IT IS being hailed as one of the most
,epochal' moments in the history of
unmanned space exploration by the
National Aeronautics and Space
Administration (NASA), USA: Jupiter, the
largest planet in Our solar system, now
has an Earthly visitor - Galileo.
Defying adverse predictions, Sur
mounting all delays, disasters, and temperamental equipment, the'Rolls Royce
of all American spacecrafts' has Finally
made it to Jupiter. During its two-year
spin around Jupiter and its lunar retinue, Galileo is expected to provide richest scientific information ever procured
,about the giant gaseous planet.
The 1, 180-kg (two and a half tonne)
NASA spacecraft went into orbit around
Jupiter on December 7, 1995, after it
successfully hurled a 'suicide mission'
probe into the depth's of the
planet's atmosphere to r a
detailed study of the Jovian
system.
"All of its were thrilled when
it was confirmed that the Galileo
orbiter was receiving a signal
from the probe. These are the
moments that make all the hard
work worthwhile," an exuberant
Wesley T Huntress Jr, NASA associate administrator for Space sciences, told Down To Earth.
More the astronomers examined
Jupiter from afar, more than recognised
its twin attractions. First, the planet
itself could hold more than a thousand
Earths, arid it is 318 times more massive
arid 1,400 times more voluminous than
Earth.
Second, it resembles a small star and
some scientists believe that the suit arid
Jupiter was born as unequal partners in
the binary star system. it is composed
almost entirely of hydrogen (89 per
cent) arid heliurn (10 per cent) - principle ingredients of gaseous clouds from
which the suit arid nine planets are
believed to have formed.
Five American spacecrafts have previously skirted by Jupiter, managing
fleeting glances. Galileo marks the first
ambitious attempt to follow up in detail
the earlier quests.
Just before Galileo's tryst with destiny, its 746-pound heat shield covered
atmospheric probe, which was separated from the mother craft in July 1995
and flew independently since, pierced
Jupiter's thick ammonia clouded enter
atmosphere to explore the volatile mass
beneath.
Even as scientists, 600 million miles
away, at the NASA jet Propulsion
Laboratory (JPL), Pasadena, California,
received this crucial confirmation, the
'suicide' probe was well into its mission,
Built for NASA by the Hughes Space
arid Communications, Los Angeles, the
atmospheric probe carried six experiments to analyse Jupiter's atmosphere,
and transmitted the data back to
Galileo, positioned 13,300 miles
above the planet - all expected
to be done within 75 minutes
before it succumbed to extreme
heat and pressure.
The probe demanded one of
the trickiest manouevres NASA
has ever sought to accomplish.
Had the entry angle been too
shallow, the probe would have
bounced out of Jupiter's atmosphere; anti if it were to be too
steep, the probe would have been
instantly consumed by heat and
pressure.
Descending on Jupiter at the
speed of 170,000 km/hr, the
probe hit the Jovian atmosphere
with 3,50 times the force of gravity - more than 40 times the
gravitational force a pilot might
encounter in a high performance jet.
Friction from the Jovian atmosphere raised the temperature around
the probe to 28,000oC, more than two
arid ii half times the temperature on the
sun's surface.
The heat shield covering the probe
was then discarded, thus exposing the
sensors, which would gather the first data on Jovian composition, temperature, pressure, electrical activity and
wind speed, sulasquently to be transmitted to Galileo for relay to Earth.
Some scientists speculate that the
probe was able to penetrate about
400 miles into the Jovian atmosphere.
But scientists at the JPL have now confirmed that Galileo's atmospheric probe
had survived its daring dive and lived
long enough to beam back nearly
57 minutes of invaluable information
during its fatal descent.
"We are absolutely ecstatic that
our ... first ever penetration of an outer
planet's atmosphere has been so wonderfully successful," exclaims William
O'Neil, Galileo project manager at the
IPL. The full suite of the tape-recorded
observation would, however, not be
played until February this year.
just after the probe completed its
mission, the mother craft had its own
moment of glory. A 49-minute rocket
firing put it in such a precise orbit that
an earlier planned course correction
mission was not required.
Galileo began its two-year tour
around Jupiter equipped with the highly
advanced and sensitive CCD camera,
compared to the less accurate vidicon
camera earlier carried by Voyager. It
also has a near-infrared mapping spectrometer - a lesser-known technology
during Voyager's odyssey. Moreover,
the two-year mission allows the craft to
study Jupiter's temporal changes.
Although the probe was destined to
be the most dramatic part of the mission, Galileo has more responsibilities.
The spacecraft will make 11 orbits, 10 of
them close flybys of three of the 16
moons of Jupiter - Europa, Callisto
and Ganymede - each time using the
moon's gravitational Pull to Swing it
into a new orbit for the next encounter.
It is also expected to study Jupiter's
fourth major moon Io, which is volcanically active, but from a safe distance.
NASA Scientists have now predicted
that the craft should reach its next target, Ganymede, on June 27, 1996,
instead of July 4, 1996, as previously
assumed. "Galileo will go very close to
three of the four major moons of Jupiter
- as close as 200 km. We should receive
images 100-1,000 times better than
what Voyager got," says O'Neil.
