LASER COMMUNICATIONS FOR CUBESATS: A 50 MBPS LASER/RADIO HYBRID TRANSCEIVER IN A PC-104 FORM FACTOR CARD

Abstract

In early 2018 the Irvine Cubesat STEM Program (ICSP) from California-USA, requested that the Ecuadorian Space Agency (EXA) supply a miniaturized LASER emitter for the IRVINE02 cubesat to be launched on board the NASA ELaNa 24 slot in November 2018. The device was requested to meet certain conditions like a minimum output power of 0.7 Watts, operate at a maximum temperature of 50 degrees Celsius, use a maximum electrical power of 3 Watts and be NMOS operated through a UART modulation circuit at a minimum speed of 100 Kilobits per second. The resulting device was shipped one month later to ICSP exceeding all initial requirements. This device is currently in orbit and its denomination is PLM01. To date, it is the most compact laser ever own on board a cubesat as small as 1U form factor; this work was funded by the Irvine Public Schools Foundation. This paper will describe the methodology for stabilizing the LASER in its various electrical and thermal dimensions, tests performed, mechanical, electrical and thermal design and tools used. It also will describe the new generation of laser transceivers PLM02 and PLM03 to be installed in the IRVINE03 and IRVINE04 1U cubesat satellites which will combine radio communications in VHF and UHF frequencies, from 200 MHz to 900 MHz range for uplink and optional downlink and a LASER emitter in the 405nm to 450nm wavelength, operating at a minimum of 10 Mbps and a maximum of 50 Mbps in OOK modulation. Different challenges to achieve this performance are discussed, such as the power budget, thermal dissipation techniques, processor speed, data bus speeds, bus technology selection, data processing approaches and techniques. That allows this hybrid transceiver to be used by a wide range of cubesat architectures, even those based on relatively slow speed data transfer buses like I2C and CAN bus, and those based on faster data transfer buses like SPI, USB and USART. It also details optical link budgets, detector technology and how geometry selection matrices have to be applied to achieve the objectives of having cost-effective high data rate transfers from orbit to ground, using a very compact and efficient device that can be installed in wide range of satellites, from 1U cubesats to full-size satellites.

Full text

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IAF SPACE COMMUNICATIONS AND NAVIGATION SYMPOSIUM (B2)
Advanced Technologies for Space Communications (1)
Author: Prof. Ronnie Nader
Ecuadorian Civilian Space Agency (EXA), Ecuador, rnader@exa.ec
Mr. Jules Nader
Ecuadorian Civilian Space Agency (EXA), Ecuador, jnader@exa.ec
LASER COMMUNICATIONS FOR CUBESATS: A 50 MBPS LASER/RADIO HYBRID
TRANSCEIVER IN A PC-104 FORM FACTOR CARD
Abstract
In early 2018 the Irvine Cubesat STEM Program (ICSP) from California - USA, requested that the Ecuadorian
Space Agency (EXA) supply a miniaturized LASER emitter for the IRVINE02 cubesat to be launched on board
the NASA ELaNa 24 slot in November 2018. The device was requested to meet certain conditions like a
minimum output power of 0.7 Watts, operate at a maximum temperature of 50 degrees Celsius, use a maximum
electrical power of 3 Watts and be NMOS operated through a UART modulation circuit at a minimum speed of
100 Kilobits per second. The resulting device was shipped one month later to ICSP exceeding all initial
requirements. This device is currently in orbit and its denomination is PLM01. To date, it is the most compact
laser ever own on board a cubesat as small as 1U form factor; this work was funded by the Irvine Public Schools
Foundation.
This paper will describe the methodology for stabilizing the LASER in its various electrical and thermal
dimensions, tests performed, mechanical, electrical and thermal design and tools used. It also will describe the
new generation of laser transceivers PLM02 and PLM03 to be installed in the IRVINE03 and IRVINE04 1U
cubesat satellites which will combine radio communications in VHF and UHF frequencies, from 200 MHz to
900 MHz range for uplink and optional downlink and a LASER emitter in the 405nm to 450nm wavelength,
operating at a minimum of 10 Mbps and a maximum of 50 Mbps in OOK modulation. Different challenges to
achieve this performance are discussed, such as the power budget, thermal dissipation techniques, processor
speed, data bus speeds, bus technology selection, data processing approaches and techniques. That allows this
hybrid transceiver to be used by a wide range of cubesat architectures, even those based on relatively slow speed
data transfer buses like I2C and CAN bus, and those based on faster data transfer buses like SPI, USB and
USART. It also details optical link budgets, detector technology and how geometry selection matrices have to
be applied to achieve the objectives of having cost-effective high data rate transfers from orbit to ground, using
a very compact and efficient device that can be installed in wide range of satellites, from 1U cubesats to full-size
satellites.

