Data Set Overview = On January 14, 2005, the Huygens Probe, part of the joint NASA/ESA Cassini-Huygens mission to Saturn, entered the atmosphere of Titan, descended for 2.5 hours under a parachute and eventually landed softly on the surface of Titan [LEBRETONETAL2005]. Six experiments collected data during the descent and on ground. The data set, which this data set catalog belongs to, is the archive of the Huygens Doppler Wind Experiment (DWE), which was designed to measure Titan's zonal winds by Doppler tracking Huygens from Cassini and from Earth [BIRDETAL2005]. In contrast to the other five experiments, DWE was not designed to collect data aboard Huygens. Instead, it was designed to measure the frequency of the Huygens carrier signal received aboard Cassini and on Earth. The radio link between Huygens and Cassini had two independent and partially redundant channels. One of them (channel A) was used for DWE Doppler tracking of Huygens. The accuracy desired by DWE required the use of special Ultra-Stable Oscillators (USO) for the channel A transmitter aboard Huygens and for the channel A receiver aboard Cassini. For the reception on Earth, a USO was not required, as the accuracy of the H-maser driven radio antennas is much higher than that of a USO. The data rate of the Huygens signal was 8 kHz. It was recorded, decoded and stored aboard Cassini in real-time for later transmission to Earth via the Cassini High Gain Antenna. The Huygens signal level was, however, to weak to be decoded on Earth. The minimum integration time for the detection of the Huygens signal on Earth was of the order of 1 sec. Due to an error in the sequence, which was executed by Cassini during the Huygens mission, the receiver USO was not switched on for the mission. Consequently, the channel A receiver aboard Cassini could not lock onto the channel A signal from Huygens and all data transmitted via this channel including the D...WE frequency measurement were lost. Due to this flaw, DWE relies now entirely on the data collected by Earth based telescopes. The DWE data set consists of the sky frequencies measured at the Green Bank and Parkes telescopes (data from other stations may be included when they become available; see [BIRDETAL2005]), the retrieved zonal wind speed along the descent path, geometrical parameters used to separate the Huygens velocity components and documentation. It is organized in six directories, which we describe in the following. DATA Directory The DATA directory contains the measured sky frequencies after signal processing in two files, one for Green Bank and one for Parkes. It is not intended to archive raw recordings of the signal. The signal processing method is described in [FOLKNERETAL2006]. Furthermore, it contains the retrieved zonal wind speed, the primary DWE result. The zonal wind speed was computed from each frequency sample, so that the total number of rows in the zonal wind table matches the sum of the frequency samples from Green Bank and Parkes. The time tags for the frequencies is Earth Received Time (ERT), whereas the time tags for the zonal wind speed is Spacecraft Event Time (SCET). (By the way: Also START_TIME and STOP_TIME of this object, the DATA_SET_INFORMATION, are given in ERT.) The latter is a derived quantity, computed by subtracting the one-way-light-time from ERT. The one-way-light-time between Titan and the receiving antenna during the Huygens mission was 67 min and 6.4 sec at the beginning of the mission, decreasing by approximately 0.1 sec over the duration of DWE data recordings. For the computation of the zonal wind speed, we used its precise value determined by our software, which made use of the SPICE toolkit (available from JPL). The precise value for the one-way-light-time can be reconstructed by subtracting our SCET time tags from the ERT time tags e.g. in the files HUYGENS_STATE.TAB and ANTENNA_STATE.TAB in the GEOMETRY directory (all data and geometry files have an identical number of rows that corresponds to the number of DWE sky frequency samples). The data collected at Green Bank have a mean integration time of 2 sec. At Parkes, the mean integration time was 3 sec before landing and 5 sec thereafter. There is a 25-min gap between the last sample from Green Bank and the first sample from Parkes, which may possibly be filled by measurements of other VLBA stations in the future, albeit with a lower time resolution as the gain of those stations is significantly smaller than that of Green Bank or Parkes. After launch, it was decided that in addition to the DWE Doppler tracking Huygens should also be tracked using a technique known as Very Long Baseline Interferometry (VLBI) [POGREBENKOETAL2004]. The VLBI group used a number of radio antennas, among them also Green Bank and Parkes, which were jointly used by the VLBI and DWE teams. The VLBI techique requires a continuous calibration with an extragalactic radio source, i.e. a quasar. As no quasar was in the beam when the antennas were pointed towards Huygens, they had to be nodded continuously. It was agreed among the teams that, in order to meet the