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Suborbital vs Orbital Space Flight
throwing_thb_110.pngSuborbital space flight and orbital space flight are two very different things.

When comparing a suborbital rocket with an orbital rocket it would be like comparing a car which makes a top speed of 30 km/h with a car which makes 200 km/h. The difference is fundamental - the following page tries to explain why.

Definition of "orbital"

In order to understand what means "orbital" you can think of the following:

When throwing for instance a ball anywhere on Earth, the trajectory of the ball is a curve called a parabola (approximately). If the ball is thrown stronger, the trajectory becomes flatter, this means less curved. Now if the ball was thrown really fast, the curvature of the trajectory could become the same as the curvature of the Earth. If in addition the ball had been thrown in the vacuum of space, the ball would keep flying along the curvature of Earth and actually never fall back to Earth. This is exactly what happens to a satellite after it has been successfully launched ("thrown") by a rocket into an Earth orbit. In such a case we speak of orbital space flight.

The velocity required to stay in an orbit is called orbital velocity and depends on the altitude of the orbit. For a 200 km circular orbit the orbital velocity is 7780 m/s (28000 km/h or 17400 mph). It is actually this incredibly high speed which makes orbital space flight technically so complex and therefore expensive. 

Definition of "suborbital"

We consider a suborbital flight to be any flight outside the Earth atmosphere with a maximum flight speed below the orbital velocity.

If a rocket does not achieve orbital velocity, it falls back to Earth and re-enters the atmosphere within a few minutes after engine shutdown.

Required Velocities for Suborbital Flights

A rocket which is flying along a vertical trajectory at the moment of main engine shut-down will achieve the highest altitudes. The following examples show the velocities which are required to attain the corresponding altitude along a vertical trajectory:

max. altitude
required max. flight speed 
100 km
950 m/s (Mach 2.9) 
200 km
1650 m/s (Mach 5.1) 
400 km 2500 m/s (Mach 7.7) 

 

As soon as the rocket is out of the atmosphere and the rocket engines are shut off, the passengers will experience seeming weightlessness and would be floating freely through the cabin if they would unbuckle their seatbelts. 

Microgravity Durations

Microgravity ends when the rocket re-enters the atmosphere. The duration of microgravity is most of all a function of the maximum altitude which is reached during the flight. A few examples:

max. altitude
micro-gravity duration
100 km 3:10 min 
200 km 5:45 min
400 km
9:10 min

Conclusions

The flight speed which is required to achieve an altitude of 100 km during a suborbital flight (950 m/s) is about 8 times smaller than the orbital velocity (7780 m/s). This tremendous difference in required flight speed has a significant impact on the vehicle design. For this reason suborbital vehicles are smaller in size and mass, technically simpler and therefore cheaper in design and operation and most importantly, they can be made safe and reusable.

In our view, safety and reusability are the key to success of commercial suborbital flight. For this reason, Orbspace is currently concentrating its research efforts on these two topics.

 
 
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