Suborbital vehicles

 Will we soon be overflown by a multitude of suborbital vehicles?

In 2004, SpaceShipOne carried out the first flight of a private aircraft at an altitude higher than 100 km. 

This success opened the path to several suborbital vehicle development projects, the most well-known being Richard Branson's who launched Virgin Galactic with the aim of being able to transport passengers into space for a few minutes.

Other players also launched into the suborbital flight race: XCOR aerospace with its rocket-plane called Lynx or Blue origin with its reusable New Shepard launcher, in many aspects comparable to the reusable 1st stage of the Space X Falcon 9 rocket.

Initially intended to transport wealthy tourists who wanted to experience the thrills of a weightless space flight, the applications being considered since then have diversified to satellite launches, long distance passenger or freight transport.

But what exactly is a suborbital flight? The altitude of 100 km (Kármán line) is usually considered to be the frontier between the atmosphere and space.  At that altitude, aerodynamic uplift is no longer sufficient for aircraft flight. A flight becomes suborbital when it crosses this limit, without the device going into orbit.

A set of definitions is being drawn up by the International Radiocommunications Union. At this stage, a suborbital flight is defined as the “controlled flight of a vehicle that reaches space from the surface of the earth and returns to it without having completed an orbit”, and a suborbital vehicle is defined as “a vehicle designed to carry out a suborbital flight, for which all or part of the elements composing it can be reusable or not”. 

The figure below shows an example of the different phases of a suborbital flight:

The development of suborbital flights poses new questions in terms of radiocommunications regulations considering the traditional divide between space and aviation. For example:

•  Which regulations should apply to an aircraft that is no longer in the atmosphere but which cannot be considered to be a satellite or an orbital station?
• How, considering the speed of the craft, is the separation with low altitude commercial flights achieved?

The 2019 World Radiocommunications Conference will discuss this question in order to make sure that international regulations are coherent with the expected generalisation of suborbital flights.

And, on a night with clear skies perhaps you will soon be able to see the wake of a suborbital vehicle amongst a shower of shooting stars?