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Suborbital flight: Fast enough to reach space, not stay there

With Richard Branson and Jeff Bezos kicking off private space flight, several companies are looking for customers wanting to go on suborbital or even orbital journeys.

Billionaire Richard Branson floats in zero gravity on board Virgin Galactic's passenger rocket plane VSS Unity after reaching the edge of space above Spaceport America near Truth or Consequences, New Mexico. (Reuters Photo)

On Sunday, Virgin Group founder Richard Branson and five others undertook a brief trip to the “edge of space”, taking off on the VSS Unity spaceship from New Mexico and reaching an altitude of 85 km from Earth before returning.

Such a trip is called a “suborbital flight”. Another high-profile suborbital trip is coming up on June 20, when Amazon’s Jeff Bezos takes off on the Blue Origin spacecraft.

What’s suborbital

When an object travels at a horizontal speed of about 28,000 km/hr or more, it goes into orbit once it is above the atmosphere. Satellites need to reach that threshold speed in order to orbit Earth. Such a satellite would be accelerating towards the Earth due to gravity, but its horizontal movement is fast enough to offset the downward motion so that it moves along a circular path.

Any object travelling slower than 28,000 km/hr must eventually return to Earth. However, Branson’s spacecraft travelled far enough, as Bezos’s will, to reach the “edge of space”. These are suborbital flights, because they will not be travelling fast enough to orbit Earth once they reach there.

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Such a trip allows space travellers to experience a few minutes of “weightlessness”.

This photo provided by Virgin Galactic, shows the VSS Unity’s tail cone view from space on Sunday, July 11, 2021. (AP)

Branson’s flight was first carried off the ground by a larger aeroplane to an altitude of around 15 km. From here, the vehicle blasted off the plane, achieving a height of around 85 km, where it momentarily reached zero vertical velocity. At this altitude, travellers were estimated to experience about four minutes of weightlessness.

For an analogy, consider a cricket ball thrown into the air. Given that no human hand can give it a speed of 28,000 km/hr (about 8 m/sec), the ball will fly in an arc until its entire kinetic energy is swapped with potential energy. At that instant, it will lose its vertical motion momentarily, before returning to Earth under the influence of gravity. A suborbital flight is like this cricket ball, but travelling fast enough to reach the “edge of space”, and yet without enough horizontal velocity to go into orbit.


If an object travels as fast as 40,000 km/hr, it will achieve escape velocity, and never return to Earth.

Why the buzz

With Branson and Bezos kicking off private space flight, several companies are looking for customers wanting to go on suborbital or even orbital journeys.

At Branson’s Virgin Galactic, around 600 people have already paid deposits for tickets that are priced up to $250,000 (Rs 1.86 crore). However, Bezos’s Blue Origin, which uses the reusable New Shepard rocket, is yet to announce commercialisation plans, according to the BBC.


There is also excitement among scientists who want to use suborbital flights for microgravity research. Such flights, as per a report, would be far less expensive than carrying experiments and people to the International Space Station. Suborbital flights could also be an alternative to parabolic flights in aeroplanes that space agencies currently use to simulate zero gravity.

Safety concerns

The Branson flight comes seven years after his company’s first rocket, called Enterprise, crashed during a test flight, killing one of the pilots on board. The other survived after parachuting out.

The current rocket is also not certified by the US Federal Aviation Administration, which is prohibited to do so by law until 2023. According to The New York Times, this is because the government does not want to burden companies like Virgin Atlantic with regulations during their “learning” period, when they can innovate by trying out different designs and procedures.

Passengers who go on such trips need to sign “informed consent” forms, similar to the ones before going for skydiving or bungee jumping, the report said.

First published on: 12-07-2021 at 04:20:03 am
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