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Making Phone Calls via Satellite By Dr David Maddison Being able to instantly communicate with anyone on Earth at any time has long been a dream of mankind. It first became at least partly realisable with the development of radio and the conventional telephone system. However, radio and mobile cellular telephone systems still have their limitations. Here’s how you can now make a phone call from anywhere to anywhere, via satellites orbiting high above you in space. . . 24 24  S Silicon Chip Celebrating Celebrating30 30Years Years siliconchip.com.au T HE ULTIMATE COMMUNICATIONS SYSTEM is one in which each person has their own small, wireless, handheld personal communications device which will work anywhere on Earth at an affordable cost – and preferably offering high speed data transfer with Internet connectivity. Conventional mobile phones come close to this ideal but can only work within the limited range of a cellular tower. With 4G cellular service, this might be several tens of kilometres under ideal conditions but much less in common scenarios. In a large country like Australia or in undeveloped countries it is simply not economically feasible to install base stations in enough locations to offer universal coverage. Nor is it possible to have base stations at sea, nor base stations continuously accessible by aircraft, so other solutions are necessary. As early as 1945 Arthur C. Clarke recognised the problems of the limited range of central radio transmitters and proposed a system of orbiting “rocket stations” (or satellites as we now know them) to provide global coverage of radio broadcasts. You can read his original article titled “World Extra-Terrestrial Relays – Can Rocket Stations Give Word-wide Radio Coverage?” from the October 1945 Wireless World at siliconchip.com.au/l/aaeo Geostationary vs LEO orbits Satellites can be placed into two possible orbital configurations: geostationary, where the satellite will appear to remain at the same point above the Earth; or low Earth orbit (LEO), where the satellites move rapidly and can only maintain contact with a particular point on the Earth for a limited time, usually just a few minutes. To provide global or closeto-global coverage, at least three or more geostationary satellites are required – or a much larger number of LEO satellites. In the case of LEO satellites they must be able to hand over any existing radio link to the next satellite that will become visible to a linked Earth station (eg, a phone). Some satellite phone systems don’t aim for global coverage but only regional coverage so fewer satellites are needed. Geostationary satellites orbit at an altitude of 35,786km above the Earth’s equator and their orbital period is the same as the Earth; thus they appear to be stationary to a ground observer. Any fixed satellite dish you see will be pointing at such a satellite. There are several disadvantages of these satellites for telephony. One is that there is a noticeable delay in speech due to the great distance the radio signal has to travel (each siliconchip.com.au Diagram from Arthur C. Clarke’s 1945 article showing how three orbiting geosynchronous satellites could provide global radio coverage. The satellites would also be able to communicate with each other. The first maritime telecommunication satellite system, Marisat used this scheme when its three satellites were launched in 1976. leg of the trip takes around 0.12 seconds or 0.24 seconds round trip). Also, compared with LEO satellites, a larger amount of transmitter power is required in both directions due to the greater distance. The line-of-sight between the Earth station and the satellite can be interfered with by objects such a s b u i l dings, trees or geographical features. The Earth station is also limited to below 7080° north or south of the equator. LEO satellites typically orbit at an altitude of between 640 and 1120km, giving an orbital period of 1hr 37m to 1hr 47m and a velocity of 7.5 to 7.3km per second respectively. For an altitude of 760km, which gives a 1hr 40min orbital period, a coverage cell on the ground of around 2800km raOn these pages: an artist’s impression of Inmarsat’s Alphasat, one of four satellite phone providers available in Australia. This image does not convey the huge size of this satellite with the solar array spanning 45m and the antenna some 9m in diameter. Celebrating Years Celebrating 3030 Years N November ovember 2017  25 2017  25 with each other so a link can be seamlessly handed over to the next satellite that comes into view and the views must overlap to prevent the call being lost or interrupted. Satellite phones Another diagram from Clarke’s article showing “extraterrestrial relay services”. The direction of the arrows represent uplinks or downlinks. dius can be provided. A typical link with a ground station (phone) will last from about 4-15 minutes depending on the