8 Glossary of Acronyms

 

ACIS

AXAF CCD Imaging Spectrometer, one of two focal plane instruments aboard AXAF, consisting of two arrays of CCD chips supporting imaging and transmission spectroscopy. It provides simultaneous imaging and non-dispersive moderate resolution spectroscopy.

ACIS-I

Term referring to Imaging CCD array.

ACIS-S

Term referring to Spectroscopic CCD array, which supports the use of the AXAF transmission gratings.

ADC

Analog-to-Digital Converter, provides digital equivalent to analog signals.

ADU

Analog-to-Digital Unit, unit defining integer values resulting from an analog to digital conversion.

AQLC

ACIS Quick Look Computer, one of two computers used at the X-ray Calibration Facility to assess ACIS data. The AQLC reduces and displays data in near real time to evaluate the scientific validity of the data.

ASC

AXAF Science Center, center for the analysis of AXAF data and general scientific support and analysis in the post-launch AXAF phase.

ADS

Two meanings based on context:

1.

Aspect Determination System, AXAF system determining the satellite pointing and orientation,

2.

Astrophysics Data System, NASA Astrophysics Division supported system for the access, dissemination and utilization of archival astrophysical data.

AXAF

Advanced X-ray Astrophysical Facility, the spacecraft carrying the ACIS experiment and the high resolution X-ray telescopes.

BESSY

The Berlin synchrotron light source used to establish the reference calibration of CCDs used during the MIT pre-assembly calibration measurements to achieve an absolute quantum efficiency calibration.

BEP

Backend Processor, digital signal processor and control processor which packetizes data for downlink and controls the CCDs.

BI

Backside Illuminated, term applied to a type of CCD chip, in which the normal thick silicon substrate is removed and X-rays illuminate the back of the device. BI chips have good low energy quantum efficiency.

BND

Beam Normalization Detector, an X-ray counter used at the XRCF to measure the intensity of the incident X-ray beam, and hence allow normalization of any measurements made at the XRCF.

BNL

Brookhaven National Laboratory, site of a synchrotron used as an X-ray source during ACIS filter calibration.

CCD

Charged Coupled Device, the active detector elements in ACIS.

CDR

Critical Design Review, formal meeting certifying the start of full production of the overall hardware and software design.

CEI

Contract End Item, item specified in the NASA contract which must be delivered by the ACIS team.

CIT

Calibration Implementation Team, a group combining the CTT, MSFC Project and support staff, and TRW, which will implement the XRCF calibration of AXAF.

CTE

Charge Transfer Efficiency, ratio of charge remaining after one pixel clocking to the charge before clocking.

CTI

Charge Transfer Inefficiency, deviation of CTE from unity. Convenient because CTE is often very close to one.

CTT

Calibration Task Team, a scientifically orientation group drawn from the Project and SI teams, charged with the responsibility of planning AXAF calibration.

DA

Detector Assembly, houses CCD arrays, fiducial lights and an X-ray calibration source. Functionally equivalent to term `CCD Camera'.

DEA

Digital Electronics Assembly, ACIS digital signal processing section.

DPA

Digital Processing Assembly, ACIS analog signal processing section.

DPS

Detector & Processor Subsystem, subsystem dedicated to the detection and processing of X-rays, consisting of the DA, DEA and DPA.

DR

Data Requirement, a formal NASA specification for required documentation format, content and delivery dates.

EGSE

Electronic Ground Support Equipment, one of two computers used at the X-ray Calibration Facility to assess ACIS data. The EGSE generates commands and monitors housekeeping data to assure the health and safety of the instrument.

EMI

Electro-Magnetic Interference, electro-magnetically induced noise appearing on electrical signal wires. Usually referred to in the context of eliminating or shielding to prevent EMI.

FEP

Frontend Processor, digital signal processor, part of the DPA which does initial processing on raw CCD pixel data.

FI

Frontside Illuminated, a traditional CCD chip design where the chip is illuminated from the front layer, which requires the X-rays to traverse the electronic gate structures. The low energy quantum efficiency of FI chips is low, but the energy resolution is superior to BI chips.

FP

Focal Plane, the sub-assembly portion of the ACIS experiment which holds the CCD chips.

FWHM

Full Width at Half Maximum, a measure of the width of a distribution, frequently used to describe the resolving power of the CCD for spectral emission lines.

GSE

Ground Support Equipment, auxiliary equipment needed to operate the ACIS experiment during assembly and ground testing.

HETG

High Energy Transmission Gratings, used to provide dispersed X-ray spectra appropriate to the higher energy X-rays collected by the HRMA. The HETG uses the ACIS as its prime detector system.

HRC

High Resolution Camera, the other focal plane instrument on AXAF, based on a micro-channel plate X-ray detector.

