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U P D A T E # 3 4 Part 1: Galileo
gets new flight software May 23, 1996 Today the Galileo spacecraft began operating on its newly- installed flight software, the operating system for its computers. It is now transmitting data in a new format at 32 bits per second. During the last two weeks the Galileo flight team loaded most of the new flight software into the Jupiter-orbiting spacecraft computers, which are in the attitude and articulation control and command and data subsystems. About half the scientific instruments have also been reprogrammed. In the next few days, the team will finish the process, reprogramming several remaining instruments and completing the inevitable clean-up commanding. The process of specifying, writing and testing the new software and preparing it for installation in the spacecraft now orbiting Jupiter took more than three years and involved more than 100 members of the Galileo project team. This is the second time Galileo has been massively reprogrammed with new flight software. In February 1995 new software was installed for the approach and initial encounter at Jupiter and for the support of Galileo's atmospheric probe mission. The new software goes a long way further, providing for data compression and other new facilities to maximize the science return from the orbital tour, using the tape recorder and the low-gain antenna. Galileo is now about five weeks from its first encounter with the Jovian moon Ganymede. The largest of the Galilean satellites, Ganymede orbits at roughly one million kilometers (620,000 miles) from Jupiter and has a diameter of almost 5,300 kilometers (about 3300 miles), larger than the planet Mercury. June 4, 1996 Yesterday marked the start of the return of scientific data recorded by NASA's Galileo spacecraft during its close flyby of Jupiter's moon Io last December 7. The data will be sent back at the rate of 20 to 80 bits per second over the next two-and-a-half weeks. Among the data being returned are long-awaited measurements of the Io torus, an invisible doughnut-shaped ring around Jupiter populated in part by charged ions of oxygen and sulfur emanating from the volcanic moon Io. The measurements Galileo made of this energetic region are of great interest to scientists attempting to understand the complex interplay of magnetic forces and matter in Jupiter's magnetosphere. Planning continues for Galileo's upcoming June 27 encounter with the moon Ganymede. Yesterday's data return from the spacecraft included an optical navigation image of Ganymede (see below) and a reference star to help fine-tune targeting of Galileo's 844-kilometer (524-mile) altitude flyby of that big moon. The navigation images of Ganymede are not meant to be scientific images, but instead are highly edited onboard the spacecraft so that only the most basic data is returned to show Ganymede's location relative to the position of selected stars. Still, Galileo Project Scientist Dr. Torrence Johnson points out that the resolution of the Ganymede optical navigation images already exceeds that of the Hubble Space Telescope's resolution on the Jupiter satellites. Ganymede is the largest satellite in the solar system. With a diameter of 5,300 kilometers (about 3,300 miles), it is three-quarters the size of Mars. The return of the Io data and the optical navigation frame were enabled by the extensive new software that was radioed to the Galileo spacecraft last month. Galileo is now equipped to perform its orbital mission with this new software. Galileo is now 10.8 million kilometers (6.7 million miles) from Jupiter, and 653 million kilometers (405.7 million miles) from Earth. One-way communication time is 37 minutes. Galileo's speed in orbit around Jupiter is 3.2 kilometers per second, about 7,300 miles per hour. June 13, 1996 More optical navigation images of Jupiter's moon Ganymede were received from the Galileo spacecraft this week. The second of three scheduled "orbit trim maneuvers" to refine Galileo's approach path to Ganymede were successfully executed by the spacecraft yesterday. Galileo project officials report that so far, the new flight software installed onboard the spacecraft three weeks ago is working flawlessly. The return of the Io torus data stored on Galileo's tape recorder started on schedule last week and continues as planned. The Galileo Orbiter is operating normally in dual-spin mode.
Ron Balke, the Galileo Home Page Curator, reports that an optical
navigation image of Ganymede returned from the Galileo spacecraft
on June 3, 1996 is now available on the Galileo home page:
http://www.jpl.nasa.gov/galileo/
The caption file for the image is appended below.
Galileo optical navigation image of Ganymede
NASA's Galileo spacecraft, now in orbit around Jupiter, returned this
optical navigation image June 3, 1996, showing that the spacecraft is
accurately targeted for its first flyby of the giant moon Ganymede on June
27. The missing data in the frame is the result of a special editing feature
recently added to the spacecraft's computer to transmit navigation images
more quickly.
This is first in a series of optical navigation frames, highly edited
onboard the spacecraft, that will be used to fine-tune the spacecraft's
trajectory as Galileo approaches Ganymede. The image, used for navigation
purposes only, is the product of new computer processing capabilities on the
spacecraft that allow Galileo to send back only the information required to
show the spacecraft is properly targeted and that Ganymede is where
navigators calculate it to be.
"This navigation image is totally different from the pictures we'll be
taking for scientific study of Ganymede when we get close to it later this
month," said Galileo Project Scientist Dr. Torrence Johnson. On June 27,
Galileo will fly just 844 kilometers (524 miles) above Ganymede and return
the most detailed, full-frame, high-resolution images and other measurements
of the satellite ever obtained. Icy Ganymede is the largest moon in the
solar system and three-quarters the size of Mars. It is one of the four
large Jovian moons that are special targets of study for the Galileo
mission.
