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Monitoring our world
– and beyond –
with tiny satellites
Swarms of miniature satellites – some so small you can fit them in
the palm of your hand – are watching us from way out in space. They
take millions of pictures every day, beaming images down to Earth to
enable changes on our planet surface to be monitored in minute detail.
And one of the main factors providing the capabilities these
tiny satellites is the incredible progress in smart phone technology. In
effect, smart phone bits are watching us from up there!
by Dr David Maddison
14
Silicon Chip
Celebrating 30 Years
siliconchip.com.au
W
hile you may not have realised it, a modern
“smart” mobile phone has nearly all the components you need in an Earth-imaging satellite.
Relatively inexpensive, it has a high performance processor, a large amount of memory, cameras, accelerometers,
gyroscope, 3-axis Hall Effect magnetometer, GPS and GLONASS, a built-in battery and rugged construction.
Assuming its components will stand up to radiation, a
vacuum and temperatures between about -40°C and +80°C,
the only extra components needed are an external power
supply to keep the battery charged and a means to send
data back to Earth (smart phone signals won’t work from
space and no, ET can’t phone home!)
Another advantage of a smart phone is an open source
operating system such as Android which enables custom
software to be written to control the device.
If the electronics of the smart phone were to be built
from scratch, for a boutique application it would be an extremely expensive exercise.
But the development of phones is funded by billions of
terrestrial users – you and I – which is why these devices
are so affordable.
In 2011 NASA developed PhoneSat 1.0, with a CubeSat
form factor but actually based on the Nexus One smart
phone, using the Android operating system. It used an external Arduino processor as a “watchdog” to monitor the
phone and reboot it, in case it suffered a software crash.
The purpose of this exercise was to demonstrate the concept and to prove that the phone could survive in space
and send back its own status and picture data.
NASA launched some additional PhoneSats and in 2014
launched PhoneSat 2.5 with a mass of about 1kg. The PhoneSat 2 series is based around a Nexus S-series phone. The
mission objective was to test longer term missions in the
higher radiation environment of space to use smartphone
technology to control attitude control, data handling and
communications.
PhoneSat 2.5 used reaction wheels for attitude control
(see panel). It had a two way S-band radio (2 - 4GHz) with
a high gain antenna so it could be controlled from Earth.
PhoneSat 2.5 remained in orbit from 18 April until 15
May 2014.
Oil tanks usually have floating tops, so called “external
floating roof tanks” so by imaging these tanks and analysing
their shadows it is possible to infer, for example, how much
oil a country is exporting or about to export. The daily
imagery provided by Planet allows a daily update of oil data
that can be used by people working in the crude oil market.
Downlink data was received by radio amateurs around
the world and sent to NASA.
From tiny satellites . . . to teeny ones!
Satellite sizes are normally classified by mass. At the
lower end of the size range, femtosatellites are between 10
and 100g, picosatellites are 100g to 1kg, nanosatellites are
1 to 10kg, microsatellites are 10 to 100kg and small satellites are 100 to 500kg. Of these categories the nano and micro size satellites segments are growing the most rapidly.
CubeSats (see siliconchip.com.au/Series/281) which are
based on one or more 10 x 10 x 10cm standard units are
NanoRacks CubeSat Deployer
CubeSats are normally launched as opportunistic payloads attached to other satellite launch platforms but once in space they
still have to be somehow ejected away from the main spacecraft.
This is normally done by a deployment module which contains a
spring which pushes the satellite away.
One device designed to do this, shown on page 19, is the CubeSat Deployer made by a company called NanoRacks. It is intended
to launch CubeSats from the International Space Station (ISS)
where they have been taken as part of a normal cargo delivery.
