section_path: Phases/Reaching space
section_name: Reaching space
paragraph_text: Reaching space
  
  The most commonly used definition of outer space is everything beyond the Kármán line, which is 100 kilometers (62 mi) above the Earth's surface. The United States sometimes defines outer space as everything beyond 50 miles (80 km) in altitude.
  
  Rocket engines are the only currently practical means of reaching space. Conventional airplane engines cannot reach space due to the lack of oxygen. Rocket engines expel propellant to provide forward thrust that generates enough delta-v (change in velocity) to reach orbit.
  
  For crewed launch systems launch escape systems are frequently fitted to allow astronauts to escape in the case of emergency.