- So the other night I'm doing the dishes,
and I get a text from a friend of mine
saying that she heard something about some UFOs,
these lights flying across the sky in a straight line.
And then her daughter had gone outside
that very night for a walk
and she saw this string of UFOs flying
in perfect single-file formation across the sky.
Yeah, it's Starlink.
Yeah, but then it was doing this and it was moving--
Yeah, it's Starlink.
Well, how do you know?
Because if we don't do something about Starlink soon,
it's going to ruin astronomy.
Now, I was being maybe a little bit hyperbolic,
but like a lot of astronomers I have
a love-hate relationship with the whole idea of Starlink.
I mean, as a person who uses the internet,
I love the idea that they are going to be able
to bring broadband service to the world at very low cost.
But as an astronomer,
I'm well aware of the challenges
that many observatories are facing by having
these unexpected streaks showing up in their images,
and the streaks are a little bit
more than just an annoyance,
they are a real problem that has to be dealt with.
Now, it turns out that SpaceX
have actually been pretty candid
and upfront about wanting to reduce,
and in fact, ideally eliminate any adverse impact
they may have on astronomy,.
But first, before we get into all the mitigation efforts,
we may as well just kind of quickly recap
just what Starlink is all about.
Starlink is designed to put together
basically a huge megaconstellation
of satellites that can provide low--
Well, sorry, low latency internet.
In other words, think of internet basically traveling
at the speed of light.
Right now we do all that using fiber optic cables
which are laid across the ground and even under the ocean,
but light travels up to 50% slower through fiber optic
than it can in a vacuum,
so if you could have a relay of spacecraft
that are flying in very low earth orbit,
you can get very low latency internet,
and even better, they can provide that internet access
at low cost to people around the globe,
including the majority of the human population
that don't have internet access at all.
Now, normally when we think of using satellites,
we are often thinking of the low-earth-orbiting satellites.
These are spacecrafts that typically operate
at altitudes of 1,000 or more kilometers above the surface.
The problem with using those types
of satellites are twofold.
First of all, you have a longer travel path
for light to take from the ground,
to the spacecraft, to the ground again.
This is actually gonna result in a longer latency period
than just using old-fashioned fiber optic.
The second problem, is orbital debris.
I mean, these spacecraft are supposed to deorbit
after their mission lifetime,
but if for whatever reason they can't bring
the spacecraft down on command,
then they have to just wait
until the orbit just naturally decays,
and the higher up the spacecraft is,
the longer it's going to take for its orbit to decay.
So you end up with a whole bunch of unwanted space debris.
But SpaceX is going to do something different with Starlink.
They're operating them at about 550 kilometers,
and this has two advantages.
The first is that it has a shorter path for light to travel
so you get lowest possible latency.
And the second is the fact that it
is deeper in the diffuse outer atmosphere of the Earth
which allows them to deorbit
pretty quickly once their mission lifetime is over.
However, the closer the spacecraft are to the surface,
the smaller their field of view,
and therefore you have to have a network of satellites
essentially crisscrossing each other
all around the globe in order to act as a relay
for data from one point on the ground to another.
And this results in a lot of satellites, how many?
Well, SpaceX's initial plan is for 1,584
of these satellites, that is Phase One.
But eventually they'd like to raise
that number to be higher,
as many as 42,000 of these satellites.
Now, these satellites are first deployed
at an altitude of something like 300,
maybe 350 kilometers above the surface.
That's actually too low for their operational orbit.
They're actually trying to raise them
by about another 200 kilometers or so.
So they spend the first few weeks of their mission
just raising their orbit using some tiny ion thrusters,
and these thrusters are very low thrust,
so they have to spend a couple of weeks
getting themselves up to that operational orbit.
While they're flying in the orbit raise configuration,
they're trying to keep the spacecraft as flat as possible.
So that means each individual spacecraft
deploys its solar array
but aims the solar array down along the direction
of their travel so as to slice through the atmosphere
with as little drag as possible.
However, it's these solar panels plus the body
of the spacecraft that are reflecting
light back to the surface,
and so we initially see these
as the bright string of pearls
that cross the skies over time.
