Purpose of the flight and payload description
The objective of the flight was to test a new type of vehicle developed at the Service d'Aeronomie du CNRS, in Paris, France, during 1977 by J.P. Pommereau and A.Hauchecorne. It was a hot-air balloon called solar montgolfiere, where the air was heated by natural source: it's buoyancy was provided by solar heating. Because of the large value of the solar flux, the system was fairly simple, the balloon was made of a single material which had to absorb the solar light and to emit as little as possible. When the top valve was closed, the solar energy heated the inner gas and the balloon ascended; a barometer opened the valve at a predetermined altitude allowing the air to renew and cool and the balloon descended to another predetermined altitude where the barometer closed the valve. A series of vertical explorations were thus obtained during the day. This first balloon test had a volume of 300 m3 and was made of black cloth. The balloon itself had a weight of 50 g per square meter.
Details of the balloon flight
Balloon launched on: 2/25/1977
Launch site: Paardefontein Tracking Station, Pretoria, Southafrica
Balloon launched by: Service d'Aeronomie - CNRS
Balloon manufacturer/size/composition: Montgolfier Infrared 300 m3
End of flight (L for landing time, W for last contact, otherwise termination time): 2/25/1977
Payload weight: 2 kg
The balloon was launched from the grounds of the Satellite Tracking Station of CNES in Paardefontein, near Pretoria on February 25, 1977 by a crew of the Service d'Aeronomie. The balloon carried a payload of 2 kg. During the flight the valve was commanded automatically on board by timers and a pressure sensor. The altitude pressure and temperatures inside and outside the balloon were telemetered. As predicted, the balloon performed a series of 3 vertical excursions between 14.5 and 19 km of altitude. The maximum vertical speed recorded during the ascent was 2.5 meters per second while 8 meters per second was the speed achieved during the descent.
The measured temperatures inside and outside the balloon in this flight and the first one performed on February 17 from the same place, were fitted to a simulation model developed subsequently that proved the feasibility of scaling up the balloon size up to 40.000 m3 of volume capable of lifting a 50 kg payload. Instead of pursuing the development of such a balloon which could not flight during the night, the development effort would shift to the Infrared Montgolfier, a hot-air balloon whose buoyancy was provided by the IR thermal flux of the planet.