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[Music]
so our speakers lonus and Nicholas have
devoted their professional careers to
ESO they've been visitors to Congress
since 30C 3 and now from our previous
talk about a space-based telescope we
are going to learn all about the EXT
extremely large telescope which is based
here on planet
Earth hello everyone and good evening um
we are going to talk about the extremely
large
telescope um first about us uh we both
work at the European Southern
Observatory or short ESO uh Nicholas
works as uh an software engineer here on
the observatory Control software and
lenus works on Adaptive Optics Control
software now let me start with a few
words about the European Organization
for astronomical research in the
Southern Hemisphere or a bit shorter
European Southern Observatory or usually
by its acronym ISO it is an
intergovernmental organization that has
been formed in
1962 and at the moment has 16 member
states which are the ones with the flags
that you here and one special member
state which is Chile which is our host
country and in addition we also have
Australia as a strategic partner these
member states Define eso's mission which
is to design build and operate Advanced
groundbased observatories and to Foster
International collaboration for
astronomy ISO is I think from our or at
least from my personal experience not so
widely known so often we are confused
with Isa Isa is a completely different
organization founded a couple C of years
later Isa does space telescopes Rockets
satellites these kind of things ISO does
groundbased
astronomy so our headquarters are
located in Gin by minin this is at the
same campus where uh for example the T
Munich has a number of uh departments
and also various Max Blan institutes are
there our all our telescopes are
actually located in the atakama desert
in Northern Chile we have about 750
staff two3 of them are working from ging
and one3 of them is working in Chile the
member State's contribution in 2021 was
€12 Million EUR so this is these are
your tax Euros that is spent on
ISO and here you see the locations of
our observatories so uh Santiago is the
capital of Chile and the oldest
Observatory is lasa that we have which
is close to La Serena and then uh The
paranal Observatory on the mountain s
paranal which is close to
anagasta then chantor close to San Pedro
de
atakama close so which is then close to
Bolivia and the Argentinian border and
the elt which will be located or is
being constructed at sah
amazones so why are all those telescopes
in the atakama desert well if you look
at this picture which was taken on a
service mission of the h space telescope
you see that there are no clouds it is a
desert that is very arid so no humidity
uh goes in this area and in addition
there are very high mountains and this
makes a very good uh conditions for
astronomy for groundbased astronomy in
particular so laa as said was our first
Observatory that started in the 1970s
there are a few telescopes from us but
nowadays also a lot of telescopes from
the National Institutes for example from
the max Blancas airshaft and they reuse
the infrastructure that we have um at at
the site and just operate their own
telescopes there as
well now uh on the mountain cop paranal
we have uh for example the very large
telescope VT which consists of four uh
unit telescopes with 8.2 M diameter so
these are the the big ones and then in
addition for small telescopes with 1.8 m
uh diameter which are called auxiliary
telescopes and uh in the optical
Spectrum uh The paranal Observatory is
considered our Flagship facility at the
moment then a couple of years later
there was also um the the atakama large
millimeter and submillimeter array went
into operation it is located at an
altitude of 5,000 m which is very high
on a plateau called Shor and uh this is
a joint project by ISO and North
American and East Asian
partners and these are 66 radio antennas
that can also be moved around and also
operate as an
interferometer okay so why do we want to
build another
telescope um scientists or specifically
astronomers want to study earthlike
exoplanets they want to look for
biomarkers on
exoplanets there's the dark matter which
they want to study and understand better
and there are faint objects in our solar
system which are difficult to uh to
observe but um also interesting for
astronomers therefore we need a
telescope which has a high angular
resolution which means that we need a
larger primary mirror
diameter and we want want to increase
the light collecting
surface so we need to increase the
mirror size and with more light more
fainter objects are observable and we
can use shorter exposure times to see
them so this is a rendering of the elt
what it is going to look like
roughly um it is uh it will have a 39 .3
M primary mirror if you look at this
room from the the width of this room is
36 M so the primary mirror would not
even fit in here this is the amount of
this is the sheer size of the
mirror the site is a s amazonus which is
at
3,45
M which is roughly 23 km East of Sanel
where the very large telescope is it
