Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT_ZIP/jplpaper/921230.ZIP/921230.UNI

Text File | 1993-08-11 | 25KB | 459 lines

Jet Propulsion Laboratory UNIVERSE
Pasadena, California - Vol. 22, No. 37 - December 30, 1992
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GOPEX reaches Galileo via laser beam

By Mark Whalen
     JPL researchers took advantage of Galileo's recent pass by
Earth to achieve a major milestone in space communications, by
successfully transmitting laser beams fired from the ground to
the spacecraft at distances of up to 6 million kilometers (3.7
million miles).
     "This experiment is part of a program to show that future
deep space missions can use laser beams to send back to Earth
larger volumes of space-acquired data than is currently possible
using radio signals," said Dr. James Lesh, supervisor of the
Optical Communications Group and principal investigator for the
Galileo Optical Experiment (GOPEX).
     The experiment's objectives, said Lesh, were to show that an
uplink beacon laser -- required as a reference for pointing a
return beam back to Earth -- could be successfully pointed to a
distant spacecraft based only on the navigational predicts of the
spacecraft trajectory. To do this, the distortions produced by
Earth's atmosphere had to be predicted and accommodated.
     The GOPEX demonstration began on Dec. 9 (one day after
Galileo made its closest Earth approach on its way to Jupiter) at
600,000 kilometers (370,000 miles), and continued through Dec.
16. Laser beams were simultaneously transmitted to the spacecraft
from a 61-centimeter (24-inch-diameter) telescope at the Table
Mountain Observatory near Wrightwood, Calif. and from a 1.5-meter
(60-inch) telescope at the U.S. Air Force Phillips Laboratory's
Starfire Optical Range near Albuquerque, N.M.
     The transmissions, which were detected by Galileo's onboard
camera, established a record for the farthest known transmission
and reception of a laser beam, a final distance of 6 million
kilometers.
     "GOPEX was extremely successful," said Lesh. "A real
pleasant surprise in the experiment was that we conducted the
experiment so repeatedly. Each day we made transmissions, we had
extremely reliable detections on the spacecraft camera.
     "We would predict ahead of time, `on this frame, we're going
to see a series of pulses about so high on the picture,' and as
soon as we got the image back, sure enough, there they were," he
said.
     Spacecraft signals produced by current radio-frequency
systems are used for three purposes, according to Lesh --
communications, navigation and science investigations. "There are
completely analogous applications in the laser area," he said.
     "We can communicate at substantially higher rates while
occupying much less room on the spacecraft," said Lesh. "The
antenna is the main feature on the spacecraft with radio
frequencies, often reaching diameters in excess of four meters.
At laser frequencies, 10-50 centimeter telescopes are quite
adequate.
     "We can also use optical beams for navigation," Lesh
continued. "When viewed from Earth, the light beam from a
spacecraft will look like a blinking star. We can view it in the
context of the stellar grid, or relative to target bodies we are
approaching. That information can be used to derive angular
coordinates of the spacecraft.
     "Laser signals also can be used to determine the
spacecraft's range, which, together with the angle information,
can be used to locate the spacecraft," said Lesh.
     As far as science investigations are concerned, Lesh claims
that scientists could use optical signals to probe phenomena such
as planetary atmospheres, to measure scattering from the
interplanetary dust particle distribution, or to make spatially
selective measurements of planetary ring systems using very short
wavelengths (below one micron).
     "Also," Lesh added, "optical signals are not corrupted by
solar wind fluctuations, like radio frequencies are. Some past
investigations of gravitational bending of radio waves have been
limited by charged particle fluctuations in the solar wind."
     Lesh also said laser communications technology will yield a
data rate increase "of about one-to-two orders of magnitude" over
radio frequencies.
     The idea of testing a laser uplink is not a new one. Lesh
said that the GOPEX demonstration was originally proposed in June
1984, but was rejected at the time because there were no plans
for Galileo to view Earth on its way to Jupiter.
     But the 1986 Space Shuttle Challenger accident prompted
changes in Galileo's launch system and necessitated a new flight
path, which included two gravity-assisted flybys of Earth. "At
the same time," he said, "Earth viewing became part of Galileo's
priorities, and the climate became much more receptive to our
doing the experiment, subject to us demonstrating beyond any
doubt that we would not damage any instrument on board the
spacecraft."
