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What do you think
when I say
lasers in space,
lightsabers,
what do you think about when
I say space and airborne
laser platforms?
Deathstar, what else?
What do you think about when I
say laser based
propulsion for space travel?
Oh, frickin complicated navigation
math with way too many variables.
OK, no, seriously,
in the next talks, we will learn what's
really behind this terms.
Peter Bush camp would teach us
not only basic physics,
but he will also teach us about
the boundaries of lasers
in space.
And we will learn about space travel with
lasers, which absolutely sounds like
science fiction, but apparently
is already a reality.
Peter Buscombe works for
the infrared group of the Max
Planck Institute for Extraterrestrial
Physics, where
he's building the world's most sensitive
instruments for space observation.
He's also active in the Munich Pyfrom
community where he's building backbones.
And he was the head of the Public
Astronomical Observatory in Bielefeld.
Are you sure about the Bielefeld
part?
Yeah, please give a
warm hand for applause for Roskam.
All right.
Yeah, this is essentially a follow up
talk from
last year.
I don't know who was there last year.
I talked about how to shoot
lasers into the sky and
use them for astronomical purposes,
essentially to correct the atmosphere
above us, to get
clean and undisturbed images
here on the ground and not just
from space
telescopes on satellite platforms.
So this year, it's lasers in the sky.
I'm.
It's only 30 minutes.
Sorry, I
will give a brief overview of
some topics, what is actually
now already flying above our heads,
what is what
some people think should be flying
soon above our heads, and
some others are pure speculation.
So first, want to talk about laser
propulsion?
Actually, this is the second reason
this talk came to be because I was
talking to Liz and she wanted to do
something about interstellar and
interplanetary colonization and said, OK,
cool, maybe we can combine it
and then talk about also about
photonic propulsion and so on.
And then we just skipped it into the next
talk to have more time for other stuff in
the other talk.
After that, we're talking about
laser brooms,
how to clear up the skies
above us with lasers.
It's going to be about laser sensing,
which is routinely employed every day.
If you look up the weather on your
smartphones, there's a
fair chance that you will be looking at
some refined laser data that has
been taken either from ground into
space or from space to ground.
And to
finish, we'll talk a bit about laser
communication.
Of course, this is something a lot of
people here in the audience are also
interested in.
It's the chaos communication Congress,
after all, and this is
something that takes place above our
heads, is being built right now
and is actually pretty exciting.
So first, let's talk about laser
propulsion.
Laser propulsion is a
method of pushing something
forward with just light.
How does this work?
Well, I mean, photons are not just there
to illuminate things, which
they do a pretty great job.
And they also, of course, carry momentum.
It's just a tiny bit.
It's the energy divided by the
speed of light.
But still, there is a bit
of momentum being transferred from a
photon when it hits some surface.
To get a rough idea how much this
is, if you are in Earth orbit,
you get
the amount of photons from the Sun, which
is equivalent to the so-called solar
constant, which is one thousand
three hundred sixty one,
I guess if I remember correctly,
watts per square meter.
This translates then if you have a
solar cell which you
put into Earth orbit and just
let the photons from the Sun push it
forward, which is equivalent
to well, it depends a bit on your
orientation of the scale.
And if it's a black cell of photons get
absorbed or they get ideally reflected
if you have. So that means if you have an
inelastic collision on an elastic
collision for the physicists in the room,
but roughly you get around seven
micron Newton,
that's not much.
Of course that's not much.
Well, you can say a scale
up our yossele.
It's not just one square meter.
Maybe it's 100 by 100 meters
that the point is it may be just
a very tiny fraction from each
photons, but there are a lot of photons
and this is for free.
So if you maybe have a mission, which you
just want to push far away and you have
time on your hands, maybe this is
something you want to do because this is
constant.
It's not like a chemical which burns
off after some time.
You don't have to bring huge amounts
of propellant into space for that.
This may be an option.
Is this pure science fiction right now?
