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Subject: SPACE Digest V13 #316

SPACE Digest                                     Volume 13 : Issue 316

Today's Topics:
                SIRTF
     Space Station Press Conference Scheduled (Forwarded)

Administrivia:

    Submissions to the SPACE Digest/sci.space should be mailed to
  [e-mail].  Other mail, esp. [un]subscription requests,
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Date: 20 Mar 91 19:03:19 GMT
From: magnus.acs.ohio-state.edu!zaphod.mps.ohio-state.edu!usc!snorkelwacker.mit.edu!hsdndev!frooz![e-mail]  (Steve Willner, OIR)
Subject: SIRTF

The Bahcall committee has just released its 10-year report on priorities
for new astronomical instrumentation.  The highest priority is the Space
Infrared Telescope Facility (SIRTF).  Following is a JPL press release
describing SIRTF with my comments in [brackets].  [Note: I have the
information that SIRTF is number 1 from a reliable source but not directly
from the committee announcement, so it is possible that one of us has
misunderstood.  Lengthy reports on the Bahcall committee recommendations
will be published in Physics Today and in Sky and Telescope.]

            SPACE INFRARED TELESCOPE FACILITY (SIRTF)

     A NASA mission that could probe hundreds of thousands of celestial
objects invisible to conventional telescopes is under study at the Jet
Propulsion Laboratory.

     The Space Infrared Telescope Facility (SIRTF) would launch an
orbiting observatory to study the universe in the infrared.  SIRTF --
pronounced sir-tiff -- is proposed as a NASA new start in fiscal year
1994.

     During its five years of operation the telescope would collect
images of the birth of stars and galaxies; study objects ranging from
nearby comets and asteroids to the distant beacons of quasars; and
search for solar systems around other stars in ways impossible for
optical telescopes.

     SIRTF would complete NASA's series of "Great Observatories,"
telescopes in Earth orbit that study the universe at wavelengths
ranging from visible light to X-rays and gamma rays.

     The new spacecraft would render its images not from the palette of
colors in visible light but rather from the infrared energy -- or,
simply, radiated heat -- from celestial objects.

     Conventional optical telescopes can only study stars and other
objects that are glowing brightly enough to emit light in the visible
spectrum.

     Yet many of the most intriguing phenomena in the universe --
planets forming around other stars, vast stretches of dark dust, stars
in the process of birth -- are invisible in the regular spectrum.  They
are bright, however, in the infrared.

     Other celestial objects that give off visible light are hurtling
away from us so rapidly that the effect of "red shift" moves the light
energy we see into the infrared.

     Because any heat from SIRTF itself would interfere with
observations of distant celestial objects, special cooling equipment
must be installed onboard the orbiting telescope.

     The telescope itself would be surrounded by a massive cooling
system filled with liquid helium.  The equivalent of a giant Thermos
bottle, the system keeps the infrared detectors and the telescope
cooled to less than 2 degrees Celsius (4 degrees Fahrenheit) above
absolute zero, -273 C (-459 F).

     As currently envisioned, SIRTF could be launched in 2001 on a
Titan IV rocket into an orbit 100,000 kilometers (about 60,000 miles)
above Earth.

     The unusually high orbit -- higher even than that of geostationary
communications satellites -- is designed to put SIRTF beyond not only
Earth's obscuring atmosphere but also the Van Allen radiation belts
encircling Earth.

     The spacecraft's 90-centimeter-diameter (35-inch) mirror will be
teamed with three sensitive instruments:  the Infrared Array Camera and
the Multiband Imaging Photometer, which together will provide imaging
at all infrared wavelengths; and the Infrared Spectrograph, which will
study the chemical spectra of objects.

     SIRTF is a follow-on to the Infrared Astronomical Satellite
(IRAS), a joint mission of the United States, the Netherlands and the
United Kingdom.  Launched in 1983, IRAS gave astronomers a profoundly
new view of the universe -- revealing hundreds of thousands of new
stars and galaxies, discovering new comets and offering the first
glimpses of solar systems forming around other stars.

[They might also have mentioned the Infrared Space Observatory (ISO),
which is scheduled to be launched by ESA in 1993.  ISO is sort of
intermediate between IRAS and SIRTF, with an 18 month lifetime,
pointing capability, and more detectors than IRAS but far fewer than
SIRTF.]

     The IRAS mission, however, was designed only to conduct a
relatively brief sky survey.  The mission ended when the helium coolant
onboard IRAS was depleted after 10 months in orbit.

     SIRTF will be at least 1,000 times more sensitive than IRAS and
will operate six times longer.  Whereas IRAS used a system of 60
infrared detectors, SIRTF will take advantage of new types of arrays
with up to hundreds of thousands of detectors.  Combined, those
capabilities will allow SIRTF to carry out a rich diversity of highly
detailed observations pushing considerably beyond the general sky
survey provided by the previous satellite.

