Concorde: how was the unusual supersonic chase of a solar eclipse?

concorde

Total solar eclipses are the perfect opportunity to learn more about our star. When the Sun is fully occulted by the Moon, it is possible to observe and study the corona, an enigmatic region that continues to baffle astronomers. However, total occultation lasts only a few minutes and it would be months until the next one. In response, a group of researchers would use the supersonic Concorde jet to chase the lunar shadow on Earth and obtain record viewing time for the 1973 total solar eclipse.

Aerospatiale BAC Concorde 001 F WTSS
Fotografía en vuelo del avión francés Concorde 001. Créditos: Aérospatiale.

Reinventing commercial flights

World War II had left a strong legacy for the world of aviation, and the various nations involved devoted resources to improving the aircraft available. One of the branches of research was to increase speed and overcome the sound barrier, requiring new engines.

El 14 de octubre de 1947, empleando un motor cohete, el avión Bell X-1 fue el primero en superar la velocidad del sonido, alcanzando 1.05 Mach. Opening the door to a new flight regime with the potential to connect the world in record time.

While supersonic aircraft were for military use, a collaboration between France and the UK wanted to revolutionise commercial flight.. Connecting the world with an aircraft capable of exceeding the speed of sound, considerably reducing travel time. It was named Concorde and was in operation between 1976 and 2003.

It had the ability to reach a flight speed of slightly more than twice the speed of sound, as well as reaching an altitude of 18,300 kilometres, showing a clear sky. This allowed for less drag with the atmosphere, increasing efficiency for longer flights above the clouds.

Concorde eclipse
Composite image of a British Concorde aircraft seen from a Boeing NC-135 aircraft taken by Arthur Gibson. The solar eclipse would be added later.

Planning

In 1972, the astronomer Pierre Léna proposed to use Concorde to chase the shadow of the eclipse, thus considerably extending the observation time of the phenomenon. On board would carry several scientific experiments from five different institutions that would allow a better understanding of the Sun, as well as the different processes occurring around it.

Several numerical simulations were performed to find out how feasible it would be to chase the shadow of the eclipse, as well as the total observation time and the best area of the trajectory to perform the flight, as well as the take-off site to optimize the available fuel. The chosen eclipse would occur on June 30, 1973, with a maximum duration of 7 minutes and 4 seconds, over the Sahara desert.

Trayectoria eclipse
Path of the total solar eclipse of 30 June 1973. Credits: Timeanddate.

Four months before the total solar eclipse, the project was approved and one of the French Concorde prototypes would receive several modifications. Among them, the installation of observation windows on the roof of the aircraft capable of surviving supersonic travel. A decision also had to be made as to who would travel on board to operate the equipment and collect as much data as possible.

Hunting the shadow of the eclipse

On 30 June 1973, at 10:08 a.m., Concorde 001 would take off from Las Palmas de Gran Canaria to intercept the shadow of the Moon over Mauritania. It was over the Atlantic Ocean travelling at 1900 kilometres per hour.

elcipse
Photograph of the totality of the 1973 solar eclipse, as seen from Akjoujt Mauritania. Credits: Dennis Cassia.

While the researchers checked and calibrated the instruments, the pilots tried to follow the previously planned trajectory perfectly. The encounter took place one second later than expected, initiating a 74-minute observation of the totality of the eclipse. Studies of the solar corona, comet searches, among others, were carried out. While much information was collected, no groundbreaking discoveries were made. Translated with DeepL.com (free version)

Throughout the period of Concorde's operation, several solar eclipse chases were carried out, although they were tourist flights. For example, for the last eclipse of the 20th century, two British and one French were used, with tickets costing around 2400 dollars. Nowadays, different satellites and space probes offer much more and better quality information at any time about all parts of the Sun.

Francisco Andrés Forero Daza