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33-405: BlackSky Pathfinder-1 is an Earth imaging satellite . The satellite is equipped with payloads from Harris Corporation designed to image an area approximately 4.4 × 6.6 km (2.7 × 4.1 mi). It is a demonstration satellite for BlackSky Global , a Seattle -based company intending to field a fleet of 60 spacecraft to offer on-demand high-resolution images of any place on

66-404: A = 7200 km , i.e., for an altitude a − R E ≈ 800 km of the spacecraft over Earth's surface, this formula gives a Sun-synchronous inclination of 98.7°. Note that according to this approximation cos i equals −1 when the semi-major axis equals 12 352  km , which means that only lower orbits can be Sun-synchronous. The period can be in the range from 88 minutes for

99-595: A Sun-synchronous orbit. The angular precession per orbit for an Earth orbiting satellite is approximately given by where An orbit will be Sun-synchronous when the precession rate ρ = ⁠ d Ω / d t ⁠ equals the mean motion of the Earth about the Sun n E , which is 360° per sidereal year ( 1.990 968 71 × 10   rad /s ), so we must set n E = ⁠ Δ Ω E / T E ⁠ = ρ = ⁠ Δ Ω / T ⁠ , where T E

132-410: A planet, in which the satellite passes over any given point of the planet's surface at the same local mean solar time . More technically, it is an orbit arranged so that it precesses through one complete revolution each year, so it always maintains the same relationship with the Sun. A Sun-synchronous orbit is useful for imaging , reconnaissance , and weather satellites , because every time that

165-540: A relatively low altitude. Most orbit at altitudes above 500 to 600 kilometers (310 to 370 mi). Lower orbits have significant air-drag , which makes frequent orbit reboost maneuvers necessary. The Earth observation satellites ERS-1, ERS-2 and Envisat of European Space Agency as well as the MetOp spacecraft of EUMETSAT are all operated at altitudes of about 800 km (500 mi). The Proba-1 , Proba-2 and SMOS spacecraft of European Space Agency are observing

198-470: A satellite in Sun-synchronous orbit might ascend across the equator twelve times a day, each time at approximately 15:00 mean local time. Special cases of the Sun-synchronous orbit are the noon/midnight orbit , where the local mean solar time of passage for equatorial latitudes is around noon or midnight, and the dawn/dusk orbit , where the local mean solar time of passage for equatorial latitudes

231-525: A spot on the Earth at the same local time each time, this refers to mean solar time , not to apparent solar time . The Sun will not be in exactly the same position in the sky during the course of the year (see Equation of time and Analemma ). Sun-synchronous orbits are mostly selected for Earth observation satellites , with an altitude typically between 600 and 1000 km over the Earth surface. Even if an orbit remains Sun-synchronous, however, other orbital parameters such as argument of periapsis and

264-412: A very low orbit ( a = 6554 km , i = 96°) to 3.8 hours ( a = 12 352  km , but this orbit would be equatorial, with i = 180°). A period longer than 3.8 hours may be possible by using an eccentric orbit with p < 12 352  km but a > 12 352  km . If one wants a satellite to fly over some given spot on Earth every day at the same hour, the satellite must complete

297-402: A whole number of orbits per day. Assuming a circular orbit, this comes down to between 7 and 16 orbits per day, as doing less than 7 orbits would require an altitude above the maximum for a Sun-synchronous orbit, and doing more than 16 would require an orbit inside the Earth's atmosphere or surface. The resulting valid orbits are shown in the following table. (The table has been calculated assuming

330-407: Is around sunrise or sunset, so that the satellite rides the terminator between day and night. Riding the terminator is useful for active radar satellites, as the satellites' solar panels can always see the Sun, without being shadowed by the Earth. It is also useful for some satellites with passive instruments that need to limit the Sun's influence on the measurements, as it is possible to always point

363-519: Is classified in accordance with ITU Radio Regulations (article 1) as follows: Fixed service (article 1.20) The allocation of radio frequencies is provided according to Article 5 of the ITU Radio Regulations (edition 2012). In order to improve harmonisation in spectrum utilisation, the majority of service-allocations stipulated in this document were incorporated in national Tables of Frequency Allocations and Utilisations which

