Astrionics is the science and technology of the development and application of electronic systems, sub-systems, and components used in spacecraft. The electronic systems on board a spacecraft include attitude determination and control, communications, command and telemetry, and computer systems. Sensors refers to the electronic components on board a spacecraft.

For engineers one of the most important considerations that must be made in the design process is the environment in which the spacecraft systems and components must operate and endure. The challenges of designing systems and components for the space environment include more than the fact that space is a vacuum.

Attitude determination and control


One of the most vital roles electronics and sensors play in a mission and performance of a spacecraft is to determine and control its attitude, or how it is orientated in space. The orientation of a spacecraft varies depending on the mission. The spacecraft may need to be stationary and always pointed at Earth, which is the case for a weather or communications satellite. However, there may also be the need to fix the spacecraft about an axis and then have it spin. The attitude determination and control system, ACS, ensures the spacecraft is behaving correctly. Below are several ways in which ACS can obtain the necessary measurements to determine this.


This device measures the strength of the Earth's magnetic field in one direction. For measurements on all three axes, the device would consist of three orthogonal magnetometers. Given the spacecraft's position, the magnetic field measurements can be compared to a known magnetic field which is given by the International Geomagnetic Reference Field model. Measurements made by magnetometers are affected by noise consisting of alignment error, scale factor errors, and spacecraft electrical activity. For near Earth orbits, the error in the modeled field direction may vary from 0.5 degrees near the Equator to 3 degrees near the magnetic poles, where erratic auroral currents play a large role.[1]:258 The limitation of such a device is that in orbits far from Earth, the magnetic field is too weak and is actually dominated by the interplanetary field which is complicated and unpredictable.

Sun sensors

This device works on the light entering a thin slit on top of a rectangular chamber that casts an image of a thin line on the bottom of the chamber, which is lined with a network of light-sensitive cells. These cells measure the distance of the image from a centerline and using the height of the chamber can determine the angle of refraction. The cells operate based on the photoelectric effect. Incoming photons excite electrons and therefore causing a voltage across the cell, which are in turn converted into a digital signal. By placing two sensors perpendicular to each other the complete direction of the sun with respect to the sensor axes can be measured.

Digital solar aspect detectors

Also known as DSADs, these devices are purely digital Sun sensors. They determine the angles of the Sun by determining which of the light-sensitive cells in the sensor is the most strongly illuminated. By knowing the intensity of light striking neighboring pixels, the direction of the centroid of the sun can be calculated to within a few arcseconds.[1]:261

Earth horizon sensor


Static Earth horizon sensors contain a number of sensors and sense infrared radiation from the Earth’s surface with a field of view slightly larger than the Earth. The accuracy of determining the geocenter is 0.1 degrees in near-Earth orbit to 0.01 degrees at GEO. Their use is generally restricted to spacecraft with a circular orbit.[1]:262


Scanning Earth horizon sensors use a spinning mirror or prism and focus a narrow beam of light onto a sensing element usually called a bolometer. The spinning causes the device to sweep out the area of a cone and electronics inside the sensor detect when the infrared signal from Earth is first received and then lost. The time between is used to determine Earth’s width. From this the roll angle can be determined. A factor that plays into the accuracy of such sensors is the fact the Earth is not perfectly circular. Another is that the sensor does not detect land or ocean, but infrared in the atmosphere which can reach certain intensities due to the season and latitude.


This sensor is simple in that using one signal many characteristics can be determined. A signal carries satellite identification, position, the duration of the propagated signal and clock information.[2] Using a constellation of 36 GPS satellites, of which only four are needed, navigation, positioning, precise time, orbit, and attitude can be determined. One advantage of GPS is all orbits from Low Earth orbit to Geosynchronous orbit can use GPS for ACS.

Command and telemetry


Another system which is vital to a spacecraft is the command and telemetry system, so much in fact, that it is the first system to be redundant. The communication from the ground to the spacecraft is the responsibility of the command system. The telemetry system handles communications from the spacecraft to the ground. Signals from ground stations are sent to command the spacecraft what to do, while telemetry reports back on the status of those commands including spacecraft vitals and mission specific data.