     In that regard, preperations were made to conduct GOPEX
during the Earth-1 encounter in December 1990. But inconclusive
data turned up on a test to determine if the experiment might
harm the Galileo orbiter's Near-Infrared Mapping Spectrometer, so
"about three days before the experiment, we were waved off," said
Lesh. In the intervening two years, testing of the effects of
laser signals on the NIMS and Solid State Imaging Camera
detectors concluded that "we were safe to substantially higher
levels than we would ever produce at the spacecraft," said Lesh.
     What's next for the program? Lesh said proposed plans call
for a flight experimental terminal to be flown aboard a space
shuttle in the latter half of the 1990s. "We are developing the
base technology for this now," he said, "and are trying to
augment the base program with some new flight experiment monies
that will allow us to do the (shuttle) demonstration."
     Operational use of this technology is anticipated some time
after the year 2000, Lesh added.
     "We expect that the first deep space mission to fly optical
will fly it as a mission enhancement experiment," said Lesh,
"although this could change with the new emphasis on low-cost
microspacecraft.
     "I believe that there are missions that can be best served
by laser frequencies, and there are those that are best served by
radio frequencies," he said. "Laser beams do require a certain
amount of pointing, for example. If you have large uncertainty
about the spacecraft pointing direction, it may be better to use
radio waves. However, most missions currently flying or on the
drawing boards provide adequate attitude control to use laser
communications.
     "Nevertheless," said Lesh, "I don't see us de-implementing
any capabilities in the future; I see us providing an additional
capability that will allow future missions to plan for and make
best use of the available technologies." ###
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Lab adds some magic to Rose Parade

By Diane Ainsworth
     Pasadena's grand old tradition  -- the Tournament of Roses -
- is something of a tradition at JPL too.Unbeknownst to most of
the estimated 1 million spectators oohing and ahhing over the
promenade of floats on New Year's Day will be a dozen JPL staff
who volunteered their technical talents and civic-mindedness to
make it all happen.
     This year's 104th annual Tournament of Roses features three
floats in keeping with the theme  -- "Entertainment on Parade" --
that were either artistically or mechanically and structurally
designed by JPL mechanical engineer Michael R. Johnson and his
wife, Renee.
     Perhaps the most bewildering is "Prestidigitation on
Parade," sponsored by ARCO and the first animated float to
perform what Johnson considers "true magic."  The float is a 25-
foot-tall magical rabbit that makes a school bus filled with real
kids disappear and, 30 seconds later, reappear, by waving its
magic wand.
     "It's a vanishing act," said Johnson, of the Mechanical
Systems Section 352, who created the mechanical and structural
design and whose wife came up with the artistic design, "and it's
true magic because it's not obvious how the trick is performed.
     "Depending on where you are standing along the parade route,
you'll either see the rabbit holding the box with a bus full of
kids or, presto, you'll see the rabbit wave its magic wand, a
puff of smoke will go up, and the kids and bus will disappear.
The rabbit will be holding an empty box."
     Johnson also did the mechanical and structural design for
"Bungee Fun at the Big Top," sponsored by Nestle USA, Inc.  Atop
a 72-foot-high totem pole of floral clowns will be the star clown
pouring a bucketful of real bungee jumpers into the air.  Some of
the jumpers will be making as many as 90 bungee jumps during the
five-mile-long parade route.
     If those can be topped, Honda's "Come Ride With Us" float
pays tribute to American ingenuity with a display of two double
Ferris wheels spinning above an antique steam calliope. Johnson's
wife painted the artist's rendering, while Johnson created the
structural design. Six kids will be waving from each spinning
Ferris wheel. The Ferris wheel debuted at the Chicago World's
Fair in 1892, according to the TofR parade program, two years
after the first Rose Parade.
     Johnson, who has spent 14 years applying his engineering
skills to Rose Parade floats, found all of the float designs
intriguing. As the floats progressed, though, he found his
greatest challenges professionally in some of the more intricate
mechanical requirements.
     "What I thought would be the biggest challenge this year was
making the bus and kids inside the rabbit's magic box disappear,"
he said. "But actually, the challenge was to make the doors of
the box open and close."
