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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.

Martin Schröder
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Coomie
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    Offhand, I can think of SCORE/Atlas 10B which orbited with no upper stage. – 2012rcampion Nov 04 '15 at 06:18
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    The Atlas-B did drop the booster engines ("stage-and-a-half" configuration), so I'm not sure if that qualifies. – Brian Lynch Nov 04 '15 at 07:27
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    @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." – 2012rcampion Nov 04 '15 at 10:18
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    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. – Brian Lynch Nov 04 '15 at 11:19
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    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. – SF. Nov 04 '15 at 12:37
  • Wasn't Explorer I put into orbit by a single rocket? – Mikey Nov 05 '15 at 21:13
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    @Mikey: Nope. It just didn't jettison its second stage. – Joshua Nov 06 '15 at 02:32

7 Answers7

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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.

Brian Lynch
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    Technically, you have answered the question asked. But I did mean Earth... You get a vote up for such a great answer. – Coomie Nov 05 '15 at 01:22
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    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. – Brian Lynch Nov 05 '15 at 01:54
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    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. – rspeed Nov 06 '15 at 08:41
  • Agreed, the Shuttle was definitely not SSTO, but Coomie's question is also referring to launch vehicles that carried the first stage to orbit. – Brian Lynch Nov 06 '15 at 08:55
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    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. – rspeed Nov 06 '15 at 13:11
  • I agree, check the revision history of my answer if you want. – Brian Lynch Nov 06 '15 at 13:19
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    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 – Andrew is gone Nov 11 '15 at 23:16
  • Would also love to know that answer, just haven't got around to doing the math. Should be pretty easy if you recompute the expected Delta-V's and compare. – Brian Lynch Nov 11 '15 at 23:23
  • elon musk claimed a falcon 9 first stage could reach orbit without payload https://twitter.com/elonmusk/status/669132749500887040 – Arthur D Jul 28 '16 at 13:21
  • "Yyou are technically correct -- the best kind of correct." – RonJohn Dec 04 '19 at 20:10
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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.

Mark Adler
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  • Wow, that is very interesting. The designation system is very confusing but I assume you mean this ("Redirected from atlas B") https://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. – Level River St Nov 04 '15 at 18:34
  • 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). – LocalFluff Nov 05 '15 at 11:45
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    @LocalFluff an anti-satellite missile only has to reach orbital height, but not orbital velocity, in order to intercept a satellite. – Level River St Nov 05 '15 at 13:27
  • The F-15-launched ASAT missile ASM-135 was a three-stage design anyway, besides being (I think) suborbital. – Organic Marble Nov 05 '15 at 15:30
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    The aircraft also counts as a stage. – rspeed Nov 06 '15 at 08:43
  • Sooo close. 2/3 the mass of the engine: 428 kg Payload mass: 70kg. I wonder if they sacrificed that 70kg for fuel, they would be able to go without jettissoning the two engines. (and also go for orbit just a notch above 100km instead of 185.) – SF. Nov 06 '15 at 12:23
  • @SF where did you get 428kg from? http://www.astronautix.com/lvs/atlasb.htm gives a payload of 70kg to 185km which agrees with your data, a mass of 3980kg(empty)/107610(gross) for stage 1, and 3050kg(empty)/3050kg(gross) for stage 0. By which I understand that the dropped mass was 3050kg, almost half the empty weight. – Level River St Nov 07 '15 at 02:55
  • @steveverrill: http://www.astronautix.com/engines/xlr895.htm the engine mass; 2/3 of 643 kg. Stage 0 Gross=Empty makes no sense. It looks more to me that 3980-3050=930kg was dropped as engines and stage0 propellant. – SF. Nov 07 '15 at 23:55
  • @SF stage 0 Gross=Empty makes perfect sense, since the stage consisted just of 2 engines, a bit of fairing,plumbing and structural steel, and no propellant. The 2 engines weighed 643kg x 2 = 1286kg. Stage 1 carried all the propellant as Mark said, and its engine was a completely different type, an XLR-105-5, smaller at 460kg, much lower thrust, but more complex as it had vernier thrusters . You cannot multiply engine masses by 2/3, especially when they are different engines. – Level River St Nov 08 '15 at 02:11
  • @steveverrill: Okay, that explains it a bit, although I'm still baffled why would the final stage engine have worse ISp than the launch stage. Usually you put lousy ISp, good thrust for launch, and then switch that over when gravity drag drops. – SF. Nov 08 '15 at 21:28
  • @SF it's not worse, just different. Stage 0 XLR-89-5 282 sec (248 sec sea level) stage 1 XLR-105-5 309 sec (215 sec sea level) on the same fuel tanks. Stage 0 engine is optimized for atmospheric, whereas the stage 1 has to go all the way from sea level to full vacuum. The other thing that hurts the stage 1 engine is, it's both smaller and more complex (vernier thrusters.) That explains the big difference in thrust/weight ratio (120 for stage 0, 80 for stage 1.) Better ISp for upper stages normally comes with a change of propellant chemistry, which isn't an option here with single tank design. – Level River St Nov 08 '15 at 21:49
  • @SF: Isp is not all that matters. The dry mass ratio is also important. Solid rocket motors can make excellent launch vehicle upper stages, even though their Isp is lower, since they have such a small dry mass ratio. – Mark Adler Nov 08 '15 at 22:02
  • @MarkAdler: the problem is that the trade-off is against the whole vehicle, not just the engine. Even the lightest engine with lousy ISp is worse against a heavy payload than a heavier engine with good ISp. But yes, in this case 3,980 kg of dry mass make a strong case. – SF. Nov 09 '15 at 09:11
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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.