will cost around 1.3
billion and that is for the construction
period from 2014 to
2028 and the first light will be um
approximately on 2028 at the end of 2028
there are two similar projects there's
the giant megalin telescope which is 25
M and a 30 m telescope which is 30 m in
size
now if you you can see here is a size
comparison of the El and the left this
is the berina Broner
tour um I don't know how many of you
have been to Berlin uh this is 20 M High
the Dome or the the building of the El
will be 80 M High the Dome so the top
part will have a diameter of 88 M and
the building on the ground this is the
auxiliary um building will have a
diameter of 120
M uh the Dome so the top part is there
to protect the telescope from the
environment so this is the sun the wind
the temperature so temperature
differences dust from the desert and
Rain there is a ventilation and air
conditioning system to prevent Dome
seeeing Dome seeeing is when you have a
different air temperature inside the
Dome than outside so you have an air
movement from inside the Dome to outside
and that creates distortions of the
light which you want to avoid so the
Dome is cooled to the outside
temperature and this ventilation and air
conditioning system
needs three megawatts to for
operation this is this allows the Dome
to be cooled down by 10° over a period
of 12
hours there's also wind screen which you
can see between the two doors this is to
deflect away the wind that is directed
at the
telescope um the reason for that is that
if there is wind pushing against the
mirrors it would make pointing of the
diff of the telescope difficult so in
order to prevent pin the wind of pushing
too much against the MSE there is this
wind screen also because we are in a
geologically active region we have
seismic isolators for the telescope
itself and the telescope and the
Dome so the main structure is the
telescope and the Dome are on different
foundations
actually so so this is the main
structure so the inside what is inside
the Dome um you can
see this is the platform on which it
rotates so horizontally where it will
rotate like this then you have the
primary mirror here there's a mirror
Tower where the other mirrors are there
are two instrument platforms here and
here so the instrument is basically what
collects the light and analyzes it or is
a camera or can be a spectrograph for
example so to see what Spectra of light
is emitted by some part on the
sky and there is also the altitude axis
which goes through here so the pointing
and the
height so the elt has a unique Optical
design um which consists of five mirrors
you can see here uh so the mirrors are
just was called by the order in which
the light hits the mirror so M1 is the
primary mirror then there's a secondary
mirror M2 and so on um M4 is also
interesting because it has a hole so
basically the light goes from M2 through
M4 onto the M3 so here this animation
shows this a bit nicer so the light hits
first M1 M2 goes through M4 hits M3 now
it goes to M4 is reflected a bit off
axis onto M5 and now to the instrument
platform
and then overall of course there are
more mirrors than just those five but
those are the main mirrors in the
telescope
itself so the primary mirror um there's
usually the problem when building
mirrors if we if you use a monolith
piece of glass you can go up to
approximately 10 m diameter so for
example for the VT it's 8.2 M so
nowadays okay one could probably go a
bit more but um the problem is that as
you increase the diameter of the mirror
if you tilt the mirror for example to
the Horizon it will deform under its own
weight so you have to increase the
stiffness of the mirror you can achieve
this by making it thicker so you need
you add more glass you add more mass and
then it gets still reasonably uh stiff
so that it does not deform that much
under its own weight um but you hit a
certain limit at roughly 10 m so for
example for the VT we have about 30 cm
of
glass uh and for 8.2 M so it's basically
just the glass itself is about 23 tons
this of course makes the mirrors very
expensive uh also very difficult to
produce because you need a very high
quality glass that has no um no no
errors basically in the glass no air
pockets whatever in it and it's also
very difficult to transport for example
by truck or by ship if you think of it
for 39 M mirror you cannot transport it
on any road think of this the size of
this room so what is done for those
larger mirrors is to segment them so
here you can see a rendering uh you see
all those small little segments and
these together so these have to work
together these are individual segments
but they have to work together to form
the optical shape as if it was a
monolithic
mirror if we if we look at this for
example uh for the M1 of the elt it
means we have 798 of those hexagonal
segments each segment is about 1.9 M
across in addition we have 33
spares they have a coating made out of
silver which has to be renewed every two
years and in order to not have to stop
operations for many years recode all the
mirror segments basically we have to ex
exchange two segments per day and put
