United States Department of Defense
The Department of Defense is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government concerned directly with national security and the United States Armed Forces. The department is the largest employer in the world, with nearly 1.3 million active duty servicemen and women as of 2016. Adding to its employees are over 826,000 National Guardsmen and Reservists from the four services, over 732,000 civilians bringing the total to over 2.8 million employees. Headquartered at the Pentagon in Arlington, just outside Washington, D. C. the DoD's stated mission is to provide "the military forces needed to deter war and ensure our nation's security". The Department of Defense is headed by the Secretary of Defense, a cabinet-level head who reports directly to the President of the United States. Beneath the Department of Defense are three subordinate military departments: the United States Department of the Army, the United States Department of the Navy, the United States Department of the Air Force.
In addition, four national intelligence services are subordinate to the Department of Defense: the Defense Intelligence Agency, the National Security Agency, the National Geospatial-Intelligence Agency, the National Reconnaissance Office. Other Defense Agencies include the Defense Advanced Research Projects Agency, the Defense Logistics Agency, the Missile Defense Agency, the Defense Health Agency, Defense Threat Reduction Agency, the Defense Security Service, the Pentagon Force Protection Agency, all of which are under the command of the Secretary of Defense. Additionally, the Defense Contract Management Agency provides acquisition insight that matters, by delivering actionable acquisition intelligence from factory floor to the warfighter. Military operations are managed by ten functional Unified combatant commands; the Department of Defense operates several joint services schools, including the Eisenhower School and the National War College. The history of the defense of the United States started with the Continental Congress in 1775.
The creation of the United States Army was enacted on 14 June 1775. This coincides with the American holiday Flag Day; the Second Continental Congress would charter the United States Navy, on 13 October 1775, create the United States Marine Corps on 10 November 1775. The Preamble of the United States Constitution gave the authority to the federal government to defend its citizens: We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America. Upon the seating of the first Congress on 4 March 1789, legislation to create a military defense force stagnated as they focused on other concerns relevant to setting up the new government. President George Washington went to Congress to remind them of their duty to establish a military twice during this time.
On the last day of the session, 29 September 1789, Congress created the War Department, historic forerunner of the Department of Defense. The War Department handled naval affairs until Congress created the Navy Department in 1798; the secretaries of each of these departments reported directly to the president as cabinet-level advisors until 1949, when all military departments became subordinate to the Secretary of Defense. After the end of World War II, President Harry Truman proposed creation of a unified department of national defense. In a special message to Congress on 19 December 1945, the President cited both wasteful military spending and inter-departmental conflicts. Deliberations in Congress went on for months focusing on the role of the military in society and the threat of granting too much military power to the executive. On 26 July 1947, Truman signed the National Security Act of 1947, which set up a unified military command known as the "National Military Establishment", as well as creating the Central Intelligence Agency, the National Security Council, National Security Resources Board, United States Air Force and the Joint Chiefs of Staff.
The act placed the National Military Establishment under the control of a single Secretary of Defense. The National Military Establishment formally began operations on 18 September, the day after the Senate confirmed James V. Forrestal as the first Secretary of Defense; the National Military Establishment was renamed the "Department of Defense" on 10 August 1949 and absorbed the three cabinet-level military departments, in an amendment to the original 1947 law. Under the Department of Defense Reorganization Act of 1958, channels of authority within the department were streamlined, while still maintaining the ordinary authority of the Military Departments to organize and equip their associated forces; the Act clarified the overall decision-making authority of the Secretary of Defense with respect to these subordinate Military Departments and more defined the operational chain of command over U. S. military forces as running from the president to the Secretary of Defense and to the unified combatant commanders.
