Friday, March 6, 2009

Resurrecting the Delta Clipper

by Marcel F. Williams

"The effort required to resurrect the Delta Clipper program wouldn’t be very great. Many tests showing the proof that the concept works have already been conducted, and the vehicle’s capabilities have already been proven. Therefore, the Delta Clipper is simply a space vehicle nearly ready for use. All that remains is some final testing,building a full-size vehicle, and then putting the spacecraft to work."

Jason Moore & Ashraf Shaikh
Delta Clipper: A Path to the Future

In 1996, Vice President Al Gore and NASA Administrator Dan Golden announced to reporters that had been gathered at the Jet Propulsion Laboratory in California that the successor to America's Space Shuttle would be a revolutionary new Single Stage To Orbit (SSTO) vehicle dubbed “the Venturestar, a reusable spacecraft designed by Lockheed Martin’s Skunk Works. The triangular shaped Venturestar was to be designed to take off vertically, transporting astronauts and up to 27 tonnes of payload into low Earth orbit (LEO) while landing horizontally like the Space Shuttle upon its return to Earth.

But Gore and Golden's choice of the Venturestar came as a shock to many space enthusiast. Most people had expected the Delta Clipper SSTO to be the choice for America's next manned space vehicle especially since the Ballistic Missile Defense Organization in the Pentagon had already successfully tested a small Delta Clipper proto-type that had shown its capability of taking off and landing in a vertical position.

Unfortunately, after several years of technical difficulties attempting to develop the Venturestar and $1.3 billion in Federal expenditures, the project was finally canceled by the Bush administration in 2001.

Eventually, the Ares 1 was chosen by NASA as the successor to the Space Shuttle program and as part of the new Constellation program to return humans to the moon. The Ares 1 will be designed as a two stage vehicle capable of lifting astronauts and payload of 25 tonnes into LEO. The first stage will consist of a solid reusable rocket booster derived from the current Space Shuttle solid rocket boosters. The second stage will utilize a J-2X liquid hydrogen and liquid oxygen rocket booster that will take the astronauts and their payload into orbit. The first human launch of the Ares 1 is scheduled for the year 2014. The last manned missions of the Space Shuttle are scheduled to end in the year 2010. So once the Space Shuttle program ends, there will probably be a 4 or 5 year gap before Americans return to space aboard an American spacecraft. Thank you George Bush!

Critics of the Ares 1 concept argue that we already have launch vehicles capable of doing the job that the future Ares 1 is supposed to do. Although they are expendable vehicles, the US military's Delta IV rockets are already capable of lifting up to 26 tonnes into LEO. Whether such vehicles can be man-rated (capable of safely lifting human passengers into low Earth orbit) is the question. However, there are also questions about whether or not humans would be able to withstand the vibrations that are going to be endured during the launch of humans above a single solid rocket booster aboard the Ares 1. NASA, of course, believes that the Ares 1 can and will be a man rated space vehicle.

This brings us back to the vehicle that Gore and Golden decided not to choose as the Space Shuttle successor, the Delta Clipper. The Delta Clipper was to be designed to take off vertically, go into orbit, and return to Earth by landing in a vertical position. Navigation for the spacecraft was to be provided by global positioning satellites.

In 2008 dollars, the Space Shuttle has been estimated to cost 1.5 billion per launch for 25 tonnes of payload in addition to up to 11 astronauts. But the shuttle was designed to land with only 20 tonnes aboard. If the payload cabin were designed to house an additional 40 astronauts then a round trip flight would cost approximately $29 million per passenger. However, when fully operational, the Delta Clipper was estimated, in 1990 dollars, to cost around $40,000 to 140,000 ($50,000 to $170,000 in 2008 dollars) per passenger. Why so low?

First of all, it takes over 30,000 people to prepare and launch the Space Shuttle. The DC-X test flights, however, only required 15 people to prepare and launch the reusable vehicle.
Once it was fully operational, the Delta Clipper was to be flown almost like a typical commercial airliner. In fact, there were plans to have the Delta Clipper certified by the Department of Transportation, Office of Commercial Space flight and would be able to operate from 'spaceports' located in any state in the union. Sonic booms during take off would have been largely restricted to the spaceport area. And during its return to Earth, sonic booms would have been barely audible since the vehicle would have slowed down to sub-sonic speeds more than 20 kilometers above the Earth's surface. As far as safety is concerned, the fully operational vehicle would have eight or more rocket engines which would provide a safe return engine out capability. And unlike the Space Shuttle, the Delta Clipper would have been capable of landing on practically any flat surface.

The entire cost of developing the first flight certified Delta Clippers was estimated at $5.06 billion, including production of four flight vehicles. And if it had been fully funded in 1991, the first fully operational orbital missions would have began in 1997, and we wouldn't be having this discussion.

The Delta Clipper was originally designed to use liquid hydrogen and liquid oxygen. But there are new fuel concepts that could significantly lower the mass of this VTOVL vehicle. A 50/50 mix of liquid hydrogen and solid methane would require an 8% increase in additional fuel relative to an equal mass of liquid hydrogen which would be more than compensated by a 200% increase fuel density which would substantially reduce the bulk of the fuel tanks.

It would probably cost over 6 billion to develop four fully operational SSTO vehicles, if the Obama administration decided to resurrect the Delta Clipper program today. But the Delta Clipper would revolutionize manned space travel because it would give humans cheap and easy access to orbit. There have already been 6 space tourist that have payed close to or more than 30 million dollars each just to visit the International Space Station. Could you imagine how many wealthy individuals and companies would be willing to pay less than $200,000 to travel into low Earth orbit.