them to the recoding and take out two
segments from a spare set of segments
and move them back in there are there's
a six-fold symmetry so which is what you
can see here so you see here all these
are individual segments and there's a
sixfold symmetry within one of this uh
those sectors with 133 segments every
segment has a unique shape so we cannot
simply swap out segments as we want so
that's why we need a complete
um spare sector of 133 segments and they
all as said they have have to work
together to keep their position and
their shape as if it was a a monolithic
mirror and it has to be to accuracy of a
couple of tens of
nanometers so here's a a rendering of
one of those segment units so this is
one
segment um the part that will be coded
uh consists of uh 15
mm thick piece of zeru which is a
special glass ceramic which has a very
low thermal expansion uh you can compare
this uh to tan which is basically the
more consumer grade product and zeroda
is the industrial gr product of this
glass CTIC as said it has about 1.4 met
across the segment itself comes with a
so-called segment support so some
mechanic mechanical structures
underneath it which uh the entire unit
then uh has a weight of about 250 kg and
this is what is lifted out and
replaced the segments have a couple of
degrees of freedom so for example here
on the bottom you see those
three cylindrical things which are
called position actuators these allowed
to change the piston tip and tilt of the
segment changing the Piston means if we
have two segments you can move them move
a segment up up or down and uh the
Piston has to be done in a way that the
phase so the um the position of the
segment basically has no jump going from
one segment to the other segment tip til
means we can rotate basically the
segment around two
AIS how do we know the shape of the
overall mirror so this is done by
so-called Edge sensors which are located
here at the edge of the segment these
are coming in pairs so there's basically
one transmitter element here and a
receiver element on the neighboring
segment and here uh vice versa and this
allow us to measure piston Gap and Shear
to the adjacent segment so overall this
is about 4 half thousand of those Edge
sensor Pairs and in addition there are
nine shape actuators which are called
warping harness these allow us to push
or pull on certain areas of the mirror
to move it a bit up or down by a couple
of nanometers or micrometers and change
the optical characteristics of the
segment this is necessary for example
for seasonal changes if we have a 36 m
uh mirror 39 M mirror we have uh about 2
cm of thermal expansion just of the
steel structure underneath and then it
would not fit anymore their actual
placement uh as it was foreseen of the
mirror so this is why the shape has to
be adjustable on a slow scale over
seasonal temperature changes for the
edge sensors and position actuators uh
the control Loop runs at 500 HZ so every
2 millisecond We Gather all the sensor
data from all the segments
it goes into a big Matrix Vector
multiplication and the control Matrix
and the output is uh are the new
positions for the for the position
actuators every 2
milliseconds so this is for example
these are a couple of uh segments at the
factory of the polisher and you can see
some humans here in the back so the
segments themselves are not really that
uh that big you can see here that this
is just the glass as it is without any
coating and you can also see some of the
bond pads where basically the support
structure is glued
onto now the M2 and M3 are relatively
simple uh mirrors um but the M2 is uh
complex to produce so it is a convex
mirror with about 4 met diameter and
highly aspheric and it's the largest
secondary mirror that has ever been
produced and uh yeah because it's highly
aspheric that also makes it very
difficult and to prod use M4 is a bit
simpler Just 4 M and uh yeah not so
complicated both of those U mirror units
are um can be controlled with a hexapod
system that has to have a submicron
Precision so it's about 3 tons of glass
and 12 tons for the total
assembly okay so when you look from the
ground into the into the sky you go
through the
atmosphere and when there are different
layers with different temperature in the
air you get the Distortion you see this
when you look over a street and a h day
you see this that the light is basically
distorted objects will appear blurry and
if you look in the sky at the night when
you see stars twinkle this is the same
effect to counter this there is a
technique called Adaptive Optics so it
makes the Optics adapt to the
Distortion how this works there's a
short video
so you have some Galaxy that you want to
look at you see the the light is coming
here from this object and when it goes
through the atmosphere it is
distorted and when it comes to your
telescope you will get a blurry image so
what you do is you take an image with a
special camera of a so-called reference
star and you use this camera data to
calculate the shape of a deformable
mirror and this is done by the Adaptive
optic system which does this a thousand
times a second so this adaptive this uh
