Although not completely set in stone, it is extremely likely that any future launch vehicles NASA develops will divide the roles of lifting people and cargo into Earth orbit."It's always up for debate," Martin said, noting that launch vehicles such as the Atlas 5 and Delta 4 seem ideal to carry into orbit an OSP with astronauts aboard, while shuttle derived hardware might best solve the larger cargo needs.
"We are poised to make a much safer system now, a much more reliable system, based on new technologies. And at the same time bring down the overall costs," Martin said of the OSP specifically and NASA's space transportation needs in general.
Exactly how much any of these ideas will cost to build or operate hasnt been determined yet, and support in Congress for programs such as the OSP is facing some challenges these days.
Martin said its likely that NASA isn't "articulating the vision very well. I think that what Congress is asking is how does (OSP) fit within the larger picture, and we're developing that."
"The United States, if its going to be a spacefaring nation, and its going to continue exploring the solar system, is going to need a reliable, upgraded system. The next step, past what the shuttle was in technology in order to keep moving forward," Martin said.
But if the OSP is adopted as the next piloted spaceship -- whether it's a winged vehicle or shaped like an Apollo-era capsule -- NASA still will need a way to lift large amounts of cargo into Earth orbit.
How much cargo?
Martin said some studies completed regarding a return to the Moon mission would require launching 265,000 to 440,000 pounds (120 to 200 metric tons) just to get the project started. The goal would be to launch that weight in as few missions as possible hoping to minimize risk and cost -- but there's no easy answer.
"We're looking all across the board. And shuttle derivatives are a very important part of that because, quite frankly, the shuttle has quite a lot of up lift capability," Martin said.
The space shuttle as it is today is designed to carry up to 65,000 pounds (29,480 kilograms) to a low inclination, low Earth orbit. That number quickly shrinks when flying into the higher inclination orbit where the International Space Station circles the planet.
By comparison, the most powerful version of the Atlas 5 is advertised as being able to lift 45,238 pounds (20,520 kilograms) to low Earth orbit.
With the three remaining shuttle orbiters still around after the OSP begins operations, along with a launch site and several factories nationwide configured for shuttle hardware, Martin says it makes sense to consider ways take advantage of the existing infrastructure.
Back to the drawing board
The idea of a cargo-only shuttle is not new. During the 1970s and 1980s the idea was studied and developed somewhat by the Marshall Space Flight Center in Huntsville, Ala. The spacecraft was known as Shuttle-C.
The plan was to use the same external tank, solid rocket boosters and main engines to lift a wingless cargo canister to low Earth orbit, where awaiting astronauts could use an orbital maneuvering vehicle or robot arm-equipped spaceship to handle the load.
Like the shuttle program, the external tank would be discarded and the booster rockets recovered. But with this concept the spacecraft's main engines also would be recovered, returning to Earth as part of a pod equipped with a heatshield and parachutes.
A full-scale mockup of the cargo element and its propulsion pod was built at Marshall, with plans to send it to the Kennedy Space Center for fit checks at the launch pad. Initial launch capability was expected by 1995.
But in 1990, as NASA sought for ways to pay for a new shuttle (what became Endeavour) and space station Freedom, the agency called off its Shuttle-C work.
Depending on the exact configuration, a Shuttle-C could lift two or three times more weight than a standard shuttle.
It's interesting to note that while space advocates lament the loss of the heavy lifting Saturn 5 Moon rocket, many fail to appreciate the shuttle is, in effect, a heavy-lift booster in the Saturn 5 class. It's just that 100 tons of that cargo is in the form of the reusable winged orbiter.
According to Martin the cargo-only shuttle idea remains on the table, but not necessarily in the way as originally proposed for Shuttle-C.
The autonomous orbiter
"Everyone uses the term Shuttle-C, including myself. But it really means a much more generic look at the pieces that make up the shuttle," Martin said, noting the improved shuttle main engines and recent test firing of a five-segment solid rocket motor help make the shuttle more attractive.
"It's a whole family of capability based on the reliable shuttle parts that we know and understand very well," Martin said.
In fact, Martin said, the shuttle is so well-known that even after it is no longer needed to carry people, Discovery, Atlantis and Endeavour still could be pressed into service flying in a robot mode -- what NASA is calling the autonomous orbiter.
Although never proved in flight, the shuttle is capable of landing by itself except for one critical detail: the landing gear must be lowered by an astronaut. That switch has never been automated, allegedly to ensure job security for the astronauts.
"If there are any out of the ordinary disturbances there's no way to deal with it very easily," Martin said, talking about a shuttle flying its final approach to the runway. "That's where a human can make some really quick decisions. However, it is a doable activity"
But landing isn't necessarily the toughest part of flying a shuttle without a crew. The rendezvous and docking portion of a flight to the space station is more worrisome.
"What we're trying to do is to understand how hard that is," Martin said. "These are not trivial questions. Docking autonomously with the kind of mass the shuttle has, well, you know the risks are high."
More from SPACE.com:
advertisement
