NASA Technical Reports Server (NTRS) 19930009803: Extreme Ultraviolet Explorer. Long look at the next window

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by  NASA Technical Reports Server (NTRS)

NASA-TM-108618
Extreme Ultraviolet Explorer
Long Look
at the
Next Window
(NASA-TM-108618) EXTREME N93-18992
ULTRAVIOLET EXPLORER. LONG LOOK AT
THE NEXT WINDOW (NASA) 26 p
Unclas
G3/90 0131697
OR PAGE
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NASA
"Produce ships and sails that can be used In
the celestial atmosphere. Then you will also
find men to man them, men not afraid of
the vast emptiness of space."
lohannes Kepler
ORIGINAL CONTAINS Table of Contents
COLOR ILLUSTRATE
Unexplored Window 3
Extreme Ultraviolet Explorer 3
Unique Spacecraft 3
Advanced Technology 4
Cosmic Survey 4
Astronomical Windows 4
New Secrets 5
Extreme Ultraviolet Radiation 6
Roadblocks to Extreme Ultraviolet Astronomy 7
Accepted Knowledge 7
Technological Limitations 7
Geocoronal Interference 7
Extreme Ultraviolet Astronomy Becomes Possible 8
Thin Bubble 8
Apollo-Soyuz 9
White Dwarfs 9
Exploring Space: Rockets, Explorers, and Observatories 10
Scorpius X-1 10
Uhuru 10
Opening the Extreme Ultraviolet 11
The EUVE Mission 12
Orbital Checkout 12
All-Sky Survey 12
Deep Survey 12
Survey Phase 13
Spectroscopy Phase 13
Better Than Voyager 13
Retrieval 13
The EUVE Instruments 14
Smooth Mirrors 14
Spectrometer 15
Sir Isaac \e\\ton 15
Cutting Edge 15
The Explorer Platform 76
Solar Arrays 76
Toaster Oven 76
10-Year Lifetime 17
Command and Control 17
Tracking Satellite 17
Newton's Law 17
What Will EUVE Find? 18
Mapping Galactic Gas 18
Not Ordinary 18
White Dwarfs 79
Neutron Stars 79
Red Dwarfs 20
B Stars 21
Dwarf Novae 21
lo Torus 22
Quasars 22
EUVE Mission Management 24
EUVE Team 25
* *• "
Unexplored Windows
A NASA satellite designed to scan the Extreme Ultraviolet Explorer and other sources of EUV radiation,
heavens in one of the last largely unex- EUVE will map the entire sky to maybe even quasars.
plored windows of the electromagnetic determine the existence, direction, bright- EUV radiation, a principal emission of
spectrum will be launched from Cape ness, and temperature of thousands of many types of celestial objects, is wholly
Canaveral, Florida in 1991. The Extreme objects that are sources of so-called blocked by the Earth's atmosphere.
Ultraviolet Explorer (EUVE) will be a extreme ultraviolet (EUV) radiation. The Until recently, it was believed to be
vital element in astronomers' efforts to EUV spectral region is located between blocked by the interstellar gas of our
understand the universe by discovering the x-ray and ultraviolet regions of the Milky Way galaxy as well. As such, it
what objects are present, and how they electromagnetic spectrum. From the sky was sometimes known as "the
form, change, and die. Scientists want survey by EUVE, astronomers will deter- unobservable ultraviolet."
to learn what natural processes are at mine the nature of sources of EUV light Unique Spacecraft
work in the alien environment of space, in our galaxy, and infer the distribution The EUVE will be a spacecraft of a
where the everyday physical conditions of interstellar gas for hundreds of light
new type. Its scientific instruments will
are often so unlike those on Earth that years around the solar system. It is from be mounted in a single module on an
they cannot be duplicated usefully in this gas and the accompanying dust in orbiting platform, or spacecraft "bus,"
the laboratory. space that new stars and solar systems like containerized cargo that is easily
are born and to which evolving and
transferred from an ocean freighter to a
dying stars return much of their railway flatcar. The platform will provide
material in an endless cosmic cycle of
electrical power, communications,
birth, death, and rebirth. Besides
mechanical support and pointing
surveying the sky, astronomers will
control for the EUVE module. Although
make detailed studies of selected
EUVE will be launched on an
objects with EUVE to determine their
expendable rocket, a new module,
physical properties and chemical containing new scientific instruments,
compositions. Also, they will learn
will be transported to it by the Space
about the conditions that prevail and Shuttle once the EUVE mission is
the processes at work in stars, planets, completed. The new module will be
PRECD€ !NG PAGE BLANK NOT HLMtU
Three examples of interstellar gas and dust.
LEFT: The North American Nebula in
Cygnus
TOP: Ring Nebula in Lyra
ABOVE: Orion's Horsehead Nebula
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RIGHT: Artist conception of the EUVE
spacecraft in orbit
swapped for the EUVE unit by the ground control centers. Goddard also followed by a spectroscopy phase of at
crew, using the Shuttle's Remote pioneered the development and least one year.
