Iridium Communications
Iridium is a global satellite communications system of 66 active satellites in six orbits, and in addition one or more spare satellites per orbit. Originally 77 satellites were planned for this satellite constellation; the system is therefore named after the chemical element iridium with the atomic number 77.
The Iridium network has the primaries 8816 and 8817. The assigned by the ITU network identifier is 901-03.
Development
The idea for iridium was born in 1985 at Motorola. It should enable the global voice and data communications services through satellite phones and PDAs. By 1988, the concept was made for it. 1991, the company Iridium Inc. was founded, which developed the system, and in September 1998 took into operation. For the design of the system had to be spent 5 billion dollars.
The call charges were initially very high, at approximately eight US-Dollar/min, the terminal expensive and much bulkier than planned. This meant that instead of the planned two million users could be won only about 55,000 customers.
On August 23, 2000 it had Iridium Inc. bankruptcy. The satellite should be directed into the Earth's atmosphere, to make them deliberately burn out. From a planned shutdown in March 2000, expeditions would have been affected. They had to rely in advance on the accessibility and had no other communication systems. These Rune Gjeldnes and Torry Larsen listed on a Norwegian Polar Expedition, Prince Frederik to Denmark on a dog sled expedition in Greenland and the French adventurer Jo Le Guen, who crossed the Pacific alone in his 9 -meter-long rowing boat. They received a call from the company, which announced to them the end of operation. Finally, the shutdown was moved to public pressure to some extent.
On 1 January 2001, the Iridium system was taken over by the newly founded Iridium Satellite LLC. The satellites are operated and maintained by Boeing. Commercial operation was resumed on 30 March 2001. The largest single customer with 13% revenue share is the military, especially the U.S. Department of Defense. Other users are shipping lines, airlines, scientists or companies in the natural resource development. The main difference compared to the previous operation is that no roaming with GSM SIM cards in the Iridium network as well with Iridium SIM card in the GSM network is possible.
In 2005, the price of equipment were significantly decreased, and one minute phone call to the fixed network or mobile network costs depending on the ordered minute volume still between $ 0.90 and $ 1.50. Significantly cheaper the fees with SIM cards that can be used only regionally restricted, as in America or Africa. A new Iridium phone costs about 1300 €. The annual subscription for access to the Iridium satellite network with an Iridium phone costs around $ 450. The available for several years pre-paid SIM cards are available from $ 130 U.S.. Iridium decreed in July 2012 over 576,000 customers. Iridium intends to offer in the future global broadband Internet access. A first step in this direction is Iridium Open Port, Internet access for shipping with a maximum data transfer rate of 128 kbit / s
Network coverage
Communication with Iridium is available from any location on the earth's surface at any time if clear view of the sky in all directions is from an elevation angle of 8.2 °. In order to ensure a flawless, uninterrupted communication with iridium, no object from an elevation angle of 8.2 ° is allowed to disturb the view of the sky. As a rule of thumb, clenched fist in horizontally outstretched arm. The height of the clenched fist is approximately the elevation angle of 8.2 °. No object may be higher than the clenched fist to the sky tower.
Network coverage in deep gorges and valleys, elevation angle 21 °
Rule of thumb for proper Iridium reception
At a site with objects that violate the rule of thumb, such as in a deep canyon, it can cause disconnections. Even shrubs, trees, house and cabin walls can interfere with the Iridium communications. In a very deep ravine, is the only full view of the sky at the zenith, there is no communication in the worst case, over 120 minutes possible because no Iridium satellite comes in this time period in sight. Due to the rotation of the Earth, another Iridium satellite is located after about 120 minutes later in the zenith.
Due to the polar satellite orbits the supply density in the polar regions is particularly high. Iridium is the only reliable means of communication, the uninterrupted communication with the outside world makes in the polar regions. For example, iridium at the research stations in Antarctica ( Amundsen -Scott South Pole Station, Neumayer Station III) for uninterrupted communication with the outside world.
For an uninterruptible Iridium communication is needed near the polar caps less clear view of the sky than at the equator.
Visible Iridium satellite in Thule on 12 December 2011 at 22:25
For long telephone conversations in the section must be changed every nine minutes of the Iridium satellite because the satellite previously used disappears below the horizon. The satellite change is fully automatic. The parties will notice from the satellite change anything as long as the rule of " no objects with elevation angle about 8.2 ° " is respected. If the rule of thumb is not observed (objects with elevation angle to 8.2 ° ), it can lead to an interruption of the call connection if the old satellite disappears over the horizon and the new satellite is not yet in sight.
Technical
The main advantage of satellite-based communication system is that large areas without terrestrial stations can be covered. The terminals (terminals) communicate directly with the satellites. The satellite network is connected through multiple gateways with existing terrestrial telephone networks. Iridium phones can be used worldwide.
In the case of iridium, the individual satellites are in addition interconnected by inter-satellite links ( ISLs ). An active connection is as long as mediated by satellite to satellite until one of these satellite is within range of an exchange on the earth's surface. About this then finds its way into the conversation the traditional telephone networks.
The transmitting power of mobile phones is limited due to health reasons. However, to enable a connection with a low transmission power, the Iridium satellites were put into a low, a high nichtgeosynchrone orbit inclination. Huge parabolic mirrors with a very high antenna gain, which would have allowed a geosynchronous orbit, stood at start of the project was not yet available and would also not allow global coverage. The Iridium satellites orbiting the earth at an altitude of about 780 km in six nearly polar orbits ( orbital inclination = 86.4 degrees), each with eleven, is located ligands in active use, satellites and one spare satellites per orbit. For the orbit of the Earth, a satellite takes about 100 minutes.