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1. Background:
In late 2015, The Ecuadorian Space Agency (EXA) was
awarded a contract to provide cubesat batteries and solar
panels to the Irvine Cubesat STEM Program (ICSP) from
California - USA, for a fleet of 12 cubesats spanning 12
years. [1]
In early 2018 the ICSP requested that the EXA supply a
miniaturized LASER emitter for the IRVINE02 cubesat,
shown in Figure 1, to be launched on board the NASA
ELaNa 24 slot in November 2018. The device was
requested to meet certain conditions, which include a
maximum operating wavelength of 455 nm, minimum
output power of 0.7 Watts, maximum operating
temperature of 50 degrees Celsius, use a maximum
electrical power of 3 Watts and be NMOS operated
through an UART modulation circuit, at a minimum
speed of 100 Kilobits per second. The resulting device
was shipped one month later to ICSP exceeding all the
initial requirements. To date, it is the most compact laser
ever flown on board a cubesat as small as 1U form
factor; this work was funded by the Irvine Public
Schools Foundation (IPSF). [2]
Figure 1: IRVINE02 Cubesat, launched in December 2018
We will describe the methodology for stabilizing the
LASER in its various electrical and thermal dimensions,
tests performed, mechanical, electrical and thermal
design and tools used. Also will describe the new
generation of laser transceivers PLM02 and PLM03 to be
installed in the IRVINE03 and IRVINE04 1U cubesat
satellites, respectively, which will combine radio
communications in VHF and UHF frequencies, from 200
MHz to 900 MHz range for uplink and optional
downlink and a LASER emitter in the 405nm to 450nm
wavelength operating at a minimum of 10 Mbps and a
maximum of 50 Mbps in OOK modulation. Different
challenges to achieve this performance are to be
discussed, such as power budget, thermal dissipation
techniques, processor speed, data bus speeds, bus
technology selection, data processing approaches and
techniques. That allows this hybrid transceiver to be
used by a wide range of cubesat architectures like those
based in relative slow speed data transfer buses like I2C
and CAN bus and also those based in faster data transfer
buses like SPI, USB and USART. Also discussed are the
optical link budgets, detector technology and how
geometry selection matrices have to be applied to
achieve the objectives of having cost-effective high data
rate transfers from orbit to ground using a very compact
and efficient device that can be installed in wide range of
satellites, from 1U cubesats to full-size satellites.
2. PLM01: Pulsed Laser Module requirements and
design
2.1. Customer Requirements:
• Minimum output power: 0.7 Watts
• Maximum operating wavelength: 455 nm
• Maximum operating temperature: 50 C
• Maximum electrical power: 3 Watts
• Operation: NMOS through UART modulation
• Minimum speed: 100 Kbps.
2.2. Final Design:
• Minimum output power: 0.80 Watts
• Maximum output power: 1.6 Watts
• Maximum operating wavelength: 450 nm
• Maximum operating temperature: 40 C
• Maximum electrical power: 2.5 Watts
• Operation: NMOS through UART modulation
• Minimum speed: 115 Kbps.
• Maximum speed: 1 Mbps.
To achieve the above listed parameters, many challenges
were met successfully, which include:
• Miniaturization to fit the required space
• Effective and efficient passive cooling
• Electrical vs. Thermal efficiency
• Efficient Laser Driver switching method
• Only 30 days to deliver
3. Meeting the Challenges:
The challenges listed above, especially the delivery time,
needed a lot of experience in solid state laser technology.
Fortunately, EXA has a research division that had
worked in the very same challenges for different
application during the development of Project ARPIA
that started in 2012 and ended successfully in 2015 [3].
The short delivery time period also needed an existing
stock of parts that we already had, due the nature of our
own research programs.

