Galaxy IV was a model HS-601 satellite built by Hughes Space and Communications Company (HSC). The satellite, which carried a payload of both C band and K u band transponders , was launched on June 24, 1993 and operated by PanAmSat Corporation. It was in geostationary orbit at 99°W.
49-476: Control of Galaxy IV was lost on May 19, 1998 when the satellite's primary control processor failed. The backup control processor had suffered a previously undetected anomaly, and PanAmSat was not able to regain control of the spacecraft. Galaxy IV was declared a loss on May 20, 1998. Failure of the primary control processor was attributed to tin whisker growth, a phenomenon in which tendrils grow from solder, causing an electrical short circuit. Engineers believe that
98-510: A 2003 NASA internal memorandum. The effects of metal whiskering were chronicled on History Channel 's program Engineering Disasters 19. Several approaches are used to reduce or eliminate whisker growth, with ongoing research in the area. Conformal compound coatings stop the whiskers from penetrating a barrier, reaching a nearby termination and forming a short. Termination finishes of nickel, gold or palladium have been shown to eliminate whisker formation in controlled trials. Galaxy IV
147-535: A consequence of different frames of measurement. The fact that the two field variations can be reproduced just by changing the motion of the observer is further evidence that there is only a single actual field involved which is simply being observed differently. The two Maxwell equations, Faraday's Law and the Ampère–Maxwell Law, illustrate a very practical feature of the electromagnetic field. Faraday's Law may be stated roughly as "a changing magnetic field inside
196-476: A disturbance in the electric field can create a disturbance in the magnetic field which in turn affects the electric field, leading to an oscillation that propagates through space, known as an electromagnetic wave . The way in which charges and currents (i.e. streams of charges) interact with the electromagnetic field is described by Maxwell's equations and the Lorentz force law . Maxwell's equations detail how
245-476: A hole developed in the conformal wax coating over the solder, allowing whiskers to develop. The satellite manufacturer, Hughes, has replaced pure tin plating with nickel to alleviate the problem in newer designs, adding 100 to 200 pounds (50 to 90 kg) per payload. The loss of this satellite was very disruptive to telecommunications in the United States . 80% of pager service in the U.S. went down; service
294-418: A loop creates an electric voltage around the loop". This is the principle behind the electric generator . Ampere's Law roughly states that "an electrical current around a loop creates a magnetic field through the loop". Thus, this law can be applied to generate a magnetic field and run an electric motor . Maxwell's equations can be combined to derive wave equations . The solutions of these equations take
343-515: A magnetic field will be, in a relatively moving reference frame, described by a combination of fields. The rules for relating the fields required in different reference frames are the Lorentz transformations of the fields . Thus, electrostatics and magnetostatics are now seen as studies of the static EM field when a particular frame has been selected to suppress the other type of field, and since an EM field with both electric and magnetic will appear in any other frame, these "simpler" effects are merely
392-457: A nearby compass needle, establishing that electricity and magnetism are closely related phenomena. Faraday then made the seminal observation that time-varying magnetic fields could induce electric currents in 1831. In 1861, James Clerk Maxwell synthesized all the work to date on electrical and magnetic phenomena into a single mathematical theory, from which he then deduced that light is an electromagnetic wave. Maxwell's continuous field theory
441-455: A particular failure mode for tin whiskers in vacuum (such as in space), where in high-power components a short-circuiting tin whisker is ionized into a plasma that is capable of conducting hundreds of amperes of current, massively increasing the damaging effect of the short circuit. The possible increase in the use of pure tin in electronics due to the RoHS directive drove JEDEC and IPC to release
490-546: A rate of up to a millimeter per year with a diameter of a few micrometers. Whiskers can form on the underside of zinc electroplated floor tiles on raised floors. These whiskers can then become airborne within the floor plenum when the tiles are disturbed, usually during maintenance. Whiskers can be small enough to pass through air filters and can settle inside equipment, resulting in short circuits and system failure. Tin whiskers do not have to be airborne to damage equipment, as they are typically already growing directly in
539-585: A source of dielectric heating . Otherwise, they appear parasitically around conductors which absorb EMR, and around antennas which have the purpose of generating EMR at greater distances. Changing magnetic dipole fields (i.e., magnetic near-fields) are used commercially for many types of magnetic induction devices. These include motors and electrical transformers at low frequencies, and devices such as RFID tags, metal detectors , and MRI scanner coils at higher frequencies. The potential effects of electromagnetic fields on human health vary widely depending on
SECTION 10
