After the establishment on French soil of the first permanent launch base for stratospheric balloons in Aire Sur L'Adour the Centre National d'Etudes Spatiales (CNES), assumed the need for an alternative site from which to make such flights in summer when the winds over the region of Landes changed direction.
The problem was that during the reversal of the winds, the balloons released from Aire sur l'Adour were normally directed to the west and the ocean which reduced the value of the flights. This was frustrating because while the winds were ideal for stratospheric flight (slow in speed and very stable in direction) at the time, CNES was not prepared for payload recoveries at sea. This lead the agency to try to find a suitable launch spot located in the east part of the country. The only condition was to maintain a nearby latitude respect from the Aire Sur L'Adour base due to the lower population density of the southern part of the country and also to allow an easier recovery of the payloads flown.
After an study and survey of the few airports located in the departments of the east side of the country, the choice fell on a small airfield located in the heart of the French Alpes. The aerodrome of Gap-Tallard is located in Tallard, 12 km south-southwest of Gap, both communes in the Hautes-Alpes department of the Provence-Alpes-Côte d'Azur region. It provided an ideal site for launching balloons not only by his location -in the midst of a valley- but also due to the fact that the area presents very stable conditions in their wind pattern over the 25,000 meters.
The first launches from there were performed in 1966.
The infrastructure available at Gap-Tallard was obviously much more modest than the one present at Aire Sur L'Adour. To support the launches at the aerodrome, CNES occupied a hangar which at the time was empty. Over the years, it was partitioned so that ended up having an integration room for the scientific payloads that participated in the campaign, a storage area for the balloons and one for the preparation of flight chains, an operational control room for managing the aerial security of the launch and recovery operations, radio communications, and finally various offices.
The Ceussette relay station
Althought the location of the launch site was superb from the operative point of view, there was a big constrain: the hilly nature of the terrain and the location of the airfield in the bottom of a valley, turned very difficult the communication with the flying balloons. This difficult was rather serious to the west of the base, that was the direction that all the summer flights would take.
The telemetry and telecommand of the balloon itself and their associated systems, were operated from Gap-Tallard since launch until the balloon reached float altitude. From that moment on, the balloon was in sight of the communications systems of the main base of Aire Sur L'Adour which took the control of it until termination. However, the scientific users in Gap-Tallard, once the balloon moved away to the west and the line of sight signal was blocked by the mountains, could not communicate with the balloon in flight to send any command to their instruments or to receive the data in real time.
Two solutions were evaluated to overcome this: to establish a dedicated phone line based link between the two bases, receiving the data from the balloon in Aire Sur L'Adour and relaying it to Gap-Tallard, or to create a microwave based relay station in an elevated position in sight of the Gap-Tallard base, to operate the balloons directly from there. The second idea prevailed and soon CNES initiated a survey to locate the right place.
The site choosen was a small plateau in the Ceusette, a 1600 meters height hill located northwest of the airfield which counted with a relatively easy access. After permission was granted from local authorities, some work was needed to improve the access road and to create a flat soil area to receive the shelter that would home the transmission equipment, the antennas and more important, the operators.
Operating in the 400 MHz band, the Ceusette station allowed thereafter complete control of the flight from Gap-Tallard launch base both for telemetry and telecommand of the balloon functions as well to monitor the scientific data or to send commands to the payload in real time.
Year after year new equipment and technological advances were introduced, reflecting the evolution and innovation in the communication infrastructure of the CNES balloon program. This included a second mobile station of the STAREL telemetry system which was already in use in Aire Sur L'Adour and later the introduction of the much complex and modern ETNA system. In all, the Ceusette relay station would continue operations for more than two decades.
Althought dismantled in the last years of operation of the site, in the Ceusette plateau nowadays still can be seen the concrete basement on which the station modules rested.
The site was very active in terms of stratospheric balloon launches between the decades of 1970 and 1980, with a slow decreasing in the amount of flights by the 1990 decade. At the same time, Gap-Tallard slowly acquired world reputation as a destination for aerial sports, being nowadays one of the main active centers in France. Among the aviation related activities that take place now on the aerodrome can be mentioned skydiving, and flights on light aircrafts, biplanes, helicopters, gliders, and hot air balloons.
CNES performed his last balloon launch campaign at Gap-Tallard in 2001. After that, a great hiatus opened in the activity at the site, and the focus of scientific balloon activities in France was back on Aire Sur L'Adour.
However, in June 2009 as a result of an increment in the failure and safety requeriments on regard scientific ballooning, issued by the French aerial authority, both bases Gap and Aire Sur L'Adour became inactive. The greater population density, and the subsequent increasing of the air and ground traffic were the main reasons to halt all scientific balloon flights in France until a whole new strategy for solving safety issues could be outlined. This included the development of new control systems to make precision landings feasible among other factors.
Many of the improvements in CNES balloon systems had been developed in the last years and already been tested during recent campaigns performed by the agency in Canada. Moreover, this year, CNES performed a succesful balloon flight test from Aire Sur L'Adour that would lead to the biggest change of paradigm in balloon operations in french soil since the inception of the program: to fly balloons over water and recover the payloads directly from the sea.
Under this new CNES operative scheme, it's hard to know how this would affect the future of the Gap-Tallard installation as a viable launch site for stratospheric ballons.
Time will tell.
Part of the text and images contained in this article was obtained from the excellent website "Nos Premières années dans l'espace" ("Our first years in space") run by Michel Taillade. The specific section about the french balloon program is located in http://nospremieresannees.fr/ballons/entreeballons.html