In The Beginning |
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In October of 1957, the Russian Sputnik I became
the first man-made satellite in space, and in November of that same year a dog named "Laika" became the first living creature to experience low earth orbit. Just three months later, on the first day of February of 1958, the number of countries with a "successful" space program doubled, with the launch of Explorer I by the United States of America--and so the race was joined. In those early days of satellite deployment, mission-success was defined in rather simple terms: Did the launch technology work as planned, and did the satellite acquire the intended orbit? But today, with over 3500 satellites in orbit around the earth, the definition of mission-success has evolved to reflect the increasingly sophisticated scientific, commercial and military applications that have become the raison d'etre of space: intelligence-gathering, global communications, scientific research, land and sea navigation, deep-space astronomy and a host of other pursuits. The payloads and electronic subsystems of today's satellites are as sophisticated as their missions: image processing systems, global positioning systems, thermal control systems, transponders, stabilizers, gyroscopes, telescopes, solar arrays, scatterometers, radiometers, microwave sounding units, radiation sensors, and dozens of other specialized instruments and devices. And as is the case with most electronic equipment and "black-box" technologies of this type, electrical interconnects play an important role in their manufacture, assembly, installation and maintenance. Many of today's satellites are tasked with scientific or other civil application endeavors, such as environmental and earth science. Such satellites carry instruments to study the sun, measure magnetic fields or to examine the universe in the different energy wavelengths of the electromagnetic spectrum. Others, such as NASA's Hubble Space Telescope, are used to study the stars in nearby galaxies and to plot the evolution of supernovas and black holes. Landsat satellites make accurate maps of the Earth's surface in both visible and infrared light. Such maps are useful as checks on existing maps, for determining where vegetation is healthy or diseased, or as tools for monitoring pollution. The French SPOT satellite (Satellite Probatoire de L' Observation de la Terre), was used to study the environmental damage caused by the explosion of the former Soviet Union's nuclear reactor in Chernobyl. Other satellites are used in testing and developing ways to improve global weather forecasting. Communications satellites are by far the most prolific Earth orbiters. Their principal role is to relay telephone calls, television signals, Internet traffic and other data and voice communications from ground-based stations to other points on Earth. Communication satellites can also be used to relay voice communications between astronauts orbiting in space stations and their mission controllers on Earth. While a few communications satellites are owned and operated by governments, private companies operate and control most of the systems currently in orbit around the Earth. Nordic Satellite AB (NSAB), for example, owns and operates a network of satellites called Sirius. The Sirius system covers the Nordic area, the Baltics, Poland and Western Russia with high-powered telecommunications services including direct-to-home television, cable television, data distribution, and mobile phone services. The Sirius system of Nordic satellites is typical of many satellite development efforts, with a large number of partners and suppliers combining forces to produce the final system. The latest Nordic satellite, Sirius 3, was launched on October 5 from French government facilities in Kourou in French Guiana. The satellite was built by Hughes (now Boeing) Space & Communications in the U.S. Among the industrial partners, Saab Ericcson Space of Sweden supplied antennas and the data management system. Aerospatiale was awarded the overall procurement and project management contract. GE International has contracted to share operating costs and transmission bandwidth for its own digital broadcasting services. Truly an international effort. If asked to describe a communications satellite, most of us would picture something along the lines of Figure 3. But the first successful communication satellites were nothing more than aluminum-coated balloons, such as the original Echo balloon (Figure 4), launched in 1960. The Echo was classified as a "passive" satellite because radio signals simply reflected off the balloon's surface rather than being captured and retransmitted from the satellite. Because of the obvious limitations of such a system, "active" transmitting satellites soon followed. The modern generation of communications satellites receives a signal from an appropriate antenna, amplifies the signal with onboard devices, and retransmits it to other receiving stations on Earth. On the military front, satellites provide jam-proof, ultra high frequency and high data-rate communications to link bombers, missiles, submarines, fighter pilots and troops on the