requirements for the VLBI tracking, the antennas were pointed about 100 sec towards Huygens and 80 sec towards the VLBI calibration source in a 3-min cycle. These interruptions can consequently also be seen in the DWE data set. GEOMETRY Directory This directory contains state vectors of Huygens and the receiving antennas and the resulting projection angles for the various velocity components. The time tags of the state vectors of Huygens and the projection angles are given as SCET, whereas the time tags for the state vectors of the receiving antennas is given as ERT to account for retardation. See the file GEOMINFO.TXT in the GEOMETRY directory for more information. The altitude and meridional drift profiles of Huygens used for the generation of these files were provided by the Huygens Descent Trajectory Working Group (DTWG; see corresponding archive). The initial longitude (longitude at the time of the first DWE sky frequency sample) was taken from DTWG as well, whereas the subsequent longitude values were obtained by integration of the measured zonal wind speed. It is clear that any change of the DTWG profile will affect the retrieved zonal wind. For this version of the archive, we used the 4th DTWG delivery (DTWG#4), published in May 2006. Thus far, all DTWG deliveries including those which had not yet incorporated the image derived meridional drift, lead similar zonal wind profiles. There are no significant differences between the various zonal wind retrievals in the upper atmosphere. Near the surface, where the winds are generally weak, a slightly different descent speed or meridional drift profile could, however, lead to a significant change in the retrieved zonal wind speed. The state vectors of the receiving antennas and Titan were computed using the software SPICE and the following kernels: vlba.bsp, earth_000101_050808_050517.bpc, earthstns_itrf93_040916.bsp, 050214R_SCPSE_04336_05015.bsp, naif0007.tls, cpck19May2005.tpc SPICE and the accompanying kernels are available at http://naif.jpl.nasa.gov/naif/ DOCUMENT Directory This directory contains the most important DWE documents and the DWE Health Report, which describes the performance of the DWE USOs during the Huygens mission. Although the paper [FOLKNERETAL2006] is considered an important document too, it was not included, because at the time of this writing, it was not yet published. More documentation is listed in the reference catalog in the CATALOG directory. CALIB Directory = The CALIB directory contains a report that provides information on the DWE performance during pre-launch and in-flight tests and describes the final calibration of the frequency measurement. CATALOG Directory = This directory contains general information about the data set, such as involved personnel, instrument description, references, etc. INDEX Directory = needed internally by archive. Review The Huygens data sets were reviewed in two steps: (1) a review of the Experimenter-to-archive-ICD, in 2004. (2) a review of the data sets, in 2006. Procedures and details of this process can be obtained from the ESA archive team: Olivier Witasse or Joe Zender ESA ESTEC Keplerlaan 1 2200 AG Noordwijk The Netherlands Olivier.Witasse@esa.int or Joe.Zender@esa.int The Experimenter-to-archive-ICD was reviewed by V. Dehant (Royal Observatory of Brussels) and by D. Strobel (John Hopkins University). This data set was reviewed by D. Strobel and by R. Lorenz (University of Arizona).
The majority of the text in this file was extracted from the Cassini Mission Plan Document, D. Seal, 2003. [JPLD-5564] The Cassini spacecraft, including the Huygens Probe, was launched on 15 October 1997 using a Titan IV/B launch vehicle with Solid Rocket Motor Upgrade (SRMU) strap-ons and a Centaur upper stage. The spacecraft used a 6.7-year Venus-Venus-Earth-Jupiter Gravity Assist (VVEJGA) trajectory to Saturn, during which cruise observations were conducted to check out, calibrate, and maintain the instruments as well as to perform limited science. After Saturn Orbit Insertion (SOI) (1 July 2004), the Huygens Probe separated and, on the third encounter with Titan, entered the satellite's atmosphere to make in situ measurements during an approximately 150 minute descent (14 January 2005). The Orbiter continued a tour of the Saturn system until mid-2008 collecting data on the planet and its satellites, rings, and environment. The Cassini Orbiter (CO) was a three-axis stabilized spacecraft equipped with one high gain antenna (HGA) and two low gain antennas (LGAs), three Radioisotope Thermoelectric Generators (RTGs) for power, main engines, attitude thrusters, and reaction wheels. It carried twelve orbiter instruments designed to carry out 27 diverse science investigations. The Huygens Probe (HP) was equipped with six instruments designed to study the atmosphere and surface of Titan. It entered the upper atmosphere protected by a heat shield, then deployed parachutes to descend slowly to the surface from an altitude of about 200 km. The instruments, with acronym and Principal Investigator (PI) or Team Leader (TL), are summarized below: Instrument