Elon Musk is at the centre of a controversy, again. This time, the astronomers are up in arms. The reason: Musk’s SpaceX recently launched 60 satellites as a prototype for the company’s planned Starlink satellite project. In the next few years, SpaceX plans to launch dozens more satellites into low-Earth orbit, with the goal to provide internet access worldwide at a supposedly low cost. Ultimately, the constellation is expected to span 12,000 satellites orbiting Earth in three shells between 340 and 1,150 km.
The problem is that these satellites have shiny metal surfaces and solar panels that strongly reflect sunlight, making them very bright, sometimes so much so that they are visible to the naked eye. Many amateur astronomers have already managed to capture a ‘train’ of some of these satellites moving through the night sky.
The astronomy community’s protest was almost immediate, and included both amateur astrophotographers and professional astronomers. A thousand-dozen satellites would outnumber stars visible to the naked eye (although only about 80 are visible simultaneously from any location) and will be some of the brightest objects in the night sky. This doesn’t bode well for stargazers and astrophotographers, whose field of view is bound to be marred.
Further, unlike astrophotography, astronomy banks on deeper observations of the sky, with telescopes’ exposures lasting up to a few hours, sometimes more. These instruments are typically sensitive to very faint light, and bright satellites foregrounding stars could ruin observations. It is notable that these observations are very expensive: those with world-class facilities can cost several thousand dollars per hour, not to mention many hours of labour as well as the opportunity cost.
Radio telescopes will be affected even more. Radio signals arriving from astronomical sources in distant parts of the universe are extremely weak. A mobile phone on the Moon emits enough radio-frequency radiation to be the strongest source in the sky. Thus, human-made signals often mask astronomical signals and contaminate the data, or add artefacts in images that can lead to misinterpretation.
Frequencies in the radio part of the electromagnetic spectrum that are useful to humans are into bands: AM, FM, TV broadcast, military, etc. Certain bands are reserved for astronomical observations because of their scientific importance. For example, the 1.4 GHz band is used to study the abundance of hydrogen in the universe. So to facilitate their observations, radio observatories are built in places where there are few humans, called radio-quiet zones.
However, the Starlink satellites could disturb this hard-earned peace, disrupting important signals as they pass over the telescope. Considering SpaceX intends Starlink’s signals to reach remote areas and providing internet access in under-served regions, the constellation will be visible from most places on Earth and will likely interfere with most current and future radio observatories.
At present, the extent of this disturbance vis-à-vis professional astronomy is not fully clear. The Large Synoptic Survey Telescope, which will be able to scan the entire sky in just three nights of observations, said after a preliminary study that their observations will be largely unaffected thanks to modifications its team will be able to make to the instrument’s imaging strategy and algorithm.
But other observatories – especially small- and medium-scale telescopes – that study exoplanets, monitoring asteroids, perform all-sky surveys, etc. will be affected more. The Starlink constellation will be using the K-a and K-u radio bands, which overlap with the operating frequencies of the Square Kilometre Array (SKA), an ambitious radio telescope on which India is an important partner. Although SpaceX later said that the satellites will not use one of the bands, other companies or countries may not be so sympathetic.
Musk also countered, with his now-typical bombast, on Twitter that scientists should be moving their telescopes to space anyway. This is not possible. Astronomers already have access to some space telescopes, such as the Hubble and AstroSat; a subset of them can only function in space – such as the Chandra and the Fermi – because the X-rays and gamma rays they study are blocked by Earth’s atmosphere. But the majority of astronomy research still banks on ground-based instruments that perform follow-up observations, large-scale, all-sky surveys, deep exposures, etc. – none of which we can pull off with space telescopes.
There are already 4900 satellites in orbit, which people notice ~0% of the time. Starlink won’t be seen by anyone unless looking very carefully & will have ~0% impact on advancements in astronomy. We need to move telelscopes to orbit anyway. Atmospheric attenuation is terrible. pic.twitter.com/OuWYfNmw0D
— Elon Musk (@elonmusk) May 27, 2019
Sending telescopes to space is expensive and risky. They are very hard to maintain and upgrade, if not entirely impossible. Their sizes and therefore abilities are limited by the rockets that can launch them. Terrestrial observatories, on the other hand, are much larger, cheaper and easier to maintain. For example, the Extremely Large Telescope (ELT), to be built by the European Southern Observatory, will cost only $1.25 billion (Rs 8,671 crore) with a 40-metre-wide telescope mirror. On the other hand, the upcoming James Webb Space Telescope will have a mirror 6.5 metres wide but will cost nearly $10 billion (Rs 69,370 crore).
In effect, the ELT will – assisted by adaptive optics – collect more light than all other current 10-metre-class telescopes combined for about 12% of the price of a less capable space-based telescope. If he insists, Musk is of course welcome to help secure a trillion dollars to replace terrestrial telescopes with space-based ones.
These complaints from the astronomy community are also joined by concerns about reliability and national security. While many companies are trying to improve access to affordable internet services in the world’s more under-serviced areas, the cost is likely to be high relative to data piped through fibre-optic cables and 4G networks. Additionally, given its importance as a resource, governments like to be in control of internet availability and access within their borders.
However, the companies remain undeterred; and after SpaceX’s initial success, they are only bound to increase their efforts. So now is a good time for astronomers to plan for satellite interference.
Several professional organisations, including the International Astronomical Union, the European Southern Observatory, the Royal Astronomical Society, the National Radio Astronomy Observatory (NRAO) and the SKA team, have released statements calling on companies to consult with them before spamming the sky with satellites. The NRAO has also said that it is in touch with the Starlink team to discuss how to minimise radio interference. These organisations, and their members, should also campaign for international standards to prevent surprises of this sort in the future.
The night sky has an important place in the cultural heritage of humankind. After the Starlink controversy broke out, many experts noticed similarities with the construction of the Thirty Meter Telescope on Mauna Kea, Hawaii; the island’s native inhabitants consider the mountain sacred. In both cases, one group acted unilaterally, in the name of technology and progress as it saw fit, without giving much thought to adjusting for or preserving the other’s access to entities and resources that the latter considers culturally significant.
This is a lesson in many things but perhaps most of all, it should teach us of the importance of communication. If SpaceX had consulted with those professional organisations, as well as with organisations that recognise the cultural importance of the night sky, before launching the satellites, and if Musk had got off his high horse, the ongoing controversy could have been avoided. We should learn to consult with all stakeholders and keep ourselves open to constructive dialogue, and thus craft mutually beneficial solutions.
Abhijeet Borkar is a postdoctoral researcher at the Astronomy Institute of the Czech Academy of Sciences, Ondřejov.