Command systems

The purpose of a command system is to give the spacecraft a set of instructions to perform. Commands for a spacecraft are executed based on priority. Some commands require immediate execution; other may specify particular delay times that must elapse prior to their execution, an absolute time at which the command must be executed, or an event or combination of events that must occur before the command is executed.[1]:600 Spacecraft perform a range of functions based on the command they receive. These include: power to be applied to or removed from a spacecraft subsystem or experiment, alter operating modes of the subsystem, and control various functions of the spacecraft guidance and ACS. Commands also control booms, antennas, solar cell arrays, and protective covers. A command system may also be used to upload entire programs into the RAM of programmable, micro-processor based, onboard subsystems.[1]:601

The radio-frequency signal that is transmitted from the ground is received by the command receiver and is amplified and demodulated. Amplification is necessary because the signal is very weak after traveling the long distance. Next in the command system is the command decoder. This device examines the subcarrier signal and detects the command message that it is carrying. The output for the decoder is normally non-return-to-zero data. The command decoder also provides clock information to the command logic and this tells the command logic when a bit is valid on the serial data line. The command bit stream that is sent to the command processor has a unique feature for spacecraft. Among the different types of bits sent, the first are spacecraft address bits. These carry a specific identification code for a particular spacecraft and prevent the intended command from being performed by another spacecraft. This is necessary because there are many satellites using the same frequency and modulation type.[1]:606

The microprocessor receives inputs from the command decoder, operates on these inputs in accordance with a program that is stored in ROM or RAM, and then outputs the results to the interface circuitry. Because there is such a wide variety of command types and messages, most command systems are implemented using programmable micro-processors. The type of interface circuitry needed is based on the command sent by the processor. These commands include relay, pulse, level, and data commands. Relay commands activate the coils of electromagnetic relays in the central power switching unit. Pulse commands are short pulses of voltage or current that is sent by the command logic to the appropriate subsystem. A level command is exactly like a logic pulse command except that a logic level is delivered instead of a logic pulse. Data commands transfer data words to the destination subsystem.[1]:612-615

Telemetry systems

Commands to a spacecraft would be useless if ground control did not know what the spacecraft was doing. Telemetry includes information such as:

  • Status data concerning spacecraft resources, health, attitude and mode of operation
  • Scientific data gathered by onboard sensors (telescopes, spectrometers, magnetometers, accelerometers, electrometers, thermometers, etc.)
  • Specific spacecraft orbit and timing data that may be used for guidance and navigation by ground, sea, or air vehicles
  • Images captured by onboard cameras (visible or infrared)
  • Locations of other objects, either on the Earth or in space, that are being tracked by the spacecraft
  • Telemetry data that has been relayed from the ground or from another spacecraft in a satellite constellation[1]:617

The telemetry system is responsible for acquisition from the sensors, conditioners, selectors, and converters, for processing, including compression, format, and storage, and finally for transmission, which includes encoding, modulating, transmitting and the antenna.

There are several unique features of telemetry system design for spacecraft. One of these is the approach to the fact that for any given satellite in LEO, because it is traveling so quickly, it may only be in contact with a particular station for ten to twenty minutes. This would require hundreds of ground stations to stay in constant communication, which is not at all practical. One solution to this is onboard data storage. Data storage can accumulate data slowly throughout the orbit and dump it quickly when over a ground station. In deep space missions, the recorder is often used the opposite way, to capture high-rate data and play it back slowly over data-rate-limited links.[1]:567 Another solution is data relay satellites. NASA has satellites in GEO called TDRS, Tracking and Data Relay Satellites, which relay commands and telemetry from LEO satellites. Prior to TDRS, astronauts could communicate with the Earth for only about 15% of the orbit, using 14 NASA ground stations around the world. With TDRS, coverage of low-altitude satellites is global, from a single ground station at White Sands, New Mexico.[1]:569

Another unique feature of telemetry systems is autonomy. Spacecraft require the ability to monitor their internal functions and act on information without ground control interaction. The need for autonomy originates from problems such as insufficient ground coverage, communication geometry, being too near the Earth-Sun line (where solar noise interferes with radio frequencies), or simply for security purposes. Autonomy is important so that the telemetry system already has the capability to monitor the spacecraft functions and the command systems have the ability to give the necessary commands to reconfigure based on the needs of the action to be taken. There are three steps to this process:

1. The telemetry system must be able to recognize when one of the functions it's monitoring deviates beyond the normal ranges.

