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U P D A T E # 1
PART 1: Welcome
to Online From Jupiter
Welcome to the "Online from Jupiter" project!
Over the next three months, you will receive a unique perspective
on NASA's Galileo mission to Jupiter. Through this maillist, you will
receive frequent Field Journals from the men and women of the
Galileo team. These behind-the-scenes reports will provide insights
in the day-to-day work required to make this NASA interplanetary
probe successful, including the broad diversity of skills needed.
ONLINE FROM JUPITER will include a dedicated online archive
housing the complete collection of Field Journals, biographies of
Galileo's people, a photo gallery, and much more. This online resource
will be housed in Web and Gopher formats on quest.arc.nasa.gov and
will become available shortly.
ONLINE FROM JUPITER will provide special opportunities for K-12
teachers and students. The specifics will evolve over time in this
dynamic project, but at a minimum will include the following items
to help Jupiter and Galileo become relevant in classrooms:
- some lesson plans and curriculum supplements
- an opportunity to email questions to the Galileo team from
November 21 1995 through January 1996; each question will
receive a personal answer
- special activities such as "Will the Probe Get Squashed?" contest
challenging students to estimate how factors like Jupiter's high
pressure and temperature will affect the probe
- a video introducing some members of the Galileo team
- online mechanisms to help teachers connect with one another to share
ideas about incorporating ONLINE FROM JUPITER into their classrooms.
Presently, we plan to publish these email updates every Monday and
Thursday. The frequency may change as the spacecraft nears Jupiter.
For those unfamiliar with the Galileo mission, here is a brief introduction:
On December 7 1995, the two-part Galileo spacecraft, consisting of an
orbiter and an atmospheric probe will arrive at Jupiter. On that day, the
probe will impact Jupiter's atmosphere at roughly 102,000 miles per hour
and subsequently descend by parachute to measure the temperature,
pressure, composition, atmospheric structure, and other aspects of the largest
planet in the solar system. Several questions raised by the impact of comet
Shoemaker-Levy/9 with Jupiter in July 1994 may be answered by the
probe mission, and scientists are eagerly awaiting this unique event.
Immediately after the probe's mission, the orbiter will enter orbit for a
2-year tour of the giant planet's system, including studies of Jupiter's
atmosphere, its satellites and its huge magnetosphere.
Additional information can now be found online on the Web at:
http://www.jpl.nasa.gov/galileo/
http://ccf.arc.nasa.gov/galileo_probe/
Throughout the ONLINE FROM JUPITER project, our team will be interested in
receiving your ideas and feedback. Send any comments to
marc@quest.arc.nasa.gov.
If at any time you wish to stop receiving these electronic mailings, send
an email to listmanager@quest.arc.nasa.gov. In the message body, write these
words: unsubscribe updates-jup
We hope that ONLINE FROM JUPITER will prove to be an exciting
learning resource for you and your students.
Dr. Jo Pitesky Marc Siegel
Galileo Mission Planning Office NASA K-12 Internet Initiative
Jim Erickson Week of October 2: This week started out with a problem. The Extreme Ultraviolet instrument was turned on and its first science data return showed that the instrument had not turned on properly. This was a previously known risk from testing , so a plan for re-starting the instrument was quickly put together. The instrument team identified what commands needed to be sent, the Mission Director was informed of the problem and the proposed solution. After deliberate thought and discussion, we were given the go ahead to get all the commands ready. We generated the necessary commands, and after careful review of them by the Orbiter Engineering Team to ensure safety to the rest of the spacecraft, the Mission Director gave the final go ahead for transmission of the commands up to the spacecraft. We should get the first confirmation of a successful re-load on Tuesday of next week. This illustrated a big advantage of advance planning. During the initial planning of when instruments are turned on and observations taken, we almost always turn on an instrument earlier than it's real need. This allows time to correct any anomalies (as in this case). An anomaly is an engineering term for an unusual event or problem. For this instrument, next week will be the start of it's prime Jupiter approach data. The time between the turn on and next week's science requirement allowed us to discover this problem, and successfully resolve it without major science loss. If we had waited to turn on the instrument until just before the good data began, we would have had some unhappy scientists. But it also was a very good week in other ways. Our dust instrument had been monitoring a dust stream from Jupiter (there was a big press release about it, and our dust detector science coordinator was swamped by phone calls for a day) and was given approval to increase its observations through real time commanding to a 10 hour observation. Most commands are stored on board in advance and the project doesn't like to send any extra commands unless necessary. Of course we had no idea that the dust storm was going to occur, so the only way to get the data was to send the real time commands. This would allow a complete sample of the dust stream over the period of a Jupiter rotation to allow analysis which might correlate it to part of the planet or part of the magnetosphere surrounding it. All the data was successfully received and sent off to Germany for analysis by the Principal Investigator. Jim Erickson Steven Tyler October 7, 1995 Here's what I did for the last couple of days...my journal topic for now: December 7 of this year will be a very busy day for Galileo. We'll have our encounter with Io, our closest approach to Jupiter, our passage through the most dangerous part of Jupiter's radiation environment, the relay of data from the Galileo Probe (which separated from our Orbiter in July and will fall into Jupiter on December 7), and the biggest burn of our "big" 400 Newton engine (which supplies about 100 pounds of thrust). This burn will put Galileo's Orbiter into an orbit around Jupiter; if the burn fails, we will fly