ground. The ability to communicate instantly with front-line forces or to "see" battlefield images in something approaching real-time is the driving force behind the next generation of military communications and spy satellites. In addition to imagery intelligence (IMINT) and signal intelligence (SIGINT) satellite systems, work is also underway to develop satellite-based missile defense systems. This technology includes space-based missile defense systems with the potential to perform anti-satellite missions and dedicated missile systems (supported with satellite targeting) that could destroy ballistic missiles in flight. These exo-atmospheric missiles and satellite systems will carry sophisticated targeting and tracking equipment, much of which will be interconnected with miniaturized connectors, such as the Micro-D's shown in Figure 5. Worldwide, the satellite industry produces over $US30 billion in revenue from the sales of satellites, launch vehicles and missiles, according to the Aerospace Industries Association. More than 92,000 people work in the space vehicles and missiles sector according to association estimates. Satellite manufacturing is highly specialized, and there are only a handful of major satellite makers worldwide. Scientific and commercial satellites can be rocket-launched under contract with aero-space companies working for the U.S., Russian and Chinese governments as well as the European Space Agency. The owner of the satellite typically pays for the launch, and assumes a full-measure of risk for mission success. Satellite owners may purchase insurance to cover potential losses caused by catastrophic failure of the launch. Satellite manufacturers also sometimes retain ownership, and lease completed systems to telecommunications service providers or other customers. Commercial launches are performed at only a handful of sites worldwide. Commercial launches in the U.S. occur mainly in Florida. The French launch their satellites in New Guinea. In the U.S., military and commercial satellites may also be transported into space within the belly of the Space Shuttle-- which is owned by NASA, the U.S. space agency. The satellite is placed into orbit by releasing it from the shuttle's cargo bay doors. Satellite Anatomy A satellite is any smaller object traveling around a larger object. By this definition, the Moon is a satellite to the Earth and the Earth is a satellite to the Sun. For our purposes, a satellite is a man-made spacecraft placed in space to orbit another body. These spacecraft can be crewed, such as the Space Shuttle, or uncrewed, such as NASA's Hubble Space Telescope. They can be sent into space with the intention that they will not be recovered, or they can be designed to be recovered or repaired by Space Shuttle crews. Satellites may be either active or passive. Passive satellites contain no radio transmitters or other energy signals, but rather only reflect signals beamed at them from Earth. Active satellites collect data and emit radio signals that transmit the information down to Earth. Satellites differ markedly in size and weight. The first U.S. satellite, Explorer I, was 6.6 feet (2 meters) long and weighed 17.6 pounds (8 kilograms). In contrast, NASA's Compton Gamma Ray Observatory, launched in April 1991, measures 70 feet (21.3 meters) from the tip of one solar array to the tip of the other solar array and weighs more than 17 tons. While satellites may vary in size and weight, there are elements that all satellites share: a satellite housing, a power system, an antenna system, a command and control system, a station keeping system, and transponders. Housing: The shape of the satellite housing is a function of the technology used to stabilize the satellite in its orbital slot. Three axis-stabilized satellites use internal gyroscopes rotating at 4,000 to 6,000 revolutions per minute (RPM) to maintain the attitude of the satellite. The housing for this type of satellite is typically rectangular with external features such as those shown in Figure 7. In "Spin Stabilized" satellites (see Figure 3), a cylindrical housing which rotates on its axis is used. Spin stabilized satellites rotate at 60 to 70 RPM to produce a gyroscopic effect. The antenna is main-tained in its fixed orientation by connecting it to the body of the satellite with a rotating bearing. The solar cells which generate power for satellite operations are mounted on the surface of the housing. Power: All satellites need a power source. Most are powered by solar cells, which gather energy from the Sun and convert the energy directly to electricity to power internal systems. Interplanetary satellites that travel far away from the Sun, such as Voyagers 1 and 2, launched in 1977, and Ulysses, launched in 1990, use radioisotope thermoelectric generators--a nuclear power source. Whatever source is specified, satellite power must be continuous and uninterrupted. Since satellites in geosynchronous orbit experience solar eclipses (the sun is obscured by the earth), batteries are used as a supplemental on-board energy source. Antennas: Satellite antennas have two principal functions: The first is to receive and retransmit uplink signals. The second is to receive