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Å Angstrom
aberration Property of an optical system that causes an image to have certain easily recognizable flaws. Aberrations are caused by geometrical factors such as the shapes of surfaces, their spacing, and alignments. Image problems caused by factors such as scratches or contamination are not called aberrations.
ACE Actuator Control Electronics
ACS Advanced Camera for Surveys
acquisition, target Orienting the HST line of sight to place incoming target light in an instrument's aperture
actuator Small, high-precision, motor-driven device that can adjust the location and orientation of an optical element in very fine steps, making fine improvements to the focus of the image
Advanced Computer A 486-based computer that will replace the DF-224 on SM-3A. Performs onboard computations and handles data and command transmissions between HST systems and the ground system.
AFM Adjustable Fold Mirror
aft Rear of the spacecraft
alignment Process of mounting optical elements and adjusting their positions and orientations so that light follows exactly the desired path through the instrument and each optical element performs its function as planned
altitude Height in space
AMA Actuator Mechanism Assembly
AME Actuator Mechanism Electronics
aperture Opening that allows light to fall onto an instrument's optics
aplanatic Image corrected everywhere in the field of view
apodizer Masking device that blocks stray light
arcsec A wedge of angle, 1/3600th of one degree, in the 360-degree �pie� that makes up the sky. An arcminute is 60 seconds; a degree is 60 minutes.
ASCS Aft Shroud Cooling System
ASLR Aft Shroud Latch Repair (kits)
ASIPE Axial Scientific Instrument Protective Enclosure
astigmatism Failure of an optical system, such as a lens or a mirror, to image a point as a single point
astrometry Geometrical relations of the celestial bodies and their real and apparent motions
ATM Auxiliary Transport Module
attitude Orientation of the spacecraft's axes relative to Earth
AURA Association of Universities for Research in Astronomy
axial science instruments Four instruments � the STIS, NICMOS, FOC, and COSTAR � located behind the primary mirror. Their long dimensions run parallel to the optical axis of the HST.
baffle Material that extracts stray light from an incoming image
BAPS Berthing and Positioning System
BPS BAPS Support Post
C Celsius
Cassegrain Popular design for large, two-mirror reflecting telescopes in which the primary mirror has a concave parabolic shape and the secondary mirror has a convex hyperbolic shape. A hole in the primary allows the image plane to be located behind the large mirror.
CAT Crew Aids and Tools
CCC Charge Current Controller
CCD Charge-coupled device
CCS Control Center System
CDI Command data interface
change-out Exchanging a unit on the satellite
cm Centimeter
collimate To straighten or make parallel two light paths
coma Lens aberration that gives an image a �tail�
concave Mirror surface that bends outward to expand an image
convex Mirror surface that bends inward to concentrate on an image
coronograph Device that allows viewing a light object's corona
COS Cosmic Origins Spectrograph
COSTAR Corrective Optics Space Telescope Axial Replacement
CPM Central Processor Module
CPU Central Processing Unit
CTVC Color television camera
CU/SDF Control Unit/Science Data Formatter
CSS Coarse Sun Sensor
diffraction grating Device that splits light into a spectrum of the component wavelengths
DIU Data Interface Unit
DMS Data Management Subsystem
DMU Data Management Unit
drag, atmospheric Effect of atmosphere that slows a spacecraft and forces its orbit to decay
ECA Electronic Control Assembly
ECU Electronics Control Unit
electron Small particle of electricity
ellipsoid Surface whose intersection with every plane is an ellipse (or circle)
EPDSU Enhanced Power Distribution and Switching Unit
EPS Electrical Power Subsystem
EP/TCE Electrical Power/Thermal Control Electronics
ESA European Space Agency
E/STR engineering/science data recorders
EVA extravehicular activity
extravehicular Outside the spacecraft; activity in space conducted by suited astronauts
F Fahrenheit
FGE Fine Guidance Electronics
FGS Fine Guidance Sensor
FHST Fixed Head Star Tracker
FOC Faint Object Camera
focal plane Axis or geometric plane where incoming light is focused by the telescope
FOSR Flexible optical solar reflector
FOV Field of view
FPS Focal plane structure
FPSA Focal plane structure assembly
FRB Fastener retention block
FS Forward Shell
FSIPE FGS Scientific Instrument Protective Enclosure
FSS Flight Support System
GA Gallium arsenide
G/E Graphite-epoxy
GE General Electric
GGM Gravity Gradient Mode
GSE Ground support equipment
GSFC Goddard Space Flight Center
GSSS Guide Star Selection System
GSTDN Ground Spaceflight Tracking and Data Network
HGA High Gain Antenna
HST Hubble Space Telescope