Provided in this legislation was a centralized research authority, the Advanced Research Projects Agency known as DARPA. The act was written and promoted by the Eisenhower administration, was signed into law 6 August 1958; the Secretary of Defense, appointed by the president with the advice and consent of the Senate, is by federal law (1
Dragonfly is a proposed spacecraft and mission that would send a mobile robotic rotorcraft lander to Titan, the largest moon of Saturn, in order to study prebiotic chemistry and extraterrestrial habitability at various locations where it would perform vertical-takeoff and landings. Titan is unique in having an abundant and diverse carbon-rich chemistry on the surface of a water-ice-dominated world with an interior water ocean, making it a high-priority target for astrobiology and origin of life studies; the mission was proposed in April 2017 to NASA's New Frontiers program by the Johns Hopkins Applied Physics Laboratory, it was selected as one of two finalists in December 2017 to further refine the mission's concept. Dragonfly is a proposal for an astrobiology mission to Titan to assess its microbial habitability and study its prebiotic chemistry at various locations. If selected for launch, Dragonfly would perform controlled flights and vertical takeoffs and landings between locations, while powered by a radioisotope thermoelectric generator.
The mission would involve flights to multiple different locations on the surface, which allows sampling diverse regions and geological contexts. Titan is a compelling astrobiology target because its surface contains abundant complex carbon-rich chemistry and because both liquid water and liquid hydrocarbons can occur on its surface forming a prebiotic primordial soup; the initial Dragonfly conception took place over a dinner conversation between scientists Jason W. Barnes and Ralph D. Lorenz and it took 15 months to make it a detailed mission proposal; the Principal Investigator is Elizabeth Turtle, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory. The Dragonfly mission concept builds on several earlier studies of Titan mobile aerial exploration, including the 2007 Titan Explorer Flagship study, which advocated a Montgolfière balloon for regional exploration, AVIATR, an airplane concept considered for the Discovery program; the concept of a rotorcraft lander that flew on battery power, recharged during the 8-Earth-day Titan night from a radioisotope power source, was proposed by Lorenz in 2000.
More recent discussion has included 2014 Titan rotorcraft study by Larry Matthies, at the Jet Propulsion Laboratory, that would have a small rotorcraft deployed from a lander or a balloon. The hot-air balloon concepts would have used the heat from a radioisotope thermoelectric generator. Leveraging proven rotorcraft systems and technologies, Dragonfly would use a multi-rotor vehicle to transport its instrument suite to multiple locations to make measurements of surface composition, atmospheric conditions, geologic processes. NASA plans to select one of two proposals in July 2019 to build and launch in 2024 or 2025 as the New Frontiers program Mission 4; the CAESAR and Dragonfly missions received $4 million funding each through the end of 2018 to further develop and mature their concepts. NASA plans to select one of these two proposals in July 2019 to build and launch in 2024 or 2025; the selected mission will be the fourth in NASA's New Frontiers portfolio, a series of principal investigator-led planetary science investigations that fall under a development cost cap of $850 million.
The Penn State Vertical Lift Research Center of Excellence is responsible for rotor design and analysis, rotorcraft flight-control development, scaled rotorcraft testbed development, ground testing support, flight performance assessment. In 2005, the European Space Agency's Huygens lander acquired some atmospheric and surface measurements on Titan, it detected tholins, which are a mix of hydrocarbons on the surface. Because Titan's atmosphere obscures the surface at many wavelengths, the specific compositions of solid hydrocarbon materials on Titan's surface remain unknown. Measuring the compositions of materials in different geologic settings will reveal how far prebiotic chemistry has progressed in environments that provide known key ingredients for life, such as pyrimidines and amino acids, the building blocks of proteins. Areas of particular interest are sites where extraterrestrial liquid water in impact melt or potential cryovolcanic flows may have interacted with the abundant organic compounds.