Acronym PI/TL ----------------------------------------------- ------------ Orbiter: Cassini Plasma Spectrometer CAPS Young Cosmic Dust Analyzer CDA Srama Composite Infrared Spectrometer CIRS Flasar Ion and Neutral Mass Spectrometer INMS Waite Imaging Science Subsystem ISS Por...co Magnetometer MAG Dougherty Magnetospheric Imaging Instrument MIMI Krimigis Cassini Radar RADAR Elachi Radio and Plasma Wave Science RPWS Gurnett Radio Science Subsystem RSS Kliore Ultraviolet Imaging Spectrograph UVIS Esposito Visible and Infrared Mapping Spectrometer VIMS Brown Probe: Aerosol Collector and Pyrolyser ACP Israel Descent Imager Spectral Radiometer DISR Tomasko Doppler Wind Experiment DWE Bird Gas Chromatograph Mass Spectrometer GCMS Niemann Huygens Atmospheric Structure Instrument HASI Fulchignoni Surface Science Package SSP Zarnecki Mission Phases LAUNCH 1997-10-15 to 1997-10-17 1997-288 to 1997-290 ------ Cassini successfully lifted-off from the Cape Canaveral Air Station complex 40 on 15 October 1997 at 08:55 UTC. The solid rocket motors burned from liftoff to separation at 2 min 23 sec at an altitude of 68,300 m. Stage 1 ignition began at 2 min 11 sec at an altitude of 58,500 m, and Stage 2 ignition (and Stage 1 separation) occurred at 5 min 23 sec after liftoff at 167,300 m. During the first three minutes and 27 seconds of flight, the payload fairing shrouded the spacecraft, protecting it from direct solar illumination. The Centaur upper stage separated from the launch vehicle at 9 min 13 sec at 206,700 m. The first Centaur burn began at 9 min 13 sec and lasted approximately two minutes. This burn placed the Cassini spacecraft into an elliptical, 170 km by 445 km parking orbit with an inclination of about 30 degrees. After 17 minutes in the parking orbit, the Centaur fired again and launched Cassini toward Venus en route to Saturn. The injection C3 was 16.6 km^2/s^2. Immediately after separation from the Centaur (date?), the spacecraft's Attitude and Articulation Control Subsystem (AACS) pointed the HGA toward the Sun to achieve a thermally safe attitude in which the HGA served as an umbrella for the remainder of the spacecraft. X-band uplink and downlink was established through the LGAs, the Radio and Plasma Wave Science (RPWS) Langmuir Probe was deployed, instrument replacement heaters and main engine oxidizer valve heaters were turned on, and the Stellar Reference Unit (SRU), Imaging Science Subsystem (ISS), and Visible and Infrared Mapping Spectrometer (VIMS) decontaminations were started. TCM 1 1997-10-18 to 1997-11-14 1997-291 to 1997-318 ----- The Trajectory Correction Maneuver 1 (TCM 1) phase comprised four one-week sequences. During most of the TCM 1 phase, the spacecraft was in a relatively quiescent state with the HGA pointed toward the Sun. Telemetry downlinked by the spacecraft was utilized to make an initial characterization of the spacecraft and to assess whether its various subsystems survived the launch. Deployment, decontamination, tank heating, and AACS checkout activities were started. Before the maneuver itself, the fuel and oxidizer tanks were heated in order to avoid an irreversible overpressure in the propellant lines. If the tanks fully pressurized before the spacecraft passed through the peak temperature regime, then (when the spacecraft did enter the maximum thermal environment) the tank pressure would climb without there being a way to bring it back down, possibly causing an overpressure. TCM 1 was an Earth injection clean-up maneuver placed at 25 days after launch. TCM 1 was executed using the main engine with a delta-V magnitude of 2.8 m/s. The burn sequence included holding the spacecraft off-Sun after burn completion to allow the spacecraft heating to be characterized in a relatively benign environment. INTERPLANETARY CRUISE 1997-11-14 to 1999-11-07 1997-318 to 1999-311 --------------------- The Interplanetary Cruise Phase extended from 14 November 1997 to 7 November 1999. It consisted of three subphases: Venus 1 Cruise, Instrument Checkout 1, and Venus 2 - Earth Cruise. During most of this phase, Cassini's proximity to the Sun constrained the spacecraft to remain Sun-pointed, and communications were conducted using the Low Gain Antennas. The downlink capability of the LGAs at large spacecraft-Earth ranges was very limited. Between 30 and 150 days after launch, for example, the downlink data rate decreased from 948 to 20 bps. Beginning on 28 December 1998, the spacecraft approached opposition and the HGA could be pointed towards Earth for a period of 25 days while the Probe equipment temperature remained within the required range. This provided a high data rate window during which checkout activities could be accomplished. VENUS 1 CRUISE 1997-11-14 to 1998-09-13 1997-318 to 1998-256 -------------- The Venus 1 Cruise subphase started on 14 November 1997 and continued through 13 September 1998. The subphase encompassed sequences C5 through C9 and included two TCMs, one planetary swingby, and three switches between LGA1 and LGA2. Most of the period was dedicated to engineering and instrument maintenance activities. VENUS 