GHRS Instrument Handbook
Section on page 112).
CyclesProposals to use HST are solicited and reviewed on roughly an annual basis. However, because HST's properties changed fundamentally when COSTAR and WFPC2 were installed, Cycle 3 was defined to end at the time of the Servicing Mission. Cycle 4 began at the end of SMOV. Cycle 6 will end at the time of the 1997 Servicing Mission.
CVZContinuous Viewing Zones. The inclined orbit of HST allows for uninterrupted observations of objects in some declination ranges at certain times. See the Call for Proposals for further information.
DEFCAL, which measures the instantaneous location of the images on the onboard spectrum lamps and then compares that location to the nominal coordinates stored in the onboard database. The differences can range over several deflection steps in response to thermal and magnetic drifts. The offsets are applied to the database coordinates of the science apertures to provide an updated estimate of their location.
IMAGEs. The focus diodes are 25 microns square.
GIMPGeomagnetically-induced image motion problem. This problem underlies our recommendation to have no single exposure be longer than about 5 minutes in length.
GSCGuide Star Catalog, the list used to find stars upon which the Fine Guidance Sensors can lock to control the pointing of HST.
LSALarge Science Aperture. This is a square opening at the front of the GHRS that is used to acquire stars and for some science observations. Its dimensions were 2.00 arcsec square before COSTAR is installed and 1.74 arcsec square afterwards. The name used for the LSA will continue to be "
OPUSThe "OSS and PODPS Unified System." The Observation Support System was the facility located at STScI for real-time interaction between the ground and the HST spacecraft, and PODPS was the pipeline data reduction system. They have now been combined into ne operation called OPUS.
Phase IA Phase I proposal for HST includes just the information need by the Telescope Allocation Committee (TAC) and STScI to judge scientific merit and technical feasibility. In addition to the scientific justification, you are asked to provide a list of the targets that you wish to observe and a brief description of the observations themselves. We recommend adding comments to provide a clearer explanation of what you intend, even if they are not required.
Phase IIThe Phase II proposal is written once the Phase I proposal has been accepted for the HST science program. The Phase II proposal includes all the detailed specifications that are needed to turn your science program into the commands that the spacecraft will execute. As with Phase I, we recommend the liberal use of comments to help ensure that your goals will be achieved.
Ripple FunctionSee Blaze Function
SAASouth Atlantic Anomaly. A region lying over southeastern South America where the earth's radiation belts dip low, leading to high particle background rates for satellites in Low Earth Orbit. GHRS observations are suspended during passage through the SAA.
Side 1, Side 2GHRS is split into two "sides," one for the short-wavelength detector (D1) and one for the long-wavelength detector (D2). The sides operate independently but depend on each other for communication with the spacecraft. The installation of the GHRS Repair Kit during the HST Servicing Mission has meant that all GHRS communications are now through Side 2. Moreover, Side 2 now solely controls the grating carrousel and LSA shutter.
SPYBALconsists of a quick observation of the spectrum calibration lamp SC2 at a standard wavelength setting to ensure that the spectrum is properly centered on the diodes in the cross-dispersion direction. The y position at this standard wavelength is compared to a stored value and the difference is applied to the observations made with the proposal configuration until another
SPYBALis done. A
SPYBALis normally done before each new use of a different spectrum element, such as a grating. The resultant spectrum is provided to the observer and can be used to improve the default wavelength calibration.
SSASmall Science Aperture. The nominal (pre-COSTAR) size was 0.25 arcsec square, but after COSTAR it is 0.22 arcsec square. The name for this aperture will continue to be "
STEISSpace Telescope Electronic Information Service. This service provides on-line news, information, and documents via anonymous ftp. To use it, ftp to stsci.edu (Internet node 126.96.36.199) and login with username anonymous, using your last name as password. Use get to transfer the README file in the entry directory; this will provide a general explanation of how to access STEIS information. STEIS is now obsolete and the World Wide Web should be used instead. The URL for GHRS information is:
STEP-PATTis the pattern of operations undertaken in an
ACCUM. A typical
STEP-PATTdefines the relative proportions of time spent accumulating on the science diodes versus time with the background diodes. See Section on page 112.
STEP-TIMEis the exposure time for the smallest unit of an exposure. For example, during an acquisition,
STEP-TIMEis the amount of time spent at each dwell point while executing a spiral search pattern. During an
ACCUM, the detector integrates for a
STEP-TIMEbefore reading the diodes and adding their contents to the memory. A unit of
STEP-TIMEis spent executing each portion of a
STEP-PATT, for example.