deformable mirror changes the shape so
that the wavefront that is before
distorted is now corrected and is no
longer distorted and in the end you will
have an image that is a sh as if you
wouldn't have the atmosphere at
all so you need a reference star um you
need a bright one not always you will
have a bright one that is near the image
or near where you want to take the image
so what we do is we take
glazers which have 20 WS of optical
power and we shoot them in the sky they
excite sodium atoms in the upper
atmosphere which is at 80 to 105
km and also the system has an automatic
shut off when an airplane
approaches to
prevent accidentally uh blinding the
pilot so here's an image which compares
the nonadaptive Optics versus Adaptive
Optics this is of Neptune has taken with
the same telescope just switching off
the AO the Adaptive optic system and as
you can see the resolution is increased
dramatically so the deformable mirror of
the elt is the M4 it is a 2.4 M diameter
mirror it is only 1.95 mm thick it is so
it is um um put on a reference body
which is made out of silicon carbide for
the stiffness and low weight and there
are
5,352 voice call actuators which is a
similar principle than loudspeaker so
these are magnets that push or pull on
parts of the
mirror the mirror is actually made out
of six parts you can see this on the
reference body uh this is not visible
here but it's basically the The Mirror
Has the same parts
and the displacement can be by up to
five uh 50 micrometers in each Direction
and the mirrors can be updated up to one
at one uh
Kilz this is an bigger image of the M4
together with the reference body and
then we have the
M5 the this is a flat mirror it's
elliptical it does a tip tilt correction
so again movement like this to
stabilized image this is also part of
the AO where you just do this part on on
a different mirror this mirror must be
lightweight and very rigid because you
want to do these Corrections very fast
and you don't want the mirror to deform
and you want it to be light so that
inertia isn't a
problem and there's also a switching
mechanism for the M5 which is different
from the tip tilt which allows you to
switch between the two inst ment
platforms which are on opposite
sides so now this uh video takes you on
our flight into the El so first you see
the mountain s amazonus with the elt on
top the Dome as said has an height of 80
M and if we now enter the Dome we can
see the main structure
[Music]
inside
Now we move up to the platform uh that
rotates so that horizontally rotates the
asimut
platform and you can see also here in
yellow these parts are the um laser
launch telescopes for the uh laser guide
Stars
basically so this platform here has or
is about 10 m above the ground and now
we go to 27 m above the ground to the
instrument platform which is then where
all the the spectrographs and imaging
cameras and so on will be
located here on the right you see the
two so the the closed doors of uh the
Dome and the wind
screen the doors now
open and the wind screen moves up
together with the altitude movement of
the
telescope and now also the lasers turn
on so so far you have only seen uh the
renderings but how does it look like at
the moment um as we said it is under
construction so it's not yet complete
but this is a photograph taken I think
about four months ago so you see that
actually you can already see the Dome
you can also see all the auxiliary
buildings these are cranes actually
quite big
cranes um we can also look inside so
here there are also some cranes but also
here there are humans the construction
workers that are currently working there
so this is about the size of of this uh
telescope also here is a crane inside
the Dome and there's another one here in
the
middle and with this we want to thank
you for your attention uh here are our
contact details and we can now also
answer your
[Applause]
questions so for those of you in the
room we have four microphones set up not
5,000 voice coils just four and for
those of you on the internet we are
monitoring Matrix we are monitoring IRC
we are monitoring your thoughts if you
post them in
Mastadon we are in the Grandville room
so please use the appropriate hashtags
and RSC channels and we will try and
bring your questions we
have more than 10 minutes for questions
so I think we'll be able to get through
quite a few and I see that there are
quite a few lining up everywhere
let's start in the
back hi uh thank you for your talk um I
have a question question about uh
disturbance in the uh in in space
because there is a lot of uh space trash
the uh satellites uh something like
stalling or um and I heard that these
are um disturbing the images taken from
astrus so um is this a problem for you
as well um and is the project still a um
yeah um in you usable in uh like 5
years um so there was a study that was
made by ESO and we looked at especially
starlink and it was it had an impact but
you you can eliminate the the start so
the trails of the satellites from your
images if you take multiple images you
can reject the pixels from that one
image and it wasn't so bad as we
