- 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,
please do make sure you subscribe
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Until next time, stay home, stay health,
and stay curious, my friends.