The Delta Clipper could serve as the first component of a cheap and reusable space infrastructure that would allow humans to easily travel to the Moon if reusable space tugs, fuel tankers and lunar landers were placed into orbit by the Ares V heavy lift vehicles. The Delta Clipper could also serve as a reusable Mars landing vehicle if combined with a drag plate to decelerate the vehicle during reentry into the thin Martian atmosphere.

Additionally, the Delta Clipper could serve as a sub-orbital test vehicle for larger future commercial passenger intercontinental rapid transit vehicles capable of traveling to any point on Earth in less than 45 minutes.

While the Ares 1 merely gets Americans back into space, the Delta Clipper would revolutionize manned space travel allowing both NASA and private industry easy and affordable access to orbit and to the rest of the solar system.

References and Links

1. Delta Clipper: A Pathway to the Future

2. DC-X (Astronautix)

3. DC-Y

4. The legacy of DC-X

5. McDonnell Douglas DC-X

6. DC-X Frequently Asked Questions

7. A New Constellation And Its Legacy

8. Single Stage To Orbit (SSTO)


10. Cryogenic Fuels

11. Rockets, not air-breathing planes, will be tomorrow's spaceships

12. Alternate Propellants for SSTO Launchers

13. Frontiers of Space
Philip Bono and Kenneth Gatland (1976)

14. The Constellation Program

15. The Ares 1

16. Cryogenic propellants and method for producing cryogenic propellants

17. A Single-Stage-to-Orbit Thought Experiment


Marcel F. Williams said...

On Mar 9, 9:08 am, wrote:
> "The DC-X was not a meaningful prototype of a working
> spaceship, but merely the world's most inefficient VTOL
> aircraft, scarcely more advanced than the "Flying Bedstead"
> prototypes of the 1950s."
> Source:
> I wonder if the "Roton" design would've been any better?
> Remember that Roton used rotor blades for landing, so
> you didn't have to worry about keeping the fuel and
> oxidizer cool during re-entry.

The DC-X prototypes were obviously not designed to transport payloads into orbit. They were simply demonstrations of the vertical landing concept for a rocket-shaped vehicle. The next steps would have built ships large enough and with mass fuel ratios large enough to achieve orbit. We already know that the US can build single stage to orbit booster that can achieve orbit. The question is, can that vehicle achieve orbit with the additional heat shielding required for safe return to Earth.

Simply increasing the size of the vessel would increases fuel volume relative to structural mass. Replacing liquid hydrogen fuel with a liquid hydrogen-solid methane slush, would reduce the mass of the fuel tanks dramatically. Using kerosene solely for landing fuel might reduce the structure size even further. Replacing passive heat shields and rocket engines with a plug-nozzle design might reduce the structural mass even further.

But the principal advantage of a Delta Clipper-like ship is as an affordable people shuttle to transport perhaps 6 to 10 people into orbit. People don't weigh much. So the original Delta Clipper concept goal of lifting ten tonnes into equatorial orbit would be unnecessary. Just 5 tonnes of payload capability would probably be needed to transport 8 passengers plus two pilots into orbit inside of a pressurized passenger compartment. So such a small payload wouldn't be big deal.

Obviously, such a vehicle would probably have a much higher capital cost and fuel cost than an expendable rocket. But the dramatic cost savings for such a SSTO vehicle will come from the dramatically reduced labor cost with perhaps only a few hundred personal required to launch and maintain the SSTO vehicle vs. the tens of thousands of personal required to launch and maintain and expendable rocket.

Marcel F. Williams

John K. Strickland said...

I was present at the second flight of the DC-X in 1993, (the one where it was proved that a rocket could be re-used). The BIG mistake of that program was to aim too high. They should have aimed for a two-stage re-usable rocket program to see how far they could go. The demonstrator had no heat shield and could never have even gone as high as an X-15. It was designed to test the landing and maneuvering capacity of such a vehicle. It was a complete success.

The follow-on vehicle could have been designed to carry a second stage, tapered and cone shaped as the first, with the first stage alone being recovered by landing itself just like the DC-X. Imagine how much cheaper rocket launches would be if just the first stage (the largest and most expensive part) was recovered.

There are several different ways of recovering the first stage, such as horizontal flyback, vertically on land, parachutes and airbags on land, parachutes into the water, Engine pod recovery only, etc. They all need to be investigated by developing a prototype of each kind to see how well it works and how much of a second stage and payload it can carry if all versions of the first stage are about the same mass.

Some existing companies like Space-X and Blue Horizon, are working on this problem, but only a couple of methods are being pursued currently (as far as we know). This would be a very tough and expensive, but incredibly worth-while effort to complete.

There is also no guarantee that another government-sponsored program would help or hurt the effort to create a commercial re-usable rocket.

John Strickland

Marcel F. Williams said...

Thanks for the comment John. I wish I could have been there to see one of the Delta Clipper flights.

But if the Delta Clipper folks aimed too high then Al Gore and NASA aimed-- even higher-- when they chose the Venturestar, a far more complex SSTO vehicle.

The military also wanted the Delta Clipper to be a polar orbiting satellite launcher which would have added even more to the complexity when all we really needed was a reusable vehicle that could easily transport a few people into equatorial orbit and back.

Its still going to require billions of dollars of dedicated investment to develop a manned SSTO vehicle, IMO.

But if such a vehicle is ever developed that can be launched anywhere in the US and in the world, then I think that hundreds, if not thousands, of people will be going into space every year and maybe even to future facilities on the moon-- and a new age of space commercialization and industrialization will have begun.

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