This past month's launch of SpaceX Starlink
satellites was a moment long planned Elon
Musk and SpaceX.
Known as a satellite constellation, the company
has sent 60 of a planned 12000 satellites
into orbit.
The brilliant "train" in the night sky that
is SpaceX's first 60 Starlink satellites has
wowed some sky watchers.
What Elon Musk and SpaceX did not expect,
though.
Astronomers have already raised concerns about
the effect these and similar launches could
have on our ability to view the stars.
Now, the International Astronomical Union
(IAU) and International Dark Sky Association
have weighed in on the issue and underlined
the potential problems to science that SpaceX
satellite launches could cause.
The Starlink constellations, it turns out,
could be threatening the study of the night
sky.
Many in the astronomy community are concerned
that this SpaceX Starlink mega constellation
might be too bright, and the sheer number
of satellites that SpaceX wants to launch
could muck up their telescope observations
of the Universe.
SpaceX launched the Starlink satellites Thursday,
May 23rd into an initial orbit 273 miles (440
kilometers) above Earth.
Each satellite is equipped with Krypton ion
thrusters to raise its orbit to a final 342
miles (550 km).
"I know people are excited about those images
of the train of SpaceX Starlink satellites,
but it gives me pause," planetary astronomer
Alex Parker wrote on Twitter as the first
videos of the Starlink "train" were popping
up.
"They're bright, and there are going to be
a lot of them."
In a series of Twitter posts, Musk assured
astronomers and the public that the SpaceX
Starlink constellation shouldn't pose an issue
for astronomy.
In this video Engineering Today analyzes,With
SpaceX Starlink, why Astronomers Fear They
Are Losing the Fight to Preserve the Night
Sky?
Why International Astronomical Union and International
Dark Sky Association have weighed in on the
issue and underlined the potential problems
to science that SpaceX satellite launches
could cause?
Let’s get into details.
Light pollution is a serious problem for astronomers,
as it makes it harder to see dim stars in
the sky.
Anyone who has lived in a busy and well-lit
city knows that urban light pollution blocks
the view of most stars.
In fact, estimates state that around half
of all Americans can barely see any stars
in the sky at all.
When discussing light pollution, we are usually
talking about light generated here on Earth,
from streetlights and other sources on the
surface.
But the large number of satellites launched
like SpaceX Starlink in the last decade has
raised concerns about light pollution in the
atmosphere and in the sky as well.
In particular, satellite constellations, in
which whole networks of satellites are launched
together, are a source of worry.
Satellites are already an issue for astronomers
studying celestial objects in deep space.
In order to get detailed images of objects
many light-years away from Earth, astronomers
take long-exposure shots of the sky with their
telescopes.
This type of imaging entails leaving the telescope
exposed to light for minutes or hours.
As a result, scientists can gather light from
a very distant, faint object and figure out
more about it.
For instance, it’s a great way to learn
what kinds of gases are in a faraway galaxy.
Each type of gas emits different types of
light, which astronomers can detect and identify.
But whenever a super bright object like SpaceX
Starlink Satellite passes through the field
of view of a long-exposure shot, the observation
gets muddied.
The light from that object tears through the
image, causing a long, bright streak through
the sky.
Satellites can be particularly bright since
they’re often made with reflective materials
or have solar panels that bounce light from
the Sun.
The International Astronomical Union has issued
a statement saying it is "concerned" about
satellite constellations and what they mean
for the future of astronomy.
"We do not yet understand the impact of thousands
of these visible SpaceX Starlink satellites
scattered across the night sky and despite
their good intentions, these satellite constellations
may threaten both" nocturnal wildlife and
astronomical research, the IAU says.
The risks are twofold—the satellite constellations
could affect both visible and radio waves.
The International Astronomical Union argue
that the SpaceX Starlink satellites will affect
readings from highly sensitive telescopes
like the Extremely Large Telescope.
Because the SpaceX satellites are made of
reflective metal, they reflect light from
the sun at sunrise and sunset and cause bright
white lines to appear across telescope images.
The problem is there is very little public
data on how such giant constellations could
pollute the night sky with light.
There’s been a lot of discussion about how
these mega constellations will potentially
run into each other, causing debris that could
pose a danger to other satellites in the sky.
But the discussion of light pollution exploded
over the weekend after amateur astronomers
released footage of the SpaceX Starlink satellites,
showing them to be much brighter than people
imagined.
But exactly how often this interference will
happen remains to be seen.
It all depends on where the satellites are
above the Earth, the time of day, and the
time of year.
Satellites can be seen for a few hours around
dusk and dawn when they catch the light from
the Sun as the sky dims, but they won’t
reflect light for many hours of the night
whenever they are in the shadow of the Earth.
