SpaceX’s Starlink satellite system has been in the news for both good and bad lately. The “mega-constellation” of around 2,800 satellites added a further 53 satellites to its program just last week. But while it could someday provide high-speed internet for all of humanity, it’s already causing a massive headache for a certain segment of humanity — astronomers. Starlink satellites are reflective due to the solar panels they have to power themselves.
This is especially bad in the early evening and just before sunrise, when the sun falls on these high-heavy panels before illuminating the Earth itself. But so far, only naked-eye observations have tracked the satellites as they course through the sky, with the exception of a team of University of Arizona students. They recently published a peer-reviewed paper about their data collected from a number of Starlink satellites using a home-built sensor.
Starlinks are undeniably easy to spot with the naked eye at dusk and dawn. They can be seen hurtling across the sky at a speed that appears like an airplane is moving slightly faster than normal. But for an astronomer, these bright light sources are an absolute nuisance.
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Typically, astronomy research, and much astrophotography in general, requires long exposure times, which means the telescope’s lens must be continuously exposed to the light it’s trying to capture for long periods of time, typically hours. If a Starlink satellite streaks across the sky at this point, the exposure will be ruined. The astronomer must either start over or attempt to eliminate the acquired data with the satellite, which would most likely appear as a streak of light on the image.
There is no shortage of articles bemoaning this side effect of the development of the space economy. SpaceX itself is aware of the issue, having developed several methods to lower its satellite’s brightness profiles, including using darker materials and even an entirely separate visor floating alongside it. The first solution, while reducing the satellite’s brightness by an order of magnitude of 4.6, also caused the satellite to heat up to unsustainable levels and was therefore abandoned. The visor solution, known as VisorSat, is what all current Starlink models, including the 53 launched last week, are currently designed as.
Despite all the consternation these satellites have caused, no one has been able to quantify the data on the brightness and orbit of these satellites. Astronomers had to rely on naked-eye observations and a government tracking resource called the Space Track Catalog. So a team of students from the University of Arizona, with the help of professors in charge of the Space Domain Awareness Lab, set out to provide better data.
However, while collecting this data, they encountered a problem. Conventional astronomical observation devices are not well suited to fast-moving (and bright) satellites. That’s why people get upset about them in the first place. So the students invented one with a small sensor with a camera lens.
They then tracked 61 satellites with 353 different measurements over two years and compared their results to the predicted values from the Space Track Catalog. The results were amazing – their data differed from the actual catalog by only 0.3 arcseconds. Most likely, this difference, which is tiny in astronomical terms, is due to data lags in the government’s estimates, which are just that – estimates. But it also means there is a relatively accurate source of truth for astronomers interested in sparing themselves the pain of having their image ruined by a satellite.
There’s definitely plenty of that. One of the team members estimates that the entire Starlink megaconstellation, which will total around 42,000 satellites, could negatively impact up to 30% of all telescopic images. That’s a potentially devastating blow to a field that up to this point in history has only had to worry about weather in its data collection plans. But scientists are nothing but inventive, so there will undoubtedly be a way to deal with this problem that will still allow humans to expand into space. Knowing where not to look is undoubtedly a step in that direction.
UA – As reflecting satellites fill the sky, students at UArizona are making sure astronomers can adapt
Halferty et al. – Photometric characterization and trajectory accuracy of Starlink satellites: implications for ground-based astronomical surveys
UT – Starlink satellites are still bright
UT – 20% of Twilight observations contain satellite passes
Grace Halferty, lead author of the article, with the photometry instrument that she and others are helping to build.
Credit – Kyle Mittan / University Communications