hyperboloidal Slightly deeper curve, mathematically, than a parabola; shape of the primary mirror
Hz Hertz (cycles per second)
IBM International Business Machines Corporation
in. Inches
interstellar Between celestial objects; often refers to matter in space that is not a star, such as clouds of dust and gas
intravehicular Inside the spacecraft
IOU Input/output unit
IR Infrared
IV Intravehicular
IVA Intravehicular activity
JPL Jet Propulsion Laboratory
JSC Johnson Space Center
k Kilo (1000)
kB Kilobytes
kg Kilogram
km Kilometer
KSC Kennedy Space Center
Latch Mechanical device that attaches one component, such as a science instrument, to the structure of the telescope and holds it in precisely the right place
lb Pound
LGA Low Gain Antenna
LGA PC Low Gain Antenna Protective Cover
Light year The distance traveled by light in one year, approximately six trillion miles
LMMS Lockheed Martin Missiles & Space
LOPE Large ORU Protective Enclosure
LOS Line of sight
LS Light Shield
luminosity Intensity of a star's brightness
m Meter
µm Micrometer; one millionth of a meter
mm Millimeter
MA Multiple access
magnitude, absolute How bright a star appears without any correction made for its distance
magnitude, apparent How bright a star would appear if it were viewed at a standard distance
MAMA Multi-Anode Microchannel Plate Array
MAT Multiple Access Transponder
MCC Mission Control Center
MCP Microchannel plate
metrology Process of making extremely precise measurements of the relative positions and orientations of the different optical and mechanical components
MFR Manipulator Foot Restraint
MHz Megahertz
MLI Multi-layer insulation
Mpc Megaparsec (one million parsecs)
MOPE Multimission ORU Protective Enclosure
MSFC Marshall Space Flight Center
MSM Mode Selection Mechanism
MSS Magnetic Sensing System
MT Magnetic torquer
MTA Metering Truss Assembly
MTS Metering Truss Structure
M Absolute visual magnitude
m Apparent visual magnitude
NASA National Aeronautics and Space Administration
NBL Neutral Buoyancy Laboratory at JSC
NASCOM NASA Communications Network
NCC Network Control Center
NCS NICMOS Cooling System
nebula Mass of luminous interstellar dust and gas, often produced after a stellar nova
NICMOS Near Infrared Camera and Multi-Object Spectrometer
nm Nanometers
nmi Nautical miles
NOBL New Outer Blanket Layer
nova Star that suddenly becomes explosively bright
NPE NOBL Protective Enclosure
NSSC-I NASA Standard Spacecraft Computer, Model-I
occultation Eclipsing one body with another
OCE Optical Control Electronics
OCE-EK OCE Enhancement Kit
OCS Optical Control Subsystem
Orientation Position in space relative to Earth
ORU Orbital Replacement Unit
ORUC Orbital Replacement Unit Carrier
OSS Office of Space Science, NASA Headquarters
OTA Optical Telescope Assembly
PACOR Packet Processing Facility
parallax Change in the apparent relative orientations of objects when viewed from different positions
parsec A distance equal to 3.26 light years
PCEA Pointing Control Electronics Assembly
PCS Pointing Control Subsystem
PCU Power Control Unit
PDA Photon Detector Assembly
PDM Primary Deployment Mechanism
PDU Power Distribution Unit
PFR Portable Foot Restraint
photon Unit of electromagnetic energy
PIP Push in-pull out (pin)
pixel Single picture element of a detection device
POCC Payload Operations Control Center
polarity Light magnetized to move along certain planes. Polarimetric observation studies the light moving along a given plane.
primary mirror Large mirror in a reflecting telescope the size of which determines the light-gathering power of the instrument
prism Device that breaks light into its composite wavelength spectrum
PSEA Pointing/Safemode Electronics Assembly
PSO HST Project Science Office at GSFC
quasar Quasi-stellar object of unknown origin or composition
RAM Random-access memory
radial Perpendicular to a plane (i.e., instruments placed at a 90-degree angle from the optical axis of the HST)
RBM Radial Bay Module
RDA Rotary Drive Actuator
reboost To boost a satellite back into its original orbit after the orbit has decayed because of atmospheric drag
reflecting telescope Telescope that uses mirrors to collect and focus incoming light
refracting telescope Telescope that uses lenses to collect and focus light
resolution Ability to discriminate fine detail in data. In an image, resolution refers to the ability to distinguish two objects very close together in space. In a spectrum, it is the ability to measure closely separated wavelengths.
resolution, spectral Determines how well closely spaced features in the wavelength spectrum can be detected
resolution, angular Determines how clearly an instrument forms an image
RF Radio frequency
RGA Rate Gyro Assembly
Ritchey-Chretien A modern optical design for two-mirror reflecting telescopes. It is a derivative of the Cassegrain concept in which the primary mirror has a hyperbolic cross-section.
