MODERATOR: Hello, again, everyone. Welcome back to the Platypus Hall in PyConline 2021. It is 2021.
Next up we have Mars Buttfield-Addison with "Python VS Space Junk".
She is a computer engineering PhD student and has a really cool talk lined up.
>> I am Mars and I thought I would like to say hello at the start because I won't have time at
the end. My talk goes right up until the end of the time slot. I will be sitting in chat
and I will take up text questions or via email or Twitter. I really, really hope you enjoy the talk.
Thank you very much. >>
Hello and welcome to Python VS space junk. I am a PhD candidate and do a bunch of other
things. My talk is related to my PhD research. The focus my research is how sensors not made
for space tracking such as made for astronomy or this can be harnessed to space without
impact meaning it will improve the precision and reliability of location and collision predictions.
Today I am going to tell you a story about space junk where it comes from, what we plan to do
about it and what we do about it right now. There is a little Python at the end that you
can play along on your own time. Let start with what is space junk and where does it come from.
If you ask any person on the street most are familiar with about the first
1-5 satellite. You have Sputnik and Vanguard one the oldest remaining object in space.
They might know fewer more significant ones such as space stations, ISS, or the hubble telescope
or the hot topic telecommunications such as star link. Australians of a certain age will remember
when sky lab came down. I am pretty sure we as a nation are a bit more aware of space stuff
than other nations that don't have a space program. Those things don't add up to this.
Let's talk about what this is made of and how it got there. We have launched more things over time.
There are more space capability countries, more providers, cheaper materials and brought down
the price per weight of getting something to orbit and more people want a piece of the pie.
We are launching about 1400 objects per year and about 55-60% of those are just star link
satellites. It is not just more often but we are launching larger and longer lasting objects
which means they have bigger and longer laster impacts on the orbit over time.
Space debris doesn't include satellites. Let's put the beef are constalitons. Debris gets into space
from satellites breaking, launch waste and astronaut error.
Satellites breaking or running out of power -- there are many satellites that have run out of
power and become inactive mostly after living a full life and run out of fuel or batteries.
Some fail on launch. They properly detach from the launch vehicle or battery didn't connect properly
and broken as soon as they left the bay and might never have fulfilled their experiment or purpose
and now they are debris. We have mass simulators also otherwise called boilerplate spacecraft. The
tesla roadstar is the most obvious case. It is going around the sun and might end up in orbit.
A mass simulator is when you need to test your rocket and need to know before you put people in
the spacecraft that your rocket can handle the shape and distribution weight. You build a fake
spacecraft that's like one solid plate with a mass equal to the astronauts you will send
and their equipment. It has to be deployed so I don't know it will detach and come back down. We
have multi-stage rockets such as the third stage one here. This one is really funny to me.
A few years ago, there were all these headlines about how we found this new object. We can see
it. Not very well but there is something in the earth and we think it is a comet or astroid
because it isn't associated with any launch. It must be a new tiny captive moon. Oh, my goodness
earth has a tiny moon. When they pointed a high powered task, it is actually a rocket. None of
our rockets from recent launches are missing. If we propagate it backwards, this is the stage from
the launch all of the way around and back, and has been caught on the return flight.
Hilarious. Of course, most astronomers were like it would be unusual for it to be a comet
or astroid. It was funny to find out it is this thing that had been on a long space journey.
Also, there is the 100 million tool bag, didn't really cost 100 million but it was a $100 million
worth of loss where a shuttle pilot was coming to do repairs outside the ISS and they have special
tool bags and accidently let it go and came down and ended up in the atmosphere. That was expensive
mistake. But the ISS semi frequently creates debris because if you have a module you have to
replace and it isn't feasible to bring the old one back down they have to chuck it off into space.
It is unfortunate but true. Stuff we know where it comes from gets registered in a catalog
with details of when it was launched and physical characteristics.
Now a number of debris objects have formed in orbit. Same amount of mass but broken up into more
fragments. This is dangerous because at orbital speeds which is thousands of tens of thousands
of kilometers, a break up averages more than 10 items capable of force destruction. Something this
big will create 10 pieces that can smash into and destroy 10 more things that are this big.
We get this flow effect but it is a growing flow effect.
In some cases it is exponential on average. In some pay ways, breaking into smaller objects is
better but they have to be microscopically small before they stop being an issue on their own.
We have rocket body explosions which are main debris forming events. We had laws pasted in
decades meaning if you are going to launch something in orbit with flammable materials
you need to vent it out into space or drive it until it runs out of fuel because we can't keep
having things blowing up and taking out things near them and creating enormous clouds of debris.
