- Sub-orbital launch refers to vehicles that travel high enough to reach the edge of outer space but do not have the energy to achieve orbit. Typically, these vehicles reach a maximum speed of about 2 – 6 times the speed of sound.
- Orbital spacecraft should travel about 25 times the speed of sound to orbit the Earth without falling back due to gravity.
- Significance of Sub-orbital launch: Space Tourism, Film & Television, Surveillance etc.,
- Sounding Rocket means a rocket used especially to obtain information concerning atmospheric conditions at various altitudes. They carry scientific instruments into space.

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