A geocentric orbit or Earth orbit involves any object orbiting Planet Earth, such as the Moon or artificial satellites. In 1997 NASA estimated there were approximately 2,465 artificial satellite payloads orbiting the Earth and 6,216 pieces of space debris as tracked by the Goddard Space Flight Center. Over 16,291 previously launched objects have decayed into the Earth's atmosphere.
A spacecraft enters orbit when its centripetal acceleration due to gravity is less than or equal to the centrifugal acceleration due to the horizontal component of its velocity. For a low Earth orbit, this velocity is about 7,800 m/s (28,100 km/h; 17,400 mph); by contrast, the fastest manned airplane speed ever achieved (excluding speeds achieved by deorbiting spacecraft) was 2,200 m/s (7,900 km/h; 4,900 mph) in 1967 by the North American X-15. The energy required to reach Earth orbital velocity at an altitude of 600 km (370 mi) is about 36 MJ/kg, which is six times the energy needed merely to climb to the corresponding altitude.
Spacecraft with a perigee below about 2,000 km (1,200 mi) are subject to drag from the Earth's atmosphere, which decreases the orbital altitude. The rate of orbital decay depends on the satellite's cross-sectional area and mass, as well as variations in the air density of the upper atmosphere. Below about 300 km (190 mi), decay becomes more rapid with lifetimes measured in days. Once a satellite descends to 180 km (110 mi), it has only hours before it vaporizes in the atmosphere. The escape velocity required to pull free of Earth's gravitational field altogether and move into interplanetary space is about 11,200 m/s (40,300 km/h; 25,100 mph).
The following is a list of different geocentric orbit classifications.
the Earth's surface
|Speed||Orbital period||Specific orbital energy|
|Earth's own rotation at surface (for comparison – not an orbit)||6,378 km||0 km||465.1 m/s (1,674 km/h or 1,040 mph)||23 h 56 min||−62.6 MJ/kg|
|Orbiting at Earth's surface (equator)||6,378 km||0 km||7.9 km/s (28,440 km/h or 17,672 mph)||1 h 24 min 18 sec||−31.2 MJ/kg|
|Low Earth orbit||6,600–8,400 km||200–2,000 km||
||1 h 29 min – 2 h 8 min||−29.8 MJ/kg|
|Molniya orbit||6,900–46,300 km||500–39,900 km||1.5–10.0 km/s (5,400–36,000 km/h or 3,335–22,370 mph) respectively||11 h 58 min||−4.7 MJ/kg|
|Geostationary||42,000 km||35,786 km||3.1 km/s (11,600 km/h or 6,935 mph)||23 h 56 min||−4.6 MJ/kg|
|Orbit of the Moon||363,000–406,000 km||357,000–399,000 km||0.97–1.08 km/s (3,492–3,888 km/h or 2,170–2,416 mph) respectively||27.3 days||−0.5 MJ/kg|
An areocentric orbit is an orbit around the planet Mars.
The areo- prefix is derived from the ancient Greek word Ares which is the personification of the planet Mars in Greek mythology. The name is an analogue to the term "geocentric orbit" for an orbit around Earth.
The first artificial satellites in areocentric orbit and the first orbiters of another celestial body (other than the Moon) were the U.S. Mariner 9 probe and Soviet Mars 2 and Mars 3 orbiters in 1971, 14 November and 27 November respectively. Later they were followed by many probes.Compass-1
Compass-1 (also known as Compass One) is a German amateur CubeSat picosatellite, built and operated in the late 2000s by Aachen University of Applied Science. It was launched by the Indian Space Research Organisation, aboard a PSLV rocket as a secondary payload to the CartoSat-2A primary spacecraft on 28 April 2008. It was launched into a Geocentric orbit with an altitude of 597 km. Its primary mission is remote sensing; however, it also contains some technology demonstration experiments regarding the use of small satellites and GPS tracking.
On 10 August 2008, the satellite developed a problem and switched into "emergency mode". Initial attempts to rectify this problem failed; however, normal operations were resumed on 10 September, with help from amateur radio operators around the world.Deliberate crash landings on extraterrestrial bodies
These are tables of space probes (typically orbiters or components thereof) which have been deliberately destroyed at their objects of study, typically by hard landings or crash landings at the end of their respective missions and/or functionality. This suicidal endeavor not only precludes the hazards of orbital space debris and planetary contamination, but also provides the opportunity in some cases for terminal science given that the transient light released by the kinetic energy may be available for spectroscopy; the physical ejecta remains in place for further study. Even after soft landings had been mastered, NASA used crash landings to test whether Moon craters contained ice by crashing space probes into craters and testing the debris that got thrown out.Several rocket stages utilized during the Apollo space program were deliberately crashed on the Moon to aid seismic research, and four of the ascent stages of Apollo Lunar Modules were deliberately crashed onto the Moon after they had fulfilled their function.
