- Welcome to Space Place, and thank you for coming tonight.
Tonight we have a talk of special significance,
because we just passed the 50th anniversary
of the launch of the Orbiting Astronomical Observatory 2,
the first successful space observatory.
And it had very important connections and roots here
in Wisconsin, and so I've asked a historian of astronomy,
who's actually done research on the OAO program
and published on that topic, to give the talk here tonight.
That's Jordan Marchè, and Jordan got his PhD
in the History of Science from Indiana University,
and then has been working here in Madison, Wisconsin
for a few years, and I imposed on him to give us a talk
tonight about the history of the OAO project.
So, let's welcome Jordan up here to the front.
(audience applauding)
Thank you, Jim, for that very kind introduction.
And good evening, ladies and gentlemen.
So, welcome to this public celebration
of the 50th anniversary of the launching of the
Orbiting Astronomical Observatory or OAO-2 satellite.
And the reason why we are hosting this celebration
is again because the principle
and longest-lasting component of this device,
termed the Wisconsin Experiment Package or WEP,
which is what I'll be referring to it as,
was designed and constructed by a team of researchers
from the astronomy department here,
although they couldn't do it entirely along, of course.
Now, OAO-2 was the first true stellar space observatory.
And in its day it represented a greater
technological step forward than did the
much larger and more sophisticated
Hubble Space Telescope that was launched in 1990.
And explaining the hows and whys behind that claim
will take up perhaps the majority
of our time here this evening.
But that's not all that we have to share with you tonight.
The WEP which occupied one-half of the OAO-2 satellite,
and which is highlighted in white there,
lasted for 50 months until February 14th of 1973,
when its power supply finally failed.
Yet, during that time it managed to observe
more than a thousand celestial objects of many kinds.
There were chiefly stars, including one nova, plus nebulae
and galaxies that lay well beyond our solar system,
along with certain planets and active comets within it.
So, we will highlight some of the scientific discoveries
toward the end of this talk.
Now, we will see that OAO, and especially the WEP,
marked a significant turning point in the way
that astronomical research was conducted up to that time.
And without the usage of high-speed, digital computers,
shown there on the right for example,
then virtually none of these observations
and discoveries with OAO-2 would have been possible.
Now, please note here that we're talking
about room-sized mainframe computers,
and/or refrigerator-sized minicomputers,
not personal or desktop computers,
which hadn't been invented yet.
And as we'll see, these digital computing means were
absolutely necessary to handle the data gathering
and storage and transmission and analysis that was conducted
with OAO-2, so this too is one of the principle legacies
of that observatory and the WEP.
Now, we're extremely fortunate to have here,
just beyond that wall, in this very building a full-scale
engineering model of the OAO-2, here at Space Place.
And if you've seen it or will,
this will make it much easier for you to visualize,
perhaps, the scale and complexity of the various devices
and things that we are going to be talking about tonight.
In fact, there is no other full-scale model of the OAO
anywhere on earth, correct, Jim?
(audience member chattering faintly)
Not even at the Smithsonian Air and Space Museum.
So, we have the one and only example
of its kind left in the world.
But now let us pretend to travel even a little further
back in time, by about another decade or so,
to around the beginning of the space age, and to look
into the origins of the this remarkable
Orbiting Astronomical Observatory.
Now, to most people the space age began with a jolt
on the evening of October 4th, 1957,
when they heard the surprise news
that the Soviet Union had launched
the world's first artificial satellite named Sputnik.
But in fact both the United States and the Soviet Union
had announced plans several years earlier,
that they would try to launch such a satellite
in conjunction with the International Geophysical Year,
or IGY for short, which was a cooperative scientific venture
that began on July 1st, 1957.
And this involved a group of around 60 nations altogether
that performed experiments in concert
over the coming 18-month period.
Thus, the US was really in no hurry to try
and launch the first IGY satellite,
which was named Vanguard, and most officials
strongly doubted that the Soviet Union
even had the launch capabilities to perform such a feat.
Although those experts were mistaken,
and the launch of Sputnik touched off
what some historians have called a crisis
of confidence here in the US.
Now, this development strongly hastened
the subsequent creation of NASA,
the National Aeronautics and Space Administration,
roughly one year later in October of 1958.
