Hello everyone, I'm Manolis from Liber Space Foundation and today I will present you the
seedlock which is a new telecommunication standard that we started to propose in order to identify
and localize satellites that are orbiting the Earth. So before I start, are you aware of the
TLEs, two line elements? How many of you? Okay, a lot of people. So TLEs is two lines, two text lines
that describe the orbit of an orbiting object. Okay, so what is the problem and the motivation
behind the seedlock? Those orbital data are coming from limited sources, they are public but not
Libre. So these sources are mostly military, so we have one source that is US military and France
military and they announce them publicly but of course we have already restrictions that the
military has. A very distinct limitation is that they provide public data only for
space objects that are larger than 10 centimeters and someone may say okay, 10 centimeters
are enough for satellite but I know some very annoying people behind there that they build
satellites at smaller than 10 centimeters. Actually this is a cubic platform that we flown a year ago
into space and with a firefly mission and it was a very very good use case because
the second stage of the firefly rocket failed to deliver the satellites on the correct orbit,
so it was 100 kilometers less if I recall correctly. So the orbit was not the one that we have
prepared for our mission and it was changing very rapidly because due to the drug.
Okay and the traditional ways of getting the orbital data rely on radars. This is the space
surveillance network of US military that has few radars across the world, they are quite huge
okay and in order to get a new orbital formation for your satellite the satellite
must pass through the aperture of such a radar okay and again if it is small it is not guaranteed
that you will get your orbital data for your satellite. So the idea of seedlock is to put
a tiny beacon on a space object for example a rocket body, a satellite or anything that you want to
fly and by transmitting specific signals you utilize existing ground station networks like the
satnags or whatever you want, do the processing, extract the frequency offset and due to the Doppler
and then by making cure fitting techniques you can estimate very accurately the orbit and this
is something that we have already done with on satnags using the STRF, I don't know if
some one of you are available with STRF okay and it has proven that it can produce a quite accurate
orbit. So the goal of seedlock is to have a very low power transmitter on board the satellite or a
space object to have low cost let's say reasonable cost for a space mission and also to be zero
maintenance so you attach this beacon on your satellite and you don't have to do anything else
of course all of the satellite operators want to in order to integrate such a solution
wants to be as easy to integrate as possible so that's why we miniserize a lot the beacon and it's
this form is for example is three times larger than required I will talk about later why
and as I said before it can take advantage and also existing ground station network
the other characteristics of the seedlock is we envision to use a UHS band and 401 to 402 especially
this is quite dangerous band let's say because the
meteorological satellites use it so there was an independent research from MISA if we can use it
and by taking into consideration the power spectrum that we produce on such frequency
it seems that we can coexist with meteorological satellites the band that the seedlock uses it's
at around one megahertz and it it transmits a bpsk signal that is generated by a
die sequence spectrum system we use the gold cores I don't know if some of you are familiar with
them they have excellent cross-correlation properties and especially and more precisely we repeat 10
times its gold sequence it has to do with the decoding procedure that's why the the repetitions
and the effective rate is only 50 bits per second per second it's a frame of seedlock
has a duration of about 12 to 14 seconds so quite low in data rate but quite resilient in the
lowest in our scenarios the TX power is very low it's only 25 dbm
so here describe a bit the process of the TX of the spreading you have a cheap rate which is
much higher than the data rate as I said before this is one megahertz and you just so you perform
the the XOR of the gold sequence with the initial data to produce a absurd noise sequence that is
quite higher in bandwidth so this is the the transmission flow graph that we use in order
to test and view the simulations actually it's quite it's quite simple most of the blocks are
the the the ignore radio core blocks and we have created two additional ones which is the spreading
and and the spreading and one that actually compiles the frame of the seedlock very very simple
on the other side however as you may know everything comes with a cost okay so
the the RX procedure is quite expensive and potentially intensive so we have to deal with
terms of doing this in real time or or not have enough sensitivity to identify something and then
start doing something more let's say robust so there are three major three major techniques to
to to decode the the dss single it's the auto correlation one which from the from which we can
get directly the frequency offset without any issue but it is the it doesn't perform well in
low westerner environments okay the other one is the cross correlation with coherent integration
which is i think the the most sensitive one but right now as we stand as we stand at this point
we cannot do decoding real decoding in real time in nice seven so this is a very big deal
and there is also the cross correlation with non-coherent integration which is something
in the middle so the idea is to use to use auto correlation only to say hey probably a seedlock
transmission is is currently active and then switch to cross correlation with non-coherent
integration to extract the frame type and whatever it is needed to to be extracted in order to get
the full the full frame and then offline if the snr is not enough switch to cross correlation
with coherent integration in order to get the the whole frame so seedlock supports three different
types of beacons the the minimal which is a super minimal amount of amount of information in order to
identify which satellite you are currently receiving the full which has also