The Deep Impact mission had its own purpose-built impactor which hit Comet 9P/Tempel 1. Terminal approaches to gas giants which resulted in the destruction of the space probe count as crash landings for the purposes of this article.
The crash landing sites themselves are of interest to space archeology.
Luna 1, not itself a lunar orbiter, was the first spacecraft designed as an impactor. It failed to hit the Moon in 1959, however, thus inadvertently becoming the first man-made object to leave geocentric orbit and enter a heliocentric orbit, where it remains to this day.Explorer 13
Explorer 13 (also called S-55A) was an American satellite launched as part of Explorers program. Was launched on August 25, 1961 from Wallops Flight Facility, Virginia, U.S..High Earth orbit
A high Earth orbit is a geocentric orbit with an altitude entirely above that of a geosynchronous orbit (35,786 kilometres (22,236 mi)). The orbital periods of such orbits are greater than 24 hours, therefore satellites in such orbits have an apparent retrograde motion – that is, even if they are in a prograde orbit (90° > inclination ≥ 0°), their orbital velocity is lower than Earth's rotational speed, causing their ground track to move westward on Earth's surface.Infrared Space Observatory
The Infrared Space Observatory (ISO) was a space telescope for infrared light designed and operated by the European Space Agency (ESA), in cooperation with ISAS (part of JAXA as of 2003) and NASA. The ISO was designed to study infrared light at wavelengths of 2.5 to 240 micrometres.The €480.1-million satellite was launched on 17 November 1995 from the ELA-2 launch pad at the Guiana Space Centre near Kourou in French Guiana. The launch vehicle, an Ariane 44P rocket, placed ISO successfully into a highly elliptical geocentric orbit, completing one revolution around the Earth every 24 hours. The primary mirror of its Ritchey-Chrétien telescope measured 60 cm in diameter and was cooled to 1.7 kelvins by means of superfluid helium. The ISO satellite contained four instruments that allowed for imaging and photometry from 2.5 to 240 micrometres and spectroscopy from 2.5 to 196.8 micrometers.
Currently, ESA and IPAC continue efforts to improve the data pipelines and specialized software analysis tools to yield the best quality calibration and data reduction methods from the mission. IPAC supports ISO observers and data archive users through in-house visits and workshops.J002E3
J002E3 is the designation given to an object in space discovered on September 3, 2002, by amateur astronomer Bill Yeung. Initially thought to be an asteroid, it has since been tentatively identified as the S-IVB third stage of the Apollo 12 Saturn V rocket (designated S-IVB-507), based on spectrographic evidence consistent with the paint used on the rockets. The stage was intended to be injected into a permanent heliocentric orbit in November 1969, but is now believed instead to have gone into an unstable high Earth orbit which left Earth's proximity in 1971 and again in June 2003, with an approximately 40-year cycle between heliocentric and geocentric orbit.Kosmos 21
Kosmos 21 (Russian: Космос 21 meaning Cosmos 21) was a Soviet spacecraft with an unknown mission. This mission has been tentatively identified by NASA as a technology test of the Venera series space probes. It may have been an attempted Venus flyby, presumably similar to the later Kosmos 27 mission, or it may have been intended from the beginning to remain in geocentric orbit. In any case, the spacecraft never left Earth orbit after insertion by the SL-6/A-2-e launcher. The orbit decayed on November 14, three days after launch.
Cosmos 21 was launched at 06:23:35 UTC on 11 November 1963, atop a Molniya 8K78 carrier rocket flying from Site 1/5 at the Baikonur Cosmodrome. Its original development name before being given the Cosmos 21 denomination once it reached orbit was 3MV-1 No. 1.Beginning in 1962, the name Kosmos was given to Soviet spacecraft which remained in Earth orbit, regardless of whether that was their intended final destination. The designation of this mission as an intended planetary probe is based on evidence from Soviet and non-Soviet sources and historical documents. Typically Soviet planetary missions were initially put into an Earth parking orbit as a launch platform with a rocket engine and attached probe. The probes were then launched toward their targets with an engine burn with a duration of roughly 4 minutes. If the engine misfired or the burn was not completed, the probes would be left in Earth orbit and given a Kosmos designation.Land Remote-Sensing Commercialization Act of 1984
The Land Remote-Sensing Commercialization Act of 1984 is a United States statute establishing a system to further the utilization of satellite imagery data obtained from Earth observation satellites located in a geocentric orbit above the atmosphere of Earth.