It didn't stop the explosions. We started calling them energetic events. Here are examples. This
breeze am in Russian is a good example because four have exploded since 2007.
The other ones are Chinese and French repect -- respectively.
Satellites can break apart. A certain design can be prone to break up. If you launch a fleet they
will break up at the same age. One example is the transit sats, a precursor to GPS where about half
a dozen have broken up in the same way. Or the Noah surface and radar sats where I think 15 and
most were recent. They haven't been up there long but three have broken up into pieces.
Basically big solar panels and lots of appendages means at low altitude you can
be constantly dragging in the atmosphere until you fall apart and can't take it.
Now we are up to anti-satellite weapons. Here are the companies that shot them down
and orange are missile capability countries meaning you have a missile that can shoot
down other missiles and we theorize would be capable of taking down a satellite.
In 2008, the U.S. shot down a satellite with a ship-based missile. The target was a satellite
of their own that had malfunctioned shortly after launch. The explanation was the orbit was
decaying and it had fuel on board meant it was an ex explosion risk if it managed to hit the ground.
However, that seemed strange at the time. We went oh, OK. Even though you were one of the
main countries that made this illegal you go ahead and break your own rules.
It came out later it was a highly classified synthetic radar surface surveillance spy that was
the size of a basketball court. The U.S. scored the first hit in 1985 when a 2B satellite was hit.
There is nothing dangerous about that satellite. It was just to prove they could, where guess.
Before this -- I guess -- tests from the 1960 said and '70s used thermo nuclear warheads fired
from the ground. That same form factor was later used to launch satellites into orbit themselves.
Back then they were far less precise but a dead -- detonation in the atmosphere released a pulse
that would destroy anything within 8 kilo meters. They want to make sure if the soviets launched
a spy satellite they could kill it before it hit orbit. In China in 2007 they shot a truck
magnetic kill missile as a test. This event produced the most space debris out of any
single fragmentation event in history. They made 3,500 plus fragments from a satellite that was 1.5
meters cube thereabouts. India joined in 2019 and shot down their own and it fragmented less. There
is the classic two things hit each other in space. The most famous is the showdown in 2009 where both
lost and produced about 2,000 fragments of two tons of debris. Half of those rocket explosions
I talked about before have already caused full on collisions with other objects. One took out
another market body and a French one took out a satellite and the breeze am just a matter of time.
There are also a bunch of near misses or collisions with small objects.
We only know if one of of the satellites is large and active enough with cameras on the outside.
Or months later when we figure out the orbit must have changed and manage to extrapolate and think
it must have been hit with something with this amount of force. One day they checked out this
and saw the dent and looked at how it happened and how the orbit changed. Even the ISS gets hit. They
had to dodge debris three times in 2020. They found something punched through the part that's
responsible for grabbing and docking incoming spacecraft. They didn't know they had been hit.
Thank goodness the arm is working because that's an impossible thing to replace.
Here we consider the growth in the number of objects in orbit from the design grating.
It brings down things already up there by sending up to already get it.
There are lots of ideas bouncing around. Targeting with brooms to mostly slow down the object until
the orbit decays. There are more ambitious graber type ones that look like it is going
up and dragging down the satellites and bringing them back to the spacecraft. There have been
ideas but none have been tested where they get something and bring it back to the mothership.
ADR is like a holy grail of space debris research but no option has proven and is reliable enough
to be deployed. If we keep sending these up and they are not doing a good enough job and there
is no foreseeable future where we can scoop it all up because we need things in orbit
despite the risk. We do need a stop gap. What do we do about it today? We keep track of everything
and use that to predict and maneuver things out of the way if they go and hit each other. This is
very much like air traffic control but for space. We call this Space Traffic Management or STM.
The air traffic control is kind of false because STM is so much harder.
You don't have a transponder on every satellite telling you what it is and where it is and you
can't use GPS to see where they are. They don't have reliable tracking of where they were in the
past. Even if we knew where ithorp we can't point them on the path where they want them to. Most
can't be maneuvered. We can't use a linear path. You could point them in a straight line and it
doesn't mean they will stick. They are impacted by solar flairs that change the pressure around
the earth. We put stations all over the globe to monitor the sky such as this one from Hawaii. This
is a few from all ground base sensors in the space surveillance network. It is the largest
network of sensors worldwide. Others tend to be one or a handful of sensors. A few commercial
companies track the stats but sell the data back to operators for a small fortune. They
tend to concentrate in the northern hemisphere. Australia can see parts of the sky they can't.