Of the more than 5 million bits contained in a single image, Galileo
performed on-board editing to send back a mere 24,000 bits containing the
essential information needed to assure proper targeting. Only the
light-to-dark transitions of the crescent Ganymede and reference star
locations were transmitted to Earth. The navigation image was taken from a
distance of 9.8 million kilometers (6.1 million miles). On June 27th, the
spacecraft will be 10,000 times closer to Ganymede.
Ron Balke Web to the following URL for big fun: http://www.jpl.nasa.gov/galileo/countdown/ The Galileo spacecraft is currently in orbit around Jupiter, and has begun its 2 year orbital tour. Galileo's orbital tour consists of 11 elliptical orbits around Jupiter, and each orbit (except one) will include a close flyby and gravity assist of one of the Galilean moons (Ganymede, Callisto or Europa). In addition to close-up observations of a Galilean moon, distant scientific encounters with additional satellites are scheduled for a number of orbits, and Io will be observed at medium range on every orbit. The first satellite encounter is scheduled for Ganymede on June 27, 1996 (also referred to as Ganymede 1). With a diameter of 5,262 km, Ganymede is the largest satellite in the solar system. Ganymede is larger than Mercury and Pluto, and three-quarters the size of Mars. Galileo is will flyby Ganymede at a distance of only 844 km on June 27, which is over 70 times closer than the Voyager's closest approach. Highlights of the Countdown to Ganymede home page: o Computer-generated Jupiter approach images are displayed at the top of the home page, including Galileo's view of Jupiter and an overhead view of the Jovian system. These images will be updated daily until arrival day, and on arrival day will be updated every five minutes. o The latest Galileo status reports reporting on the Ganymede 1 encounter. o Galileo's current position, updated every minute. This includes the distances from Jupiter, the Earth and Sun, and relative speeds. o Ganymede fact sheet. o A detailed timeline of events and sequences that the spacecraft will perform for the Ganymede 1 encounter. o Galileo SSI planning images provided by the Galileo imaging team. o Galileo images of Ganymede (high-resolution images expected in July 1996). o Voyager 1 & 2 images of Ganymede. o Hubble Space Telescope images of the Galilean satellite. o Pioneer 10 & 11 images of Ganymede. o Images of Comet Shoemaker-Levy 9 & Ganymede. o Live events on June 27, 1996, as they become available. o Ganymede animation - fly over the surface of Ganymede. May 21, 1996
Measurements returned by NASA's Galileo probe into Jupiter
have provided dramatic new evidence about circulation
processes within the planet's atmosphere and prompted
scientists to propose radical new theories about Jupiter's
original formation.
The new concepts arise from the probe's successful
parachute-borne descent into Jupiter on Dec. 7, 1995. The
probe made the first quantitative measurements of the Jovian
atmosphere below its outer clouds, reaching a region below
where heat from the Sun can penetrate. This means the probe
sampled the upper part of what is believed to be Jupiter's
well-mixed, relatively uniform "interior atmosphere."
Several members of the probe scientific team announced new
mid-term findings today at a meeting of the American
Geophysical Union in Baltimore. "The returns from the probe's
scientific instruments have sparked a lively worldwide
scientific debate about theories of planetary formation and
about internal mechanisms in the huge Jovian atmosphere,"
according to Dr. Richard Young, Galileo probe scientist at NASA's
Ames Research Center, Mountain View, CA.
Prior to the probe mission, the leading theory of Jovian
weather assumed that, like on Earth, most action occurs in the
thin, cloudy, solar-heated exterior region -- the so-called
"skin of the apple." Winds within Earth's 100-mile-deep
atmosphere are primarily the result of differential sunlight
at the poles versus the equator, and heat released due to
water condensation.
According to mission scientists, Galileo probe data
strongly suggest that circulation patterns in Jupiter's cloud
tops and its interior (which runs 10,000 miles deep) are part
of one continuous process. Dr. David Atkinson of the
University of Idaho continues to report persistent Jovian wind
velocities of over 400 mph. The probe detected no reduction
in wind speed, even at its deepest levels of measurement,
approximately 100 miles below Jupiter's clouds.
Galileo scientists regard this finding as confirmation
that the main driving force of Jupiter's winds is internal
heat radiating upward from the planet's deep interior. The
strength of the Jovian winds and the fact that they do not
subside with depth is very significant, according to Dr.
Andrew Ingersoll of the California Institute of Technology,
Pasadena, CA.
"This may be evidence that Jupiter has high-speed wind
currents extending thousands of miles deep into its hot, dense
atmosphere," Ingersoll said. Such interior currents are
believed by probe scientists to be the source of the dramatic
banded appearance of Jupiter's cloud tops.