The H.R. 5155 legislation was passed by the 98th U.S. Congressional session and enacted into law by the 40th President of the United States Ronald Reagan on July 17, 1984.Longitude of the ascending node
The longitude of the ascending node (☊ or Ω) is one of the orbital elements used to specify the orbit of an object in space. It is the angle from a reference direction, called the origin of longitude, to the direction of the ascending node, measured in a reference plane. The ascending node is the point where the orbit of the object passes through the plane of reference, as seen in the adjacent image. Commonly used reference planes and origins of longitude include:
For a geocentric orbit, Earth's equatorial plane as the reference plane, and the First Point of Aries as the origin of longitude. In this case, the longitude is also called the right ascension of the ascending node, or RAAN. The angle is measured eastwards (or, as seen from the north, counterclockwise) from the First Point of Aries to the node.
For a heliocentric orbit, the ecliptic as the reference plane, and the First Point of Aries as the origin of longitude. The angle is measured counterclockwise (as seen from north of the ecliptic) from the First Point of Aries to the node.
For an orbit outside the Solar System, the plane tangent to the celestial sphere at the point of interest (called the plane of the sky) as the reference plane, and north, i.e. the perpendicular projection of the direction from the observer to the North Celestial Pole onto the plane of the sky, as the origin of longitude. The angle is measured eastwards (or, as seen by the observer, counterclockwise) from north to the node., pp. 40, 72, 137; , chap. 17.In the case of a binary star known only from visual observations, it is not possible to tell which node is ascending and which is descending. In this case the orbital parameter which is recorded is the longitude of the node, Ω, which is the longitude of whichever node has a longitude between 0 and 180 degrees., chap. 17;, p. 72.Luna 1
Luna 1, also known as Mechta (Russian: Мечта [mʲɪt͡ɕˈta], lit.: Dream), E-1 No.4 and First Lunar Rover , was the first spacecraft to reach the vicinity of the Earth's Moon, and the first spacecraft to be placed in heliocentric orbit. Intended as an impactor, Luna 1 was launched as part of the Soviet Luna programme in 1959, however due to an incorrectly timed upper stage burn during its launch, it missed the Moon, in the process becoming the first spacecraft to leave geocentric orbit.
While traveling through the outer Van Allen radiation belt, the spacecraft's scintillator made observations indicating that a small number of high-energy particles exist in the outer belt. The measurements obtained during this mission provided new data on the Earth's radiation belt and outer space. The Moon was found to have no detectable magnetic field. The first-ever direct observations and measurements of the solar wind, a strong flow of ionized plasma emanating from the Sun and streaming through interplanetary space, were performed. That ionized plasma concentration was measured to be some 700 particles per cm3 at altitudes 20–25 thousand km and 300 to 400 particles per cm3 at altitudes 100–150,000 km. The spacecraft also marked the first instance of radio communication at the half-million-kilometer distance.
A malfunction in the ground-based control system caused an error in the rocket's burntime, and the spacecraft missed the target and flew by the Moon at a distance of 5,900 km at the closest point. Luna 1 then became the first man-made object to reach heliocentric orbit and was then dubbed a "new planet" and renamed Mechta (Dream). Luna 1 was also referred to as the "First Cosmic Rocket", in reference to its achievement of escape velocity.Luna E-6 No.2
Luna E-6 No.2, also identified as No.1, and sometimes known in the West as Sputnik 25, was a Soviet spacecraft which launched in 1963, but was placed into a useless orbit due to a problem with the upper stage of the rocket that launched it. It was a 1,500-kilogram (3,300 lb) Luna E-6 spacecraft, the first of twelve to be launched, It was intended to be the first spacecraft to perform a soft landing on the Moon, a goal which would eventually be accomplished by the final E-6 spacecraft, Luna 9.