Dragonfly would provide the capability to explore diverse locations to characterize the habitability of Titan's environment, investigate how far prebiotic chemistry has progressed, search for biosignatures indicative of life based on water as solvent and hypothetical types of biochemistry. The atmosphere contains plentiful nitrogen and methane, strong evidence indicates that liquid methane exists on the surface. Evidence indicates the presence of liquid water and ammonia under the surface, which may be delivered to the surface by cryovolcanic activity. Dragonfly would be a rotorcraft lander, much like a large quadcopter with double rotors, an octocopter; such redundant rotor configuration would be able to tolerate the loss of at least one rotor or motor. Each of the eight rotors would be about 1 m in diameter; the aircraft would travel at about 10 m/s or 36 km/h and climbs up to 4 km altitude would be desired for best scientific value. Aerial flight on Titan is aerodynamically benign as Titan has low gravity, low winds, its thick atmosphere allows for efficient rotor propulsion.
The RTG power source has been proven in multiple spacecraft, the extensive use of quad drones on Earth provides a well-understood flight system, being complemented with algorithms for independent actions in real time. The craft will be
Laurel is a city in northern Prince George's County, Maryland, in the United States, located midway between Washington, D. C. and Baltimore on the banks of the Patuxent River. Founded as a mill town in the early 19th century, the arrival of the Baltimore & Ohio Railroad in 1835 expanded local industry and enabled the city to become an early commuter town for Washington and Baltimore workers. Residential today, the city maintains a historic district centered on its Main Street, highlighting its industrial past; the Department of Defense is a prominent presence in the Laurel area today, with the Fort Meade Army base, the National Security Agency, Johns Hopkins University's Applied Physics Laboratory all located nearby. Laurel Park, a thoroughbred horse racetrack, is located just outside city limits. Many dinosaur fossils from the Cretaceous Era are preserved in a 7.5-acre park in Laurel. The site, which among other finds has yielded fossilized teeth from Astrodon and Priconodon species, has been called the most prolific in the eastern United States.
From the Late Glacial age in 10,700 B. C. to 8,500 B. C. Laurel's climate changed from a spruce forest to a hardwood forest. In the Late Archaic period from 4,000 to 1,000 B. C. Laurel would have been covered with an oak and hickory forest. Laurel was formed from land on the fall line of the Patuxent River patented by the Snowden family in 1658 as part of the 12,250-acre New Birmingham plantation, which included the Montpelier; the Washington Turnpike Road Company built Route 1 between 1796 and 1812, creating a major North-South land route. Milstead's Hotel halfway house was built in town to serve four stage lines a day in 1816. Nicholas Snowden built a grist mill on the site circa 1811 which grew to a small cotton mill by the 1820s. In 1828, a detailed survey was conducted to build a canal from Baltimore to Georgetown to connect to the proposed C&O canal; the route from Elkridge Landing to Bladensburg would have built a waterway aligning with modern U. S. Route 1 and Kenilworth Avenue, with special consideration not to harm the water power for Savage Mill.
The project did not go forward. In 1835, coinciding with the opening of the Capital Subdivision rail line from Baltimore to Washington, the Patuxent Manufacturing Company was chartered by Horace Capon, Edward Snowden, Theodore Jenkins, W. C. Shaw, A. E. Hall, O. C. Tiffany and the mill expanded with the addition of the Avondale Mill building in 1844. Mill president Horace Capron with his partners built housing for close to 300 workers, a bigger cotton mill. Cotton duck from the mill was shipped down what would become Laurel's Main Street by rail to Baltimore. A substantial dam was built in 1850; as a mill town, Laurel was somewhat unusual in Prince George's County and was surrounded by agricultural endeavors. The community was known as "Laurel Factory" when Edward Snowden became the first postmaster in 1837 and was a true company town, with a school and shops, many of the mill workers' homes owned until the 1860s by the company. During the 1840s, three historic churches in the community—the Methodist Est.
1842, St. Mary of the Mills Est. 1845, St. Philip's Est. 1839 —established what are still vigorous congregations. During the Civil War, Laurel Factory, like much of Maryland, was a divided community, but with many Southern sympathizers. Union soldiers patrolled the railroad, for a time there was a Union hospital. During the latter half of the 19th century, while it still operated its factories, manufacturing played a less important role in the community. Laurel evolved into an early suburban town. Many of its residents commuted by rail to jobs in Baltimore; the town was incorporated in 1870 and reincorporated in 1890 to coincide with a new electric power plant and paved streets and boarded sidewalks. By this time, the town had grown to a population of 2,080, the city banned livestock from the streets. In 1870, the Patuxent Bank of Laurel was founded on the corner of Washington Avenue. In 1874 a delegation was sent to Annapolis to introduce legislation to make Laurel its own county of 10,000 residents with land from Prince George's, Anne Arundel counties.