Manipulator System. This design allows operation of the first reusable In the spectroscopy phase, individual
reuse of unmanned spacecraft just as unmanned spacecraft designed specifically targets, whether discovered in the all-sky
the Shuttle allows reuse of a manned for recovery and servicing in space. and deep-sky surveys or identified from
vehicle. This concept also allows for Advanced Technology other information, will be analyzed in
ready servicing in space, should space- EUVE will carry a full complement of detail through individual observations
craft subsystems or instruments degrade. telescopes, detectors, and a spec- made with an on-board EUV spectrometer.
To develop the EUVE, NASA enlisted trometer. The equipment incorporates Typically, a spectrometer observation
the University of California at Berkeley advanced technology from the United will last from one to several days. The
and the NASA/Coddard Space Flight States and Japan. The EUVE instrumen- EUVE surveys will be conducted by the
Center in Creenbelt, Maryland. The tation will be mounted in a Payload Berkeley astronomers, while the spectro-
Berkeley astronomers and physicists, Module on NASA's new reusable Explorer scopic studies will be performed by
led by Professor Stuart Bowyer, have Platform, designed and managed by the Guest Observers who may be associated
pioneered the exploration of space in Coddard Space Flight Center (GSFC) with scientific or educational
the extreme ultraviolet with investi- and built by the Fairchild Space institutions. NASA Headquarters, in
gations by sounding rockets and Company. The Payload Module was Washington, D.C., will select these
manned spacecraft. Also Berkeley has designed, built and tested at GSFC. Guest Observers from throughout the
developed the necessary technology United States and around the world, on
Cosmic Survey
and instruments for EUV astronomy, the basis of scientific merit.
The scientific mission of EUVE will
and pioneered the scientific When the extreme ultraviolet astronomy
consist of a six-month all-sky survey, in
interpretation of the results of such research is complete, a Space Shuttle
which the heavens are mapped in four
experiments. Coddard has a proud will dock with the EUVE so that the
channels of the extreme ultraviolet
history as the developer of unmanned Shuttle crew can bring it onboard with
spectrum while a narrow band in the
Explorer-class and observatory-class the Remote Manipulator System (robot
sky is mapped at even greater sensitivity
satellites, a world-wide tracking/ arm). The extreme ultraviolet astronomy
in a deep-sky survey. This will be
communications network, and associated payload will be replaced with the
payload for a new scientific investi-
gation, the X-ray Timing Explorer (XTE).
Astronomical Windows
The EUVE studies come as a logical
complement to past Explorers that have
scanned space in the infrared,
ultraviolet, x-ray, and gamma-ray
regions. As each of these so-called
"windows" of the universe has been
opened to detailed study by Explorer-
class instruments, wholly unexpected
objects and phenomena have been
discovered, and unusual physical
Milky Way Galaxy as a satellite streaks in
front of it
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processes have been found to be at with a single kind of microscope, one member is almost surely a black
work. Astronomers learned that they chemical tool, or analytical procedure. hole. A black hole is a condensed dead
can no more study our galaxy—or a Just as each kind of biochemical star whose gravity is so powerful that
single star—in proper depth with one technique involves different types of even light cannot escape it.
kind of telescope operating in a single laboratory apparatus or a different set The International Ultraviolet Explorer
spectral region, than biomedical of chemical reagents, each form of (IUE), operated jointly by NASA, the
researchers can study the human body electromagnetic radiation or light European Space Agency and the United
requires distinct types of telescopes, Kingdom Science and Engineering
Final inflation stage of balloon carrying
associated instruments, and sensors for Research Council, found a hot corona
scientific instruments at sunrise near
Palestine. Texas. its study. surrounding our Milky Way galaxy. IUE
New Secrets also discovered a glowing shell of gas
Each new window brings unexpected caused by the collision of high- and
marvels into the astronomers' view. low-speed winds emitted by a star that
Mapping the sky in infrared light, the later exploded as a supernova, and a
Infrared Astronomical Satellite, a joint previously undetected form of sulfur in
United States-United Kingdom- a comet that made a close swing past
Netherlands spacecraft, discovered the Earth.
what may be planetary systems in Telescopes sensitive to gamma rays
formation, circling stars beyond the aboard balloons, rockets, and the Solar
Sun, and the eerie glow of dust trails of Maximum Mission satellite detected a
long-vanished comets that once orbited spectral emission from the central
in our solar system. region of the Milky Way that is caused
Einstein, as the High Energy by the mutual annihilation of matter
Astrophysics Observatory-3 satellite was and antimatter. The message is clear:
popularly known, found and open a new window on space and we
investigated binary stars in the Milky are sure to find as-yet-unknown secrets
Way and a neighbor galaxy in which of the universe.
