CASSINI RPWS STATUS
CASSINI RPWS STATUS
Slight modifications were made to some of the RPWS Jupiter observation modes today. These make minor changes in receiver and sensor combinations to improve the Jupiter science return. Experience gained over the last several weeks of Jupiter observations led to the decision to make these changes. The RPWS instrument continues to operate nominally and is returning spectacular data, particularly on Jovian radio emissions in the frequency range from about 10 kHz to 16 MHz.
Early this morning Cassini turned to begin its 6-month long intensive study of Jupiter centered on a closest approach on 30 December. RPWS was configured for this new mission phase just before, by raising its nominal data rate from the 200 bits per second it has been at for several months to 1000 bits per second. For the next several weeks, the spacecraft will execute a complicated sequence of observations repeating once every 5 days. As part of this "template" RPWS will acquire high resolution data during a few brief periods designed to study particular features of Jupiter's complex radio spectrum. The RPWS is healthy and the team is ready for the analysis of what promises to be an exciting data set.
Jovian
radio emissions as viewed by Cassini RPWS
Cassini is well into the so-called C22 sequence, which is the first of 4 sequences which have Jupiter observations as a prime objective. RPWS has observed Jupiter ever since its first turn-on ten days after launch, but as the distance to Jupiter has been decreasing the signal level from this very intense radio source has been increasing. The figure above shows a typical set of observations taken over a ~10-hour Jupiter rotation which shows examples of several of the known Jovian radio emissions. The format of the display is the intensity of radio waves as a function of frequency (vertical axis) and time (horizontal axis) with intensity encoded via the color bar at the right. At the time of these observations, Cassini was about 1,350 Jovian radii from the planet, or a little over one-half of an Astronomical Unit. The various emissions are labeled with the established jargon of planetary radio astronomers. For example, the Io-B emission is an intensification of the decametric radiation when Io is in a particular phase of its orbit as seen by the observer, in this case near 90 degrees. That is, at this time, Io is at its greatest eastern elongation with respect to Jupiter. The non-Io-A emission is an emission which is independent of Io's position, but occurs over a range of longitudes centered near 300 degrees. The hectometric radiation at somewhat lower frequencies seems to blend seamlessly into the decametric emissions at higher frequencies especially near 0800 spacecraft event time (SCET), demonstrating the difficulty in understanding whether the decametric and hectometric emissions are truly different in any respect other than frequency. The broadband kilometric radiation is usually observed when the spacecraft is at a magnetic latitude of greater than about 10 degrees. The decametric, hectometric, and broadband kilometric radiation are all thought to be generated over a range of altitudes over the Jovian auroral zones and are intimately related to the aurora. The narrowband kilometric radiation, on the other hand, is generated on the outer edge of the Io plasma torus, probably by a totally diffferent generation mechanism.
The RPWS has been on for a good part of this year making observations of plasma waves in the solar wind and early observations of Jovian radio emissions, as a prelude to this fall and winter's intensive Jupiter campaign. The instrument was turned on 6 Feb. 2000 and then turned off on 5 Mar. for Cassini's AACS flight software load. RPWS was back on again from 22 April to 27 July but received only spotty data during solar conjunction in May. A flight software update for the RPWS was successfully performed on 1 June. Since 27 July, the instrument has been off for the Probe Checkout and CDS flight software load operations. RPWS is currently scheduled to be turned back on on 4 September for 6 months of continuous Jupiter studies centered around closest approach on 30 December.
The RPWS instrument was turned off by a sequenced command as planned today. The instrument performed flawlessly during its month-long operation during and following the Earth swingby. The next planned science operation is to be in February 2000 when the high gain antenna can be pointed towards Earth indefinitely.
A summary
of the Cassini RPWS Earth encounter observations
The above spectrogram illustrates the myriad of radio and plasma wave signals detected by the RPWS instrument as it flew by Earth on 18 August 1999. These observations are our best indication so far that the instrument and, indeed, the Cassini spacecraft will return excellent information on the Saturnian system in 2004.
The RPWS instrument was turned on August 13, 1999 in preparation for its Earth swingby operations. Beginning today around 10:00 GMT, science telemetry from the instrument was acquired and it appears that the instrument is healthy and performing as expected. During the swingby, two special modes of the instrument will be verified. One of these enables the identification of plasma wave modes by providing information on polarization and direction of propagation. The other mode provides direction-finding and polarization measurements of radio waves, such as those produced naturally in Earth's auroral zones.
