At a double observatory atop Mount Teide on the Spanish island of Tenerife, a powerful laser is being deployed to track fragments of space debris in orbit and warn when these fragments threaten satellites. Soon, it could even be used to push space debris away from a collision course with a satellite.
The Izaña-1 and Izaña-2 laser-ranging stations are operated by the European Space Agency (ESA) and were constructed by the German company DiGOS, which specializes in laser ranging. Izaña-1 has been active since 2021 and has already been employed in satellite laser-ranging, but with Izaña-2 now complete, the pair of telescopes have a much more ambitious task as part of ESA’s Space Safety Program.
The two telescopes operate synchronously: Izaña-2 fires laser pulses at a piece of space debris high overhead, and Izaña-1 detects the reflected light. In doing so, the system is able to track the path of the debris, charting its orbit and determining whether it could potentially collide with a satellite.
“We had to scale up the power of the laser on Izaña-2 because the plan is to illuminate non-comparative targets; therefore, the amount of photons transmitted back towards the station is limited and we compensate with more energetic pulses,” said Andrea Di Mira, an ESA optical system engineer, in a promotional video on the ESA website.
An orbital collision could range from bad to potentially very bad. An individual satellite may be severely damaged, which could result in a financial loss, or the loss of research data if the satellite is a scientific one. In the worst-case scenario, a collision could smash a satellite into many more pieces of space debris, which each then go on to collide with more satellites, which produces more chunks of space junk, and so on and so forth. This could result in a runaway and very dangerous cascade called the Kessler Syndrome, after the NASA scientist Donald Kessler, who first described it. In such a scenario, large sections of low Earth orbit could become unusable because the density of space debris becomes too great.
It is therefore vital that space junk is tracked, so that satellites can maneuver to get out of the way before they are hit.
The Izaña system currently runs semi-automatically, and can even be used in the daytime. While everything is automated, a team of humans remotely supervise Izaña-1 and Izaña-2, but the aim is for it to one day be completely autonomous.
“As part of the development roadmap, we’re planning to go to [full] automation. This has the great advantage [of] increasing data productivity,” said Di Mira.
The ambition doesn’t stop there. Presently, if the Izaña system detects a fragment of space debris hurtling towards a satellite, the satellite then has to take evasive action, firing thrusters to push it out of the way.
There may, however, be another way, called “laser momentum transfer.”
“One possibility is laser momentum transfer to gently push the space debris on its orbit a little bit away so it doesn’t collide with orbiting satellites,” said André Kloth, Managing Director at DiGOS, in the video.
The laser on Izaña-2 could push space junk out of the way, in the same way that a laser can push a solar sail through the momentum of photons impacting on it. With the laser coming to the rescue, a satellite doesn’t have to move out of the way, so it can conserve its fuel, helping to prolong the mission for as long as possible.
With Izaña-1 tracking space debris and satellites and Izaña-2 pushing the debris away, ESA potentially has an all-in-one space debris avoidance scheme on its hands that feeds into another of the agency’s projects called OMLET, or Orbital Maintenance via Laser momEntum Transfer. OMLET would supply satellite operators with an on-demand system of knowing exactly where their satellites are in relation to space debris, and then the capability to push that debris out of the way. In a sense, OMLET would be like a space-traffic cop, marshaling the orbits of satellites and debris.
There’s even the potential that the laser on Izaña-2 could pull double duty as a testbed for laser communication, firing lasers encoded with data up to satellites that can then relay those laser messages to their destinations. Besides there being less interference than at radio waves, optical and infrared lasers also support quantum encryption — what’s known as QKD, or quantum key distribution, in which the key to encrypting the data is encoded into the quantum superposition of the photons.
Even on a cloudy day, today’s lasers can still push through and reach their target. Indeed, orbiting Earth-observation satellites routinely use lasers for light-detection and ranging (lidar) on the planet’s surface, despite the clouds and smog, while Chinese scientists have recently conducted the first ever daytime laser-ranging experiment from Earth to the moon.
Sixty-five years after their invention, it seems that lasers are still lighting the way to a better future in space.