The most difficult probe finding for scientists to explain
continues to be the extreme lack of water detected in the
Jovian atmosphere. Pre-probe mission scientific estimates
based on planetary formation theories, data from the earlier
NASA Voyager spacecraft flybys of Jupiter and observations
from the impacts of the fragments of Comet Shoemaker-Levy 9
with Jupiter forecast Jovian water levels at or well above
those found in the Sun. However, probe scientists report that
Jupiter is extremely dry -- with water levels (based on oxygen
content) at one-fifth to one-tenth of the solar amount.
This finding is now well established, having been
confirmed by analysis of data from five of the probe's science
instruments. For example, the virtual absence of Jovian water
clouds and the low relative frequency of lightning are all
consistent with dry atmospheric conditions. Where is the
water that should remain from Jupiter's formation in the same
primitive nebula of gas and dust that spawned the Sun and the
other planets? Several theories have been proposed.
According to one theory, Jupiter's true total water levels
are probably at or above solar, with the bulk of Jovian water
trapped in the planet's deep interior. According to this
view, Jupiter began as a solid, rocky/icy proto-planet that
grew to 8-10 times the mass of the Earth by gathering up ice
grains and dust in the original primordial cloud. This
process may well have concentrated water ice in the solid
body, trapping it in the core while drying out surrounding regions.
As the solid body of the proto-Jupiter became larger, it
attracted the already-dried-out surrounding lighter gases,
mixing them with its existing atmosphere. This atmosphere
would contain carbon and other gases that were originally
locked in the core but had escaped as methane, ammonia,
hydrogen sulfide and other volatiles as the core heated up.
This process would produce a gas mixture similar to that found
by the Galileo probe. It also would explain the enhanced
carbon, sulfur and nitrogen levels found on Jupiter, which are
significantly enriched relative to their abundance on the Sun.
In fact, this water-locked-in-the-Jovian-interior theory
explains many of the measurements made by the probe. However,
"there are problems with this new view, as there are with all
the other current theories," said Dr. Tobias Owen of the
University of Hawaii. "The primary one being, how does the
ice stay in the hot planetary core while carbon-containing
gases escape?"
An alternative theory suggests that the probe entered the
Jovian atmosphere in an area comparable to the Earth's desert
regions. This theory is supported by Earth-based telescopes
and other spacecraft that observed extreme dryness at the
probe's entry point on Jupiter's north equatorial belt. This
theory holds that, like on Earth, Jupiter's atmosphere is
heated by the Sun at the equator, causing air to rise until
clouds form and water is lost. The dry air then may flow
north and south, descending in "desert" regions. If a large
enough downdraft exists, it might be sufficient to explain the
dryness that the Galileo probe encountered.
However, several scientists find fault with this "huge
downdraft" theory, doubting that such a massive downdraft and
continued dryness could exist at the depth and pressure levels
to which the probe descended. While such a downdraft might
explain the observed dryness, its persistence down to 20 times
Earth's atmospheric pressure is very hard to explain,
according to Ingersoll.
"This explanation is particularly difficult when
considering that Jupiter emits more heat from its interior
than it receives from the Sun," he said. "This up-flowing
interior heat should block a huge, deep downflow of dry air.
It should evenly mix Jupiter's atmospheric water vapor at this
pressure level, preventing the existence of a very dry region
such as that found by the probe."
One possibility, Owen responds, is that "perhaps Jupiter's
interior heat comes out only in certain regions where
ascending currents bring up hot material from the planet's
interior, like the heat escaping from the Earth's interior" in
volcanoes and mid-ocean floor spreading zones.
A variation on the dry-region theory has been advanced by
Young and others. "Jovian water distribution may vary
radically over large latitude regions, with much of Jupiter's
water being concentrated at high latitudes where most of the
planet's lightning has been detected," he said. "More of
Jupiter's interior heat is also emitted at high latitudes.
Unfortunately, at the moment, we can't put all of this into a
mechanism to explain how major parts of Jovian water could be
concentrated uniquely at these high latitudes."
The Galileo probe successfully accomplished the most
difficult planetary atmospheric entry ever attempted. It
relayed a total of 61 minutes of unique science data to the
Galileo orbiter passing 100,000 miles overhead for subsequent
transmission to Earth. The probe descended about 400 miles
into the Jovian atmosphere, taking measurements down to a
level corresponding to 20 times Earth's atmospheric pressure.
The Galileo orbiter has since embarked on a two-year tour of
Jupiter and its moons.
Additional information on the Galileo probe, including a
discussion of the craft's science instruments and a non-
technical summary of the first scientific papers on the probe
mission that were published in the May 10 issue of Science
magazine, can be found on the Internet at the following URL:
http://ccf.arc.nasa.gov/galileo_probe/
If this is your first message from the updates-jup list, welcome! We are presently in a down mode where an update will be sent about once per month. We hope to reactivate the project more fully after a variety of science data begins streaming in. The likely timeframe for any such reactivation is early 1997. To catch up on back issues, please visit the following Internet URL: gopher://quest.arc.nasa.gov:70/11/interactive-projects/jupiter/journals
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