and transmit the Tracking, Telemetry, and Control (TT&C) information used to maintain the operation of the satellite in orbit. TT&C is a vital function, as any disruption could lead to catastrophic failure in internal systems or cause the satellite to spin out of control into space, or perish in an unintended re-entry of the Earth's atmosphere. Passive antennas, metal structures which simply capture and launch radio waves, are found throughout satellite communication systems. But if power amplifiers, low noise amplifiers or other electronic devices are integrated into the antenna it is considered "active". This is the case with most phased array antenna systems, which process signals into their correct electrical relationships (phases) as an integral function of reception and transmission. Command and Control System: As noted above, every satellite has a Tracking, Telemetry and Control (TT&C) system for monitoring critical satellite operations. This system includes telemetry circuits for relaying diagnostic information to the ground, a system for receiving and interpreting commands sent to the satellite, and a command system for controlling the operation of the satellite. Station Keeping: Station keeping is the maintenance of a satellite in its assigned orbital slot and in its proper orientation (Figure 8). Every satellite's orbit will change with time due to atmospheric drag-- or the pull of gravity--on the spacecraft. Frequent adjustment of the satellite is necessary to keep its solar panels facing the Sun and to align the satellite with its target region. Consequently, all satellites carry scientific and engineering sensors to measure changes in the satellite and its surroundings. Horizon seekers, star trackers, and Sun seekers, are examples of sensors used to help determine the satellite's position. Other instruments detect changes in the power supply, the temperature, and the pressure of the satellite. The physical mechanism for station keeping is the controlled ejection of hydrazine gas from thruster nozzles which protrude from the satellite housing. For this reason, the service life of a satellite ends when its hydrazine supply is exhausted--typically in about ten to fifteen years. Transponders: A transponder is an electronic component of a satellite that works hand-in-hand with the antenna, to convert the frequency of an uplink signal for subsequent amplification and re-transmission of the signal to earth. Transponders have a typical output of 5 to 10 watts. Communication satellites usually have between 12 and 24 on-board transponders. Come Fly with Me Each satellite has a set path in space above the Earth's atmosphere called an orbit. If a satellite traveled through the atmosphere, air would push against it and slow the satellite down. To be completely free of such atmospheric drag, satellites orbit at least 180 miles (300 kilometers) above sea level. Sir Isaac Newton first theorized about the possibilities of human made satellites in the 17th century. But it wasn't until almost 300 years after Newton's death that the first artificial satellite was put into orbit. The velocity (speed) at which a satellite is launched, and the inclination (angle) of the launch relative to the equator, determines the satellite's orbit. Satellites are launched into a variety of orbits, depending on the satellite's purpose (see Figure 9). Polar or near polar orbits are launched at an inclination of approximately 90 degrees to the equator. These satellites travel in a circular pattern over the North and South Poles so that they can survey a major portion of the Earth as it turns below them. Some weather satellites use this type of orbit to track the approach or development of a storm. Another type of orbit is a geosynchronous orbit (GEO), which is exactly 22,300 miles (35,888 kilometers) above the equator. At this height, a satellite's velocity matches that of a point on the Earth's equator. Seen from Earth, the satellite appears to be floating over a certain spot on the equator. Weather and communications satellites use geosynchronous orbits. Other satellites take an elliptical orbit around the Earth. This orbit is useful for making scientific measurements---such as ozone levels at various altitudes. Many satellites are placed into a low-Earth orbit (LEO) about 200 miles (320 kilometers) above the Earth. This is the height where the Space Shuttle takes up orbit. Until its demise earlier this year, the Russian Mir space station also occupied low-earth orbit. Scientific satellites, such as the Hubble Space Telescope and Compton Gamma-Ray Observatory also use a low-Earth orbit. The most distant point of a satellite's orbit from Earth is called its apogee; its closest point to Earth is its perigee. The difference between the apogee and the perigee is known as the degree of eccentricity of the orbit. Ground Control Satellite communications begin at an earth station--a ground based installation equipped to transmit and receive satellite signals. The earth station transmits information in the form of high-powered, high frequency (GHz range) signals to target satellites which receive and then retransmit the signals back to other earth stations in the coverage, or