But the desire to launch a new breed
of scientific satellites actually preceded NASA's creation,
as we'll see, and this is where we must look
for the origins of the OAO.
Now, in June of 1958 a 15-member panel,
which called itself the Space Science Board, or SSB,
was created by the US National Academy of Sciences.
And the board was headed by a geophysicist named
Lloyd Berkner, who shortly afterwards sent telegrams,
and not email messages (snickering)
to a number of leading US astronomers,
asking for suggestions about scientific experiments
that could be performed aboard future orbiting satellites.
And one of those who received such a telegram was
Dr. Arthur D. Code, the newly appointed director
of the Washburn Observatory here at UW-Madison,
but first we must digress a bit.
Professor Code was a native of Brooklyn, New York,
who had earned his PhD in Theoretical Astrophysics
from the University of Chicago, in 1950.
Yet, he was that rare sort of individual
who was both an outstanding theorist,
and here on the process of radiative transfer
in Stellar Interiors, as well as in
equally talented experimentalist, where he had gained
vast experience with electronic equipment
in the US Navy during World War II.
Now, Code was first hired on to the faculty
of the Department of Astronomy at UW-Madison, in 1951,
and he remained until 1956.
Now, he specialized in the photoelectric photometry of stars,
but in that year he was hired away
by the California Institute of Technology, or Caltech
in Pasadena, which awarded him a tenured position.
But the launching of Sputnik, as we'll see,
was to change all of that.
Now, when Code and a colleague there,
Professor Donald Osterbrock,
another former Wisconsin astronomer,
observed the passage of Sputnik over the Caltech campus
in the fall of 1957, Code realized that it should now
be possible to measure the ultraviolet energies
of the stars from an orbiting satellite.
And why this should be such a big deal is
what will require and get a little more of an explanation.
Now, first of all, the hottest stars emit most
of their energy in the ultraviolet portion of the spectrum.
And they appear bluish-white to the unaided eye.
But while the earth's atmosphere is transparent
to visible light and longer radio waves,
it is essentially opaque to all other forms of energy
that are shorter in wavelength than visible light.
So, those to the right side of that diagram up there.
So that is the atmosphere blocks and absorbs
most ultraviolet and then all X-ray and gamma ray energies
that come to us from astronomical objects.
Now, if that were not the case,
these ionizing forms of radiation would make life
on earth's surface nearly impossible.
And we would likely not be here.
But to a ground-based astronomer,
the inability to examine and measure those other shorter
wavelengths made a more detailed understanding
of the properties of stars pretty much impossible.
So, only by getting above the atmosphere
where all of those wavelengths can be observed
could significant progress then be made along those lines.
And as far back as 1960, Code had written there
that carrying out such observations from
above the atmosphere, "Cannot fail to have a tremendous
"impact on the future course of stellar astronomy."
And he was certainly right.
Now, what happened next for Professor Code's career path
may be regarded as mixture of fortunate timing
and opportunity, but also entailed a somewhat unusual
and potentially risk-filled decision on his part,
namely he resigned from his tenured position at Caltech.
And effective on July 1st, 1958, returned here
to UW-Madison as a full tenured professor,
as head of the Astronomy Department
and director of the Washburn Observatory.
Now, the Wisconsin position offered him the autonomy
to pursue research in space astronomy that almost
certainly would have been lacking had he remained at
Caltech, which housed the 200-inch Mount Palomar Reflector
shown there in the lower left,
which was the then largest ground-based optical telescope
in the world, but he knew that the 200-inch telescope
could never see into the ultraviolet,
and that it therefore remained a
somewhat limited instrument in his judgment.
Now, also, critical to his decision to return to Wisconsin
was the commitment expressed by the UW administration
to rapidly enlarge the Department of Astronomy,
and to establish a full graduate-level program here.
These were steps that had not yet been taken
by Code's predecessor, Professor Albert Whitford,
but which had been recommended by him.
And Whitford went on to become the director
of the Lick Observatory in California.
So, Code goes back-and-forth returning to Wisconsin.
Now, the upshot of all of this is that by the end
of 1958 Code was appointed as a member of
the Space Science Board, which after the formation
of NASA evolved into that organization's
Space Science Working Group, or SSWG, shown here,
which consisted of four or five key teams and institutions
who then carved out niches for themselves, starting in 1959.
