Swiss-made laser altimeter blasting off for Mercury

10 Oct 2016

First such laser-based system designed for inter-planetary flight built in Europe is part of ESA's BepiColombo mission to map the planet in 3D.

The University of Bern’s Laser Altimeter has been successfully tested during September and its final components delivered to ESA on October 5th. The first laser altimeter for inter-planetary flight to be built in Europe is part of the ESA BepiColombo mission to Mercury. Starting operations in 2024, the altimeter will provide data about the planet’s surface.

Known as BELA (for BepiColombo Laser Altimeter), the system has been developed by a Swiss-German-Spanish team led by the University of Bern. The instrument is specified to measure the topography of the Mercury, from onboard ESA’s space mission, BepiColombo, which is due to launch in April 2018. After making its 80 million kilometer journey, BepiColombo is set to go into orbit around Mercury in 2024.

“Cameras can give us a 2D picture of planet. BELA is designed to give us the third dimension,” said Nicolas Thomas, co-Principal Investigator and the hardware leader of the project.

BELA uses a high-power laser to determine the distance from the spacecraft to Mercury’s surface. Short pulses from an infrared laser are fired at the planet. The light is reflected back to a Swiss-designed ultra-lightweight telescope and the time of flight of the laser pulse is measured.

This approach allows BELA to measure the topography of mercury to an accuracy of better than one meter from a distance of 1000 km. Thomas added, “It is a bit like measuring the distance to the North face of the Eiger in Switzerland to one meter accuracy from Hamburg, Germany, some 1000km distant.”

Challenges

"Together with our industrial partners in Switzerland, Germany, and Spain, we have developed a really advanced piece of equipment," said Karsten Seiferlin, the BELA Project Manager. "On Earth, laser rangefinders are common these days, but putting one in space to range over distances of over 1000 km and weighing under 14kg is extremely challenging.”

The returned laser pulse comprises only a few hundred photons, requiring a sophisticated detection scheme. Constructing this was especially difficult because Mercury is the nearest planet to the Sun and so the team also had to consider the temperatures which reach around 200°C on the spacecraft’s outer skin.

However, the huge power consumption of the laser in a very short time was the biggest problem faced by the developers. “This surge produces noise on the electrical signals. We had to far exceed the requirements normally used for space instruments for grounding the electronics,” said Thomas.

Inspired by Einstein

He continued, “The electronics for BELA required six different organizations to work together. We ended up having to develop several new technical solutions to make the experiment work. But BELA will contribute a lot to understanding Mercury.

”Einstein’s studies of the motion of Mercury have been so important to the theory of general relativity. It is nice to think that with this instrument, the University of Bern, where he used to work, can play a leading role in studying this particular planet in detail.”

BepiColombo mission

The BepiColombo mission comprises two spacecraft, the Mercury Planetary Orbiter (MPO) to be built by ESA and the Mercury Magnetospheric Orbiter (MMO) to be built by JAXA. The two spacecraft will fly to Mercury together in a coupled system until reaching Mercury orbit.

The MMO will then be released into a 400 x 19200 km orbit to allow detailed study of the magnetospheric interaction between the planet and the solar wind. The MPO will then descend to a 400 x 1500 km orbit which is optimum for remote-sensing of the planet's surface.