relative position of a satellite and ground station. Consider the cell of 2800km radius mentioned above, that would be traversed in about 12.5 minutes at 7.47km per second, the orbital velocity of a satellite at 760km altitude. The round-trip delay for that LEO satellite is very much shorter than geostationery– just 0.005 seconds (compared to the 0.24 seconds mentioned earlier). However, since LEO satellites do not remain in the same place, they must be in placed in orbit in communication There are several satellite phone systems currently in use, with more on the horizon. Systems which use geosynchronous satellites include those provided by AceS, Inmarsat, Thuraya, MSAT/SkyTerra, Terrestar and Pendrell Corporation (yet to be placed into service). Systems which use LEO satellites are provided by Globalstar and Iridium. Satellite phones operate in the “L” band which is defined by the Institute of Electrical and Electronics Engineers (IEEE) as the band from 1GHz to 2GHz. Iridium phones operate in the range from 1616MHz to 1626.5MHz; Inmarsat phones operate in the range from 1525MHz to 1646.5MHz; while Thuraya phones use the range from 1525MHz to 1661MHz. Compare this with land-based mobile phones which operate in the 800MHz to 900MHz and 1800MHz to 1900MHz bands (although there are other bands coming on line as other services are moved). Note that while the L band is used for mobile uplinks and downlinks, the satellites may use other bands for control and management purposes and for communicating with their companion satellites. Satellite phone physical format Portable satellite phones come in three main physical forms. These are: a standalone handset, which is usually larger than a modern mobile, mainly because of the relatively large external antenna; a separate “hot spot” device that wirelessly connects to a standard mobile and uses dedicated Apps on the mobile; or a “sleeve” into which a standard The Thuraya Satsleeve+. It clips to the back of a smartphone and establishes Inmarsat IsatPhone 2 handset. This a wireless connection. The phone (with the appropriate App) acts as phone is said to register onto the Iridium Extreme 9575 handset. It is compact, satellite network within 45 seconds the user interface. A dedicated model for the iPhone also plugs in via the rugged, water and dust resistant and offers and also has a standby time of 160 four hours talk time and 30 hours standby time. hours and a talk time of eight hours. phone’s Lightning connector. 26 Silicon Chip Celebrating 30 Years siliconchip.com.au Operational scheme for Iridium. The abbreviation AES stands for Aircraft Earth Station and is for communications between an aircraft and the satellite while ISU means Iridium Subscriber Unit, for a handset or modem. Note the communications links between the satellites. smart phone is inserted and like the hot spot device, uses dedicated Apps on the phone. In addition to these devices, there is also a wide variety of dedicated marine, data and other products. Antenna systems One challenge of satellite phones designers is to provide a highly efficient antenna in a small package. Arguably, it is one of the most important elements of a satellite phone. Inmarsat Wideye iSavi terminal for the Inmarsat IsatHub service. The IsatHub service offers stated data speeds of 240kbps uplink or 384kbps downlink, a high quality voice line and ability to send texts, emails and access the internet. It can be connected to an iPhone or Android mobile phone. siliconchip.com.au One type of antenna used as an external antenna for Iridium phone equipment is a “hockey puck” style and has a gain of 3dBic (dBic is gain over isotropic, circular polarisation), 50 ohm impedance and uses right hand circular polarisation. Another antenna type used for Iridium handset devices is the 14mm by 33mm Maruwa MWSL-3105 dielectric-loaded decafilar-helix (containing ten radiating helical elements which we will discuss shortly) which provides excellent beamwidth (>135°). Its gain is 2dBic at the zenith and it has a 50-ohm impedance. Circular polarisation of the radio signals means that for each wavelength, the plane of polarisations rotates through 360° in a corkscrew fashion and energy is radiated in all planes between horizontal and vertical. It is like having a “spinning” traditional dipole antenna (this analogy will be important to recall later). This is in contrast to traditional linear Globalstar’s Sat-Fi will provide a satellite-connected “hot spot” for your mobile device when out of cellular range. Celebrating 30 Years November 2017  27 A standard helical antenna design. B and E are support structures, S is the helical radiating element, R is the ground plane and C is the feedline. Author: Ulfbastel Maruwa antenna with cover as used in Iridium devices. It is designed to produce signals with right hand circular polarisation. polarisation produced by a dipole antenna which radiates energy in one plane only. Typically the