The Comet Shoemaker-Levy 9 (SL9) Collision
A Project of the Jupiter Space Station
The Jupiter Space Station Project at Tri-County Technical College started out in the Summer of '93 as a routine radio telescope monitoring project of Jupiter at 1420 MHz, and then temporarily veered off into a decametric receiving station. In the Fall of 1993 it became clear that comet Shoemaker-Levy 9 (SL9) was on a collision course with Jupiter. While working on the JSS project student enthusiasm and interest mounted as the projections and speculation poured in from research institutions and scientists about the collision with Jupiter.
The Jupiter Space Station Project was a combination of a radio telescope system, which can be operated as an unmanned, automatic system completely controlled by student-written software, and a group of interested students from Tri-County Technical College. Supporting advisors included scientists, educators, engineers, and technicians.
The educational mission of the Jupiter Space Station was to provide students at Tri-County Technical College an interdisciplinary, hands-on project work experience which captures the spirit of quality at the source, teamwork, and science/technology enterprise. Jupiter and Comet Shoemaker-Levy 9 were the catalysts.
The project team was composed of business, technology, and science students who participated in the design, development, construction, and operation of a completely automated, unmanned radio telescope. The system would be capable of monitoring the hydrogen line radio signals known to be emitted from Jupiter's hydrogen mantle-magnetosphere as well as from many other sources in the Universe.
Upon completion of the construction of the Jupiter Space Station, a two year college level investigative science project was initiated to monitor the collision of Shoemaker-Levy 9 (SL9) with Jupiter at the Decametric frequencies from 18 - 30 MHz.
This project work began during the Summer of 1993 when a group of four Computer Technology students completed their course requirements early for C Programming. The four students decided to write a radio telescope control simulator program for fun.
The program was running precision perfect by the end of the Summer and the fun became contagious. Thirteen computer students continued the work, and Electronics Engineering and Industrial Mechanics faculty and students began consulting and helping.
In late summer the actual construction of the Jupiter Space Station began on a 20 acre property outside Pendleton, SC, with station start-up beginning in early Spring, 1994. The radio telescope actually began tracking in February under control of student created software and hardware.
On July 16, 1994 we were locked on the SL9/Jupiter Collision with our system (see Diagram 1) at 20-30 MHz (Decametric) and on two events we received and captured a strong, broadband signal which coincided with known Jupiter magnetic radio noise phenomena (Non Io B and Non Io C) and the impact of SL9 fragments A and H.
These recorded signals lasted approximately 30 - 40 minutes and each occurred 45 -65 minutes after fragment impact on the backside of the planet. Descriptions with 3D Surface Waveforms and a Spectrogram are included as Figures 1 - 5.
This data was sent to UC-Berkeley and University of Florida for collaboration purposes and we presented our findings in a poster session of the 1995 Association of Lunar and Planetary Observers meeting in Washington [sic International Astronomical Union Colloquium 156 in Baltimore]. We also presented our findings at the Southern Regional meeting of the Society of Amateur Radio Astronomers (SARA) in February, 1995 and at the April annual meeting of the South Carolina Academy of Science.
To briefly summarize a few successes, one of our students was selected from among 400 candidates by NASA to attend the 1994 Space Life Sciences Training Program at the Kennedy Space Center. The South Carolina Academy of Science selected 8 of our students' technical papers for a Special Two Year College Focus Session, and inducted 15 members into the Academy. These students were selected co-winners of the Most Outstanding Paper Competition.
These eight papers are integrally linked to the work on the Jupiter Space Station Project and covered such diverse areas as radio astronomy receiver design, telescope hardware control, radio telescope automation, astronomy software functions, computer software control interfacing, astronomical data collection, and custom software for graphical and statistical processing.
Two of our students had their 'C' software, written to control a new product for a Canadian company, internationally distributed on the sample diskette given with that company's new board. The JSS project was selected for presentation at both the 1994 national meetings of the Society of Amateur Radio Astronomers (SARA) at Green Bank, West Virginia and at the National Tech Prep Conference in Baltimore.
In addition the project team and the JSS System has collected unique, unexplained signals from the SL9/Jupiter collision, and we have analyzed the data and prepared the data for presentations.
