Selected Articles from the
November 1999 Odyssey
Editor: Craig E. Ward
October Skies over Los Angeles
By Steve Bartlett
Editors Note: On October 2, BMDO tested an antiballistic missile system. The ICBM target was launched from Vandenberg AFB. The anti-ICBM was launched from the Kwajalen Missile Range and destroyed the target. This is one report on what was visible from Southern California.
Tina and I had just left a friend’s house at 7 and were headed westbound on the 134 when we saw the Minuteman ascending right in front of us. The missile climbed slowly toward the southwest on a brilliant white plume. As it got higher and higher in the atmosphere, you could easily see the plume expanding.
We watched as the missile turned toward the west just before first stage burnout, presenting us with a tail-end view. It looked like there was this glowing star surrounded by a gray cloud sitting rock steady in the sky.
When
the second stage kicked in, we could see what appeared to be six streamers
radiating from the center and the "star" in the center turning gradually
hazier and hazier until it disappeared.
We saw the upper regions of the plume spreading out and refracting the sunlight into a beautiful semi-circular rainbow. We also noticed that the winds at all altitudes must have been fairly low,because the exhaust trail hung in the air without much change for a LONG time. (Bear in mind that I was watching all of this while driving and avoiding traffic on several miles of the 134/101 freeways.)
About half an hour later, after we'd gotten home and I was checking my email, I realized that Mir was due to be flying overhead in the next few minutes. I went out to my front yard, half expecting to see nothing because of the light pollution in the L.A. basin. Looking to the northwest, I spied a bright star tracing an arc across the heavens.
A young couple walking along the sidewalk saw me looking up at the sky and the woman remarked, "Beautiful night." I said to her, "Yes, it is. In fact, you can see the Mir space station right now." They stopped and said, "Really? Where?" I pointed out the "star" moving against the background sky. They turned their heads up and watched the station until it disappeared.
The man said, "Whoa . . . cool." n
Kill Vehicle Illustration from Ballistic Missle Defense Organization.
Reading Braille
Part 2
By Robert Gounley
Editor's note: Part 1 of Reading Braille can be found in the October 1999 issue.
About 6 AM on a warm July day in Southern California, about a dozen members of Deep Space 1's flight team received an urgent pager message. Their spacecraft just had a problem. While taking navigation images of asteroid Braille, something caused internal fault protection routines to stop what the spacecraft was doing, turn towards the Sun, and wait for instructions. In the nine months of operating DS1, we'd encountered problems like this before and commanded it back to full operation in about a day. Ordinarily, this would be only a minor inconvenience.
However, today wasn't an ordinary day. DS1 was going to fly in the vicinity of a small asteroid named Braille in about 15 hours. This would be the only science gathering encounter of the prime mission. If we didn't pull things back to normal in about eight hours, we'd miss critical maneuvers required to place the spacecraft on a proper course. On board,the camera had only just detected the mile-wide rock the night before and we'd need every opportunity to be certain that we didn't miss the target. That meant we'd have to restore normal operations in record time. There was no time for mistakes.
Within an hour, DS1 engineers were gathered in front of their computer monitors. What they saw told them DS1 was safe following some internal confusion in its inboard computer. It seemed ready to start up again, but were we missing something? Tests with simulators on the ground showed no problem with the optical navigation sequence the spacecraft had just aborted from. The sequence DS1 had to complete for the asteroid encounter was much more complicated.
By the time the rest of JPL had begun arriving for work, the DS1 Flight Team was already assembling a long list of commands from contingency procedures planned for just such emergencies. First, we'd need to turn the spacecraft back to its original Earth-facing attitude. Once there, we could converse at a proper speed using DS1's high-gain antenna dish rather than the slow whisper sustainable through omnidirectional antennae that work whatever the orientation. Other commands would turn instruments back on and select the proper antennas. Things had seemed to be going smoothly. While one team worked to prepare the spacecraft, another was busy trying to understand what had gone wrong only a few hours earlier.