Now, the first four teams shown here all shared an interest
in pursuing ultraviolet astronomy from space,
while the fifth group went on to create
the first Orbiting Solar Observatories, or OSOs,
some of which preceded the OAOs.
So that was the breakdown.
In 1959, Professor Code,
along with Professor Theodore Houck here,
founded the Space Astronomy Laboratory
or SAL as it is known here at UW-Madison.
Sal was the first of several notable startups
in Professor Code's career, which even came
to include the later Space Telescope Science Institute.
And Professor Houck was a recent PhD graduate
of the astronomy department.
Incidentally, the order of these four individuals
from left to right, Code, Houck, McNall, whom I'll get to,
and Professor Bless there on the right.
They were joined by Professor Robert C. Bless,
a recent PhD graduate from the University of Michigan,
who began as a postdoctoral researcher in 1958,
before becoming a permanent member
of the Astronomy Department.
Both Houck and Bless had done their research
on the photoelectric photometry of so-called
early-type stars, that is OB and A Stars.
And then the fourth original member of SAL was
Professor John McNall, standing there in the back,
whose expertise lay in electrical engineering
and computer science most especially.
And this, as we will see, played a crucial role
in the success of OAO-2.
Now, SAL was originally housed in Sterling Hall,
but this soon became overcrowded and
among several temporary relocations, including buildings
such as this on South Park Street, that were
far from glorious, it finally acquired a permanent home
in adjoining Chamberlain Hall.
In spite of the somewhat adverse working conditions
early on, the four researchers developed a strong
camaraderie among themselves and formed a
rather loose-knit organization which
seemingly enjoyed an absence of bureaucratic red tape.
(audience members chuckling)
Now, well before OAO was launched,
the team received financial support from NASA,
and constructed some early prototypes of their photometers,
and so on, and their worthiness under
near space-flight conditions was first tested
aboard high-altitude weather balloons,
shown there in the middle, although this is not their balloon,
it's just a balloon, starting in 1961.
Then aboard Aerobee sounding rockets, shown there
on the lower-left, that were launched from
White Sands, New Mexico, starting in 1962,
and also on several flights of NASA's X-15 rocket plane,
shown there in the lower-right.
And one departmental PhD graduate Charles or Chuck Lily
performed research on the interstellar radiation field,
using an Aerobee sounding rocket, in the mid-1960s.
Now, when the Space Science Working Group
was first organized, a satellite payload
of around 100 to maybe 150 pounds was considered
the maximum possible weight that could be lifted
into space using existing rocket boosters
of the project Vanguard class.
And so this is an early concept of
one of those possible satellites, but by 1960
with the development of much larger boosters
in preparation for the manned project Mercury series,
the payload capacity was then raised to around 5,000 pounds.
And this, of course, had enormous implications
for the planning of individual experiment packages
by the various teams.
And based on this newer weight capacity,
NASA also announced a crucial decision
that would impact all of the teams in the working group.
And this was the choice to adopt a
so-called modular approach that would enable
all of the experiment packages to be flown
inside a standardized platform or bus,
that would be carried into orbit.
Now, on the one hand, that decision made perfect sense,
because all of the experiment packages would share
common pointing requirements, and they would all derive
their electrical power from a pair of solar panels
that were attached on the outside of the platform.
And standardization is usually a good thing and is followed.
Now, the module itself was to be a single tube
roughly 10 feet long and around 40 inches in diameter.
Now, NASA also felt that perhaps two or more
of the experiment packages should be combined
and operated jointly within the same module.
But now how is this to be done?
And here there was an interesting twist
or outcome to the story.
When this requirement was announced,
Professors Code and Houck suggested that two
of the packages, namely those from Wisconsin
and the Smithsonian's Project Celescope,
which we'll describe more coming up,
could be placed at opposite ends of the same tube.
But NASA engineers immediately countered that
such a configuration would be impossible
to execute in actual operation.
However, about two weeks later they changed their minds,
and then agreed that the Wisconsin team's suggestion
posed an optimal solution to that problem.
Thus, we have this arrangement.
And with that said, we can now turn towards
some of the challenges that were to be overcome in operating
a full-fledged astronomical observatory in space.
