A couple of years after it was first conceived, a Melbourne University-led infrared astronomy cubesat proposal called SkyHopper is gathering momentum.
Vulture South found itself intrigued by a simple question, which we found time to put to one of the project's founders, astrophysicist Dr Katie Mack: what useful astronomy can you achieve with a cubesat?
After all, compared to the famous space telescopes – Kepler, Hubble, Chandra X-Ray and so on – a 12U cubesat is tiny.
The surprising (to us) answer, Mack said, is that cubesats offer genuine bang-for-buck if you choose the right missions – and for SkyHopper, the mission is infrared astronomy.
A cubesat, she explained, is a relatively easy way to get an instrument outside the atmosphere, and because the atmosphere is really good at absorbing infrared radiation (see “climate change”), that's a pretty good multiplier of an instrument's effectiveness.
“Going to space, you can take a 20cm mirror and get the same amount of light as you'd get with a two-metre mirror on the ground”, she explained.
Instead of a huge telescope on top of a mountain, which is fairly limited in its field of view, “when you're in space, you get a better view in all directions … [SkyHopper is] orbiting every 90 minutes, so you can see a lot more of the sky”.
Fair enough: but what's so interesting about infrared observations?
The infrared is a bit of a hot field in astronomy, Mack said, because it plays into two “big question” areas: events from the oldest galaxies in the universe, and exoplanet studies.
A long time ago …
Take ancient – that is, extremely distant – transient phenomena like gamma ray bursts. They're a good observational target, because “if they're really distant, they're going to be red-shifted” all the way down to the infrared.
“We're trying to understand how those work, by looking at the afterglow,” Mack said. “We'll see things in the infrared that we can't see with optical telescopes.”
SkyHopper would be a candidate to work with other instruments – on detection of the gamma ray burst, it will be able to “slew onto the target” and take follow-up observations very quickly.
What the boffins want in the hunt for transients is better information about what causes gamma ray bursts – they're poorly understood, although they're “some of the most powerful explosions in the universe.”
“One theory is that they come from a super-supernova; another way is from the collision of two neutron stars.”
Either possibility, Mack said, has implications for gravitational wave detection: “you might see a collision that the LIGO instruments can see. If we can see the afterglow, and LIGO can see the gravitational wave signals, that could be really important.”
Infrared observations could similarly help understand the even more mysterious transients, fast radio bursts (FRBs).
And infrared observations can help us understand star formation in the early universe, the period known as the epoch of re-ionisation (beginning about 400 million years after the Big Bang) – the era also sought by huge Earth-bound projects like the Square Kilometre Array.
… planets (not galaxies, sorry) far, far away
The other main science case, Mack told Vulture South, is in the search for exoplanets: “one of the exciting areas of exoplanet research is planets on orbits around red dwarf stars.”
That's because those cooler red dwarfs have a habitable zone much closer to the star than hotter planets.
“That makes it easier to see the planets' transits,” she explained, and it's a great observational approach because “there are way more of those cooler red stars … Trappist-1 is that kind of system”.
For cool red stars, infrared observations are more efficient than in optical wavelengths.
2020 launch target
Speed also makes cubesats an attractive proposition: in an era where going from first proposal to first light can take years or decades, SkyHopper's launch target (2020 or 2021) is quick, but not especially ambitious.
“We have some seed funding, we're working on the preliminary design, we're designing the instruments. We have a group building the optics, doing interesting things getting the right kinds of optics for this small telescope,” Mack said.
“We have a systems engineer working on putting together how the instruments work together, and how it'll be laid out in the telescopes”.
To help develop Australian space capabilities, the project is hiring student interns to work on different aspects of the project; there's funding from the University of Melbourne and from overseas, and the group is applying for more funding from the Australian Research Council.
And the funding requirements aren't so terribly daunting: instead of the billions astronomy can need, Sky Hopper should be able to complete its missions with between AU$8 million and $10 million (partly because it's so much cheaper to launch a cubesat as an extra payload on a bigger launch, compared to devoting a whole launch to one satellite).
For that, the group hopes to be able to spot as many as five gamma ray bursts a year in its two-year observation mission. If that doesn't sound like much, it would “double the sample size of the known GR bursts in the early universe”, and that's in addition to “quite a lot” of exoplanets the group hopes to turn up.
“Because it's the special niche of the IR in space, it could have outsized impacts compared to the investment”, she said.
The project site is here. ®