In 1879 Laurel Academy of Music was built along Route 1. The building was converted to a movie theatre in 1915, with a parking garage on the lower floor of the wood structure. In 1888 inventor David J. Weems tested an unmanned electric train on a two-mile banked circular track near Laurel Station; the three-ton vehicle reached speeds of up to 120 mph for twenty minutes. In 1890, Citizens National Bank opened its doors on Main Street, as Prince George's County's first nationally chartered bank. Charles H. Stanley was the bank's first president, it remained independently managed and with the same name until acquired by PNC Financial Services in 2007. Branch services are still provided from the original building. At the turn of the century, Louis Barret operated a hotel called the "Half Way House" called the Milstead Hotel, which served as a stop for the four stage lines operating between Baltimore and Washington. In 1898, a stable fire spread to the 100-year-old hotel and burned adjacent buildings along Main Street.
With only bucket brigades, Mayor Phelps telegraphed Baltimore to send a special train with fireman and engine number 10. One fireman was crushed by the rolling fire engine, returned in a casket saved from the burning mortuary; the resulting losses inspired efforts to
Messenger was a NASA robotic spacecraft that orbited the planet Mercury between 2011 and 2015. The probe was launched aboard a Delta II rocket in August 2004 to study Mercury's chemical composition and magnetic field; the instruments carried by MESSENGER were used on a complex series of flybys – the spacecraft flew by Earth once, Venus twice, Mercury itself three times, allowing it to decelerate relative to Mercury using minimal fuel. During its first flyby of Mercury in January 2008, MESSENGER became the second mission after Mariner 10's 1975 flyby to reach Mercury. MESSENGER entered orbit around Mercury on March 2011, becoming the first spacecraft to do so, it completed its primary mission in 2012. Following two mission extensions, the MESSENGER spacecraft used the last of its maneuvering propellant and deorbited as planned, impacting the surface of Mercury on April 30, 2015. MESSENGER's formal data collection mission began on April 4, 2011; the primary mission was completed on March 2012, having collected close to 100,000 images.
MESSENGER achieved 100% mapping of Mercury on March 6, 2013, completed its first year-long extended mission on March 17, 2013. MESSENGER's second extended mission lasted for over two years, but as its low orbit degraded, it required reboosts to avoid impact, it conducted its final reboost burns on October 24, 2014, January 21, 2015, before crashing into Mercury on April 30, 2015. During its stay in Mercury orbit, MESSENGER's instruments yielded significant data, including a characterization of Mercury's magnetic field and the discovery of water ice at the planet's north pole, which had long been suspected on the basis of Earth-based radar data. In 1973, Mariner 10 was launched by NASA to make multiple flyby encounters of Mercury. Mariner 10 provided the first detailed data of Mercury, mapping 40–45% of the surface. Mariner 10's final flyby of Mercury occurred on March 16, 1975. No subsequent close-range observations of the planet would take place for more than 30 years. In 1998, a study detailed a proposed mission to send an orbiting spacecraft to Mercury, as the planet was at that point the least-explored of the inner planets.
In the years following the Mariner 10 mission, subsequent mission proposals to revisit Mercury had appeared too costly, requiring large quantities of propellant and a heavy lift launch vehicle. Moreover, inserting a spacecraft into orbit around Mercury is difficult, because a probe approaching on a direct path from Earth would be accelerated by the Sun's gravity and pass Mercury far too to orbit it. However, using a trajectory designed by Chen-wan Yen in 1985, the study showed it was possible to seek a Discovery-class mission by using multiple, consecutive gravity assist,'swingby' maneuvers around Venus and Mercury, in combination with minor propulsive trajectory corrections, to slow the spacecraft and thereby minimize propellant needs; the MESSENGER mission was designed to study the characteristics and environment of Mercury from orbit. The scientific objectives of the mission were: to characterize the chemical composition of Mercury's surface. To study the planet's geologic history. To elucidate the nature of the global magnetic field.