polarisation is vertical, requiring vertical antennas. Circularly polarised signals are less dependent on antenna orientation and they are better at penetrating obstacles such as trees, buildings or even adverse weather. Circularly polarised signals can be either left or righthanded, which varies per carrier; Globalstar left, Inmarsat right, Iridium right, Thuraya left. There is no particular advantage for either polarisation except one might be used over another to avoid interference with nearby emission sources, in which case one would choose the opposite polarisation to the nearby source. A problem with traditional circular-polarised antennas is that a signal is emitted from both above and below the antenna, one signal right-hand and the other left-hand polarised, representing wasted energy. The problem is solved by using a ground plane, which acts as a “mirror” and changes the polarisation of one signal and reflects it in the desired direction. However, the ground plane has to be about one quarter of the signal wavelength (which would mean a ground plane Murawa deca-filar antenna. There are five pairs of helices, with each adjacent pair of helices having a phase-shift between them to synthesise the effect of an upward travelling spinning dipole. The green arrow is the direction of the current around the base and the purple arrow shows the resonant wave travelling up an individual helix. of around 4.6cm diameter for Iridium signals) which is difficult because the phone has to be as compact as possible. The Murawa multi-filar (it contains multiple helical elements) antenna solves the problem of a ground plane – in fact it eliminates it, by producing a corkscrew radiation pattern that travels up the antenna. It uses multiple pairs of helical elements with a different phase between sequentially activated adjacent pairs. These suppress the reverse-going wave by allowing the signal to propagate only in the desired direction since a reverse-going wave will be cancelled with an additional wave going in the desired direction that is generated by the next helical pair. In the deca-filar antenna used for Iridium applications, there are five pairs of helical antenna elements. The physical structure of the Murawa antenna is in the form of a metal pattern printed onto a low loss dielectric base. The lower metallised part of the structure forms a sleeve balun (a type of transformer, to connect a balanced load to an unbalanced load). This serves to isolate the antenna radiation from the ground plane of the device, so that antenna resonance is independent other structures in Orange: Optimum reception Yellow: Marginal reception Grey: Fringe reception White: No reception Coverage area for Thuraya. Note that it is not global but services most of Africa, Europe, the Middle East and South East Asia. The area is serviced by two geostationary satellites, Thuraya 2 and 3. Thuraya 1 was defective and was parked in a junk orbit and permanently retired. 28 Silicon Chip Globalstar coverage map for voice, duplex data and Sat-fi. Sat-Fi is a Globalstar product which which establishes a satellite link and also connects via a Wi-Fi link to any device running Globalstar Apps such as a smart phone or other suitable wireless device. This enables it to make voice calls and send and receive SMS messages or establish a data connection. It is like a wireless hotspot for your phone but the wireless router connection is replaced with a Globalstar satellite connection. Celebrating 30 Years siliconchip.com.au Satellite orbit IRIDIUM GLOBALSTAR THURAYA INMARSAT LEO LEO Geostationary Geostationary Coverage Total global coverage Not global due to smaller constellation than Iridium. Not global, Australian coverage can be selected geographical limited in the far north – coverage but just need to wait until the available Australia wide. satellite is in view. Small, low cost. Small, sleeve concept Handset features Small, rugged. Rugged handsets available for smart phones. available. Rugged models available. 2.4kbps 60kbps down uncompressed on 9.6kbps uncompressed, 15kbps up on handset Data available handset, 1.5Mbps or on handset and 144kbps with 8Mbps on data with kit. terminal. terminals. Example cost of voice call from one Australian provider 40c to 99c per 30s plus 40c flagfall plus $40 to $99 monthly fee. 80c to $1 per minute plus monthly fee of $20 to $70. 80c to 99c per minute plus $15 to $65 monthly fee. Global except for latitudes higher than 82° (ie, no polar coverage). Medium cost. Rugged handsets available. 