Science Operations
JADE science operations are broken into orbital regions as defined by time and key locations. The orbital events that define JADE operations are perijove and the magnetic equator (current sheet) crossing around apojove. High rate science (HRS) data are taken at ±3 hours around perijove and Bin Recording Burst data are taken over the auroral zone (indicated by green regions in Fig. 69). The majority of the orbit is spent in LRS mode with typical accumulation times of 5 or 10 minutes, depending on available telemetry. In the transition region approaching and leaving perijove, but before HRS, we collect LRS data with an intermediate rate of 30 or 60 s, again depending on available telemetry. This intermediate rate LRS will also be used near the equatorial current sheet around apojove.
The Juno attitude difference during MWR and GRAV orbits (see Fig. 70), affects the quality of JADE electron data. In general, a non-deflected data set is more accurate than a deflected one, and due to observational geometry, even a perfectly deflected beam is not equal to a non-deflected beam. Because of this, orbits where the JADE FOV is more field aligned in the auroral regions, such as most early MWR orbits, provide better science collection because they require less deflection.
Periapsis
JADE primary science is collected ±3 hours around perijove, where the spacecraft passes through the auroral region in the northern hemisphere, the Jovian equatorial plane and the auroral region in the southern hemisphere. Due to both the variability associated with the auroral regions on short time scales, and the fast spacecraft motion, high time resolution data is needed.
Three hours before perijove JADE enters HRS, with all sensors collecting data, JADE-I sweeping ESA and DFL by table, JADE-E sweeping ESA by table, and deflectors set to remain field aligned based on the real time MAG data. During this time high-fidelity histograms and direct events (as bandwidth allows) are collected (as described in Sect. 4.2). While JADE passes through the northern auroral region, Burst is enabled. The location of the auroral crossing changes slightly with each orbit, thus the amount of time Burst is enabled and the timing relative to perijove changes each orbit (see Bagenal et al. 2013, this issue). Each auroral crossing captures approximately seven 60-second Waves-triggered Burst intervals, as described below. Between auroral crossings JADE is in HRS collecting high fidelity histograms and direct events (as bandwidth allows) across the equatorial region. At the southern auroral zone JADE is again put into Burst mode. Because of the orbit evolution, the spacecraft altitude is lower and southern auroral mapping is better earlier in the mission.
4.1.1.1 Burst During Auroral Field Line Crossings
The most critical JADE measurements occur on the auroral field-line crossings. Active field lines are small—less than 1,000 km wide according to HST observations. Juno crosses these field lines at ∼50 km/s, and the critical data occur in ∼20 s intervals, with the exact timing of the crossings unknown.
Burst mode is designed to capture these auroral crossings. The highest possible resolution data is captured and prioritized by how ‘interesting’ the data is, as defined by the Waves quality factor (see Sect. 4.4.2.6 for Burst details). Waves flight software sets the quality flag based on (1) the number of solitary structures in the Waves wideband data, (2) the amplitude of waves near the electron cyclotron frequency, and (3) sudden changes in broadcast magnetic field direction or magnitude (Kurth et al. 2013, this issue). Waves broadcasts a Burst trigger when the quality flag rating is above a threshold. When a Waves trigger is broadcast, the spacecraft continues collecting data for 30 s; data ±30 s from the trigger are stored with the associated quality flag. There is telemetry to transmit ∼7 60-s bursts during each perijove, and more are added to the plan as bandwidth allows.
JADE can only store burst data if it is in Burst mode when the Waves trigger is sent. Burst mode recording sessions are defined by time-tagged command loads uploaded 2 orbits in advance of execution. These recording sessions are planned during the auroral crossings using trajectory and field-line model predictions.
Intermediate Accumulation LRS Near Perijove
It is preferred to have a ramp-up of data capture both just before and just after HRS around perijove. Therefore, JADE has an intermediate rate LRS period in these transition regions where the histogram accumulation rate is increased to 30 or 60 s, depending on availability of telemetry. This allows JADE to acquire higher time resolution data over regions of interest flanking the Juno-defined perijove regions.
Orbital Trim Maneuver (OTM)
Each orbit an OTM is needed to precisely time the orbits with respect to Jupiter’s rotation rate so that evenly spaced global maps of Jupiter can be gathered. These OTMs are scheduled for 4 hours after each perijove, although the precise timing may evolve. Because of the use of the Juno thrusters for the OTM, JADE pauses data collection and JADE-I MCP and TOF are set to 0 V. The spacecraft mini-sequence that commands OTMs also contains commands to ramp the noted JADE voltages down prior to the maneuver, and then ramp them back up after the maneuver. Once the voltages are restored to nominal operating voltage, data collection resumes in LRS.