To determine the size and state of the core. To determine the volatile inventory at the poles. to study the nature of Mercury's exosphere. The MESSENGER spacecraft was designed and built at the Johns Hopkins University Applied Physics Laboratory. Science operations were managed by Sean Solomon as principal investigator, mission operations were conducted at JHU/APL; the MESSENGER bus measured 1.85 meters tall, 1.42 m wide, 1.27 m deep. The bus was constructed with four graphite fiber / cyanate ester composite panels that supported the propellant tanks, the large velocity adjust thruster, attitude monitors and correction thrusters, the antennas, the instrument pallet, a large ceramic-cloth sunshade, measuring 2.5 m tall and 2 m wide, for passive thermal control. At launch, the spacecraft weighed 1,100 kilograms with its full load of propellant. MESSENGER's total mission cost, including the cost of the spacecraft's construction, was estimated at under US$450 million. Main propulsion was provided by 317 sec.
Isp bipropellant large velocity assist thruster. The model used was the LEROS 1b, developed and manufactured at AMPAC‐ISP's Westcott works, in the United Kingdom; the spacecraft was designed to carry 607.8 kilograms of propellant and helium pressurizer for the LVA. Four 22 N monopropellant thrusters provided spacecraft steering during main thruster burns, twelve 4.4 N monopropellant thrusters were used for attitude control. For precision attitude control, a reaction wheel attitude control system was included. Information for attitude control was provided by star trackers, an inertial measurement unit and six sun sensors; the probe included two small deep space transponders for communications with the Deep Space Network and three kinds of antennas: a high gain phased array whose main beam could be electronically steered in one plane, a medium-gain "fan-beam" antenna and a low gain horn with a broad pattern. The high gain antenna was used as transmit-only at 8.4 GHz, the medium-gain and low gain antennas transmit at 8.4 GHz and receive at 7.2 GHz, all three antennas operate with right-hand circularly polarized radiation.
One of each of these antennas was mounted on the front of the probe facing the Sun, one of each wa
The Convair RIM-2 Terrier was a two-stage medium-range naval surface-to-air missile, was among the earliest surface-to-air missiles to equip United States Navy ships. It underwent significant upgrades while in service, starting with a beam-riding system with 10-nautical-mile range at a speed of Mach 1.8, ending as a semi-active radar homing system with a range of 40 nmi at speeds as high as Mach 3. It was replaced in service by the RIM-67 Standard ER. Terrier has been used as a sounding rocket; the Terrier was a development of the Bumblebee Project, the United States Navy's effort to develop a surface-to-air missile to provide a middle layer of defense against air attack. It was test launched from USS Mississippi on January 28, 1953, first deployed operationally on the Boston-class cruisers and Canberra in the mid-1950s, with Canberra being the first to achieve operational status June 15, 1956, its US Navy designation was SAM-N-7 until 1963 when it was re-designated RIM-2. For a brief time during the mid-1950s the United States Marine Corps had two Terrier battalions equipped with specially modified twin sea launchers for land use that fired the SAM-N-7.
The Terrier was the first surface-to-air missile operational with the USMC. The launchers were reloaded by a special vehicle; the Terrier used radar beam-riding guidance, forward aerodynamic controls, a conventional warhead. It had a top speed of only Mach 1.8, a range of only 10 nmi, was only useful against subsonic targets. The Terrier had a launch thrust of 23 kN, weight of 1,392 kg, its original dimensions were a diameter of 340 mm, a length of 8.08 m, a fin span of 1.59 m. Cost per missile in 1957 was an estimated $60,000. Before it was in widespread service it was seeing major improvements; the RIM-2C, named the Terrier BT-3 was introduced in 1958. The forward control fins were replaced with fixed strakes, the tail became the control surface; the BT-3 had a new motor, featured extended range, Mach 3 speed, better maneuverability. The RIM-2D Terrier BT-3A entered service in 1962 with a W30 1kt nuclear warhead, but all other variants used a 218 lb controlled-fragmentation warhead; the RIM-2E introduced semi-active radar homing, for greater effectiveness against low-flying targets.