on past the planet, and our opportunity for getting into orbit will be lost. You might wonder about a couple of things. First, what if our burn is off by just a little bit? Can we correct it afterwards? Second, do we practice for problems like this with some sort of "dry run" of the actual work? It turns out that we do. One of the most interesting dry runs happened in the last few days. We pretended that we'd had a little bad luck and that our trajectory near Io was a little bit off. In addition, we pretended that the accelerometer (which is supposed to measure how much our velocity has changed) was also a little bit off, and that these two errors added. In this case, we would have to figure out what commands to send to the Orbiter, and then send them. The whole process would have to be done in less than 18 hours? Could our team do it? Why do we have only 18 hours to send up a maneuver to the spacecraft? You may think that we'd need to do it before Galileo gets too far past Jupiter, but that isn't the real problem. The real problem is that every day, the Sun gets closer to getting between us and the spacecraft. When the Sun is right between us and Galileo, we can't get commands to the Orbiter. When the angle between us, the spacecraft, and the Sun gets too small, the commands we send start to get too much noise in them. This is scary: you tell the Orbiter to do one thing and it does something else...something unexpected. We've decided that once the Earth-spacecraft-Sun angle gets to be less than 7 degrees, we won't send any more commands until Galileo gets out from behind the Sun (back to an angle of at least 7 degrees). We'll reach this 7 degree angle on December 9, just 2 days after our big Orbit Insertion burn, and we don't get back out until December 28. So we have only a short time to figure out how bad our burn was, design the commands to clean up our mistakes, and send them. If we can't get the work done in time, we'll need to wait another three weeks, and by then it may be too late to get back to the Tour we've planned. In the first part of our exercise, the Navigation Team takes practically all of its allotted 5 hours to figure out what maneuver we'll need to perform (on the basis of rather limited information). This is a very tough test for them, and they do a great job. I'm sure they must be thinking that the rest of the exercise will be easier than their part was. We merely have to do what they tell us to. The Navigation Team is aware of the kinds of problems the Orbit Engineering Team may have in creating the appropriate sequence. They know that we have to decide how to divide up the pulses of the little 10 Newton thrusters, make sure that the spacecraft is pointing the right way, doesn't overheat or get too cold, and so forth. They have taken a little time to make sure that we can fit all these engine pulses into the roughly 17 hours we have to perform the maneuver. They also know that the commands will take up space in the spacecraft computer, and they want to be sure that we'll have enough space to fit everything in. I'm the coordinator for the Orbiter Engineering Team. We get the proposed maneuver from the Navigation Team and have 5 hours to design our burn sequence. Unlike the Navigation Team, we're not completely prepared. We haven't decided on a strategy for fitting a big maneuver like this into a small box. If we put too many pulses into each segment of the maneuver, before we readjust the spacecraft spin and pointing, it might endanger the whole maneuver. Of course, this is just a test ... we won't send it to the spacecraft ...so we could try something a little risky now, and change our minds for the real event. We decide to try a very conservative maneuver for this test, leaving out none of what would be our normally scheduled spin and pointing corrections. I like this: if we had to send such a maneuver to the spacecraft, it would be less risky. The downside is that rather than give the Navigation team all (or maybe 99%) of what it wants, we're giving them about 60%. But in December, our maneuver would save the Tour, while doing nothing would lose about a third of it. Now, can we get the work done in 5 hours? No, we can't. Someone else is using one of our computer files, and it takes 2 hours to access it. There's some confusion about what spin state we belong in, and our first try at a sequence overruns the computer data space we've been given. When the dust clears, we're more than 3 hours late! But the test isn't over. There's over 4 hours of pad in the schedule before the maneuver has to be sent to the spacecraft. If we miss our first "uplink window", there's a backup window which ends just minutes before the start of our maneuver. The Sequence Team has its turn next. They aren't ready either. They have to merge our sequence with the proper background sequence. But right now, it's October, not December, and the final touches have not been applied to their background sequence. They don't have the right one. This costs them two hours. But they aren't late: they were allotted 5 hours and get done 30 minutes early! Now, the Orbiter Engineering Team gets 4 hours to review the Sequence product. All of us have previously prepared checklists of questions to ask about the sequence, and we inspect the product to make sure it's all right. This time we make our deadline easily. Most of us are ready in 2 hours. Our maneuver is presented to the Project (which already saw it after Navigation proposed it and after we designed it). Since we're not really sending this to the spacecraft (not now, in October, at any rate), Project does not approve it. However, had this been December, with the Sequence Team having the right background sequence, this maneuver might well have been on time and approved. Tomorrow, we get to tell the Galileo Project management what we learned from our test. We've learned plenty about what we'll need to do to get our job done in time. Much of the work will need to be done well in advance, or we won't have a chance. I'm going to argue that we put a couple of sample maneuvers on our shelves, and make only the minimum changes between one of them and the real one when December comes around. --- Steven Tyler Headquarters, Washington, DC October 20, 1995 RELEASE: 95-188
Engineers will transmit a series of commands to
NASA's Jupiter-bound Galileo spacecraft today in an effort
to assess the state of its balky onboard tape recorder.