Luna E-6 No.2 was launched at 08:49 UTC on 4 January 1963, atop a Molniya-L 8K78L carrier rocket, flying from Site 1/5 at the Baikonur Cosmodrome. The lower stages of the rocket performed nominally, delivering the upper stage and payload into low Earth orbit, however a transformer in the upper stage malfunctioned, which resulted in its ullage motors failing to ignite when the stage began its start-up sequence, sixty six minutes after launch. It remained in low Earth orbit until it decayed on 11 January 1963. It was the first spacecraft to be launched in 1963, and consequently the first to be assigned an International Designator, under the new system which had been introduced at the start of the year.The spacecraft consisted of a cylindrical section containing rockets and fuel for manoeuvring, attitude control and landing, as well as radio transmitters, and a 100-kilogram (220 lb) instrumented probe, which would have been ejected onto the surface after the spacecraft landed, carrying a camera and devices to measure radiation. It was intended to return data on the mechanical characteristics of the lunar surface, the hazards presented by the topology such as craters, rocks, and other obstructions, and radiation, in preparation for future manned landings.
The designations Sputnik 33, and later Sputnik 25 were used by the United States Naval Space Command to identify the spacecraft in its Satellite Situation Summary documents, since the Soviet Union did not release the internal designations of its spacecraft at that time, and had not assigned it an official name due to its failure to depart geocentric orbit.Mars 2MV-3 No.1
Mars 2MV-3 No.1 also known as Sputnik 24 in the West, was a Soviet spacecraft, which was launched in 1962 as part of the Mars program, and was intended to land on the surface of Mars. Due to a problem with the rocket which launched it, it did not depart low Earth orbit, and it decayed several days later. It was the only Mars 2MV-3 spacecraft to be launched.Mars 2MV-4 No.1
Mars 2MV-4 No.1 also known as Sputnik 22 in the West, was a Soviet spacecraft, which was launched in 1962 as part of the Mars programme, and was intended to make a flyby of Mars, and transmit images of the planet back to Earth. Due to a problem with the rocket which launched it, it was destroyed in low Earth orbit. It was the first of two Mars 2MV-4 spacecraft to be launched, the other being the Mars 1 spacecraft which was launched eight days later.Shin'en (spacecraft)
Shin'en, known before launch as UNITEC-1 or UNISEC Technology Experiment Carrier 1, is a Japanese student spacecraft which was intended to make a flyby of Venus in order to study the effects of interplanetary spaceflight on spacecraft computers. In doing so, it was intended to become the first student-built spacecraft to operate beyond geocentric orbit. It was operated by UNISEC, a collaboration between several Japanese universities.
Contact was lost shortly after launch.Spitzer Space Telescope
The Spitzer Space Telescope (SST), formerly the Space Infrared Telescope Facility (SIRTF), is an infrared space telescope launched in 2003 and still operating as of 2019.
The planned mission period was to be 2.5 years with a pre-launch expectation that the mission could extend to five or slightly more years until the onboard liquid helium supply was exhausted. This occurred on 15 May 2009. Without liquid helium to cool the telescope to the very low temperatures needed to operate, most of the instruments are no longer usable. However, the two shortest-wavelength modules of the IRAC camera are still operable with the same sensitivity as before the cryogen was exhausted, and have continued to be used to the present in the Spitzer Warm Mission. All Spitzer data, from both the primary and warm phases, are archived at the Infrared Science Archive (IRSA).
In keeping with NASA tradition, the telescope was renamed after its successful demonstration of operation, on 18 December 2003. Unlike most telescopes that are named after famous deceased astronomers by a board of scientists, the new name for SIRTF was obtained from a contest open to the general public.