And this is where we can begin to demonstrate
why the OAO-2 satellite represented a greater technological
step forward in its day than the launching
of the Hubble Space Telescope, more than two decades later.
Now, the OAOs would be placed into an orbit
some three to 400 miles above the earth's surface,
and they would circle the earth roughly
every 90 to 100 minutes or so.
And of course for each half of the orbit the OAO
was in sunlight, then during the other half
it was in earth's shadow.
But now the sun and earth and moon are
constantly changing their positions,
and so everything must be recalculated in advance
to know where they are, and thus the OAOs demanded
a "Complex stabilization and control system,"
in order to make all of this happen.
So, essentially there are four principle tasks
that need to be done in order to operate
such a telescope in space, and I'll go over each
of these briefly to help us understand
how each one was to be solved.
And when they're considered as a whole,
I think you'll see why high-speed, digital computers
are absolutely essential for performing these tasks.
So, number one, you always need to know
what the telescope's orientation is at all times,
and this is accomplished with six star trackers.
Two, I assume on the end of each of three axes
that look out in opposite directions,
and so that will tell you where you are at the moment.
But then when you get ready to observe something else,
you have to generate slewing commands that will move
the telescope from one position or one object to another.
And this also needs to be done in an efficient manner
in order to save fuel in these maneuvers.
And I might also mention both one and two there
require a pointing accuracy of better than one arc minute.
Now that's less than 1/60th of a degree in angle on the sky,
so this is a high precision operation.
You also need to know when the celestial objects
might appear too close to the sun or moon or wind up
behind the earth, and where they could not be observed.
So, you have these safety checks.
And then every so often, at least, you also have
to reposition the spacecraft as a whole
to allow the solar panels then to recharge its batteries.
And those require additional slewing commands.
So, all of these things must be accomplished.
The OAOs like any satellite or spacecraft use an independent
coordinate system with three axes of rotation that are known
as roll, pitch and yaw, respectively.
So to solve all four of those principle tasks
required the writing of a complex computer program,
that would enable it to perform all of the calculations
to make the many logical decisions needed
to carry out the slewing commands,
and perform the safety checks to know
whether you could or could not observe a celestial object
at a particular time, and no other system
of this complexity had ever been created before.
Now, the computer program which was written in FORTRAN
was developed by UW graduate student,
Harry or Curt Heacox, the name he goes by,
which earned him a master's degree
from the Department of Astronomy,
and there is the title page of his thesis there on the left.
The program was named HARUSPEX,
an acronym I won't explain here.
But Heacox's advisor was SAL Scientist John McNall.
And Heacox is there on the right in that image,
beside him is Kathy Stittleburg who began
as an assistant and ended up staying a long time
with the program, and becoming associate director
of SAL after something like 20 to 30 years.
So, that as far as I know is the only image we have
of Heacox from that time frame.
Now, this program was then run on an
IBM 360 mainframe computer at the Goddard Spaceflight Center
there in the Greenbelt, Maryland,
which was the overall manager of the OAO program.
But the program also provided an interface
to the Wisconsin team's ground operating station,
shown with people around it here,
which ran on a smaller Digital Equipment Corporation
minicomputer.
This machine had only 32 kilobytes,
not megabytes of memory,
and was operated by a teletype.
How things have changed.
The minicomputer displayed the status
of the Wisconsin team's equipment,
such as the filter positions, gains, voltages,
and temperatures of all of the instruments.
And if an emergency arose, it could communicate
directly with OAO assuming that the ground station
was in contact with the satellite.
And the program HARUSPEX was also used
to prepare future observing schedules,
which might extend for about a week's time.
Well, it's now time to talk about the three kinds
of scientific instruments that went into
the Wisconsin Experiment Package,
or WEP, and how they were assembled into a single unit.
Now, NASA had previously selected the Grumman Corporation
from Long Island, New York as the prime contractor
of the OAO's standard platform, shown there.
And that alone had a weight of roughly 3,400 pounds.
Each team's payload was then restricted
to a weight of around 500 pounds.
Now, to be clear the Wisconsin and Smithsonian packages
were to be united in the first OAO satellite,
although each team had significantly different goals,
as well as working styles.