2.4kbps on handset and 492kbps with BGAN terminal for standard IP data. 40c to 75c per minute for outgoing calls plus 40c flagfall plus $40 to $99 monthly fee. Table 1: comparison of various satellite phone systems. According to one Australian dealer that sells phones for all these networks, the overall plan costs from cheapest to most expensive are Thuraya, Globalstar, Inmarsat and Iridium. Notably, the two cheapest systems offer the most limited coverage and the two most expensive offer near global or global coverage. Data rates available depend on various options selected. Note also that faster speeds are often quoted but these figures are for compressed data. Costs are examples only; like all mobile plans, a detailed comparison should be done for your circumstances. the housing or unwanted loading caused by the body of the person holding it. Networks available in Australia The four satellite phone networks commercially available in Australia are Globalstar, Inmarsat, Iridium and Thuraya. Iridium gives global coverage, Inmarsat is near global coverage except polar regions while Globalstar and Thuraya are for specific regions. Inmarsat was founded in 1979, then Globalstar (original company founded 1991, restructured 2003), followed by Thuraya in 1997 and then Iridium (original service launched 1998, bankrupt 1999, company restarted 2001). These dates don’t necessarily reflect these company’s offerings for handheld satellite phones however. Iridium introduced a handset in 1998, Globalstar in 2000, Thuraya Coverage map for Inmarsat’s Alphasat and Inmarsat-4 satellites whose purpose is to cover the main landmasses of the world. Only the Arctic and Antarctic areas above about 82° are not covered. siliconchip.com.au had a limited service from 2001 and Inmarsat introduced a handset in 2006. All services have specific strengths, weaknesses, coverage areas and costs (as of mid-2017) – see Table 1. Iridium Iridium were the first company to offer handheld satellite phones in 1998 although the company soon went bankrupt in 1999 due to the high cost of handsets, the call costs and poor management. Originally, the bankruptcy meant that the unused satellites would have to be de-orbited so they did not take up valuable orbital slots but this fortunately did not happen, mainly due to the efforts of one man, Dan Colussy. The retired former President of Pan Am put together an unlikely group of investors and purchased the assets of Spot beam coverage areas for Inmarsat’s geostationary I-4 series satellites. Each colour represents a different satellite. The satellites are part of Inmarsat’s BGAN Broadband Global Area Network and offer data rates of up to 492kbps to the highest capacity ground terminals. Celebrating 30 Years November 2017  29 the bankrupt company at a bargain price of US$35 million (original cost US$6 billion!) and relaunched it in 2001. (See the panel elsewhere detailing the book “Eccentric Orbits – the Iridium Story”, described as a “monumental piece of nonfiction” and “high scientific journalism, exciting business journalism and a rattling good tale.”) Iridium was originally intended to have 77 LEO satellites – which happens to correspond to the atomic number of iridium, hence the name. However, it was found that only 66 satellites were needed, although spare satellites are kept in orbit. Iridium satellites are in polar orbit and occupy six orbital planes. Each of the satellites communicates with up to four neighbouring satellites in the constellation, two in the same orbital plane and two in adjacent orbital planes – one to the front and one to the rear. The current satellites are being replaced with Iridium NEXT satellites which will provide superior features such as more bandwidth and higher data speeds. The new satellites will be backwardly-compatible with existing ones ensuring there is no loss of service and existing equipment can be used. The NEXT satellites that replace the existing ones will also consist of a constellation of 66 satellites and will have 6 in-orbit spares and 9 on-ground spares. They will offer voice at 2.4kbps and data speeds of from 128kbps to 1.5Mbps on L band and up to 8Mbps on large transportable or fixed terminals using Ka band (19.4GHz to 19.6GHz downlink and 29.1GHz to 29.3GHz uplink). An additional feature of the Iridium NEXT satellites is they can carry third party “hosted” payloads (see box). Argo buoys (see S ILICON C HIP July 2014 – www. siliconchip.com.au/Article/7932) use Iridium communications to transmit their data. Iridium technology can also be built into devices such as wildlife tracking collars. Globalstar Globalstar consists of a constellation of 24 LEO satellites which provide coverage of up to 80 percent of the Earth’s surface (excepting polar regions and oceanic regions for True global tracking of aircraft with ADS-B via Iridium NEXT satellites Aireon is an example of a hosted payload that is being fitted to Iridium NEXT satellites. It is a space-based aircraft tracking system which will provide global tracking of aircraft in near real-time using ADS-B (Automatic Dependent Surveillance-Broadcast), a tracking system fitted to aircraft that automatically transmits GPS coordinates, airspeed, direction, aircraft identity and other information from on-board systems. ADS-B already exists on most commercial aircraft and many private aircraft – and is in