The final version, the RIM-2F, used a new motor. The Terrier was the primary missile system of most US Navy cruisers and guided missile frigates built during the 1960s, it could be installed on much smaller ships than the longer-ranged RIM-8 Talos. A Terrier installation consisted of the Mk 10 twin-arm launcher with a 40-round rear-loading magazine, but some ships had extended magazines with 60 or 80 rounds, the installation in Boston and Canberra used a bottom-loading magazine of 72 rounds; the French Navy's Masurca missile was developed with some technology provided by the USN from Terrier. The Terrier was replaced by the extended range RIM-67 Standard missile; the RIM-67 offered the range of the much larger RIM-8 Talos in a missile the size of the Terrier. Terrier has been used as a first stage in a sounding rocket, for conducting high-altitude research; the Terrier can be equipped with various upper stages, like the Asp, the TE-416 Tomahawk or the Orion. The booster served as the basis for the MIM-3 Nike Ajax booster, larger but otherwise similar, which has seen widespread use in sounding rockets.
On April 19, 1972, a Terrier missile fired by USS Sterett shot down a North Vietnamese Air Force MiG-17F in the Battle of Dong Hoi. Marina MilitareItalian cruiser Giuseppe Garibaldi Andrea Doria-class cruiser Italian cruiser Vittorio Veneto Royal Netherlands NavyHNLMS De Zeven Provinciën United States Navy USS Norton Sound RIM-24 Tartar Terasca General Dynamics SAM-N-7/RIM-2 Terrier "US Marines Terrier" YouTube video
Asteroids are minor planets of the inner Solar System. Larger asteroids have been called planetoids; these terms have been applied to any astronomical object orbiting the Sun that did not resemble a planet-like disc and was not observed to have characteristics of an active comet such as a tail. As minor planets in the outer Solar System were discovered they were found to have volatile-rich surfaces similar to comets; as a result, they were distinguished from objects found in the main asteroid belt. In this article, the term "asteroid" refers to the minor planets of the inner Solar System including those co-orbital with Jupiter. There exist millions of asteroids, many thought to be the shattered remnants of planetesimals, bodies within the young Sun's solar nebula that never grew large enough to become planets; the vast majority of known asteroids orbit within the main asteroid belt located between the orbits of Mars and Jupiter, or are co-orbital with Jupiter. However, other orbital families exist with significant populations, including the near-Earth objects.
Individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups: C-type, M-type, S-type. These were named after and are identified with carbon-rich and silicate compositions, respectively; the sizes of asteroids varies greatly. Asteroids are differentiated from meteoroids. In the case of comets, the difference is one of composition: while asteroids are composed of mineral and rock, comets are composed of dust and ice. Furthermore, asteroids formed closer to the sun; the difference between asteroids and meteoroids is one of size: meteoroids have a diameter of one meter or less, whereas asteroids have a diameter of greater than one meter. Meteoroids can be composed of either cometary or asteroidal materials. Only one asteroid, 4 Vesta, which has a reflective surface, is visible to the naked eye, this only in dark skies when it is favorably positioned. Small asteroids passing close to Earth may be visible to the naked eye for a short time; as of October 2017, the Minor Planet Center had data on 745,000 objects in the inner and outer Solar System, of which 504,000 had enough information to be given numbered designations.