Each Deployer can hold one 6U CubeSat or six 1U or a combination of different sizes that add up to 6U. Eight 6U modules
The
picture ofper
Earth
taken from
canfirst
be deployed
ISS from
airlockspace.
cycle,Itsowas
theoretically
up atoV2
48
rocket launched from White Sands Missile Range in the US
1U
satellites
could
be
launched.
on October 24, 1946. Pictures in this article demonstrate the
Corporate
videoinshowing
CubeSats
being
deployed
from the
dramatic
increase
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ISS:that
“NanoRacks
CubeSat
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https://
since
time; even
so, the
pictures
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from
small
youtu.be/AdtiVFwlXdw
size
satellites are not the best available, better images can be
obtained from full size satellites with large optical systems.
siliconchip.com.au
Deployment in 2016 of two of the final eight of Planet Lab’s
Flock 2e’ Doves from the International Space Station. The
life-time of these tiny satellites is about one year if launched
from the ISS in a 420km altitude orbit inclined at 52°.
Celebrating 30 Years
January 2018 15
Images taken on three consecutive days by Planet Labs satellites over Port Botany in Sydney on January 21, 22 and 23 last
year showing ship and cargo movements. Automated software can be used to track shipping movements in and out of port.
classified as nanosatellites.
The cost of launching a satellite is mostly proportional
to its weight and volume so the lighter and more compact
the satellite is, lower the launch cost.
Huge numbers of small size satellites have now been
launched and in this article we will look at just a few types
that are being used to conduct Earth imaging and other
forms of monitoring.
Videos: “Android Phone as Autonomous Micro-Satellite:
PhoneSat” https://youtu.be/uXDPhkbTHpU and “PhoneSat
Mosaic of Earth” https://youtu.be/dzs2wc2JEWw
For more information on a variety of PhoneSats see http://
phonesat.org/
Planet Labs
Planet Labs, Inc (www.planet.com/) is producing small
size satellites for Earth imaging with an objective of daily
updates.
This is quite unlike Google Earth which is updated infrequently, on average every 1 to 3 years. Compared to Google
Earth though, the imagery from Planet Labs is at a lower
resolution, of around 3 to 5 metres, while Google has a resolution of between 15cm and 15 metres, depending upon
which platform was used to do the imaging.
The advantages of Planet Labs imagery are its relatively
low cost and the regular updates.
Planet refers to individual satellites as Doves and the
satellite constellation (group of satellites) as a Flock. Planet mainly uses off-the-shelf components in its satellites.
With the exception of five special satellites (RapidEye),
most of the satellites themselves are built on a standard
CubeSat platform of 3U (3 unit) size, making them nominally 10cm square and 30cm in length before solar panels
and antennas are unfolded and with an extra 4cm of length
(to make a total of 34cm), as allowed within the CubeSat
specification. The CubeSats weigh around 5kg each.
Planet satellites not based on the CubeSat model are the
RapidEye models which they acquired when they took over
another company.
RapidEye models are a more conventional design based
upon the SSTL-100 spacecraft bus (the standard basic structural frame, propulsion unit and communications that can
be used for a variety of spacecraft models).
These satellites are about one cubic metre in volume
and weigh about 150kg so are categorised as “small satellites” but we will focus primarily on the Planet CubeSats.
The first Planet CubeSats, Doves 1 through 4, were
launched in 2013 as demonstrators. Flock 1, consisting
of 28 Doves, was launched in February 2014 from the International Space Station (ISS) in a short-lived orbit of
400km altitude.
Since then a number of additional Flocks have been
launched comprising Flocks 1b, 1c, 1d, 1d’, 1e, 1f, 2b, 2e,
2e’, 2p and in February 2017, Flock 3p.
Planet looks for the cheapest launch platform available
on which to piggyback its satellites. There have been two
launch losses so far: 26 satellites were lost with the launch
failure of Flock 1d and eight were lost with Flock 1f.
The orbit life-time of these satellites is about one year if
launched from the ISS in a 420km altitude orbit inclined
at 52°, or two to three years if launched from a rocket in
a sun synchronous orbit (SSO), which is a polar orbit of
475km inclined at 98°.
