Monday, May 23, 2011

What Might Have Been, Part II

Last time, we looked at some alternate post-Apollo scenarios, with an eye towards leveraging technology that the American taxpayer had already bought and paid for. After discarding more and longer Moon missions as expensive and impractical, we settled on basing the 1970s manned space program around two long-duration space habitats: the S-IVB based Dry Workshop, and the S-IVB based Wet Workshop.

Which begs the question: why are we doing this, anyway?

Mainly, if you want to tackle manned interplanetary spaceflight at some point, you have to address the question of whether or not a human being can stay alive, healthy, and sane after spending between 400 and 600 days in free-fall. There are a lot of ways to simulate the effects of free-fall on a human body. But there's only one way to find out for sure what free-fall does to you. And the key unanswered question pretty much to this day is still this -- can we deliver a crew to Mars that's fit to work once they get there? This series of missions is intended to answer that question.

Now that we've decided that we can afford to do this, and that this is something we actually want to do ... what does the schedule look like? More to the point, what kind of operational tempo can be kept up? As it turns out, the industrial plant at Kennedy Space Center was sized for a pretty heavy workload. There were two Saturn launch pads that were in the original plans, Pad 39C and Pad 39D, that were never actually built. The VAB could have kept all four busy. To get an idea of what kind of tempo KSC would have been capable of, let's look at the schedule that was maintained from December 1972 to December 1973:

December 6, 1972: Apollo 17 (Saturn V)
May 14, 1973: Skylab 1 (Saturn V)
May 25, 1973: Skylab 2 (Saturn IB)
July 28, 1973: Skylab 3 (Saturn IB)
November 16, 1973: Skylab 4 (Saturn IB)

So, in any one calendar year, KSC could support two Saturn V flights, and three Saturn IB flights. Which means that a single Saturn V flight plus three Saturn IB flights are easily within reach. That will form the basis of our alternative schedule.

Little would have been different in the flight schedule, at least up until February 1974, when Skylab 4 returned to Earth. The Wet Workshop R&D cycle would have been running in parallel with Skylab's, and would probably have had flight-ready hardware by early- to mid-1974. The Wet Workshop concept would require a few development test flights before it could be trusted with a long-duration mission. There were no such worries with Skylab, since it could be launched all in one lump. But with the Wet Workshop, first you had to prove that you could actually vent the liquid hydrogen tank and fill it with breathable air. Then, you had to prove that you could erect living quarters inside it, and use it. After that, it's a matter of qualifying the habitat for stays of three months, six months, then a year or longer. Possibly by the fifth flight, you could be ready for your most ambitious missions. With that in mind, let's take a look at what could happen by 1981.

* WWD-1 (Saturn IB): First development flight for the Wet Workshop. After orbital insertion, the crew performs a transposition and docking maneuver, and vents the LH2 tank. In principle, this should work, and then the crew pressurizes the tank with breathing air, and spends about a day fitting out the interior of the tank as living and working space. This first development mission lasts about 30 days. As a small bonus, after undocking from the workshop, the crew chases down and docks with Skylab, boosting it up into a higher orbit. After a 10-day stay at the old station, they return to Earth.
* Skylab B (Saturn V): Bet you didn't know that the Smithsonian exhibit was actually a flight-ready backup. Under this revised plan, the Air and Space museum loses one of its more interesting conversation pieces.
* Skylab B-1 (Saturn IB): First crew to occupy Skylab B. Three-month mission.
* Skylab B-2 (Saturn IB): Second crew to occupy Skylab B. Three-month mission. The intent, more or less, is to try to have Skylab B occupied continuously for as long as its consumables hold out. My guess is that Skylab B will have a design lifetime of two years, from mid-1974 to mid-1976.

* WWD-2 (Saturn V): This is the second development flight for the Wet Workshop. It involves both a more energetic trajectory, and a slightly more ambitious goal. This three-month mission inserts a S-IVB lab module into lunar orbit. Yes, it's actually possible to use a more-or-less stock Saturn V to put an empty S-IVB stage in orbit around the Moon. There was a McDonnell-Douglas design study in 1970 that worked out some of the details. Plus, I've flown this profile in Orbiter, so I know it's doable.
* Skylab B-3 (Saturn IB): Third crew to occupy Skylab B.
* Skylab B-4 (Saturn IB): Fourth crew to occupy Skylab B. It's more or less at this point that a Soyuz crew pulls alongside, docks, and spends about a week on board conducting joint experiments.
* Skylab B-5 (Saturn IB): Fifth crew to occupy Skylab B.