Level River St
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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.

Organic Marble
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    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. – rspeed Nov 06 '15 at 08:45
  • The number and kind of engine types used is irrelevant to whether it was SSTO or not; otherwise I agree w/ you. – Organic Marble Nov 06 '15 at 12:34
  • 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. – rspeed Nov 06 '15 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

peterh
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    Powerpoint craft do not count. – Organic Marble Nov 04 '15 at 16:24
  • @OrganicMarble 85% ready craft which was only abandoned by a fixable problem is much more as a powerpoint. – peterh Nov 04 '15 at 16:35
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    85% constructed does not equal 85% ready! – Brian Lynch Nov 04 '15 at 19:46
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    Once your prototype reaches 100% construction, the next step is finding and fixing the flaws. This can easily take two to three times as long as the original construction. – Mark Nov 04 '15 at 23:01
  • @BrianLynch Maybe you could read the link I referred. Which is important, is not a pointless debate about the exact meaning of not exact words, but it is about the fact, that the X-33 was an almost ready SSTO craft. – peterh Nov 05 '15 at 00:05
  • @Mark Yes, but at this point there are already a relatively strong demonstration of the feasibility of the technology. See, for example, the ITER project (sorry for the non-space reference). It is possible, that essential problems will be found after that, but unsolvable isn't. – peterh Nov 05 '15 at 00:08
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    No need to be hostile! Firstly, I did read your link, which is the Wikipedia entry about the X-33. Secondly, this is not a debate about the meaning of words -- 85% constructed really is not equivalent to 85% ready and an almost ready prototype is not an almost ready flight model. Thirdly, a "relatively strong demonstration of the feasiblity of the technology" is very far away from a flight-ready spacecraft that uses that technology. Aerospace is a field that relies on heritage, and new concepts take a very long time to get off the ground. – Brian Lynch Nov 05 '15 at 00:24
  • @BrianLynch And, on my opinion, the reason of the failure of the project was your last sentence, and not really unsolvable problems. – peterh Nov 05 '15 at 00:29
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    @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. – Mark Nov 05 '15 at 01:31
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    @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: – peterh Nov 05 '15 at 01:36
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    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 (http://www.astronautix.com/engines/rs2200.htm) so that 85% complete you mention....well, 80% of the effort is in the final 20% of a project. – Organic Marble Nov 05 '15 at 02:31
  • @OrganicMarble Right, but they aren't programmers. Real engineering projects have much better statistics as the software projects. In the case of the ITER and also in the case of the LHC, both times were found critical design mistakes lately, despite that they could be fixed. The only unfixable problem is, if the government stops the financial support. – peterh Nov 05 '15 at 02:36
  • @OrganicMarble Even the telescope of the HST had a critical problem, which as clear only in the space. It could be repaired. I think, the X-33 / VentureStar had been also fixable, if they construction was viable. Somewhere I've heard that the design came from the cold war, and that in the reality it was unfeasible from the very beginning, and its real goal was to further demoralize the soviets and to sink them furhter into the space race. If it is true, then it was maybe really not working. But if not... then it is surely not the most glorious chapter of the human space exploration. – peterh Nov 05 '15 at 03:59
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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

Enthurzan
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    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. – Brian Lynch Nov 08 '15 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.

Nathan Tuggy
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user12252
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    Wouldn't the B-52 count as the first stage? – Nathan Tuggy Nov 06 '15 at 04:14
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    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. https://en.wikipedia.org/wiki/Pegasus_%28rocket%29 – Organic Marble Nov 06 '15 at 05:03