Neither team however had the full in-house resources needed
to build the packages themselves,
and so both teams solicited bids from outside contractors
for their respective packages.
But the Wisconsin teams' reluctance to place its investment
in the hands of a large bureaucratic organization
that was located perhaps one or two thousand miles away.
So, instead they selected the much smaller
and nearer Cook Technological Center.
It was located at Morton Grove,
Illinois, outside of Chicago.
And this regional company more nearly matched
their own less formal organizational style,
and perhaps most important of all,
they could drive down there in about two hours and see it.
So, Cook thus designed and tested all
of the electronic circuitry used in the WEP,
although the SAL team performed the actual assembly.
And the chief electronics engineer
there at Cook was Curtis Bendell.
Now, for reasons of redundancy as well as to maximize
the UV spectral ranges that could be observed in the WEP,
they consisted of seven co-aligned scientific instruments
[unintelligible]
and the longest one shown here which took up
the central portion of the cylinder
was a 16-inch diameter reflecting telescope,
that was equipped with a photoelectric photometer.
And with it having the largest light grasp
of the OAO telescopes, it was used to examine
the ultraviolet spectrum of nebulae and galaxies,
and other extended objects.
Now, it was surrounded by four identical eight-inch,
off-axis telescopes that were also equipped
with photoelectric photometers.
And these were used you upon stellar
or other point-source targets,
and had narrow fields of view, and thus
requiring the high pointing accuracy.
Now, between the eight and the 16-inch telescopes,
they gave SAL scientists a range of sensitivity
of somewhere between about four and six orders of magnitude,
that is powers of 10, in their observations.
Now, the final two instruments were
nearly identical scanning spectrometers,
that also employed eight-inch diameter optical systems,
but what made them different was the incoming UV light
was first directed onto a plane grating,
which dispersed that light into its component colors.
And the light was then directed into a telescope
and finally focused onto a photometer.
But now during an observation, the grating was
slowly tilted by a drive motor, and which
then allowed the brightness measurements
to be made in 100 equal steps along the spectrum.
And I'd like to emphasize that these spectrometers produced
very accurate readings of the ultraviolet energies
of stars, and were what Professor Code had envisioned
in the beginning in the wake of Sputnik.
Now, in the light of what was to come,
I also need to briefly describe the other instrument package
aboard the OAO-2 satellite, and this was the one constructed
by the Smithsonian Astrophysical Observatory,
or SAO for short.
And it was named Project Celescope,
short for celestial telescope.
And they planned to install four roughly identical,
ultraviolet-sensitive television cameras
into the other end of the module.
And their goal was to photograph long-exposure,
two-degree-by-two-degree images of the sky
whose characteristics could then be examined afterwards.
This also meant that the pointing accuracy needed
for Celescope was actually far less critical than
that needed for the narrow-angle instruments aboard the WEP.
Now, by 1966,
the WEP had passed all of its pre-flight inspections,
and was declared ready for launch.
However, Project Celescope remained incomplete
from their inability to secure the UV-sensitive
cameras from its contractor.
And I guess the expected delays were thought
to maybe last another year or so,
before they could be resolved, and thus
NASA was forced to come up with a last-minute
substitution for the Celescope experiment.
And then in its place, two MIT physicists named
William Kraushaar and George Clark
were made principle investigators on a gamma ray detector,
while two other physicists, Phillip Fisher
and Kenneth Frost, were the principle investigators
on two soft X-ray experiments.
Now, Professor Kraushaar later joined the faculty
of the Physics Department here at Madison.
And by April of 1966 these two substitute experiments were
also deemed ready to launch, although in retrospect
this may have been a somewhat poor management decision
on NASA's part, because the rush nature
of these latter two experiments
may well have led to their failures.
Now, when the first five or six launch attempts
of OAO-1 were scrubbed for various reasons,
the Wisconsin team had to go on virtually no sleep
to prepare for the next attempt,
because they've got to reprogram the computers
and everything to be ready.
But at last on April 8th, 1966,
OAO-1 was successfully launched
from the Kennedy Space Center in Florida.
But major problems soon developed with the satellite's power
and guidance systems, and it's thought
that one of its batteries may have exploded
from some high-voltage arcing.