The United Nations declared 30 June as International Asteroid Day to educate the public about asteroids. The date of International Asteroid Day commemorates the anniversary of the Tunguska asteroid impact over Siberia, Russian Federation, on 30 June 1908. In April 2018, the B612 Foundation reported "It's 100 percent certain we'll be hit, but we're not 100 percent sure when." In 2018, physicist Stephen Hawking, in his final book Brief Answers to the Big Questions, considered an asteroid collision to be the biggest threat to the planet. In June 2018, the US National Science and Technology Council warned that America is unprepared for an asteroid impact event, has developed and released the "National Near-Earth Object Preparedness Strategy Action Plan" to better prepare. According to expert testimony in the United States Congress in 2013, NASA would require at least five years of preparation before a mission to intercept an asteroid could be launched; the first asteroid to be discovered, was considered to be a new planet.
This was followed by the discovery of other similar bodies, with the equipment of the time, appeared to be points of light, like stars, showing little or no planetary disc, though distinguishable from stars due to their apparent motions. This prompted the astronomer Sir William Herschel to propose the term "asteroid", coined in Greek as ἀστεροειδής, or asteroeidēs, meaning'star-like, star-shaped', derived from the Ancient Greek ἀστήρ astēr'star, planet'. In the early second half of the nineteenth century, the terms "asteroid" and "planet" were still used interchangeably. Overview of discovery timeline: 10 by 1849 1 Ceres, 1801 2 Pallas – 1802 3 Juno – 1804 4 Vesta – 1807 5 Astraea – 1845 in 1846, planet Neptune was discovered 6 Hebe – July 1847 7 Iris – August 1847 8 Flora – October 1847 9 Metis – 25 April 1848 10 Hygiea – 12 April 1849 tenth asteroid discovered 100 asteroids by 1868 1,000 by 1921 10,000 by 1989 100,000 by 2005 ~700,000 by 2015 Asteroid discovery methods have improved over the past two centuries.
In the last years of the 18th century, Baron Franz Xaver von Zach organized a group of 24 astronomers to search the sky for the missing planet predicted at about 2.8 AU from the Sun by the Titius-Bode law because of the discovery, by Sir William Herschel in 1781, of the planet Uranus at the distance predicted by the law. This task required that hand-drawn sky charts be prepared for all stars in the zodiacal band down to an agreed-upon limit of faintness. On subsequent nights, the sky would be charted again and any moving object would be spotted; the expected motion of the missing planet was about 30 seconds of arc per hour discernible by observers. The first object, was not discovered by a member of the group, but rather by accident in 1801 by Giuseppe Piazzi, director of the observatory of Palermo in Sicily, he discovered a new star-like object in Taurus and followed the displacement of this object during several nights. That year, Carl Friedrich Gauss used these observations to calculate the orbit of this unknown object, found to be between the planets Mars and Jupiter.
Piazzi named it after Ceres, the Roman goddess of agriculture. Three other asteroids (2 Pallas, 3 Juno, 4 Ves
The Near Earth Asteroid Rendezvous – Shoemaker, renamed after its 1996 launch in honor of planetary scientist Eugene Shoemaker, was a robotic space probe designed by the Johns Hopkins University Applied Physics Laboratory for NASA to study the near-Earth asteroid Eros from close orbit over a period of a year. The mission succeeded in closing in with the asteroid and orbited it several times terminating by touching down on the asteroid on 12 February 2001; the primary scientific objective of NEAR was to return data on the bulk properties, mineralogy, internal mass distribution and magnetic field of Eros. Secondary objectives include studies of regolith properties, interactions with the solar wind, possible current activity as indicated by dust or gas, the asteroid spin state; this data will be used to help understand the characteristics of asteroids in general, their relationship to meteoroids and comets, the conditions in the early Solar System. To accomplish these goals, the spacecraft was equipped with an X-ray/gamma-ray spectrometer, a near-infrared imaging spectrograph, a multi-spectral camera fitted with a CCD imaging detector, a laser rangefinder, a magnetometer.
