Selected Articles from the
October 1998 Odyssey
Editor: Norm Cook
"This is only a Test..."
By Robert Gounley
The meeting had taken longer than anticipated. It was already an hour since I left the Test Bed. It was still simulating how our spacecraft will behave in flight.
The Test Bed looks quite ordinary. Through windows, a visitor sees only a large white room with olive drab computer racks and heavy tables. >From assorted electronics, cables drape like ivy to find root under the floorboards to emerge again from another nook. Engineers in their lab coats watch numbers flicker on computer monitors. When our spacecraft flies, screens like these will tell us where it is pointed, how warm it is, what computer programs it's running, and a hundred other things we will want to know. In space, you can't pull a spacecraft aside to look under the hood, but you can be sure you have a good instrument panel.
Today we simulated activities scheduled for a week after launch. When we do it for real, our commands will cause the spacecraft to slowly turn until a part kept in shadow sees the full sunlight. Under this gentle baking, contaminants picked up during launch evaporate, allowing us to operate delicate equipment safely. A day later, our programmed instructions point the spacecraft back to its original direction. All the while, folks like me study the data the spacecraft sends back, hoping to fill their daily reports with words like "nominal" and "as expected."
Earlier, I had taken the commands and packaged them into electronic files to be loaded onto a computer that behaves just like the real spacecraft. Test time is too precious to use up a whole day, so my procedure calls for us to "jump the clock." With software trickery, we can make the simulated spacecraft pretend to do something today, then quickly make it think it is already time to do tomorrow's chores.
On a real spacecraft, resetting the clock could be a traumatic if done incorrectly. One way or another, everything uses the spacecraft clock and software designed to protect against faults could get horribly confused and perhaps cause harm. To a spacecraft in flight, the jump clock procedure is a blunt instrument to be used only in extraordinary circumstances. In the Test Bed, it's a powerful "time-saving" tool.
Today's test is running well. The Test Conductor and I sent instructions and the simulation obediently responded. In a cyberspace universe, the spacecraft warmed its cold feet in the sun. Next, we exercise our god-like powers to jump the clock, command a turn back, and finish the remainder of the test. We might even go home before dark!
First, we commanded the programs which point the spacecraft to their most passive mode--without this step, jumping the clock could trigger a violent reaction as they try to comprehend how Earth and Sun could move so much in an instant. That done, we set a new spacecraft clock time and prepared to clean up a few loose ends. That's when the data on our screens froze.
The server that channels telemetry from the simulation to our workstations can quit at inconvenient times. This time, it happened just prior to a meeting I needed to attend. We call in the techs to fix the problem, trusting the simulation to keep running until we could see data again.
When the Test Conductor and I came back, telemetry was working again. As an afterthought, I wondered aloud if it was safe to leave the simulation in an idle state for so long. While we speculated, our screens showed that the simulated spacecraft had taken matters into its own hands.
Left free to drift in cyberspace for over an hour, the solar panels had tilted away from the simulated Sun. When the panels stopped producing enough power for the simulated spacecraft, its batteries began to provide simulated power. When their charge had emptied dangerously, onboard programs kicked in, turned off non-essential loads, and aggressively pointed the spacecraft and its panels back to the Sun.
This was all a test, but the consequences were concrete for us. We'd have to repeat the simulation, but only after the batteries had fully charged. That would take hours--just like in flight. That part has no speed-up feature.
Humbled by this experience, we completed our task slowly and deliberately. We cut no corners. In the end, we had did everything required with just minor frustration to the two of us. It was only a test.
In less than two weeks our spacecraft launches. Then it will be real.
Jupiter's "White Ovals" Take Scientists by Storm
As powerful hurricanes pummel coastal areas on Earth, NASA space scientists are studying similar giant, swirling storms on distant Jupiter that have combined to spawn a storm as large as Earth itself.
Three separate cold storms, called "white ovals" because of their color and egg shapes, have been observed in one band around Jupiter's mid-section for half a century. Two of the storms recently merged to form a larger white oval, according to scientists studying data from NASA's Galileo spacecraft, the Hubble Space Telescope, and the Agency's Infrared Telescope Facility atop Mauna Kea, HI.
"The newly merged white oval is the strongest storm in our Solar System, with the exception of Jupiter's 200-year-old 'Great Red Spot' storm," according to Dr. Glenn Orton, senior research scientist at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA. "This may be the first time humans have ever observed such a large interaction between two storm systems."
Each of the white ovals that merged were about two-thirds the diameter of the Earth before the merger, when they combined to form a feature as large as the Earth's disc. Although scientists have observed the end result of the merger of the two white ovals, the actual "collision" took place under cover of darkness while Jupiter was turned away from view.
This new, powerful white oval has a mysterious trait, according to Orton. "We can see it, along with the other white ovals, at visible light and some infrared wavelengths, but we cannot see the new white oval at certain infrared wavelengths that peer underneath the storm's upper cloud layers," Orton said. This might mean the storm is in a transition stage, undergoing a rebirth after the merging of the two storms.
"With mature white ovals, we can see the upwelling of winds in the center, which in turn leads to downwelling around it," Orton said. The new white oval has a very cold center (about -251 degrees F or -157 degrees C) that is about one degree colder than its surroundings. "Because of this, the oval may have generated a thick cloud system which obscures the downwelling," Orton said, which could explain the new oval's "disappearing act" at some wavelengths.
Adding to the mystery is the fact that a nearby storm rotating in the opposite direction to the new white oval used to be warmer than its surrounding. "This probably means that the feature contained mostly downwelling winds," said Orton. However, Galileo's photopolarimeter radiometer instrument showed this feature had cooled down to temperatures that were about the same as its surroundings.
Orton suspects that this storm somehow lost power and is no longer spinning as fast or downwelling as strongly as a year ago. This storm was once positioned between the two smaller white ovals that merged, and Orton theorized that when this storm system lost power, it removed the buffering mechanism that kept the two original white ovals apart.
Orton and his colleague, Dr. Brendan Fisher, a Caltech postdoctoral fellow at JPL, based their conclusions about the temperatures using data gathered by Galileo on July 20, 1998, during the spacecraft's 17th orbit of Jupiter and its moons. Although much data from the flyby of Europa in that time period was lost because of a problem with the spacecraft's gyroscope, Galileo's photopolarimeter radiometer gathered the new data on the white ovals before the anomaly occurred.
The photopolarimeter radiometer measures temperature profiles and energy balance of Jupiter's atmosphere, helping scientists study the huge planet's cloud characteristics and composition. Scientists believe that the bright, visible clouds of the white ovals are composed of ammonia.
Galileo has been in orbit around Jupiter and its moons for 2 1/2 years, and is currently in the midst of a two-year mission extension, known as the Galileo Europa Mission. JPL manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is a division of Caltech, Pasadena, CA.
Related images and information on the Galileo mission are available on the Internet at the Galileo website: http://www.jpl.nasa.gov/galileo.
NASA at 40
Historic articles, dramatic video, and photos from the archives of The New York Times recalling the high points and low points of NASA's four decades of space exploration are available in a special report on The Times on the Web, http://www.nytimes.com/library/national/science/nasa/index.html.Site registration or paid subscription may be required.
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