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3.1. Miniaturization to fit the available space:
This was selected as the main system driver for the task
ahead, and it was the challenge that defined all the
subsequent challenges; In solid state lasers, space is what
defines electrical and thermal dimensions. A preliminary
model was created as shown in Figure 2 and, from that,
the required parts were modeled and manufactured.
Figure 2: PLM01 laser emitter and driver
ICSP requested that the laser emitter be mounted over
one of the walls of the cubesat, which was a 1U format,
within a specific location that fit the existing hardware,
so the final design looked like Figure 3.
Figure 3: PLM01 laser emitter and driver mounted over a
sidewall behind the NEMEA shielding
Once the dimensional constraints were indentified and
validated with the actual hardware and 3D models, the
next challenges became clear and ready to be engaged.
3.2. Effective and efficient passive cooling:
Solid state lasers present unique properties different to
other types of laser devices. They are much more
compact, which makes them the obvious choice in the
task at hand. However, that same property makes them
much more difficult to stabilize their operation at the
relatively high levels of current and temperature required
for this application.
The main problem is the quantum cascade phenomena
that takes place in the
V
ertical-Cavity Surface-Emitting
Laser (VCSEL) of the laser diode: At low levels of
current the cascade behaves like a crystalline stream of
water, non-turbulent and smooth. However, ramping up
the current levels causes this photon emission cascade to
become increasingly turbulent, in turn causing the
electrical power to become less efficient, and produces
increased levels of heat instead of an increased amount
of photons in the desired wavelength. The phenomena is
cumulative and, in time, it overheats the diode, which
shuts down and ultimately fails.
The key to control this phenomenon is to move the heat
out of the diode as soon as possible. To that end, we
designed a passive cooler based solely on the careful
application of materials that actually rendered the desired
results shown in Figures 4 and 5.
Figure 4: PLM01 laser emitter and driver being tested in
continuous emission of 15 minutes, demonstrating low diode
temperature, current usage and laser output stability.
Figure 5: PLM01 laser emitter and driver being tested in 2
cycles of continuous emission of 15 minutes each.
The test report graph describes a vacuum test at 4.5 x
10E-5 Mbar in two cycles of continuous emission of 15
minutes each. The maximum temperature on the diode is
32 degrees Celsius, while the cooler plate reaches 41
degrees Celsius, effectively and efficiently cooling the
diode. Appendix A provides further details.

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The combination of materials and structure of the passive
cooling system proved very effective and efficient as
supported by the test data. Moreover, initial thermal
simulations, as shown in Figure 6, were in accordance
with experimental data
Figure 6: Thermal simulation of the laser diode head
3.3 Electrical vs. Thermal efficiency:
The laser diode was running within a voltage range from
3.8 to 4.14 volts and at a current range from 0.6 to 0.8
amps. This could only be possible if the thermal
runaway effect could be controlled, which we were able
to achieve with the passive cooling system.
3.4 Efficient Laser Driver switching method
In order to achieve the target communication speed
requested, we needed a switching method that allows the
diode to restart the quantum cascade, rapidly reducing
the impedance of the whole laser emitter assembly.
However, this application did not need faster speeds and
the minimum required speed was at 115Kbps, implying a
switching frequency of only 115Khz. Considering the
rise and fall times (as well as turn on and turn off times)
of the NMOS channel was important, but not critical for
this application, a common NMOS was selected and
tested at 100Khz to validate switching speed
assumptions, as reflected in Figure 7.
Figure 7: NMOS switching at 100KHz
Using the test setup depicted in Figure 8, we generated
test pulses from an Arduino board [4] to validate the
operation of the whole system.
Figure 8: PLM01 laser emitter and driver test setup
The lowest speed was 100 Kbps and maximum speed
was 1 Mbps. As shown on Figure 9, the result in this test
report comes directly from the photo detector, meaning
that it is the laser signal detected and converted to
electrical pulses.
However, as we ramped up the modulation speed, the
intensity of the laser emission diminished, so the faster
the modulation, the fainter the emission. According to
the laser link budget, the emission will be undetectable at
speeds greater than 400 Kbps. Fortunately, the minimum
speed required was only 115 Kbps.

