It's easy to lose track of the Lynx with all the attention being showered on the spacecraft like Space's Dragon angling to carry cargo and crew for NASA and the behemoths like Stratolaunch and SpaceShipTwo. But in the same Mojave Desert airfield where Scaled Composites is developing SpaceShipTwo to carry passengers for Virgin Galactic, XCOR's hot rod is coming together. The first test flights could begin as early as the end of this year, with the first revenue flights potentially to come before the end of 2013.
The Lynx has only two seats?one for a pilot, and one for a so-called spaceflight participant (a space tourist or a scientific researcher). But, like the actual Corvette sports car (which was the ride of choice for early NASA astronauts), its low weight and high octane fuel give it some important advantages. These include direct runway launches without the complication and expense of a mother ship and the ability to fly several times per day?both of which XCOR expects to add up to cheaper flights. Like SpaceShipTwo, the Lynx is essentially a rocket-powered airplane. But from there, the two vehicles diverge significantly.
The Lynx's small size makes it quicker off the line. Its takeoff speed is 190 knots, and it can get airborne with only 1200 feet of runway. "The last fighter that took off at those speeds that I recall is the -F104," says XCOR chief test pilot Rick Searfoss, a former Air Force fighter pilot and space shuttle commander.
Four XCOR-built kerosene and liquid oxygen engines power the Lynx, creating 3000 pounds of thrust apiece. The all-liquid design is more efficient than SpaceShipTwo's hybrid propulsion, providing more thrust per pound of fuel. That, plus the lower overall vehicle weight, lets the craft take off from the runway under its own power (rather than being dropped from a plane for an air launch). All-liquid fuel should give it faster turnaround between flights, too. Crews can just top off the tanks and go again; SpaceShipTwo's engine has to be replaced between flights. The XCOR team (which currently numbers about 45) envision eventually being able to pull off four flights per day with only a couple of hours of turnaround time. That's presuming clear skies, which Mojave has in ample supply.
"The whole idea of having liquid rocket engines with piston pumps is that it really does promote that very low cost of operation and quick turnaround," XCOR chief operating officer Andrew Nelson says. "The less you have to touch the vehicle with human hands between flights, we believe the safer it will be.? If you have to replace two-thirds of the engine every single flight, you've got a bunch of mechanics that have to open up the engine every single flight. We don't think that's the best way to do things."
The vehicle coming together in Mojave is designated the Mark I. It's a prototype, designed to reach two times the speed of sound and a maximum altitude of 200,000 feet. The K?rm?n line?the internationally accepted boundary of space?is at 100 kilometers, or approximately 328,000 feet. The planned ceiling of the production model Lynx, the Mark II, is 350,000 feet.
"The external skin on the prototype is going to be a different material than the production model," Nelson says. The Mark I's carbon-composite skin will be more easily modifiable as the flight test program progresses, which will let XCOR adjust the vehicle's aerodynamics. The production model will be a cyanate ester?based composite, he says, that will better withstand the heating caused by atmospheric reentry at higher speed. "The altitude's going to be limited by the thermal properties of the skin."
Looking even further ahead, the Lynx Mark III will include an enclosed bay on the top, from which a separate rocket booster will be able to launch a small satellite or from which a space telescope will be able to operate. For now, researchers purchasing rides for their instruments on the Lynx will have to be content with space for experiment packages in the seat next to the pilot, in the space behind the pilot's seat, or at the rear of the craft, in an area that can be selectively exposed to the atmosphere at high altitude or the vacuum of space.
Passengers?each paying $95,000, or just under half of the SpaceShipTwo ticket price?will ride beside the pilot. Both pilot and passenger will wear pressure suits as a safety measure in case cabin pressure is lost during the flight. Unlike aboard SpaceShipTwo, passengers on the Lynx will not be able to unstrap and float about the cabin after the engines cut off and the vehicle goes into free-fall. Still, the view will be just as spectacular, with the passenger treated to a vista of Earth's curves set against the black sky of space.
XCOR president Jeff Greason says he hopes to see "air under the wheels" on the first test flights of the Lynx by the end of 2012. The flight test program will last 12 to 18 months beyond that. "That six months' uncertainty is just based on stuff that we don't know of that will come up [and] that we have to deal with," Searfoss says.
It remains to be seen whether SpaceShipTwo, still to start powered test flights of its own, will be able to fly its first passengers within that time frame. It just might get smoked coming off the line by the space Corvette.
Michael Belfiore is the author of Rocketeers: How a Visionary Band of Business Leaders, Engineers, and Pilots Is Boldly Privatizing Space, and is a frequent contributor to Popular Mechanics.
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