A visible green laser shone from ESA’s Optical Ground Station (OGS). Part of Teide Observatory, the OGS, 2400 m above sea level on the volcanic island of Tenerife, is used for the development of optical communication systems for space, such as space debris and research for near-Earth objects and quantum communication experiments. Credit: IAC– Daniel López
Lasers on Earth are used to measure the position of spacecraft high above, and provide crucial information on how to prevent collisions in space. So far, this technique has suffered from a fatal error.
For a while, lasers could only be used to measure the distance to space debris during the few twilight hours during which the ‘laser range’ station on Earth is in darkness, but debris objects high above baths still in the last of the sun.
In the same way that the moon is brightest when it is shining in sunlight when it is on Earth at night, spacecraft are easier to see when the sun’s reflects light, seen from a dark vantage point.
Because pun objects are so close to Earth, there is only a small window in which they are illuminated, but observers on Earth are not.
Now, a recent study has proven that it is indeed possible, in broad daylight, to use lasers to determine the distance to waste. This new method of laser access will help to improve orbits for track objects, make the time available too drastic to make observations and keep valuable spacecraft safe.
Distribution of space-pun in orbit around Earth.
By using a special combination of telescopes, detectors and light filters at specific wavelengths, researchers have found that it is indeed possible to increase the contrast of objects regarding the air of daylight, with revelations of objects previously hidden were in sight.
“We are accustomed to the idea that you can only see stars at night, and the same is true for observing puns with telescopes, except with a much smaller time window to observe low-orbit objects,” explains Tim Flohrer, head of ESAs Space Debris Office.
“Using this new technique will make it possible to track previously ‘invisible’ objects that were drawn into the blue sky, which means we can work all day with laser to support collision avoidance.”
The growing problem of space debris. Credit: Spacejunk3D, LLC
Debris dancing in darkness
Our planet is shrouded in a veil of rubble – millions of tiny, yet dangerous, fragments left over from previous space launches and explosions and collisions in orbit.
They are connected by hundreds of huge, but detached, spaceship and missile bodies that have failed or been abandoned, and run unrestrictedly through space.
Even fragments of millimeters traveling at about seven kilometers per second can damage a satellite in impact, but collision with a dead spaceship as large fragments can completely destroy functioning missions.
Concept for future space structure surveillance system using ground-based optical, radar, and laser technology as well as in-orbit research tools. Credit: ESA / Alan Baker, CC BY-SA 3.0 IGO
As such, it is important to understand where fragment fragments are so that we can avoid them – but getting this information is not easy.
Laser range is a highly established technology that uses a laser on Earth to send pulses of light to a satellite with a reflector.
By measuring how long it takes for the signal to return to a telescope on Earth, known as the ‘two-way travel time’, the distance to the satellite can be accurately determined.
Unfortunately, few satellites carry a ‘retro-reflector’ that allows light to be easily reflected and returned to Earth. Determining the distance to such objects was demonstrated only a few years ago, and the development of related technologies is accelerating rapidly.
ESA’s Optical Ground Station (OGS) is located 2400 m above sea level on the volcanic island of Tenerife. Visible green laser beams are used to stabilize the transmission and reception of telescopes on the two islands. Credit: IQOQI Vienna, Austrian Academy of Sciences
Detection of pun in daylight
In recent tests, 40 different pun objects (and stars about 10 times faster than what can be seen with the naked eye) were observed with the new technique, standing out against a blue sky, first observed in the middle of the day – something that had not been possible before.
“We expect that these results will significantly increase the observation times of pun in the very near future,” explains Michael Steindorfer of the Austrian Academy of Sciences.
“Ultimately, it means that we will know the pun population better, so that we can better protect Europe’s space infrastructure.”
Further development of such technologies is a core objective of ESA’s Space Safety program, including the establishment of a network of space station laser stations.
A new laser station next to ESA’s renowned Optical Ground Station in the Canary Islands is awaiting deployment, which will serve as a ‘test bed’ for laser-ranging technologies, as well as developing network concepts.