#1732870172088588-546: A tin whisker acceptance testing standard and mitigation practices guideline intended to help manufacturers reduce the risk of tin whiskers in lead-free products. Silver whiskers often appear in conjunction with a layer of silver sulfide , which forms on the surface of silver electrical contacts operating in an atmosphere rich in hydrogen sulfide and high humidity . Such atmospheres can exist in sewage treatment plants and paper mills . Whiskers over 20 μm in length were observed on gold-plated surfaces and noted in
637-461: Is constant in time, the field is said to be an electrostatic field . Similarly, if only the magnetic field ( B ) is non-zero and is constant in time, the field is said to be a magnetostatic field . However, if either the electric or magnetic field has a time-dependence, then both fields must be considered together as a coupled electromagnetic field using Maxwell's equations . With the advent of special relativity , physical laws became amenable to
686-407: Is motionless and electrically neutral: the current, composed of negatively charged electrons, moves against a background of positively charged ions, and the densities of positive and negative charges cancel each other out. A test charge near the wire would feel no electrical force from the wire. However, if the test charge is in motion parallel to the current, the situation changes. In the rest frame of
735-431: Is needed, ultimately leading to the theory of quantum electrodynamics . Practical applications of the new understanding of electromagnetic fields emerged in the late 1800s. The electrical generator and motor were invented using only the empirical findings like Faraday's and Ampere's laws combined with practical experience. There are different mathematical ways of representing the electromagnetic field. The first one views
784-480: Is produced when the charge is stationary with respect to an observer measuring the properties of the charge, and a magnetic field as well as an electric field are produced when the charge moves, creating an electric current with respect to this observer. Over time, it was realized that the electric and magnetic fields are better thought of as two parts of a greater whole—the electromagnetic field. In 1820, Hans Christian Ørsted showed that an electric current can deflect
833-425: Is the charge density, which is a function of time and position, ε 0 {\displaystyle \varepsilon _{0}} is the vacuum permittivity , μ 0 {\displaystyle \mu _{0}} is the vacuum permeability , and J is the current density vector, also a function of time and position. Inside a linear material, Maxwell's equations change by switching
882-490: The National Highway Traffic Safety Administration (NHTSA) and a large group of other NASA researchers that found no electronic defects. In 2012, NHTSA maintained: "We do not believe that tin whiskers are a plausible explanation for these incidents...[the likely cause was] pedal misapplication ." Toyota also maintains that tin whiskers were not the cause of any stuck accelerator issues: "In
931-411: The quantization of the electromagnetic field and the development of quantum electrodynamics . The empirical investigation of electromagnetism is at least as old as the ancient Greek philosopher, mathematician and scientist Thales of Miletus , who around 600 BCE described his experiments rubbing fur of animals on various materials such as amber creating static electricity. By the 18th century, it
980-423: The vacuum tube era of electronics early in the 20th century in equipment that used pure, or almost pure, tin solder in their production. It was noticed that small metal hairs or tendrils grew between metal solder pads, causing short circuits . Metal whiskers form in the presence of compressive stress. Germanium , zinc , cadmium , and even lead whiskers have been documented. Many techniques are used to mitigate
1029-606: The "high-tech trash" problem, leading to a re-focusing on the issue of whisker formation in lead-free solders . Metal whiskering is a crystalline metallurgical phenomenon involving the spontaneous growth of tiny, filiform hairs from a metallic surface. The effect is primarily seen on elemental metals but also occurs with alloys . The mechanism behind metal whisker growth is not well understood , but seems to be encouraged by compressive mechanical stresses including: Metal whiskers differ from metallic dendrites in several respects: dendrites are fern -shaped and grow across
SECTION 20
#17328701720881078-556: The Sun powers all life on Earth that either makes or uses oxygen. A changing electromagnetic field which is physically close to currents and charges (see near and far field for a definition of "close") will have a dipole characteristic that is dominated by either a changing electric dipole , or a changing magnetic dipole . This type of dipole field near sources is called an electromagnetic near-field . Changing electric dipole fields, as such, are used commercially as near-fields mainly as
1127-400: The addition of a displacement current term to Ampere's circuital law . This unified the physical understanding of electricity, magnetism, and light: visible light is but one portion of the full range of electromagnetic waves, the electromagnetic spectrum . An electromagnetic field very far from currents and charges (sources) is called electromagnetic radiation (EMR) since it radiates from