The contest led to the telescope being named in honor of astronomer Lyman Spitzer, who had promoted the concept of space telescopes in the 1940s. Spitzer wrote a 1946 report for RAND Corporation describing the advantages of an extraterrestrial observatory and how it could be realized with available or upcoming technology. He has been cited for his pioneering contributions to rocketry and astronomy, as well as "his vision and leadership in articulating the advantages and benefits to be realized from the Space Telescope Program."The US$720 million Spitzer was launched on 25 August 2003 at 05:35:39 UTC from Cape Canaveral SLC-17B aboard a Delta II 7920H rocket.It follows a heliocentric instead of geocentric orbit, trailing and drifting away from Earth's orbit at approximately 0.1 astronomical units per year (a so-called "earth-trailing" orbit). The primary mirror is 85 centimeters (33 in) in diameter, f/12, made of beryllium and was cooled to 5.5 K (−268 °C; −450 °F). The satellite contains three instruments that allow it to perform astronomical imaging and photometry from 3.6 to 160 micrometers, spectroscopy from 5.2 to 38 micrometers, and spectrophotometry from 5 to 100 micrometers.Venera 2MV-1 No.1
Venera 2MV-1 No.1, also known as Sputnik 19 in the West, was a Soviet spacecraft, which was launched in 1962 as part of the Venera programme, and was intended to become the first spacecraft to land on Venus. Due to a problem with its upper stage it failed to leave low Earth orbit, and reentered the atmosphere a few days later. It was the first of two Venera 2MV-1 spacecraft, both of which failed to leave Earth orbit.Venera 2MV-1 No.1 was launched at 02:18:45 UTC on 25 August 1962, atop a Molniya 8K78 carrier rocket flying from Site 1/5 at the Baikonur Cosmodrome. The first three stages of the rocket operated nominally, injecting the fourth stage and payload into a low Earth orbit. The fourth stage then coasted until one hour and fifty seconds after launch, when it fired its ullage motors in preparation for ignition. One of the ullage motors failed to fire, and when the main engine ignited for a four-minute burn to place the spacecraft into heliocentric orbit, the stage began to tumble out of control. Forty-five seconds later, its engine cut off, leaving the spacecraft stranded in Earth orbit. It reentered the atmosphere on 28 August 1962, three days after it had been launched.The designations Sputnik 23, and later Sputnik 19 was used by the United States Naval Space Command to identify the spacecraft in its Satellite Situation Summary documents, since the Soviet Union did not release the internal designations of its spacecraft at that time, and had not assigned it an official name due to its failure to depart geocentric orbit.Venera 2MV-1 No.2
Venera 2MV-1 No.2, also known as Sputnik 20 in the Western world, was a Soviet spacecraft, which was launched in 1962 as part of the Venera programme, and was intended to become the first spacecraft to land on Venus. Due to a problem with its upper stage it failed to leave low Earth orbit, and reentered the atmosphere a few days later. It was the second of two Venera 2MV-1 spacecraft, both of which failed to leave Earth orbit. The previous mission, Venera 2MV-1 No.1, was launched several days earlier.Venera 2MV-1 No.2 was launched at 02:12:30 UTC on 1 September 1962, atop a Molniya 8K78 carrier rocket flying from Site 1/5 at the Baikonur Cosmodrome. The lower stages of the rocket operated nominally, injecting the fourth stage and payload into a low Earth orbit. Following a coast phase, the upper stage was to have ignited around sixty-one minutes and thirty seconds after launch, in order to place the spacecraft into heliocentric orbit. The ignition command did not reach the engine however, and the fuel valves did not open, so the upper stage failed to ignite leaving the payload in geocentric orbit. It reentered the atmosphere on 6 September 1962, five days after it had been launched.The designations Sputnik 24, and later Sputnik 20 were used by the United States Naval Space Command to identify the spacecraft in its Satellite Situation Summary documents, since the Soviet Union did not release the internal designations of its spacecraft at that time, and had not assigned it an official name due to its failure to depart Earth orbit.Venera 2MV-2 No.1
Venera 2MV-2 No.1, also known as Sputnik 21 in the West, was a Soviet spacecraft, which was launched in 1962 as part of the Venera programme, and was intended to make a flyby of Venus. Due to a problem with the rocket which launched it, it failed to leave low Earth orbit, and reentered the atmosphere a few days later. It was the second Venera 2MV-2 spacecraft, both of which failed to leave Earth orbit.Venera 2MV-2 No.1 was launched at 00:59:13 UTC on 12 September 1962, atop a Molniya 8K78 carrier rocket flying from Site 1/5 at the Baikonur Cosmodrome. The rocket performed nominally until cutoff of the Blok I stage, following injection into a low Earth orbit. Following cutoff, one of the oxidiser valves failed to close, and liquid oxygen was allowed to flow into the combustion chamber of one of the vernier thrusters. The vernier thruster exploded, causing the rocket to tumble out of control. This led to the formation of bubbles in the upper stage oxidiser pump, which caused the upper stage engine to fail less than a second after ignition. It reentered the atmosphere on 14 September 1962, two days after it had been launched.The designations Sputnik 25, and later Sputnik 21 were used by the United States Naval Space Command to identify the spacecraft in its Satellite Situation Summary documents, since the Soviet Union did not release the internal designations of its spacecraft at that time, and had not assigned it an official name due to its failure to depart geocentric orbit.