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Competition to Build the Space Shuttle's Successor
Neil Halelamien writes "The competition for the prime contract to build the Crew Exploration Vehicle, the successor to the Space Shuttle, is ramping up. Currently, 11 different companies are creating preliminary designs for systems and vehicles which could be useful in implementing NASA's Vision for Space Exploration. By the end of the year, NASA will select two teams to independently develop and build a CEV design. The two teams will launch competing unmanned prototypes in 2008, at which point NASA will award a final winning contract. Aerospace giants Boeing and Northrop Grumman have formed one team. Another "all-star" team, announced a couple of days ago, is headed by Lockheed Martin. A third team in the running is underdog t/Space, a company with a free enterprise approach to space exploration, which includes notable figures from the commercial spaceflight arena, such as Burt Rutan and Gary Hudson. There is concern that a NASA budget boost to help pay for the exploration program could draw some opposition, as most other government programs are anticipating budget cuts."
At a certain point it becomes counter-productive. Just tell me which one to click on to get the article.
For example, they self-orient on reentry, they don't have expensive and heavy control surfaces or landing gear, and from their position on the top of the rocket they can use escape systems like those in the Mercury, Gemini and Apollo programs.
About the only thing they can't do is bring things back down from orbit. But, really, if we want a real future in space the biggest issue is getting things up there.
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Bruce
Bruce Perens.
The trouble with a spaceplane is its inefficiency. Too much of the energy expended in a Shuttle launch goes to carry the orbiter's main engines, wings and other structure into orbit. If you could leave those off, with a capsule design, you could either save a whole lot of fuel and get a cheaper launch, or use the same amount of fuel and carry a much larger payload.
The idea behind the Shuttle was that the engines were worth keeping, and reusing them could save money. Apollo used to drop its main engines into the sea... But it turns out that there are plenty of factories on Earth capable of producing rocket engines very cheaply, so that economy didn't really work out.
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BTW, the real problem with a space plane is in the aerodynamics. To avoid superheating on reentry (compared to which the space shuttle would be freezing during renetry), all leading surfaces must be big round things. That's why the shuttle looks so un-sexy compared to fighter jets. The wings leading edges cannot be sharp - no known material would survive at 50,000 C. By making the leading edges round, they lower the temperature baring within range of Carbon-Carbon - but that makes the wing have a terrible L/D ratio. In addition, instead of a nice sleek body which could be lightweight, you now have a ponderous blob which must be reinforced at every point.
Taking aerodynamics into consideration, the best design is really like a sphere. The closer you are to a sphere, the better. Apollo took a cone and made a good aproximation of a sphere. The shuttle takes an airplane and makes a bad approximation of a sphere. Lifting body designs look a lot more like a sphere, but soon we probably will know if they are close enough to a sphere.
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First of all, I think that China will probably beat the US in terms of manned space exploration. They will go back to the moon before the US even finishes their new space vehicles. This is sad because China apparently understand economics better than current US leaders do. It might seem that the Apollo program was just a big expensive government program but the truth is that all the expensive science generated far more money that it spent. Science is good for the economy for it provides people with technology that lifts the economy and increases growth in the country. As complicated as going to the Moon and Mars and expensive as it seems might be, it is good for the economy. All the new technologies generate new industries which will further the economic growth. Our leaders in the US have forgotten that by limiting science funding and cancelling things like the particle accelerator in Texas. Second and most important, it is too expensive to think of old ways to get out of this planet. The best and most efficient way is to build the SPACE ELEVATOR. Fund nanotechnologies to get the cable for the elevator built. It is estimated that it would cost $100 a pound at the beginning to lift things into orbit using the elevator and maybe even go down to $1 a pound as more elevators are built. Science fiction but so was landing on the moon before Apollo 11.
I disagree. Spaceplanes may be inherently inefficient *per mission* compared to a disposable capsule design, but if maintainance costs were lower, they would easily outshine capsules with disposable rockets.
:)
And maintainance doesn't *need* to be high. If the shuttle had the budget for its initial design plan (a titanium frame, no solid boosters), it never would have had any of the problems that it's had that led to high maintainence costs and its 2% failure rate.
A couple of things about your list:
* A hugely increased heat shield: Not really hugely increased. An optimal shape for reentry is a large, slowly curved surface, and the further from that shape, the larger amount of shielding you need for a given size and density. However, the shuttle manages relatively well given its size and density compared to what an equivalent capsule would be by turning its bottom side into the direction of incoming air.
* Hydraulic motors for flaps: Not necessarily. Hydraulics in space are problematic because of temperature regulation (in the tanks, in the cylinders, in the lines, etc). However, it is possible to use electric actuators to replace them for most, if not all, tasks. Electric actuators are increasingly being used in high force tasks.
However, the key issue is reusability. Reusable capsules have never really come into their own - they tend to have a pretty rough landing. The more payload return you want them to be able to bring back, the rougher it is.
If one can get reusability without high maintainence, in any design, that truly is the holy grail of spacecraft design.
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