Today, private space tourism company Virgin Galactic unveiled the new version of its SpaceShipTwo vehicle, dubbed the VSS Unity. It’s the spacecraft that the company wants to use to send paying customers into sub-orbital space someday. The VSS Unity will ultimately replace Virgin Galactic's former SpaceShipTwo plane, called the VSS Enterprise, which crashed during a test flight in 2014; the accident claimed the life of one the vehicle's pilots and severely injured the co-pilot.

The VSS Unity was shown off today at a special ceremony at the Mojave Air and Spaceport in California, where Virgin Galactic conducts its flight tests. Outwardly, the vehicle is nearly identical to its predecessor. It will also launch and re-enter the Earth's atmosphere the same as before. But the spacecraft differs from the previous vehicle in a few key areas. For one, this version is much more automated. The first SpaceShipTwo crashed partly because of pilot error, so this vehicle has new fail-safes in place to protect pilots from making critical mistakes during flight. The vehicle's rocket engine will also use a different rubber-like fuel, something that will make combustion more efficient, the company said; but this new fuel has also been known to cause Virgin Galactic engine trouble in the past.

These vehicle changes haven't been tested in flight yet, though. Today's ceremony was just to unveil the new vehicle, which has taken close to four years to build. Its name, Unity, actually came from Stephen Hawking. "Space Exploration has already been a great unifier," he said. "We seem to be able to cooperate between nations in space in a way we can only envy on Earth."

The first test flights are slated to begin later this year, according to Will Pomerantz, vice president of special projects at Virgin Galactic. Testing will show if SpaceShipTwo is capable of safely performing its maiden voyages — many of which have already been booked. More than 700 people have paid the $250,000 price to reserve a seat on the sub-orbital spaceplane. Future passengers include numerous celebrities like Ashton Kutcher, Leonardo DiCaprio, Angelina Jolie, and Justin Bieber.

But before these customers can ride, Virgin Galactic has to prove the changes it has made to the vehicle will make it safer. And not all industry experts are optimistic. "They’ve struggled with the technology," says Charles Miller, president of NexGenSpace, a spaceflight consulting firm. "A lot of people have been critical about their technical choices from the beginning." But Miller says it's critical that Virgin Galactic soldier ahead despite the failures the company has experienced. "If they keep going, they’ll eventually overcome these problems. It’s the process of rapidly iterating new engineering, learning, and then doing something different."

SpaceShipTwo

The VSS Unity is now Virgin Galactic's only rocket-powered spacecraft, designed to take six passengers and two pilots to the edge of space. But the reusable vehicle doesn't launch from the ground like most typical rockets do. It must first be carried to an altitude of around 50,000 feet by a jet carrier aircraft known as WhiteKnightTwo. This carrier looks like two planes that have merged into one; it sports four engines and two main cabins, which are connected together by a wing-like bridge. SpaceShipTwo rides up to its launching altitude underneath this bridge.

Once at 50,000 feet, SpaceShipTwo deploys and ignites its rocket engine. During future crewed flights, the engine is meant to propel the spacecraft to a maximum speed of Mach 3.4, or around 2,600 miles per hour. The engine will then cut off after just 70 seconds, and the vehicle will coast to its maximum height of up to 70 miles above the Earth's surface. That's about 8 miles above the Kármán line — the imaginary boundary separating our planet's atmosphere from outer space.

Then to re-enter the Earth’s atmosphere, the vehicle must reposition its wings — a maneuver known as feathering. The pilots must pull two levers just as the vehicle climbs to its peak height in space; the wings then move from their horizontal position to a 65-degree upright angle. This shift helps to slow down the spaceplane during its descent. The wings eventually shift back to their normal position so that SpaceShipTwo can glide to a runway.

A safer ride

The NTSB investigates the SpaceShipTwo accident site. (NTSB)

The feathering system is crucial for SpaceShipTwo’s safe descent, but it also helped cause the crash of the VSS Enterprise in 2014. Co-pilot Michael Alsbury — who died in the accident — unlocked the feathering system too early during the test flight, when the vehicle was traveling at Mach 0.92 instead of the intended speed of Mach 1.4. At this speed, the forces surrounding the spacecraft overwhelmed the feathering system motor, causing the wings to shift without the pilots pulling any levers. The wings are only meant to shift in space after the engine has cut off and the vehicle is moving much more slowly. Instead, the wings rotated when SpaceShipTwo was accelerating at transonic speeds, placing too many G forces on the vehicle and causing it to break apart.

Scaled Composites, the company that made the first SpaceShipTwo, admitted that it hadn't even considered the possibility of pilot error when constructing the spacecraft. "[Scaled Composites] had a philosophy of keeping it as simple as possible," says Miller. "Don't introduce automation and electronic controls into the cockpit; hire the best pilots, and they won’t mistakes. But humans are frail, and even the best pilots make mistakes."

But Virgin Galactic says it has learned from this tragic accident. The company has made changes to the feathering system that will prevent pilots from unlocking it early. The company has also altered how pilots communicate with each other and mission control during flights, according to Pomerantz. Now, the pilots are required to have more open dialogue about the actions they take in the air.

Old fuel makes a comeback

The new SpaceShipTwo will also use a different type of rocket fuel than the last vehicle. Virgin Galactic is returning to a rubber-like fuel, known as hydroxyl-terminated polybutadiene (HTPB), for its engine. HTPB fuel was originally supposed to be used in the engine all along, but Virgin Galactic switched to a polyamide fuel in 2014 when HTPB proved to be too unstable. That polyamide fuel was powering the SpaceShipTwo engine when the vehicle crashed in 2014; however, the fuel did not contribute to the accident in any way, according to investigation by the National Transportation and Safety Board.

Regardless, the company has decided to switch back to HTPB. The decision was based on recent engine testing, which showed HTPB to have better "combustion quality" than the polymide, according to Virgin Galactic CEO George Whitesides. But there's been some controversy surrounding the company's use of HTPB. "It doesn’t burn very easily, and it's very heavy on the back of the spaceship," says Miller. Additionally, the fuel used to make the engine on SpaceShipTwo shake violently. Early reports said that these vibrations were so intense that test pilots could only keep the engine burning 20 seconds, for fear the vehicle might break apart. But the company says it has made a number of breakthroughs with the HTPB engine that make it a smoother ride, according to Mike Moses, senior vice president of operations at Virgin Galactic. However, Moses did not specify what those breakthroughs are.

For now, it's unclear if the automation and fuel upgrades will make SpaceShipTwo a safer spacecraft. Only testing can prove if the fixes work. The vehicle will first go through numerous electrical tests on the ground, followed by flight tests. And the company plans to do several glide flights — where the spaceplane glides without firing its engine — before rocket-powered tests begin. It will be some time before SpaceShipTwo goes to space.

But Miller is hopeful that Virgin Galactic's new vehicle will accomplish the company's tourism goals. "The fact that [Blue Origin founder] Jeff Bezos is out there is maybe getting their juices flying," he says. "We'll have multiple vehicles flying people to space very soon."