     Johnson starts from nearly scratch to design the frames and
mechanical, moving parts of a float. The work begins almost as
soon as the parade is over, if it hasn't already begun. From
line-drawings submitted by artists, Johnson designs the chassis
of a float and its framework.
     The float's skeleton is usually constructed of steel beams
and uses chicken wire, screening or wire mesh to form the shapes
of characters, animals, plants and objects on the float. The type
of material used depends primarily on what types of flowers will
be applied.
     The frame is "cocooned," covered with a polyvinyl material
that was used to moth-ball Navy ships after World War II, Johnson
said. Then the frames are painted in the colors of the flowers
that will be used to adorn the floats starting on Dec. 26.
     Every centimeter of every float must be covered with flowers
or other natural materials, such as leaves, seeds, bark or
powders. Flowers large and small can be secured on the floats by
sticking the stems through wire meshing, screen or chicken wire.
Other flowers are simply glued on flat surfaces such as wood.
Delicate flowers, such as roses and orchids, must be placed in
tiny vials of water that are then tied or wired to the float. On
average, each float is decorated with more flowers than the
typical florist would use in five years.
     Float construction is a science unto itself, as is
organizing this monumental annual tournament.  Other individuals
at the Lab have earned their TofR stripes by helping with the
logistics of the Rose Parade. All in all, it takes 875 volunteers
and 29 Tournament of Roses committees to put the multi-million-
dollar enterprise together.
     Neil Nickle, on the technical staff of the Office of Space
Science and Instruments, has been a member of the Tournament of
Roses Association for 20 years, serving on many of the
Association's committees.
     This year he is chairman of the Community Relations
Committee, which acts like a speaker's bureau, providing talks,
slide shows and video presentations about different aspects of
the Rose Parade to service clubs, churches, schools, civic groups
and retirement clubs.
     "We've got 10 speakers on our committee this year who give
community presentations.  Depending on what the group is
requesting, we'll give talks on anything from the way floats are
built to selection of the Rose Queen and her royal court."
     Of all the committees he's worked on over the years, Nickle
said the Float Construction Committee was his favorite.
     "You're more involved in that, he said. "It's tougher and
requires more of your time, but you get much more involved with
all of the floats and you get to know them."
     Brooks Vinson, an engineer in the Electronic Parts
Reliability Section 514, is a 19-year Association member and
currently a member of the Communications and Credentials
Committee. The committee is charged with issuing all of the
ribbons, armbands and paper windshield passes to parade security
officers, workers, volunteers and residents in the Pasadena area.
Last year the committee issued about 10,000 passes. He
anticipates even more this year.
     Of all of his years with the Rose Parade, Vinson's most
vivid memory comes from his early days as an active parade
volunteer standing watch at a traffic barricade on Green Street
at about 2 a.m. the morning of the parade.
     "I saw some large vehicle moving toward me in the dark,"
Vinson recalled, "but I wasn't able to make it out until it was
almost in front of me. It was a lady in costume riding a huge
elephant.
     "I knew there weren't any elephants in the parade, so I told
her no vehicles were allowed until the parade was over," he said.
     "She looked down at me and told me she was not in a vehicle,
but on an elephant. By then, a motorcycle officer had arrived,
and that elephant was getting pretty mad because he reached out
his trunk and almost pulled the officer off his bike."
     After a lot of laughter and jokes, it turned out that the
woman and her elephant had been invited to a private New Year's
Eve party. Apparently, she was just out "joyriding."
     The 1993 parade will feature 57 floats, 21 marching bands
and 29 equestrian units. Floats will be on display for two days
after the New Year's Day parade, at Sierra Madre Boulevard
between Washington Boulevard and Sierra Madre Villa Avenue, and
on Washington Boulevard between Sierra Madre Boulevard and
Woodlyn Road.
     Viewing areas are open to the public on Friday, Jan. 1, from
1:30 p.m. to 4 p.m., and on Saturday, Jan. 2 and Sunday, Jan. 3,
from 9 a.m. to 4 p.m. On Jan. 2 and 3, the post-parade viewing
areas will also be open to the mobility-impaired and senior
citizens from 7 a.m. to 9 a.m.  Admission is $1 per person. ###
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Where in the world?