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Figure 9: PLM01 laser pulses detected by the photo detector
modulating at 1 Mbps
This problem arise from the choosing of the switching
method, which was driver switching: The driver circuitry
did not have the proper design and structure to be able to
cope with fast rise and fall times of the signal, this was
not a problem with the diode, but a problem with the
driver design that we solved on the next generation
module PLM02
3.5 Delivery
Once TVC tests were performed, the system was packed
and sent to ICSP at day 29 of the 30 days allotted for the
task
Figure10: PLM01 laser communication system ready for
delivery.
Once it arrived, the PLM01 was mounted on IRVINE02,
no problems were observed in the mechanical fit of the
wall and electrical connections, other that the addition of
an SSR relay to solve a discrepancy arising from the
implementation of the cubesat’s UART controller. The
subassembly is shown in Figure 11.
Figure 11: PLM01 laser communication system installed on
IRVINE02.
Tests were performed by the students of the ICSP
program; the first was to check the electrical and
command pathway integration into IRVINE02, the
second was to send a file trough the laser towards the
detector in the laboratory at 115 Kbps. Both tests
achieved very satisfactory results, as shown in Figures
12 and 13. Later, the cubesat passed VTV tests
satisfactory and was integrated into the POD for launch.
Figure 12: Dr. Brent Freeze, Technical Director of ICSP
reports successful laser integration test [5].

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Figure 13: Dr. Brent Freeze, Technical Director of ICSP
reports successful file transmission over laser test [6].
4. In-Orbit test
IRVINE02 was successfully launched from the SSOA
Falcon 9 mission for NASA ELaNA 24 on December 2,
2018 [7]. It was detected fully operative in orbit just a
few hours later by amateur radio operators around the
world, as shown in Figure 14.
Figure 14: IRVINE02 reports alive to ground radio amateurs.
However, a few days later it felt silent, as well as some
other cubesats deployed in the same batch. After further
radio, radar and optical searches, it was noted that many
more objects were detected on the same orbital path,
suggesting an anomaly had occurred affecting the
cubesats in the vicinity of that group and, among them,
IRVINE02.
ICSP did not have the chance to test the laser
communication in orbit due this anomaly, even when all
tests were successful on the ground.
5. The New Generation of laser emitters, PLM02.
ICSP continued on to the next 1U in the program and the
bus for IRVINE03 was already contracted to EXA. This
new instance of the Irvine Trainer Fleet is completely
different from its predecessors. Designed from scratch,
it integrates all of the bus functions in one card, the
Irvine Class Electrical Power System (ICEPS) Core,
based entirely on USB 2.0, having the characteristics
listed in Table 1.
Bus type USB 2.0
OBC Dual-core ARM Cortex A9 CPU @733
MHz, 512 MB of DDR3L RAM
OBC/OS Linux computer running IIOS
Radio SDR from 70Mhz to 6GHz
EIRP 28.5 dBm integrated LNB
Sensitivity -110 dBm
Antenna 2 RX and 1 Transceiver (TX/RX)
System Storage 512 Gigabytes
Number of ports 14 total: 8 ext, 6 int; USB2.0 60MB/s r/w
High Speed Laser
communications
405nm or 450 nm, 10 Mbps, variable
aperture. Integrated temp. sensor
Power rails 5V@3A; 12V@3A, 3v3@3.6A; 4.2 ~ 3.6
(unreg) @ 12A ; 1 auxiliar APU
Battery packs One or two at 3.7@6A, 50W max
nominal
Power delivery 50W Nominal, 65W Max, 100W peak
2.5s.
Solar Mngt 4 UMPPT channels 16V@2A max each
Solar charger Based on TP5100 2A continuously, 1S,
2S,3S
Internal sensors 20 internal sensors; integrated IMU
Actuators Automatic management of
Release/deploy mechanisms ; automatic
LNB/PA switching
Built in protection RBL; 10A Activation switch w/
MTBF>1000, 2A and 7A resettable fuses
Inertial
Measurement
Unit
6-axis MTD: (3-axis gyroscope, 3-axis
accelerometer) TDK ICM-20602
Mass 100 grams
Operating
temperature
-50 C to +125 C
Dimensions 96x96x25 mm – PC104
Table 1: ICEPS System Core specifications
ICEPS also includes an integrated laser communication
device designated PLM02, with a minimum speed of 115