Here in Australia we turned on the first AU based sensor. A telescope shipped from New Mexico just
for us. They operate a sea band radar from the opposite side. An Australia company has started
building a dedicated radar array and a few Australian observing have located space junk.
You are thinking we have so many telescopes here, why aren't they all tracking space
junk? We have a notable amount. There are a two simple answers to that question.
Those systems are needed fell -- for astronomers to do their work.
This amounts to why would we waste time just to do space management tracking poorly?
Some people are working on it. Myself and engineers are doing experimentation and adaptation
for them and there is a fellow who is working with physics to do the same. I know people at variousb
universities around Australia are doing the same. This is a super amount of work and there are key
limitations. One is that the design constraints and priorities of a telescope designed to look at
space are different than a software and hardware level. They commonly point at one thing for days
or longer to build up an image that is maybe only a few pixels wide. The most important thing
is that the telescope can stay as stable as possible while tracking the earth's rotation and
it can reacquire the object so it can get as much information as possible out of those few pixels.
STM just wants timely as information as possible. If you observe this triangle as a representation
of the competing constraints of the imaging system, we can picture this as the amount
of pixels, colors, and the amount of frames in a video. More pixels less frames and colors, more
frames less pixels and colors and astronomy is many pixels and colors as possible, please, space
tracking management is in the give me a snapshot as often as possible at any cost to quality.
The amounts can prohibit -- the mountains can prohibit this tracking. Picture my hand as a
telescope. A space tracking telescope could ideally track something all of the way across
the sky. They can't do that. They have to track up, and spin all of the way around and go become
down meaning they have a blind sight and that is not fast enough to track something in the sky.
It turns out even the normal tracking rate isn't fast enough to hit something in lower earth orbit.
They are just going too fast. If you manage to track and catch the data you are looking for,
the radio receivers are focused specifically to eliminate transmissions in the field,
AKA, anything near to earth than the great distance is it is designed to look at.
An optical telescope can't observe unless it is in darkness and being lit meaning it has to
be nighttime but near enough to dawn or dusk so the sun is bethrough -- below the horizon.
If we did a ray trace, from the satellite to the telescope to the sun, they can see each other
but the telescope and sun can't see each other. Optical doesn't work because it is too bright or
overcast. A radio telescope needs the reflection of a transmission that may be preturbed.
Why would an astronomy telescope be built to rely signals? Very few can. We have this
network responsible for talking to spacecrafts for NASA whenever the Spain or California stations are
facing their own way. 30% of the time we are the answering machine for everything out in
space in that direction. Most receivers try to observe space junk using reflections from these
transmissions but they are so busy wrangling all the spacecraft their experience is very limited.
Back to thinking OK, fine. We will just build costume sensors. But they cost billions or more
often billions each and woe need to cover the globe and have more. They can't be effectively
used for astronomy or near earth imaging for things such as comets. It is based on doing
that one task and being a good global citizen. You can see how a country might not be the best
at that. How does it work? There is a generalized process of steps. First you have to identify an
object that you want to look for or a region of space you want to look at to target a specific
object or objects. Then you have to transmit a signal if you want to observe a radar response.
Collect data using an optical sensor and analyze that data and there are many steps of its own.
You need to predict the future trajectory and adjust the trajectory of objects when necessary.
From step one, you figure out based on previous locations of objects and predictions of where
they will be, what part of the sky you need to look at. There is error in cascades. Then
targeting requires conversion between geo centric meaning if you have a center of the earth acting
as a coordinate system's origin and XY and Z like a 3d image versus a random point on earth
is the origin and you have coordinates to rotate north, east or go up altitude. You can see
they don't go one-to-one even if the earth was a sphere but it is not. It is slightly flat. Also,
the surface of the earth isn't completely regular. Already that introduces slightly more error.
If you transmit noise, that means finding a ban on the spectrum you are allowed to transmit on
and giving individual permission for each transmission that you do to check that this
won't interfere with spacecraft. If big daddy NASA says yes, you collect the signal in the
big telescope or sensor and that travels a huge difference back through the atmosphere,
potentially introducing error and the hardware is prone to error from everything to temperature
to nearby mobile phones to wind speeds to everything. And digitizing and continuous analog
signal means losing more information. You then have to use things like Doppler to figure out
where the things are, how fast it is going and in which direction. You have to get those relative to
earth and doing the translation you did backwards but also the telescope is on a rotating earth so
it is moving as it is tracking. You have to do that for every frame and integration window.