Planet aims to have up to 55 satellites in ISS orbit and
100-150 in SSO. In ISS orbit the equator crossing time is
variable and in SSO it occurs between 9:30-11:30AM local solar time.
The communication frequencies used by the Doves are
A Planet
Labs Dove CubeSat. Note the
artwork which is
applied to their satellites.
At right is a Flock 2e’ Dove after
its launch from the ISS, with its
solar panels now unfolded. It appears
much larger here than it actually is!
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siliconchip.com.au
Perhaps even more dramatic, these images from Planet Labs satellites show the “development” of illegal gold mining in a
protected area of Peru – the left photo on 29 January 2016 and the right on 4 November 2016. The Amazon Conservation
Association used this imagery to issue alerts about this activity and the Peruvian Government intervened to stop it.
X-band: 8025-8400MHz for downlink and 2025-2110MHz
for uplink with additional backup frequencies. Ground
stations are located in the US, UK, NZ, Germany and Australia and utilise a 5m dish antenna.
There are three generations of Dove optical sensors, the
earliest being 11MP resolution and the latest being 29MP.
The most recent launch of Planet CubeSats was the successful deployment, on 31 October, of six SkySats and four
Doves (flock 3m) on Orbital-ATK Minotaur-C rocket.
After this launch there were 160+ Doves and 4 Planet
satellites in orbit, enabling the fulfilment of the objective
of being able to image the entire Earth’s surface every day.
This launch constituted the largest number of satellites
launched on one rocket and the constellation of 149 satellites is also the world’s largest privately-owned constellation.
Each of the Flock 3p satellites has a 200Mbps data downlink and produces two million square kilometres (a little
more than the area of Queensland) of imagery per day.
See video “Mission 1: A Record-Breaking Launch” https://
youtu.be/6VuDsCfuoM8
Sailing in the upper atmosphere
Once released from their launch vehicle, Planet’s satellites navigate to their desired positions in an unusual way.
Even at orbital altitudes there are minute traces of atmosphere so the solar panels are used as “sails” to navigate to
the desired position.
When they are at right angles to the orbital track they
offer seven times more “wind resistance” than when they
are edge on.
Tilting the solar panels is used to manoeuvre the satellites into the desired position by increasing or decreasing
the drag caused by the panels.
Once in the correct position the satellites need to be
oriented correctly and use magnetorquers and reaction
An example image from Planet Explorer using their free account, showing part of the Latrobe Valley in Victoria with
several coal mines and the recently-closed Hazelwood Power Station (barely visible) just south of Morwell. Note the the
timeline along the bottom of the image, you can drag the cursor along this to see how the landscape changes with time.
Higher resolution is available with a paid account.
siliconchip.com.au
Celebrating 30 Years
January 2018 17
Spire’s Lemur-2 3U CubSat for monitoring shipping
movements and weather.
Video: “Tiny satellites that photograph the entire planet,
every day | Will Marshall” https://youtu.be/UHkEbemburs
NASA’s PhoneSat 1.0 and PhoneSat 2.5. PhoneSat 2.5 has
solar cells on its surface. The satellites are based upon
a 1U CubeSat form factor (10 x 10 x 10cm). The antenna
really is a piece of metal tape measure… and why not?
wheels. (See the separate panels for more information on
these devices).
Planet’s imagery has a wide variety of uses, mainly involved with observing changes in areas of interest with time.
As examples, one can look at the development of mines,
changes in forestry due to logging, ship movements in and
out of port, changes in the urban environment and monitor crop growth and health.
You can set up a free account with Planet to explore your
own areas of interest, although the imagery available will
be at a lower resolution than a paid account. It could be
good for school projects, especially watching changes in
the landscape throughout the year. Some user stories can
be read at https://medium.com/planet-stories
Spire Global, Inc.
Spire (https://spire.com/) is a company that has a number
of CubeSats and describes its business as “space to cloud
data and analytics”.
In addition to acquiring data from its own constellation
of satellites, it also offers data analysis services. It specialises in data for ship tracking, weather, aviation (in the near
future) and custom data acquisition.
