Starlink opens final frontier for radio astronomers
Is it wrong to wish on space hardware?
Opinion There isn’t an astronomer on the planet who isn’t in two minds about modern technology. The same advances in material science, computers and radio technology that have given humanity spectacular new views of the universe also clutter the skies and deafen the radio bands with swarms of noisy, shiny, satellites. Now, though, the worst offenders are opening up one of astronomy’s final frontiers in unexplored space.
That prime high-tech lightning rod for the stargazers’ ire is of course Starlink, SpaceX’s orchestra of Internet satellites in 550km orbits. At the time of writing, nearly 4000 of these have been lofted, with tens of thousands to come, and there are at least three credible competitors aiming to join them. That's a lot of spots before your eyes.
They can also make eyes light up. One group of astronomers, headquartered at MIT’s Haystack radio observatory in Westford Massachusetts, looked at Starlink and saw a possibility for brand new science.
Originally a military research institution, a role continued by other outfits on the site, Haystack runs a broad range of radio and ionospheric studies, but it and every other radio observatory on Earth is blind to a whole slice of the cosmic spectrum. What’s worse, until now physics has put that out of the reach of space-based telescopes too. Then Starlink turned on the lights.
The space radio blind spot is frequencies below around 10 MHz, which are permanently shielded by the ionosphere, the electrically charged layers of high altitude atmosphere that also bounce shortwave signals back and host the aurora. Incoming signals from space below 10 MHz just can’t get through. And putting your telescope in space doesn’t help much, because those signals can have wavelengths from 30 metres down to hundreds of kilometres. To be any good, a telescope has to be multiples of its target wavelength big, and even Musk would baulk at putting thousand kilometre dishes into orbit.
There is a third option, Very Long Baseline Interferometry or VLBI. This is already deployed on ground-based observatories, to increase sensitivity and resolution for higher frequency signals. Synchronised chains of dishes, some in local clusters, some working together across the globe, create huge virtual telescopes up to the same size as the planet. It’s an extremely powerful and flexible system, and entirely dependent on big data computational analysis and cutting-edge networking. The limitation is the size of the planet - no such barriers in space, but the expense of putting multiple huge satellites up precluded all but a couple of experiments.
Then Starlink came along, with its closely-choreographed high performance swarm of data driven satellites - and low frequency VLBI in space started to look doable. Enter Haystack’s Great Observatory for Long Wavelengths - GO-LoW, an audacious proposal that has just received its first slug on NASA funding.
GO-LoW is, like Starlink, a large fleet of small satellites. There the resemblance ends. While Starlink proposes a maximum constellation of a paltry 30,000 satellites, GO-LoW is thinking of 100,000. Instead of Starlink’s 550 km orbit, GO-LoW will live in two clusters at the inherently stable Lagrange 4 and Lagrange 5 points, 150 million km ahead of and behind Earth. In Earth’s orbit. That’s putting the V into VLBI, and will give coverage down to the wavelengths where the interstellar medium itself becomes opaque to radio waves - a physical fact about which we can do nothing.
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What will it find? There are many energetic sources of low-frequency electromagnetic radiation in the cosmos, and the ability to map these in new frequency bands will greatly aid discovery of their mechanisms and nature.
Much will be learned of the interstellar and intergalactic cosmic media. The biggest prize, though, is the direct observation of exoplanet magnetospheres, the magnetic fields which shield ecosystems from stellar radiation, and which are thus crucial to creating life-friendly environments. GO-LoW should also be capable of observing these on exoplanets that aren’t detectable by optical means due to their orientation around their stars. It’s also a tenet of science that whenever you look somewhere new, you find something unexpected.
There are plenty of questions to answer before the first batch of longwave sniffer sats gets blasted into space. How do you begin to deal with the huge amounts of data over such a long range? What mixture of antennas and sensors will be practical and useful on such small craft? NASA is impressed enough by the concept to give GO-LoW the money to start to answer these.
There are many inherent benefits besides the raw concept. At long wavelengths, you don't need the pinpoint guidance and targeting other telescopes require; a much smaller initial fleet can start to deliver new science and guide the full deployment. There's no single point of failure. Updates and augmentations are possible without manned repair missions.
GO-LoW is a truly visionary project that promises much new science and new techniques for other missions. Looking from New England, that’s something to brag about. ®