Mission & Spacecraft Library

Glossary of Terms

Below are definitions of some of the various terms and acronyms used in MSL.

Launch Sites

Eastern Space and Missile Center. Previously called Eastern Test Range (ETR), this US launch site is located at Cape Canaveral on the east coast of Florida at 28.5 deg N, 80.6 deg W. This site is primarily used for low inclination orbits (including geostationary) and for all manned missions.

Western Space and Missile Center. Previously called Western Test Range (WTR), this US launch facility is located within Vandenberg Air Force Base (VAFB) on the west coast of California. The site is located at 34.7 deg N, 120.6 deg W, and is primarily used for polar orbiting missions.

The US's Wallops Island is located on the east coast of Virginia, and is an older launch site only used for small launch vehicles and suborbital launches. The site is located at 36.9 deg N, 75.5 deg W.

Kaputsin Yar
The Russian launch complex, Kaputsin Yar, is located at 48.4 deg N, 45.8 deg E. Although used fairly often during the 60's, the number of launches performed by this site fell dramatically during the 70's and 80's, during which the site averaged about 1 orbital launch per year. The most recent launch occurred in 1987.

The Russian launch complex, Plesetsk, is located at 62.8 deg N, 40.4 deg E, and has launched the most satellites since the beginning of the Space Age.

The Russian launch complex, Tyuratam (a.k.a. Baikonur Cosmodrome), is located in Kazakhstan at 45.6 deg N, 63.3 deg E. Although typically not quite as active as Plesetsk, this site is used for all Russian planetary and manned missions.

Kourou, in French Guiana (South America), is owned by ESA and operated by Arianespace. It is also called the Guiana Space Center (CSG) and is ideal for launching geosynchronous spacecraft due to its low latitude. The site also supports polar orbiting missions. Kourou is located at 5.2 deg N, 52.8 deg W.

Shuang Cheng Tzu
The Chinese launch center Shuang Cheng Tzu, also called JSLC (Jiquan Satellite Launch Center), is located at approximately 40.6 deg N, 99.9 deg E in the Gobi desert. The facility is used for LEO launches into inclinations between 57 and 70 degrees.

The Chinese launch center Taiyuan (TSLC), also known as Wuzhai, supports missions with highly inclined (polar) orbits. The site is located at 37.5 deg N, 112.6 deg E in the Shanxi province.

The Chinese launch center Xichang (XSLC) is used to launch GEO spacecraft. It is located approximately 28.3 deg N, 102.0 deg E in the Sichuan province.

Kagoshima Space Center
The Japanese launch center, Kagoshima, is located at 31.3 deg N, 131 deg E on the east coast of the Ohsumi peninsula. This launch site is dedicated to missions for Japan's ISAS space agency. Launches from this site are restricted to January/February and August/September due to range safety procedures established as a result of pressure from Japanese fisherman.

Tanegashima Space Center
The Japanese launch center, Tanegashima, is located at 30.2 deg N, 130.9 deg E on the island of Tanegashima. This is the largest launch site in Japan, and is used for missions for Japan's NASDA space agency. Launches from this site are restricted to January/February and August/September due to range safety procedures established as a result of pressure from Japanese fisherman.

Sriharikota Range
The Sriharikota Range Center (SHAR) is located on Sriharikota Island in India at 13.9 deg N, 80.3 deg E. Severe range safety restrictions on launch azimuth make it inefficient to launch into polar orbits.

San Marco
Italy's San Marco launch site consists of two offshore platforms located in the Indian Ocean just off of the coast of Kenya (2.9 deg. S, 40.3 deg. E). The platforms' near equatorial location makes it ideal for low inclination launches.

The classified Israeli launch complex, Yavne, is located at 31.5 deg N, 34.5 deg E in or near Palmachim AFB. Launches are restricted to retrograde orbits due to range safety restrictions.

Located at a military base in the Sahara desert, Hammaguir was used by France to orbit 4 satellites during the mid '60s. However, the establishment of Algerian independence in 1967 forced France to abandon the facility.

The Australian launch complex, Woomera, is located at 31.1 deg S, 136.8 deg. E. Although used twice in the late 60's-early 70's to launch orbital payloads (with 2 other launch failures), the facility was shut down due to funding cuts. No more orbital missions are currently planned from this site, although it is still occasionally used for sub-orbital launches.

Orbit Categories

Low Earth Orbit. Although definitions of LEO vary from source to source, MSL defines LEO as orbits having apogees and perigees below 3000 km. The large majority of all satellites are in Low Earth Orbit.

Medium Earth Orbit. Although definitions of MEO vary from source to source, MSL defines MEO as orbits having apogees greater than 3000 km but less that 30000 km. These are sometimes used by navigation (e.g., GPS) and communications (e.g., Odyssey) missions.

