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).
|Acquisition of signal
|ASTROS Star Tracker
|Advanced Star/Target Reference Optical Sensor
|Digital Display Unit
|Dedicated Experiment Processor
|Environmental Control Cannister
|Experiment Computer Applications Software
|Experiment Computer Operating System
|Fixed-head Star Tracker
|Ground Support Equipment
|HUT Doors and Camera
|HUT Mirrors and Heaters
|Hubble Space Telescope
|HST Guide Star Catalogue
|Hopkins Ultraviolet Telescope
|Image Motion Compensation
|Image Motion Compensation System
|Instrument Pointing System
|Interactive Reduction and Analysis Facility
|Integrated Radiator System
|International Ultraviolet Explorer
|Jet Propulsion Laboratory
|Johnson Spaceflight Center
|Loss of signal
|Lock on target
|Mass Memory Unit
|Mission Planning Handbook and Integration Requiements Document
|Marshall Spaceflight Center
|Mission Target List
|National Institute of Standards and Technology
|Operation Change Request
|Operation Managment Information System
|Optical Sensor Package
|Optical Sensor Package Calibration
|Payload Activity Planner
|Problem analyst and trouble-shooting investigator
|Payload Operations Control Center
|Point spread function
|Program Target List
|Random Access Memory
|Remote Acquisition Unit
|Silicon Integrating Target
|Science Operations Planning Group
|Space Transportation System
|Synchrotron Ultraviolet Radiation Facility
|Short wavelength prime
|Tracking and Data Relay Satellite
|Telemetry experiment ground support equipment
|Ultraviolet Imaging Telescope
|Wisconsin Ultraviolet Photopolarimeter Experiment