Suborbital spaceflight is a launch that reaches space but does not go fast enough sideways to stay in orbit. The spacecraft follows a high arc above Earth, crosses the Kármán line near 100 km altitude, and then falls back through the atmosphere. This kind of flight matters because it gives astronauts, researchers, and passengers a short experience of space without the speed and cost of a full orbital mission.
It also helps engineers test spacecraft systems before longer flights.
Key Facts
- Suborbital flight reaches space but does not complete one full orbit around Earth.
- The Kármán line is commonly defined as 100 km above sea level.
- Weightlessness occurs when the spacecraft and passengers are in free fall together.
- Orbital speed near low Earth orbit is about 7.8 km/s, much faster than most suborbital flights.
- Maximum height can be estimated by h = v0^2 / (2g) if air resistance and engine thrust after launch are ignored.
- During free fall, apparent weight is near zero even though gravity is still acting.
Vocabulary
- Suborbital flight
- A flight that reaches space but returns to Earth before completing an orbit.
- Kármán line
- A commonly used boundary of space located about 100 km above Earth.
- Free fall
- Motion under the influence of gravity alone, with no support force holding the object up.
- Weightlessness
- The feeling of having no apparent weight because you and your spacecraft are accelerating together.
- Trajectory
- The curved path followed by a moving object, such as a spacecraft during flight.
Common Mistakes to Avoid
- Thinking suborbital means the spacecraft stops in space, which is wrong because it is always moving along a curved path under gravity.
- Confusing reaching space with entering orbit, which is wrong because orbit requires enough sideways speed to keep missing Earth as you fall.
- Saying weightlessness happens because there is no gravity, which is wrong because gravity is still strong near Earth and causes the free-fall motion.
- Ignoring air resistance during launch and reentry, which is wrong because drag strongly affects speed, heating, and the shape of the real flight path.
Practice Questions
- 1 A suborbital spacecraft reaches a maximum altitude of 110 km. How many kilometers above the 100 km Kármán line does it travel?
- 2 Ignoring air resistance, what initial upward speed is needed to reach 100 km if g = 9.8 m/s^2? Use h = v0^2 / (2g).
- 3 Explain why passengers can feel weightless during a suborbital flight even though Earth’s gravity is still pulling on them.