* WWD-3 (Saturn V): This is the third Wet Workshop development mission. It will be launched on a trajectory that will place the S-IVB lab module into an orbit 23,500 miles above the Earth, at an inclination of 28 degrees. This is almost, but not quite, like a geostationary satellite orbit. Instead of remaining stationary over the same point on Earth's surface, it will trace out a figure-8 between 28 degrees North and 28 degrees South. There was a proposal to fly the mission such that the figure-8 is anchored over Europe and Africa. Over the course of six months, seasonal change can be observed in both the Northern and Southern hemispheres. This is a tricky mark to hit from a piloting standpoint, but it's well within the Saturn V's capability.
* Skylab B-5 (Saturn IB): Sixth and last crew to occupy Skylab B.
* Skylab C (Saturn V): Third Dry Workshop station. This one is built with some resupply capability in mind. I expect this model will last for about three, maybe four years.
* Skylab C-1 (Saturn IB): First crew to occupy Skylab C.
* Skylab C-2 (Saturn IB): Second crew to occupy Skylab C.

* WWD-4 (Saturn V): Fourth Wet Workshop development flight. The mission profile is similar to WWD-3, but with a duration of at least one year. One possible wrinkle is that, instead of a fixed figure-8, the station is placed either slightly above or slightly below synchronous altitude. Then, instead of a perfectly-fixed figure-8, the figure-8 wanders eastward or westward with time. I found this out by accident, when I tried to nail a perfectly-fixed figure-8 and failed. There's some possible value in this: you get long loiter times over a region, but over the course of the whole mission you could cover the entire Earth, at least between 28 North and 28 South. With the successful conclusion of this mission, the Wet Workshop is considered proven for longer-duration missions.
* Skylab C-3 (Saturn IB): Third crew to occupy Skylab C.
* Skylab C-4 (Saturn IB): Fourth crew to occupy Skylab C.
* Skylab C-5 (Saturn IB): Fifth crew to occupy Skylab C.

* Skylab C-6 (Saturn IB): Sixth crew to occupy Skylab C.
* Skylab C-7 (Saturn IB): Seventh crew to occupy Skylab C.
* Skylab C-8 (Saturn IB): Eighth crew to occupy Skylab C.
* Manned Venus Flyby: And here's the payoff for having developed the Wet Workshop capability. As mentioned previously, you don't need to stay in Earth orbit exclusively. Once you've proven the technology, you can go strut your funky stuff across the Solar System ... within reason.

The dates are wildly optimistic, though ... starting from 1968, there's no way, no way at all, that this mission would be ready for launch by October 1973.

1977 and beyond:
* Skylab C-9, C-10, C-11, C-12: These are the last missions to Skylab C. Skylab D will probably fly in 1978, and will be used into the 1980s.
* Manned Mars Flyby: The other obvious target, accessible within a reasonable time frame.
* Manned Asteroid Flyby: This is contingent on finding a suitable target. Eros would be a good candidate. Or Icarus. It's just a matter of finding one or two that come close enough to make a flyby worthwhile.

And, The Downside...

Every option taken carries with it an opportunity cost. For example, having decided to build the Space Shuttle, we closed the door on getting the most out of our investment in the technology built for Project Apollo. This program is no exception. Having decided on a more ambitious manned program in the 1970s, the development work that would have led to the Shuttle is never accomplished. Which means that some of the Shuttle's unique advantages are not available in the 1980s. Such as:

No Hubble Space Telescope. Honestly, I could stop here. If you had to pick one single instrument that has revolutionized our knowledge of the Universe more than any other in the last 25 years, you'd have to pick Hubble, hands down. No Shuttle means no Hubble. That means no Hubble Deep Field. And none of the stunning images we've become accustomed to. Hubble was a key instrument in the observations of Supernova 1987A, and of the Shoemaker-Levy 9 impacts on Jupiter. And if that weren't enough all by itself...

Fewer Scientists In Space. The Shuttle can carry seven people at a time, only two of whom have to be pilots. Apollo could only carry three, two of whom were pilots. This, the fact that the Shuttle can carry up to five scientists at a time, made things like the Spacelab module possible. Now, after thirty years of Shuttle flights, I think it's probably safe to say that most of the people who've flown in space have been scientists or engineers; this would not have been the case otherwise.

So, as glorious as this alternate program would have been, I have to say that it's just as well that we didn't. Maybe this really is the best of all possible worlds.

Next in this series: Once upon a time, it was thought that Space Shuttles would fly fairly often, as many as fifty flights a year for the whole fleet. What would have to have happened to make that possible?

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