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Active Sensor
A type of sensor that is emitting energy in order to obtain information on a celestial body of interest, e.g., geological structure of the Earth and the state of and movement of Earth’s oceans, or another space system, e.g., radar ranging during rendezvous and docking.

Amplitude Modulation (AM)
A technique used in electronic communication for transmitting information via a radio carrier frequency that varies (modulates) the transmitted signal strength (amplitude) in relation to the information being sent.

A signal that is continuous, constant and carries the original data on its signal.

A metallic structure or conductor that captures and/or transmits radio electromagnetic waves.

Antenna Array
A group of identical, smaller antennas which combine their radio signals to produce a signal similar to that of a large antenna.

A point in the Earth satellite’s orbit where the satellite is furthest from Earth – opposite of perigee.

Organizational structure of a system or component, their relationships, and the principles and guidelines governing their design and evolution over time.

The position or orientation of an aircraft, spacecraft either in motion or in rest determined by the relationship between its axes and a reference line.

Attitude Determination
The process of determining the rotational state (time tagged attitude and attitude rate) in relation to its direction of motion. Attitude determination may entail estimation of an updated attitude state by incorporation of sensor data or simply a state propagation with environment models.

Horizontal direction or bearing – expressed as the angular distances from a reference point – measured from 0 degrees to 360 degrees.


A term used to designate the frequencies at which the data is processed.

Bent Pipe
Forwarding of a signal without any information processing.

Information having two states (0 or 1) on a digital signal.

Binary digit.

A contiguous sequence of 8 bits.


Directive to a processor or system to perform a particular action or function. Parameters can be specified at the time of command initiation; it can be an instruction for a spacecraft.

Conventional or Legacy Radio
Non-programmable radio designed for one fixed configuration for producing a single waveform at a specified frequency. The radio may have limited options for tuning, data rate, etc. or may even carry multiple types of data, but is incapable of adapting to new waveforms.

Customer Service Management Element (CSME)
The Phase 2 SCaN Network element operated by the Mission Commitment Office.

Cycle (Spectrum)
The entire pattern of a radio wave, before it repeats itself


Deep Space
Space at distances from the Earth equal to or greater than 2 million kilometers

A signal that is not constant, but has the same wave height (amplitude) each time. The pulse it creates carries binary code (0s and 1s)

Mating of two independently operating spacecraft or other systems in space using independent control of the two vehicles’ flight paths and attitudes during contact and capture. Docking begins at the time of initial contact of the vehicles’ docking mechanisms and concludes when full rigidization of the interface is achieved. Final mating is generally accomplished by the docking mechanism.

The change in frequency of a signal due to the movement of sender or receiver.

Link from space asset to ground assets.


Physical entities that have functional capabilities allocated to them necessary to satisfy system-level mission objectives. Elements can perform all allocated system functions within a mission phase, or through mated operations with other elements or systems.

Spans the entire SCaN network architecture, from the service interface at the user mission platform to the service interface at the user mission ground system.

Extra Vehicular Activity (EVA)
Operations performed by suited crew outside the pressurized environment of a flight vehicle or habitat (during space flight or on a destination surface).


Forward Link or Uplink
The path from the ground to a spacecraft in space.

Frequency (Spectrum)
The number of cycles, of times that a radio wave repeats in a second, measured in hertz (Hz).


Coordinate system with the Earth at the center.

The study of the Earth’s shape, size and the exact positions of points on its surface with descriptions of variation of its gravitational field- specifically used in surveying and navigation.

Geosynchronous Orbit (GEO)
An orbit in which the satellite is always in the same position in respect to the rotating Earth. Satellites in this orbit sit above 35,000 kilometers.

Ground Station
A ground antenna and the supporting local hardware and software.

Ground Station Site (GSS)
A geographic site containing one or more ground stations and associated data processing and control equipment (e.g., White Sands Ground Terminal, Svalbard, Goldstone Deep Space Communications Complex).


Hertz (Hz)
Frequency of one cycle per second

Highly Elliptical Orbit
A high Earth orbit that is above geosynchronous – satellites in this orbit change their inclination due to gravitational forces of neighboring celestial bodies. Their perigee average is around 1000 kilometer and its apogee average is 36,000 kilometers above the Earth’s surface.


Integrated Network Architecture (INA)
The SCaN Network architecture in Phase 2 and beyond. The architecture includes the service management, network control, and service execution.

Integrated Network Planning System (INPS)
The system which facilitates generation and storage of service planning documentation (Service Level Agreements, Service Agreements and profiles); provides mission planning analysis capabilities.