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396-473: Is designed for three-year lifetimes and will have an imaging resolution of about 1 m (3 ft 3 in) from an altitude of 450 km (280 mi). This is first in a series of 30 satellites planned to deploy the BlackSky constellation that will provide near real-time images in about 90 minutes to produce images that are more current and wide-ranging to increase global transparency. The satellite

429-411: Is the earth orbital period while T is the period of the spacecraft around the earth. As the orbital period of a spacecraft is where a is the semi-major axis of the orbit, and μ is the standard gravitational parameter of the planet ( 398 600 .440 km /s for Earth); as p ≈ a for a circular or almost circular orbit, it follows that or when ρ is 360° per year, As an example, with

462-403: Is with-in the responsibility of the appropriate national administration. The allocation might be primary, secondary, exclusive, and shared. However, military usage, in bands where there is civil usage, will be in accordance with the ITU Radio Regulations. Sun-synchronous orbit A Sun-synchronous orbit ( SSO ), also called a heliosynchronous orbit , is a nearly polar orbit around

495-439: The ionosphere . The United States Army Ballistic Missile Agency launched the first American satellite, Explorer 1 , for NASA's Jet Propulsion Laboratory on January 31, 1958. The information sent back from its radiation detector led to the discovery of the Earth's Van Allen radiation belts . The TIROS-1 spacecraft, launched on April 1, 1960, as part of NASA's Television Infrared Observation Satellite (TIROS) program, sent back

528-418: The orbital eccentricity evolve, due to higher-order perturbations in the Earth's gravitational field, the pressure of sunlight, and other causes. Earth observation satellites, in particular, prefer orbits with constant altitude when passing over the same spot. Careful selection of eccentricity and location of perigee reveals specific combinations where the rate of change of perturbations are minimized, and hence

561-399: The 96–100- minute range, and inclinations of around 98°. This is slightly retrograde compared to the direction of Earth's rotation: 0° represents an equatorial orbit, and 90° represents a polar orbit. Sun-synchronous orbits are possible around other oblate planets, such as Mars . A satellite orbiting a planet such as Venus that is almost spherical will need an outside push to maintain

594-558: The Earth from an altitude of about 700 km (430 mi). The Earth observation satellites of UAE, DubaiSat-1 & DubaiSat-2 are also placed in Low Earth orbits (LEO) orbits and providing satellite imagery of various parts of the Earth. To get global coverage with a low orbit, a polar orbit is used. A low orbit will have an orbital period of roughly 100 minutes and the Earth will rotate around its polar axis about 25° between successive orbits. The ground track moves towards

627-581: The Earth's movement around the Sun . This precession is achieved by tuning the inclination to the altitude of the orbit (see Technical details ) such that Earth's equatorial bulge , which perturbs inclined orbits, causes the orbital plane of the spacecraft to precess with the desired rate. The plane of the orbit is not fixed in space relative to the distant stars, but rotates slowly about the Earth's axis. Typical Sun-synchronous orbits around Earth are about 600–800 km (370–500 mi) in altitude, with periods in

660-647: The current vegetation state to its long term average. For example, the 2002 oil spill off the northwest coast of Spain was watched carefully by the European ENVISAT , which, though not a weather satellite, flies an instrument (ASAR) which can see changes in the sea surface. Anthropogenic emissions can be monitored by evaluating data of tropospheric NO 2 and SO 2 . These types of satellites are almost always in Sun-synchronous and "frozen" orbits. A Sun-synchronous orbit passes over each spot on

693-455: The first television footage of weather patterns to be taken from space. In 2008, more than 150 Earth observation satellites were in orbit, recording data with both passive and active sensors and acquiring more than 10 terabits of data daily. By 2021, that total had grown to over 950, with the largest number of satellites operated by US-based company Planet Labs . Most Earth observation satellites carry instruments that should be operated at

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726-411: The ground at the same time of day, so that observations from each pass can be more easily compared, since the Sun is in the same spot in each observation. A "frozen" orbit is the closest possible orbit to a circular orbit that is undisturbed by the oblateness of the Earth , gravitational attraction from the Sun and Moon, solar radiation pressure , and air drag . Terrain can be mapped from space with