A radio science experiment was performed using the NEAR tracking system to estimate the gravity field of the asteroid. The total mass of the instruments was 56 kg, they required 80 W power. A previous plan for the mission was for it to go to 4660 Nereus and do a flyby of 2019 Van Albada en route. In January 2000 it would rendezvous with Nereus but instead of staying it would visit multiple asteroids and comets; some of the choices that were discussed were 2P/Encke, 433 Eros, 1036 Ganymed, 4 Vesta, 4015 Wilson–Harrington. The Small-Body Grand Tour was a plan for visiting two asteroids and two comets over a span of a decade with the spacecraft; the primary goal of the mission was to study the near-Earth asteroid 433 Eros from orbit for one year. Eros is an S-type asteroid 13 × 13 × 33 km in size, the second largest near-Earth asteroid; the orbit was circular with a radius of 200 km. The radius of the orbit was brought down in stages to a 50 × 50 km orbit on 30 April 2000 and decreased to 35 × 35 km on July 14, 2000.
The orbit was raised over succeeding months to a 200 × 200 km orbit and slowly decreased and altered to a 35 × 35 km retrograde orbit on December 13, 2000. The mission ended with a touchdown in the "saddle" region of Eros on February 12, 2001; some scientists claim that the ultimate goal of the mission was to link Eros, an asteroidal body, to meteorites recovered on Earth. With sufficient data on chemical composition, a causal link could be established between Eros and other S-type asteroids, those meteorites believed to be pieces of S-type asteroids. Once this connection is established, meteorite material can be studied with large and evolving equipment, the results extrapolated to bodies in space. NEAR-Shoemaker did not disprove this link to the satisfaction of scientists. Between December 1999 and February 2001 NEAR Shoemaker used its gamma-ray spectrometer to detect gamma-ray bursts as part of the InterPlanetary Network. After launch on a Delta 7925-8 and exit from Earth orbit, NEAR entered the first part of its cruise phase.
NEAR spent most of the cruise phase in a minimal activity "hibernation" state, which ended a few days before the flyby of the 61 km diameter asteroid 253 Mathilde. On 27 June 1997, NEAR flew by Mathilde within 1200 km at 12:56 UT at 9.93 km/s, returning imaging and other instrument data. The flyby produced over 500 images, covering 60% of Mathilde's surface, as well as gravitational data allowing calculations of Mathilde's dimensions and mass. On July 3, 1997, NEAR executed the first major deep space maneuver, a two-part burn of the main 450 N thruster; this decreased the velocity by 279 m/s and lowered perihelion from 0.99 AU to 0.95 AU. The Earth gravity assist swingby occurred on January 23, 1998 at 7:23 UT; the closest approach was 540 km, altering the orbital inclination from 0.5 to 10.2 degrees, the aphelion distance from 2.17 to 1.77 AU, nearly matching those of Eros. Instrumentation was active at this time; the first of four scheduled rendezvous burns was attempted on December 20, 1998 at 22:00 UT.
The burn sequence was initiated but aborted. The spacecraft subsequently began tumbling; the spacecraft's thrusters fired thousands of times during the anomaly, which expended 29 kg of propellant reducing the program's propellant margin to zero. This anomaly resulted in the loss of the spacecraft due to lack of solar orientation and subsequent battery drain. Contact between the spacecraft and mission control could not be established for over 24 hours; the root cause of this incident has not been determined, but software and operational errors contributed to the severity of the anomaly. The original mission plan called for the four burns to be followed by an orbit insertion burn on January 10, 1999, but the abort of the first burn and loss of communication made this impossible. A new plan was put into effect in which NEAR flew by Eros on December 23, 1998 at 18:41:23 UT at a speed of 965 m/s and a distance of 3827 km from the center of mass of Eros. Images of Eros were taken by the camera, data were collected by the near IR spectrograph, radio tracking was performed during the flyby.
A rendezvous maneuver was performed on January 3, 1999 involving a thruster burn to match NEAR's orbital speed to that of Eros. A hydrazine thruster burn. On August 12 a two-minute thruster burn slow