Sharp-eyed software engineers caught the problem. We had tested the optical navigation sequences individually and rebooted the Tested after each test. The sequences worked fine by themselves, but on the spacecraft a software pointer was being indexed each time. Due to a coding error, the last OPNAV moved the pointer outside of its prescribed memory area and the inboard computer tried to interpret stored data as instructions. Correctly, fault routines inboard determined that something had gone awry and shut things down.
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| DS1 encounter of Braille. NASA artwork. |
This particular problem was specific to what we were doing that morning and would not recur in activities planned for later that day. We could continue with our preparations of repowering the combination camera/spectrometer, designed to image the asteroid and measure its composition, and the ion/electron spectrometer that would try to detect any charged particles swept off the surface by solar wind. However, when the spacecraft's computer rebooted, it cleared data gathered to compute its position and velocity relative to Braille. We knew we were approximately on course, but there was no room for approximations. Even with our camera's powerful optics, Braille would be little more than a dim speck unless DS1 could swing within tens of kilometers of the surface. Without more pictures telling us where Braille was, the flyby could easily miss by hundreds of kilometers.
We had planned a couple more opportunities for DS1 to chart its course and correct itself. These would be within six hours of closest approach. We'd hoped these last few corrections would amount to minor improvements in the trajectory, but now they were critical. So close to the asteroid, the spacecraft must do everything itself -- there wasn't time to look over its shoulder to catch new problems in the programming. This one shot would be for all the marbles.
The flight team worked quickly, but deliberately. Sending the wrong command could cause another reboot that would put the spacecraft right where it had started, with no hope of recovery in time. Cautiously, we watched hibernating systems come back to life. Everything appeared to be well. Finally, we loaded and activated the sequence that would guide the spacecraft to a flyby of the asteroid. There was perhaps twenty minutes to spare.
The team was exhausted, but still riding an adrenaline rush. Against difficult obstacles, DS1 looked ready. However, everyone held there cheering until we could see how DS1 would behave.
To find its position, DS1 must turn away from the Earth to point its camera towards Braille. While detailed information about what DS1 was seeing and doing poured into its inboard memory, the spacecraft's low-gain antennae could only give us a few hints of what was going on. Watching the radio signal we could see when the spacecraft was turning and when it was firing engines to correct course. Everything we could see appeared reasonable.
News of the excitement that morning had spread to the entire Lab. By early evening, folks who had worked on the project years earlier had found themselves a corner to watch what was going on. Within an hour of the flyby, the control room had filled to about three times its normal capacity. No one complained. This had become a family affair; their offspring was about to perform in front of entire world.
All of us had the script nearby. Even if DS1 got close, its camera would still have to track a quickly moving target. The best opportunities would last only a few minutes. We had programmed the spacecraft to pick Braille out from amongst other stars, which were not much dimmer, and stay pointed at it while the camera shuttered. The proof of how well it had done would come as the pictures were played back the following day. As we watched, there were only a few numbers flashing across our screens that attempted to summarize how well DS1 was completing its tasks.
The room counted the seconds until flyby and applauded the moment it passed. DS1 was still operating and still taking pictures. As the elation subsided, small pockets of conversation simultaneously rose in different corners of the room. The little bits of information were telling us that DS1 was having trouble finding Braille. It could be doing just fine, but it was telling us that it wasn't sure that it was pointing properly. It might be seeing a very dark surface, hard to detect from dark sky that would garner front-page photos around the world. Or the pictures might be of dark sky, the asteroid just beyond the camera's field of view.
Everyone left for home that night in uneasy anticipation. We had rescued the spacecraft well enough, but the public expects no less of us. To be judged worthwhile, there would have to be some noteworthy scientific discovery in the data collected. We even know what we had until tomorrow.
That seemed a very long way away.
TO BE CONTINUED...
DS1 graphic from NASA/JPL/CalTech.
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