No, actually not.
Um,
this is a representation
of a test solar
sail satellite from the
Japanese Space Agency,
which has been launched in 2010.
It's called EQUASS.
And then you get a rough idea
of what this is actually looks like,
because if you just let this is just a
sail with something in the middle.
But, yeah, this is actually flying right
now. They hope to they last communicated
with it in 2014 and they
hope to communicate
in the next year with it again.
And what you see here is in the middle,
for example, there is the little payload.
So some experiments,
a little transmitter to communicate back
to Earth. And these blue
stripes you see around the middle, these
are actually solar cells, which then
produce the electricity for the
experiments on board
because this thing is 40 meters by 40
meters. So this is not much, but it's
a nice technical demonstration platform.
Of course, if you want to go really
into serious propulsion
with that, you'd rather look
maybe at sales, which one hundred meters
by 100 meters.
Or even a kilometer, we don't have
a real clue yet how to make them how to
bring them into space, what to use
actually as the sailing material, how
to unfold it properly, but will
eventually get them.
Another thing you could be thinking of
is, of course, not the sun, but of
course, to shine a big
laser on this, maybe a ground
based laser, maybe a space based laser
that is, of course, project star shot.
It's going through the media all over the
place right now.
This is a very interesting concept which
uses a ground based or maybe space
based laser.
And of course, there you have targeted
and directed laser light.
So you don't have the
the one over R-squared
problem from the for the when you get far
away from the from the sun.
This is an option, another option.
Using lasers in a in
a in a
similar manner is not to just
push the sail forward with your
laser but to use the laser actually to
transfer energy to your spacecraft
and these so-called laser energized
laser based propulsion.
This is nothing like a sail,
although this might be look like it.
I like these 60s and 70s space
and so on.
The very on the very left, you see
a laser array here in some, uh,
um, orbit around
one of the moons of Jupiter.
I think it should be either because of
the guys down there anyway.
So this is sending out a powerful
laser beam to one of these reflectors
on the spacecraft itself in
the front. Again, that's the payload at
the very real again, that's the engine
in the middle. There's everything else.
And so what we do here is we
do have propellant on board.
Um, but unlike in the
chemical rocket where we use the
propellant for the for the energy
and also the debris from the
propellant, the dust and the
after the what comes out after the
reaction for the thrust here,
we use some external means of energy
transfer on a propellant which gets
then pushed out of the
of the nozzle of our
propulsion system and then pushes the
whole thing forward.
If you think of a normal jet engine,
it's the same you use it's the medium
and you use kerosene as the
as the energy
to actually drive the engine.
Um, another very
interesting thing which is
being discussed in the
scientific literature right now is
the so-called photonic laser thruster.
Um, and for some applications
also in military application,
there is the the great wish for
having formation
flying satellites, which
also maybe are flying together like this,
and then they expand into a nice
formation and have a nice long bass
line between them and they should get
together again, um,
for some radar, for some interferometry
of radar on the ground to see where,
you know, uh, yeah.
All this kind of stuff.
Um, this can be done with
teachers to just have
a rope between those.
But if you have small satellites,
um, you maybe want to
think about something else and this is
then what you do.
So you have a laser between those two
vehicles. The mission vehicle and the
resource vehicle can also be
of comparable size.
Doesn't matter. The interesting thing is
here you do reduce the photons.
It's not just that you shine them on a
reflecting surface, like on a sale
or as we've seen
in the in the other case.
But you have them actually enter
like a laser cavity.
They are mirrors to each side of this.
And so you reduce the photons.
And this is very efficient in pushing two
small masses out of each other.
And then if you just switch it off, they
will gravitate together again.
This is a very nice thing to
have formation of light, at least as
proposed. It's not yet demonstrated in
space, but we'll soon will see
this.
Laser brooms,
if you look at the earth from far
away, or maybe not even so far away
within the orbit
of our moon, around the
Earth, and if you exaggerate a bit, this
is how it looks like Earth is enshrouded
by junk right now.