Just ask a GPS satellite

By Franklin O'Donnell
     Knowing where you are isn't an ultra-high-precision question
for most spacecraft. Typically, Earth satellites or even the
space shuttle are doing well if they know their whereabouts to
within a kilometer or so.
     When JPL's TOPEX/Poseidon satellite was launched from French
Guiana last summer, however, the mission's aim dictated a much
tighter need. To measure heights of ocean surfaces around the
world, flight controllers needed to know TOPEX/Poseidon's
position to within a few centimeters.
     To accomplish that, mission designers turned to not one but
three different technologies. One of them has been used by JPL
researchers for years to monitor the slow northern creep of the
western part of California, as well as movements of continental
plates in other parts of the world.
     That technology -- the Defense Department's Global
Positioning System (GPS) -- is employed as well in many
industries, and may someday turn up on the dashboards of "smart
cars" that know their own position on a city's streets.
     "GPS has turned out to be a very effective approach for us
in precision position determination," said Dr. Nick Renzetti,
manager of JPL's Telecommunications and Data Acquisition Science
Office.
     Since the launch of the first Navstar GPS satellites in the
late 1970s, JPL has devised ways of using them to a variety of
ends.
     The Navstar satellites send out a constant beacon signal
that is time-tagged to an ultra-precise clock onboard each
satellite. Each satellite sends the beacon on two separate
frequencies, which helps cancel out transmission errors caused by
water vapor in Earth's atmosphere.
     When all of the Navstars have been launched -- anticipated
in late 1993 -- a total of 24 satellites will circle the Earth.
Currently 20 are in orbit.
     Equipped with a special receiver, a user on the ground can
take the signal from a Navstar satellite and use the time codes
embedded in it to determine how long the signal took to arrive --
and, thus, how far she or he is from the satellite.
     With distances calculated to several different satellites,
the user can fix her or his position on Earth.
     To support the TOPEX/Poseidon mission, Renzetti's office put
together a network of six ground stations around the globe. In
addition to Deep Space Network sites in California, Spain and
Australia, the locations include GPS receivers in Japan, Chile
and a South African site operated by the French space agency.
     Each of the six sites constantly monitors GPS satellites in
orbit to provide an extremely precise frame of reference against
which to measure TOPEX/Poseidon's location.
     The GPS system is only one of three methods used to pinpoint
the location of TOPEX/Poseidon. Another method uses laser beams
fired from the ground and bounced off reflectors on the
satellite.
     The third method uses a French receiver onboard the
satellite which listens to microwave signals sent up from
stations on the ground. This uses a technique called doppler
ranging which measures slight changes in the frequency of the
received signal to determine TOPEX/Poseidon's velocity.
     "The advantage of the GPS approach is that it offers
continuous coverage, high accuracy and low cost for the ground
stations," said Tom Yunck, deputy manager of JPL's Tracking
Systems and Applications Section 335.
     Renzetti says he plans to enlarge the network of GPS ground
stations to support future missions such as Aristotle, a joint
NASA-European Space Agency satellite that will study Earth's
gravity field in the late 1990s.
     The Aristotle mission will require 12 ground stations, or
twice as many as currently support TOPEX/Poseidon.
     Apart from playing a role in such satellite missions, GPS
also finds other uses at JPL. Since the earliest days of the
Navstar satellite launches, Lab researchers have used their
signals to study movements of tectonic plates, noted Dr. Bill
Melbourne, manager of JPL's Geodynamics Program.
     When the GPS system was being designed in the 1970s, JPL had
used several other techniques for years to measure precise
positions for studies in such areas as plate tectonics, according
to Melbourne.
     One approach -- called very long baseline interferometry, or
VLBI -- uses radio telescopes observing quasars on the edge of
the universe. This technique can be used to establish the
distance between two radio telescopes on opposite ends of the
United States to within a centimeter.
     Another approach uses laser beams sent up from the Earth and
bounced off a mirror-studded orbiting satellite, such as the
LAGEOS spacecraft deployed by the space shuttle in September.
Its accuracy is similar to that of VLBI.
     "Both allow you to measure your position to an accuracy
under one centimeter, but they both call for expensive mobile
systems, said Melbourne. "The real revolution with GPS has been
the low cost of the receivers."
     To measure tectonic plate motion, researchers are sent out
into the field with receivers about the size of a laptop
computer. By taking readings of several GPS satellites they can
establish the location of a survey marker; returning to the
marker months or years later, they can see if the marker's
position has changed.