footprint area, of the satellite. The part of the transmission system linking the earth station to the satellite is called the uplink, while the satellite to earth station leg is called the downlink. Uplink and downlink traffic typically occurs in the C, Ku, and Ka frequency bands. C-band and Ku-band are the most common frequency spectrums used by commercial communication satellites. C-band satellite transmissions occupy the 4 to 8 GHz frequency range, with Ku-band transmissions at 11 to 17 GHz and Ka-band in the 20 to 30 GHz frequency range. The low frequency (large wave-length) transmission of the C-band requires a large satellite antenna (dish) to gather the minimum signal strength. This is because of the inverse relationship between frequency and wavelength. When frequency increases, wavelength decreases and smaller antennas may be used to gather the signal. A typical C-band antenna is approximately 2-3 meters--much larger than the antenna required to service both Ku- or Ka-band transmissions. Ku-band antennas can be as small as 40 cm in diameter. Qualified to Fly The rigors of the launch, and the unique environment of space, place some rather heavy de-mands on the materials and equipment which are selected for use in satellite systems. Commercial and Military specifications for EEE parts for launchers, satellites, space stations and other spacecraft are more stringent than for any other application environment. NASA's 311-INST-001 Revision A Instructions for EEE Parts Selection, Screening, and Qualification is a useful reference for the broad range of performance requirements which must be addressed when designing electrical components for use in space. Outgassing, atomic oxygen, UV radiation, thermal shock, and pressure sensitivity are just a few of the unique performance requirements which must be considered for orbital and deep-space applications. NASA Screening Levels provide a guideline for component selection, and are used by Glenair in engineering connectors and accessories for various missions in space. Glenair space grade Micro-D connectors, composite accessories, as well as our space-grade circular Sav-Con connector savers are all engineered to perform at the highest levels required. Level 1: Highest reliability. "Parts shall be selected and processed to this level for missions requiring the lowest acceptable level of risk". Level 2: Higher reliability. "Low to moderate level of risk balanced by cost constraints and mission objectives". Level 2 is the most typical level of screening for NASA missions. Level 3: Standard reliability. "Parts shall be selected and processed to this level for missions where a moderate level of risk may be acceptable, as permitted by cost constraints." As noted above, performance requirements for interconnect components in space go well beyond standard electrical and mechanical specifications. And one of the key reasons is that any form of contamination in the spacecraft environment can lead to system performance degradation and failure. The presence of contamination on spacecraft surfaces, or the presence of a contamination cloud around the spacecraft, can damage optical surfaces, mirrors and filters in surveillance systems. Contaminant build-up on surfaces can create thermal control problems. Contamination on solar arrays can lead to transmission loss across the array. Particulate matter can damage sensors and generate false reading in electronic control systems. Non-metallic materials such as rubber, plastic, adhesives, and potting compounds can give off gases when subjected to a vacuum. The NASA specification provides for outgassing processing, which requires parts be sent to a lab for thermal vacuum outgassing. This "bakeout" assures that all volatile materials are removed. Glenair connector accessories, used on the International Space Station, must go through a bakeout process of this type to insure their safe use in space. Our Aracon braid product, which was used on the Cassini Saturn Probe (Figure 11), did not require a bakeout process, but did receive special ultrasonic cleaning. Again, such precautions are due to the serious potential for contamination of any kind to damage satellite instruments and equipment. Base metals and surface finishes are additional sources of contamination due to both outgassing (as is the case with cadmium plating) as well as corrosion hazards resulting from atomic oxygen. In low-Earth orbits, satellites encounter a very low-density residual atmosphere. This atmosphere is composed primarily of oxygen in an atomic state. On the ground, oxygen exists predominantly in the molecular (O2) state, but at the top of the atmosphere solar UV breaks down the molecular bonds to create free AO which is highly reactive and can produce serious surface corrosion through oxidation ( see QwikConnect Volume 7 Number 4, Rust Never Sleeps, for more information on the science of corrosion). It is for this reason that gold and electroless nickel platings are preferred for space-grade applications. The Eye in the Sky Perhaps the most significant new development in satellite systems (at least from the perspective of the interconnect industry) will come from an effort spearheaded by the National