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The Dragon Lives!
A few months ago, NASA approved the critical design review (CDR) for the initial flight of the company’s Dragon spacecraft on the Falcon 9 rocket booster. F9/Dragon is intended to provide crew and cargo service to the International Space Station (ISS) after the Space Shuttle retires in 2010—passing this review was no small matter.

Apart from the flight itself, this was, arguably, the most important mark of progress in the NASA Commercial Orbital Transportation Services (COTS) program.

In addressing NASA’s requirements, SpaceX submitted a package of 486 documents encompassing every aspect of the F9/Dragon—design, engineering, testing, manufacturing, and flight operations. In terms of overall design maturity of the Falcon 9 project, we are ahead of the curve for a typical program of this size. It is unusual for a CDR to feature this quantity of hardware in fabrication, assembly, integration, and test phases.

Progress Highlights

  • About 95 percent of F9/Dragon drawings (actually 3D CAD models) released
  • First stage:
    • Propellant tanks passed pressure and leak tests
    • Thrust structure and composite skirt proof tested
    • Plumbing and wiring for all nine engines installed
    • First stage fully assembled and lifted atop the big test stand
    • Stage and test stand cold flow tests completed
    • Electrical, data and sensor system integrity verified
    • Merlin 1C regeneratively cooled engine finished development, now in qualification phase
    • Avionics architecture developed; triple redundant for F9, and quadruple redundant for Dragon
    • Avionics board level testing underway, including flight and engine computers, valve controllers, communication systems, power, lithium polymer batteries, etc.
    • Wind tunnel testing completed
The Falcon 9 program remains on track for demonstration of cargo delivery to the International Space Station by the end of 2009.

Big Dragon Update

The SpaceX Dragon Spacecraft will carry up to seven crewmembers, or over three metric tons of cargo, to the International Space Station as well as to future private destinations such as those envisioned by Bigelow Aerospace. Like Apollo, Soyuz, and the future Orion spacecraft, Dragon is a capsule design.

Some may wonder if the lack of wings represents a step backwards. Fundamentally, for orbital vehicles spending the vast majority of their time in space, the arguments against wings are strong (although for low energy, sub-orbital craft such as SpaceShipOne, which spend most of their journey in the atmosphere, there are still good arguments in favor of wings).

Wings have a performance penalty on the way up, are useless in the vacuum of space, and become a hazard on reentry, due to the fragile nature of the high temperature material protecting the wing’s leading surface. In addition, returning as a glider offers only one chance at a safe landing. If any problems develop with the control surfaces, you’re out of luck.

Finally, consider how, with years of Shuttle experience, NASA chose to return to a capsule architecture for the Orion lunar spacecraft. Thus, we favor the capsule design for reliable and economical transport to and from Earth orbit.

Dragon on the Road to the ISS

Several months ago, we completed the first of three phases of review required by NASA’s Safety Review Panel (SRP) to send the Dragon spacecraft to the ISS. The review covered 23 specific hazards, with extra attention paid to the danger of collision, one of the most complicated hazards to mitigate, and generally considered one of the most difficult areas for “visiting vehicles”. The fact that we passed in under a week speaks well of our team’s capabilities.

Dragon Details

When we fly the three COTS cargo missions to the ISS, we will also be flight qualifying a huge number of systems that will eventually support passenger space travel. Whether we’re flying cargo or crew, the essential systems for Dragon remain the same:
  • A pressurized interior section for the people or pressurized cargo
  • An unpressurized service section ring around the base of the capsule
  • Protective layers for aerodynamic and thermal forces
  • A Passive Common Berthing Mechanism (PCBM) for mating with the ISS
  • 18 bi-propellant thrusters for orientation and orbital maneuvering
  • Eight propellant tanks and two pressurant tanks
  • Redundant drogue and main parachutes
  • Base and backshell heat shield
  • Micrometeorite shields
  • Proximity operations navigation and berthing system
  • A trunk section to hold unpressurized cargo, solar panels and thermal radiator
Draco Thrusters Take Shape

We’re developing a small rocket engine called Draco that generates 90 pounds (400 Newtons) of thrust, using monomethyl hydrazine as a fuel and nitrogen tetroxide as an oxidizer. These are the same propellants used for orbital maneuvering by the Space Shuttle. Dragon will have a total of 18 Draco thrusters for both attitude control and orbital maneuvering.

Our propulsion team has completed the first Draco development engine, and it will soon begin testing at our new MMH/NTO vacuum test chamber in Texas.

Dragon Heat Shield Shapes Up

The base heat shield is an extremely important part of Dragon’s design. Although one can do a lot of testing on the ground with plasma torches and arc jets, nothing on the surface of the Earth can test for the actual conditions that are encountered upon reentry at 25 times the speed of sound. Considerable safety margins must be applied to address the model uncertainty, which leads to a relatively heavy heat shield. However, as we are able to anchor our models with empirical flight data, the mass efficiency of the heat shield can be much improved.

A few months ago, we completed the full-scale engineering unit of Dragon’s heat shield. Shaped like the heat shields that protected the Apollo capsules during their high-speed returns from the Moon, Dragon’s heat shield uses phenolic impregnated carbon ablator (PICA), the highest heat resistance material known. At heat fluxes that would vaporize steel, PICA is barely scathed.

Developed by the NASA Ames Research Center, PICA demonstrated its abilities in protecting the Stardust sample return mission. Stardust holds the record for the fastest mission reentry speed—nearly 28,000 miles per hour. Dragon will return at under than a third of that speed.

Dragon Makes a Big Splash

Dragon will return to Earth and land in the ocean (although it can be modified to land on land, as well). As with the Falcon 9 wind tunnel testing described above, we’re using scale models of our Dragon capsule to verify our digital models of recovery and splash down.

Dragon will be steerable during reentry, allowing us to hit a target zone of under 1 mile in radius. Initial splashdowns will occur off the California coast.

Article and illustrations excerpted from Elon Musk’s web update at SpaceX.com
Courtesy of:
Space Exploration Technologies
1 Rocket Road
Hawthorne CA 90250