2. The command system must know how to interpret abnormal functions, so that it can generate a proper command response.

3. The command and telemetry systems must be capable of communicating with each other.[1]:623


Sensors can be classified into two categories: health sensors and payload sensors. Health sensors monitor the spacecraft or payload functionality and can include temperature sensors, strain gauges, gyros and accelerometers. Payload sensors may include radar imaging systems and IR cameras. While payload sensors represent some of the reason the mission exists, it is the health sensors that measure and control systems to ensure optimum operation.

See also


  1. ^ a b c d e f g h i j k Pisacane, Vincent L. Fundamentals of Space Systems. New York, Oxford University Press, 2005
  2. ^ Abid, Mohamed M. Spacecraft Sensors. West Sussex, John Wiley and Sons Ltd., 2005, p301

External links

  • "Scope and Subject Category Guide - Category 19 - Spacecraft Instrumentation and Astrionics". NASA.

Spacecraft Electronics & Space Electronics


AZUSA refers to a ground-based radar tracking system installed at Cape Canaveral, Florida and the NASA Kennedy Space Center. AZUSA was named after the southern California town Azusa, California where the system was devised in the early 1950s.


Hazcams (short for hazard avoidance cameras) are photographic cameras mounted on the front and rear of NASA's Spirit, Opportunity and Curiosity rover missions to Mars and on the lower front portion of Chinese Yutu rover mission to the Moon.

List of German aerospace engineers in the United States

The following lists contain names of engineers, scientists and technicians specializing in rocketry who originally came from Germany but spent most of their careers working for the NASA space program in Huntsville, Alabama.

Particularly after World War II, many engineers left Germany to pursue further rocket projects in the U.S. The majority had been involved with the V-2 in Peenemünde, and 127 of them eventually entered the U.S. through Operation Paperclip. They were also known as the Von Braun Group.Before and after Operation Paperclip, other German experts arrived in the US by individual immigration without government links and would only later join various space projects, primarily at NASA.

List of Sherman Fairchild companies

Sherman Mills Fairchild was an American businessman and inventor whose career spanned the middle of the 20th century. His vast business holdings may never be fully known, but a former Fairchild employee, Theron Rinehart, rescued from destruction an incomplete list of companies that Fairchild owned. The following is a list of companies that Sherman Fairchild established throughout his long business career;

1920 Fairchild Aerial Camera Corporation

1922 Fairchild Aerial Surveys (of Canada) Limited

1924 Fairchild Aerial Surveys, Inc

1924 S.M. Fairchild Flying Corporation

1925 Fairchild Aerial Camera

1925 Fairchild Caminez Engine Corporation

1925 Fairchild Airplane Manufacturing Corporation

1925 Fairchild Flying Company(name changed from S.M. Fairchild Flying Corporation)

1925 Fairchild Aviation Corporation (holding company for Fairchild Aerial Camera Corporation, Fairchild Aerial Surveys, Inc., Fairchild Flying Company, Inc., Fairchild Caminez Engine Corporation, Fairchild Airplane Manufacturing Corporation and Fairchild Aerial Surveys (of Canada) Ltd.

1925 Fairchild Aerial Camera Corporation

1926 Elliot-Fairchild Air Services, Ltd.

1926 Elliot-Fairchild Air Transport, Ltd.

1927 Fairchild Aviation, Ltd. (reorganization and refinancing of the following subsidiaries and minority holdings; Fairchild Aerial Camera Corporation, Fairchild Aerial Surveys, Inc., Fairchild Flying Company, Inc., Fairchild Caminez Engine Corporation, Fairchild Airplane Manufacturing Corporation, Fairchild Aviation, Ltd., Compañía Mexicana de Aviación, S.A. (20% stock) and International Aerial Engineering Company (20% stock)

