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7th March 2019

New heights reached in Virgin Galactic spaceflight

‘Spaceplanes’ are notoriously difficult to take off and re-enter the atmosphere — so how did Virgin do it?
New heights reached in Virgin Galactic spaceflight
Photo: Roderick Eime @ Flickr

Last month’s flight of Virgin Galactic’s Unity spacecraft marks the first time a passenger has been taken aboard a commercial spaceflight. Upon landing, the three crew members were given commercial astronaut wings by the US Federal Aviation Administration, a medal received by only four people before them.

Bringing passengers to space is an important milestone in the field of commercial space exploration, a business model favoured by Richard Branson’s Virgin Galactic, Jeff Bezos’ Blue Origin, and to a certain extent Elon Musk’s SpaceX.

The landmark flight has been lauded as a victory for Branson, but in this round, there’s been some accusations of foul play.

The controversy arises from ambiguity in the definition of space. There’s no clear boundary marking where the atmosphere ends and space begins since the Earth’s atmosphere thins gradually until it merges with the near-vacuum of interplanetary space. On the international stage, a threshold of 100km above the Earth’s surface is commonly accepted, but in the US, the FAA gives the astronaut title to anyone who’s flown over 80km.

On this mission in particular, the Unity spacecraft reached only 89km at the highest point of its suborbital hop, bringing some to question whether the mission should be classified as a spaceflight.

Flying any kind of spacecraft is very tricky, but ‘spaceplanes’ are notoriously hard to get off the ground. While the idea has been played with by many since the space race, the one success story was littered with failures. The Space Shuttle program overstepped its budget by more than a billion dollars every time it flew, failing its main goal of providing cheap, reusable orbital capability. Over its 30 year lifetime, hardware faults due to its unconventional launch configuration led to two total mission failures, killing 14 people in total.

The aerospace industry has come a long way since the Shuttle era and is understandably a little more prudent, but the concepts behind flying a modern spaceplane like Unity are more or less the same.

There are three main stages to a spaceplane’s flight. First, it must get to high up in the atmosphere where the air is thin enough so it won’t produce much drag. Secondly, it must accelerate to exceedingly high speeds, pushing its trajectory high out of the atmosphere. Finally, at the highest point of its arc, the spaceplane must push its speed high enough such that its trajectory lifts above the ground, reaching a stable orbit of the Earth.

The Space Shuttle used huge solid-fuel boosters to reach the upper atmosphere in its first stage of flight, using a vertical launch configuration similar to conventional rockets. Unity uses a less ostentatious method. A mothership takes off from a runway and carries the spacecraft up to 50,000ft (about one-and-a-half times the cruising height of a Boeing 747), then Unity detaches. After gliding for a few seconds, it activates its rocket engine, sending it blasting off to the edge of space.

Re-entry is another dangerous element of any space mission, and the Unity spacecraft makes some necessary improvements over the Shuttle here as well. Suborbital velocities are fast, and orbital velocities are even faster. Most orbital facilities like the International Space Station circle the Earth once every 90 minutes, about 30-times the top speed of a 747. If a spacecraft doesn’t slow down enough in the thin upper atmosphere, the high drag conditions of the soupy lower atmosphere will cause so much heating that the spacecraft risks burning up.

The Shuttle avoided overheating in the lower atmosphere by plastering its lower half in thermal tiles, leading to its distinct black and white look. Unity takes a more adventurous approach, and the spaceplane undergoes a dramatic transformation in the upper atmosphere. The entire back end of the spacecraft rotates and the whole vehicle folds upon itself, making the spacecraft much less streamlined. In this configuration, Unity’s high drag slows it down enough in the upper atmosphere so when it reaches the lower atmosphere, it can glide deftly back to the runway it took off from.

From take-off on the mothership, the whole flight takes about an hour and a half, spending some 15 minutes in the upper atmosphere. Entering space or not, the crew got some incredible views over North America – and bringing a passenger even to the edge of space is certainly still a significant achievement for commercial spaceflight.

Branson has often attracted criticism for his company’s over-optimistic promises. While putting a passenger in orbit is still far away on the horizon, it’s clear Virgin Galactic is striving ever higher in the pursuit of commercial space exploration.

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