This junk has been put there
by us.
We are 50 years of space exploration,
upper stages of rockets having collided,
tanks being ripped off,
satellites.
We have collided.
And this makes up a huge amount
of space debris, as it is called.
There are around 30000
objects of the size of 10 centimeters
in space around Earth, about
several hundred thousand of the size of
one centimeter. So some thumb size
and over almost 200 millions
of them smaller than
one millimeter. So the ring you see here
is the, of course, the geosynchronous
orbit. And in low earth orbit,
you also see this.
Is this a problem? Yes, this is a
problem.
Here you see a nice image from ESA
at the end, I think it was in this
September. Twenty sixteen
Sentinel one A is one
of the new class Earth observation
satellites from ESA.
And actually on the left you see how
the one of the solar panels looked like
before the impact.
And then on the right you'll see, yeah,
there was some space
debris hitting the satellite and that's
about 40 centimeters in
diameter damage on one of the solar
panels.
And this roughly corresponds to
some space debris, junk piece
of around five millimeters or
even less.
So we have to think about if
now space traffic is
increasing and how to how to get
rid of this.
Um, one concept is to
actually shoot up this from the ground.
Of course, not in a matter
that you now destroy these
pieces and just split them up and even
smaller pieces.
This is not what we want to do.
Of course not, because we want to reduce
the size. How do we reduce the size of
these things?
Well, if we get them
into an orbit, that they will just
gradually go down in Earth's atmosphere
and just burn up in the Earth's
atmosphere. Problem solved.
And this is actually what we what is
being proposed right
now. And if you take a
commercial
high power laser at around five to 10
kilowatt, which you can buy and put
it on a decent telescope,
you could
move the orbits or the orbital
velocity of space
debris of around one to
10 centimeters by one millimeter per
second in
only shining your laser
at it again, it's like a solar sail.
It's just pushing the stuff with photons.
So it would it will have
a slightly different orbit.
It will then go into Earth's atmosphere
and then just burn up.
Of course, this has also been proposed
from space.
Actually, this is the same guy who
is now in this project started
a project looking
at all that and at all
despite two thousand and fifteen,
if you want to look up those papers, that
quite interesting reads.
And for example, this is a proposed
satellite that flies
now in deeper space.
They did not just think about
deflecting space debris,
but also here targeting
asteroids. So this is a
platform which has big arrays
of solar cells to power the onboard
lasers. And then we just
shine this laser at the asteroid
for quite some time.
It could be a year. It could be maybe 10
years. If we identify the threat to
Earth early enough.
This is easy.
Also, by the way, if you're interested in
this stuff, there is a
conference about planetary defense
conference.
Just look it up so you can take part.
This is people are discussing seriously
about this.
Um, what you do then is not
to just push the asteroid with your
photons, but here
asteroids.
Very often contain frozen
frozen material, frozen gases,
so you sublimate those gases
and actually while the gas
sublimates from the from the asteroid
itself, it creates a bit of thrust.
Of course, it's
just like a little chemical rockets
thruster and that gradually
pushes things out of the way.
This is the so-called Starlight
Mission, as it's called.
There's also a disaster which then
proposes to have a dedicated
shown on the left, a a platform with
even more powerful lasers and then
have an array of
mirrors somewhere in space to direct
this, for example, to an asteroid.
Maybe this just needs half, half
a day each each day for
four or five years to be deflected.
So it will not hit us in 30
years from now. And then we turn this
mirror in another direction.
And just to push a bit, our spacecraft,
our solar sail spacecraft, like the
project star
thingy, which we want to push through
space. This could be done.
It's shown here in detail how
you would do this with an asteroid as
a set. You just,
uh, sublimate the the
gases there and use them as thrusters.
This is, of course, not what we do
have in space right now.
It's being proposed.
What we do have in space right now
is laser sensing,
laser sensing, so-called light
on its light detection and ranging
like radar.