The Radio Telescope System
Originally the team decided to attempt to have the 1420 MHz antenna and receiver system ready for the Jupiter/SL9 collision, however in March at the recommendation of the student project leaders and from advice of several noted astronomers including Dr. Imke De Pater at UC - Berkeley, we dropped back to the decametric system. This was an interesting decision for several reasons. First, we relied on a panel of experts (professional astronomers, engineers, SARA members, ham radio operators, and local industry employees) to help us plan our system. Second, the student project leaders came up with the recommendation themselves after seeing the hard realities.
The team backed off the 1420 MHz system because we realized that tuning our 10' disk, feed horn, and receiver system to be sensitive to a 5 to 50 Jansky signal could take a year of debugging and incredible optimizing. Further, Dr. De Pater suggested that the "richer" data may well be in the decametric domain anyway. Our center frequency design was set for 20 MHz.
Our system configuration, setup by Doug Starwalt, is described in Diagram 1. An 18" loop antenna fabricated by Paul Tankersley, was mounted inside a 10' parabolic dish. The dish acts as a shielded ground plane and masks side lobes of the loop. The copper tubing antenna design was taken from an excerpt about a Bob Sickle's loop design in the December, 1989 Sky and Telescope, and other articles in the SARA Journals.
It is my opinion that the specifications for this loop are not critical for this radio astronomy application because we could receive annoying signals from Australia at 8 MHz and all the CB channels at 27 MHz, loud and clear. It should be pointed out that anyone could get into this Jupiter game with the simplest of equipment including inexpensive radios and tape recorders.
The student software and controller could point the dish anywhere in the sky with 1/4 degree accuracy. For Jupiter work at 20 MHz, one only needs to point the loop to the nearest quadrant of the sky where Jupiter happens to be at that time.
Back to Diagram 1: at the antenna we ran the signal through a Mini-Circuits low pass filter to knock out higher frequency interference, and then we amplified the signal with a Mini-Circuits 24 db pre-amp for the 100' run to the radio shack. We had a very high quality RG-8 cable run, until my dog Jupiter ate the 16' coming out of the ground. Jupiter and his sister Saturn were adopted at the pound in the Summer of '93 when we started this project. After they stopped laughing the Northland Cable Company of Liberty, simply by being asked, replaced the 16' out of the ground piece of cable with connectors for free.
Once inside the shack we immediately used another 24 db pre-amp because we were driving both receivers and a spectrum analyzer. A Mini-Circuits splitter was employed to send the signal to an expensive Tektronix spectrum analyzer and to the two continuous coverage radios. The spectrum analyzer was loaned to us by AT&T, Liberty, SC. As the comet crash approached Dr. Francisco Reyes at the University of Florida suggested that if we had a spectrum analyzer then the tuning for a Jupiter signal would be easier as we could "see" an entire 10 MHz frequency spectrum. He was right... as the signal arrived from Jupiter the spectrum analyzer lit up like comb teeth.
At the suggestion of both Doug Starwalt and Jim Carroll of SARA, the audio signal was recorded on VHS stereo video tape. Our ICOM 71-A has a 70 MHz IF output which we routed to a small detector built by a SARA member, Carl Lyster (Knoxville, TN), and which in turn was fed to the computer (386 Clone) via an A/D card made by Prairie Digital. Our students developed the software to capture, graph, and store these signal strengths off this board.
Finally, the motors' controller (RA and Declination) was developed by students, faculty, and alumni of the Electronics Engineering Department at the College. Our Computer Technology students, again, developed the driver software for the telescope motor controller and the Jupiter astronomical algorithms for where to point the telescope.
Diagram 2 is a chart of some of the accessories used on the project which are components described in Diagram 1.
Diagram 2 - Accessories List
|Mini-Circuits LP Filter||> 32 MHz Stop Band||
|Mini-Circuits Pre-Amp||+24 db, < 400 MHz||
|Mini-Circuits Splitter||-3 db, < 400 MHz||
|JSS Ephemeris Software||Jupiter Events Ephemeris||
|Sound Blaster 16 ASP||16 Bit Audio A/D||
|Spectra Plus Version 3||Spectral Analysis Software||
|Carl Lyster Detector||5 - 75 MHz In / 0-5v Out||
|Prairie Digital A/D||PC 8 Bit A/D, 24 PIO Control||
The Game Plan
Having a receiving system is only half the battle. A game plan of training, scheduling, dry runs, and coordination was critical to the success of the project. Our radio man, Doug Starwalt is an amateur radio operator and he is always hustling... he entrapped another Ham, Buz Johnson, from Easley, SC to fill in as the radio team leader because Doug had to go to Kennedy Space Center. Buz also supplied the Kenwood HF transceiver used in parallel with our ICOM 71A receiver. Ham radio operators make natural amateur radio astronomers. Five students who graduated in May formed a group to man the system during the seven day crash period. Kim Fisher, Barry Wyatt, Matt Brazier, Ken Elrod, and Geri Schauer trained on the system, collected preliminary data, and monitored the six crash nights.