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Kbps and a maximum speed of 10 Mbps. ICEPS and the
laser are featured in Figure 15.
Key to achieving higher speeds is the way the laser
driver is modulated; In PLM01 we were using laser
driver switching, but in this next generation we are using
a technique known as Quantum Square Pulse. This
technique allows not only higher modulation speeds, but
also enables driving more power to the laser emitter,
without by the dimming problem that affected PLM01.
Figure 15: ICEPS System Core for IRVINE03
6. Closing the link budget: Pointing accuracy vs.
Power density.
In order to ensure proper communication between two
points, a link budget must “close,” meaning that it
ensures the signal is not only detectable at the receiving
end, above ambient or system noise, but also that the
modulation of that signal is clearly detected, to be
properly processed at the terminus of the communication
pipeline.
In space communications, a mandatory condition is to
ensure enough photon flux density at the terminal for the
signal to at least be detected. Without this, no
communication link can be established. When the
transmission medium is laser radiation, a common
approach is to maintain high pointing accuracy of the
cubesat or spacecraft, so as to concentrate the laser beam
enough for it to reach a photon flux density that is over
the terminal’s detection threshold by at least ½ order of
magnitude, while maintaining low optical power output,
this way, a laser beam at a power level as low as 500
mW can be detected at distances as far as the orbit of the
moon, as demonstrated by LLCD on board LADEE
(NASA) in 2015.[8].
However, the pointing accuracy necessary for this kind
of spacecraft that ranges in the hundreds of kilograms is
outside the level that can be readily achieved by
cubesats, due to technical and budgetary restrictions.
Therefore, other methods must be used to achieve a
detectable photon flux density at the ground terminal.
Our approach to this problem is not trying to match
pointing accuracy, but to brute-force the optical power
delivered to the ground.
Optical power actually means a denser photon flux, no
more or less. Just more photons reaching the surface and
coupling that approach with photons of higher energy,
the same or better results can be achieved than with high-
end point accuracy systems that are beyond the reach of
most cubesats. In the case of LLCD and other spacecraft
using lasers, the frequency of choice is 1550 nm [9],
mostly because of the hardware availability for this
frequency as a legacy from the fiber optics industry, as
well as the relatively low atmospheric extinction that
frequency is subject to. Our approach is to use a 450 nm
frequency that is more than 3 times as energetic than the
1550 nm, so each visible photon packs 344% more
energy than IR photons.
It is true also that the 450 nm frequency suffers much
more atmospheric extinction than the 1550 nm.
However, laser link budget calculations show that the
energy per photon far outweighs the atmospheric
extinction problem, as shown in Figure 16.
Figure 16: Atmospheric transmissivity for visible
wavelengths
This approach then allows a bigger aperture angle and, as
such, a large beam footprint or “swath,” so the pointing

