In the last months leading up to North American Rockwell winning the contract for the space shuttle, there was still plenty of push for some totally different designs. Since at least the beginning of 1971, TAOS, or "Thrust Augmented Orbiter System" was becoming the leading concept. In this design, there would no longer be a flyback booster. Instead, the shuttle would carry drop tanks for its own engines, and use boosters to provide crucial thrust at liftoff.
The older designs persisted, but it was becoming apparent that they wouldn't make the final round. The leading orbiter design, MSC-040, was a delta winged spacecraft that would carry 3 engines and an orbital maneuvering system on a vehicle that was equipped with a 15' x 60' cargo bay.
A variation of this design was MSC-042A.
This design was a glider.
In plan, it was essentially identical to the MSC-040 designs, though one variation, MSC-042B, did revert to the straight winged Faget DC-3 derived designs. Otherwise, the specifications were similar, though sometimes stated as having a smaller cargo bay, 12' x 40', and with a lower capacity.
To carry MSC-042A (and B) aloft, a booster would be used.
This idea had several proponents, notably George Low, deputy administrator of NASA. The Office of Management and Budget also liked it, as its development would be far less costly, or so it was hoped.
To lift this large space plane into orbit, a Saturn IB class booster would be required. The folks at Martin Marietta had such a design in mind.
The Titan IIIL.
This was not just an evolved Titan II/III. This rocket was a beast. The liquid fueled core would be 15' in diameter and be equipped with four engines. It could be flown with two, four or six solid fuel boosters, stretched versions of the ones found on the Titan III series.
|Courtesy the Aerospace Projects Review Blog|
George Low, and others, felt that this approach might lead to a more incremental development path for the shuttle that was potentially lower in costs.
From late summer of 1971 to at least November, this design was considered. However, it had its opponents, among them LeRoy Day, the deputy director of the shuttle program. In T.A. Heppenheimer's "The Space Shuttle Decision", you find this from Day -
"You had to put this thing on top of on enormous booster which you had to
throw away each time. And so you had an operating cost that was getting to
be kind of ridiculous. The vehicle size and everything — it didn 't have much
utility. It was kind of a demonstration. It would certainly have been a
research vehicle that you could have studied re-entry with. When you got all
through with that then you would have said, ''Gee, that would be nice if it was
big enough to really do something." Then you would have to turn around and
build another vehicle. And with the way the budget climate looked, we were
pretty sure that we 'd be shut out. We 'd never be able to say, "Okay, now let's
start up a real program and build another one that will be an enlarged version
and have more capability." The 0MB and Congress would never support
it; it would be like two different programs, and we said, "That'll be the death
of it for sure."
He probably had a point. NASA was already reeling from one cut after another to its human spaceflight program, and the shuttle was beginning to become unpopular. In the end, the glider design would never progress. There were studies undertaken in the 1980's (prior to the loss of Challenger) that proposed an engineless orbiter being carried into space on a stack where the three SSME's would be moved to the bottom of the external tank (the so-called "Class IV Shuttle Derived Vehicle). The company conducting these studies? None other than Martin Marietta.
If NASA had gone with a glider, it is of little doubt that the program would have been entirely different. In many ways, it would have been like an American version of the Buran, which was essentially the same idea.
When you study the history of the program, one thing you notice, early on, is how closely North American Rockwell's designs were to official NASA designs, and vice versa. I have always suspected that they were in the lead for winning the contract from the beginning. If they had gone with the MSC-042A design, I wonder if NAR would have wanted to participate; most of their designs relied on TAOS or flyback boosters. In my study, I chose an MSC-042A that was based on an MSC-040 derived design from McDonnell Douglas. It would have been a pure delta, but still familiar. It also would have been very tall, between the height of a Saturn V and Saturn IB. We see it after the six solid rocket motors have ignited, and the whole stack has begun to move.
Like LeRoy Day, I believe that if NASA had gone that route, the outcome might have proven to be a far cry from what finally happened, and not necessarily for the better. With the big stack design like the MSC-042A/Titan IIIL6, there was plenty of room for error.
In the end, we can only speculate.