1 ENCOUNTER 1998-04-26 1998-116 The first Venus encounter occurred on 26 April 1998. The spacecraft approached Venus from a sunward direction, and closest approach occurred just after the spacecraft entered the Sun's shadow for a period of about 15 minutes. At closest approach, the altitude was 284 km, with a velocity relative to Venus of 11.8 km/s. The spacecraft was occulted from Earth for about 2 hours. The Earth occultation zone started about 15 minutes after the spacecraft left the Sun occultation zone. Accuracy for the Venus flyby was assured by using two TCMs (Trajectory Correction Maneuvers), 60 and 20 days before closest approach, and a clean-up maneuver 20 days after the flyby. INSTRUMENT CHECKOUT 1 1998-09-14 to 1999-03-14 1998-257 to 1999-073 --------------------- The Instrument Checkout 1 subphase (ICO-1) started on 14 September 1998, continued through 14 March 1999, and consisted of sequences C10-C13. This subphase was characterized by the opposition that occurred on 9 January 1999, which allowed use of the HGA for downlink since the Earth and Sun were nearly aligned as seen from Cassini. All instruments scheduled checkout activities within the 25 day period centered on opposition. This was the first opportunity since launch to exercise and check the status of most instruments outside of routine maintenance. The 'Quiet Test', for example, allowed each instrument to monitor other instruments as they turned on and off and provided valuable insight into how to integrate science observations during the Saturn tour. During instrument checkout activities, the spacecraft autonomously went into a safe state. Accumulating star position errors from the slow turn required to keep the Sun on the -x-axis triggered AACS fault protection. Most of the instrument checkout activities were rescheduled after a 10 day safing period. Those that were not completed were rescheduled for the ICO-2 subphase during Outer Cruise. VENUS 2 - EARTH CRUISE 1999-03-15 to 1999-11-07 1999-074 to 1999-311 ---------------------- The Venus 2 - Earth Cruise subphase started on 15 March 1999, 45 days prior to the second Venus flyby, and continued through 7 November 1999, which was 82 days after the Earth flyby. The subphase encompassed sequences C13 through C16, and included seven scheduled TCMs, two planetary swingbys, and 25 science activities in addition to normal engineering activities. Science activities included maintenance, calibration, checkout, and science observations using all of the Cassini instruments except INMS and CIRS. VENUS 2 ENCOUNTER 1999-06-24 1999-175 TCM-7 was executed 37 days before the Venus 2 Encounter. TCM-8 was scheduled 21 days prior to Venus 2, but it was canceled. DSN (Deep Space Network) coverage increased from one to three passes per day in support of the flyby. EARTH ENCOUNTER 1999-08-18 1999-230 The Earth flyby occurred 55 days after the Venus 2 flyby. The spacecraft approached the Earth from approximately the direction of the Sun. Closest approach occurred right after the spacecraft entered the Sun occultation zone. The occultation lasted approximately 30 minutes. The altitude at closest approach was 1175 km, with an Earth-relative velocity of 19.0 km/s. Trajectory correction maneuvers took place 43, 30, 15 and 6.5 days before closest approach, and a clean-up maneuver was executed 13 days after the flyby. Continuous DSN coverage began at the Venus 2 flyby and continued through the Earth flyby. A week after the Earth Encounter, DSN coverage dropped to one pass every two days. Five instruments conducted observations as Cassini passed through the Earth's magnetotail. OUTER CRUISE 1999-11-08 to 2002-07-07 1999-312 to 2002-188 ------------ The Outer Cruise Phase consisted of four subphases: HGA Transition, Instrument Checkout 2, Jupiter Cruise, and Quiet Cruise. The Outer Cruise phase extended from 8 November 1999 (when the spacecraft reached a Sun range of 2.7 AU) to 7 July 2002 (about two years before Saturn Orbit Insertion). At 2.7 AU (1 February 2000), the HGA began continuous Earth- pointing. The one planetary encounter in this phase was the flyby of Jupiter in December 2000. Science at Jupiter was an opportunity to test Saturn observation strategies with HGA data rates. HIGH GAIN ANTENNA TRANSITION 1999-11-08 to 2000-05-06 1999-312 to 2000-127 ---------------------------- This subphase included sequences C17 to C19, operation of ISS and VIMS decontamination heaters, CDA dust calibrations, and Magnetosphere and Plasma Science (MAPS) observations after the HGA was pointed toward Earth. During the initial part of the subphase (C17 and part of C18), telecommunications were via LGA1, and the spacecraft was at the farthest distance from Earth before transitioning to the HGA for regular use. Therefore, data rates were very low and activities were kept to a minimum. C17 included standard maintenance and one Periodic Engineering Maintenance (PEM) activity. Activities during the LGA1 portion of C18 included a Periodic Instrument Maintenance (PIM); observations by ISS, VIMS, and UVIS of the asteroid Masursky near closest approach (1,634,000 km); and ISS dark frame calibration images directly following the Masursky observations. The HGA was turned toward Earth for regular use on 1 February 2000, during C18. Several activities took place during the rest of C18, using the greater telemetry capabilities available with the HGA: playback of the Masursky data and ISS dark frames, a Probe checkout, a Huygens Probe S-band Relay to Cassini Test, a Telemetry-Ranging Interference Test, MAG calibrations, and a PEM. Regular MAPS observations by CAPS, CDA, MAG, MIMI, and RPWS began within a few days after transitioning to the HGA. The first 6 weeks of C19 were used for a checkout of new Flight Software. The AACS version A7 software was uploaded near the beginning of this period, and the first 2 weeks were devoted to AACS tests. The next 4 weeks were originally scheduled for CDS tests of version V7.0. However, these tests were delayed to late July and August of 2000 to allow time for additional regression testing. During the AACS checkout period, MAPS activity ceased. Several activities took place during the last 3 weeks of C19: resumption of MAPS observations, three RSS activities (HGA pattern calibration, HGA boresight calibration, and USO characterization), CIRS Cooler Cover release, and a PIM. A few days before the end of C19, the command loss timer setting was increased slightly, to account for the 10-day period at the beginning of C20 during which superior conjunction made commanding problematic. INSTRUMENT CHECKOUT 2 2000-05-06 to 2000-11-05 2000-127 to 2000-310 --------------------- The second instrument checkout subphase (ICO-2) was scheduled from 6 May 2000 to 5 November of 2000, after the Spacecraft Office had completed its engineering checkout activities. ICO-2 included instrument checkout that required reaction wheel stability and any instrument checkouts that were not successfully completed during ICO-1. But the CDS Flight Software V7 uplink and checkout, which was delayed from March, was rescheduled to late July through early September 2000, causing many ICO-2 activities to be compressed into a shorter and more intense period. Some activities were postponed until after the Jupiter observations were completed in 2001. The subphase began with a superior conjunction which precluded early science or engineering activities. MAPS instruments remained on; but data return was not attempted during conjunction. Two TCMs were scheduled for Jupiter targeting, in June and September. Engineering activities included the continuous use of reaction wheels and, beginning on 1 October 2000, dual Solid State Recorders (SSRs). There were no scheduled instrument PIMs during ICO-2 since all instruments had other activities that accomplished this function. Other engineering activities included two Reaction Wheel Assembly (RWA) friction tests, two PEMs, and an SRU calibration. Science activities began with the MAPS instruments continuing from C19. New flight software was loaded for eight instruments in late May, and a CDA software update was done in September. New Quiet Tests, while operating on reaction wheels, were done in July for most instruments. RSS Quiet Tests were done in September, and RADAR related tests were done in late June. A Probe checkout occurred in late July. Spacecraft turns were done for RADAR observations of the Sun and Jupiter in June and again in September. The star Alpha Piscis Austrinus (Fomalhaut) was also observed in September by VIMS with ISS and UVIS doing ride-along science. No other science turns were scheduled until October. On 1 October, science began using a repeating 5-day template to gather Jupiter science. This involved 11 turns in a 5 day period, including two downlinks. The turns in the 5-day template involved 4 orientations: Orbiter Remote Science (ORS) boresights to Jupiter, Z axis parallel to ecliptic HGA to Sun, rolling about Z axis Probe to Sun, rotating about X axis HGA to Earth, Probe offset from Sun for CDA, not rotating, downlink orientation JUPITER CRUISE 2000-11-05 to 2001-04-30 2000-310 to 2001-120 -------------- The Jupiter Cruise subphase extended from 6 November 2000 to 29 April 2001 and included sequences C23 to C25. However Jupiter remote sensing observations actually began on 1 October 2000, in C22. JUPITER ENCOUNTER 2000-12-30 2000-365 The Jupiter flyby occurred on 30 December 2000 at an altitude of 9.7 million km. This gravity assist rotated the trajectory 12 deg and increased the heliocentric velocity by 2 km/s. The Jupiter relative speed at closest approach was 11.6 km/s. At closest approach, Jupiter filled the Narrow Angle Camera (NAC) field of view. Extensive Jupiter science was performed which required additional DSN support: up to two passes every five days, and a maximum of one pass every 30 hours in the 10 days on either side of closest approach. Science at Jupiter was an opportunity to test how to build and execute viable Saturn sequences. A problem with the RWAs occurred on 16 December 2000. Increased friction on one of the wheels caused the spacecraft to switch autonomously to the Reaction Control Subsystem (RCS) for attitude