759-525: The ground using radio, but fell short of the idea of using satellites for mass broadcasting and as telecommunications relays. The onset of the Cold War prompted the rapid development of Satellite launch systems and camera technology capable of sufficient Earth observation to garner intelligence on enemy military infrastructure and evaluate nuclear posture. Following the U-2 incident in 1960, which highlighted

792-421: The instruments towards the night side of the Earth. The dawn/dusk orbit has been used for solar-observing scientific satellites such as TRACE , Hinode and PROBA-2 , affording them a nearly continuous view of the Sun. A Sun-synchronous orbit is achieved by having the osculating orbital plane precess (rotate) approximately one degree eastward each day with respect to the celestial sphere to keep pace with

825-403: The periods given. The orbital period that should be used is actually slightly longer. For instance, a retrograde equatorial orbit that passes over the same spot after 24 hours has a true period about ⁠ 365 / 364 ⁠ ≈ 1.0027 times longer than the time between overpasses. For non-equatorial orbits the factor is closer to 1.) When one says that a Sun-synchronous orbit goes over

858-451: The planet. The U.S.-built Earth observing platform weighed about 44 kg (97 lb), and will lay the foundation for BlackSky's commercial remote sensing business, which officials announced in June 2015. The main objective of the pathfinder is to return imagery, an achievement that would prove the basic technology behind the planned commercial Earth-observing satellite fleet. The satellite

891-728: The risks of aerial spying, the U.S. accelerated surveillance satellite programs like CORONA . Satellites largely replaced aircraft overflights for surveillance after 1960. A weather satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth . These meteorological satellites, however, see more than clouds and cloud systems. City lights, fires , effects of pollution , auroras , sand and dust storms , snow cover, ice mapping, boundaries of ocean currents , energy flows, etc., are other types of environmental information collected using weather satellites. Weather satellite images helped in monitoring

924-430: The satellite is overhead, the surface illumination angle on the planet underneath it is nearly the same. This consistent lighting is a useful characteristic for satellites that image the Earth's surface in visible or infrared wavelengths, such as weather and spy satellites, and for other remote-sensing satellites, such as those carrying ocean and atmospheric remote-sensing instruments that require sunlight. For example,

957-740: The use of satellites, such as Radarsat-1 and TerraSAR-X . According to the International Telecommunication Union (ITU), Earth exploration-satellite service (also: Earth exploration-satellite radiocommunication service ) is – according to Article 1.51 of the ITU Radio Regulations (RR) – defined as: A radiocommunication service between earth stations and one or more space stations , which may include links between space stations, in which: This service may also include feeder links necessary for its operation. This radiocommunication service

990-478: The volcanic ash cloud from Mount St. Helens and activity from other volcanoes such as Mount Etna . Smoke from fires in the western United States such as Colorado and Utah have also been monitored. Other environmental satellites can assist environmental monitoring by detecting changes in the Earth's vegetation, atmospheric trace gas content, sea state, ocean color, and ice fields. By monitoring vegetation changes over time, droughts can be monitored by comparing

1023-445: The west 25° each orbit, allowing a different section of the globe to be scanned with each orbit. Most are in Sun-synchronous orbits . A geostationary orbit , at 36,000 km (22,000 mi), allows a satellite to hover over a constant spot on the earth since the orbital period at this altitude is 24 hours. This allows uninterrupted coverage of more than 1/3 of the Earth per satellite, so three satellites, spaced 120° apart, can cover

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1056-552: The whole Earth. This type of orbit is mainly used for meteorological satellites . Herman Potočnik explored the idea of using orbiting spacecraft for detailed peaceful and military observation of the ground in his 1928 book, The Problem of Space Travel . He described how the special conditions of space could be useful for scientific experiments. The book described geostationary satellites (first put forward by Konstantin Tsiolkovsky ) and discussed communication between them and

1089-521: Was launched at 03:42 UTC on 26 September 2016 by Indian Space Research Organisation (ISRO) using the PSLV-C35 launch vehicle . Earth observation satellite The first occurrence of satellite remote sensing can be dated to the launch of the first artificial satellite, Sputnik 1 , by the Soviet Union on October 4, 1957. Sputnik 1 sent back radio signals, which scientists used to study

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