fact now mandatory in the airspace of many countries. It even has anti-terrorism features built-in, where that can be a problem. (See the fascinating feature on ADS-B in the August 2013 issue: siliconchip.com.au/Article/4204 and how to 30 Silicon Chip use it in conjunction with flightradar24.com). The problem is that the radio frequency used, 1090MHz, is limited to line-of-sight and coverage depends on the aircraft altitude, distance to the ground receiver station and terrain and weather conditions. Aireon doesn’t replace the existing ground-based ADSB receiver network but augments it, with space-based receivers to achieve true global coverage. (Incidentally, as well as viewing ADS-B data from anywhere in the world on your computer, you can receive ADS-B signals themselves, in your local area, with a bit of hardware and software. See how to build one yourself at low cost using a cheap USB DVB-T dongle, also in the August 2013 issue: siliconchip.com.au/Article/4209). Celebrating 30 Years siliconchip.com.au Oops! Iridium satellite collision In 2009 an operational Iridium (number 33) satellite collided with a retired Russian military communications satellite, Kosmos-2251, that had never been deorbited. The impact occurred at a combined speed of 42,120kph or 11.7 kilometres per second. Around 2000 pieces of debris larger than 10cm resulted from the collision and in 2011 the International Space Station (ISS) had to perform an avoidance manoeuvre. As well, the Chinese were concerned about debris hitting some of their satellites. In 2012 debris again came near the ISS and astronauts temporarily took refuge inside Soyuz capsules until it passed. Software designed to track satellite orbits had predicted that they should have missed each other by just 584m. Such events are rare but emphasise the importance of deorbiting unused satellites or placing them into “graveyard” orbits. Here is a video of a simulation of the collision: “Iridium 33 and Cosmos 2251 Collision - Evolve Based Debris” siliconchip.com.au/l/aaf0 Also see “LLNL TESSA Simulation of 2009 Cosmos+ Iridium Satellite Collision” siliconchip.com.au/l/aaf1 simplex data and less so for voice). When a satellite receives a call from a handset it relays the call to a terrestrial gateway which then directs the call to the fixed or cellular phone network or internet. With Globalstar’s second generation satellites, other satellites are able to pick up a call simultaneously and if the first satellite moves out of range, others handle the call. According to Globalstar the use of terrestrial gateways allows key technology and equipment to be kept on the ground and accessible and integrated to other phone networks, making Globalstar easier to expand and improve. The technology is referred to as “bent pipe” architecture meaning that the satellite is an analog repeater (like a mirror in the sky according to Globalstar) and can be simple and cheap with the more complex technology of what is essentially a large cellular base station kept on the ground. There are 24 terrestrial gateways around the world each of which can handle 10,000 simultaneous phone calls. Globalstar uses CDMA technology. The calculated debris field 50 minutes after the collision between Iridium 33 and Kosmos 2251. Author: Rlandmann. voice services except for above 82° latitude. Mobile handsets such as the Inmarsat IsatPhone 2 mentioned above use the Alphasat and Inmarsat-4 satellite constellation (see coverage map). The Alphasat is a very large satellite with a mass of 6.6 tonnes and dimensions of 7m x 2.9m x 2.3m. Its solar array span of 45m producing 12kW of power for communications, with extra power for hosted payloads (see panel). Its unfolded antenna reflector is 9m across. It uses chemical and plasma ion thrusters for station keeping. A notable use of Inmarsat was in the search for missing aircraft MH370. The aircraft used their Classic Aero Service to transmit routine engine information to the manufacturer. While this does not provide location information, rough locations were determined by mathematical analysis of the data. Thuraya The Thuraya system uses two geostationary satellites to offer regional rather than global coverage. In addition to satellite communications, Thuraya handsets can communicate with regular terrestrial networks just like any regular mobile phone and they can do this in a large number of countries due to extensive roaming agreements with other carriers. Thuraya handsets can be in the form of either a dedicated phone or in the form of a “sleeve” which attaches to a smart phone. Inmarsat Inmarsat uses 12 geostationary satellites for various services and is global in coverage except for polar regions. It is a well-established network (1979) that was initially offered to maritime operators (hence the name) but now offers a wide variety of voice and data services, including terrestrial, for all types of customers. Coverage is global for siliconchip.com.au