location the location of the satellite if the satellite supports
uh uh location estimation through a gps let's say and they they integrate it which is all it's
similar to the full but uh the the satellite can pass can piggyback some uh minor information on the
data on the on the seedlock frame itself so if everything goes wrong on the satellite
operators could still have a clue if for example the satellite was never
pinked the the seedlock beacon so it could be a clue that the it was a catastrophic failure of the
satellite let's say these are the full beacon fields most of them most of them are related to the
position the most interesting of them are two it's the sink word which is all all ones
and the the satellite ID which is a unique identifier for its space both it's orbiting
both let's say the the all ones is a bit weird for a preamble but imagine that you using a spreading
you spread these all ones so you have a repeated pseudo noise sequence and if you if you keep it
the same you can integrate it on on a larger time window so you could potentially identify easier
the existence of siddler so the reference design of the siddler beacon uses an stm
32 l4 series mcu which handles the main control of of the order of the hardware and the peripherals
we have the for the for the single generation we use the 80 86 rf
215 ic in iq mode so this particular transceivers can be set can be configured to operate in iq
and the the whole dsp and the iq generation is done on the ecp5 fpj that we have on board
so all of these components are inside this cube
regarding its size it could be far smaller but we got an opportunity to fly with a ryan a ryan 6
the new rocket from isa and a ryan and actually they mandate to have a deep sub nine connector
so regard it is huge compared to the to the to the whole stack and manfos do you recall we had the
m5 screws yes they they they required m5 screws which was yeah on this we use mv2.5 2.5 yes yes
okay so the the the beacons could should be larger of course
this is a flight model this will this will actually fly with ryan
and it had passed the vibration testing this is the vibration pod that you that you shake it and
in order to see if everything holds and of course the divac procedure so we we did also a deployment
of the antenna inside the divac in order to to see if the the beacon can deploy its antenna in the
cold plateau at minus 20 around minus 20 and actually we are quite happy with the sitlock because it's
uh okay Libre space foundation produces everything in open source and open hardware way
but our previous comms board had this limitation from xylem so we used in xylem's fpga so we had
to rely on vivado in order to build the the beacon but this time we selected the properly the hardware
in order to to use to in order to produce everything from open open tools so yeah we are quite
proud about it so the the the projects involved is of course key card for the pcb is new radio for the
ground station decoding and simulations free card for the mechanical
uh zeffy arthos plus ecp 5 for the uh on board controller and uh liptix plus yosis plus trellis
and xpnr for the ecp 5 bit 3 so that's all for me uh you can find more information on our github
repositories everything is there from pcb to to software and also you can join our matrix
transform more information from that's all for me thank you a lot
so any questions
like the box or is there any like special you know
paper or for quite for example students who wants to uh implement it in their own designs
so what about the about widths and all that so the question is uh if uh someone can uh can
make it out of the box and use it for its own so yes you can do that it's everything there uh
but of course you have to respect the the frequency um the the frequency that we'll use
okay so for this particular uh beacon it's uh at the frequency that uh i i told you before it's uh
for uh 401 uh to 402
thing is that this uh i'm at all for our frequency basically so you chose it from your project
i mean from your system as well not not really because we would like to to stay at uh ucf okay
because uh it is a compromise between uh the Doppler and Doppler shift and
um and path loss okay so ideally we would like to have to to to to to use higher frequencies
because the Doppler there is larger so your quantization there and the Doppler estimation
is less okay but then you have the path loss is larger so it's a chicken a problem let's say yeah
yeah
this space sorry
hmm yes the question is uh who is doing the uh the spacecraft id coordination that's a very good
question um actually there is um uh there is an idea to to to use the ui d's and the posture of it
take the 76 bits of it and place it at the supply to identify it um but for now we focus mainly on
on the modulation and post processing uh staff and i think that if we see that hey this is a valuable
way to get uh accurate orbits and and rapidly then some we can we can think about an authority or
registration form that you get an id so you know that in order to be sure that it's unique
yes yeah so uh i see you're using the stm32 uh but there's no uh like red hard equivalent i know that
you are using only cross components and that it's maybe not the core but there are other like
microcontrollers out there that have like a radiation hardened equivalent that might be
interesting for the future if you want to equip like geocentrelites for example um so uh what is there
like a version two coming or something like that when you were thinking about that yeah so the question
is uh if the stm32 microcontrollers is the only choice or we can move to other other choices that
are also radiation hardened um so we there was no big reason to to to use the stm32 um only for
convenience let's say because we are familiar with them uh or we can easily find uh artos that are
already support them uh but as i said this is um this is the demonstrators the demonstrators
demonstrators sorry uh we want to let's say focus on the modulation around the rf part to see to show
that this is feasible and it can scale also uh and not on the hardware itself so i'll focus
mainly on the protocol specification rather than the the actual hardware so the the protocol will be
is open source so uh if someone wants to implement a beacon uh with red hard components
he is free to do that
or no more questions thank you again thank you