1176-687: The behavior of the field changes according to the properties of the media. The Maxwell equations simplify when the charge density at each point in space does not change over time and all electric currents likewise remain constant. All of the time derivatives vanish from the equations, leaving two expressions that involve the electric field, ∇ ⋅ E = ρ ϵ 0 {\displaystyle \nabla \cdot \mathbf {E} ={\frac {\rho }{\epsilon _{0}}}} and ∇ × E = 0 , {\displaystyle \nabla \times \mathbf {E} =0,} along with two formulae that involve
1225-429: The charges and currents in the source. Such radiation can occur across a wide range of frequencies called the electromagnetic spectrum , including radio waves , microwave , infrared , visible light , ultraviolet light , X-rays , and gamma rays . The many commercial applications of these radiations are discussed in the named and linked articles. A notable application of visible light is that this type of energy from
1274-404: The corresponding area of magnetic phenomena. Whether a physical effect is attributable to an electric field or to a magnetic field is dependent upon the observer, in a way that special relativity makes mathematically precise. For example, suppose that a laboratory contains a long straight wire that carries an electrical current. In the frame of reference where the laboratory is at rest, the wire
1323-409: The electric and magnetic fields as three-dimensional vector fields . These vector fields each have a value defined at every point of space and time and are thus often regarded as functions of the space and time coordinates. As such, they are often written as E ( x , y , z , t ) ( electric field ) and B ( x , y , z , t ) ( magnetic field ). If only the electric field ( E ) is non-zero, and
1372-416: The electric field converges towards or diverges away from electric charges, how the magnetic field curls around electrical currents, and how changes in the electric and magnetic fields influence each other. The Lorentz force law states that a charge subject to an electric field feels a force along the direction of the field, and a charge moving through a magnetic field feels a force that is perpendicular both to
1421-565: The environment where they can produce short circuits, i.e., the electronic equipment itself. At frequencies above 6 GHz or in fast digital circuits, tin whiskers can act like miniature antennas , affecting the circuit impedance and causing reflections. In computer disk drives they can break off and cause head crashes or bearing failures. Tin whiskers often cause failures in relays and have been found upon examination of failed relays in nuclear power facilities. Pacemakers have been recalled due to tin whiskers. Research has also identified
1470-402: The first place." Electromagnetic field An electromagnetic field (also EM field ) is a physical field , mathematical functions of position and time, representing the influences on and due to electric charges . The field at any point in space and time can be regarded as a combination of an electric field and a magnetic field . Because of the interrelationship between the fields,
1519-400: The form of an electromagnetic wave . In a volume of space not containing charges or currents ( free space ) – that is, where ρ {\displaystyle \rho } and J are zero, the electric and magnetic fields satisfy these electromagnetic wave equations : James Clerk Maxwell was the first to obtain this relationship by his completion of Maxwell's equations with
Galaxy IV - Misplaced Pages Continue
1568-445: The formalism of tensors . Maxwell's equations can be written in tensor form, generally viewed by physicists as a more elegant means of expressing physical laws. The behavior of electric and magnetic fields, whether in cases of electrostatics, magnetostatics, or electrodynamics (electromagnetic fields), is governed by Maxwell's equations. In the vector field formalism, these are: where ρ {\displaystyle \rho }
1617-466: The logic board responsible for monitoring the steam pressure lines in the power plant. In September 2011, three NASA investigators claimed that they identified tin whiskers on the accelerator position sensors of sampled Toyota Camry models that could contribute to the "stuck accelerator" crashes affecting certain Toyota models during 2005–2010. This contradicted an earlier 10-month joint investigation by
1666-428: The magnetic field and to its direction of motion. The electromagnetic field is described by classical electrodynamics , an example of a classical field theory . This theory describes many macroscopic physical phenomena accurately. However, it was unable to explain the photoelectric effect and atomic absorption spectroscopy , experiments at the atomic scale. That required the use of quantum mechanics , specifically
1715-452: The magnetic field: ∇ ⋅ B = 0 {\displaystyle \nabla \cdot \mathbf {B} =0} and ∇ × B = μ 0 J . {\displaystyle \nabla \times \mathbf {B} =\mu _{0}\mathbf {J} .} These expressions are the basic equations of electrostatics , which focuses on situations where electrical charges do not move, and magnetostatics ,
1764-406: The metal or the presence of an electromagnetic field. Whiskers can cause short circuits and arcing in electrical equipment. The phenomenon was discovered by telephone companies in the late 1940s and it was later found that the addition of lead to tin solder provided mitigation. The European Restriction of Hazardous Substances Directive (RoHS), which took effect on July 1, 2006, restricted
1813-425: The permeability and permittivity of free space with the permeability and permittivity of the linear material in question. Inside other materials which possess more complex responses to electromagnetic fields, these terms are often represented by complex numbers, or tensors. The Lorentz force law governs the interaction of the electromagnetic field with charged matter. When a field travels across to different media,
