Black Day at White Sands
What goes up, must come down. In the Delta Clipper's case, really hard.
- By Preston Lerner
- Air & Space magazine, August 2010
The DC-X backs into its parking spot at White Sands in September 1993.
© Roger Ressmeyer/Corbis
The Delta Clipper, as the McDonnell Douglas single-stage-to-orbit vehicle was dubbed, was designed to take off and land vertically like the spacecraft in 1950s sci-fi flicks. Promoted as a cheap, uncomplicated vehicle that would make spaceflight affordable, the DC-X crashed and burned—literally—on its 12th flight, in 1996. John Logsdon, founder of George Washington University’s Space Policy Institute, offers a postmortem analysis: “It wasn’t strong enough to survive political reservations.”
The project was the brainchild of Max Hunter, who in the 1960s had promoted nuclear-powered spacecraft as an alternative to expendable rockets. In 1989, Hunter, science fiction author Jerry Pournelle, and retired Army Lieutenant General Daniel O. Graham, an advocate of missile defense, pitched the program to Vice President Dan Quayle. With Quayle’s backing, the project was funded by the Strategic Defense Initiative Organization, the agency running the missile defense program derisively nicknamed Star Wars.
Single-stage-to-orbit appeals to seekers of cheap access to space because in theory, it’s far more efficient than the multi-stage rockets that dominate the launch industry. But the technology needed to make single-stage to orbit a reality didn’t—and still doesn’t—exist, so McDonnell Douglas focused on demonstrating that a small crew could launch a spacecraft with lightning-fast turnaround times and at low cost—as long as the system was kept simple.
Neither graceful nor imposing, the Delta Clipper looked like an elongated pyramid. On its first flight, at the White Sands Missile Range in New Mexico in August 1993, mission control—a trailer—held a crew of seven, led by former Apollo astronaut Pete Conrad. At liftoff, the DC-X popped out of the smoke produced by four Pratt & Whitney RL10A-5 liquid-fuel rocket motors and rose to 150 feet. After hovering briefly, and still maintaining its nose-up attitude, it “translated,” or moved sideways, 350 feet, propelled by gimbaled engines. Then, with the engines throttled back to half power, the Delta Clipper descended slowly on a fiery plume and, 59 seconds after liftoff, landed on its tail.
By the end of September, the DC-X had made three flights. But the Delta Clipper was a political hot potato in Washington, and with the cold war over, supporters found it increasingly difficult to carve money out of military budgets. The DC-X was transferred to NASA’s Reusable Launch Vehicle program. On flight eight, a hard landing damaged the exterior “aeroshell,” so the Delta Clipper was put on a crash diet to make single-stage-to-orbit more plausible.
The vehicle got lighter fuel tanks and an upgraded control system. The new and improved model was christened the DC-XA and dubbed the Clipper Graham, in honor of its early advocate, who died in 1995. The team returned to White Sands and embarked on a series of flight tests, highlighted by two launches within 26 hours of each other. On June 8, 1996, the DC-XA flew for 142 seconds and reached 10,332 feet. But on July 31, 1996, due to a maintenance glitch, one of the four landing struts failed to extend at touchdown. The vehicle tipped over and was consumed in a fire fueled by the liquid oxygen oxidizer.
There was no money left to repair Clipper Graham, and NASA preferred to pursue its own reusable launch idea, the Lockheed Martin X-33 VentureStar. More damning, the Clipper didn’t fundamentally advance the science of spaceflight, leading critics to deride it as “single stage to nowhere.” But Clipper fans may get the last laugh. Several DC-X engineers are involved in Blue Origin, the commercial space project funded by amazon.com’s Jeff Bezos. And in recent years, Masten Space Systems and Armadillo Aerospace, two upstarts in the privatization of space, have demonstrated that the vertical-takeoff-and-landing approach works.
Frequent contributor Preston Lerner most recently wrote about Arizona’s Thunderbird Field, a World War II training complex, in the Feb./Mar. 2010 issue.
Comments (3)
"More damning, the Clipper didn’t fundamentally advance the science of spaceflight, leading critics to deride it as 'single stage to nowhere.'"
That's silly. Of course, it advanced the science of spaceflight just as many X projects did previously even when they did not immediately lead to an operational vehicle. The DC-C successfully fulfilled all of its goals. These included proving that LH2/LOX engines could be reused repeatedly with minimal maintenance, demonstrating fast turnaround of a rocket vehicle, demonstrating flight with lightweight composite tanks and structures, demonstrating fast prototyping for both hardware and software, etc.
Perhaps most fundamentally, it showed that a 1950s style X-project with a small talented team could accomplish its goals at a fraction of the cost of most modern aerospace projects. The total cost of the DC-X/XA project, which was allowed to operate under non-standard procurement rules, came to about a tenth what the project cost models at the AF and NASA predicted it should cost.
The DC-X was meant to be the first in a series of prototypes that would lead to a single stage to orbit. However, even if SSTO proved too difficult, these prototypes would still provide invaluable lessons on how to build a fully reusable two-stage-to-orbit vehicle.
One final note, Jerry Pournelle often tells the story that after the DC-X was turned over to NASA, a JSC team did a "non-destructive" structural test on the hydrogen tank that resulted in a crack. They patched it up but when the vehicle fell over on it's final flight, it was along that crack that it split, spilling the fuel that resulted in the fire that destroyed the vehicle.
Posted by Clark Lindsey on July 16,2010 | 10:23 PM
Prior to DC/X many contended that it was impossible to control a vertical landing rocket because the speeds were too low and there could not be enough control authority to keep it upright and certainly not enough to move it horizontally. DC/X demonstrated that ability on the first flight. In another flight it was angled from nose up to 11 degrees nose down, then back to nose up, showing that it could go from reentry to vertical for landing. This was mostly what DC/X was intended to prove. We also learned a lot more about flight control programs.
DC/X was an enormously successful X project. Unlike X-33 which was not an X project at all, DC/X didn't cost much and we learned a lot from it.
Jerry Pournelle
www.jerrypoutnelle.com
Posted by Jerry Pournelle on July 30,2010 | 02:10 AM
X-33 taught us quite a bit about fabricating large composite cryogenic-storage structures. Had Lockheed Space Systems been permitted to continue with the program, it would have resulted in flyable hardware--perhaps not an SSTO, but then DC/X wasn't an SSTO either. Unfortunately, the program had been budgeted and scheduled with the '100% success' assumption, and the degree of public/civilian visibility meant that the first failure would kill the program (and that's what happened.)
When you wonder why everything in aerospace is classified these days, look at DC/X and X-33. In a public program, one failure means cancellation.
Posted by DensityDuck on August 8,2010 | 07:45 PM