RIU Remote Interface Unit
RMGA Retrieval Mode Gyro Assembly
RMS Remote Manipulator System
ROM Read-only memory
RS Reed-Solomon
RSU Rate Sensor Unit
RWA Reaction Wheel Assembly
SA Solar Array
SAA South Atlantic Anomaly
SAC Second Axial Carrier
SAD Solar Array Drive
SADE Solar Array Drive Electronics
SADM Solar Array Drive Mechanism
SAGA Solar Array Gain Augmentation
SBA Secondary Baffle Assembly
SBC Single-Board Computer
SCP Stored Command Processor
SDAS Science Data Analysis Software
SDM Secondary Deployment Mechanism
secondary mirror In a two-mirror reflecting telescope, the secondary mirror sits in front of the larger primary mirror and reflects light to the point at which it will be detected and recorded by an instrument. In simple telescopes, the secondary mirror is flat and bounces the light out the side of the tube to an eyepiece. In more complex and larger telescopes, it is convex and reflects light through a hole in the primary mirror.
Servicing Mission NASA's plan to have the Space Shuttle retrieve the HST and have astronauts perform repairs and upgrades to equipment in space
SI Science Instrument
SI C&DH SI Control and Data Handling (subsystem)
SIPE Science Instrument Protective Enclosure
SM Secondary Mirror
SMA Secondary Mirror Assembly
SM1 First HST Servicing Mission, December 1993
SM2 Second HST Servicing Mission, February 1997
SM3A HST Servicing Mission 3A, November 1999
SM3B HST Servicing Mission 3B, planned for December 2000
SOFA Selectable Optical Filter Assembly
SOGS Science Operations Ground System
SOPE Small ORU Protective Enclosure
spectral devices These include spectrographs, instruments that photograph the spectrum of light within a wavelength range; spectrometers, which measure the position of spectral lines; and spectrophotometers, which determine energy distribution in a spectrum.
spectrograph Instrument that breaks light up into its constituent wavelengths and allows quantitative measurements of intensity to be made
spectrum Wavelength range of light in an image
spherical aberration Image defect caused by a mismatch in the shapes of the reflecting surfaces of the primary and secondary mirrors. Light from different annular regions on the primary mirror comes to a focus at different distances from the secondary mirror, and there is no one position where all of the light is in focus.
SSAT S-band Single-Access Transmitter
SSC Science Support Center
SSE Space Support Equipment
SSM Support Systems Module
SSM-ES SSM Equipment Section
SSR Solid State Recorder
SSRF Shell/Shield Repair Fabric
STDN Space (flight) Tracking and Data Network
STINT Standard interface
STIS Space Telescope Imaging Spectrograph
STOCC Space Telescope Operations Control Center
STS Space Transportation System
STScI Space Telescope Science Institute
TA Translation Aids
TAG Two-axis gimbal
TCE Thermal Control Electronics
TCS Thermal Control Subsystem
TDRS Tracking and Data Relay Satellite
TDRSS TDRS System
TECI Thermoelectric-cooled inner (shield)
TECO Thermoelectric-cooled outer (shield)
telemetry Data and commands sent from the spacecraft to ground stations
TLM Telemetry
UDM Umbilical disconnect mechanism
ULE Ultralow expansion
USA United States Army
USAF United States Air Force
USN United States Navy
UV ultraviolet
V Volt
V1, V2, V3 HST axes
VCS Vapor-cooled shield
VIK Voltage/Temperature Improvement Kit
W Watt
Wavelength Spectral range of light in an image
WFC Wide Field Camera
WFPC Wide Field and Planetary Camera. The camera currently in use is the second-generation instrument WFPC2, installed during the First Servicing Mission in December 1993. It replaced WFPC1 and was built with optics to correct for the spherical aberration of the primary mirror.