And what we do is we do have
a transmitter on a spacecraft.
Um, it shines down into the
atmosphere. It's a pulsed laser,
just like the laser in last year's talk,
which we shoot upwards.
So we know exactly when
we started the pulse and where it is
after a given time.
So if the pulse travels down into the
atmosphere, it will, of course,
traverse different parts of the
atmosphere
and thereby probe different layers, maybe
high clouds, high winds, more lower
winds or something like that.
And it will back scatter.
And we, of course, know the time the
light travels downward and upward.
And so if you make a graph of the signal
intensity versus time, we can learn
about the different heights in the
atmosphere.
We cannot just do this with one leg so we
can maybe do it with two lasers
and therefore use different wavelength.
That means looking at how the
one wavelength is
absorbed by the atmosphere and then
looking at how the other wavelength is
absorbed by the atmosphere and then
correlate this and then maybe even learn
something about the chemical,
uh, chemical composition
of the Earth in our line
of sight.
Or we do something like Doppler shift
measurements. And they are we can learn
about, for example, how wind is
blowing in the atmosphere.
So our timeline is essentially a set
the distance from our spacecraft, which
then translates to altitude so short
it just means it's near to me.
It's the high atmosphere and the far
away time signal is,
of course, then the grantly are maybe
this is hopefully being launched
next year.
This mission has been on the menu
a bit longer. It was a bit delayed.
This is Isa's new satellite
for just profiling the wind.
And you'll see an artist's description on
the on the right.
The only actual instrument on this on the
satellite will be this wind glider.
And it would probe down into the
atmosphere and give you exact
measurements how the wind is blowing.
So this will then use this Doppler
method where you send out
a signal and just measure, um,
the, um, the
shift in frequency from the return
signal, which is then influenced by if
you have maybe hit something that is
receding from you or coming towards you,
of course, you have to calculate out the
satellite motions itself and earth motion
at double-blind, whatnot.
So this is hugely complicated.
And if you want to have a look at the
instrument, it's looking like this.
And this is another lesson.
We had this in in the talk before.
Space technology is really,
really hard. I'm not saying it's not
possible. It is possible.
It's it is being built.
But it's not just you don't just
fumble something together.
And who has ever
put a I mean, we
have heard by Andre's talk
about the the microscopes and how to
build your own microscopes for
for maybe
doing laser microscopes
to to enhance the resolution and
how to build them on a on
a on a on a typical optical
lab bench
here. You do it essentially the
same, but also you have to launch this
thing and actually.
This is the most critical part because
this would be shaken like hell, and
whoever has just had a laser ready
resonator alone
mostly is not a fan of.
Yeah, just come into my lap and kick my
table a couple of times and let's see
if it's still working.
This will be happening during launch.
And so you have to really make it perfect
and tested and tested and tested and
tested and tested and tested again.
And when you think you have not done
enough testing your test.
No.
Um, another thing, of course,
you can make distance measurements, this
is used on the, uh, on the
European Autonomous
Autonomous Transfer Vehicle, the ATV
that docked to the International Space
Station.
This is how it looks like.
And there's a little lighter interface on
the side and it
sees the International Space Station then
in falls colors, which mean
this green stuff is very
new to me. This it's the French
way I have to dock.
And the red part is then
at the very back. This is the truss
structure of the International Space
Station. And the whitish thing in the
middle is one of the Soyuz capsules that
is right now docking on the International
Space Station.
So this is being used routinely
now in space and said
you can maybe see it in your
weather app on your smartphone every day.
I'm not talking about this one.
This will be in the later, actually,
maybe in the next talk.
You can also do gravitational waves
and then you have to communicate between
different satellites, not
in terms of just exchanging data, but
you're actually flying a Michelsen
interferometer in space and measure
the relative distances between
three satellites separated by
thousands of kilometers in space to
detect gravitational waves.
We'll learn about this in the next talk,
some of the remaining time.