Reconnaissance Office (NRO), the U.S. Government spy satellite agency. The NRO is developing a Future Imagery Architecture (FIA), which will capitalize on available small satellite systems and new image acquisition technologies to build the next generation of reconnaissance satellites. The Future Imagery Architecture is meant to operate for the next several decades and will represent a significant improvement over current surveillance systems. The next-generation spy satellites promise to deliver many times the data at a much-reduced interval between pictures. FIA has the potential to revolutionize the way the U.S. and its allies employ their military forces. And it can also greatly complicate the lives of terrorists, drug lords, and weapons smugglers who pose national security challenges. FIA, to be implemented over the next decade, will be the most expensive program in the history of the intelligence community. On 27 April 1999 Raytheon Company was awarded a contract by the NRO to develop and integrate the ground infrastructure portion of the Future Imagery Architecture. This program, known as the Mission Integration and Development (MIND) Program, will extend from 1999 through 2013, plus two one-year options for additional operations and maintenance. A key objective of the MIND team will be to provide the NRO with a state-of-the-art intelligence infrastructure as it enters the 21st century--combining numerous space and ground components into one integrated system. On 3 September 1999 the NRO awarded a contract to the Boeing Company, Seal Beach, CA, to provide launch integration and operate the nation's next generation of imagery reconnaissance satellites. This award was the largest element of the NRO's Future Imagery Architecture program. The multi-year effort will provide a more capable but less costly means of fulfilling U.S and NATO imagery needs and includes the ability to accommodate COTS products. While the ability to "see the battlefield" is certainly not a new development, the FIA proves to be the most significant step ever taken in the history of imaging reconnaissance. During Desert Storm, for example, imagery played an important role both at the tactical and strategic levels. Satellite imaging technology takes several forms, and although the NRO's FIA project is highly classified, the technologies which will be deployed will certainly consist of both imaging radar as well as electro-optical systems. Imaging radar operates by emitting an EM pulse which illuminates or paints the target area. The emitted energy then reflects off the target back to the aircraft where the signal is recorded. The amount of energy that returns and the time it takes that energy to return is calculated to produce a radar image. Imaging radar works much the same way as sonar on a submarine. The "ping" on sonar is the returning energy. The time it takes the ping to return and its intensity determines the size and location of the target. Very accurate pictures of the surface, its bumps (like mountains, hills, and valleys), its textures (like forests, lakes, and cities), and its changing moods (like volcanos, floods, and earthquakes) can be generated from such information. But perhaps the greatest capability of imaging radar is to detect moving targets. A moving object produces a "Doppler shift" and is displayed as a "dot" on radar imagery. With the sophistication of today's systems, the moving object's speed and direction can be determined. And imaging radar can function both day or night, cloudy or clear. And since the radar imaging systems are data linked to ground stations, the information is near real-time. Electro-Optical systems (EO) collect imagery in the visual range using an array of detectors that sample light at fixed points. Electro-optical systems can capture both visible light as well as infrared images. Perhaps the greatest capability of EO is the ability to manipulate images using digital techniques. The human eye can detect about 30 shades of gray. An EO system can detect 256 shades of gray. If an object was parked in the shadow of a building you could change the individual pixel value of the image to identify targets that otherwise could not be seen by the human eye. The next generation of NRO spy satellites are designed to carry the most advanced payloads of optical and electronic systems ever launched into space. While these systems are certainly a far cry from the electronics that accompanied Sputnik into space, they have at least one important element in common: the utilization of interconnect technologies to facilitate assembly, test, installation and maintenance. At Glenair we are ready for space with a broad range of interconnect technologies--including Micro and Nano-D connectors, composite accessories, QwikClamp strain-reliefs, fiber-optic termini and connectors, Aracon Braid, Sav-Con Connector Savers and more--each product designed to lighten the load and improve the reliability of space-grade interconnect cabling. For more information on Glenair products specifically designed for use in space environments, please contact your local office, or visit our website at www.glenair.com. |
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