(1) The ability of a system to work with or use the parts or equipment of another system.
(2) The capability of different radio systems or radio networks to communicate and exchange information with each other. Dissimilar systems or network may achieve interoperability by changing their operating parameters to a common compatible format or operating through a bridge that translates between incompatible formats. An alternate definition is to determine and adapt all radio parameters required for broadcast communication compatibility across all target networks.


Lagrange Points
Points in vicinity of two celestial bodies where each other’s gravities balance. There are five points labeled L1 through L5.

The connection between a sender and receiver.

Low Earth Orbit (LEO)
A geocentric orbit with an altitude much less than the Earth’s radius. Satellites in this orbit are between 80 and 2000 kilometers above the Earth’s surface.


Medium Earth Orbit (MEO)
A satellite in this orbit sits between 2,000 and 36,000 kilometers above the Earth’s surface – most commonly around 20,000 kilometers.

A flight to a destination in space, intended to accomplish specific scientific and technical objectives.

The variation of a property of an electromagnetic wave or signal, such as its amplitude, frequency, or phase.

Multiple Access
A method by which two or more users can operate simultaneous communication links while sharing the same frequency spectrum. 


The process of determining the translational state (time tagged position and velocity). Navigation may entail estimation of an updated state by incorporation of sensor data or simply a state propagation/prediction with environment models.

Network Operations Node (NON)
The system that performs network management functions (network scheduling, high-level network control, accounting), in part or in whole, for one or more ground station sites.

Unwanted or undesirable signals.


Performing functions/tasks while a satellite is orbiting in space.

Operations and Maintenance (O&M)
A phrase used to describe all the functions of a facility, from day-to-day tasks to long term planning and upkeep of the facility in order to perform at its peak.

A device that generates a wave with a selected frequency.


Passive Sensor
A type of radio sensor that emits no energy; measures natural emissions from the Earth’s constituents and its atmosphere at specific frequencies in order to provide a description of the earth’s environment.

Equipment required to meet defined mission objectives as well as equipment and samples that must be returned to Earth for analysis.

Pull Technology
A technology that is mission requirement driven, a technology needed to fulfill specific mission objective.

Push Technology
A technology that is not directed to or required by a specific space mission, but instead would provide a generic capability which could enable or enhance future space missions.

A point in the satellite’s orbit where it is closest to the Earth – opposite of apogee.


Device that transmits a radio signal and receives the reflectors from selected object to determine the characteristics of that object.

Radio Frequency
A band of frequencies that can travel long distance, are used to carry information.

Radio Wave (Spectrum)
The basic building block of radio communications – a series of repeating peaks and valleys.

Any instrument that quantitatively measures the electromagnetic radiation in some interval of the electromagnetic spectrum.

Measurements using a radio signal.

A technique to measure distance between a signal source and selected spacecraft.

A devise that captures and processes a desired signal.

​Reconfigurable Radio
A reconfigurable radio is a radio whose functionality can be changed either through manual reconfiguration of radio modules or can be changed under software control. Software reconfiguration control of such radios may involve any element of the radio-communication network. Software defined radios are a subset of reconfigurable radios.

Information that is forwarded without modification.

Return Link
The communication path for data from spacecraft to ground.


A body that orbits around another body in space, either natural or man-made. (e.g., Tracking and Data Relay Satellites (TDRS))

Service Portal
The primary access point for user missions to interface with the SCaN Network for service planning, service request scheduling, network monitoring and control, and service accountability reporting.

SCaN Network
The collection of systems utilized by SCaN that provide communication and navigation services to the user missions.

Software Defined Radio (SDR)
A radio in which some or all of the physical layer functions are implemented in software.

Spectrum Allocation
Distribution of frequencies to radio services.

Spectrum Management
Oversight of radio frequency usage.


Data transmitted by radio or other means from remote sources to receiving stations for recording and analysis.

Locking on and following a selected signal.


Very Long Baseline Interferometry (VLBI)
A technique of observing the same known radio signal from one or more location on the Earth, separated by a great distance at the same time; then observing another desired radio signal to compute the angular position of the source of the desired signal.


Set of transformations applied to information (e.g., voice or data) that is transmitted over the air and the corresponding set of transformations to convert received signals back to their information contents. Traditionally a waveform was simply an electromagnetic signal whose amplitude varies with time.

Wavelength (Spectrum)
The distance a radio wave takes to complete a cycle.