Let me briefly
give you an overview of how
our communication is actually affected
by lasers in Sky.
This is mostly developing right now.
So the first satellites
who employ this on commercial platforms
are already in space.
The next will be launched next year and
the years after that.
Why do we want to do this
laser communication?
I mean, can we just do the normal
KNU or Cuban
radio frequencies, which we are
using? I mean, satellite TV, it's
working fine.
The thing is, of course, with the laser
communications, you do have a much higher
bandwidth and that means you
have several tens of gigabits per
second per channel.
It's very, very efficient.
And this is actually interesting for
space. And again, because have learned in
the previous talks that each
kilogram you want to put into space
costs you a real a lot
of euros.
And so if you look at radio frequency,
you get about a point
five megabits per second per
watt. So electrical
consumption and kilogram, if you're
using it as a tool, if you're looking
at a laser communication system, it's
more in the range of five
megabits per watt and kg.
Um, the communication terminals are
smaller and they are.
And if you, for example, have a satellite
pointing just down on earth
with its radio footprint, the radio
footprint is really, really large.
If you do laser communications,
you can get down.
You are even with a small telescope
of about 20 centimeter size in
diameter on you on your spacecraft.
You can get down your footprint
on the Earth to about six
kilometers. So this is a very, very tiny
spot. So if you're the only one who sits
in the middle of the desert observing the
signal, so nobody is going to be
eavesdropping on you.
Also, there are some ideas
how to do this interferer metrically.
And then if you actually were to
intercept the signal, you would destroy
the interference pattern.
And this is not going to work on
this is how roughly looks like what we
want to do. So this is what we have right
now. It's the radio link between a ground
station, also called ground segment
in, uh, in space lingo.
And this is the satellite bus up there.
Yeah, it's called satellite bus.
Don't be uh, it's
just called, um,
and it has the payload on top.
So if you ever payload on satellite by
satellite, but the satellite and payload
is the stuff you put on them to do the
actual thing you want to do.
Um, this is for example, in geostationary
orbit for satellite TV.
Um, but there are other things also
flying around in geostationary orbit
or in low earth orbit and in low
Earth orbit. You see that the orbit
just vanishes behind the
horizon there. So if you have maybe
a satellite that looks at
Earth like probing of the wind
like we've seen before, it is only
visible from your ground segment from
your ground station for a brief period
of time. Who has done
SDR radio on
the no satellites.
Anyone?
Oh, yeah. OK, so those people
do know what I'm talking about, so you
have about 10, 20 minutes
if you have a real nice
position where you can see the satellite,
where you can record the weather
image that gets transmitted from the but
after then nothing.
So it would be nice, for example, to have
an optical link, high data rates
said to one of the geostationary
satellites and then have them maybe
over, then talk to your
low Earth orbit, maybe then over other
hubs when it gets out of the reach of the
one geostationary satellite and so
on. So this could be really interesting.
Again, yes, maybe radio also, but
ESET high data rates
and all the
pluses that come with the lasers.
So for the technically inclined
in this audience, it's
how do we communicate?
We have three different types of
modulation. This is the one off keying
the OK, that just means you
just switch your laser on and off
Marsing.
It's what you have in your fiber line
cut. Maybe at home
it's what you do from ground to space.
You have postposition modulation.
This is what you have in your TV remote
and actually.
Jump, jump, jump, jump, jump, jump,
jump, jump.
Perfect.
So this is what you do.
All right.
This is what you do from ground to space,
because this is very,
very immune to
disturbances by the atmosphere.
You still have to look through the
atmosphere.
If you have nothing in your line of
sight, you can, of course, go to nice
modulation principles
like a binary face shifting
or higher
modulation schemes.
But this means that if you modulate
the phase that you do not want to have a
medium in between, which is disturbing
your your face and this is the
atmosphere. So this is only used for
space to space links.
This is how a laser communications
terminal looks like.