1928 Faircam Reality Corporation

1928 Fairchild Boats, Inc.

1928 Fairchild Engine Corporation

1928 V.E. Clark Corporation

1928 West Indian Aerial Express, Inc.

1928 Fairchild Aviation of Illinois

1929 Kreider-Resner Aircraft Company, Inc. (82% stock)

1929 Fairchild Shares Corporation

1929 Fairchild Aircraft Ltd.

1930 Fairchild-American Photo Aerial Surveys, S.A.

1932 Fairchild Airplane Sales Corporation

1934 Fairchild Aircraft Corporation

1936 Fairchild Aviation, Inc.

1936 Fairchild Engine and Airplane Corporation (holding company for Fairchild Aircraft Corporation, Ranger Engineering Corporation and Fairchild Aircraft, Ltd. (50% stock)

1937 Duramold Aircraft Corporation

1938 Clark Corporation

1938 Fairchild Investments Corporation

1938 Molded Aircraft Corporation (name changed from Duramold Aircraft Corporation)

1938 Duramold Aircraft Corporation

1939 Ranger Corporation

1941 AL-FIN Corporation

1945 Fairchild Pilotless Planes Division formed by Fairchild Engine and Airplane Corporation

1945 Fairchild Personal Planes Division formed by Fairchild Engine and Airplane Division

1946 Fairchild-NEPA (Nuclear-powered aircraft engines) Division is formed by Fairchild Engine Engine and Airplane Corporation

1949 Fairchild Guided Missiles Division (name change from Pioletless Planes Division)

1953 Fairchild Speed Control Division formed by Fairchild Engine and Airplane Corporation

1953 Fairchild Aviation, (Holland) N.V.

1954 American Helicopter Division formed by Fairchild Engine and Airplane Corporation

1954 Fairchild Kinetics Division formed by Fairchild Engine and Airplane Corporation

1955 Fairchild Armalite Division formed by Fairchild Engine and Airplane Corporation

1956 Fairchild Electronics Division (name change from Fairchild Guided Missiles Division

1957 Jonco Aircraft Corporation

1958 Fairchild Astronautics Division (name change from Fairchild Guided Missiles Division

1958 International Aluminum Structures Inc.

1960 Astrionics Division (name changed from Electronics Division)

1960 Aircraft Service Division

1961 Fairchild Stratos Corporation ( operating division; subsidiaries and affiliates: Aircraft Missiles Division, Aircraft Service Division, Electronic System Division, Stratos Division, Fairchild Arms International Ltd., Fairchild Aviation (Holland) N.V., and Aerotest Laboratories, Inc.)

1962 Space Systems Division formed by Fairchild Stratos Corporation

1962 Hiller Aircraft Company, Inc.

1964 Fairchild-Hiller Corporation (name change from Fairchild Stratos Corporation; division and subsidiaries; Aircraft Missiles Division, Aircraft Services Division, Electronics Systems Division, Inc., Fairchild Aviation (Holland) N.V. and Fairchild Arms International, Inc.

1965 Republic Aviation Company

1965 Republic Aviation Division

1965 Electronic and Information Division (formed by combining Electronic Systems Division, Data Systems Engineering and similar disciplines from Republic Aviation Company

1966 Burnes Aero Seat Company, Inc.

1966 Fairchild-Hiller-FRG Corporation

1966 Aircraft Division formed by combining Space Systems Division and Electronic and Information Systems Division

1966 Industrial Products Division forms from the Industrial Products branch of Stratos Division

1967 S.J. Industries, Inc.

1967 Air Carrier Engine Services, Inc.

1967 Fairchild Chemical Corporation

1967 EWR-Fairchild International

1968 Fairchild Marketing Company


1969 Fairchild-Germantown Development Company, Inc.

1970 Fairchild Aviation (Asia) Ltd.

1971 Fairchild Industries, Inc. Name change from Fairchild Hiller Corporation, division and subsidiaries: Fairchild Aircraft Marketing Company, Fairchild Aircraft Services Division, Fairchild Republic Division, Fairchild Space and Electronics Division, Fairchild Stratos Division, Burns Aero Seat Company, Inc., Fairchild Arms International, Ltd., Fairchild Aviation (Asia) Ltd., Fairchild Aviation (Holland) N.V., Fairchild-Germantown Development Company, Inc. and S.J. Industries, Inc