HRMA

High Resolution Mirror Assembly, the AXAF X-ray telescope mirror assembly, consisting of four nested confocal Wolter I optical systems.

HST

High Speed Tap, a high speed data path providing raw CCD pixel data into the ACIS EGSE computers. These data are similar to the sub-assembly calibration data, and form a direct check on the flight telemetry format data. The HST also offers a much higher bandwidth data path valuable during ground calibration. The HST will not be available during flight.

ICD

Interface Control Document, documents defining the observatory interfaces.

IPI

Instrument Principal Investigator, scientist in charge of the development of the instrument and leader of the team submitting the proposal and executing the task. For ACIS the IPI is Prof. Gordon Garmire.

kbs

kilobit per second, a data transfer rate measured in thousands of bits per second.

LMA

Lockheed Martin Astronautics, sub-contractor providing some of the fabrication of the ACIS instrument, formerly named MMAG.

LETG

Low Energy Transmission Gratings, disperse X-ray spectra appropriate to the lower energy X-rays collected by the HRMA. The LETG uses the HRC as its prime detector system.

MCC

Master Control Computer, central coordinating computer at the XRCF facilty during AXAF calibration.

MMAG

Martin Marietta Aerospace Group, sub-contractor providing the fabrication of the ACIS instrument, name now changed to LMA.

MIT

Massachusetts Institute of Technology, home institution of ACIS CCD development work and camera design.

MSFC

Marshall Space Flight Center, the home institution for the AXAF Project.

OBC

On-Board Computer, the AXAF spacecraft computer which transmits commands to ACIS and which receives telemetry data for transmission to the ground.

OBDS

On-Board Data System, the computing system for ACIS on-board the satellite.

OBF

Optical Blocking Filter, a thin free-standing polyimide plastic film with aluminum overcoats on both sides which is placed between the telescope mirrors and the CCD detectors. This filter blocks out optical, UV and infrared light which would otherwise interfere with X-ray detection by the CCDs, but is thin enough to allow X-rays to pass through.

OV

Orbital Verification, the first period of orbital operations, in which the instruments and spacecraft are turned on and proper operations are verified.

PDR

Preliminary Design Review, formal meeting reviewing the overall hardware and software design.

PRAM

Program Random-Access Memory, radiation resistant on-board non-volatile memory which is used to store instructions for CCD readout.

PSMC

Power Supply and Mechanism Controller, supplies power and mechanism control to ACIS.

PSU

Penn State University, home institution for the ACIS Principal Investigator and ground software development.

PTS

Power & Thermal control Subsystem, ACIS subsystem which delivers power and maintains thermal control of the experiment.

RCTU

Remote Command and Telemetry Unit, TRW supplied interface box supplying connection to spacecraft data and power busses.

SDS

Software Design Specification, document specifying the software design for each build of the ground software.

SEU

Single Event Upset, single bit errors introduced into memory or processors, resistance to which reflects more robust processor performance in a space environment.

SIM

Science Interface Module, a translational mechanical structure which moves to allow insertion of either the HRC and ACIS into the telescope focal plane, and to shift between the ACIS-I and S arrays.

SIN

Science Instrument Notebook, ASC reference document on all AXAF Science Instruments.

SOP01

Science Instrument Operations Manual [this document], required deliverable for the ACIS team, presenting the information needed to properly operate the ACIS experiment.

SRAM

Sequencer Random-Access Memory, highly radiation resistant memory used to store instructions for the ACIS CCD readout.

SRR

Software Requirements Review, formal meeting reviewing the adequacy and accuracy of the Software Requirements.

SRS

Software Requirements Specification, document specifying the ACIS software requirements.

SRC

Synchrotron Radiation Center, a synchrotron facility run by the University of Wisconsin, Madison, used for ACIS flight filter calibration.

ST

STatus information, information ancillary to the scientific data which is appended to the science analysis data.

SWG

Science Working Group, the team of scientists, consisting of the Instrument PIs, the Telescope Scientist, the Interdisciplinary Scientists and the Project Scientist, who work as a top-level advisory team to assure the AXAF Project remains faithful to the scientific goals of the program.

TBS, TBR, TBD

To Be Supplied, Revised, Determined, terms holding space for specific numbers or text which are to be supplied, revised or determined at a later time.

VVA

Vent Valve Assembly, provides a commandable opening and closing path to vent the inside of ACIS.

WBS

Work Breakdown Structure, management document and numbering scheme for formalizing and categorizing the various tasks associated with this project into a tiered hierarchy with associated dependencies to enable the efficient identification and tracking of progress on the assigned goals.

XRCF

X-ray Calibration Facility, the X-ray facility built at Marshall Space Flight Center to support AXAF calibration of the joint HRMA-Science Instrument system.