Transporting Space Tourists at 4x the Speed of Sound

"Ladies and gentlemen, we hope you enjoyed your suborbital flight. While we expect a smooth landing in New Mexico, we now ask that you please make sure your seatbelts are fastened and your tray tables stowed as we begin our descent back into the Earth's 7Gs. Thank you."

On Sept. 28, 2006, British billionaire Richard Branson unveiled a prototype design of the first spacecraft to be used by his Virgin Galactic space tourism service. SpaceShipTwo (SS2), the new spacecraft designed specifically for space tourism, will be three times the size of its predecessor and will include a flatscreen TV and reclining passenger seats.

It will also rocket passengers at four times the speed of sound through the atmosphere on a suborbital flight, reports BBC News. (Other accounts say three times the speed of sound.)

The vehicle is designed by Burt Rutan's Scaled Composites LLC and based on the company's SpaceShipOne (SS1) design. In 2004, SpaceShipOne captured the $10 million Ansari X PRIZE for being the first private manned ship to reach space twice in a span of two weeks.

According to an interview with Rutan, the new craft will fly higher and have a longer downrange than SS1, 100 or 200 miles. The maximum capacity will be eight people: six passengers (who pay $200,000 each) and two pilots.

The overall flight profile, though extended, will mimic that of SS1. The enormous WhiteKnight Two (WK2) mothership — which will be larger than a 757 and have a cabin identical to SS2, permitting the aircraft to be used as a training vehicle for the Virgin Galactic passengers — will carry the 60 ft.-long SS2 to 10 miles above sea level, about 50,000 feet, and release it. SS2's hybrid motor will then ignite, accelerating passengers at four Gs to 3-4 times the speed of sound, to an apogee of 140km.

SS1 used a nontoxic hybrid propulsion system of liquid nitrous oxide (N20, or laughing gas) and rubber fuel (hydroxyl-terminated polybutadiene, or HTPB). Designed specifically for SS1, its unique design simplified mounting and reduced leak paths. The composite nitrous tank and case/throat/nozzle components were developed at Scaled Composites, with Thiokel providing the tank's filament wound over-wrap, and AAE Aerospace supplying the ablative nozzle. Development of the "rocket science" (fuel, bulkhead, controller, valve, injector, igniter and ground test program) was completed for the X PRIZE competition with the help of two rocket motor developers, Environmental Aeroscience Corp (eAc) and SpaceDev, according to Scaled.

The craft returns to Earth, making a conventional landing , via Popular Science.jpgThe first flight into space exceeded 100 kilometers of altitude by only a little more than 100 meters. There was concern that the motor lacked sufficient impulse to attain the X PRIZE goal of 100 kilometers altitude when carrying one human pilot and two passengers or 400 pounds of ballast. In the end, though, the performance of the basic engine was improved without needing extra boosters. As such, the two official X PRIZE flights did exceed 100 kilometers by comfortable margins.

SS2 will also be powered by a hybrid motor, but of a somewhat different design than that used by SS1; the company has declined to offer details.

For re-entry, SS2's wings will pitch upward, "feathering" in a shuttlecock formation to automatically position the ship for the steep descent. At 70,000 feet, the wings will return to a horizontal glide formation for the runway landing.

The recently unveiled SS2 cabin, scaled up and more complex, is more than three times as large as that of the X PRIZE-winning SS1, permitting plenty of float-around possibilities during the estimated five minutes of weightlessness the vehicle will achieve at the peak of its ascent, Popular Science noted.

The new cabin also suggests that Rutan's strategy for making the spaceflight experience user-friendly for anyone other than hardcore test pilots could work nicely. Specifically, the designer of both SpaceShips and WhiteKnights had to address the issue of the high-G climb out and the re-entry, both of which were extraordinarily violent for the pilots on the three SS1 suborbital flights.

Pilots Brian Binnie and Mike Melvill, who flew 2004's SS1 flights, experienced "a howling sound for about 20s and shuddering for 5s, just before main engine cut-off," Flight International reported last June.

"The shuddering was due to the valve situated in the oxidiser tank," said Binnie, who is also a Scaled Composites program manager overseeing SS2's cockpit. "We can fix that, but it might not eliminate the shuddering entirely."

The shuddering was caused by intermittent injection of oxidiser from its tank due to the low levels left. Due to its slim design margins, it is unlikely SS2 will be able to retain enough oxidiser to prevent that. During the 5 minutes of weightlessness, passengers could float around, but for the descent, they will have to be back on their reclined seats, needed for passengers to cope with the expected seven-G re-entry loads.

Now, seven-G re-entry is a lot of acceleration force to expose "tourists" to, although that's probably unavoidable given the higher altitudes SS2 will fly to. That makes the development of seats that can protect passengers from the worst accelerations all the more important. As shown in the prototype design unveiled last month, SS2's cabin has ergonomic seats that automatically recline to orient the passengers' bodies to best absorb the G-forces. They will be at a 60-degree upright angle for the ascent and then recline to a nearly horizontal attitude for the descent, with the passengers' legs comfortably bent in order to tolerate the high-G ride and the extreme buffeting that accompanies it. Once back in the atmosphere, the seats will return to a 60-degree angle for the glide back to the spaceport.

Neither SpaceShipTwo nor WhiteKnight Two will be unveiled until late 2007, when flight tests are expected.

Rutan and Branson inked a deal last year to form The Spaceship Co., which will manufacture and sell personal spacecraft. Virgin Galactic plans to launch about one flight a week starting in 2009, first from Mojave, Calif., and later from the private Spaceport America in New Mexico.

The tourism service could launch a new wave of high-speed global travel, Branson said. In fact, Branson and Virgin Galactic president Will Whitehorn have said that they see SS2 as a stepping stone to an orbital vehicle, SpaceShipThree, that would be able to carry passengers but also satellites and scientific payloads at a fraction of the cost of existing vehicles.


Earlier: New Mexico: Spacecraft Landings and Liftoffs


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