Training is an interesting aspect of this process. One has to know what to listen for. One has to conduct tuning strategies to locate a Jupiter signal. On our two receivers we employed both the "scan" strategy and the "sit and listen" strategy. In scan strategy we would tune 50 - 60 kilohertz, listen twenty seconds for the tell-tale signals, and tune again. The noises of Jupiter vary: waves breaking on a beach (L Waves) or the ranging machine-gun fire waves (S Bursts). Upon identifying a potential signal the operator performs two tests. In test one you check the "broad bandedness" of the signal (40 - 100 KHz) and in test two you would check for CW or SSB man-made induced false signals. We used tape recordings of Jupiter signals to sensitize the monitoring team to the sounds of the various radio-magnetic events of Jupiter.
The scheduling of observing time is almost an art form. Jupiter radiates signals from three strong storm regions of its hydrogen mantle-magnetosphere. Magnetic regions are labeled A, B, and C. When the inner moon Io comes into proximity of these regions, the Jupiter signals are more intense. Our team characterized these six signals as Io-A, Io-B, Io-C, Non Io-A, Non Io-B, and Non Io-C. Finding an accurate program to tell us when these events may be radiating towards Earth is not simplistic. As an amateur there are hours and hours of wrong times to be listening for signals from Jupiter. Even during predicted times capturing signals range from 10 to 40 percent.
We therefore developed the Jupiter Space Station Ephemeris Program which not only gives accurate positional and ephemeris information about Jupiter, but also included a graphical simulation of these six events. This program was distributed free through SARA's Jupiter Group chaired by Tom Crowley out of Atlanta. It was free for SARA registered Jupiter Group observers and a small fee for all other interested observers. Jeffrey Lichtman of SARA sells the software to interested parties with a portion of the proceeds going to SARA's Robert M. Sickles Amateur Radio Student Fund. A copy of the User Guide was subsequently put on the JSS Web Site.
Coordination is the last element of a successful game plan. When potential signals are captured, one needs to immediately confirm these signals. By telephone Tom Crowley of SARA's Jupiter Group served as a focal point for relaying and confirming suspicious signals. On our first signal reporting of July 16, Tom put a message on an Internet BBS and we received confirmation from both Germany and New Mexico. We also reported to Dr. Francisco Reyes at the University of Florida as we found potential signals.
Jupiter versus SL9
On Saturday, July 16 when the first fragment (A) struck Jupiter we were surprised by what happened on the radio. First, the Jupiter signals arrived uncharacteristically in late afternoon. The fragment struck around 1600 EDT (light time iteration factored in) but the resultant radio signal arrived about 1700 EDT. Our team was scheduled to work 1800 - 0130 EDT but astronomers were suggesting that we might hear something in the afternoon if Jupiter's magnetosphere was dramatically impacted, especially in the higher frequencies (20 - 30 MHz). We happened to be sitting around the receivers (locked on fixed frequencies) when the spectrum analyzer lit up like a Christmas tree and a low rumbling came over the receivers for 40 minutes. It startled us enough that we went outside looking for the blimp overhead. The signal was captured at 26.5 MHz and was broadbanded (10 MHz) with in and out fading.
We will not speculate on the origin of this signal (leaving it to professionals) but there was some uncertainty as to whether the signal was related to the SL9 collision. Our uncertainty was laid to rest on Monday afternoon, July 18 when again, one hour after fragment H went in, we captured the same signal a second time. This frequency however was at 22.0 MHz. This rumbling signal has not been received on other days.
