All About Space


Rawls speaks to All About Space about the impact of low-Earth orbit satellites on ground-based astronomy and how our experience of the night sky is going to change

- Interviewe­d by Daisy Dobrijevic

How do low-Earth orbit satellites pose a problem for ground-based astronomy?

The main thing is that there are so many of them that are currently being launched, and are planned to be launched, and they reflect sunlight, so they can be really bright. The brightness actually surprised some of the satellite operators – they hadn’t anticipate­d how bright their satellites were actually going to be. Astronomer­s were used to sometimes seeing satellites, but now it’s an order of magnitude more, and they’re going to be showing up very commonly in observatio­ns from groundbase­d telescopes.

We have had low-Earth orbit satellites for many years. Have they always been a problem?

When I was at grad school, as an observatio­nal astronomer you learn that there’s a lot of stuff you’re going to have to deal with. To take a picture of some stars or galaxies there’s a bunch of Earth atmosphere effects. There might be light pollution, so there might be background levels of effects that you have to subtract from your observatio­ns – lots of steps to take just to try and get an image that’s representa­tive of what’s actually going on in space. Until recently, to me satellites were just another one of those things that occasional­ly would happen. It wasn’t something that was at the forefront of my mind until relatively recently.

Are all aspects of astronomy affected?

I tend to be very biased towards ground-based optical astronomy because that’s our human experience with the night sky, and they’re the main kinds of observatio­ns that I was trained in as a student. But radio astronomy is maybe going to be even more severely impacted than optical astronomy. It’s complicate­d.

Radio astronomer­s have been competing for years for a frequency spectrum. They have these national and internatio­nal relations about who gets what frequencie­s on the radio spectrum – your mobile phone service, your WiFi, any gadget that transmits has to have approval. Radio astronomer­s have fought long and hard to make their presence known and say: “We need this chunk of the spectrum because that’s where hydrogen emits. We can’t change that.” In the US they go to lobbying meetings to make their voices heard, so there is already a presence of radio astronomer­s in some of these regulatory spaces.

The issue with growing numbers of lowEarth orbit satellite constellat­ions is that one of the main goals they have is to send down high amounts of data for internet access, so they’ll be constantly beaming loud radio signals down to Earth so people can get their internet connection. This is potentiall­y going to cover a large amount of ground.

There are some things that they could do to try and lower the effects on radio astronomy, for example turning off their transmitte­rs when they are over radio telescopes. But the reality is that if you have located a set of frequencie­s that you are going to use, physically these waves spill over the edges. You cannot have a sharp cut off… it’s just not how waves work.

 ??  ?? Right: A longexposu­re image showing one of SpaceX’s launches
Right: A longexposu­re image showing one of SpaceX’s launches

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