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Future High-Altitude Flight - an Attractive Commercial Niche?

Final Report Summary - FLACON (Future High-Altitude Flight - an Attractive Commercial Niche?)

The objective of the FLACON study was to identify and assess the long-term potential of commercial high-altitude flight in Europe for selected mission requirements, in view of the activities in the USA following the successful space ship one (SS1) demonstration and the efforts performed to arrive at the next generation space ship 2 as well as aspirations by other companies. While the common understanding of the European community is that the sub-orbital high-altitude flight is technically feasible within a few years, building on the available knowledge in aviation, it has never been proven experimentally. The USA have achieved with SS1 an air-launched X-vehicle, which, however, requires significant effort before becoming a commercial, routinely used transport vehicle such as SS2.

Key objectives of the project were to:
1. assess worldwide activities and define reasonable mission requirements;
2. identify potential show stoppers, technical but in particular non-technical ones, and missing elements for carrying out commercial high-altitude flight;
3. propose a way forward to achieve commercial sub-orbital flight, including potential self-sustained development steps leading to human hypersonic flight, and a funding scenario for a first experimental flight.

Although credible concepts exist also for single vehicle concepts based on a combination of aircraft engine and rocket propulsion, the study emphasised the two-vehicle air-launch concept based on an aircraft carrier and the space vehicle. This has a number of benefits, where one major advantage concerns legal considerations, namely that a clear distinction is possible between aircraft and space vehicle.

The resulting figures showed that the g loads can be reduced most if one equips the vehicle with sufficient energy to reach 1 000 m/s horizontal speed at maximum altitude, while increasing further the speed is not such beneficial. The figures also indicated the beneficial influence of increasing the angle of attack during re-entry. However, one has to keep in mind that the dynamic pressure during the re-entry flight increases possibly to values which are detrimental to the aircraft. A similar situation arises for thermal loads. Hence, some optimisation will be required to arrive at the best and safest operational solution. The FLACON low acceleration reference trajectory for descent as elaborated by DLR (and IRS) has thus to be seen as an attempt to arrive at a trajectory with very low prescribed g loads (< roughly 2 in body-axis direction) regardless of the consequences with respect to associated mechanical and thermal loads. It is worthwhile to mention these investigations indicate that ballistic suborbital flight can be considered as an entry point towards long-distance suborbital transportation.

A particular question is when air law and when space law applies. While the national and international air law is clearly defined, and the aircraft is defined by its characteristics, this is not the case for the national and international space law. The latter is under development, and the definition of the space vehicle / object is e.g. derived from the intended mission altitude of the trajectory. The delimitation is under discussion in Europe. In general the jurisdiction of the state of registration has to be applied. The rights of the crew and the passengers will be defined by the state of registration.

Inquiries within Onera's departments for the air-launched transport suggest that the integration of suborbital transportation activities into the European air traffic regulation should be possible, provided the airports used are not heavily frequented by normal air traffic. The combined starting phase and the - in this case gliding - entry phase are comparable to regular air traffic. The rocket propelled phase is very short and in near vertical direction so that the regular air traffic should not be disturbed.

A website FLACON has been opened by ESA / ESTEC which contains all presentations during the six progress meetings as well as the kick-off and close-out meetings, including the corresponding minutes as prepared by the coordinator and agreed by the participants. The site can be reached by searching for FLACON on the ESA portal page. The more specific and detailed information is pass word protected for use by the consortium.