The Iridium GO! is a satellite hot spot that wirelessly connects to a smart phone or tablet at a range of up to 30m and satellite calls and data are sent to and from the device while the smart device acts as the user interface. Video: “Iridium GO! Tutorial Video” siliconchip.com.au/l/aaf3 Celebrating 30 Years November 2017  31 A usage map for Iridium showing phone usage by location (the white dots) for the week beginning 22nd July 2007. Unfortunately this is the latest such map that Iridium published. Note how major shipping routes are traced out and heavy use in Australia – and also a number of uses from Antarctica. Satellite telephones that use geostationary satellites do not work beyond about 70-80° of latitude so LEO satellites, such as Iridium, are needed in such locations. Phone number plan for satellite phones In 1996 the International Telecommunications Union (ITU) assigned a “country code” under the Global Mobile Satellite System (GMSS) number space. For satellite phones it’s normally +881 plus one or two digits depending on which carrier is being used. For example, Iridium is assigned +881 6 and +881 7. However, Thuraya has been allocated +882 16 which is in the number space for “International Networks”, telephone services not exclusively dedicated to a particular country but not generally for satellite telephony. Presumably, there were no allocations available under the +881 number space by the time Thuraya was launched. Inmarsat, which predates the allocation, had already been assigned +870 to +874. Particular carriers may elect to provide a country-specific phone number. For example, Iridium in the US provides an Arizona-based number for those people unwilling to dial the expensive GMSS number, while Globalstar provides a local number in the country in which the user is based. In Australia all available satellite phones using an Australian carrier or provider can be given an Australian 04xx mobile number. If purchasing a satellite phone in Australia, you should ensure that your provider is able to offer an Australian number for the phone of your choice. Iridium phones have an 8-digit number after the GMSS number, Inmarsat have a 9-digit number and Thuraya have an 8-digit number. To dial the phones directly using their GMSS numbers rather than the local numbers, you would dial the international access code, eg 0011 from Australia, followed by the GMSS number, say 8816 followed by the 8 digit phone number, eg 0011 8816 99393295. To make a call from a satellite phone when not using the assigned local number you would dial 00 for outbound calls How resistant are satphones to eavesdropping? Most security experts seem to be of the opinion that satellite phones do not offer a high level of security against eavesdropping by unauthorised individuals. In 2012 researchers Benedikt Driessen and Ralf Hund managed to break the two common encryption schemes on satellite phones, GMR-1 and GMR-2. They were able to do this because the phones do not use private keys for their encryption and all that is therefore needed is to understand the mathematical algorithm used. With a private key encryption scheme you cannot decipher the encrypted data 32 Silicon Chip even if you know the algorithm used. Of course, in practice the likelihood of anyone intercepting your call except for the government is likely to be low but it is important to be conscious of the risk. The report on the encryption weakness “Don’t Trust Satellite Phones: A Security Analysis of Two Satphone Standards” can be read at siliconchip.com.au/l/aaep Hacking Iridium A presentation was given at the Eleventh Hope conference in 2016 on security issues with Iridium and how the claimed high level of security arises from the complexity of the Celebrating 30 Years system rather than specific security protocols that have been implemented. It showed how they reverse engineered the data structure of Iridium which was not publicly documented and gained great insight into the workings of the system. Signals were received with RTL-SDR or HackRF/Rad1o. Of course, what they did may not be legal depending on jurisdiction. Their video of the talk including a demonstration of connecting to a “secure” telephone line of a C-37 aircraft of the US 310th Airlift Squadron and some very high level technical information is at “Iridium Satellite Hacking HOPE XI 2016”: siliconchip.com.au/l/aaez siliconchip.com.au Hosted payloads on Iridium NEXT and Inmarsat Of the satphone providers, Iridium NEXT and Inmarsat’s Alphasat are able to accommodate a third party “hosted payload”. A hosted payload is a semi-independent piece of hardware attached to the satellite such as a sensor or instrument of some kind that uses the host satellite for a “piggyback” ride into space. It will typically use the host satellite’s power supply and transponders for power and to send and receive data. Advantages of hosted payloads include: • a shorter time to get the payload into space