1971 Fairchild KLIF, Inc.

1971 Swearingen Aviation Corporation

1972 American Satellite Corporation

1972 Fairchild Minnesota, Inc.

1972 Fairchild International Sales Corporation

1979 Bunker Ramo Corporation (18.4% stock)

1980 American Satellite Company

1980 Space Communications Company (Spacecom) (25% stock)

1980 Saab-Fairchild HB

1981 Fairchild Swearingen Corporation (name changed from Swearingen Aviation Corporation, see SyberJet Aircraft)

1982 Fairchild Credit Corporation

1982 Fairchild Control Systems Company

1983 Fairchild Space Company and Fairchild Electronics Company (formed from Fairchild Space and Electronics Company


Navcam, short for navigational camera, is a type of camera found on certain robotic rovers or spacecraft used for navigation without interfering with scientific instruments. Navcams typically take wide angle photographs that are used to plan the next moves of the vehicle or object tracking.


The ODOP (Offset DOPpler) radar tracking system is essentially the same as the UDOP system used for many years at the Atlantic Missile Range, but ODOP operates at different frequencies. It is a phase-coherent, multistation Doppler tracking system which measures position of a vehicle equipped with the ODOP transponder. ODOP stations are located at and around Cape Kennedy. The ODOP transponder is carried in the first stage (S-IB or S-IC) of the Saturn vehicles and, therefore, ODOP tracking data is limited to the flight of the first stage only. The ODOP tracking system provides data immediately following lift-off while other tracking systems cannot "see" the vehicle or their accuracy is reduced by multipath propagation during the early phase of the flight.

The ODOP system is a radar interferometer tracking system which determines the position of a vehicle-borne transponder. The ground transmitter radiates a CW signal of 890 MHz to the transponder in the vehicle. The transponder shifts the received signal in frequency by 70 MHz and retransmits it to the receiving stations (R1, R2, R3). The signal from the transponder received at the ground stations contains a 2-way Doppler shift fD which is extracted by mixing the received signal (fi = 960 MHz + fD) with the reference frequency (fR = 960 MHz) derived from the transmitter frequency. Actually, a reference frequency of 53.33 MHz is transmitted over a VHF link to each transmitter station and then multiplied by a factor of 18, yielding 959.94 MHz. When this frequency is combined with the signal received from the transponder, the Doppler shift is obtained with a 60 kHz bias frequency (60 kHz + fD). The UDOP system used a transmitter frequency of 450 MHz which was doubled in the transponder (900 MHz). The higher frequency in the ODOP system (890 MHz versus 450 MHz) is less affected by the ionosphere and the result is increased tracking accuracy.

The Doppler frequencies, fD, (including the bias frequency) from all receiving stations are transmitted to the central station and recorded on magnetic tape. Integration of the Doppler frequency received at a particular station provides the range sum, i.e., the distance transmitter-transponder receiver. At least three range sums (for three different stations) are necessary to compute the position of the vehicle (transponder). The ODOP system uses 20 receiver stations around Cape Kennedy for redundancy and optimum tracking geometry. ODOP tracking data is not available in real time but is obtained from post-flight evaluation.


Each Pancam is one of two electronic stereo cameras on Mars Exploration Rovers Spirit and Opportunity. It has a filter wheel assembly that enables it to view different wavelengths of light and the pair of Pancams are mounted beside two NavCams on the MER camera bar assembly.According to Cornell University it can work with Mini-TES to analyze surroundings.According to a paper about Mars by JPL, the Pancam system can achieve an angular resolution of 300 microradians, which is three times better than the human eye. It can observe 14 spectral bands, and with two side-by side camera's can generate stereoscopic views of Mars, supporting the creation of large Mars panoroama's in excess of 10 Gbit uncompressed. Spirit rover took the highest resolution image ever taken on the surface of another planet up to that time when it landed in 2004.

ST-124-M3 inertial platform

The ST-124-M3 inertial platform was a device for measuring acceleration and attitude of the Saturn V launch vehicle. It was carried by the Saturn V Instrument Unit, a 3-foot-high (0.91 m), 22-foot-diameter (6.7 m) section of the Saturn V that fit between the third stage (S-IVB) and the Apollo spacecraft. Its nomenclature means "stable table" (ST) for use in the moon mission (M), and it has 3 gimbals.