     A launch in 2001 would put SIRTF in orbit two centuries after
infrared energy was discovered by the German-English astronomer Sir
William Herschel in 1800.

     Herschel -- also known as the discoverer of the planet Uranus --
was examining how sunlight is broken down into various colors by a
prism.  While carrying out experiments he decided to compare the
temperatures of the various colors of light.

     After placing thermometers in patches of colored light cast by a
prism, Herschel happened to place a thermometer in the seemingly dark
area beyond the red patch of light.  He was surprised to find that
there, too, the thermometer registered a temperature increase.

     In his paper reporting the experiment, Herschel told of his
discovery of "invisible rays of the Sun" transporting radiant heat --
what would become known as infrared energy.

     The first infrared observation of a star other than the Sun was
made not by a professional astronomer but by the American inventor
Thomas Alva Edison in 1878.

     A year after his invention of the phonograph, the 31-year-old
Edison -- then the holder of 89 patents -- learned of a total solar
eclipse that would be visible from the western United States.

     For the occasion, Edison fabricated an infrared sensor he called a
"tasimeter" capable of detecting temperature changes of as little as a
millionth of a degree.

     Traveling by train to the Wyoming Territory, Edison met up with
astronomers and set up his equipment in a frontier hen house to observe
the eclipse.  While adjusting his device he trained it on Arcturus, a
bright star in the constellation Bootes -- thus inaugurating the
discipline of infrared astronomy.

     Edison's astronomical interests soon fell by the wayside as he put
his energies into the incandescent light bulb and his other inventions
to come.  Most of the attention in astronomy shifted to the very large
optical telescopes being built on mountaintops around the turn of the
century.

     By the mid-20th century, improvements in technology allowed
astronomers to extend their vision beyond visible light to study unseen
radiation -- radio waves, X-rays -- coming from sources in the
universe.

     Infrared energy proved more difficult to study, however, because
most of the faint amounts coming from distant stars and galaxies is
blocked by Earth's atmosphere.

[A much greater problem is infrared emission from the atmosphere and
from the telescope itself.]

     In the 1960s astronomers worked to overcome this obstacle by
placing infrared instruments in NASA jets flying at altitudes of up to
50,000 feet, and on balloons ascending as high as 100,000 feet.

     Although revealing, these studies were inevitably limited because
of the short duration of the jet flights and the difficulty of
controlling the balloons precisely.

[All this gives rather short shrift to ground-based infrared
astronomy.  Before IRAS, a compilation found that something like 10000
celestial objects had been studied in the infrared, mostly from the
ground.  A sky survey completed in the mid-60's cataloged about 5000
objects.  It is still quite true that SIRTF will be an enormous advance
over all previous work.]

     The most dramatic look at the infrared universe thus still awaited
astronomers until the launch of IRAS in January 1983.  During its 10
months in orbit, IRAS amassed a sky catalog of some 250,000 objects.

     Directed at the bright star Vega in the constellation Lyra, IRAS
found too much heat to be accounted for by the star alone.  Astronomers
concluded Vega is surrounded by an orbiting swarm of pebble-sized dust
grains that could be remnants from the formation of a planetary
system.

     Sifting through IRAS data, astronomers have since identified more
than a dozen other stars that appear to be orbited by such solar system
debris.

     The 1983 satellite also captured intriguing views of stars in the
process of birth and decline, as well as the first assessment of dark
dust woven through the Milky Way Galaxy between the visible stars.

     Within the solar system, IRAS discovered a half dozen new comets,
including one that passed within 3 million miles of Earth as it swept
inward toward the Sun.

     Because of its limited lifetime -- dictated by the amount of
liquid helium onboard -- and the capabilities of its sensors, IRAS was
destined to provide a general sky survey that raised as many questions
as it answered.

     Such questions are the focus for the SIRTF mission.

     One area SIRTF will be able to probe is the realm of very young
galaxies in the process of forming.  Many of the stars in such galaxies
are cool red giants that are most visible in the infrared spectrum.
Visible light from such galaxies is often obscured by dust surrounding
the galaxies.

     Violent collisions between galaxies that could be responsible for
the origin of quasars is another topic for SIRTF study.  Quasars and
other active galactic nuclei are thought to be powered by massive black
holes at their centers, but much of this activity is obscured by gas
and dust.  SIRTF will provide a better picture in the infrared.

     Gas and dust similarly throw a cloak around the birth of stars,
both nearby within the galaxy and beyond.  SIRTF will be able to study
star formation in areas including nearby stellar nurseries where stars
like the Sun are being created.