Geosynchronous orbit. A satellite in circular orbit around the Earth's equator at 23000 miles altitude (36000 km) will remain stationary over the same location on Earth (i.e., the spacecraft goes around once in its orbit for every revolution of the Earth). This feature is very useful for communications satellites (allowing one satellite to provide continual coverage to a given area of the Earth's surface). As a result, the majority of satellites in geostationary orbit are commsats. Some satellites have orbits slightly higher or lower than GEO, but for simplicity sake, all satellites with apogees and perigees between 30000 and 40000 km are termed GEO.

Highly Elliptical Orbit. This class covers orbits which have large eccentricities (are highly elliptical). Molnyia orbits are a common example of this type of orbit. Although definitions of HEO vary from source to source, MSL defines HEO as orbits having perigees below 3000 km with apogees above 30000 km.

Very High Orbit. This type of orbit includes all orbits which have perigees at or above GEO and apogees above GEO, yet remain in orbit around the Earth (or Earth-Moon system). Orbits in this class are often highly elliptical, with apogees several hundred thousand kilometers in altitude.

The Solar orbit class includes all missions where the spacecraft has achieved Earth escape velocity and goes in orbit about the Sun. This class includes missions designed to observe the Sun, as well as planetary flyby missions which entered solar orbit following rendezvous with their targets.

The Lunar orbit class includes all missions which went into orbit around the Moon or impacted the lunar surface.

The Venus orbit class includes all missions which went into orbit around Venus or impacted the planet's surface.

The Mars orbit class includes all missions which went into orbit around Mars or impacted the planet's surface.

The Jupiter orbit class includes all missions which went into orbit around Jupiter or entered the Jovian atmosphere.

Solar System Escape Trajectory
The Solar System Escape Trajectory class includes all missions have achieved Solar escape velocity and will thus (eventually) depart the Solar system.

Mission Categories

Amateur Radio
Amateur radio satellites are used to relay messages between amateur ham radio operators. These satellites are typically small and simple in design, and are often built by universities. Due to their small size and typically low budgets, these satellites are usually launched as secondary payloads along with much larger primary payloads.

Astronomy satellites are dedicated to the study of stellar objects, ranging from extremely distant galaxies, nebulae, etc. our own nearby Sun.

Domestic Communications
Domestic communication missions relay domestic transmissions, such as telephone, radio, and TV signals, from one point on the Earth's surface to another.

Direct Broadcast Satellites (DBS) are a subset of the domestic communications class. These missions broadcast television or radio signals directly to subscriber's ground-based satellite dishes.

Earth Resources
This mission class refers to missions which collect information about the Earth's atmosphere, land and oceans for scientific research and resource management.

Geodetic spacecraft are used to measure the location of points on the Earth's surface with great accuracy. These measurements are used to determine the exact size and shape of the Earth, act as references for mapping, and track movements of the Earth's crust.

Lunar missions are designed to gather information about the Earth's Moon or the purpose of scientific research. This class includes orbiters, flybys, hard landers, and soft landers (including manned missions).

Navigation systems are designed to assist in air, land and oceanic navigation. These include such missions as Transit, GPS and Glonass.

Planetary missions leave the Earth's gravitational field to perform up close observations of other planets, asteroiods, and comets. These types of missions can range from quick flybys to long term observations from orbits around the body. Planetary missions have also dropped probes into planets' atmospheres, soft and hard landed (i.e., crashed) on planets' surfaces, and flown in formation with comets and asteroids.

This general class of missions includes the many space science disciplines not falling into any of the other mission categories. A few examples include zero-g materials processing tests, biological studies, and space physics experiments.

Space Stations
Space stations are large orbiting structures designed to support manned operations for extended periods of time (months to years). Space stations have performed both military and civilian objectives.

This general class of missions includes all missions designed as technical tests of satellite or ground based systems. Examples include tests of new satellite components, investigations of launch vehicle performance, calibration of ground based systems (such as radar), and demonstration of new sensor technologies.

Transport missions include all spacecraft that are used to ferry people or materials from the Earth to orbit without performing significant research. Missions in this class include space station resupply vehicles and Shuttle missions whose primary purpose is to carry satellites into orbit for deployment.

Weather satellites monitor the Earth's atmospheric conditions and provide data to help predict / understand the Earth's weather patterns.

ASAT (Anti-Satellite)
ASAT missions are related to the development of vehicles used to destroy orbiting satellites. This category includes the ASAT interceptors themselves, as well as vehicles placed into orbit as test targets.

ELINT (Elect. Intelligence)
ELINT satellites are military spacecraft used to monitor (spy on) the military and domestic electronic communications of other nations. These types of satellites are also known as ferrets.

EW (Early Warning)
Military spacecraft used to detect the launch of missiles and rockets from the Earth's surface are called early warning satellites. Information from these satellites is used to quickly detect the launch of offensive missiles, as well as track the long-term patterns of foreign countries' space programs.