The RPWS instrument completed a 24-hour maintenance activity today. For this activity, a bias of 32 Volts is applied to the Langmuir probe. This bias attracts electrons to the probe and the electrons help to clean any contaminants from the surface of the probe.
Data have begun to return from the RPWS observations during the 24 June Cassini flyby of Venus. All indications are that the instrument performed precisely as expected and the quality of the data received thus far is excellent. Playback of the Venus data will continue throughout this week.
The RPWS instrument completed a 24-hour maintenance activity today. For this activity, a bias of 32 Volts is applied to the Langmuir probe. This bias attracts electrons to the probe and the electrons help to clean any contaminants from the surface of the probe.
The RPWS instrument completed a 24-hour maintenance activity today. For this activity, a bias of 32 Volts is applied to the Langmuir probe. This bias attracts electrons to the probe and the electrons help to clean any contaminants from the surface of the probe.
The RPWS was turned off early today as expected via a command in the sequence controlling Cassini's operations throughout the instrument checkout period. Since December 30th, the instrument has performed flawlessly and has proven itself ready to make important contributions to our understanding of the Saturnian system.
RPWS was turned on again after Cassini was brought back to its High Gain Antenna to Earth-Point configuration. The instrument is in excellent health and is monitoring instrument checkout activities.
RPWS remains on and is functioning well. The team has now had a chance to try some preliminary background subtraction on some of the high frequency data and the two spectrograms below show some results.
Type III Solar
Radio Burst Storm
The first is a set of relatively intense bursts observed on 31 December with Langmuir waves accompanying them at lower frequencies. The abrupt change toward the end of this spectrogram represents the beginning of some of the RPWS checkout activities; the horizontal lines are interference sources on the spacecraft which appear amplified by the crude background subtraction employed here. Note that the amplitude scale is only relative in this background-subtracted presentation.
The second shows a "storm" on 4 January of a large number of solar bursts, most of which at relatively low intensities.
Type III Solar
Radio Burst and Langmuir Waves
These are examples of solar wind wave phenomena observed by the Cassini RPWS instrument during its first day of monitoring after its checkout. Type III bursts are radio waves excited in the solar wind by fast electrons released by solar flares and associated dynamic phenomena on the sun. Ion acoustic waves and Langmuir waves are naturally-occurring plasma waves commonly found in the solar wind.
The RPWS is functioning well. Later today and through tomorrow the instrument will exercise several different scientific observational modes.
The RPWS checkout has just completed successfully. To the best of our capability to analyze the data in real time, it appears that all aspects of the checkout were successful and each instrument mode functioned as expected. Substantial analysis will be required to fully assess the noise characteristics of the RPWS in its stand-alone state (all other instruments off, except for MAG), but we are generally impressed with the noise levels observed during the test.
DSN and JPL support during the checkout were superb; we know of only one short period of a few minutes when data were lost due to going two-way near the beginning of the checkout, however, this was during the initial turn-on and did not affect any of the specific tests we performed. Also, our IEB (Instrument Expanded Block) was uploaded successfully on the first try, even though we followed this with a second upload to be on the safe side. The data flow to Iowa was never more than a few seconds behind, even during the high rate portion of our test.
RPWS is currently in a monitoring state which will be used to observe any interference which might be caused by other activities on the spacecraft, including the checkout of other instruments in the coming weeks. The next RPWS activity will be a day-long exercise of a series of science observation modes which begins near the end of December 31, UT.
Updated flight software has been successfully uplinked to the spacecraft and stored on the solid state recorder. This is the software which will be used by the RPWS instrument when it is turned on December 30 for Instrument Checkout activities.
This spectrogram shows Jovian decametric arcs between about 4 and 11 MHz as seen by the Cassini RPWS high frequency receiver after its antenna deployment. The basic structures are arc-like, appearing somewhat like parentheses in this display. The narrowband fixed-frequency (horizontal) bands near 6, 7.3, 9.5, 12, and 15.3 MHz are shortwave radio emissions originating at Earth. Get postscript version here.
A sample of the data obtained from the RPWS following the successful deployment of its three 10-meter electric antennas on October 25. These data are from one of several RPWS receivers and cover the frequency range of 3.5 - 319 kHz. Color is used to indicate the amplitude of waves where red is used for the most intense emissions and blue for the least intense. In the upper frequency range of this panel a series of radio emissions from Earth can be seen. Since these emissions are known to be associated with the same process which produces the northern lights, they are called auroral kilometric radiation or AKR, for short.
