First Laser Space Debris Detection Made… in Daylight

A new technique may prove to be a powerful tool in the battle to mitigate space debris.

As the Space Age continues into its seventh decade, space debris is now growing at an exponential rate. Most of this debris is in Low Earth Orbit (LEO), and ranges from bus-sized discarded rocket boosters and defunct satellites, to tiny millimeter-sized fragments.

Obviously, knowing the exact position and orbit of these fragments is essential to operations in LEO. The International Space Station, for example, must routinely perform debris avoidance maneuvers (DAMs) to avoid inbound debris, with the crew often sitting out the pass inside their Soyuz escape vehicles. The new era of communications constellations spearheaded by SpaceX’s Starlink initiative will also add on to this burden in coming years.

The Challenge of Tracking Debris

One existing tracking technique is known as laser ranging, and allows for space agencies to precisely model the orbit of a given object by bouncing a laser beam off of it sent from a ground-based station and measuring the return time. While effective, this technique traditionally suffers from a crucial drawback: it only works when satellites are visible.

This dilemma is familiar to amateur astronomers and satellite spotters. Go out under the twilight sky at dawn or dusk and watch for a few minutes, and you’re likely to see a satellite (or more likely, a discarded rocket booster), looking like a wandering ‘star’ moving silently across the sky. These shine because of reflected sunlight, making them visible to automated tracking systems as well. The problem is, this visibility window is narrow, and limited to dawn and dusk. At local midnight, satellites are still up there in the darkness of the Earth’s shadow. They’re still present in the daytime as well, illuminated by the Sun but also swamped out in the Sun’s glare against the blue sky.

Now, a recent study from The Institute for Space Research (IWF) in Graz, Austria, has demonstrated a new technique to acquire and track satellites… in the daytime. The IWF recently tested the method using telescopes at the Graz Lustbühel laser station working in concert with study co-authors Tim Flohrer and Beatriz Jilete at the European Space Agency’s Space Debris Office based in Darmstadt, Germany. The technique uses a combination of light filters looking at a specific wavelength, which increases the contrast of the target object in orbit against the deep blue background sky.

“For the visual observations of space debris, wavelengths above approximately 700 nanometers were used,” Michael Steindorfer (Austrian Academy of Sciences) told Universe Today. The visual observations are necessary to pre-center the target due to inaccurate orbit predictions.”

The study successfully tracked 40 objects in the daytime using this new technique. The method employed an 80 cm (31.5-inch) aperture telescope, and was also able to capture daytime stars 10 times fainter than are visible to the naked eye at night, down to an amazing +8^th magnitude.

“We expect that these results will significantly increase debris observation times in the near future,” says Steindorfer in a recent press release. Ultimately, it means we will get to know the debris population better, allowing us to better protect Europe’s space infrastructure.”

Laser ranging for satellite tracking has only become available to researchers in the past few years, and the new method for daytime tracking with enable researchers to greatly extend this capability. Now, the next step is to test the capability at the ESA’s Optical Ground tracking Station based in the Canary Islands off the coast of Morocco.

One wonders if this could potentially open up a new realm of ‘daytime astronomy,’ and if this technology could trickle down to the amateur sector.

“In principle, this technique could be used to detect any point-like objects of a certain brightness,” Steindorfer told Universe Today. “However, you will be limited in terms of the pointing accuracy of your telescope mount model.”

Space debris may be a mounting concern, but this new method will extend our ability to chronicle the situation… and perhaps soon, astronomy and satellite-tracking won’t end at sunrise.

Lead image credit: A future full scale space debris tracking network. Credit: ESA