Military (Unknown/Unique)
This category includes all military satellites whose purpose is either unknown (such as still-secret surveillance, ELINT, and EW spacecraft) or unique in nature.

Military Communications
Military communications satellites are dedicated to relaying signals between elements of a nation's armed forces.

Nuclear Detection
Nuclear detection satellites are used to detect nuclear explosions on the Earth's surface. Although primarily used to observe nuclear treaty compliance, nuclear detection spacecraft have also been used to detect / observe galictic events, such as supernovae.

Surveillance spacecraft are military vehicles which provide imagery reconaissance data. These missions include visible, infrared, and radar imaging. Information about these satellites (as well as most other military missions) is very often secret. As a result, the information on these vehicles is often sketchy, and is often derived from indirect observations.

Space Agencies and Organizations

American Telephone and Telegraph Corporation.
Communication Satellite Corporation
Defense Advanced Research Projects Agency. (U.S. government agency.)
European Launcher Development Organization (Precursor to ESA)

Earth Observation Satellite Company
European Space Agency
European Space Research Organization (Precursor to ESA)
Environmental Sciences Services Administration (U.S. government agency. Precursor to NOAA)
North Atlantic Treaty Organization
National Oceanic and Atmospheric Organization (U.S. government agency)

National Aeronautics and Space Administration

Spacecraft Systems (Hardware and Stuff)

Attitude Control System. This is the spacecraft subsystem which is responsible for pointing the spacecraft in the desired direction and knowing where the spacecraft is pointed at all times.

Code Division Multiple Access. A multiple access scheme for digital communications which uses spread spectrum modulation and orthogonal codes to avoid interference and permit many users to occupy all of the transponder bandwidth all of the time.

Common Pressure Vessel. This refers to a particular packaging technique in batteries where more than one battery cell is housed within a single pressure vessel. This increases the specific energy of the battery assembly.

Radioisotope Thermoelectric Generator. These power sources are ideal for planetary missions because of their long life and steady power in sunlight or darkness. RTGs use banks of thermoelectric elements (typically Si-Ge unicouples) to convert the heat generated by radioisotope decay (typically plutonium 238) into electric power. They are heavy and produce radiation which can interfere with electronics and science instruments. They are typically mounted at some distance from the spacecraft to reduce the effects of both nuclear and thermal radiation. RTGs are also very expensive.

Nickel Cadmium is the most popular battery type used in spacecraft. These batteries are rechargable and can withstand thousands of charge/discharge cycles. The electrolyte is a diluted potassium hydroxide solution.

Gallium Arsenide. GaAs solar cells have an efficiency in the range of 17 - 19 percent. In addition to having a higher efficiency than silicon cells, they are more resistant to radiation effects, however, they have a higher density and higher cost compared to silicon cells.

Graphite Fiber Reinforced Plastic. GFRP is a generic term for advanced graphite epoxy composite materials. While more expensive than aluminum construction, composites offer high stiffness-to-weight ratios and low thermal expansion / contraction properties. These are constructed by bonding together layers of composite fabric using various fiber orientations. Other fibers in these composites include boron, Kevlar, and glass.

Quadrature Phase Shift Keying. QPSK is the most popular modulation technique for digital satellite communications. Basically, a digital data stream is taken two bits at a time to generate one of four possible phase states of the transmitted carrier. In geek-speak : QPSK is the superposition of two biphase PSK signals in time quadrature.

High Gain Antenna. These are frequently parabolic dishes and serve to provide high amplification of RF signals (either transmitting or receiving). These antennas much be pointing accurately toe useful.

Low Gain Antenna. These are small antennas which provide low amplification of RF signals and have very wide antenna patterns - not requiring precise antenna pointing.

Multi-Layer Insulation (MLI) is commonly used to provide thermal insulation. MLI usually consists of 25 µ m thick polyester or polyamide layers or films that are metallized with aluminum or gold on one or both sides by vacuum deposition to achieve low emittance. Glass-fiber paper, plastic and silk netting, thin sheets of foam, and embossed plastic film might be used to separate these sheets and minimize the conductance between layers. Some MLI has no discrete spacer material and instead the material is crinkled so the conductance between layers is minimized.

Hydrazine is the name for the most commonly used monopropellant fuel. The composition of monopropellant hydrazine is N2H4. The hydrazine is ignited by passing it over a heated catalyst to decompose the fuel. This produces exhaust gasses of NH3, N2, and H2. The catalyst consists of alumina pellets impregnated with iridium, and the most common brand name is Shell 405. The specific impulse of hydrazine systems is typically in the range of 200 to 220 seconds.

Reaction Control System. This is a type of attitude control system which uses reaction jets (small thrusters) to control the orientation of the spacecraft. These systems usually use a cold gas such as nitrogen, however, some have used hydrazine. Typical pointing accuracies achieved are 0.5 to 0.1 degrees.


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