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Rattlesnake Mountain
Observatory
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Rattlesnake Mountain Observatory (RMO) is a professional-class astronomical
research facility located at the summit of Rattlesnake Mountain, about
27 km (17 miles) northwest of Richland, Washington. |
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Geographic Details
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Longitude: |
119.59 W |
Latitude: |
46.39 N |
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Height (above mean sea level): 1050 meters |
Local Standard Time = UTC - 8 hours
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The observatory’s primary astronomical instrument is a 0.8-meter Cassegrain-style
reflecting telescope, housed in the large (24-foot diameter) dome in
the lower portion of the photograph at left. The telescope was
designed, constructed, and installed at the observatory in 1971 by scientists
working at, what is now, Pacific Northwest National Laboratory (PNNL).
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Rattlesnake Mountain is the highest elevation within a 100-km (60-mile)
radius. A significant portion, including the observatory, lies
within the ecologically sensitve Fitzner-Eberhardt Arid Lands Ecology
(ALE) Reserve—an area of shrub-steppe wilderness largely untouched by
human activity. The photograph at right was taken from the lower
portion of the access road which runs across the Reserve and up to the
observatory.
The semi-arid conditions of the Lower Columbia Basin
provide some of the best climatic conditions for astronomical work
in Washington State. The area enjoys over 200 clear days per
year, low humidity, and less than 7 inches total annual precipitation.
Although clear skies are quite common throughout the year, an
especially clear period starts at the beginning of July and lasts
well into October.
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One of the first uses of the telescope was to support the on-going
studies of auroral phenomena in Earth’s upper atmosphere high above
the Pacific Northwest. Over the next several years, the instrument
was key in other research projects—many involving Saturn’s moon Titan,
white dwarf stars, and searches for black holes. Around the mid-1980s,
much of the research activity had ceased, and for the next 10 or so years,
the telescope, and the rest of the observatory, had been relegated to
"mothballed" status.
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The mounting, the optics, the hardware for mechanically moving
it to point at different objects in the sky, and the electronics for
interacting with the hardware, were all custom-designed for this specific
instrument. In essence, no other telescope precisely like it
exists in the world. Moreover, this telescope was a pioneer in the use
of friction rollers to effect its motion as opposed to gears.
And it remains the largest, most powerful, optical research-grade telescope
in Washington State.
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AASTA assumed management and operational authority of the observatory
in 1996, with the goal of refurbishing and upgrading the telescope so
that it may become a resource for enhancing opportunities science education.
By this time, the telescope was showing significant deterioration.
Rust spots were appearing on the outside of the tube, and the control
electronics (below), while still functional, no longer provided reliable
positional information of the telescope.
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The primary mirror (in the photograph below), at the base of the optical
tube, had accumulated a layer of dust; its reflective coating was severely
oxidized, and it had lost perhaps 50% of its original reflectivity.
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Still, the telescope was operational, and the roller mechanisims were
mechanically sound (albeit with evidence that some creative repairs had
been made over the years).
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Because of its location on the ALE Reserve, it should be apparent
that physically bringing the number of students to the telescope to make
it anywhere near effective as an educational tool is essentially impossible.
Rather, a much more feasible approach is to enable the use of the telescope
remotely, via the Internet. In other words, if the students cannot
be brought to the telescope, bring the telescope to the students. |
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At the time of the project’s inception, the World Wide Web was
just beginning to see widespread use, and some promising software technologies,
including Java applets, were coming into being. Remote access
to the telescope was to be accomplished through the development of custom
Java applets that would appear in the user’s web browser. These
applets would present a view of the telescope in way such that its operation
was as intuitive as possible. User interactions would be communicated
back over the Internet to the telescope control computer (TCC), which
would activate the telescope hardware to carry out the user’s command.
Data, most likely in the form of images, would be transmitted back to
the user’s computer for processing and analysis.
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This approach has some distinct advantages. The applet code
that provides the interface is resident on, and hosted by, a web server,
which is under the control of observatory staff. No special software
is needed on the user’s computer other than one of the widely available
(and free) web browsers, such as Microsoft Internet Explorer, Netscape
Navigator, or Firefox. Modifications to the interface code, perhaps
to correct undesired behavior, or to enhance the operation, could be
applied at the observatory’s web server, without requiring software upgrades
on the part of the end-user. The user would see the enhancements
the very next time the telescope was accessed.
Java applets, if developed properly, are “write once, run
anywhere”, meaning that the same applet will run on any of the popular
platforms, including Windows, Macintosh, and Linux. Separate
versions of the applet for each platform are not needed. Moreover,
it is entirely possible to tailor the interface according to the level
of sophistication of the user. A classroom of students in a middle-school
would see a different interface to the telescope than a graduate student
in astronomy. Additionally, there is no geographic restriction to
using the telescope; users from the other side of the globe would access
it just as easily as those within the local community.
Of course, this means a significant amount of work on
the part of those operating the observatory. If the telescope
is to function as a remote and automatic instrument, its operation
must be smooth, reliable, and essentially fool-proof. It must
be able to operate autonomously, scheduling observations according
to the placement of objects in the sky, and deciding when weather conditions
permit its safe operation. If a failure should occur, it must be
able to detect it, put itself into a safe state, and alert observatory
personnel to the situation. The telescope would be used primarily
for science education, so the interface presented to the user must be
intuitive. More often than not—and this is particularly true within
the software development realm—if it is easy to use, it has been hard
to make.
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A telescope designed and built with late-1960s and early-1970s
technology, no matter how “state-of-the-art” at the time, is not what
we today might call “Internet-ready”. Hardware incompatible
with its new role would need to be removed and excessed; the remainder
would need to be refurbished to operational quality, involving a great
deal of mechanical and electrical work. Moreover, no commercial
market exists that directly supports telescopes of this size; the collection
of hardware devices that effect its operation is unique to this instrument.