Spire originally started out to create the crowd-funded
Arduino-controlled ArduSat CubeSat on which people
could do their own experiments.
Spire currently uses their 3U CubeSat Lemur-2 satellite
for ship tracking and weather observation. It carries as a
payload both STRATOS (GPS radio occultation payload)
for weather monitoring and SENSE (AIS payload) for monitoring ship movements.
(In GPS radio occultation, a low-Earth-orbit satellite
receives a signal from a GPS satellite, which has to pass
Spire uses its constellation of at least 40 CubeSats to monitor world-wide ship movements by monitoring signals from the
Automatic Identification Systems (AIS) of boats and ships. AIS automatically transmits a vessel’s identity, position, course
and speed. When it was originally developed in the 1990s AIS was intended for surface use only and was not intended to
be or thought to be trackable from space. There are significant issues related to receiving the signals from space, partly
due to the Time Division Multiple Access (TDMA) nature of the AIS signal, which utilises 4500 data slots per minute.
Due to the large view of the surface the satellite has, it might be overwhelmed by more signals than this. The problem is
resolved by Spire by undertaking extensive data analysis to extract the desired information.
18
Silicon Chip
Celebrating 30 Years
siliconchip.com.au
RECEIVER
SOURCE
PLANET
Principle of GPS radio
occultation. The refraction
ATMOSPHERE
of the GPS radio signal is
measured in order to establish an atmospheric profile.
Image author: MPRennie.
Comparison of actual measured data obtained from Spire
and that from the Global Forecast System (GFS) numerical
weather model showing a high degree of correlation.
through the atmosphere and gets refracted along the way.
The magnitude of the refraction depends on the temperature and water vapour concentration in the atmosphere).
Monitoring ship movements with AIS
To monitor shipping, Spire’s constellation listens to
the Automatic Identification System (AIS) of over 75,000
maritime vessels on the ocean at any given time and enters
them into their database. Over 28 million AIS messages are
intercepted each day.
The information can be used by shipping companies to
keep track of their ships and make sure they don’t enter
areas they are not meant to go or determine if they will arrive in port on time.
Other customers can also gain access to the location
and probable destination of any of over 300,000 ships in
the database.
The likely destination of any given ship is determined
by machine learning algorithms based on the history of the
particular ship of interest and this information is valuable
to competing shipping companies.
SILICON CHIP has featured two articles on AIS, in August
GPS limitations in space
A common complaint about developers of small size satellites is the regulatory environment with respect to the sale of
GPS receivers. There are restrictions to civilian GPS receivers
under the Wassenaar Arrangement to prevent the proliferation
of technologies with dual military and civilian use.
Since GPS can be used to guide an ICBM to within a few metres of its target, there are restrictions imposed on GPS manufacturers on the maximum altitude and speed at which they can
operate before the GPS ceases operation. The limits are set at
18,000m altitude and 1,900km/h. These restrictions are also a
frustration for high altitude balloon and model rocket operators.
Unrestricted GPS receivers are available but under
great bureaucratic frustration and regulatory controls.
Most space-qualified GPS
receivers are quite expensive
(thousands of dollars) but we
have noted a Venus838FLPxL GPS module, as commonly
used in phones, for sale with customised firmware suitable for
space applications (unrestricted speed and altitude) for US$99.
siliconchip.com.au
2009 (www.siliconchip.com.au/Article/1528) and January
2010 (www.siliconchip.com.au/Article/41).
When it was originally developed in the 1990s, AIS was
intended for surface use only and was not intended to be,
nor thought to be, trackable from space.
In fact, there are significant issues related to receiving
the signals from space. This is partly due to the Time Division Multiple Access (TDMA) nature of the AIS signal
NanoRacks CubeSat Deployer
CubeSats are normally launched as opportunistic payloads attached to other satellite launch platforms but once in space they
still have to be somehow ejected away from the main spacecraft.
This is normally done by a deployment module which contains a spring which pushes the satellite away.