Over time though, the orbit does get raised,
and by the time is reaches its operational altitude,
it's now able to transition to its on-station deployment,
and the solar array raises
to a vertical configuration called a shark fin.
Now the solar array is able to provide
the maximum amount of power to the spacecraft,
and the spacecraft is reflecting
far less light to the surface.
Now, it's important to point out that these satellites
are only gonna be visible during the twilight hours
after sunset and before sunrise.
That's when the sun angles just right to catch a glint
of light reflecting off of them back to Earth.
Once twilight is over,
you really don't have to worry about them too much.
But during the orbit raise period,
the satellites are very bright.
They're as low as third magnitude,
and sometimes people have seen them even brighter.
Once they get on-station, it's a lot better,
but they're still kind of bright at magnitude five.
I mean, that is certainly faint enough to be
invisible from urban and suburban regions,
but telescopes operate under very dark skies,
out of the cities, on purpose, right?
Just to avoid light pollution.
So even fifth magnitude is still plenty bright
to saturate our detectors.
So one way to mitigate is to just wait
until after astronomical twilight
to start your observations.
But then you are giving up precious observing time,
and that's especially a problem during the summer months
when the nights are already at their shortest.
But the Starlinks are definitely bright enough to saturate
detectors and even create ghost images,
and that can just render entire observations useless.
And one way to mitigate this would be
to at least have some advanced notice
as to where the spacecraft are
and where they're going to be so that you
could take short exposures,
and try to avoid as many of those
satellite streaks as possible.
That might be doable with 1,584 satellites,
but when you get to 10,000, or 20,000, or 42,000 satellites,
it's really just no way we could think
of to actually overcome this.
Now, if you're field of view is small enough,
then maybe you do have a chance
at avoiding some contamination.
Maybe you'll just get lucky.
But if you're doing a wide survey
like the Dark Energy Camera,
then you're just gonna get streaks
that are going to render entire datasets useless.
In fact, no other observatory is going to be
more affected by Starlink than the Vera C. Rubin Observatory
which we formally used to call
the Large Synoptic Survey Telescope or LSST.
Its job is to scan the entire sky for a decade
looking for anything that moves or changes brightness,
anything that might go bump in the night.
To do that, it uses an ultra-wide field camera
that is larger than 40 times the full Moon.
And it will take up to 2,000 exposures a night
and just systematically scan the sky
for anything that's changing.
Among those things would be finding new asteroids
which could potentially pose a hazard to earth.
So the last thing we want to see happen
is our inability to protect ourselves from an asteroid impact
because we have too many satellites in the way.
Now, I do want to say that I don't think
SpaceX is really the villain here
because they've been on the record as trying
to mitigate their impact to astronomy,
they're well aware of the problem.
And yeah, Elon Musk got a little bit of heat
because his initial response was to say,
"Well, let's just put telescopes in space
"and not have to worry about that,"
but that just isn't gonna work.
I mean, read the room, man.
I mean, come on, that's not gonna happen, right?
It turns out launching a telescope into space
is really not the cost driver.
It's really operating the telescope,
designing it, building it, and operating it
that really costs a lot of money.
Ground-based astronomy is always gonna be cheaper
and easier to manage, both on smaller
and even on some larger scales.
Plus you just get to have bigger telescopes that way
which are necessary for things
like the Rubin Observatory and others.
Anyway, SpaceX has made it
clear that their goals are twofold.
First, they want to reduce the naked-eye visibility
of the satellites from a few weeks
to basically down to one week.
So minimize the amount of time
that the satellites are really, really bright.
A second goal is then they want to keep the satellites
as dark as possible even when they
are on-station in order to prevent any contamination.
To that end, SpaceX actually spoke last week
at a meeting at the National Academy of Sciences
to a panel of astronomers that were trying to work out
mitigation strategies against these megaconstellations.
It was a private meeting,
so there's no recordings that are being
made available as far as I know.
But they did release some slides,
and the also produced a really cool article,
and they have that on their website that you can check out.
I'll put a link in the description.
But they basically outlined what they're trying to do.
So for example, when the spacecraft
are operating on-station,
they want to reduce the reflection on antennae
during both sunset and sunrise.
And then during the orbit raise,
they want to change the orientation to reduce
the reflection of both the antenna and the array.