Any control software that was to operate the telescope hardware and the
auxiliary systems, would have to be developed “in-house”.
Despite the challenges, the team of dedicated and very
talented individuals, working entirely as volunteers on behalf of
AASTA, has made tremendous progress. Since the project inception,
these volunteers have...
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Replaced the old stepper-motor drive system with a high-quality servo-controlled
motor system
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Identified, purchased, and installed an industrial-grade rack-mount
computer (plus expansion cards) for controlling the telescope and its
subsystems
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Refurbished the optical encoders on each of the two axes of the telescope
to provide precise positional information
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Upgraded the power to the dome, to accommodate the increased electrical
demand of the new control systems
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Designed and developed software for interacting with the various
systems, and integrating their behavior into a comprehensive control
and automation system, with object selection and quick access to positional
and other information from on-line star catalogues
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Designed and built a digital hand-paddle to enable local operation
of the telescope by an observer at the eyepiece
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Replaced the mechanically-operated dome control system with one
that can be computer controlled
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Redesigned the secondary mirror focus motor control
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Identified and purchased various optical elements (eyepieces, focuser,
etc.) for local use at the telescope;
Also identified and purchased a digital (CCD) camera, as well
as astronomical video cameras for obtaining images (both static and
dynamic) of celestial objects
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Installed a fiber-optic computer network and 11 Mbps and 256 kBaud
radio-modem computer links to the PNNL, 17 miles away
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Cleaned the mechanical and optical components of the telescope,
and repaired the neoprene sealing on the dome
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The concurrent fundraising and public outreach activities have
supported the purchase of equipment, provided for teacher and student
stipends, and paid the annual insurance bill. We have received
cash and equipment grants from corporations such as Microsoft, Battelle,
Hewlett-Packard, Numatec, and Bechtel-Hanford. The servo-based
drive-motor system, worth about $36,000, was donated by the U.S. Department
of Energy. We have received cash donations from over 300 members
of the local community. We have hosted scores of tours at the
observatory (as seen at right), each involving a couple dozen individuals.
We have made many presentations to school, church, and community groups.
To date, some $200,000 in donations, equipment, volunteer labor, grants,
and in-kind contributions has been raised for this project.
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The current monetary value of the facility is estimated to be about
$500,000. |
The 0.8-meter telescope is now under local computerized control.
An observer, located within the dome, can control the telescope and
dome through interaction with the graphical interface on the telescope
control computer. From the computer, the user may select a celestial
object—such as a star, major planet, the moon, star clusters,
or galaxy—from one of the program’s on-line celestial databases, and
invoke the telescope to go to that object.
For each object chosen, the program calculates the effects of precession,
nutation, and aberration to the coordinates of the object as read
from the catalogue. It then reads the system clock, and (using
the geographical location of the observatory and factoring in the effect
of atmospheric refraction), calculates the position of the object
in the local sky. In the case of solar system objects, such
as the moon or one of the major planets, the program will first calculate
the position of the object within its orbit around the sun. Depending
on the object, these calculations may involve hundreds of terms.
When the position of the object is determined, the program
reads the position of the telescope, and (accounting for the rotation
of the earth while moving to the new object) determines how far the
telescope needs to move on each of its two axes. Simultaneously,
the program instructs the dome to move to the azimuth position of the
object. All these calculations take place within the span of a
few milliseconds, imperceptible to the user.
The telescope is then moved on each of its two axes—in
such a way as to eliminate the possibility that it is ever pointed
below the horizon at any time during the move. When the target
object has been reached, the program enters a tracking mode, whereby
a small velocity is applied to one of the two drive motors in order to
follow the object as it moves across the sky, due to the effect of the
earth’s rotation. A positional feedback algorithm within the program
reads the encoders every 250 milliseconds, calculates the actual velocity
of the telescope, and adjusts the speeds on the motors accordingly so
as to maintain a constant tracking motion.
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During tracking, the user may use the hand paddle to adjust the position
of the telescope. The program reads the state of the hand paddle
several times per second and applies a velocity to the motors if it
detects that one of the four directional buttons is pressed. A
“shift” mode on the hand paddle allows the observer to rotate the dome.
The program also includes utilities for testing the various hardware
components, for calibrating the position of the telescope using observations
of identifiable stars, and for determining the ratio of motor velocities
to actual axis velocities. Additional utilities are needed for
tuning the feedback algorithm—this will ensure smoother, more efficient
tracking—and for quantifying and refining the pointing accuracy of
the telescope.
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Having the telescope under local computerized control is the
necessary prerequisite for remote access. The logic for moving
the telescope from one target to the next is now in place, and the
motion of the dome is synchronized with that of the telescope.
The next step in this area is to provide the control program with the
ability to receive and respond to commands which come from another computer.
These commands would transmit the coordinates of the target to which
to move the telescope, and theoretically could come from anywhere on
the planet. In practice, measures will need to be taken that the
commands received are originated from a trusted source, and that no command
will be executed which threatens to place the telescope hardware into
a dangerous state.
It is highly likely that the selection of celestial targets
will need to be separated out of the main control program and into
its own separate application on another computer. This second
computer would then act as the client to the telescope control computer,
the latter then would have as its sole responsibility the accurate positioning
and tracking of the telescope, and the operation of the auxiliary components,
such as the dome or the secondary mirror for focusing the telescope.
It would retain the graphical interface that reports the state of
the telescope at any given instant. The client application would
provide access to the databases of celestial objects, and allow the
user to choose the object of interest and transmit it to the control
computer. In essence, this client application would be the functional
model for the eventual Java applet by which a user would interact with
the telescope from a remote location, such as a classroom, via a web browser.
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