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I'm curious about whether or not the Space Shuttle could have been used as a lunar orbit vehicle - basically, would have it been technically capable of getting to the Moon, entering orbit, then leaving orbit?

My reasoning is that since the Shuttle was designed to carry large payloads, you could easily stuff enough fuel in there to power the already-existing thrusters to do whatever you needed to. Also, the area not taken up by fuel could be used to carry food and supplies for the extended mission.

Would it be possible?

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    $\begingroup$ Consider the never-flown Shuttle-centuar. If we replace payload mass with OMS tanks we can get a lot of delta-v out of it. I'm not absolutely sure the 1km/s would be available without cryogenic fuels but ... $\endgroup$ – Joshua Nov 9 '15 at 21:35
  • $\begingroup$ An OMS payload bay kit was planned but never flown. It was to provide 500 fps delta v. $\endgroup$ – Organic Marble May 14 '17 at 16:27
  • $\begingroup$ 500fps is 152.4m/s... meager as heck. Not even close. But it occupied only about 20% of the payload bay. I wonder about SSME payload bay kit though... $\endgroup$ – SF. May 15 '17 at 11:31
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This exact problem was presented in The Artemis Project's "Why We Won't Fly a Space Shuttle to the Moon" article, so I'll just quote a few short excerpts from the points it is making, and the rest is then in the article:

  • Vehicle Mass

    Dry weight of Shuttle Orbiter is about 250,000 lbs, compared to the space-only LTV's [Lunar Transfer Vehicle] weight of perhaps 7500 lbs. We'd be accelerating a lot of mass that we don't really need in lunar orbit.

  • Refueling the Orbiter

    Since the Shuttle Orbiter gets to LEO [Low Earth Orbit] with near-zero extra fuel, we'd have to use other launches to get the fuel up there. You can work out the math. Use Isp=460 sec, delta-V=Isp*g*ln(Mo/Mf). The delta-V requirements are in the Mission Timeline. It's a lot of launches... continues in the article

  • Heat Shield

    The Orbiter's heat shield is designed for entry from low Earth orbit, about 25,000 ft/sec. Coming home from the moon, we'd hit the atmosphere at about 36,000 ft/sec. Whether the Shuttle could take that increase in kinetic energy is an unknown.

  • Atmospheric Entry Loads

    The Orbiter is designed for 3 g's max operational load. Assuming we didn't use rockets to decelerate while coming home from the moon, we'd hit up to 6 g's; even up to 12 if the piloting is just a bit off... continues in the article

  • Radiation, Vehicle Reliability, Operational Flexibility

    Shuttle wins all those issues. It has a proven track record. If we got to LEO and the Orbiter was fully operational (fuel cells and auxiliary power units all in the green), it would probably be as reliable for the rest of the mission as anything else we could design... continues in the article

Mentioned article then continues with another point that is limiting Space Shuttle STS (Space Transportation System) vehicle's actual landing on the Moon, so that's not applicable to our problem.

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    $\begingroup$ Re. the heat shield. The K.E. at 36K is more than twice it is at 25K. Given engineering solutions on Earth surface (where 'every ounce of solution' does not make that much difference in cost) rarely stretch more than 10% beyond 'designed/expected limits', I'd say the shuttle coming back from the moon would be doomed.. +1 for the rest though. $\endgroup$ – Andrew Thompson Sep 7 '13 at 2:43
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    $\begingroup$ Before dismissing a shuttle entry from lunar transfer, one would have to look at multiple aeropasses. The shuttle material is not an ablative and reusable, so in principle it should be able to take an arbitrarily large heat load if given time to cool down between passes. As it did for multiple missions. Then the question is whether the entry could be broken into enough passes to not exceed the heat rate capability of the system. It would take some fuel to raise periapsis and then lower it again after each pass to give time to cool down. $\endgroup$ – Mark Adler Sep 7 '13 at 2:58
  • $\begingroup$ @MarkAdler: I doubt you'd need to raise Periapsis at all. I suspect after the first pass you'd still take several days to hit periapsis again. By that time, you'd be cooled off suitably. You might have to repeat a few times, but I doubt it'd take more than a few hours to cool off the shuttles enough to do that, and by the time you were in such a low orbit, you could just reenter. $\endgroup$ – PearsonArtPhoto Sep 7 '13 at 12:51
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    $\begingroup$ Even if you don't need extra orbits, you will need to raise periapsis for each entry in order to have a flight path angle at entry that is both survivable and that skips you back out. When you get to the lower orbits, I don't know if two hours is enough to cool down. That's where I imagined you might want a few more orbits, requiring you to raise periapsis out of the sensible atmosphere. $\endgroup$ – Mark Adler Sep 7 '13 at 13:35
  • $\begingroup$ The dry weight of a Shuttle Orbiter was most definitely not "250,000 pounds". It was roughly 70 metric tons, or (according to Wikipedia), 151,205 lbs. And the payload capacity of about 25 metric tons could, in theory be nearly all cryogenic oxygen and hydrogen (eg, fuel for the Shuttle's main engines), although this would also require some major redesign to add plumbing to connect this fuel tank up, etc. I suspect it still wouldn't be enough to put a massive craft like the Shuttle to TLI, but it would be slightly less impossible ;-) $\endgroup$ – Kirkaiya Apr 9 '15 at 21:07
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I found different specifications for the orbiter than those quoted from Artemis Project: max takeoff weight of 240,000 lbs (109 metric tons), and useful payload of 55,025 lbs (25 metric tons).

If we fill the payload bay with fuel for the Shuttle's orbital maneuvering thrusters, and apply the rocket equation: \begin{equation}\Delta v = v_e \ln\left(\frac{m_0}{m_f}\right)\end{equation}

Using $v_e$ of 3096 m/s (derived from the 316 sec Isp of the OMS rockets), we get about 800 m/s additional ∆v provided from the fuel in the payload bay. It takes about 4100 m/s to enter lunar orbit, and another ~900 m/s to return (assuming we can use aerobraking to slow down on arrival) so we're far short of what's needed.

The main engines on the orbiter are somewhat more efficient by mass, so 1150 m/s might be possible there, but hydrogen fuel for the SSMEs is much less dense than the fuel needed by the OMS, so unlikely to physically fit in the payload bay -- and that's still far short of the required ∆v.

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    $\begingroup$ There was an "OMS Payload Bay Kit" planned that would give a considerable amount of extra delta v. It was a pallet with fuel, oxidizer, and helium tanks. Never built or flown. wired.com/2012/03/… As late as the 90s Columbia still had circuit breakers for it in the middeck. $\endgroup$ – Organic Marble May 14 '17 at 14:57
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    $\begingroup$ Shuttle-centaur was getting close to an actual flight mission. From there, it wouldn't be too hard to route the fuel lines from a two-engine centaur into two of the three SSMEs provided we took the engines off the centaur. But you'd probably do better deploying the Centaur and leaving the shuttle in low orbit even accounting for the extra burn to get back to low earth orbit. But Centuar isn't storable. Oh wait bad idea. $\endgroup$ – Joshua Jun 17 at 1:04
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    $\begingroup$ @Joshua Centaur G could get maybe 16 tons of payload to a lunar flyby, but not into orbit or back, because of propellant boiloff. $\endgroup$ – Russell Borogove Jun 17 at 1:08

protected by TildalWave Feb 25 '15 at 15:34

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