Because our data was captured as audio, we used an audio signal processing package, Spectra Plus Version 3.0, to analyze our signals by first digitizing the analog signal with a sound card (Sound Blaster 16 ASP) and then Fast Fourier Transforming (FFT) the signal from the time domain to the frequency domain. This package from Pioneer Hill Software (Poulsbo, Washington) puts professional radio spectral analysis in the hands of amateurs.
Beginning with Figure 1, one notices that this is a sample of the data collected on July 16, 1994 at approximately 21:03:30 UT. Fragment A of SL9 has gone into Jupiter 63 minutes earlier. Jupiter at this point is in the midst of a weak Non-IO B storm with Earth ionospheric conditions characterized as being very poor (which is good for radio astronomy signals attempting to pierce our ionosphere).
One can see the normal radio noise in the audio FFT transformed signal from .1 to 8 KHz. Time begins at the top of the graph (6.49 seconds) and moves downward. This is a 3D surface wave graph of the audio signal. As the signal wave arrives from Jupiter we have only speculation as to why the complete radio spectrum becomes quiescent. Then the signal energy jumps out of the frame in the .1 - 3 KHz audio spectrum. The lack of signal energy from 3 - 21 KHz catches your attention.
The signal energy is characterized by a "twin-peaks" effect founded around 300-400 Hz and 600-800 Hz. This may be responsible for the rumbling vibration we hear in the signal.
This signal is approximately a .2 second snapshot of a 16 seconds segment of the digitized signal. The 16 seconds segment is part of the larger 35 minutes of audio data received.
In Figure 2 one notices that the "twin peaks" are not uniform, but rambling. The 3D surface map is sampled at 44,100 Hz with a 512 FFT size. We used averaging to smooth out the jaggies and a Bartlett algorithm to smooth the time series discontinuity at the ends of the FFT samples.
Figure 3 (next page) shows the Jupiter signal fading and we observed that the quiescence noticed in Figure 1 was missing as the radio noise immediately rears its head as the signal fades.
Figure 4 is the 3D surface map for July 18 as Fragment H went into Jupiter. The signal is similar to Fragment A's spectral map except that the spectrum ranges out to 6 KHz instead of 3 KHz as seen in Figure 1. The "twin-peaks" are noticeable in the Fragment H surface maps and the rumbling was again heard on the receiver.
Figure 5 is a spectrogram. The amplitude of the energy is shown in shades of gray with a gray scaling/dB scale on the right side. This is simply another perspective of the 3D surface map of Figure 1 featuring signal acquisition on July 16.
We ran a spectrogram of the first 60
seconds and have produced a second set of Figures 1 3 [below] which represent our
data at the beginning of the Fragment A event. We re-sampled the data because many professionals and amateurs reported a
galactic continuum absorption hole early in the impact. Figure 1
shows a continuum spectrogram after the reported absorption hole,
Figure 2 is a spectrogram of our recorded data near Fragment A impact, and Figure
3 is a graph of the RMS levels around the Figure 2 absorption
The waveforms in Figures 1 - 5 are both representative and repetitive of all the waveforms we have received.
We have shown these signals to several people and they have made some interesting comments. The quiescence in the signal arrival may be a phenomena of the detector of the receivers in AM mode, or may be a "tsunami" wave effect caused by the giggling of either the magnetosphere/ionization layers of Jupiter or Earth. We have all heard the stories of how the water runs out of the harbor just before the tsunami hits. The gaseous shock-compression wave on Jupiter created by the fragment's impact may be responsible for triggering the strong electromagnetic waves received at Earth. If this suggestion has merit then one can only ask the next question: is there seismic information embedded in these waves? We have the data. Again, we will leave the theoretical explainations to the professionals.
In addition to the strong evidence of a radio phenome which we captured on two different fragment events, our data also confirms the widely recognized continuum absorption hole found in several fragments.
At Tri-County Technical College we believe that this Jupiter Space Station Project has been an unqualified success for all the students, faculty, and industries in our community. Local experts such as Dr. Lewis Fitch (retired) of Clemson University and regional experts such as Dusty Warner and the Southern Region SARA members assisted us unreservedly. A few of us will carry on to implement the 1420 Mhz system, and to optimize the decametric system using a scanner and custom computer software. This group will formally organize as the Jupiter Space Station Group.
In conclusion it is my professional opinion that we will be wrestling with explaining this phenomena for several years to come. As hunters we have brought home some interesting data; now all we have to do is explain it.