initially thought um yeah that's all I
can say through that and especially the
elt is a telescope that has a very
narrow field of view it is not a survey
telescope so if you only look at a very
tiny piece of the sky the probability
that exactly at that moment you have a
as one of those satellites crossing the
image is very low so the elt itself is
not affected or not really affected that
uh but uh survey telescopes for example
that regularly scan the entire Sky they
are affected and also radio telescopes
so this is why usually you have a uh an
exclusion Zone around those sides that
they do not get um uh get jammed
basically by the satellite communication
okay thank you so I've received an
optical signal from the internet that
the internet has a
question hi um we have a question why IC
and uh which is uh since there are so
many movable Parts on the different
mural how long are they estimated to
remain operational so so the minimum
lifetime for the for the elt is 30 years
we hope it will be much longer but it's
at least 30 Years thank you so here in
the front microphone number one hello um
thank you again for the very great talk
I have a question will one be able to
visit this in person because I want to
see a mirror of this
big um I don't know for the El but for
the VT there is uh the possibility I
think every Friday uh there are uh
School classes going there so you can
visit the the um the operator room and
the telescopes maybe this will be done
for the El at some point as well I don't
know um we have to see thank
you so the other side in the front hi um
do you also clean the secondary mirors
and if you do how do
you because I guess they're quite big
yes so they for meters but they have to
be cleaned regularly as well um there is
normally so for example that can be done
with um like a CO2 for example uh so
just just some some dry ice and if they
need to be recod it then it has to be
done yes then the the telescope will be
out of service for a while but the thing
is if you have basically dirt on the
mirrors means they just get a bit more
and more blind over time uh but since we
collect so much light from uh the
primary mirror at least the other
mirrors it's not that bad if they are a
bit degrading over time thank
you in the back uh hi so thanks for the
talk um so you mentioned this climate
control system for 3 megawatts and it
has to work 12 hours to reduce 10° yes
so basically my question is like when
the Night Comes the the temperature is
constantly changing and how it managed
to equalize so like you need to predict
use like a weather prediction to predict
the temperature or some yeah exactly
what the idea is that you put the
telescope Dome to the temperature that
will have when you open the Dome during
the night you will have there are
ventilation um basically Parts on the
side of the
telescope um which allow air to flow
through so then it's no longer really a
problem but during the time when when
when you open you don't want to have a
temporal a temp temperature differential
between the outside and the inside of
the Dome so it's basically uh you open
the door when the temperature stop
changing outside roughly so basically we
We are following the ambient temperature
so during the day we have to prevent the
Dome of heating up but and that's why we
cool it down to the projected
temperature at night and and then during
the night um there's still some air
conditioning going on but we can also
open those these are called Lou so these
openings on the side that basically go
around everywhere and this allow us just
to take in the air from the outside as
it is and ideally we have a a very
laminar flow of air over the primary
mirror and we can also control which
side so depending on the wind direction
for example we don't maybe we don't want
the direction where the where the wind
comes from but maybe a bit to the
so this way we can control basically um
how much air goes in and out and that
then means that the inside of the Dome
has the same temperature as ambient
temperature so we cannot we can avoid
this Dome seeing and there are also no
other heat sources like computers and so
on allowed directly in the um yeah in
inside the Dome basically and they have
to all be outside in those auxiliary
buildings got it
thanks I my eyes have detected some
stray photons beaming to us from the
internet could it be that there is
another question you were right on that
and the internet asks um if the
reflective surface is just the silver
coating on top why the mirrors need to
be made of glass and not something
lighter so uh traditionally this zero do
is chosen because it has a very low
thermal expansion um you can use for
example billum which is the material
used for the uh James James web Space
Telescope but burum is even more
expensive than
zeru up front microphone number one hi
um so there is the very large telescope
the extremely large telescope and there
were plans about an overwhelmingly large
telescope so I guess you know what I'm
asking what's behind with naming ex
except for fun of course the the naming
is because we are an international organ
organization or intergovernmental