Saturn I SA-3

Saturn-Apollo 3 (SA-3) was the third flight of the Saturn I launch vehicle, the second flight of Project Highwater, and part of the American Apollo program. The rocket was launched on November 16, 1962, from Cape Canaveral, Florida.

Saturn Launch Vehicle Digital Computer

The Saturn Launch Vehicle Digital Computer (LVDC) was a computer that provided the autopilot for the Saturn V rocket from launch to Earth orbit insertion. Designed and manufactured by IBM's Electronics Systems Center in Owego, N.Y., it was one of the major components of the Instrument Unit, fitted to the S-IVB stage of the Saturn V and Saturn IB rockets. The LVDC also supported pre- and post-launch checkout of the Saturn hardware. It was used in conjunction with the Launch Vehicle Data Adaptor (LVDA) which performed signal conditioning to the sensor inputs to the computer from the launch vehicle.

Saturn V instrument unit

The Saturn V instrument unit is a ring-shaped structure fitted to the top of the Saturn V rocket's third stage (S-IVB) and the Saturn IB's second stage (also an S-IVB). It was immediately below the SLA (Spacecraft/Lunar Module Adapter) panels that contained the Lunar Module. The instrument unit contains the guidance system for the Saturn V rocket. Some of the electronics contained within the instrument unit are a digital computer, analog flight control computer, emergency detection system, inertial guidance platform, control accelerometers, and control rate gyros. The instrument unit (IU) for Saturn V was designed by NASA at Marshall Space Flight Center (MSFC) and was developed from the Saturn I IU. NASA's contractor to manufacture the Saturn V Instrument Unit was International Business Machines (IBM).One of the unused instrument units is currently on display at the Steven F. Udvar-Hazy Center in Chantilly, Virginia. The plaque for the unit has the following inscription:

The Saturn V rocket, which sent astronauts to the Moon, used inertial guidance, a self-contained system that guided the rocket's trajectory. The rocket booster had a guidance system separate from those on the command and lunar modules. It was contained in an instrument unit like this one, a ring located between the rocket's third stage and the command and lunar modules. The ring contained the basic guidance system components—a stable platform, accelerometers, a digital computer, and control electronics—as well as radar, telemetry, and other units.

The instrument unit's stable platform was based on an experimental unit for the German V-2 rocket of World War II. The Bendix Corporation produced the platform, while IBM designed and built the unit's digital computer.


A spacecraft is a vehicle or machine designed to fly in outer space. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, space colonization, planetary exploration, and transportation of humans and cargo. All spacecraft except single-stage-to-orbit vehicles cannot get into space on their own, and require a launch vehicle (carrier rocket)

On a sub-orbital spaceflight, a space vehicle enters space and then returns to the surface, without having gone into an orbit. For orbital spaceflights, spacecraft enter closed orbits around the Earth or around other celestial bodies. Spacecraft used for human spaceflight carry people on board as crew or passengers from start or on orbit (space stations) only, whereas those used for robotic space missions operate either autonomously or telerobotically. Robotic spacecraft used to support scientific research are space probes. Robotic spacecraft that remain in orbit around a planetary body are artificial satellites. Only a handful of interstellar probes, such as Pioneer 10 and 11, Voyager 1 and 2, and New Horizons, are on trajectories that leave the Solar System.

Orbital spacecraft may be recoverable or not. By method of reentry to Earth they may be divided in non-winged space capsules and winged spaceplanes.

Humanity has achieved space flight but only a few nations have the technology for orbital launches: Russia (RSA or "Roscosmos"), the United States (NASA), the member states of the European Space Agency (ESA), Japan (JAXA), China (CNSA), India (ISRO), Taiwan (National Chung-Shan Institute of Science and Technology, Taiwan National Space Organization (NSPO), Israel (ISA), Iran (ISA), and North Korea (NADA).

Walter Haeussermann

Walter Haeussermann (also spelled Häussermann; March 2, 1914 – December 8, 2010) was a German-American aerospace engineer and member of the "von Braun rocket group", both at Peenemünde and later at Marshall Space Flight Center, where he was the director of the guidance and control laboratory. He was awarded the Decoration for Exceptional Civilian Service in 1959 for his contributions to the US rocket program.

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