The flight team, meanwhile, was buoyed by a
preliminary assessment from Galileo's science team
reporting that at least half the mission's original
scientific objectives could be obtained in the event the
tape recorder is found to be unusable.
The tape recorder, which is used mainly for onboard
storage of imaging and spectral data from Galileo's
instruments, apparently malfunctioned October 11. The
problem was detected shortly after Galileo, due to reach
Jupiter on December 7, took three consecutive images
through different filters to produce a color image of
Jupiter and its major moons. The tape recorder failed to
stop rewinding as expected after recording the imaging
data. Commands were sent to halt the tape recorder, which
has since remained in a standby mode.
"For the past week, we've looked in detail both at
data from the spacecraft and from an identical tape
recorder in the testbed laboratory here," said Galileo
Project Manager William J. O'Neil at NASA's Jet Propulsion
Laboratory (JPL), Pasadena, CA. "We've identified a number
of both mechanical and electrical failures in the tape
recorder system that could explain this problem. Our
efforts today and in coming days will help us determine
whether the tape recorder can be restored to operation."
Commands will be radioed to the spacecraft this
afternoon to play back a small sample of data stored on the
tape recorder. The tape-recorded data, along with
engineering data reporting on the recorder's performance,
first will be stored in memory located in Galileo's central
data subsystem, then transmitted to the receiving stations
of NASA's Deep Space Network this evening.
"By early next week, we will be in a position to
report the results of our efforts to operate the tape
recorder," said O'Neil. "Successful commanding of the
device would still mean additional assessment and
troubleshooting. Work concurrently continues on a backup
plan to preserve the return of imaging and spectral data in
the event the tape recorder cannot be used," he added.
Galileo's tape recorder and the spacecraft's
guidance control computer were called into service as data
compression and storage links, in a sophisticated
alternative method devised to maximize data return from
Jupiter after Galileo's main high-gain antenna failed to
open properly. Loss of the high-gain antenna meant that
all spacecraft communications must be conducted at much
lower data rates through a low-gain antenna.
New techniques have been developed to edit,
compress and encode Galileo's data, including images, in
the spacecraft's computers, then store that data for
playback to Earth. Additionally, new hardware and software
changes at ground receiving stations have been installed to
further increase the amount of data transmitted from
Galileo's low-gain antenna.
Project Scientist Dr. Torrence Johnson of JPL
reports that at least 50 percent of the mission's original
science objectives could still be achieved if the tape
recorder is found not to be working.
"The impact of a possible loss of the tape recorder
is not as bad as people assumed when we first heard about
the problem," said Johnson. "Even without the tape recorder,
we have an exciting mission that allows us to address all our
primary objectives. Although the total number of pictures
and spectra we receive would be lower than with a tape recorder,
we would still have enough to do the job."
According to Johnson, among the mission's three
major areas of science investigations, it is the data
return from remote sensing instruments such as cameras and
spectrometers that would be impacted most by loss of the
tape recorder. Data from these instruments can be saved by
re-routing them directly to memory areas in the flight computer.
"The mission will still study all aspects of the Jovian
system -- Jupiter's atmosphere, its moons and its magnetic
environment -- and we plan to make a majority of the scientific
measurements that had already been planned," said Johnson.
One hundred percent of the atmospheric probe's
science objectives can be achieved without the tape
recorder, in addition to all of the Galileo orbiter's
survey of the Jovian magnetic and charged-particle
environment, Johnson said.
"The principal loss of data, if the tape recorder
is not usable, would be the number of images and other
high-rate spectral data that could be returned by the
spacecraft," said Johnson. Galileo spacecraft and software
engineers, however, are devising new backup methods to
store imaging and spectral data in available memory areas
within the spacecraft's central data processor.
Preliminary assessments indicate that at least 150 to
300 high-resolution images of the Galilean moons of Jupiter
and additional hundreds of Jupiter and Io volcanoes-
monitoring images could be returned over the course of
Galileo's two-year orbital tour.
The Galileo mission consists of an orbiter
spacecraft and an atmospheric probe, which was released
from the orbiter in July. The probe will parachute into
and directly sample Jupiter's atmosphere on December 7.
Its data will be radioed to the Galileo orbiter overhead.
Also on December 7, shortly after the completion of the
probe's mission, the Galileo orbiter's rocket engine will
fire to brake the spacecraft into orbit around Jupiter,
beginning a two-year detailed study of the Jovian system.
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