But they've also been experimenting
with a darkened version of one of their satellites.
They call it DarkSat,
and up until now they haven't really talked
about exactly how they were going
about treating this particular spacecraft.
But now they have, now they're telling us
what they have been up to.
They have these phased array antennae,
these are the white squares that you see
at the bottom of the chassis of the spacecraft.
This is the part that faces down to Earth
and relays the communications
between the spacecraft and ground stations,
and they took one of those,
and they treated it with a darkened material.
And they were able to reduce
the apparent brightness by a fair amount,
they more or less cut it in half
which is really a good start.
However, a dark spacecraft absorbs sunlight
rather than reflects it, so it starts to heat up.
And that can result in a overheating spacecraft.
And not only that,
but can also turn the spacecraft
from a bright optical source into a bright infrared source.
So if we're trying to do infrared astronomy,
we can still get these very bright satellites
flying overhead just radiating as infrared.
So what they are hoping to do instead is introduce
a visor mechanism, they're calling it VisorSat.
And the intention here is to just deploy
these kind of foam-like visors
that are transparent to radio,
but otherwise will just be opaque to visible sunlight.
They're also going to change the orientation
of the spacecraft during the orbit-raising part of flight.
They're basically gonna roll it 90 degrees
along the long axis of the spacecraft
so that any sunlight striking it with just be
glinting off the very edge of the panel,
and that should keep the spacecraft fairly dark as well.
Now, will this work?
Well, the only way to find out is to test.
And to that end, SpaceX have already begun developing
a newer, improved version of DarkSat.
They're already looking at future version
of spacecraft designs that will further reduce
their cross section and keep them even darker.
These spacecraft are going to be replaced
every three to four years
anyway with upgraded, next-generation versions.
So over time I would like to think that this problem can
if not completely go away 'cause it never will,
but at least it'll be mitigated enough that it
won't really have a& lasting impact on astronomy.
But we're also gonna have to work out ways
to mitigate from the ground as well.
So for example, the Rubin Observatory said
that they are working on a way to reduce
the amount of ghost imaging during a satellite streak.
And we're probably gonna have to come up
with some very sophisticated models
that will help us to predict exactly where
the spacecraft are going to be at any given moment
and time our observations appropriately.
That's of course going to result
in a degradation of science efficiency,
but hopefully it's something that we can live with,
and hopefully it won't get any worse.
I do want to say though that at the end of the day,
look, we don't have a choice.
I mean, Starlink is coming,
and it's not just Starlink but Amazon are doing this,
and there's another company that's out there doing it.
And who knows, that's just what's happening now,
but who knows what's gonna happen five, ten years from now
when other companies start getting into this marketplace
as the technology becomes cheaper and cheaper.
So at least SpaceX, to their credit,
they're not under any regulation,
by the way, to support astronomers.
I mean, we actually have regulations in place
to mitigate against interference with radio astronomy,
but we don't have any regulations
in place for optical astronomy.
So SpaceX are at least stepping up,
and they're gonna probably be
the largest players in this space.
I mean, they're gonna have the largest constellation
of these types of satellites,
so I'm glad that they are helping out with it.
But I know that these string of pearls that we see
in the sky from time to time are kind of cool,
but I think everybody would get
pretty irritated if they walked out at night
and saw nothing satellites crisscrossing overhead.
I mean, I think that's gonna get pretty old pretty quick.
And to their credit,
SpaceX seems to understand that as well.
So we'll just have to see what happens,
keep trying out new ideas,
seeing how we can mitigate against this,
and just making this work better.
And by the way, the Rubin Observatory,
i.e. the LSST, is a really exciting project,
so if you're not familiar with it,
I invite you to take a look at this video
that I'll have right here.
So take a look at that when we're done over here.
And I do want to thank my Patreon supporters
for helping the make Launch Pad Astronomy go,
all for the price of a cup of coffee every month.
So if you'd like to help out,
please feel free to check out my Patreon page.
And special thanks as always to my cosmological supporters,
Steven J. Morgan and Michael Dowling.
Thank you guys so much for all of your help.
And if you would like to keep informed
on the goings on with SpaceX, Starlink,
and most of all, the universe in general,
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Until next time, stay home, stay health,
and stay curious, my friends.