Jupiter's moons have often been
regarded as some of the strangest structures in the solar system. Europa, for
instance, may be one of the moons that
holds some real surprises, claim NASA
scientists. It may be a live real water-world with a thin crust of frozen ice on
top. And Callisto, is thought to be a part
of an ancient system that contains a lot
of clues about how the moons probably
looked 4 billion years ago before they
underwent geological activity.
Scientists believe that Jupiter has
retained most of its original elements.
"Most of what Jupiter started out with,
it still has," says a probe scientist at
NASA's Ames Research Centre in
Mountain View, California. This makes
the Jovian system seem like a giant laboratory which holds answers to many
cosmological queries.
For 10,000-odd NASA scientists and
engineers associated with this $1.4 billion project, this whole mission has
been awaited with baited breath. It
gained notoriety not only because of
astronomical costs involved, but also
because of mega-technical and political
wrangles associated with this grand
space programme.
Conceived in 1976, on the recommendations of a scientific study group
headed by James Van Allen, now a
physicist it the University of Iowa, the
Galileo project was almost cancelled in
1981 for budgetary crunches and since
then, has been resuscitated twice. The
original plan was to launch the space-craft in 1982, but was defered. The next
launching was held up again because of
the Challenger disaster in January, 1986.
The Challenger experience compelled the scientists to abandon the idea
of launching Galileo by a more powerful
but potentially explosive liquid-hydrogen fuelled Centaur rocket. Instead,
they opted for a safer but less powerful
solid-fuel rocket.
Nearly 50 pounds of plutonium that
was to be used for producing electricity
on Galileo's probe, made the launching
the most disputed ever. Just before its
scheduled take-off in 1989, three
American anti-nuclear groups tried to
block the launch in a Federal District
Court in Washington, apprehending a
serious environmental onslaught.
But finally, Galileo began its six-
year, 3.8 billion-kin ride to Jupiter safely tucked in the cargo bay of the space
shuttle Atlantis, on October 18, 1989.
The unmanned nuclear powered
probe followed a bizzare, multiloop
route to Jupiter. Forced into a longer
journey, the spacecraft conducted scientific experiments, took snaps as it flew
by Venus once and Earth twice. It
encountered two asteroids, 951 Gaspra
and Ida, then discovered a small satellite, Dactyl, orbiting Ida - the first confirmed satellite ever found orbitting an
asteroid. Galileo observed huge fragments of the comet Shoemaker Levy
crashing into Jupiter, capturing images
of impacts invisible from Earth, and also endured the most intense interplanetary
storm ever measured.
Galileo's circuitous route, the most
cumbersome and Perhaps the most
risky ever undertaken by a spacecraft,
was necessary so that the spacecraft
could use the gravitational pull of Venus
and Earth for accelerating towards
Jupiter. Says Torrence Johnson, Galileo
project scientist, "All of these celestial
gymnastics, or tripple billiard shot if
you will, was designed to give Galileo enough energy to get to Jupiter."
But in 1991, Galileo's main 16-ft wide
umbrella-like radio antenna failed to
Unfurl, severely reducing its ability to
transmit scientific data to Earth. So, the
NASA scientists decided to record the
data on the craft's tape machine and
transmit it using its small navigational
antenna, Through clever changes in
software transmitted to Galileo, scientists reprogrammed the on-board computer so that information could be
stored more efficiently.
JPL engineers also devised ingenious
ways to compress the data transmitted,
rising mathematical codes so that the
same information was relayed to Earth
in fewer bits. The only hitch was that
data flow was slow. To reduce the data
volume, each on-board scientific instrument would edit its own data before
locking it in the craft tape recorder to
save space. This data would then be
played into the central computer memory, where it will again be edited and
only the most important data will be
preserved and transmitted to Earth.
The NASA scientists are both cautious and optimistic in assessing the
effects of technical snags hampering the
unique mission. "Galileo will still be
able to accomplish at least 70 per cent Of
original scientific mandate," asserts
Huntress. "if we can get this far, I have
no doubt that the mission will be successful," says Galileo project chief scientist, Richard E Young.
Regarding colossal costs involved in
the project, critics frequently cite the
loss of $1 billion when the Mars
Observer craft disappeared in 1993,
after a suspected hardware failure, and
maintain that NASA Should opt for new
generation smaller, faster and cheaper
space missions.
Preliminarly indications reveal that
NASA IS future missions may be a mix of
mega and micro projects. Whatever
happens, it is clear that the Galileo mission may not be the last Of NASA's space
dinosaurs. But what may be significant
about future launches, is not so much
their size, but an increased emphasis on
the focussed nature of their missions.
11 NASA has a very robust series of
small but focussed missions planned to
explore the solar system. The P1, is
working on a concept of some innovative, low-cost spacecraft to send to Pluto
tinder an effort called Pluto Express,"
says Huntress. The Discovery programme will be sending missions to an
asteroid, the Moon and a comet. The
New Millemium programme wil he
developing advanced technology for
future planetary missions to outer planets eadv next century, he adds.
NASA and the European Space
Agency have jointly planned a project
called Cassini to explore Saturn scheduled for launch in 1997, and arrival in
Ai) 2004. As regards Galileo, it may be
months before the data gathered is
processed and the mission declared successful, but it is hoped that the waiting
shall prove fruitful after those six long
years Galileo took to reach Jupiter.
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