However, in higher latitudes during the summer,
satellites can be seen throughout the evening.
That’s because they’re high enough in
the sky to still catch the Sun and stay out
of the Earth’s shadow.
The bottom line, If the satellites are in
lower orbits, they will be brighter but visible
for less long.
If they’re higher, they’ll be fainter
but visible for longer.
Although most of these reflections may be
so faint that they are hard to pick out with
the naked eye, they can be detrimental to
the sensitive capabilities of large ground-based
astronomical telescopes," like the Hobby–Eberly
Telescope in Texas.
The second problem relates to radio interference.
Radio waves have been responsible for some
of the biggest astronomical discoveries of
the last decade, including the first ever
photograph of a black hole.
Aggregate radio signals emitted from the satellite
constellations can still threaten astronomical
observations at radio wavelengths.
Satellites are designed to avoid interference
with the radio frequencies used in astronomy,
having many satellites in a constellation
giving off radio signals can cause problems.
It's not just scientific observations that
might be at risk.
The International Dark Sky Association (IDA),
which promotes the concept of night skies
without light pollution, has issued a statement
saying that "we do not yet understand the
impact of thousands of these visible satellites.
"As someone who cares deeply about the night
and our access to views of the universe, seeing
the SpaceX Starlink object train pass over
Tucson two nights after launch was jarring,"
Says John C. Barentine, an astronomer and
IDA's director of public policy.
"And it became clear by the end of that weekend,
based on member feedback and comments on our
website, that we had to do something.
Currently, there are about 5,000 satellites
in orbit around Earth, around 2,000 of which
are still operational, according to the most
recent report from the European Space Agency.
These objects already cause the occasional
streak and headache for astronomers.
But with the addition of SpaceX Starlink constellation,
as well as other proposed mega constellations
from OneWeb, Telesat, Kepler Communications,
and now Amazon, the number of operational
satellites could increase significantly.
And that could drastically up the risk of
satellites streaking across a telescope’s sightline.
Satellite constellations are being sent into
space with clear purposes—in SpaceX Starlink
case, to expand internet access to countries
lacking infrastructure.
The International Astronomical Union and International
Dark Sky Association both acknowledge these
as worthy goals, Barentine says, acknowledging
"good reasons to put objects in orbit for
their clear benefits to humanity."
SpaceX CEO Musk wrote on Twitter on May 27,
that he's already instructed teams to look
into making future Starlink internet communications
satellites less shiny to lower their "albedo,"
or reflectivity.
"Agreed, sent a note to Starlink team last
week specifically regarding albedo reduction,"
Musk wrote.
"We'll get a better sense of value of this
when satellites have raised orbits & arrays
are tracking to sun."
Elon Musk re-affirmed those reasons in a tweet,
saying that " potentially helping billions
of economically disadvantaged people is the
greater good," Musk wrote in response to a
comment on the service Starlink's constellation
would provide.
"That said, we'll make sure SpaceX Starlink
has no material effect on discoveries in astronomy.
We care a great deal about science."
And the satellites can be moved to reduce
reflectivity, Musk added.
"If we need to tweak sat orientation to minimize
solar reflection during critical astronomical
experiments, that's easily done," Musk wrote.
SpaceX Starlink shouldn't affect radio astronomy
research either, Musk added.
"We avoid use of certain lower Ku frequencies
specifically for radio astronomy," he wrote.
And then there's all those other satellites
up in space, he added.
"There are already 4,900 satellites in orbit,
which people notice ~0% of the time," Musk
wrote.
"SpaceXStarlink won't be seen by anyone unless
looking very carefully & will have ~0% impact
on advancements in astronomy."
But Barentine is skeptical that an easy solution
will be found.
"Simply making the satellites dark in order
to reflect less sunlight probably won’t
work, because the emission and re-radiation
of heat can actually push on the satellites
and change their orbits," he says.
"Sending them up to higher orbits doesn’t
seem feasible, either, because it would then
involve stronger radio transmissions to and
from the ground — which will certainly have
an impact on radio astronomers’ work."
But neither side will likely be going anywhere.
"The bottom line," Barentine says, "is that
there doesn’t seem to be an approach here
that will satisfy both parties, one that puts
objects of a particular nature into particular
orbits that render them essentially invisible
to astronomers but that also enables achievement
of the technical goals of the satellite constellations."
In fairness to SpaceX, the International Astronomical
Union has acknowledged that the visual impact
of the satellites is much higher in the first
few days after the launch.
The satellites have already grown less bright
and will continue to fade as they reach their
final orbital positions.
But as the IAU points out, this is an unregulated
frontier and governments and individuals should
consider the potential scientific detriment
to these kind of launches.