as a launch vehicle does not have to be organised and there are many available launches • lower launch costs as the launch vehicle and other launch facilities are shared • the possibility of more resilient infrastructure because instead of one satellite with a lot of capabilities, a larger number of hosted payloads each with a lesser number of capabilities can be used and a failure of one unit will not cause total loss of the system. One example of a hosted payload is a UHF communications payload of the Australian Defence Force that is on the Intelsat 22 spacecraft. Others include those for laser communications and a Ka band downlink for data link speeds of up to 2Gbps, Q (33GHz to 50GHz) and V (40GHz to 75GHz) band propagation experiments, flight testing of a star tracker followed by the country code, area code and phone number. You dial the country code even if you are in that country. Apart from a GMSS number and a local Australian mobile number that may be provided by an Australian carrier, ACMA (the Australian Communications and Media Authority) have also allocated the following number prefixes for Australian satellite phones: 0141, 0142, 0143, 0145 and 0147, each of which are followed by the six digits identifying that particular phone. When dialling from a satellite phone to a local Australian number with area code, you would dial numbers the same as you usually do, except you would include the area code (even if within that area code’s calling zone). For others to call that satellite phone they would simply dial the assigned local number. Note also that in Australia, if you have a standard satellite number (such as from an overseas carrier) you will not be able to call 13 or 1300 numbers, 1800 numbers or emergency numbers in the normal way and perhaps not at all. This could negate one of the main reasons people, especially travelling in the outback, buy a satellite phone in the first place. and environmental sensors on Alphasat. Aieron (see separate panel) is another hosted payload to augment the existing ground-based ADS-B global aircraft tracking system with satellite-based receivers to cover “black spots”. Iridium NEXT satellites can carry one large hosted payload or a number of smaller ones. A total payload mass of 210kg can be carried and a total of 650W of power is available with an 1100W surge while a combined data rate of 1Mbps with 10Mbps surge is available. Whether a LEO or a geostationary satellite is chosen as the host platform for a payload is dependent upon the specific application. areas are quite large. Most handsets (such as Globalstar) can give a rough location fix, with a maximum 20km radius of error based on triangulation while Iridium, Thuraya and Inmarsat can give an even-more-accurate GPS fix from phone handsets. Unlike terrestrial mobile phones, which are all built to the same hardware standards and which for an emergency call can connect to any available mobile phone carrier’s tower even if out of range of their own carrier, satphones use different technology standards and can only connect to the satellite system that the phone handset is designed for. Debunking a dangerous myth! There is a widely-held belief that if you dial the 112 emergency number from a terrestrial mobile phone (ie, a standard mobile) that it will automatically connect to a satellite if you are out of range of a tower. This is simply not true. If you are out of range of a mobile (cellular) phone tower, a non-satellite mobile phone cannot connect to a satellite and make any call – emergency or otherwise. Emergency calls from satellite phones What are “Iridium Flares”? It is mandatory for all satellite phones sold in Australia to support dialling of the Australian emergency number. In Australian territory (except Antarctica) and territorial waters out to 200 nautical miles, emergency calls go via an Australian operator. Outside of the Australian mainland but in territorial waters the Australian Maritime Safety Authority would typically be involved in an emergency call and rescue. Outside of territorial waters calls are expected to be handled by the service provider, who will pass the call to the appropriate authority for the area. An international inbound roamer in Australia could dial 112 for emergency calls but it is possible that their carrier will also support 000 calls as operators try to keep phone firmware updated and consistent with regional standards. Emergency operators will generally receive a three digit code giving the rough area of the originating call based on maps of “standardised mobile service areas” but these Iridium flares are flashes of sunlight reflected from the older Iridium satellites (but not from Iridum NEXT). The web site at siliconchip.com.au/l/aaf5 can be used to predict Iridium flares (and other things) plus there are phone Apps. siliconchip.com.au Celebrating 30 Years November 2017  33 Spot beams Interesting videos and web pages All links in SILICON