The satellite 689 kg and have a height of about four meters and a diameter of 1.3 meters. They are based on Lockheed Martin LM700A satellite bus and are perpendicular to the orbit. They have two at the upper end mounted parallel to the horizon aligned solar boom, three inclined -mounted antennas of 1.86 m by 0.88 m in size and more attached to the lower end antennas. Data transmission from the satellite to the mobile parts is carried out in L-band, and between the satellite and from the satellite to the receiving station in the Ka band. If the satellites have no contact with a receiving station itself, they conduct telephone conversations and other useful signals about other Iridium satellites on, have the contact to a receiving station. Conversations that run between Iridium users are mediated directly between satellites, but only over a ground station. The three -axis stabilized satellites were launched from May 1997 to June 2002 each to several different launchers ( five each at the start with Delta -2, seven at the start of the proton, and two each at the start of the Long March 2 or Rokot KM).
Overall view of an Iridium satellite: Links solar paddle, right antennas
When a satellite is no longer functional, it is brought into an orbit of 500 km altitude, from which it is eventually directed into the Earth's atmosphere and burns up.
Since the transmission rate of voice data with 2400 baud is extremely low, a strong be compressed codec comes with the name " Advanced Multi - Band Excitation " ( AMBE ) is used, which was developed by the North American company Digital Voice Systems, Inc.. This codec is also used in certain modes of operation of the Inmarsat network. Due to the strong compression of the voice data, voice quality corresponds to a MOS value of 3.5. Thus, the voice quality is between " neat " and "good".
Network status
The main competitor Globalstar 2007 had problems with the premature aging of the Globalstar satellite admit. Similar problems can also occur with the Iridium satellites, even if they previously had no evidence. The Globalstar satellites orbiting the earth at about 1414 km altitude. This height is usually shunned for satellite orbits due to the Van Allen Belt. Satellites in the Van Allen belts are very strong ( cosmic ) exposed to radiation, which greatly added to the electronic components of the satellites. Iridium satellites have a erdnähere orbit and are thus better protected from these harmful radiation. Professionals holding the election of the Globalstar satellite orbits for a serious mistake.
An automatic measuring system controlled test calls with the link quality. The automatic measuring system confirms the good technical condition of the Iridium satellites. Probably in 2015, the first Iridium satellites are replaced with new satellites. The replacement of old by new satellite will be gradual. During three years the Iridium satellite network will consist of both old Iridium satellites as well as from new satellite. The new satellites will be fully compatible with the old satellite. According to Iridium Satellite LLC Iridium satellites are in good condition, and it is to be expected by the time the last new Iridium NEXT satellites with no significant link quality drops.
Iridium NEXT
Unsure is the financing of the second generation of Iridium satellites. The cost of the NEXT satellite fleet are estimated at 2.9 billion U.S. dollars. Iridium Satellite LLC achieved in 2008 a surplus of 68 million U.S. dollars. In 2009 Iridium Communications Inc. generated a surplus of 61 million U.S. dollars. With a satellite lifetime of 15 years are around 1.0 billion U.S. dollars (15 × 65 million U.S. dollars ) to finance the next satellite fleet. It lacks some 1.9 billion U.S. dollars. The hole of 1.9 billion U.S. dollars, one tries to cram with the proceeds from the sale of ADS- B data.
Each Iridium NEXT satellite is equipped with an ADS -B receiver. This service allows the air traffic control in regions that are still not covered by an air traffic control radar and should be available from 2017.
Despite the uncertain funding Iridium has ordered for 2.1 billion U.S. dollars at Thales Alenia Space 81 satellites of its second generation of satellites "Iridium NEXT". In addition there are a further 800 million dollars to pay for start- iridium. The company, SpaceX was awarded the contract on 492 million dollars for a part of this launch, which should be carried out 2015-2017 with Falcon 9 rockets. As of 2015, 72 satellites will be launched into orbit, and the remaining wait as a reserve on the floor on their possible use.
The new satellites will be fully compatible with all currently known iridium devices. The new satellites enable IP-based data transfers. Internet access via Iridium NEXT is particularly interesting for ships and research stations in the polar regions. In the polar regions above the 82nd degree of latitude is not a reliable signal reception from geostationary satellites is possible.
Iridium will be the only reliable two-way communications in the polar regions in the future. On ships and aircraft that travel in polar regions, it is now required by law, that Iridium means of communication must be kept on board. However, it is expected that the carrying of Iridium communications in the near future obligation. In a few applications (eg LRIT ) the use of iridium as a means of communication is a must today.
Vessels must announce their current position by means of LRIT. In the polar waters ( sea area A4) the current ship position via Iridium is communicated. It is expected that is with the commissioning of Iridium NEXT in the sea area A4 Iridium as a communications tool for distress communication to the procedure. Today, airplanes on flights over remote areas can use Iridium communications for air traffic control ( FANS ). Is likely in the near future for flights on the 82nd Latitude FANS -1 / A over Iridium equipment for duty.
Observation
The satellites can be observed from the Earth at certain times for a few seconds with the naked eye as a so-called Iridium flares. Here are reflections of sunlight on the antenna surfaces, leading to the brightest luminous phenomena that cause artificial celestial bodies. They grow to around a thousand times brighter ( at -9 mag) than Sirius, the brightest star in the night sky, and are thus visually with a passing light bullet that light emission for a short time will increase enormously. The satellite as a bright light strip will appear on photos with exposure times of a few seconds in flight direction on both sides tapering foothills. The exact times for Iridium flares can be calculated ( see Related links ) based on the orbital data for any location on Earth online.
The angular velocity is significantly higher than the aircraft, but below that of meteor. Acoustic phenomena do not occur.
Satellite collision in 2009
On 10 February 2009, the Iridium satellite 33 collided with a relative velocity of 11.6 km / s with the retired Russian military communications satellite Cosmos 2251 together. Both satellites were destroyed.