Laser Altimeter developed by Switzerland has been installed on Mercury Planet Orbiter

Coupling system

The instrument will measure the topography of Mercury on the Mercury Planet Orbiter and will be one of the two spacecraft orbiting the planet, which is part of Colombo's mission. The Mercury Planet Orbiter is manufactured by ESA, while the Mercury Magnetosphere Orbiter (MMO) is manufactured by the Japan Aerospace Exploration Agency (JAXA).

The Colombo mission, Europe's first mercury probe program, aims to provide humans with information on Mercury, geophysics, atmospheric information, Mercury's magnetosphere and history. Both spacecraft will travel to Mercury as part of a coupling system. They will arrive at Mercury in 2024 and the MMO will conduct a study of the planet's magnetosphere through an orbit that will be closest to the surface of Mercury at a distance of 590 kilometers, while the Mercury Planet Orbiter will follow one more The near orbit is at 480 kilometers, investigating the surface and internal structure of the planet.

The BELA is one of eleven devices that the Mercury Planet Orbiter will carry. The laser meter uses a direct detection method. This high-power laser, developed and designed by Cassidian Optroniks, will emit 50 mJ pulses at 10 Hz and 1064 nm wavelength. These will be reflected from the surface of Mercury and received by the receiving telescope (RTL) after a delay of about 5 milliseconds. The images are then focused on silicon avalanche photodiodes – these are based on photodiodes of the Mars Global Sensing Spaceship and NASA's Messenger Spacecraft Laser Altimeter, which had flown around Mars between 2011 and 2015. The signal from the photodiode is analyzed by an electronic module that was developed and analyzed by the Swiss technology company RUAG to determine the time of flight (thus calculating the range and height), the integrated pulse intensity and its width.

Mirror

RTL is a double-sided reflective telescope designed and developed by RUAG. The equipment is located inside the spacecraft. It needs to cope with changes in temperature from minus 20°C to 45°C without deformation and light weight. "We decided to build the telescope to provide thermal compensation entirely from the thorium," said Nicolas Thomas, co-principal researcher at the Colombo laser altimeter. "A system with a diameter of 20 cm weighs only 600 grams." The optical surface is made of diamond processed copper deposited on the yttrium element.

Mercury is so close to the sun that Bela will have to face intense sunlight and heat. The RTL's "separator unit" can reflect 90% of sunlight to protect the equipment. “If we have a traditional black baffle, not only will the temperature reach 450°C, but we will inject more than 300 W into the spacecraft,” explains Thomas. “The outer ring (ceramic) still reaches 200°C is the worst case, but today 30W of thermal energy can be dumped into the spacecraft.” Some of the laser's small protection modules were also developed by the German Aerospace Center DLR in Germany.

Feel the heat

To handle the sun's reflected sunlight, all optical systems, light transmitted from the telescope to the photodiode, and lasers are equipped with interference filters. The optical system's filter isolates light at a laser wavelength of 1064 nanometers, while the filtered laser is a light that prevents potentially dangerous levels from reaching the system.