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Count Rates and Door States

It is important to have some idea of the count rate expected from each target, both for reference during the mission, and for instrument safety considerations. The program hutsim, described earlier in this manual, provides a mechanism for simulating spectra of each object and estimating the count rates expected, including airglow lines. (The plots from these simulations can also be placed in the Target Book used by the payload specialists to set up an observation and verify that all is proceeding nominally.)

Sources whose predicted count rates exceed 5000 counts s-1 exceed safety limits for the detector. High count rates can also present dead time problems as described earlier in this manual. These situations can be handled in a number of ways. For extended sources, selecting a smaller aperture may resolve the problem. For point sources, however, one may have to choose something other than the full telescope aperture. The flux may be attenuated by a factor of two by closing one or the other of the ``half aperture" doors at the front of the telescope. If still too bright, the large aperture doors can be closed, and one of two small aperture door positions (50 cm2 or 1 cm2) can be utilized. All of these situations can be simulated using hutsim in order to both derive expected count rates, and analyze the quality of the data resulting from one of these alternate door states.


``Far-Ultraviolet Astronomy on the Astro-1 Space Shuttle Mission," A. F. Davidsen, Science, 259, 327, (1993).

The Hopkins Ultraviolet Telescope: Collected Scientific Papers, Vol. I, ed. A. F. Davidsen, (Baltimore: Johns Hopkins University) (January 1993).

``The Hopkins Ultraviolet Telescope: Performance and Calibration During the Astro-1 Mission," A. F. Davidsen et al., Ap. J., 392, 264, (1992).

HUT Dedicated Experiment Processor Software Requirements Document, Rev. E, J. R. Dettmer & B. Ballard, (Laurel: Johns Hopkins University Applied Physics Laboratory) (April 1990).

``An Intensified Photo Diode Array Detector for Space Applications," K. S. Long, C. W. Bowers, P. D. Tennyson, and A. F. Davidsen, Advances in Electronics and Electron Physics, 64A, 239, (1985).

Mission Planning Handbook and Interface Requirements Document (MPHIRD), W. P. Blair et al., (Huntsville: Marshall Space Flight Center) (April 1993).

``Ultraviolet Spectroscopy and Remote Sensing of the Upper Atmosphere," R. R. Meier, Space Science Rev., 58, 1, (1991).


A/D Analog-to-digital
A/G Air-to-ground
AOS Acquisition of signal
AST ASTROS Star Tracker
ASTROS Advanced Star/Target Reference Optical Sensor
CCTV Closed-circuit television
CsI Cesium Iodide
DDU Digital Display Unit
DEP Dedicated Experiment Processor
EC Experiment Computer
ECC Environmental Control Cannister
ECAS Experiment Computer Applications Software
ECOS Experiment Computer Operating System
EM Electronics Module
FHST Fixed-head Star Tracker
FWHM Full-width half-maximum
GI Guest Investigator
GSE Ground Support Equipment
HAC HUT Activation
HDC HUT Doors and Camera
HMH HUT Mirrors and Heaters
HOP HUT Operations
HRM High-rate Multiplexer
HSP HUT Spectrometer
HST Hubble Space Telescope
HSTGSC HST Guide Star Catalogue
HUT Hopkins Ultraviolet Telescope
ID Identification
IDIN Identification Initial
IDOP Identification Operational
IMC Image Motion Compensation
IMCS Image Motion Compensation System
IPS Instrument Pointing System
IRAF Interactive Reduction and Analysis Facility
IRS Integrated Radiator System
ISM Interstellar medium
IUE International Ultraviolet Explorer
JPL Jet Propulsion Laboratory
JSC Johnson Spaceflight Center
LOS Loss of signal
LOT Lock on target
MCP Microchannel plate
MMU Mass Memory Unit
MPHIRD Mission Planning Handbook and Integration Requiements Document
MS Mission Specialist
MSFC Marshall Spaceflight Center
MTL Mission Target List
NIST National Institute of Standards and Technology
OCR Operation Change Request
OMIS Operation Managment Information System
OSP Optical Sensor Package
OSPCAL Optical Sensor Package Calibration
PAP Payload Activity Planner
PATSI Problem analyst and trouble-shooting investigator
PI Principal Investigator
POCC Payload Operations Control Center
PP Peripheral Processor
PS Payload Specialist
PSF Point spread function
PTL Program Target List
RAM Random Access Memory
RAU Remote Acquisition Unit
RR Replanning Request
S/N Signal-to-noise ratio
S/W Software
SCIPLAN Science Plan
SIT Silicon Integrating Target
SOPG Science Operations Planning Group
SP Spectrometer Processor
STS Space Transportation System
SURF Synchrotron Ultraviolet Radiation Facility
SWP Short wavelength prime
SiC Silicon carbide
TDRS Tracking and Data Relay Satellite
TEGSE Telemetry experiment ground support equipment
TM Telescope Module
UIT Ultraviolet Imaging Telescope
UV Ultraviolet
WUPPE Wisconsin Ultraviolet Photopolarimeter Experiment

next up previous contents
Next: About this document ... Up: Detailed Observation Planning Previous: Selecting HUT Guide Stars