Shot by Cupid’s laser
Shooting lasers through the night sky into space sounds like something from science fiction, but ANU scientists and married couple François Rigaut and Céline d’Orgeville are doing this to track space junk and create clearer images of stars, planets and galaxies. WILL WRIGHT reports.
The adaptive optics system processes the light and cleans it so that we can take advantage of the full optical resolution of the telescope.
If you’ve seen the movie Gravity, you’ll know that space junk can cause all kinds of problems for missions in Earth’s orbit.
The 300,000 bits of space junk orbiting our planet pose a serious risk to astronauts, spacecraft and the satellites we rely on for GPS and countless other modern technologies.
It is very serious.
“We could be in a situation in the near future where it is simply too dangerous to send people, or anything for that matter, into space,” says Associate Professor Céline d’Orgeville from the ANU Research School of Astronomy and Astrophysics (RSAA).
Thankfully, d’Orgeville, the Adaptive Optics Group Manager, and colleagues are working on a technology called a laser guide star to help make it safer to navigate around space junk.
A laser guide star creates an artificial star in a part of the sky where there is no bright star and allows astronomers and space scientists to make scientific measurements.
“In addition to laser guide stars, we use lasers to measure where the satellite or the debris is in space, and predict where they’re going to be in future,” she says.
Laser guide stars are part of an emerging scientific field called adaptive optics, originally developed for defence applications.
Adaptive optics are also being used in ground-based astronomical telescopes, primarily to compensate for atmospheric turbulence and help produce clearer images of objects in space.
Associate Professor François Rigaut, who works at RSAA with his spouse, d’Orgeville, says adaptive optics saves hundreds of millions of dollars that would need to be spent on launching a telescope into space to avoid atmospheric turbulence.
“Atmospheric turbulence is severely limiting what we can see,” he says.
Rigaut, the Adaptive Optics Group Principal Scientist, likens atmospheric turbulence to the phenomenon where objects appear blurry on the horizon during a hot day.
“This problem is caused by the sun releasing heat in the ground, so you have hot air moving into cold air – light is bent and distorted, so we see a distorted image,” he says.
“The issue of atmospheric turbulence when looking at stars through a telescope is that it limits quite drastically the details that you can see in the image.”
The bigger the telescope, the more details that can potentially be seen. So how does adaptive optics work?
he system is made of three parts: the deformable mirror, which corrects the deformed light wave going through the atmosphere; the wavefront sensor, which senses the distortion of the light wave; and the real-time computer, which makes the necessary corrections.
“Essentially, the adaptive optics system processes the light and cleans it so that we can take advantage of the full optical resolution of the telescope,” Rigaut says.
“When you build larger telescopes, the amount of details that you can potentially see also grows”.
He says the massive telescopes of the future such as the Giant Magellan Telescope could not be built without adaptive optics, because the image quality would be poor.
“The telescopes are so large they are intrinsically floppy,” Rigaut says. “If you want to build them rigid, they weigh too much. To compensate for the floppiness you need active optics, which is similar to, but slower than, adaptive optics.”
Rigaut and d’Orgeville are contributing their world-leading expertise in adaptive optics to the development of the Giant Magellan Telescope.
Australia and ANU are major partners in the telescope which will be among the world's largest astronomical telescopes when it comes online in Chile in the 2020s.
The telescope will look further out into space and back in time than any telescope ever built to date and will enable astronomers to detect life on planets orbiting other stars.
Its observations of faint stars and distant galaxies will also help astronomers understand the formation of galaxies and stars, and gain insight into dark matter and dark energy.
Rigaut says ANU is designing part of the adaptive optics system that will enable the telescope to take images 10 times sharper than the Hubble Space Telescope.
d’Orgeville is leading the design of the laser guide star facility for the Giant Magellan Telescope.
“This telescope will be 25 metres in diameter and will have six laser beams coming from the side of the telescope to create six laser guide stars,” she says.
“These lasers won’t just probe atmospheric turbulence in line of the one object you’re looking at, they will probe the whole volume of turbulence above the telescope.
“The laser guide stars and adaptive optics will not only make a big difference to the quality of an image, they will also make a big difference in terms of scientific information carried by the image.”
You could say Rigaut and d’Orgeville’s love originated in the stars– the pair met through their passion for adaptive optics to give humanity a clearer view of the stars.
Rigaut’s passion for the technology stems from his days as a PhD student working on the first adaptive optics system in astronomy in the late 80s and early 90s. He marvels at how far the technology has come.
“It was a very crude system, with just 19 actuators pushing on a mirror; at the time, it was a technology that needed to be proven,” he says.
“Now we have a system with 3,000 actuators acting on a mirror. The technology has evolved so much it is actually built into today’s ground-based telescopes.”
Rigaut and d’Orgeville look forward to working together on future challenges in adaptive optics, not only discussing them in advanced astronomical facilities but also across the kitchen table at home.