The third instrument maintenance activity was successfully completed today. The Langmuir probe was biased at 32 Volts for 24 hours in order to attract electrons which will help to erode any surface contamination which may have been collected during the launch phase or subsequent thruster activity. The RPWS and Cassini spacecraft continue to perform as expected.
The second instrument maintenance activity was successfully completed today. New flight software was utilized which biases the Langmuir probe at 32 Volts for 24 hours. The bias voltage attracts electrons which will help to erode any surface contamination which may have been collected during the launch phase or subsequent thruster activity. The RPWS and Cassini spacecraft continue to perform as expected.
Yesterday RPWS maintenance software which enables optimal decontamination of the Langmuir Probe was successfully uploaded to SSR-B. The RPWS Science software resides on SSR-A. Software used for the deployment of the RPWS antennas was overwritten at the same time, as this software is no longer needed. The spacecraft health continues to be excellent!
Today the RPWS successfully completed a 24-hour maintenance activity consisting of biasing the Langmuir Probe at a potential of 10 volts in order to enhance the erosion of any contaminants which may have collected on the probe during the launch phase. Minimal information is returned from this activity, sufficient only to indicate that the bias was applied.
After observing extensive storms of auroral kilometric radiation and even capturing some intense Langmuir waves near 20 kHz, the RPWS was turned off by the onboard sequence as planned. Overall, the operation of the instrument was excellent and it is certainly great to have all of our sensors successfully deployed!
All three RPWS electric antennas are fully deployed and we have detected Auroral Kilometric Radiation from Earth. Rolf Bostrom also confirms that the Langmuir Probe is properly deployed!
The RPWS Z antenna is now fully deployed to 10 meters; the full extend limit switch is set as expected. One more to go...
The RPWS -X antenna is now fully deployed to 10 meters; the full extend limit switch is set as expected. More to come...
This afternoon the C2 sequence was successfully uplinked to the spacecraft and is waiting to start clocking out on Friday. This is the sequence which will deploy the RPWS antennas.
Cassini remains in excellent health and the C1 sequence continues to execute as planned. Today the C2 sequence and Periodic Instrument Maintenance minisequence were approved. The C2 sequence includes the commands to deploy the three RPWS electric antennas. The deployment activities will begin at 00h GMT on 25 October or 7 pm CDT on 24 October.
Cassini's health is excellent with no anomalies. The spacecraft is now in its normal cruise mode. The first cruise sequence was approved and uplinked today. The RPWS electric antenna extension is scheduled to begin at 7pm CDT on Friday, 24 October. Currently, the RPWS is off. The antenna bracket temperature has settled at about 15 C and has been steady for the last 24 hours or more.
Cassini left for Saturn on time this morning at 4:43 am. The entire launch sequence seems to have gone just as planned and the spacecraft was aquired by the DSN station in Canberra alive an in the appropriate sun-pointed attitude. The only information we have from the RPWS is that the antenna bracket temperature is virtually the same as it was prior to launch -- about 23 C.
Telemetry indicated an increase in the pyro event count by 1 as an indication that the RPWS Langmuir Probe was deployed as planned, about 2 hours, 16 minutes after launch.
Work towards a launch at 4:43am on 15 October is continuing. Upper level winds appear to be the primary concern, again.
High-altitude winds which violated range safety guidelines forced Monday's launch attempt to be scrubbed. A software problem on Cassini and a ground support equipment issue with the launch vehicle were contributing factors. The earliest retry will be at 4:43am EDT on 15 October.
Cassini remains on, ready for the Titan countdown to begin. RPWS is off and the antenna temperature is about 22 C. Look here for the KSC status report.
CNN has announced that a Federal judge in Honolulu has refused to block the launch of Cassini.
Launch is currently scheduled for 4:55 am EDT on 13 October 1997. The window remains open until 7:15 am. As of approximately 11:45 am today, the spacecraft is on and the RPWS antenna bracket temperature is about 17 C. Note that the RPWS will remain off for the duration of the countdown, launch, and first 10 days or so of flight.
As of 4:30 EDT 10/10/97 the spacecraft is running nominally and being conditioned for launch. The Payload Faring doors have been closed and instrument temperatures look good. The flight software loads on the SSRs have all been verified to be correct.
Type III Solar
Radio Bursts
Type III Solar
Radio Bursts
Ion Acoustic Waves
Langmuir Waves