control. With the switch to RCS, hydrazine usage increased. Two of four joint CAPS-Hubble Space Telescope observations, a Jupiter North-South map, the Himalia 'flyby', and a UVIS torus observation were all executed on RCS before the sequence was terminated on 19 December 2000. MAPS data continued to be recorded at a reduced rate. All other planned science activities were suspended. After tests, RWA operation was resumed for attitude control on 22 December, with the wheels biased away from low RPM regions. The sequence was restarted on 29 December. QUIET CRUISE 2001-04-30 to 2002-07-08 2001-120 to 2002-189 ------------ Quiet Cruise was a 14 month subphase that started at the end of Jupiter Cruise and ended two years before SOI. During this subphase, routine maintenance, engineering, and navigation functions were carried out. One Gravitational Wave Experiment (GWE) was conducted in December 2001, and one Solar Conjunction Experiment (SCE) was conducted in June 2002. SCIENCE CRUISE 2002-07-08 to 2004-06-10 2002-189 to 2004-162 -------------- SPACE SCIENCE 2002-07-08 to 2004-01-11 2002-189 to 2004-011 The Space Science subphase began on 8 July 2002 and ran through 11 January 2004. TCMs 18 and 19, two GWEs (December 2002 and December 2003) and one SCE (June-July 2003) were conducted. APPROACH SCIENCE 2004-01-12 to 2004-06-10 2004-012 to 2004-162 The Approach Science subphase began six months before SOI and ended three weeks before SOI, when the spacecraft was approaching Saturn at a rate of 5 kilometers per second. Most of the activities during the Approach Science subphase were Saturn science observations and preparation for the Phoebe flyby, SOI, and Tour operations. The reaction wheels were turned on at the beginning of the subphase to provide a more stable viewing platform. By this point, the imaging instruments had begun atmospheric imaging, and making long-term atmospheric movies. CIRS began long integrations of Saturn's disk. At SOI - 4 months, Saturn filled one third of the NAC field of view and one half of the CIRS Far Infrared (FIR) field of view. The Saturn approach was made toward the morning terminator at a phase angle of about 75 degrees; VIMS gathered data on the temperature difference across the terminator. UVIS scans of the Saturn System began 3-4 months before SOI. Fields, particles, and waves instruments collected solar wind information and recorded Saturn emissions as the spacecraft neared the planet. Science data gathered during this period was stored on the SSR and transmitted back to Earth. Daily DSN tracking coverage began 90 days before SOI. The Phoebe approach TCM took place on 27 May 2004, 15 days before Phoebe closest approach. TOUR PRE-HUYGENS 2004-06-11 to 2004-12-24 2004-163 to 2004-359 ---------------- The Tour Pre-Huygens Phase extended from the Phoebe Encounter through Saturn Orbit Insertion to separation of the Huygens Probe from the Cassini Orbiter. PHOEBE ENCOUNTER 2004-06-11 2004-163 The flyby of Phoebe occurred on 11 June 2004, 19 days before SOI. At closest approach (19:33 UTC) the spacecraft was 2000 km above the surface. SATURN ORBIT INSERTION 2004-07-01 2004-183 During Saturn Orbit Insertion (SOI) on 1 July 2004, the spacecraft made its closest approach to the planet's surface during the entire mission at an altitude of only 0.3 Saturn radii (18,000 km). Due to this unique opportunity, the approximately 95-minute SOI burn (633 m/s total delta-V), required to place Cassini in orbit around Saturn, was executed earlier than its optimal point centered around periapsis, and instead ended near periapsis, allowing science observations immediately after burn completion. The SOI maneuver placed the spacecraft in an initial orbit with a periapsis radius of 1.3 Rs, a period of 148 days, and an inclination of 16.8 degrees. After the burn, the spacecraft was turned to allow the ORS instruments to view the Saturn inner rings that were not in shadow. After periapsis, the trajectory just grazed the occultation zones behind the planet with the Earth and Sun being occulted by Saturn. After communication with Earth was re-established, the spacecraft remained on Earth pointed for nine hours to play back engineering and science data and to give ground personnel time to evaluate the spacecraft status. After SOI a pair of cleanup maneuvers was used to correct for errors in the SOI burn. The first was immediately before superior conjunction, at SOI + 3 days, and the second was after conjunction at SOI + 16 days. Probe checkouts were scheduled at SOI + 14 days, Probe Release Maneuver (PRM) + 4 days, and ten days before separation. The partial orbit between SOI and the first apoapsis was designated orbit 0. The next three orbits were designated a, b, and c. TITAN A ENCOUNTER 2004-10-26 2004-300 TITAN B ENCOUNTER 2004-12-13 2004-348 HUYGENS DESCENT 2004-12-24 to 2005-01-14 2004-359 to 2005-014 --------------- HUYGENS PROBE SEPARATION 2004-12-24 2004-359 The probe was released from the Orbiter on 24 December 2004, 11 days after the second Titan flyby (orbit b). Two days after the Probe was released, the Orbiter executed a