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inaccuracy inherent to magnetorquer or reaction wheel
ADCS systems are not only mitigated, but actually
rendered inconsequential for effective laser
communication. As per the following formulas:
Footprint diameter:
(1)
Slant range:
(2)
Beam aperture:
(3)
Where ߙ
௅
is the beam aperture, ݄ is the circular orbital
height, and ߚ is the NADIR inclination at the ground
station.
The link budget was constructed, taking into account not
only the classical link budget parameters, but also
parameters relative to the optical medium, such as
photon energy and collector areas. The link budget is
available in Appendix B and Appendix C.
PLM02, as embedded in ICEPS, is capable of a
minimum optical power of 0.5 W using 2 Watts of
electrical power and a maximum optical power of 7 W
using the bus-limited available electrical power of 25
Watts. Figure 17 shows a test fire of this laser setup in
the lab.
Figure 17: PLM02 on board ICEPS in test firing mode
Now that we can use all of the available power to
modulate at higher speeds, thanks to the QSP technique,
speed is only a matter of the switching method. See
Figure 18, where the case of PLM02 is done via a fast N-
channel MOSFET, due the kind of power being routed
through the diode and the circuit as a whole. Also, new
cooling techniques have to be applied, to maintain the
coherence of the quantum cascade flux, since at the
maximum optical power of 7 W it will have to dissipate
the heat produced by the use of 25 Watts of electrical
power using only passive cooling. That is why we use
the batteries as heat sinks, as EXA BA03S batteries
[10][11] were designed not only for storing electrical
power, but also for storing heat, giving it back
automatically at eclipse times when such heat is most
needed, this works also in conjunction with the NEMEA
thermal shielding [12] and the very lightweight structure
we created for the IRVINE03 cubesat hull.
Figure 18: PLM02 modulation detected at a
minimum speed of 2.25Mbps delivering 1.7W of
optical power.
IRVINE03 is scheduled for an ELaNA launch in 2020.
Its bus is right now is undergoing test and debugging at
the EXA facilities in Ecuador, as shown in Figure 19.
The IRVINE03 science mission is x-ray detection of the
Crab Pulsar flux from polar Earth orbit.
Figure 19: IRVINE03 flight model currently under
testing at EXA facilities.