You have to figure out what object you point out and associate it with previous records,
classify how it is moving now because if it is tumbling or being maneuvered that will
impact the trajectory in the future. Sources are often precise but the rest can be outright wrong.
You have the prediction of where the satellite where go in the future which is the hardest part.
The models used to trace the path are complex. They are called propagation models and have to
take into consideration solar pressure, drags and earth magnetic fields interacting. Propagation
models -- keep that in mind. Being a complex physical simulation we don't have the
resources to fully compute to any great level of granularity. Most use a model called SP4 -- SGP4.
If we want actually useful predictions, we want to catch it often and
every single one of those thousands of objects. Say we do that. Every object in space every day
and we have a good idea of where everything is and will be. Now we move things, right?
Even that's hard. First, you don't get a reliable pinpoint election -- location of where each object
is. You get a litter -- little error along the axis. This makes it where the satellite
could be anywhere in here. Jow to check and this isn't a yes, no but like a weighted probability.
If they do intersect, you have to check if one or both have the ability to move which doesn't
just mean it was designed with maneuverable jets but it means does it have enough power
field to do so right now. If yes, compute a new trajectory and for each potential trajectory you
have to check if it will hit the original thing or anything down the line. If yes, go back, if no,
you have to calculate the instructions to send to the spacecraft so it will get on the new orbit
and once you set those instructions you have to figure out whether it moved into the orbit
or needs further adjustment. If we do all these things well, we can prevent some
types of collisions between objects where at least one can move some of the time.
All that work, and that's the best we can do to keep things safe in orbit. Where does Python come
into this? If we look generally there are three systems. The things that control the telescope,
maybe a single computer. A thing that does hard number crunching and this may be a supercomputer.
There is the thing that gets the STM specific information on the end which might be like the
scientist's computer or the researcher's computer. Early steps are low level and
need to be super fast and tend to be C-like. The middle step depend on the other systems.
The last is done by individuals or they are application scientific like Matt lab or system
tool kits or custom Python. This is recent happening as new players came on the scene.
Since the '70s and '80s when the only people before then doing this stuff was norad.
You had devs who had to collaborate with scientists and physicist. We ended up with
more Python over time. A bunch of scientist libraries from C, Java or obscure languages got
Python wrappers and we got more dedicated Python libraries and old tools people made for themselves
started getting appropriate open source licenses. Here are the most popular nowadays. One is written
by a space organization and the other just by one person. Commercial companies and military
space tracking organizations and tools such as these have become so widely used and tested that
people are asking to switch. It is very much like the comic here except the infrastructure here is
responsible for all of space safety and that one random person is from Ohio or somewhere in France.
The problem is far from solved because the limitations of the models are known and new
tracking operators pop up and roll their own. They don't realize that all of the models suffer
from similar limitations because that's physics. They can I can roll my on and it will be better
and we can tell -- sell the models. While we are getting better at data sharing
and using the same underlying libraries for orbit determination or propagation there is still a
severe lack of standards and nobody contributes back to core. Even if they are sharing data they
are not sharing implementation because STM data is worth too much to have people make it for free.
If you own one that can do Space Traffic Management tests, or you can force a commercial
space traffic provider to contribute back to space do that. If you know Python you can develop faster
heuristics and benchmark propagation models and anything new you make against each other.
You can see they introduce different types of errors. You can develop special case models
for objects that are small or too far away or have regular orbits or implement easier
GPU and threading support for models because the observatories are all going to GPU and Cloud.
That will make it easier for the scientists. If you are a Python dev, lots of these places
need Python devs. The work to get started is to go with a website with every detection of
every satellite since dawn of the internet in your preferred format, install the library,
play around and relace different part of the pipeline. You can take a detection from yesterday
and predict where it will be and pair where it was seen today and there you go. Space tracking.
If you need hand getting started you can go here. I have got some code for you. Let me know how you
do. Thank you for listening -- listening. You can tweet me or email me. Thanks for having me.
MODERATOR: Hello, everyone. Thank you so much for your talk, Mars. That was really informative.
Mars has been working hard on answering questions. We are going into a 45 minute break
until the next talk. Get up, stretch your legs and walk around. I highly recommend people check
out Pycon AU social to see the social events planned tonight and tomorrow. There is a dinner
meeting tonight and RPG sessions still open for applications for tomorrow as well as some other
cool stuff such as Mario Cart. Lightning talk submissions closed and they will be
an at 11:00 a.m. tomorrow if you want to watch. Check it out. I will see you all another time.