     The creation of heavy elements when stars collapse and abruptly
burst as supernovas is another area for SIRTF study.  The orbiting
telescope will be sensitive enough to examine supernovas tens of
millions of light-years away.

     SIRTF will also be able to search for brown dwarfs.  These are
bodies -- some orbiting stars, others on their own -- which are much
more massive than even giant Jupiter-sized planets but are too small to
ignite as stars themselves.  Though predicted by theory, their
existence as yet remains to be confirmed.

     IRAS's revelation of what may be signs of solar systems swirling
around other stars will be greatly improved upon by SIRTF.  The new
spacecraft will be able to examine the systems that IRAS discovered in
much greater detail, and search for other systems.

     Closer to home, SIRTF's capabilities will be useful in studying
planets, comets, asteroids and dust within the solar system.  Chemical
spectra from SIRTF's instruments will give definitive information, for
example, on the atmospheres and icy surfaces of Pluto and its moon
Chiron -- the only known planet as yet unvisited by a NASA spacecraft.

     And at the other extreme of the cosmos, SIRTF will provide data on
infrared sources that will be help astronomers understand data from
NASA's Cosmic Background Explorer (COBE) satellite.  Launched in 1989,
COBE studied background infrared and microwave radiation, including the
radiation believed to be left over from the Big Bang that gave rise to
the known universe.  Along with IRAS, COBE was the chief predecessor to
SIRTF in the technologies needed to launch a space infrared telescope.

     Many scientific inquiries will benefit from combining observations
from SIRTF with those from NASA's other "Great Observatories" -- the
Hubble Space Telescope, the Gamma Ray Observatory and the Advanced
X-ray Astrophysics Facility.

     When the nearby supernova SN 1987A burst into view four years ago,
for example, astronomers took advantage of special NASA expeditions
using balloons and airborne observatories to study the exploding star
at all wavelengths.  SIRTF and the other orbiting observatories will be
able to gather similar data on much more distant supernovas.

     Project management for SIRTF has been assigned to NASA's Jet
Propulsion Laboratory, Pasadena, Calif.  Other participating centers of
the space agency include NASA Headquarters, Washington, D.C.; NASA's
Ames Research Center, Moffett Field, Calif.; and NASA's Goddard Space
Flight Center, Greenbelt, Md.

     Participating in the development of SIRTF and its instruments are
scientists representing the California Institute of Technology; Cornell
University; Pennsylvania State University; Smithsonian Astrophysical
Observatory; Steward Observatory of the University of Arizona;
University of California, Berkeley; University of California, Los
Angeles; and University of Rochester.

     In addition to SIRTF's investigators, astronomers in the general
scientific community will be invited to use more than 85 percent of the
observing time on the orbiting telescope.

     At JPL, Richard Spehalski is SIRTF project manager.  Dr.  Michael
Werner is project scientist.  JPL manages the SIRTF project for NASA's
Office of Space Science and Applications.

                  #####
-------------------------------------------------------------------------
Steve Willner            Phone [phone]         Bitnet:   willner@cfa
Cambridge, MA 02138 USA                 Internet: [e-mail]

------------------------------

Date: 20 Mar 91 21:42:53 GMT
From: swrinde!elroy.jpl.nasa.gov!jato!mars.jpl.nasa.gov![e-mail]  (Ron Baalke)
Subject: Space Station Press Conference Scheduled (Forwarded)



Mark Hess
Headquarters, Washington, D.C.                                                                     March 20, 1991
(Phone:  [phone])


N91-21

SPACE STATION PRESS CONFERENCE SCHEDULED


        A press conference to discuss the newly restructured Space Station
Freedom will be conducted on Thursday, March 21, 1991, at 10:30 a.m. EST in
the NASA Headquarters 6th floor auditorium, 400 Maryland Avenue, S.W.,
Washington, D.C.

        Participants include Dr. William B. Lenoir, Associate Administrator
for Space Flight, and Richard H. Kohrs, Director, Space Station Freedom.

        The conference will be carried on NASA Select television with
two-way question and answer capability (Satcom F2R, transponder 13, 72 degrees
West longitude).

        The monthly Space Flight briefing, scheduled for this date, has been
cancelled.

-end-
      ___    _____     ___
     /_ /|  /____/ \  /_ /|      Ron Baalke         | [e-mail]
     | | | |  __ \ /| | | |      Jet Propulsion Lab |
  ___| | | | |__) |/  | | |___   M/S 301-355        | Change is constant.
 /___| | | |  ___/    | |/__ /|  Pasadena, CA 91109 |
 |_____|/  |_|/       |_____|/                      |

------------------------------

End of SPACE Digest V13 #316
*******************