One device to do this is made by a company called NanoRacks and is called the CubeSat Deployer. It is designed to launch
CubeSats from the International Space Station (ISS) where they
have been taken as part of a normal cargo delivery.
Each Deployer can hold one 6U CubeSat or six 1U or a combination of different sizes that add up to 6U. Eight 6U modules
can be deployed per ISS airlock cycle so theoretically up to 48
1U satellites could be launched.
Corporate video showing CubeSats being deployed from the
ISS: “NanoRacks CubeSat Deployer (NRCSD) on the ISS” https://
youtu.be/AdtiVFwlXdw
Loading a CubeSat for launch from the ISS into a
NanoRacks Deployer.
Celebrating 30 Years
January 2018 19
Orienting and propelling a
small satellite in space
Most satellites need to have a particular orientation in space so that their sensors and solar panels panels point in the
right direction.
Unlike full size satellites which might
be as large as a bus, small satellites such
as CubeSats are generally not permitted to carry chemical propellants as
they are usually opportunistic payloads
on launches of of larger satellites and the
mission safety cannot be compromised. Orienting the satellite
in space is known as attitude control.
Rare earth magnets are the simplest way to orient a spacecraft.
They align themselves with the Earth’s magnetic field lines like a
compass needle thus giving a predictable orientation although
the orien- tation of the spacecraft varies throughout the orbit.
A magnetorquer is a system of electromagnets to orient a spacecraft in orbit.
It functions much like a magnet but
the power to the coils of the electromagnets can be turned on and off in
association with a feedback system to
achieve the desired orientation.
A reaction wheel or momentum wheel is a system of motorised flywheels that allow a spacecraft to be oriented
by applying a torque to a flywheel. The spacecraft and the wheel
will rotate in opposite directions. The flywheel is stopped when
the desired orientation is reached.
While propellants are generally not permitted, one innovative idea is to use THRUSTER
water as a fuel.
O2 PLENUM
Water is launched
H2 PLENUM
with the satellite
and then electricity from solar panels is used to electrolyse the water into hydrogen
and oxygen which
together form a
rocket fuel.
Rodrigo Zele- WATER TANKS
don at Cornell
INTEGRATED SWIFT
AVIONICS
University and
also the company Tethers Unlimited Inc.
are both developing water propulsion. Using this propulsion system
it should be possible to accelerate
a 3U CubeSat to 1-2km per second.
Other thrusters that can be used on
CubeSats use compressed gas which
can be ejected cold or electrically heated to provide greater thrust.
It is sometimes necessary to have
more than one attitude control system on a spacecraft to compensate
for various disadvantages different
attitude controls systems may have.
Astro Digital image of California farmland processed using
the NDVI (normalised difference vegetation index) calculation.
which creates 4500 data slots per minute but because of
the large view of the surface the satellite has it might be
overwhelmed by more signals than this.
Spire has resolved this problem by extensive data analysis to extract the desired information.
Monitoring the weather
To monitor the weather Spire uses GPS radio occultation to derive the temperature, pressure and water vapour
content of the atmosphere.
It observes the degree of bending (refraction) of the signal
and time delay of a GPS that is low on the horizon compared to an observing satellite.
The refraction is too small to observe directly but can be
inferred by measuring the Doppler shift of the signal for a
given geometry of the transmitter and receiver.
Videos: “Small Satellites With a Huge Impact” https://
youtu.be/aQb-XacYQvw, “Why Spire Uses Satellites To
Listen To Earth’s Oceans | Forbes” https://youtu.be/JHduJEvWrN8 and “Peter Platzer talks about trying to revolutionise weather forecasting, one satellite at a time” https://
youtu.be/M_x-Jvk4lqc
GeoOptics
GeoOptics, Inc. (www.geooptics.com/) will also be using GPS radio occultation techniques to provide weather
data. (In fact, it is also possible to use other global navigation systems such as the European Galileo and the Russian GLONASS.)