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7.
The Next Generation of Laser emitters: PLM03
After PLM02 and IRVINE03,
we became aware that we
could create a hybrid laser/radio communication module
that could be added to any cubesat,
ranging from 1U to
24 U or even larger. Thus,
we began the design early
this year for a PLM03 device with the basic capability to
interface with SPI and I2C devices and with higher speed
capabilities starting from 10 Mbps and ramping up to 25
and 50 Mbps.
The module will have to be PC
compliant and dimensionally compliant with
connector’s architecture.
This is concept is rendered in
Figure 20.
On one side there is a radio receiver and in the other
there is the laser emitter, so
commands can be sen
the ground via radio at speeds as fast as 256Kbps and
laser can deliver greater amounts of data at a top speed
of 50Mbps.
Figure 20:PLM03
operation mode and
Actually, the high speed of the laser
poses the problem
that the traditional cubesat bus speed is limited by the
SPI and I2C devices to a maximum of 10Mbps, creating
a bottleneck for a laser device capable of higher
communication rates.
International Astronautical Congress
(IAC), Washington D.C., United States, 21-2
5 October 2019
Copyright ©201
9 by Ecuadorian Space Agency. All rights reserved
The Next Generation of Laser emitters: PLM03
we became aware that we
could create a hybrid laser/radio communication module
ranging from 1U to
we began the design early
this year for a PLM03 device with the basic capability to
interface with SPI and I2C devices and with higher speed
capabilities starting from 10 Mbps and ramping up to 25
The module will have to be PC
-104 format
compliant and dimensionally compliant with
the CSKB
This is concept is rendered in
On one side there is a radio receiver and in the other
commands can be sen
t from
the ground via radio at speeds as fast as 256Kbps and
laser can deliver greater amounts of data at a top speed
operation mode and
rendering
poses the problem
that the traditional cubesat bus speed is limited by the
SPI and I2C devices to a maximum of 10Mbps, creating
a bottleneck for a laser device capable of higher
The approach to solve
this problem was to develop
around
an I2C/SPI to USB bridge
and I2C compatible, but internally is USB for the
purpose of using its own MPU
connected via USB to a flash drive capable of 460
of read/write speed, being the sole device on the USB
internal network, so the OBC can transmit
or I2C to the bridge, which will
MPU, for storage on
the flash drive.
Once this operation is completed, the file is ready to be
transmitted. A
gain, the OBC will send the
the bridge for the MPU to read the file in the flash drive
then to be sent in the laser
pipeline operating at USB
speeds without the SPI/I2C bottleneck. This block
diagram and operation flow
is depicted on
Figure 21:
PLM03 Command pathway structure; To
send a file, the OBC first has to buffer it to the PLM03
512GB flash drive at I2C or SPI low speeds via the
I2C/SPI to USB bridge, then it has to send a command to
the PLM03 MPU via the same bridge
move
the file to the UART/USART Transceiver inside the
Laser driver at USB 2.0 speeds, effectively eliminating
the I2C/SPI speed bottleneck.
Experience has shown that the data sent from the ground
segment to the space segment is actually very little,
reduced to commands mostly
. W
designed PLM03 with a radio receiver
case that the laser reception is impaired by sever
atmospheric conditions, the radio on board is capable of
half duplex transmission at 256 Kbps
creates a
reasonable redundant
communication module to the telemetry and command
pathways in the spacecraft.
In reality, we set the
speed limit at 50 Mbps
. Although
allows for an upper limit of 116 Mbps
decided if the device will be available at this top speed or
at the nominal one of 50 Mbps
PLM03 will be capable of handling the same
optical/electrical power ratings as PLM02
5 October 2019
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Page 9 of 13
this problem was to develop
an I2C/SPI to USB bridge
, so the device is SPI
and I2C compatible, but internally is USB for the
purpose of using its own MPU
. That, in turn, is
connected via USB to a flash drive capable of 460
Mbps
of read/write speed, being the sole device on the USB
internal network, so the OBC can transmit
files via SPI
or I2C to the bridge, which will
then transfer them to the
the flash drive.
Once this operation is completed, the file is ready to be
gain, the OBC will send the
command to
the bridge for the MPU to read the file in the flash drive
,
pipeline operating at USB
speeds without the SPI/I2C bottleneck. This block
is depicted on
Figure 21
PLM03 Command pathway structure; To
send a file, the OBC first has to buffer it to the PLM03
512GB flash drive at I2C or SPI low speeds via the
I2C/SPI to USB bridge, then it has to send a command to
the PLM03 MPU via the same bridge
so the MPU will
the file to the UART/USART Transceiver inside the
Laser driver at USB 2.0 speeds, effectively eliminating
Experience has shown that the data sent from the ground
segment to the space segment is actually very little,
. W
ith that in mind, we
designed PLM03 with a radio receiver
. However, in
case that the laser reception is impaired by sever
e
atmospheric conditions, the radio on board is capable of
half duplex transmission at 256 Kbps
. This effectively
reasonable redundant
channel for the
communication module to the telemetry and command
In reality, we set the
laser
. Although
the circuitry on board
allows for an upper limit of 116 Mbps
, it still to be
decided if the device will be available at this top speed or
in the future.
PLM03 will be capable of handling the same
optical/electrical power ratings as PLM02
. That is, a

