Ahigh Earth orbit is ageocentric orbit with anapogee farther than that of thegeosynchronous orbit, which is 35,786 km (22,236 mi)away from Earth.[1]In this article, the non-standard abbreviation ofHEO is used for high Earth orbit.[2]
The development of HEO technology has had a significant impact onspace exploration and has paved the way forfuture missions todeep space. The ability to place satellites in HEO has allowed scientists to make groundbreaking discoveries inastronomy andEarth science, while also enablingglobal communication andnavigation systems.[3]
The Moon'sHill sphere is entered at a distance to the Moon of 60,000 km (37,000 mi),[4]lunar orbits until a distance of 690 km (430 mi) are unstable due to Earth's gravitational reach.[5]Near-rectilinear halo orbits around the Moon are within these distances to the Moon, occupyingcislunar space.Earth's hill sphere extends to a distance of 1,471,400 km (914,300 mi), encompassinghalo orbits,orbits around the Sun-Earth Lagrange points, with orbits increasinglybeing heliocentric,co-orbiting with Earth the Sun before orbits go deeper intointerplanetary space.
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| Orbit | Name |
|---|---|
| GEO | Geostationary orbit |
| GSO | Geosynchronous orbit |
| GTO | Geostationary transfer orbit |
| HEO | Highly elliptical orbit |
| NRHO | Near-rectilinear halo orbit |
Satellites in High Earth orbits are primarily used forcommunication,navigation,scientific research, andmilitary applications.[6] One of the main benefits of HEO is that it provides a nearly unobstructed view of the Earth and deep space. This makes it an ideal location for astronomical observations and Earth monitoring. In addition, satellites in HEO can provide a continuous coverage of the Earth's surface, making it very useful for communication and navigation purposes.[7] A variety of satellites, such asTESS,[8] have been placed in HEO.
There are four main reasons that most satellite are placed in lower orbits. First, a HEO can take a month or more per orbit. This is because HEOs are very large orbits and move at only 3000 m/s (11,000 km/h, 7000 mph). Meanwhile, aLEO (low Earth orbit) can take less than 90 minutes.[9] So, for satellites that need to orbit quickly, HEO is not a good fit. Second, HEOs take far more energy to place a satellite into than LEOs. To place a satellite into HEO takes nearly as much energy as to place it into aheliocentric orbit. For example, anexpendedFalcon 9 can carry 22,500 kg (50,000 lbs) to LEO. However, it can only carry around 4500 kg (10,000 lbs) to HEO.[10] This means that it costs 5 times more to place apayload in HEO versus placing it in LEO. Third, HEOs are extremely far from Earth. This means that there is a constantcommunication delay whensending signals to and from the satellite. This is actually because the signals can only travel at thespeed of light. This means that it can take around 0.1 to 4.5 seconds in delay time each way. This makes ituseless for internet, and hard to use for other things as well. The fourth reason isradiation. HEO is outside of themagnetic field of Earth. This means that there is far more radiation in HEO. As a result,spacecraft in HEO require specialized equipment andshielding to protect them from radiation. As a result, only satellites that require the unique characteristics of HEO use this orbit.
A special case of a high Earth orbit is thehighly elliptical orbit where altitude at perigee may reach as low as 2,000 km (1,200 mi).
| Name | NSSDC id. | Launch date | Perigee | Apogee | Period | Inclination |
|---|---|---|---|---|---|---|
| Vela 1A[11][12] | 1963-039A | 1963-10-17 | 101,925 km | 116,528 km | 108 hr 39 min | 37.8° |
| IBEX | 2008-051A | 2008-10-19 | 61,941 km | 290,906 km | 216 hr 3 min | 16.9° |
| TESS[8][13] | 2018-038A | 2018-04-18 | 108,000 km | 375,000 km | 328 hr 48 min | 37.00° |
| Chdryn.-3 prop. module | 2023-098B | 2023-07-14 | 115,000 km | 154,000 km | ~312 hr | 27° |
The moon's Hill sphere has a radius of 60,000 kilometres, about one-sixth of the distance between it and Earth.For mean distance and mass data for the bodies (for verification of the foregoing citation), seeWilliams, David R. (20 December 2021)."Moon Fact Sheet".NASA.gov. Greenbelt, MD: NASA Goddard Space Flight Center. Retrieved23 July 2023.
