VSS Unity: Virgin Galactic Is Back

VSS unity Flight
VSS Unity during its first test flight. Credit: Virgin Galactic.

On Thursday 5th of April 2018, Virgin Galactic’s SpaceShipTwo conducted its first powered test flight of 2018. With very little in the media from Virgin Galactic recently, this has been a welcome development in the field of space tourism, and the development of space planes. Named the VSS Unity, this space plane is the newest development from the Spaceship Company.

USS Unity engine
USS Unity with an ignited engine rapidly accelerating into the sky. Credit: Virgin Galactic.

Virgin Galactic hasn’t performed a powered test flight since 31st of October 2014 when the VSS Enterprise experienced a catastrophic mid flight failure. The incident in the first of 5 planned SpaceShipTwo aircraft ended with a tragic accident which resulted in the death of one test pilot and serious injury to the other. With the program many years behind schedule, many critics thought this could have been the end for Virgin Galactic. Fortunately, Virgin Galactic have said the fault was not in the hardware, and was a change in safety procedure rather than a design overhaul. Over the last year, Virgin Galactic has made significant progress, leading to this powered test flight.

VSS Unity Gliding
VSS Unity, gliding back to earth after it has burnt all of the fuel, it can see the curvature of the earth. Credit: Virgin Galactic.

An NTSB investigation into the accident concluded that a pilot prematurely deployed the feathering system on the spacecraft. The system is used to increase drag during reentry. Many have criticised Scaled Composites (the manufacturer) and Virgin Galactic for not having fail-safe’s in place to prevent this problem. This is what lead into the review into the safety of the craft. After the loss of the USS Enterprise, and the safety reviews, the USS Unity was not ready until february 2016. This was the first plane to be built in house by The Spaceship Company.

WhiteKnightTwo carrying VSS Unity during the flight test, it will drop the craft at 50,000 ft. Credit: Virgin Galactic.

Up until this point the testing has been more gradual than planned, with captive carry tests, and a total of 6 successful glide tests. There was a dry run rocket test on 4th of August 2017, where water was mounted in place of rocket fuel to simulate the shift in gliding with various centres of gravity, as well as the change of weight as the rocket uses up the fuel. These tests ended positively, with the Chief pilot David Mackay stating “We are really pleased with what we saw today. We collected hundreds of gigabytes of data for us to review, and from the pilots’ point of view, it felt really wonderful.”

Pilots walking
The pilots walking toward the VSS Unity to conduct the first powered test flight. Credit: Virgin Galactic.

The FAA approved a revision to Virgin Galactic’s Commercial Space Transportation Licence in 2017. This allowed Virgin Galactic to launch out of Spaceport America in New Mexico as well as Mojave Air and Space Port in California. Virgin also announced that the Kingdom of Saudi Arabia would invest $1 billion across the Spaceship Company, Virgin Galactic and Virgin Orbit.Currently under review, if approved the deal would help finance SpaceShipTwo during 2018.

WhiteKnightTwo taking off
WhiteKnightTwo taking off to conduct the first powered test light of VSS Unity being held underneath it. Credit: Virgin Galactic.

VSS Unity is powered by a hybrid rocket engine called RocketMotorTwo. The engine originally used rubber based hydroxyl-terminated polybutadiene (HTPB) as the fuel, and nitrous oxide as the oxidiser. In 2014 Virgin Galactic switched to a plastic based thermoplastic polyamide for the fuel to improve performance. Although tested, and not the cause of the crash of VSS Enterprise, Virgin Galactic opted to use HTPB after extensive testing at Mojave.

spaceport America
VSS Unity attached to WhiteKnightTwo flying over Spaceport America. Credit: Virgin Galactic.

The test used WhiteKnightTwo to lift the VSS Unity to an height of 50,000 feet, then release it. Once clear, VSS Unity ignites and ascends rapidly. The burns during the real flights will last just over a minute, but this test used a much shorter burn. This is the incremental approach that Virgin Galactic have opted for. Unlike a normal rocket, the engine thrust will decrease over time, so that the G-forces stay reasonably comfortable, as this is meant to be a pleasure ride. Once the engine cuts off, the craft coasts to the apogee and glides back to the spaceport. The tests can only get the craft to 80 km, which is not officially recognised as space, due to the extra test equipment needed. Virgin Galactic claim to be confident that the craft will reach space in the final version.