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minimum optical power of 0.5 W requiring 2 Watts of
electrical power and a maximum optical power rating of
7 W that requires 25 Watts of electrical power. Although
effective, high speed laser communications of at least 10
Mbps can be established in LEO and even MEO orbits
using less than 2 Watts of optical power. The capability
to handle 7 Watts of optical power was developed taking
into account the upcoming missions for the Latin
American Lunar Program, announced during the
IAC2018 as a joint venture sponsored by the IAF
GRULAC [13]. Under the direction of EXA, distances
as great as lunar orbit or the lunar surface will need that
kind of optical power delivery to achieve the necessary
photon flux density on the ground, using the brute-
forcing power approach to solve the challenges inherent
to cubesat architecture and financial limits.
PLM03 is still in development at the time of writing this
paper. The challenges still to be solved are clear, but
well understood. Actually, we are expecting the in-orbit
demonstration of PLM02 on board IRVINE03 in 2020 to
evaluate more precisely and realistically the limits and
performance of the technology, before moving forward
to a more commercial device that can be offered to our
community.
8. Conclusions
We think that the development of a space-to-ground laser
communications device able to be installed in cubesats as
small as 1U opens a plethora of opportunities to grow for
many applications in the space segment that right now
are limited due to radio technology. To summarize a few
advantages of laser communications technology to radio:
• Higher speeds and bandwidth using less power
• Not regulated by ITU, as it is outside the radio
spectrum
• Improved security due the laser propagation
properties.
• Zero paperwork complications
• Ground terminals as much more compact
• With the current trend of ground station
networks, operations become easier
• Less complicated link budgets due to the nature
of laser light propagation
On the other hand, there are the cons:
• Severe atmospheric conditions can impair
ground reception
• Lab testing must be done carefully, as laser light
can be dangerous at short range
• Current lack of optical ground station services
forces users to build their own
We think that due to the ever increasingly number of
users in the radio frequency spectrum, more and more, a
better solution is needed in the market for small to
medium cubesats. In this regard, the idea behind the
development of PLM03 is to offer a reasonably-
performing and safe compromise between radio and
laser.
9. References
[1] Irvine CubeSat STEM Program,
https://www.irvinecubesat.org/, (accessed
04.10.2019).
[2] Irvine Public Schools Foundation,
https://ipsf.net/, (accessed 04.10.2019).
[3] HELL: High powEred Laser moduLe for
quadcopters! 27 February 2015,
https://www.youtube.com/watch?v=UxyJaMFEKZI,
(accessed 04.10.2019).
[4] Arduino Uno Rev3,
https://store.arduino.cc/usa/arduino-uno-rev3,
(accessed 04.10.2019).
[5] B. Freeze, 9 April 2018,
https://twitter.com/DrBrentFreeze/status/983534805
982720001, (accessed 04.10.2019).
[6] B. Freeze, 28 Jun 2018,
https://twitter.com/DrBrentFreeze/status/101248918
7545583616, (accessed 04.10.2018).
[7] CNBC Television, SpaceX Launches Falcon 9
Rocket in CRS-16 Mission, 5 December 2018,
https://www.youtube.com/watch?v=UJFzELGUwo
A, (accessed 04.10.2019).
[8] R. Garner, Historic Demonstration Proves Laser
Communication Possible, 28 October 2013,
https://www.nasa.gov/content/goddard/historic-
demonstration-proves-laser-communication-
possible, (accessed 04.10.2019).
[9] Internet Society North America Bureau, The
Lunar Laser Communication Demonstration
(LLCD) -- David Israel and Donald Cornwell,
NASA, 27 January 2014,
https://www.youtube.com/watch?v=F7oJg3KUW9g,
(accessed 04.10.2019).
[10] R. Nader, High Energy Density Battery Array
for CubeSat Missions, IAC-16,B4,6B,x3240, 67th
International Astronautical Congress, Guadalajara,
Mexico, 2016, 26 - 30 September.
[11] CubeSatShop, BA0x High Energy Density
Battery Array,
https://www.cubesatshop.com/product/ba0x-high-
energy-density-battery-array/, (accessed
04.10.2019).
[12] R. Nader, SEAM/NEMEA: The Space
Environment Attenuation Manifold Shield For
Nanosatellites, IAC-11,B4,6B,x10064, 62
nd
International Astronautical Congress, Cape Town,
South Africa, 2011, 3 – 7 October.
[13] R. Nader, V. Munsami, A. Ramirez, C. Richins,
J. Thornton, P. Zamora, Latin America Beyond
LEO: Securing Regional Participation in the Moon
Village, IAC SpS, Bremen, Germany, 2018, 1 – 5
October.

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Appendix A: Vacuum testing of PLM01 Passive Cooling System

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Appendix B: PLM02 IRVINE03 Laser Link budget

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Appendix C: Pointing accuracy vs. High power delivery