They are in the process of installing a constellation of
satellites made by Tyvak, Inc (www.tyvak.com/) that are a
double-wide 6U CubeSat form factor, meaning dimensions
of 60 x 20 x 10cm.
Its satellites weigh around 10kg and produce an average
of 21W from their solar panels. They use magnetorquers
and reaction wheels for attitude control and star trackers
to determine attitude.
They named the satellite CICERO or Community Initiative for Cellular Earth Remote Observation. It will eventuPHASED 3 X 3 PATCH ARRAY
FOR GPS L1 AND L2
UHF ANTENNA
POD GPS ANTENNA
UMBILICAL AND
TEST PORTS
20
Silicon Chip
Celebrating 30 Years
MAG AND SUN
SENSOR MODULE
STAR
TRACKERS
siliconchip.com.au
Thumbsat
Circuit board
of ThumbSat
shown without
the “vane” or
the camera. The
satellite will fly
as a bare circuit
board without an
enclosure.
NDVI show areas with the highest amount of vegetation
in the brightest colours Vegetation in California is the
most active in spring.
Cutaway
view of the
Landmapper-BC,
a 6U CubeSat
with 3U
side-byside.
ally form a constellation of 24 or more satellites.
In addition to using GPS radio occultation techniques
CICERO will also observe signals reflected off the ocean
(reflectometry) to determine ocean temperatures and wind
speeds.
Landmapper
Astro Digital US, Inc (https://astrodigital.com/) has a
30-satellite constellation comprising 20 16U CubeSat 20kg
Landmapper-HD satellites and 10 6U CubeSat 10kg Landmapper-BC satellites.
The Landmapper-HD constellation images all agricultural
land on Earth every 3-4 days at a resolution of 2.5 metres
and it orbits at an altitude of 650km. Its largest component
is its telescope. It has a camera that consists of a 5-band
spectral imager taking pictures in the
blue, green, red, red edge and
near infrared parts of the
spectrum which are assembled into individual images of about 450
square km.
The spectrum bands
used match that of
Landsat so historical
images can be compared. This constellation generates 15TB of
data per day and 25 million square km are imA cutaway view of the
Landmapper-HD satellite. Most of the lower
portion of the satellite
is the telescope. This is
large for a CubeSat, at
16U size.
siliconchip.com.au
Thumbsat (www.thumbsat.com/) is a femtosatellite (10-100g)
platform, designed for researchers to get their experiments into
orbit for around US$20,000.
It coexists with a companion project, Thumbnet, which is a
network of amateur trackers using software-controlled radios
with automatic antenna pointers to receive the data and upload it
via the Internet.
EXPERIMENT (VARIABLE
These devic- HIGH DEFINITION
SIZE AND MASS)
“SELFIE” MICRO CAMERA
es have not yet ON SHAPE MEMORY
ALLOY
BOOM
been launched
TRANSMITTER
CUSTOM WHITE
but like KickCOATING FOR
Sat, show the
THERMAL BALANCE
potential for MICROCONTROLLER
BATTERY
even larger and
cheaper techGPS
nologies for
Earth surveillance.
As of July
SHAPE MEMORY ALLOY
DEPLOYABLE TAIL/ANTENNA
2017, there is
an agreement
with CubeCab
to launch 1,000
ThumbSats on
its launch veDEPLOYABLE VANE FOR
AERODYNAMIC STABILITY,
hicles.
DRAG ENHANCEMENT
AND RADAR SIGNATURE
ENHANCEMENT
Thumbsat in one possible configuration. To the left is a
vane to provide some drag in the extremely thin traces
of atmosphere and therefore stability in orbit and also to
increase visibility to radar. To the lower right is a camera
of 1048 x 1536 pixels which can be fitted with a variety of
lenses. On the main board there is a 100mW transmitter
operating in the 400MHz band, a battery and power supply,
a microcontroller, a GPS receiver and in the centre with
the red marking is the customer experimental payload
which can be up to 48 x 48mm per side and 15 to 32mm
thick with a mass of up to 25g. Note the scale at top left.