You have the laser and everything down
there somewhere at the bottom, you have
two mirrors
reflecting it. Then out of the central
aperture at the very front,
it's about 13 centimeters usually.
And this is how it looks inside.
So the laser is at the very bottom there.
And then you have diverse mirrors in
there to get actually the laser out
set. Different modulation
schemes are being used, different
frequencies are being used.
Typically, if you want to reuse
telecommunication equipment
off the shelf, if you use one thousand
five hundred fifty nanometers, you get
this in the normal telecommunications
industry. If you want to,
for example, imply a new Dunja laser,
the infrared part, you go for the
10 64 nanometer
and people are working together in
space. So, for example, here it's the
lunar laser communication demonstrator
from from NASA talking to as
ground station in Teneriffe.
And this is how it looks like from space.
Actually, there's no video online.
But yeah, um,
if you look at the communications unit,
that is the optical module, this is just
laser. But of course, internally you need
controller electronics, you need a modem.
But the nice thing about is
if you if
you do this standardized, you don't have
this complicated set up yet.
For example, seen in the experiment
for the wind measurements with the Leida
looking down here, you just take
a commercial off the shelf units from
telecommunication industry, slap it
together and you're got to go.
You can also do this for deep space
communication. This was a mission
proposed by NASA, said it was canceled
to do this up to Mars.
You can do this from satellite to
satellite.
This has been done with the Terraza
satellite from ESA and the NASA
and via satellite.
And right now, the Europeans building a
data relay system around Earth.
It's called the DRC, the European data
relay system.
Um, it's hosted on a commercial
satellite from that and
a dedicated satellite that will be
launched later.
And you'll see here the laser links, for
example, in red between the satellites or
in green to the International Space
Station. And then they have also radio
frequency links down.
The next step is already
in the works. It will be the so-called
gluconate.
So position various
satellites on a
geostationary orbit around Earth,
having intercommunication from satellite
to satellite on laser based.
And of course, the next step
will be this one.
And
my personal interest would be then to
have this one.
Is there anything else?
Yes, I know that in the abstract
I did mention.
We had stuff,
communication, laser based
from submerged submarines.
Two satellites in space,
yes, this is being done.
Downside is you will not find any
open access publications
which you can show, which can be streamed
into the Internet. Just Google for it.
You will find really nice sets of
information there.
It is that for certain frequencies
in the blue and in the green, actually,
the ocean is pretty transparent to this
laser wavelength.
And so you don't need some,
uh, some something floating on
the surface of the ocean and then maybe
have a fiber line down to your submarine
and then. No, no, no, no, no.
You just shine the laser at the ocean
and this is the other way around to
just look it up. It's pretty interesting.
Some of the stuff has been declassified.
Well, actually, that's the only source
which I also have because I don't work in
this kind of stuff.
And if I did, I couldn't tell you.
Yeah, so there's a lot of stuff going
on in space above our heads right now
and in the near future,
just watch out with your spaceship if you
do the asteroids.
We don't want to see that.
OK, next. OK, thank you.
Thank you very much for this amazing
talk.
We perhaps have time for
one short question, a really
short question.
So somebody's already on the microscope.
He's driving. How do you get a shot?
Question number two.
Yeah, try OK.
It's just about how far the
weather affects communication.
We had a company that had two
locations and tried to do laser
communication and it turned out focus,
even snow, even more evil.
So how is it from
space to earth?
Yeah, you do have these problems,
of course, too.
You do have the only
thing you can do is maybe use modulation,
which is more immune to
it. Otherwise, if you have really dense
fog at some point just out
and therefore the Groundling
segments are often still
you've seen, for example, in the Globe
Net in the European data relay system,
the Groundlings are all always at least
back up with radio links.
So it's also getting a little too
loud here to answer questions, really,
so if you have any more questions,
just come here to the front and ask Peter
directly.
And now we want to end with
a last big round of
applause to thank our speaker,
Peter.