And after two days all contact with the satellite was
permanently lost, so not a single astronomical observation
had been performed with either instrument package.
And this naturally was a devastating blow
to the Wisconsin team and others whose timing
it was later realized was marked
by a perverse symbolic coincidence,
because OAO-1 had been launched
on Good Friday and died on Easter Sunday.
(audience members laughing)
Read into that what you may, if you wish.
(audience member laughing)
But not all was lost, however,
because another full-scale prototype
of the OAO had already been built
and could be adapted to make it space worthy.
It meant, however, that the Wisconsin team would have
to completely rebuild their experiment package,
which they did.
NASA thus resorted to its original flight schedule,
as if OAO-1 had never happened,
and this finally united the new WEP
with the Smithsonian's Celescope experiment.
And it also kept the remaining Goddard
and Princeton teams and experiments
in their original pipeline, so to speak.
So, after another two and one-half years,
these teams were ready to try their luck again.
Fingers crossed.
Now, this time the OAO-2 satellite was successfully launched
by this Atlas-Centaur Rocket on December 7th, 1968.
And it was placed into a nearly circular orbit
some 480 nautical miles high,
and was inclined some 35 degrees to the earth's equator.
Now, the new mission's expected lifetime though
had been reduced to only year.
Yet, the satellite lasted more than four times that long,
making observations over a 50-month period,
that again reached over a thousand celestial objects.
Project Celescope, by contrast, only exceeded
its expected lifetime by four months.
Now, there was, however, one notable instrument failure
on the WEP that occurred roughly
two and a half months into the mission.
And there the circuitry that controlled a stepper motor,
which turned a filter wheel on the 16-inch telescope
stopped working, and the calibration source
was permanently positioned in front of the light path.
Oops.
That unfortunately eliminated any more data gathering
with the WEP's largest instrument.
But that's why you chose redundancy in your design.
Now, also troubling to the Wisconsin team
was a planned financial move on NASA's part
to shut down the OAO-2 at the end of June 1971,
because the satellite had then exceeded, I'm sorry,
its expected lifetime by two and a half times.
But the Wisconsin astronomers mounted an intensive lobbying
effort that caused the space agency to rethink
its decision, and as a result kept funding
for the still active satellite intact,
until its eventual demise.
Now, the scientific results from OAO-2 have been published
in a number of places, and a majority
of those findings were first reported
in a series of 41 successively numbered research papers,
that appeared in the Astrophysical Journal,
between 1970 and 1982, that were authored
by Professor Code and his colleagues.
This is number one in that series.
And a symposium was also convened by NASA,
and the American Astronomical Society
at Amherst, Massachusetts in August of 1971.
And its proceedings, shown there on the right,
have formed the principle monograph of the OAO-2 results,
and which was also edited by Professor Code.
And various catalogs of the OAO's data have
likewise appeared through the years, at least through 1999.
Now, in the limited time that I have left,
I'll try to present a very brief summary
of the most important findings that came from OAO-2,
but with an emphasis on those acquired by the WEP.
And at the head of that list, WEP gathered
the first true measures of the spectral energies
of hot stars in the ultraviolet,
as Professor Code had long sought to do.
And this data led to more precise determinations
of stellar temperatures and their chemical compositions.
Now, the previous temperature scale
that had been extrapolated from visual light observations
was found in fact to be too low.
And chiefly among O and B-type stars,
which were the hottest, the absolute luminosities
of around 150 of those stars were determined
to an accuracy of around 10%.
Now, around a quarter of the O and B stars
also lent themselves to an independent measurement
or derivation of the so-called interstellar extinction
or reddening factor within the Milky Way Galaxy.
And these results offered a confirmation
of the densities of interstellar hydrogen gas,
that were certainly not at variance from
other measurements taken from radio astronomy.
The spectra of a number of peculiar stars were observed,
and the strengths their ultraviolet emission lines
were measured, and that evidence suggested
that these stars were surrounded by expanding shells of gas.
And this led toward improved models of the processes
of mass loss in such highly evolved stars.
Now, a fortunate occurrence was the chance
to monitor the behavior of a nova,
that is Nova Serpentis, 1970, following its outburst.
And OAO-2 first showed that the UV brightness
continued to increase even while
the visual brightness was decreasing.