organization we cannot if you look at
other telescopes they're usually named
after people and we cannot really take
one person from one member State maybe
that would be unfair so usually all I
mean all our telescopes there's the 3.6
M telescope there's the new technology
telescope all of them they are very
generic and not not for a person yeah
more like what they are not no fancy
name except I mean extremely large is
quite fancy
seems Legend
thanks in the back um maybe more of a
personal and philosophical question why
do we need to explore the space what
does it bring us
like that's that is that is something
that you would need to ask an astronomer
which I'm not uh but like in principle
there science you want to know basic fun
fals of how things work and actually in
space there are a lot of things where we
don't know how things work and they are
quite fundamental so we yeah I mean if
we for example look at dark dark matter
we don't know how that really works is
my understanding so this impacts our our
basic physical
laws and unless we figure that out
there's there there's a basically it's
it's unclear if they're really correct
okay thank
you all right we we we go to the other
microphone in the back uh but please no
existential
questions so uh given that the telecope
uh telescope uh consumes several
megawatts of electrical power I imagine
you would need um fairly visible um
transmission lines which I didn't see on
any renderings or eror photos yet um and
neither did I see any solar farms in
nearby so how do you basically so for
the elt uh we have our own transmission
lines that go through the desert okay
they are not our own ones but they um on
that occasion for the El they also build
transmission lines through the through
the desert which did not exist before we
are connected to the Chilean grid
there's an addition in between S
amazonus and S paranal in this in this
plane in this big Valley basically there
is also a 9 megawatt photovoltaic plant
uh which during the day basically would
take some of this load um but of course
not during the night okay
thanks uh but basically yeah it's a fair
question for example the VT the very
large telescope ran for for many decades
basically on um on on diesel generators
and gas generators and also for a couple
of years now it's also connected to the
Chilean grid while we still have those
uh gas turbines which can also be used
for balancing the grid which is also a
very nice point because it's really in
the in the middle of the
desert microphone one um during the
starting question you mentioned exposure
times uh what kind of dimension of
exposure times do you usually get like
seconds minutes hours and how does it
compare with this telescope to the other
ones um I'm I'm not a scientist so I
don't I I've I've I mean I've been to
paranal but uh I don't know how much
they usually take for these exposures to
be honest um so so it's it's uh minutes
to hours okay yeah thank
you could it be that the internet has
another question that does not take
minutes to hours to
answer we can try why do we still need a
space telescopes when the atmospheric
Distortion is
correctable uh that's a very valid
question and we have a bonus slide for
that um if you look at this image uh you
will find that there are some parts of
the electric Spectrum which is basically
completely absorbed by the atmosphere so
in the gamma and x-ray Spectrum you have
this and then in the lower in the longer
range of the
infrared and in the long long long
wavelength uh radio waves and there you
basically need to go to space there's
basically no other other way because you
won't receive anything on Earth so it's
a if you look at the long infrared
that's is basically the the field of the
James web telescope for
example so I think we have time for one
more question we're going to take it
from the back oh sorry sorry sorry i'
I've just been informed by the audience
that we're taking it from the front in
the right so please
uh how is observation time divided can I
buy a time slot or Are there specific
proposals for from different groups to
use the time so basically uh there is a
process where uh the principal
investigators uh plan uh the
observations they have to say which
instruments do they use and so on and so
forth why they exactly need this instrum
those instruments those facilities that
they for example have also exhausted
alternatives for doing this um so for
example it would be a waste of time to
start or do an observation on the El
which will be overbooked probably for a
very long time over subscribed for a
very long time and uh then okay you
notice that okay you could have done the
same thing uh with another uh
investigation first on another telescope
and if you have clear evidence on those
other telescopes then probably you will
also get to the El there is no um let's
say there are no Nationwide quoters
basically Ally uh so there's a
competitive process the proposals will
be reviewed and the best ones will be
taken and most feasible ones will be
taken thank
you and let's collectively thank lonus
and Nicholas again for their fantastic
[Applause]
talk
[Music]