VISIBLE
LIGHT
GAMMA RAYS X - RAYS EXTREME ULTRAVIOLET INFRARED
ULTRAVIOLET
Angstroms 0.1 A 100A 912A 7,OOOA 10,000,OOOA (1 millimeter)
Electron volts 121,720ev 121.8ev 13.6ev 1.7ev .001ev
Interstellar
cut-off
Artist's conception of the electromagnetic spectrum
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Extreme Ultraviolet Radiation
EUV radiation is defined as the range
of the electromagnetic spectrum that
lies at shorter wavelengths (higher
energies) than ordinary ultraviolet light
and at longer wavelengths (lower
energies) than x-rays. As such, it
consists of light with wavelengths
between about 100 Angstroms and
1000 Angstroms. (One Angstrom, a unit of
length named for the Swedish physicist
Anders Angstrom, equals one one-
hundred-millionth of a centimeter, or
about four billionths of an inch.)
Both ordinary ultraviolet light and
x-rays also are blocked by the
atmosphere. They are known to reach
the Earth's vicinity from very great
distances in space, and have been
extensively studied by satellite
observatories above the atmosphere,
developed by the United States and
other technologically-advanced nations.
For example, ultraviolet radiation from
stars, nebulae and galaxies was studied
by NASA's Orbiting Astronomical
Observatories and by the Astronomy
Netherlands Satellite, and is under
investigation by the International
Ultraviolet Explorer. Sagittarius star cloud in the direction of the center of the Milky Way
X-rays from stars and galaxies have
been explored by the High Energy
Astrophysics Observatories, the Small
Astronomy Satellite "Uhuru," and by
such foreign craft as ESA's EXOSAT,
Japan's TENMA and GINCA, Germany's
ROSAT and the Soviet Union's MIR Space
Station. Yet, despite almost two decades
of work, exploration of space in the
extreme ultraviolet has been minimal.
ORiG
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Naval Research Laboratory experiment aboard Apollo 16 provided
this image of our geocorona
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Roadblocks to Extreme Ultraviolet Astronomy
The study of the universe in the primary mirror is positioned roughly around our planet, consisting of the
extreme ultraviolet, still in its infancy like the inner surface of the gun barrel, geocoronal helium ions glowing in the
despite space experiments flown since or like the inner surface of a cone extreme ultraviolet light of the Sun.
1971, has been hampered by three opening toward the incoming light. Other constituents of the geocorona
factors that astronomers can now Even if appropriate grazing incidence also scatter solar radiation. Located
surmount with the EUVE: accepted telescope mirrors are used, problems above the Earth, but below or within
"knowledge," geocoronal interference, remain. When the extreme ultraviolet the geocorona, satellite telescopes are
and technological limitations. light strikes the carefully shaped severely hampered by this geocoronal
telescope mirrors at angles of a few glow when they operate in the extreme
Accepted Knowledge
Conventional wisdom on our Milky degrees to their surfaces, the slightest ultraviolet. At some wavelengths, the
Way galaxy was painstakingly developed local irregularity interferes with the glow may be thousands of times
through extensive observations with skipping light rays, scattering them in brighter than a celestial target of
radio and optical telescopes on the wrong directions like golf balls that hit interest when viewed with a given
ground during the 1950s. These slight irregularities on the green and extreme ultraviolet telescope. There
observations suggested that the disk of veer away from the cup. Accordingly, appear to be only two ways to
our spiral-shaped galaxy is pervaded by the mirror surfaces must be made with minimize this interference: locate the
an interstellar medium of hydrogen, exceptional smoothness, even by the telescope outside the geocorona or
helium, and less abundant gases. Both demanding standards of the optician. operate it in a highly selective manner.
hydrogen and helium absorb extreme There are other technological Positioning a spacecraft such as EUVE
limitation as well. When EUV outside the geocorona would make it
ultraviolet light. Calculations indicated
that the hydrogen alone was enough to astronomy began in the 1960s, the impossible to service it with the Space
cut off the extreme ultraviolet light from available detectors—the devices that Shuttle in the event of malfunction, and
almost any known object beyond our actually sense the EUV radiation impossible to revisit it with the Shuttle
own solar system, which is located in collected by a telescope—were to replace the payload at the end of its
relatively insensitive. Also, there were intended operating life. Therefore,
the galactic disk. As early as 1959,
experts asserted that it would be no diffraction gratings—optical EUVE will be operated in low-Earth
impossible to observe objects much components that spread light into a orbit, below the geocorona, but
beyond the limits of the solar system in spectrum—that were well-suited to use generally will make observations at
the extreme ultraviolet. It was not until in the EUV. The EUV represented such night, when the geocorona causes the
1975 that a crucial experiment in a new departure for astronomers' least interference.