And this finding supported the notion of an
optically thick shell of material around the star,
that may have behaved analogously to
that of so-called planetary nebulae
seen around lower mass stars.
Now, most of these so-called dark nebulae appeared brighter
at UV wavelengths than did ordinary diffused
or gaseous nebulae when seen in visible light.
And this finding implied that interstellar dust grains,
whatever they were, had much higher UV albedos,
or reflectivities, than was expected.
And this evidence also suggested at that time
that these grains might consist of graphite particles,
although it is now considered that other kinds
of hydrocarbon compounds may in fact be the
more likely sources or makeups of those kinds of particles.
And it was found that galaxies on average are brighter
in the ultraviolet than was expected.
Just from the known main sequence stars that make them up.
And therefore, the populations of O and B stars
in these galaxies' discs evidently turned out
to be larger or higher than had been expected.
Now, some important discoveries were also made
in our own solar system.
For instance, OAO detected vast clouds of hydrogen gas
around the nuclei of two different comets.
And the hydrogen clouds were measured
to extend some 100,000 kilometers away
from the comet's nucleus, that is they were
even larger than the sun.
Now, these observations actually confirmed an
earlier prediction that such clouds might exist,
and they provided evidence that a comet's nucleus is
largely made of water ice,
which breaks down into its atomic components
under the action of intense sunlight.
And finally, OAO-2 detected the presence
of ozone gas in the atmosphere of Mars.
And this finding was later confirmed
by the orbiting Mariner spacecraft,
and is judged to have offered some important clues
to the chemistry and evolution of the martian atmosphere.
Now, if time permits, I'd just like to provide a brief set
of conclusions about the importance, again,
of OAO-2 on the 50th anniversary of its launch.
That is that OAO-2 may be credited
with a number of firsts in the field of astronomy.
And for example, it was the first true
stellar space observatory,
having been launched, again, more than two decades
before the Hubble Space Telescope.
And from its computer-operated control systems,
OAO-2 represented a greater technological step forward
in its day than did the Hubble itself.
'Cause now all of the standard control techniques that
require knowledge of the telescope's orientation
and allow efficiently moving the telescope from one object
to another, and all of the safety checks needed
to prevent potentially harmful observations,
these were all first performed successfully on OAO-2.
And as well,
it marked the first significant opening
of the electromagnetic spectrum to wavelengths shorter
than visible light, and let me just give you an analogy
here that Professor Bless often used
to describe this innovation.
The electromagnetic spectrum may be likened
to the totality of sounds or musical notes produced,
say, by a symphony orchestra, yet visible light corresponds
to a very narrow range of perhaps only a few notes
on that composite sound spectrum.
But that is all that optical astronomers had been able
to hear for centuries.
And thus, over the past 50 years or more,
astronomy has opened similar windows
into just about every part of the electromagnetic spectrum:
again, from gamma rays and X-rays and ultraviolet
up to infrared and microwave and radio waves.
So, we now pretty much covered it all.
And then perhaps most important of all,
OAO-2 marked this other significant milestone
in astronomical research, and this was the growing
dependence placed upon digital data gathering,
storage, transmission, and analysis
that is practiced throughout astronomy, and I would say
virtually all other scientific disciplines, today.
And to quote Professor Code here
from a 1969 article about OAO-2,
"High-speed computers are essential to the astronomer"
for carrying out these many tasks.
At that time, however, digital computing as we've shown
meant using mainframes, like the IBM
and smaller minicomputers
in the Wisconsin ground operating station.
Thus, it should be remembered that this transition
to digital computing took place well before
the introduction of desktop or personal computers,
starting in the late 1970s and before the so-called
charge-coupled device or CCD
became another universal piece of astronomical equipment.
So by and large, apart from the telescope,
or the spacecraft used itself,
a computer is perhaps the single most important tool
that an astronomer uses today.
So, I hope that we've been able to give you here
a greater appreciation for the significance
of OAO-2's launch, which is now 50 years behind us.
So, thank you for your attention this evening,
and if you have any questions, I will try
to answer them now, but let me just throw in one more thing.
If you'd like some more information about OAO-2,
then you might find it within this paper
that I published on its history, in reference given there.
Thank you very much.
(audience applauding)