Science1 publisher2 min readPublished
BepiColombo's laser altimeter fired into open space for the first time since 2017
The Bern-led BELA team ran the instrument's laser in 10-second, 10-minute and hour-long steps on 14 September, confirming it survived eight years of cruise. The pulses went into open space.
The Scientist · Science desk
What happened
- The BELA team at the University of Bern and DLR Berlin fully activated the instrument's laser on 14 September 2026, its first firing in space and its first since 2017.
- After a second confirmation the team repeated the 10-second run, extended the laser to 10 minutes, and only then let it operate for more than an hour.
- BepiColombo has begun separating the Mercury Transfer Module from the two orbiters, with arrival preparations underway and the scientific mission due to start in 2027.
Compiled by The ScientistSomething wrong?How this is made
Why it matters
- capability Bern's topography plan for 2027 can now be built on a transmitter that has fired in flight; before 14 September, the newest full functional data on BELA came from a laboratory in Bern in 2016.
- constraint The pulses went into open space and no echo has been detected, so ranging remains unproven in space and the accuracy of the planned three-dimensional map rests on the design alone.
- decision With a round trip near 22 minutes, the team cannot abort a run in real time, so the length of each commanded burst is the only control they have.
- contradiction The phys.org account gives 2017 as the last firing but 2016 as the last full functional test, so the dormancy is nine years or ten depending on which event you count.
At roughly 200 million kilometres from Earth, light needs about 11 minutes to make the crossing: 200 million kilometres divided by 299,792 kilometres a second is 667 seconds [18]. The first data packet from the opening burst reached the ground station about 10 minutes after the test, close to that one-way delay [11]. A command and its answer take something near 22 minutes [18]. Nobody in Bern could have stopped the laser mid-burst. Firing for 10 seconds and then reading telemetry keeps an unknown fault short, and the runs that followed went to 10 minutes and then past an hour, at least 360 times the length of the first [12][20]. More than 100 pulses inside that first 10-second window is a rate above 10 a second [19].
Liliane Burkhard, the instrument scientist for BELA at the University of Bern's Physics Institute, said "Commissioning is meant to be undramatic" [14]. Each step, she said, "is carefully designed to reveal any potential problems while the laser is operating for only 10 seconds, rather than for an hour" [15].
Pommerol said: "The laser pulses were only sent toward open space this time, not yet toward Mercury. But they could still be characterized by the instrument, providing crucial data on the health of the laser system after eight years in space and nine years since its last firing" [11]. So the transmitter has run in flight, and the instrument measured its own outgoing light, though no pulse has yet struck a surface and returned to the detector [11]. On the thermal side, Pommerol said the test "confirmed that the laser was operating reliably and that its thermal behavior remained within the expected limits" [13].
BELA is the heaviest instrument on ESA's Mercury Planetary Orbiter, designed and built at the Physics Institute of the University of Bern [4]. It was developed by a consortium led by Bern and the German Aerospace Center, with the Max Planck Institute for Solar System Research and the Institute of Astrophysics of Andalusia [7]. Its job is the shape, topography and morphology of Mercury's surface [8].
The instrument left Bern for ESA's ESTEC on 14 September 2016 to be integrated onto the orbiter, and the team switched its laser on ten years later to the day [6]. BepiColombo launched on 20 October 2018 and has spent almost eight years working toward Mercury on a sequence of planetary flybys and solar-electric propulsion [1][21]. Pommerol, a co-principal investigator for BELA, said "With BELA, we will be able to create a three-dimensional representation of Mercury with unprecedented accuracy" [9].
What to watch
- A published output power or pulse energy figure compared with BELA's 2016 laboratory values, which would show whether eight years of cruise cost the laser anything.
- Whether the Bern and DLR team reports a ranging test, with a detected return, before MPO reaches its science orbit.
- The remaining Mercury Transfer Module separation and orbit insertion steps that put MPO into its own orbit.