space, carried out by Professor Bowyer studies that there was no national A remaining source of natural
and his associates on the Apollo-Soyuz standard for calibrating laboratory interference, called the very local
mission, disproved this view. measurements of the intensity of EUV interstellar medium, hampers EUV
light. observations and cannot be overcome
Technological Limitations
Extreme ultraviolet light cannot be Geocoronal Interference with current technology. The very local
At the outer limits of the Earth's interstellar medium consists of
collected and focused usefully with
telescopes of conventional design; if atmosphere, far above almost all electrically neutral atoms of interstellar
ordinary optical telescopes were used, orbiting satellites, the ambient gases are gas that sweep through the solar system
so thin that a gas atom can orbit all the as the Sun and the planets move
most of the individual photons of
way around the Earth without striking through the Milky Way. Helium atoms
extreme ultraviolet light would be
another atom. Under such conditions, in this medium scatter EUV radiation
absorbed in the coated surfaces of the
the gases in this region readily escape from helium in the Sun, producing a
mirrors or scattered in directions away
from the optical axis. the Earth's gravity. They make up the dim, interfering glow that EUV
geocoronoa, a huge region that thins astronomers cannot avoid.
The extreme ultraviolet can be
observed usefully only with telescope out into interplanetary space.
mirrors designed for operation in In the geocorona there are also
helium ions, atoms of helium that have
grazing incidence mode, in which the
incoming light strikes a mirror at a very each lost one electron. These ions are
prevented from escaping into space by
small angle to its surface like a stone
skipping off the sea. Thus, in an the Earth's magnetic field. The helium
ions scatter, that is, reflect in all
extreme ultraviolet telescope, the
primary or light-collecting mirror does directions, EUV light emitted by similar
helium ions in the Sun.
not face directly toward the target like
the mirror in a conventional telescope As a result, if space travelers on the
or a searchlight. Moon or Mars were to look down on
the Earth with eyes somehow sensitive
Instead, while the EUV telescope
to extreme ultraviolet radiation, they
points at the target like a gun, its
would see a huge luminous zone
Extreme Ultraviolet Astronomy Becomes Possible
Recent advances in space astronomy
and in technology make it possible for
the EUVE mission to explore space in a
wavelength window previously called
the "unobservable ultraviolet." The
interstellar gas of the Milky Way was
once thought to be a smoothly
distributed, absorbing fog that
thoroughly blocks extreme ultraviolet
light. On further inspection, it was
revealed to be a complex array of
dense clouds embedded in a thinner
and hotter gas, honeycombed by very
thin regions shaped like bubbles and
tunnels, like an ant's nest or a rabbit
warren beneath the seemingly solid
ground.
Detectors, diffraction gratings,
ABOVE: American Apollo spacecraft
mirrors, filters, and calibration methods
photographed by Soviet cosmonauts in joint
have been developed and optimized for
US/USSR Apollo-Soyuz program
use in the EUVE. Detectors, the crucial
LEFT: Artist's conception of the Copernicus
components that sense the radiation
astronomical observatory
collected by the telescopes, provide a
good example. With a telescope of a
given size, a more sensitive detector sounding rockets, and interplanetary
allows the astronomer to discover and probes have detected about a dozen
measure fainter sources. At first, the EUV-emitting stars in the Milk Way.
detectors available for sensing EUV They have revealed also that there are
radiation were not very sensitive. lines of sight along which we can see
to distances of many light years from
the Earth (one light year equals about
5.9 trillion miles, or 9.5 trillion
The Berkeley scientists developed so-
kilometers).
called photon counting detectors for
DETECTOR SCHEMATIC Further, from studies by NASA's
the EUV, work recognized by the
Copernicus satellite (Orbiting
award of patents and the publication of
Astronomical Observatory-3) and the
many technical papers. At first, the
IUE, it appears that our solar system,
PHOTOCATHODE detectors were simple photometers that
MICROCHANNEL including the Earth, is located in one of
PLATE TRIPLET registered only the intensity of EUV
the thin bubbles of interstellar gas, an
radiation, but now high-resolution
ideal location from which to explore to
imaging detectors can sense the
significant distances in the extreme
position of each incoming photon of
FIELD RINGS ultraviolet. As a result of these findings
EUV light within the field of view. They
it appears that the EUVE, rather than
can record also the exact moment at
being blocked from observing beyond
which the photon was received. Like
WEDGE AND STRIP the solar system by the interstellar gas,
ANODE SOUNB QSUTRAARTTEZ the improvements in the other will be able to survey objects in our
technology areas, the improved EUV
galaxy out to a distance of about 300
detectors may prove beneficial in
applications outside astronomy.
Thin Bubble
Experimental EUV telescopes flown
on manned spacecraft, unmanned
LEFT: Schematic of EUVE detector
RIGHT: One of the EUVE flight detectors
ORIGINAL r
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