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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 space image quality that has occurred ISS:that “NanoRacks CubeSat Deployer (NRCSD) on the ISS” https:// since time; even so, the pictures presented here 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! 16    Silicon Chip Celebrating 30 Years 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! 22    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. Celebrating 30 Years siliconchip.com.au 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. Celebrating 30 Years January 2018  23