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.