Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.adass.org/adass/proceedings/adass94/kleiners.ps Äàòà èçìåíåíèÿ: Tue Jun 13 20:49:33 1995 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 01:53:25 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: arp 220

Astronomical Data Analysis Software and Systems IV
ASP Conference Series, Vol. 77, 1995
R. A. Shaw, H. E. Payne, and J. J. E. Hayes, eds.
A Graphical Planning and Scheduling Toolkit for
Astronomical Spacecraft
S. C. Kleiner
Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge
MA 02138
Abstract. A small yet powerful planning and scheduling toolkit has
been built for the Submillimeter Wave Astronomy Satellite (SWAS) Small
Explorer spacecraft. It makes extensive use of graphics to illuminate the
planning and scheduling process. The simple design, minimal resource
requirements and easy extensibility of the SWAS planning and scheduling
toolkit should make it useful for other space astronomy missions. A
release of the toolkit for general use is planned shortly.
1. The SWAS Mission
SWAS is a NASA Small Explorer spacecraft to be launched in low Earth orbit in
1995. It will investigate the chemistry and energetics of star forming molecular
clouds via the simultaneous observation of the O 2
, C i, H 2
O and 13 CO spectral
lines in the 487--557¯m (538--615GHz) range. The mission was proposed by the
Smithsonian Astrophysical Observatory in Cambridge MA, which has the re­
sponsibility for the scientific component of the mission. The mission is managed
by the Goddard Space Flight Center (GSFC).
The science instrument consists of a 0.65 m dual receiver radio telescope
with an acousto­optical spectrometer backend. The spectrometer is read out
every two seconds for the life of the mission, producing 100 MB of raw data
every day. SWAS will observe 50--100 targets per day. The minimum planned
mission duration is two years.
SWAS is the first astronomical Small Explorer, a series of missions to be
developed under a ``smaller, cheaper, faster'' imperative. The turnaround time
for SWAS , for example, should be about five years from acceptance of proposal
to launch. The SAO Science Operations Center responsible for the development
and operation of the science ground system consists of six scientists, including
Principal Investigator Gary Melnick and Project Scientist John Stauffer. The
planning toolkit described below was designed and written in two years by the
SWAS Planning Scientist.
2. The SWAS Planning and Scheduling Toolkit
This stand­alone toolkit provides all the planning and scheduling functions for
the SWAS spacecraft, including processing of the NASA predictive ephemerides,
target visibility calculations, long range planning and short term (orbit­to­orbit)
1

2
Figure 1. One­year planning display for week 20. Fifty­two weeks
run across the top of the display. The shading indicates days when a
target is visible or when Earth, Moon or Sun constraints are violated.
scheduling, slew constraint checking, nominal roll calculations, guide star selec­
tion, and generation of detailed spacecraft timelines for conversion into command
uploads. The toolkit displays its calculations graphically and makes extensive
use of coordinate transformations in order to avoid any brute force calculations,
a concept recognized by David Koch of NASA/Ames Research Center in his
development of a prototype scheduler for SWAS. A new guide star catalog for
CCD star trackers has also been developed (Stauffer 1993). The toolkit is cur­
rently generating timelines to support pre­launch testing of the flight operations
facilities at GSFC.
The toolkit has a minimalist design, consisting of independent tools or `fil­
ters' which operate on a single stream of scheduling events. Events include
orbital ascending node crossings, the rising or setting of a target above the
Earth horizon and the entry and exit of a target into pointing avoidance regions
around the Sun and the Moon. The toolkit is extended by defining new events
and adding the appropriate filters. Since SWAS uses the planets for calibration,
the toolkit can also schedule planetary pointings. Calculations are done in orbit

3
Figure 2. Pointing Constraint Display. The horizontal scale is orbital
longitude, the vertical scale orbital latitude. The labeled targets in the
central swath satisfy the Sun, Earth and Moon pointing constraints.
Figure 3. Scheduler Display for Five Orbits. The rectangles are tar­
get rise­and­set events shaded according to their scientific value and
scheduling efficiency. The heavily outlined targets have been selected
for scheduling.

4
relative time rather than absolute time to minimize the effect of uncertainties in
predictive ephemerides. The toolkit is fast enough that the same tools are used
both for long range planning and short term scheduling. The planning toolkit
consists of about a dozen tools, less than ten thousand lines of ANSI C code in
total. It makes only plain Xlib calls for the graphics and does not make any
Unix system calls.
3. SWAS Planning and Scheduling Graphics
Figure 1 is a planning display showing target visibilities over the course of the
year. The lighter bands running from top left to bottom right are days in which
the target is too close to the Sun. (SWAS must point within 75 ffi --105 ffi of the
Sun, and more than 40 ffi from the Earth and more than 15 ffi from the Moon.)
We have found by experience that long term planning is driven primarily by the
position of the Sun with respect to the target. Therefore, for any given week
targets going into the Sun soonest are given the highest scheduling priority.
Figure 2 shows pointing constraints as seen from the orbital plane. The
Sun is near the north orbital pole and the lighter swaths are regions of the sky
which violate the SWAS Sun pointing constraint. The small black squares are
potential targets, but only those which satisfy the pointing constraints at some
time in the orbit are labeled by the software.
Figure 3 is the interactive scheduling display showing five orbits. Each
rectangle represents the rise and set of a target during an orbit. The rectangles
are filled and shaded according to the target's scientific interest and scheduling
efficiency. The scheduling scientist uses a mouse to point and click to select
or de­select a target for inclusion into the timeline sent to the spacecraft, as
indicated by their heavy black outline around selected targets.
4. Distribution of the SWAS Planning and Scheduling Toolkit
The relatively severe time and manpower constraints for the development of the
SWAS Planning and Scheduling toolkit have forced it to remain small and sim­
ple. Nonetheless, it had to be powerful enough to support production scheduling
for the SWAS spacecraft and flexible enough to do year­long mission planning.
During the development of the toolkit, we realized that these attributes,
together with its ease of modification and extension, should make it useful for
other space missions and for astronomers developing future missions. We have
received a small NASA Astrophysics Data Program grant to package the toolkit
for general distribution. We anticipate a release of the toolkit shortly. Please
contact the author for sample products and more information.
References
Stauffer, J. 1993, ``Creation of a Guide Star Catalog for the BASG CT­601
Startracker,'' SWAS Technical Memorandum