     Seven ground campaigns are ongoing in areas such as Central
and South America, noted Ruth Neilan, manager for the campaigns.
The next major campaign to get under way will be one in the
southernmost areas of South America.
     Besides measuring the position of sites on solid earth,
tectonics researchers are even taking readings at sites on the
ocean floor. To accomplish this, a ship on the ocean surface
measures its position with a GPS receiver, then uses sonar to
establish a range to a marker on the ocean floor.
     Yunck noted that the Defense Department occasionally
scrambles the data transmitted by GPS satellites. The Defense
Department has also stated it will scramble transmissions around-
the-clock when the Navstar satellite constellation is completed
next year.
     "This will pose a problem for some GPS users, but the effect
should not be as great for us" at JPL, Yunck said. "We work with
the GPS satellite's signal in a way that is not as dependent on
the information encoded in the signal that will be encrypted."
###
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News briefs

     JPL is co-sponsoring the eighth annual Battery Conference on
Applications and Advances Jan. 12-14 at Cal State Long Beach.
     The meeting provides a forum for thorough examination of
issues related to analysis, design and selection of batteries and
power conditioners that meet the performance and cost goals of
various applications.
     Advance registration is $450 and includes admission to
technical sessions, proceedings, parking, lunch and reception.
Call [phone] for information.

     The fifth annual High-Tech Business Development Procurement
Conference, which is designed to aid small, minority and woman-
owned businesses, is set for March 1-2 at the Los Angeles Hyatt
Hotel.
     The two-day conference is sponsored by NASA and the Southern
California Small Business Utilization Council and is coordinated
by JPL's Procurement Contractor Capabilities Office.
     The meetings will include marketing and networking
opportunities, as well as nine how-to workshops. The $80
registration fee covers continental breakfast, lunch,
refreshments, receptions and conference packet. Call ext. 4-6093.
###
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Program aids AA degree students

By Mark Whalen
     In 1988, JPL's Professional Development Section initiated an
educational program designed to meet the needs of Lab employees
who had not had the opportunities to pursue college degrees.
     Now, almost 80 JPL staffers have taken advantage of the
Associate of Arts (AA) Degree Program, which is set up to make
class attendance easy for people who work at JPL.
     The program is conducted in conjunction with Glendale
Community College (GCC). But the convenient part is that students
don't have to travel to GCC for classes -- they are all held at
the PDC, at the Lab's Woodbury complex.
     The next session starts March 2, and information sessions
for prospective students will be held on Jan. 13 (in the Building
167 Conference Room) and Jan. 14 (Building 525-215A). Both
sessions will be held from 11:45 a.m. to 12:45 p.m.
     Betty Shultz, a personnel specialist in Professional
Development and coordinator of the AA Degree Program, said that
students who attend the full three-year program will earn 56
units transferable toward a four-year degree at any of the 20
California State University campuses.
     "With no registration lines to stand in and no commute to
Glendale, we have made it real convenient and easy for JPL
staffers to obtain an AA degree," said Shultz. Students sign up
for individual classes on the first night each one is held, but
can pre-enroll for the program during one of the information
sessions, she added. During the sessions, GCC counselors and
Professional Development staff members will be on hand to answer
questions about the program, and current and former students of
the program will be there for information as well.
     Shultz noted that students who have started AA programs on
their own, or who are just interested in taking a particular
class without an AA in mind, may also sign up for the program.
Enrollment fees range from as low as $60 to as high as $300 per
class, depending on the number of units each carries, as well as
the number of students in each class.
     Tuition reimbursement is also available for most JPL
employees, where requirements include at least a "C" grade. Once
approved, employees are eligible for up to $1,500 in tuition
reimbursement per calendar year.
     Shultz said classes are held one at a time at the
Professional Development Center, Building 605, on Tuesdays and
Thursdays from 6-10 p.m. Students starting the next program in
March without any prior units to their credit could receive their
AA degree in August 1996; Shultz has a complete class schedule
available for the three-year period.
     She added that the students who just completed the first of
the program's three-year sessions "formed a close-knit group.
They would study together, have dinner together, and help each
other out. This program is a wonderful opportunity to further
your education." ###