Celebrating 30 Years
January 2018 21
Build your own CubeSat
The are many opportunities
to build your own CubeSat or
other small-size satellites and
this can be done relatively inexpensively – although launching it is by far the biggest cost
and you will likely have to share
the cost with others or crowdfund your project.
CubeSat is by far the most The PhoneSat, developed
popular format for projects of by NASA, is a CubeSat that
this nature. In Australia there easily fits into one hand!
are CubeSat groups in Sydney, Melbourne and Perth. You can find resources at www.
cubesat.org/
Two examples of the many companies selling off-the-shelf
components for CubeSats is at www.cubesatshop.com/
products/ and at www.cubesatkit.com/
An Australian company, Freetronics, sells Arduino controllers
for CubeSats (www.freetronics.com.au/collections/ardusat).
Johnathan Oxer, the owner of Freetronics, talks about Arduinos
in space in this video: “Deploying software updates to ArduSat
in orbit - Jonathan Oxer - Friday Keynote - Linux.conf.au 2014”
https://youtu.be/0GHMTXiDqoA
EEVBlog talks to Jonathan Oxer “EEVblog #519 - Ardusat Arduino Based CubeSat Satellite” https://youtu.be/
WCfG0OBEPHM
Preliminary testing to test the concept of using a smart phone
as a phone sat by launching it on a rocket is shown here: “PhoneSat Rocket Launch Documentary” https://youtu.be/nSyWDqgNRmo and “NexusOne/Arduino PhoneSat Satellite Launch Video”
https://youtu.be/hQ7pUroGvFc
Some basic information on building your own satellite and
some links to other articles: https://makezine.com/2014/04/11/
your-own-satellite-7-things-to-know-before-you-go/
A project that does not appear to be active but was about making high resolution imagery of the earth with CubeSats contains
some useful calculations in various areas, especially for those
doing imagery and a discussion of the constraints: https://sites.
google.com/site/fiveguyscubesats/
Lunar Flashlight, a mission planned for November this
year, will detect water ice (especially in the shadows of
craters) but in addition will look for other other volatile
compounds and will use a near infrared laser and a
spectrometer to detect these materials. It will be the first
time a laser has been used to detect ice beyond Earth.
aged daily with a swath width of 25km.
The Landmapper-BC constellation satellites complement the data from Landmapper-HD and produce images
of 22-metre resolution with an area of 30,000 square km.
It takes images in the red, green and near infrared parts of
the spectrum. Like the HD it orbits at an altitude of 650km.
All of the globe is imaged daily with this lower resolution
constellation, generating 1.2TB of data per day per satellite and 150 million square km are imaged per day with a
swath width of 220km.
Both satellites are in a Sun-synchronous orbit (SSO)
which means they cross the equator at the same time each
day. Orbit lifetime is five years for both constellations.
Some examples of imagery can be viewed at https://
astrodigital.com/gallery/#aral-sea As with Planet, you can
sign up for free for a limited access account to view imagery or pay for a less restricted account.
IceCubes to the Moon
Lunar IceCube and Lunar Flashlight are two planned
NASA missions to send 6U CubeSats to the moon.
IceCube is planned for 2019, to determine the location
and extent of ice deposits on the moon. IceCube weighs
14kg and will employ a spectrometer to detect ice and a
tiny RF ion engine using iodine as the propellant and generating 1.1mN of thrust (0.1g of force) from a 50W power
input, for manoeuvring.
Lunar Flashlight, planned for launch in November this
year, will also detect water ice (especially in the shadows of
craters) but will also look for other volatile substances with
a near-infrared laser and a spectrometer. This will be the
first time a laser has been used to detect ice beyond Earth.
CubeSat mission to Mars
This image, courtesy Candadian Space Agency, (www.
asc-csa.gc.ca) shows the basic “rules” of a CubeSat.
There’s a wealth of information on the ’net if you want
to build your own – and get it into space!