deflection maneuver to place itself on the proper trajectory for the third encounter. TITAN C HUYGENS 2005-01-14 2005-014 During the third flyby (orbit c), on 14 January 2005, the Huygens Probe transmitted data to the orbiter for approximately 150 minutes during its descent through the atmosphere to the surface. Because the Orbiter was looking at Titan through most of the corresponding Goldstone tracking pass, DSN support on this day was primarily through the 70-meter antennas at the Canberra and Madrid tracking complexes. While approaching Titan, the Orbiter made its last downlink transmission (to the Madrid station, DSS 63) before switching to Probe relay mode. The Orbiter then turned nearly 180 degrees to point its HGA at the predicted Probe impact point, and the Probe Support Avionics (PSA) were configured to receive data from the Probe. Some Orbiter instruments were put into a low power state to provide additional power for the PSA. The data from the Probe were transmitted at S band in two separate data streams, and both were recorded on each SSR. Following completion of the predicted descent (maximum 150 minutes), the Orbiter listened for Probe signals for an additional 30 minutes, in case they continued after landing. When data collection from the Probe was completed, those data were write protected on each SSR. The spacecraft then turned to view Titan with optical remote sensing instruments until about one hour after closest approach for a total observing window of TBD. The Orbiter then turned the HGA towards Earth and began transmitting the recorded Probe data to the Canberra 70-m antenna. The complete, four-fold redundant set of Probe data was transmitted twice, and its receipt verified, before the write protection on that portion of the SSR was lifted by ground command. A second playback, including all of the Probe data and the Orbiter instrument observations, was returned over the subsequent Madrid 70-meter tracking pass, which was longer and at higher ^ation angles. TOUR 2005-01-14 to 2008-06-30 2005-014 to 2008-182 ---- The Tour Phase of the mission began at completion of the Huygens Probe and Orbiter-support playback and ended on 30 June 2008. It included dozens of satellite encounters and extended observations of Saturn, its rings, and its environment of particles and fields. TOUR SEQUENCE BOUNDARIES The table below shows spacecraft background sequences, orbit revolution, start epoch (including day-of-year in a separate column), and the length of the sequence. For completeness, all 'S' sequences are listed even though the first seven covered times before the Tour phase. Each orbit about Saturn was assigned a revolution identifier starting with a, b, and c, and then numerically ascending from 3 to 74; these were not synchronous with sequences, some of which covered only partial orbits. Full orbits began and ended at apoapsis; the partial orbit from SOI to the first apoapsis was orbit 0. Sequence Rev Epoch (SCET) DOY Duration In days -------- --- ----------------- --- -------- S1 - 2004-May-15 00:00 136 35 S2 0 2004-Jun-19 01:38 171 42 S3 0 2004-Jul-30 23:05 212 43 S4 a 2004-Sep-11 19:10 255 35 S5 a 2004-Oct-16 18:40 290 28 S6 a 2004-Nov-13 16:59 318 33 S7 b 2004-Dec-16 15:03 351 37 S8 c 2005-Jan-22 10:38 022 36 S9 3 2005-Feb-27 00:36 058 41 S10 6 2005-Apr-09 05:15 099 35 S11 8 2005-May-14 02:50 134 35 S12 10 2005-Jun-18 01:34 169 42 S13 12 2005-Jul-29 22:36 210 32 S14 14 2005-Aug-30 21:53 242 39 S15 16 2005-Oct-08 15:57 281 35 S16 17 2005-Nov-12 17:01 316 35 S17 19 2005-Dec-17 14:21 351 42 S18 20 2006-Jan-28 11:23 028 42 S19 22 2006-Mar-11 00:35 070 42 S20 23 2006-Apr-22 05:15 112 42 S21 24 2006-Jun-03 02:39 154 42 S22 26 2006-Jul-15 00:06 196 35 S23 27 2006-Aug-18 22:06 230 39 S24 29 2006-Sep-26 19:53 269 26 S25 31 2006-Oct-22 18:26 295 33 S26 33 2006-Nov-24 16:30 328 42 S27 36 2007-Jan-05 13:50 005 43 S28 39 2007-Feb-17 10:52 048 40 S29 41 2007-Mar-29 08:04 088 37 S30 44 2007-May-04 22:00 124 37 S31 46 2007-Jun-11 03:10 162 33 S32 48 2007-Jul-14 01:06 195 29 S33 49 2007-Aug-11 23:20 223 42 S34 50 2007-Sep-22 20:51 265 40 S35 51 2007-Nov-01 18:40 305 42 S36 54 2007-Dec-13 16:15 347 39 S37 56 2008-Jan-21 13:35 021 26 S38 59 2008-Feb-16 11:51 047 36 S39 62 2008-Mar-23 01:50 083 27 S40 65 2008-Apr-19 07:18 110 42 S41 70 2008-May-31 04:27 152 35 SATELLITE ENCOUNTER SUMMARY This table summarizes the Cassini Orbiter satellite encounters; for completeness, all recognized encounters are included even though the first eight preceded the Tour phase. Rev identifies the orbit revolution as defined above. The three character ID for the encounter is in the second column; an appended asterisk (*) denotes a non-targeted encounter. The target, date and time, and day-of-year are in the next three columns. Altitude above the surface at closest approach, sense of the encounter (whether on the inbound or outbound leg of an orbit), relative velocity at closest approach, and phase angle at closest approach round out the columns. Rev Name Satellite Epoch (SCET) DOY Alt in/ Speed Phase km out km/s deg ---- ----- --------- ---------------- --- --- --- ----- ---- 