An astronomers beef with Satellite Constellations
A little while ago, SpaceX launched it’s latest cohort of the starlink satellites in to the orbit, and it continues to outrage the astronomers.
In one of my previous articles on this blog, I was talking about various techniques that astronomers use, to look at the vast skies, in-order to observe, analyze, record and understand a wide variety of things. With years of data and the data that continues to be collected from day-to-day/periodical observations, answers to many un-understood things surface, and have surfaced over the years.
Out of many instruments that are used in this field, there are Chandra X-Ray, Spitzer, Hubble, Space Telescopes which are essentially satellites with all kinds of optical instrumentation that are crafted with atmost perfection(I mean a circle is perfect circle….and so on).
Even though astronomers find the data from these non-surface telescopes interesting satellites are at times, a worry for surface based telescopes to deal with.
Wait, what am I talking about?
Yeah, let me clear this up for you. So, We, have scientific observations, communication relays and other various kinds of operations that happen from a large number of satellites that orbit our planet. If a satellite that’s in orbit is operational, it is termed to be an active satellite. If a satellite is decommissioned or completes it’s mission period it is termed be termed a passive satellite. It is accounted to that there are a little less than 2500 satellites both active and passive satellites in orbit. Thanks to mega space corporations like SpaceX, Boeing Satellite and few others the number of these satellites in orbit is going to increase. The mission of these organizations is to provide affordable and reliable internet connectivity to otherwise hard to connect areas, and people round the globe by having a network of satellites, often termed to as a Satellite Constellation. Wikipedia defines a satellite constellation as
a group of artificial satellites working together as a system. Unlike a single satellite, a constellation can provide permanent global or near-global coverage, such that at any time everywhere on Earth at least one satellite is visible
A little bit of SatCom
Before we proceed any further let’s get to know about orbits in which the satellites orbit. According to NASA catalog there are essentially three types of earth orbits depending upon the distance of the orbit from the surface of the earth, namely,
- High Earth Orbit (~36000 KMs from surface of Earth)
- Medium Earth Orbit (~26560 KMs from surface of Earth)
- Low Earth Orbit (~2000 KMs from surface of Earth)
While there are a lot of other parameters that are involved in launching a satellite to a particular orbit, for the purpose of this article we’re only concerned about the height of the orbit.
There already a couple of hundred satellites that are orbiting in what are commonly called as MEO(Middle Earth Orbit) and GEO(Geosynchornous equatorial orbit). These constellations are at a greater height than those proposed by the organizations that offer to provide internet via the satellite. One other thing is that these satellites are not that clustered, there are like 7-10 satellites per constellation. This number goes upto mid 20’s and 30’s (In case of the most commonly used GPS satellite constellation, there are 24.)
What’s my problem?
The problem with all these things is that there are three primary arguemtns with these increasing numbers of constellations
- With a lot satellites being almost visible to the human eye, will humans still be able to fall in love with the night skies?
When the starlink was first launched, it was observed that their magnitude was around 2-3 which is very bright as far as observational astronomy is concenred. And since these are constellations, they might look like a train of light along the night sky. With the proposed final orbit height being 550 KMs it is estimated that even after raising the orbit, these satellites might still be visible to the human eye in the night dark sky.
For an astronomer, this comes more as a hard hit, becuase when there are observations happening during the summer months and the nights are shorter, we would possible be able to see these satellites more when it’s dawn-ish, twilight-ish conditions. But when the nights get longer and longer, and there is a train of these passing through your FOV, kaboom,outrage at it’s peaks.!
Mind you, there is also debris out there, like the most accurate account of these objects that have been dropped off comes close to around 18000 objects that are being actively tracked. It is said that prior to starlink there were only 200 man-made objects that were visible in the nightsky. With constellations such as starlink, there are thousands of these bright objects that add up to the current tally.
So, when there is a satellite in the FOV of a telescope that makes observations and captures images, there is a streak of line/lines that occur in the images and it is where we can’t possibly see a star in that LOS. These streaks are caused due to the photons reflected off of the surface of the satellite. With satellites such as ones in the starlink, the amount of light reflected is higher than earlier and the photons that are reflected tend to saturate a higher number of pixels. These saturations can lead to occurence of ghosts of these satellites in the series of images that are captured and this makes one crazier because it makes a considerable amount of recorded data worthless.
If one is able to understand the motion of these satellites and track the duration the satellite takes to cross the path of their FOV, this problem can be mitigated to a subtle extent, but not to the extent it should. As mentioned earlier, FOV is going to be a keyfactor in trying to get a starlink satellite out of the view of the observatory. SpaceX has also been trying to look into issue (a presentation by one of the engineers from SpaceX at the American Astronomical Society,meeting, Honolulu, Hawaii, Jan, 2020 ). A mitigation strategy was proposed where in a darkening material would be applied to one of the satellites that is launched (infact this did happen) and see if reflectivity would get lower. This is probably the first time that a satellite constellation has a converstion has had a convesation with astronomers and said
what can we do to reduce our impact on your science?
One other mitigation strategy would be to provide an open source realtime location tracking ability which will help the observatories calculate their time and duration of observations.
While the astronomy community is skeptical about all other organizations whether or not they’ll have similar or any mitigation strategies at all. With these satellites continue to grow in number why not spend some time, and look at the night skies while you have a chance to do so!
Feel free to comment, and suggest below in the comments.