pods. $\endgroup$
    – rspeed
    Nov 6, 2015 at 8:41
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    $\begingroup$ But it did drop a large, heavy component of the first stage. Even though it hangs on to the other engines, they were rendered useless. Separation event + engine transition = staging. Atlas only got around that by keeping the sustainer engine firing, hence it's considered a half-stage. $\endgroup$
    – rspeed
    Nov 6, 2015 at 13:11
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    $\begingroup$ Idle curiosity: Had the Atlas-B not dropped the engines, and carried a purely notional payload (eg an empty nose-cone to reduce drag), would it have been able to reach orbit? There wouldn't have been much point to this, granted, but it's an interesting thought experiment $\endgroup$
    – Andrew
    Nov 11, 2015 at 23:16
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The closest from Earth was the Atlas B, which I would call a 1.25 stage-to-orbit. It got to orbit with a single set of extremely light propellant tanks. It launched with three engines fed by those tanks, and dropped two of the engines on the way up. Several Mercury missions were on the Atlas (Atlas D).

I would call the Space Shuttle a 1.5 stage to orbit, where it went all the way to orbit on the same main propulsion system and tanks, but dropped two entire booster propulsion systems on the way up, which were a significant fraction of the mass at launch.

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  • $\begingroup$ Wow, that is very interesting. The designation system is very confusing but I assume you mean this ("Redirected from atlas B") en.wikipedia.org/wiki/SM-65_Atlas . Pretty impressive, especially as it was RP-1 fuelled, not hydrogen. A good example of how to get that thrust in early, which helps avoid wasting dV. $\endgroup$
    – Level River St
    Nov 4, 2015 at 18:34
  • $\begingroup$ Hasn't any air launched anti-satellite missile test beaten that? If it counts as "to orbit" to hit a satellite in orbit, (or rather simulate it in a test). $\endgroup$
    – LocalFluff
    Nov 5, 2015 at 11:45
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    $\begingroup$ @LocalFluff an anti-satellite missile only has to reach orbital height, but not orbital velocity, in order to intercept a satellite. $\endgroup$
    – Level River St
    Nov 5, 2015 at 13:27
  • $\begingroup$ The F-15-launched ASAT missile ASM-135 was a three-stage design anyway, besides being (I think) suborbital. $\endgroup$
    – Organic Marble
    Nov 5, 2015 at 15:30
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    $\begingroup$ The aircraft also counts as a stage. $\endgroup$
    – rspeed
    Nov 6, 2015 at 8:43
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No, humanity has never before launched to Earth orbit using single stage.

It's practically impossible to reach the dV required if you carry all the oxygen with you. Skylon is hydrogen-oxygen propelled. In this propellant system the oxygen weighs 8 times as much as the hydrogen (with a chemically balanced mix), if you carry it all with you. (Rocket engines tend to run a bit fuel rich and oxygen poor but anyway, that's a big difference.)

By breathing air for the first part of the ascent, one can gain significant velocity and height before one switches to oxygen from the tank. This is how Skylon makes the single stage to orbit concept theoretically possible.

Thus the engine concept is critical to the success of the vehicle and there are very few organizations in the world with experience with such engines.

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You could say that Shuttle was a single stage to orbit...albeit with very large strap-on boosters! The concept we knew as Shuttle was originally called TAOS for Thrust Augmented Orbital Shuttle. This was genned up after the original fully reusable concepts turned out to be unaffordable.

But it does meet your criterion of "launching to orbit carrying the inital stage". Just not the strap-ons.

But...a craft that launches from Earth, and arrives in orbit without shedding any structure, only consuming propellant....no. That has never been done.

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    $\begingroup$ The Shuttle also dropped the main fuel tank and used a totally separate set of engines to get the last ~1% of the way to orbit. It was certainly capable of making it all the way to orbit without doing either, but it was never attempted. $\endgroup$
    – rspeed
    Nov 6, 2015 at 8:45
  • $\begingroup$ The number and kind of engine types used is irrelevant to whether it was SSTO or not; otherwise I agree w/ you. $\endgroup$
    – Organic Marble
    Nov 6, 2015 at 12:34
  • $\begingroup$ That's not the distinguishing part. My point is that none of the "first" stage was used to make the final push to orbit. If the Shuttle had retained the external tank and still used the OMS I'd give it a pass, but that never happened. $\endgroup$
    – rspeed
    Nov 6, 2015 at 13:06
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No, but the X-33 almost did it. Its 120 tons of starting weight contained around 95 tons of fuel...

Lockheed X-33

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    $\begingroup$ Powerpoint craft do not count. $\endgroup$
    – Organic Marble
    Nov 4, 2015 at 16:24
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    $\begingroup$ 85% constructed does not equal 85% ready! $\endgroup$
    – Brian Lynch
    Nov 4, 2015 at 19:46
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    $\begingroup$ @peterh, reading through the Wikipedia article indicates there's no "almost" about the X-33: even if it hadn't been canceled, "the X-33 was never intended to fly higher than an altitude of 100 km, nor faster than one-half of orbital velocity". An incomplete prototype of a suborbital vehicle does not even remotely qualify as an SSTO. $\endgroup$
    – Mark
    Nov 5, 2015 at 1:31
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    $\begingroup$ @Mark Read also the referenced material in the wiki post, it was only the plans of the first some tests. Because the X-33 project was killed, there weren't other plans. The wiki isn't really fair in this case. Further read here: $\endgroup$
    – peterh
    Nov 5, 2015 at 1:36
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    $\begingroup$ To be precise, the X-33 was going to be a subscale suborbital technology demonstrator to validate the concept of the full-scale orbital vehicle, the Venturestar. The X-33, even if it had ever been built, was a suborbital craft. And I'm pretty sure the linear aerospike engine development was not complete (astronautix.com/engines/rs2200.htm) so that 85% complete you mention....well, 80% of the effort is in the final 20% of a project. $\endgroup$
    – Organic Marble
    Nov 5, 2015 at 2:31
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We haven't launched into LEO with an SSTO because of the rocket equation- basically, for every ounce of fuel, we have to have fuel to lift that fuel plus the entire rocket- I'm not good enough to calculate the max mass of a planet for an SSTO, but I'm sure someone whose good with physics and rocket science can work it out

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    $\begingroup$ To calculate that you would need to restrict yourself to a given rocket design -- by that I mean a given specific impulse and empty mass fraction. It makes more sense to flip it around and look at the fuel efficiency (specific impulse) that would be needed for current rocket designs, or the empty mass fraction needed with current fuels. For example, if you assume a Delta-V of 9500 m/s and an Isp of 250 s, you would need an empty mass fraction of around 2% (including payload). On the other hand, if you had an empty mass fraction of 15% you would need a fuel with an Isp of 510 s. $\endgroup$
    – Brian Lynch
    Nov 8, 2015 at 10:55
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What about Orbital Sciences Pegasus rocket? It was a single stage that took a payload (admittedly, small) to orbit. However, it was dropped from a B-52 at around 40,000 ft, not launched from the ground.

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    $\begingroup$ Wouldn't the B-52 count as the first stage? $\endgroup$
    – Nathan Tuggy
    Nov 6, 2015 at 4:14
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    $\begingroup$ Pegasus was a multistage design not even counting the B-52. It had a minimum of 3 stages with an optional fourth. Not even remotely qualifed for SSTO. en.wikipedia.org/wiki/Pegasus_%28rocket%29 $\endgroup$
    – Organic Marble
    Nov 6, 2015 at 5:03

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