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Silicon Chip
Mars Cube One or MarCO are two 6U CubeSats (MarCO
A and B) that will be the first CubeSats to leave Earth’s orbit when they are launched in May of this year.
They will go to Mars as part of NASA’s InSight Mars landing mission and will act as telemetry relays for the lander.
Since the InSight vehicle is landing beyond line of sight
from Earth, the CubeSats will establish a direct radio relay link to Earth.
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Artist’s impression of MarCO spacecraft relaying radio
signals back to Earth as the InSight landing vehicle
descends to Mars.
They are not crucial for the mission as the lander will
retransmit its data directly to Earth when line of sight is
established but they are intended to demonstrate that CubeSats can work beyond the constraints of Earth orbit and to
act as relay stations for future missions. Presumably they
could also be used for planetary imaging just as on Earth.
During the lander descent MarCO will receive data at
8kbps and relay it back to Earth at the same rate in the Xband (roughly 7 to 11GHz).
MarCO weighs around 14kg, can produce 35W from solar
panels (at Earth-Sun distance but less at Mars) and has Vacco cold gas thrusters for manoeuvring and attitude control.
It uses standard 18650B batteries (as typically used in
laptops, high performance torches and Tesla cars) configured as 3S4P. It will have a customised Iris V2 softwaredefined radio with a transmit power of 4W. Attitude determination and control will be reaction wheels, a gyro sun,
sensors and a star tracker.
Video: “MarCO: First Interplanetary CubeSat Mission”
https://youtu.be/dS Q7BFGuu0
Where to next?
We have seen how small size satellites, especially those
in the CubeSat form factor can provide daily imagery of
the Earth, can go to the moon and even go to Mars. They
are also within the capability of small, budget-constrained
groups to design, build and have launched.
SC
So where will they go next?
Rendering of MarCO, the first interplanetary CubeSat.
siliconchip.com.au
Do tiny satellites such as CubeSats
pose a risk to other satellites?
In August 2016, the European Space Agency reported that a <5
mm fragment of space junk collided with its Sentinel 1A spacecraft – and tore a hole nearly half a metre wide in one of its solar panels. Unfortunately, that produced yet more space debris!
It’s not the first collision in space. In our story on the Iridium
Satellite Phone system (SILICON CHIP, November 2017) we told
how in 2009 an errant “dead” Russian satellite (Kosmos 2251)
collided with, and destroyed, the new Iridium-33 satellite.
A French satellite was hit and damaged by debris from a French
rocket which exploded ten years earlier. And a Chinese test, which
used a missile to destroy an old weather satellite, added more
than 3000 pieces to the debris problem.
Even the Hubble telescope has had significant damage to one
of its cameras, probably caused by a collision in space.
At last count, NASA estimated there were more than 150 million fragments of space debris, ranging from a millimetre to
many tens of metres in size. Half a million are larger than a marble – and at the speed they travel, they can do immense damage.
The problem is, basically, that when satellites are decomissioned, most are left in orbit – indeed, many are out of fuel so
ground controllers can do nothing to move them out of the way.
Enter the CubeSats
The low-Earth orbit area used by the majority of CubeSats
is getting increasingly cluttered, not just with junk but with the
hundreds of CubeSats being deployed each year. Many of these
will have a relatively short-term decaying orbit then will re-enter
the Earth’s atmosphere and burn up. Problem solved?
But many won’t – and they will add to the growing concern
for space scientists. In fact, both NASA and the ESA have departments specifically set up to track space junk. Even though current
international guidelines recommend satellites be removed from
orbit within 25 years, experts say that’s simply not fast enough.
Where spacecraft are manned (eg, the ISS), NASA draws an
imaginary box measuring 50km x 50km x 1.5km around the craft.
If their monitoring predicts that any debris or another spacecraft will pass within this box, plans are made to move the craft
slightly, to “batten down the hatches” in the craft and/or to move
the crew to the safety of the more secure transport spacecraft.
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