Highly elliptical orbit in the context of Coma (comet)

The coma is the nebulous envelope around the nucleus of a comet, formed when the comet passes near the Sun in its highly elliptical orbit. As the comet warms, parts of it sublimate; this gives a comet a diffuse appearance when viewed through telescopes and distinguishes it from stars. The word coma comes from the Greek κόμη (kómē), which means "hair" and is the origin of the word comet itself.

The coma is generally made of ice and comet dust. Water composes up to 90% of the volatiles that outflow from the nucleus when the comet is within 3–4 au (280–370 million mi; 450–600 million km) from the Sun. The H₂O parent molecule is destroyed primarily through photodissociation and to a much smaller extent photoionization. The solar wind plays a minor role in the destruction of water compared to photochemistry. Larger dust particles are left along the comet's orbital path while smaller particles are pushed away from the Sun into the comet's tail by light pressure.

The Boeing X-37, also known as the Orbital Test Vehicle (OTV), is a reusable robotic spacecraft. It is boosted into space by a launch vehicle, re-enters Earth's atmosphere, and lands as a spaceplane. The X-37 is operated by the Department of the Air Force Rapid Capabilities Office, in collaboration with the United States Space Force, for orbital spaceflight missions intended to demonstrate reusable space technologies. It is a 120-percent-scaled derivative of the earlier Boeing X-40. The X-37 began as a NASA project in 1999, before being transferred to the United States Department of Defense in 2004. Until 2019, the program was managed by Air Force Space Command.

An X-37 first flew during a drop test in 2006; its first orbital mission was launched in April 2010 on an Atlas V rocket, and returned to Earth in December 2010. Subsequent flights gradually extended the mission duration, reaching 780 days in orbit for the fifth mission, the first to launch on a Falcon 9 rocket. The sixth mission launched on an Atlas V on 17 May 2020 and concluded on 12 November 2022, reaching 908 days in orbit. The seventh mission launched on 28 December 2023 on a Falcon Heavy rocket, entering a highly elliptical high Earth orbit, landing in March 2025 after 434 days in orbit.

The Proton-K, also designated Proton 8K82K after its GRAU index or SL-12 after its model number, was a Russian, previously Soviet, carrier rocket derived from the earlier Proton. It was built by Khrunichev, and launched from sites 81/23, 81/24, 200/39 and 200/40 at the Baikonur Cosmodrome in Kazakhstan.

The maiden flight on 10 March 1967 carried a Soyuz 7K-L1 as part of the Zond program. During the so-called Moon Race these Proton/Soyuz/Zond flights consisted of several uncrewed test flights of Soyuz spacecraft to highly elliptical or circumlunar orbits with the unrealized aim of landing Soviet cosmonauts on the Moon.

A Molniya orbit (Russian: Молния, IPA: [ˈmolnʲɪjə] , "Lightning") is a type of satellite orbit designed to provide communications and remote sensing coverage over high latitudes. It is a highly elliptical orbit with an inclination of 63.4 degrees, an argument of perigee of 270 degrees, and an orbital period of approximately half a sidereal day. The name comes from the Molniya satellites, a series of Soviet/Russian civilian and military communications satellites which have used this type of orbit since the mid-1960s. A variation on the Molniya orbit is the so-called Three Apogee (TAP) orbit, whose period is a third of a sidereal day.

The Molniya orbit has a long dwell time over the hemisphere of interest, while moving very quickly over the other. In practice, this places it over either Russia or Canada for the majority of its orbit, providing a high angle of view to communications and monitoring satellites covering these high-latitude areas. Geostationary orbits, which are necessarily inclined over the equator, can only view these regions from a low angle, hampering performance. In practice, a satellite in a Molniya orbit serves the same purpose for high latitudes as a geostationary satellite does for equatorial regions, except that multiple satellites are required for continuous coverage.

Transiting Exoplanet Survey Satellite (TESS) is a space telescope for NASA's Explorer program, designed to search for exoplanets using the transit method in an area 400 times larger than that covered by the Kepler mission. It was launched on 18 April 2018, atop a Falcon 9 launch vehicle and was placed into a highly elliptical 13.70-day orbit around the Earth. The first light image from TESS was taken on 7 August 2018, and released publicly on 17 September 2018.

In the two-year primary mission, TESS was expected to detect about 1,250 transiting exoplanets orbiting the targeted stars, and an additional 13,000 orbiting stars not targeted but observed. After the end of the primary mission around 4 July 2020, scientists continued to search its data for more planets, while the extended missions acquires additional data. As of 1 July 2025, TESS had identified 7,655 candidate exoplanets, of which 638 had been confirmed.

A Tundra orbit (Russian: орбита «Тундра») is a highly elliptical geosynchronous orbit with a high inclination (approximately 63.4°), an orbital period of one sidereal day, and a typical eccentricity between 0.2 and 0.3. A satellite placed in this orbit spends most of its time over a chosen area of the Earth, a phenomenon known as apogee dwell, which makes them particularly well suited for communications satellites serving high-latitude regions.

The Tundra orbit, like the Molniya orbit, was developed by Soviet scientists. The Molniya orbit was specifically designed in the 1960s to provide better communication coverage for high-latitude regions, which geostationary satellites struggled to cover effectively. The Tundra orbit, while similar in its high inclination and elliptical shape, was developed later to offer continuous coverage over specific areas by having satellites spend most of their time over a chosen region. Both orbits were innovative solutions to the unique challenges posed by the Soviet Union's geographical location and the need for reliable communication and surveillance capabilities.