By Mike Bishara
There is plenty of publicity around the commercial plans of the Virgin Galactic space tourism venture – already 500 passengers have stumped up more than US$60 million worth of deposits to get a seat on the first commercial flights to space. But not so much technical and engineering detail of the project are in the public domain.
The Spaceship Company, a joint venture between the Virgin Group and Scaled Composites, is building and testing the 18.3 metre long SpaceShipTwo and WhiteKnightTwo – the high-altitude launch vehicle that will send SpaceShipTwo and its fare paying passengers on a journey out of the atmosphere.
Scaled Composites is owned by Northrop Grumman, itself an industry leader in the design and manufacture of aircraft and well known for its expertise in the advanced use of composites to bring down the weight, and thus the fuel costs, in aircraft and now spacecraft.
The US$8 million aptly dubbed test flight hangar Faith – final assembly, integration and test hangar – opened late last year in the Mojave desert by The Spaceship Company and is the base for the assembly and testing of all SpaceShipTwo’s and WhiteKnightTwo’s now and in the future.
Virgin’s chief executive Sir Richard Branson told reporters at the opening of Faith that the 6320m2 facility was the first in the world dedicated to producing private, commercial manned space vehicles – the first purpose-built facility set up to make fixed-wing spacecraft. Ultimately it will support parallel production of two motherships and up to three spacecraft at the same time.
Spaceport America, a US$212 million spaceport in New Mexico partly funded by the state government, will become the permanent launch site when commercial launches begin.
The spaceship features two large 430mm windows for each passenger in the 3.65 metre long cabin, one on the side and one overhead. Small thrusters allow the two pilots to manoeuvre the ship once in space.
George Whitesides is the president and chief executive of both Virgin Galactic and The Spaceship Company. He says that a market apart from passenger sales is evolving for suborbital payloads to be taken aboard SpaceShipTwo. There is plenty of room in the aircraft’s interior, which can be filled with experiments – the company can get them up and down and they can be sent off for analysis very quickly, he says.
Both current spacecraft are made chiefly of carbon composites, thought to be in the form of a composite skin encasing a honeycomb core – the spars and wing of WhiteKnightTwo formed in a single piece. It is the largest all-composite aircraft ever built.
Scaled Composites says carbon fibre composite is four times the strength of steel and a quarter of its weight with “virtually unlimited fatigue life. As long as the stresses are kept below the ultimate, it does not deteriorate in use in the same way that metal fatigues. It is also easy to modify, as was proved during the SpaceShipOne programme when significant aerodynamic changes were made during the fl ight test program, simply by bonding on additional pieces.”
Virgin Galactic says it is hopeful the strenuous testing on the newly developed hybrid rocket motor will be advanced enough by the end of this year to apply for a commercial operating license from the Federal Aviation Administration. That points to the first commercial flights in 2013.
The company says hybrid motors are simple and safe and the most efficient strategy is to air-launch SpaceShipTwo from around 50,000ft, a height at which it is already above most of the Earth’s atmosphere. The rocket motor has to burn only for a very short time in order to reach space and if there were any problems during the boost phase, it could easily be shut down and the spaceship would return as a glider to the runway.
The oxidiser in the Sierra Nevada RM2 hybrid motor is Nitrous Oxide and the fuel a rubber compound – both benign, stable as well as containing none of the toxins found in solid rocket motors.
The safety of SpaceShipTwo’s feathered re-entry system was reinforced in September last year when the crew lost control of the craft during a gliding test flight – it was re-established quickly after the spaceplane entered its feathered configuration, and subsequently landed safely after a seven-minute flight.
In a feathered re-entry the aerodynamics of SpaceShipTwo’s pivoted wings act like a shuttlecock, slowing and controlling the spacecraft’s re-entry, the company says.
“Once out of the atmosphere the entire tail structure of the spaceship can be rotated upwards to about 65 degrees. The feathered configuration allows an automatic control of altitude with the fuselage parallel to the horizon.”
This creates very high drag as the spacecraft descends through the upper regions of the atmosphere. The feather configuration is also highly stable, effectively giving the pilot a hands-free re-entry capability, something that has not been possible on spacecraft before, without resorting to computer controlled systems.
The combination of high drag and low weight mean that the skin temperature during re-entry stays very low compared to previous manned spacecraft and thermal protection systems such as heat shields or tiles are not needed.
Following re-entry at around 27,000 metres the feather lowers to its original configuration and the spaceship becomes a glider for the fl ight back to the spaceport runway.
And for the future, Virgin’s charismatic leader Sir Richard Branson undoubtedly sees this investment as the first step towards the introduction of point-to-point travel where journeys from North America to Australia, for example, could be achieved in a couple of hours or less.
For the passengers
For their US$200,000 ticket Virgin Galactic passengers to space will first spend three days training, undergo medical checks and become familiar with weightlessness. On the big day, they will sit for an hour or so in SpaceShipTwo getting up to 15,240 metres (50,000 feet) – latched like a joey to the underbelly of a flying catamaran called WhiteKnightTwo.
A few seconds of calm after being unhooked from the mothership follows before the rocket motor ignites and supersonic speed is reached within seven seconds. After 70 seconds of speeds up to 4200 km/h, the rocket motor cuts out and the spacecraft, its six passengers and two pilots coast to around 100km, slipping over the Kármán line, the official boundary between the upper atmosphere and space. Here in a zero gravity environment, they will be allowed to float around for a bit less than five minutes before being coaxed back to their seats for the journey home.
At around 33,500 metres on the way home, they will experience about six times the normal force of gravity and at 27,400 metres will return to subsonic speeds. The glide back home from there will take about quarter of an hour – all in all a journey of about two and a half hours.