1862-578: The problem, including changes to the annealing process (heating and cooling), the addition of elements like copper and nickel, and the inclusion of conformal coatings . Traditionally, lead has been added to slow down whisker growth in tin-based solders. Following the Restriction of Hazardous Substances Directive (RoHS), the European Union banned the use of lead in most consumer electronic products from 2006 due to health problems associated with lead and
1911-549: The risk of whisker growth. The trade-off has been an increase in weight, adding 50 to 100 kilograms (110 to 220 lb) per payload. On April 17, 2005, the Millstone Nuclear Power Plant in Connecticut was shut down due to a "false alarm" that indicated an unsafe pressure drop in the reactor's steam system when the steam pressure was actually nominal. The false alarm was caused by a tin whisker that short circuited
1960-435: The surface of the metal, while metal whiskers are hair-like and project normal to the surface. Dendrite growth requires moisture capable of dissolving the metal into a solution of metal ions, which are then redistributed by electromigration in the presence of an electromagnetic field . While the precise mechanism for whisker formation remains unknown, it is known that whisker formation does not require either dissolution of
2009-430: The test charge being pulled towards or pushed away from the wire. So, an observer in the laboratory rest frame concludes that a magnetic field must be present. In general, a situation that one observer describes using only an electric field will be described by an observer in a different inertial frame using a combination of electric and magnetic fields. Analogously, a phenomenon that one observer describes using only
Galaxy IV - Misplaced Pages Continue
2058-414: The test charge, the positive and negative charges in the wire are moving at different speeds, and so the positive and negative charge distributions are Lorentz-contracted by different amounts. Consequently, the wire has a nonzero net charge density, and the test charge must experience a nonzero electric field and thus a nonzero force. In the rest frame of the laboratory, there is no electric field to explain
2107-488: The use of lead in various types of electronic and electrical equipment. This has driven the use of lead-free alloys with a focus on preventing whisker formation (see § Mitigation and elimination ) . Others have focused on the development of oxygen-barrier coatings to prevent whisker formation. Airborne zinc whiskers have been responsible for increased system failure rates in computer server rooms . Zinc whiskers grow from galvanized (electroplated) metal surfaces at
2156-485: The words of U.S. Transportation Secretary Ray LaHood, 'The verdict is in. There is no electronic-based cause for unintended high-speed acceleration in Toyotas. Period. ' " According to a Toyota press release, "no data indicates that tin whiskers are more prone to occur in Toyota vehicles than any other vehicle in the marketplace." Toyota also states that "their systems are designed to reduce the risk that tin whiskers will form in
2205-492: Was a telecommunications satellite that was disabled and lost due to short circuits caused by tin whiskers in 1998. It was initially thought that space weather contributed to the failure, but later it was discovered that a conformal coating had been misapplied, allowing whiskers formed in the pure tin plating to find their way through a missing coating area, causing a failure of the main control computer. The manufacturer, Hughes, has moved to nickel plating, rather than tin, to reduce
2254-647: Was briefly occupied by Galaxy 4R , and is now occupied by the Galaxy VI satellite. Galaxy VI's relocation required an emergency order from the FCC, taking one week drift time to change orbit. Galaxy IV remains in space. This article about one or more communications satellites is a stub . You can help Misplaced Pages by expanding it . Whisker (metallurgy) Metal whiskering is a phenomenon that occurs in electrical devices when metals form long whisker-like projections over time. Tin whiskers were noticed and documented in
2303-434: Was not restored until the following day. Many fast-pay gas pumps were not able to verify credit card transactions. Wire news services, like Reuters , were also affected. The TV network CBS had to use alternate means of transmitting its programs. All 600 NPR -affiliated stations (as well as numerous other broadcasters) lost access to current network shows and newscasts. After the incident, Galaxy IV's assigned orbital slot
2352-421: Was understood that objects can carry positive or negative electric charge , that two objects carrying charge of the same sign repel each other, that two objects carrying charges of opposite sign attract one another, and that the strength of this force falls off as the square of the distance between them. Michael Faraday visualized this in terms of the charges interacting via the electric field . An electric field
2401-432: Was very successful until evidence supporting the atomic model of matter emerged. Beginning in 1877, Hendrik Lorentz developed an atomic model of electromagnetism and in 1897 J. J. Thomson completed experiments that defined the electron . The Lorentz theory works for free charges in electromagnetic fields, but fails to predict the energy spectrum for bound charges in atoms and molecules. For that problem, quantum mechanics
#87912