0 0PH Phoebe 2004-Jun-11 19:33 163 1997 in 6.4 25 0 0MI* Mimas 2004-Jul-01 00:30 183 76424 in 22.3 80 0 0TI* Titan 2004-Jul-02 09:30 184 338958 out 8.3 67 a aTI Titan 2004-Oct-26 15:30 300 1200 in 6.1 91 b bTI Titan 2004-Dec-13 11:37 348 2358 in 6 98 b bDI* Dione 2004-Dec-15 02:11 350 81592 in 5.3 93 c cIA* Iapetus 2005-Jan-01 01:28 001 64907 in 2.1 106 c cTI Titan 2005-Jan-14 11:04 014 60000 in 5.4 93 3 3TI Titan 2005-Feb-15 06:54 046 950 in 6 102 3 3EN* Enceladus 2005-Feb-17 03:24 048 1179 out 6.6 98 4 4EN Enceladus 2005-Mar-09 09:06 068 499 in 6.6 43 4 4TE* Tethys 2005-Mar-09 11:42 068 82975 out 6.9 64 5 5EN* Enceladus 2005-Mar-29 20:20 088 63785 in 10.1 134 5 5TI Titan 2005-Mar-31 19:55 090 2523 out 5.9 65 6 6MI* Mimas 2005-Apr-15 01:20 105 77233 out 13.6 94 6 6TI Titan 2005-Apr-16 19:05 106 950 out 6.1 127 7 7TE* Tethys 2005-May-02 21:04 122 64990 in 10 118 7 7TI* Titan 2005-May-04 05:10 124 860004 out 10.2 153 8 8EN* Enceladus 2005-May-21 07:19 141 92997 out 8.1 81 9 9TI* Titan 2005-Jun-06 18:50 157 425973 in 5.8 82 10 10TI* Titan 2005-Jun-22 12:27 173 920423 in 3.7 65 11 11EN Enceladus 2005-Jul-14 19:57 195 1000 in 8.1 43 12 12MI* Mimas 2005-Aug-02 03:52 214 45112 in 6.5 83 12 12TI* Titan 2005-Aug-06 12:33 218 841452 out 3.8 62 13 13TI Titan 2005-Aug-22 08:39 234 4015 out 5.8 42 14 14TI Titan 2005-Sep-07 07:50 250 950 out 6.1 84 15 15TE* Tethys 2005-Sep-24 01:29 267 33295 out 7.7 76 15 15TI* Titan 2005-Sep-24 22:01 267 910272 out 10.7 148 15 15HY Hyperion 2005-Sep-26 01:41 269 990 out 5.6 45 16 16TI* Titan 2005-Oct-10 22:20 283 777198 in 9.7 65 16 16DI Dione 2005-Oct-11 17:58 284 500 in 9 66 16 16EN* Enceladus 2005-Oct-12 03:29 285 42635 out 6.6 75 17 17TI Titan 2005-Oct-28 03:58 301 1446 in 5.9 105 18 18RH Rhea 2005-Nov-26 22:35 330 500 in 7.3 87 19 19EN* Enceladus 2005-Dec-24 20:23 358 97169 in 6.9 133 19 19TI Titan 2005-Dec-26 18:54 360 10429 out 5.6 67 20 20TI Titan 2006-Jan-15 11:36 015 2042 in 5.8 121 21 21TI Titan 2006-Feb-27 08:20 058 1812 out 5.9 93 22 22TI Titan 2006-Mar-18 23:58 077 1947 in 5.8 148 22 22RH* Rhea 2006-Mar-21 07:01 080 85935 out 5.3 136 23 23TI Titan 2006-Apr-30 20:53 120 1853 out 5.8 121 24 24TI Titan 2006-May-20 12:13 140 1879 in 5.8 163 25 25TI Titan 2006-Jul-02 09:12 183 1911 out 5.8 148 26 26TI Titan 2006-Jul-22 00:25 203 950 in 6 105 27 27TI* Titan 2006-Aug-18 17:48 230 339190 out 4.8 121 28 28TI Titan 2006-Sep-07 20:12 250 950 in 6 45 28 28EN* Enceladus 2006-Sep-09 20:00 252 39842 out 10.3 116 29 29TI Titan 2006-Sep-23 18:52 266 950 in 6 90 30 30TI Titan 2006-Oct-09 17:23 282 950 in 6 81 31 31TI Titan 2006-Oct-25 15:51 298 950 in 6 25 32 32EN* Enceladus 2006-Nov-09 01:48 313 94410 out 14.1 27 33 33DI* Dione 2006-Nov-21 02:32 325 72293 out 12.3 144 33 33TI* Titan 2006-Nov-25 13:57 329 930525 out 4.5 114 35 35TI Titan 2006-Dec-12 11:35 346 950 in 6 124 36 36TI Titan 2006-Dec-28 10:00 362 1500 in 5.9 62 37 37TI Titan 2007-Jan-13 08:34 013 950 in 6 53 38 38TI Titan 2007-Jan-29 07:12 029 2776 in 5.8 73 39 39TI Titan 2007-Feb-22 03:10 053 953 out 6.3 161 40 40TI Titan 2007-Mar-10 01:47 069 956 out 6.3 149 41 41TI Titan 2007-Mar-26 00:21 085 953 out 6.3 144 42 42TI Titan 2007-Apr-10 22:57 100 951 out 6.3 137 43 43TI Titan 2007-Apr-26 21:32 116 951 out 6.3 130 44 44TI Titan 2007-May-12 20:08 132 950 out 6.3 121 45 45TE* Tethys 2007-May-26 20:57 146 97131 in 11.7 75 45 45TI Titan 2007-May-28 18:51 148 2425 out 6.1 114 46 46TI Titan 2007-Jun-13 17:46 164 950 out 6.3 107 47 47TE* Tethys 2007-Jun-27 19:53 178 16166 in 10.1 90 47 47MI* Mimas 2007-Jun-27 22:56 178 89730 in 16.2 110 47 47EN* Enceladus 2007-Jun-28 01:15 179 90769 out 9.4 55 47 47TI Titan 2007-Jun-29 17:05 180 1942 out 6.2 96 48 48TI Titan 2007-Jul-19 00:39 200 1302 in 6.2 34 49 49TE* Tethys 2007-Aug-29 11:21 241 48324 in 4.7 104 49 49RH* Rhea 2007-Aug-30 01:26 242 5098 out 6.7 46 49 49TI Titan 2007-Aug-31 06:34 243 3227 out 6.1 87 49 49IA Iapetus 2007-Sep-10 12:33 253 1000 out 2.4 65 50 50DI* Dione 2007-Sep-30 06:27 273 56523 in 5.6 47 50 50EN* Enceladus 2007-Sep-30 10:53 273 88174 in 6.1 99 50 50TI Titan 2007-Oct-02 04:48 275 950 out 6.3 67 51 51TI* Titan 2007-Oct-22 00:47 295 455697 in 4.1 29 52 52RH* Rhea 2007-Nov-16 19:52 320 78360 in 9.1 148 52 52TI Titan 2007-Nov-19 00:52 323 950 out 6.3 51 53 53MI* Mimas 2007-Dec-03 05:28 337 79272 in 14.8 138 53 53TI Titan 2007-Dec-05 00:06 339 1300 out 6.3 70 54 54TI Titan 2007-Dec-20 22:56 354 953 out 6.3 61 55 55TI Titan 2008-Jan-05 21:26 005 949 out 6.3 37 57 57TI* Titan 2008-Jan-22 21:06 022 860776 in 4.5 70 59 59TI Titan 2008-Feb-22 17:39 053 959 out 6.4 30 61 61TI* Titan 2008-Mar-10 19:15 070 922539 in 6.3 123 61 61EN Enceladus 2008-Mar-12 19:05 072 995 in 14.6 56 62 62TI Titan 2008-Mar-25 14:35 085 950 out 6.4 21 64 64MI* Mimas 2008-Apr-11 09:38 102 95428 in 16.9 137 66 66TI* Titan 2008-Apr-26 18:22 117 780589 in 5.5 94 67 67TI Titan 2008-May-12 10:09 133 950 out 6.4 35 69 69TI Titan 2008-May-28 08:33 149 1316 out 6.3 23 72 72TI* Titan 2008-Jun-13 04:17 165 372240 in 5.9 89 74 74EN* Enceladus 2008-Jun-30 08:07 182 99092 in 21.6 66 END OF PRIME MISSION 2008-06-30 2008-182 --------------------