CHIP are quicklinks to save you the hassle of keying-in (and making errors in!) sometimes long URLs. In the SILICON CHIP online edition they are all direct one-click links. Using an Inmarsat phone in the Outback “Immarsat Satellite Phone Video”  siliconchip.com.au/l/aaeq Real-time tracking by an earth station with dish antennas following Globalstar satellites. (Note that this is a fairly uneventful video but you do see the antennas moving as they track the satellites). This earth station is located in outback WA, about 770km NE of Perth. “Meekatharra Globalstar Satellite Teleport – for satphones” siliconchip.com.au/l/aaer A teardown of a 2000 vintage Globalstar satellite phone by an Australian blogger, David Jones. He has a lot of other interesting videos on his channel as well. “EEVblog #721 – Globalstar Satellite Phone Teardown” siliconchip.com.au/l/aaes The teardown of an early model Iridium phone: siliconchip.com.au/l/aaet “Globalstar Overview (2012)” siliconchip.com.au/l/aaeu “Iridium-1 Technical Webcast” siliconchip.com.au/l/aaev “The story of Inmarsat I-4” siliconchip.com.au/l/aaew “Launch of Thuraya-3 Satellite” siliconchip.com.au/l/aaex “Inmarsat – The Mobile Satellite Company” (corporate video)    siliconchip.com.au/l/aaey The reverse is not true, of course: even if you are within range of a cellular tower, with rare exception (satellite phones specifically designed for two bands) a satphone will not try to connect to a standard mobile phone tower – it will always connect via its carrier’s satellite. The international standard emergency number 112 should get you through to local emergency services wherever you are in the world and whatever phone you are using, as long as you are in range of a tower or appropriate satellite but you should confirm that your operator supports that before going on any potentially hazardous journey. In order not to waste communications bandwidth by transmitting to areas not in a satellite’s targeted geographic area and also to ensure the maximum number of communications channels are available, telephony and data satellites use spot beams. These are concentrated radio beams using high gain antennas that send and receive signals to and from limited geographic areas. Iridium’s LEO satellites’ spot beams move with the satellite but all spot beams and satellite footprints overlap. Each satellite can project 48 spot beams onto the Earth’s surface, arranged in three sectors with 16 beams each, each approximately 400km in diameter. The satellite’s full 48-beam footprint is approximately 4500km in diameter. The large number of fast-moving satellites with multiple overlapping spot beams minimises missed connections and dropped calls, since more than one satellite is usually visible from any place on Earth. Usually it’s more than that, with the constellation of interconnected, cross-linked satellites “talking” with other nearby satellites in front, behind and in adjacent orbits. For an animation of how an Iridium satellite’s coverage area moves with the orbit of the satellite see siliconchip. com.au/l/aaf4 On the other hand, Inmarsat’s I-4 geostationary satellites can each generate 19 wide regional beams and around 228 narrow spot beams. Geostationary spot beams generally remain in one area on the ground, although they can be moved to a different area if necessary. Typical ways satellites can alter their spot beam coverage is by switching antennas or electronically steering the beams with phased array antenna technology. SC Acknowledgement: The author wishes to the thank Communications Alliance Ltd for information on the operation of emergency numbers from satellite phones. “A rattling good tale” Eccentric Orbits, the Iridium Story, by John Bloom ISBN 978-0-8021-2168-4; Atlantic Monthly Press, New York It might sound like a pretty dry subject but author John Bloom has managed to turn this (true!) story into a book that you will find very hard to put down. The title page notes perhaps sum it up best of all: “How the largest manmade constellation in the heavens was built by dreamers in the Arizona desert, targeted for destruction by panicked executives and saved by a single Palm Beach retiree who battled Motorola, cajoled the Pentagon, wrestled with thirty banks, survived an attack by Congress, infiltrated the White House, found allies through the black 34 Silicon Chip Celebrating 30 Years entertainment network and wooed a mysterious Arab prince to rescue the only phone line that links every inch of the planet”. The retiree was former Pan Am president Dan Colussy, who heard of Motorola’s plans to scuttle the six billion dollar Iridium project (including all its satellites) and against a huge amount of opposition, managed to revive the project for half a cent in the dollar (just US$35 million!). The 550+ page “Eccentric Orbits” is available on line from a variety of sources and believe us, once you start reading it you definitely won’t stop! siliconchip.com.au