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

Source: Indian Express

What is the News?

Virgin Group founder Richard Branson and five others undertook a trip to the “edge of space”, and reached an altitude of 85 km from Earth before returning. Such a trip is called a Suborbital Flight.

What is Suborbital Flight?
  • Suborbital Flights occur when a spacecraft reaches space, but its velocity is such that it cannot orbit the Earth once they reach there.
How does Suborbital Flight work?
  • When an object travels at a horizontal speed of about 28,000 km/hr or more, it goes into orbit. 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.
  • This is because any object traveling slower than 28,000 km/hr must eventually return to Earth.
  • However, Unity spacecraft traveled far enough to reach the “edge of space”. These are suborbital flights because they will not be traveling fast enough to orbit Earth once they reach there.
  • Such a trip allows space travelers to experience a few minutes of “weightlessness”.
Analogy of Suborbital Flight:
  • 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 traveling 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.
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