Following the pioneer flights beyond the edges of the atmosphere at the beginning of the Sixties, which opened a period of 40 years of space exploration, there was no more talk of suborbital space flight until 1996, when the X-Prize Foundation launched a competition for rocket experts around the world.
On 21 June 2004, SpaceShipOne became the first aerospacecraft developed by a privately-owned company to successfully reach an altitude of 100 km, the generally accepted definition of "space".
But where does this "100 km Boundary" come from ?
The text reproduced below is adapted from an article written by Dr S. Sanz Fernandez de Cordoba, President of ICARE, the FAI Astronautic Records Commission :
The idea of separating Aeronautics and Astronautics
In the early 1950’s, Aeronautics and Astronautics were considered the same thing. In fact Astronautics, besides the “dreams” of a few scientists and engineers, was only a military endeavour, linked to Aeronautics in the Military Establishments of the time. But Theodore Von Karman [(1881-1963), who is considered to be one of the great aeronautical scientists of the twentieth century] had the feeling that there was a difference between the two. If such was the case, a line could be defined to separate them. The basics were there : Astronautics needed the lack of atmosphere to be viable; Aeronautics needed the presence of atmosphere. And atmosphere existed near the Earth’s surface, but did not exist far above the ground. In Astronautics, speeds impossible to maintain in atmospheric drag could be maintained for very long periods without power applied to the vehicle. In Aeronautics (heavier than air vehicles) sustained flying without power is unthinkable. And so on. Thus, both disciplines could be separated in certain important aspects just because of their dependence, in opposite ways, on atmosphere.
(…) In the mid 1950’s, Von Karman got in touch with a series of (at the time) young leading scientist and engineers in Aeronautics and Astronautics with the view of defining a separation, as far as possible, between both disciplines. He had got to know them through two international private, i.e. not government dependent, organisations. One was the recently created IAF (International Federation of Astronautics), which had held its first International Congress in 1950. The second, at the time by far more important, was the well known and very prestigious FAI (Fédération Aéronautique Internationale), organised in the first years of the XX Century, and which sanctioned and recorded all Aeronautic records. (…)
The Karman separation line : Scientific significance.
The interchange of ideas finally led to a clear cut : In Aeronautics, level flying higher and higher meant to deal with less and less dense atmosphere, thus to the need for greater and greater speeds to have the flying machine controllable by aerodynamic forces. A speed so big in fact, that, above a certain altitude, it could be close to or even bigger than the circular orbital speed at that altitude (i.e. lift was no longer needed, since centrifugal force took over; and consequently aerodynamic flight was meaningless). Conversely, in Astronautics, lower and lower orbital flying led to encountering more and more dense atmosphere, so much that it would be impossible to maintain the orbit for a number of turns around Earth without significant forward thrust (thus making the free fall, or orbiting, concept meaningless). A lot of calculations were made, and finally it was concluded and accepted by all scientists involved, that the boundary could be set at an altitude of around 100 km. (…) The 100-Km altitude, ever since named the “Karman Line”, thus came into existence as the boundary separating Aeronautics and Astronautics.
The Karman Line: Adoption in International Standards
Von Karman presented the result of this work to the IAF, which accepted it without much interest, because they were really not concerned with the problem of separating both fields. But things worked differently for the FAI, deeply involved in human records for Aeronautics. (…)
Some of the people who had been working with Von Karman were connected to FAI, among them, Sanz Aránguez from Spain, Dillaway from the U.S., several scientists from the U.S.S.R. (…) and Genty from France. They proposed to FAI to create a new category of flying machines, later named spacecraft in the FAI rules, which would have separate records. The FAI was more than willing to do so, and decided to create the International Commission of Astronautics (CIAstr; the name was changed in 1987 to International Commission of Astronautical Records, ICARE).The rules developed and approved became Chapter 8 of the FAI Sporting Code. Naturally, they started by setting the rule that a flight could only be considered an Astronautical flight, and then qualify for a record under Chapter 8 of the FAI Sporting Code, when that flight goes beyond the 100 Km line, i.e. the Karman Line. (…)
(Full article available at : http://www.fai.org/astronautics/100km.asp)
General information on the X-Prize Competition
(Source : http://space.xprize.org/ansari-x-prize)
The purpose of the Ansari X-Prize is to promote the development and flight of spaceships able to provide low-cost commercial transport of humans into space. The 10-million USD cash prize will be awarded to the first team that :
Since the launch of the competition in May 1996, the X-Prize Foundation registered more than 20 teams from seven countries to compete for the prize. According to the Foundation, the Societal Benefits of the X-Prize include :
Useful links :
X-Prize : http://space.xprize.org/ansari-x-prize
SpaceShipOne : www.scaled.com/projects/tierone/
ICARE - FAI Astronautic Records Commission : www.fai.org/astronautics/
FAI Sporting Code Section 8 (Astronautics) : www.fai.org/sporting_code/sc08.pdf