Low Rate Science (LRS) Accumulation During Bulk of Orbit
After the perijove region (and any intermediate accumulation LRS following it), JADE shifts to collecting data in low accumulation rate, for the bulk of the orbit since high time resolution is not needed away further from Jupiter in the more distant magnetosphere. In LRS, all electron and species data are binned by spin phase and only histogram data are stored. ESA sweeping is performed for both sensors, and DFL sweeping via table is performed for JADE-E. Essentially 4π viewing is available for JADE-I due to the spacecraft spin.
MCP Calibration During Current Sheet Crossing
JADE regularly (typically once every other orbit) enters MCP Calibration mode as it crosses the current sheet near apojove. Once in this mode a macro is run to perform a standard gain test on the MCPs, in order to ensure that the operating voltages are on their gain curve plateaus. As a part of normal detector degradation, the operating voltages on the MCPs may need to be increased over the mission life to maintain high count efficiency. If and when an operating voltage needs to be changed, new macros are uploaded to incorporate the new values.
Intermediate Accumulation LRS During Current Sheet Crossing
If bandwidth allows, JADE increases accumulation rates to intermediate levels while passing through the current sheet near apojove. This is performed for no less than 12 hours to allow separation of temporal and spatial signatures in the data, therefore the collection period must be longer than the Jovian rotation rate of ∼10 hours.
Other Science
4.1.7.1 Post-Perihelion Initial Ramp Up
JADE-I temperatures were ∼20∘ above those predicted by the pre-launch thermal model. JADE-I neared, but did not exceed, non-operational limits shortly after launch and fell to acceptable values for the initial high voltage turn on. Initial science observations from that turn-on are shown in Sect. 5. After perihelion, when JADE temperatures fall below post-perihelion operational limits, the instrument will be turned on again with additional precautions.
4.1.7.2 Periodic Instrument Maintenance
Juno has 3 designated week-long periods for Periodic Instrument Maintenance (PIM). JADE will not participate in Earth flyby or the first PIM due to thermal constraints. However, JADE will participate in the second PIM in 2014 and the final PIM in 2015. During these periodic maintenances, JADE starts with a gain test early in the activity, spends time in each mode including coordinated Burst mode periods with Waves, and concludes with a gain curve at the end of the activity.
4.1.7.3 Cruise Science
When bandwidth allows, and additional science can be obtained without increasing mission risk or compromising long-term objectives, JADE participates in cruise science activities using LRS mode. If bandwidth allows the standard 600 s accumulation rate will be decreased to 300, 60 or 30 s and an additional ion species may also be transmitted. Cruise science activities are conducted using standard command packages to turn on, set the initial configuration, and then dwell in that mode. Minimal changes are made to keep operations and bookkeeping as simple as possible.
4.1.7.4 Approach Science
JADE participates in approach science activities as bandwidth and power allow, on a non-interference basis with primary mission objectives. Approach science consists primarily of LRS, which can be augmented with additional activities based on consensus among the MWG and project.
4.1.7.5 Capture Orbit
JADE takes LRS data during the capture orbit, as bandwidth and power allow, on a non-interference basis with primary mission objectives. JADE is planned to operate until just a few days before JOI and then turn off for JOI. JADE will turn back on as soon after JOI as possible and resume LRS operations. A model prediction shows tens of magnetosheath crossings within the capture orbit (Bagenal et al. 2013, this issue), providing intriguing secondary science opportunities. Additionally, JADE will work with the MWG on any coordinated instrument efforts during the capture orbit.
Energy and Angle Scanning Strategy
Data Resolution by Mode
The JADE data resolution for each mode is described in this section and summarized in Table 16.
Table 16 Summary of JADE resolution by mode. PA=pitch angle; En=energy; El=Elevation; Dir=direction; Az=Azimuth; TOF=Time of Flight; sp=ion species
4.2.1.1 JADE-E Data Resolution by Mode
JADE-E has an inherent resolution of 64 energies×48 directions×1 s. Sweeping and data collapsing are dependent on mode.
In HRS and Burst the JSIB sweeps all 64 ESA/DFL pairs in 1 s. In Burst there is no collapse of energy, direction or time resolution. In HRS the data is collapsed to 32 energies×24 directions×1 s resolution, with directions collapsed according to pitch angle. Pitch angles within 0–60∘, and 120–180∘ from the magnetic field direction are uncollapsed in direction. The remaining bins are collapsed from 4 adjacent fine-pitch angle bins to 1 course pitch-angle bin as shown in Fig. 71.
In LRS and Cal, the data is not collapsed, and retains 64 energies. There is no directional energy collapse based on pitch angle because all data are taken in a plane. The deflectors are swept, but not to magnetic field alignment. Rather than 1 s resolution, the data are binned into histograms with typically 5 or 10 minute resolution for Low Rate LRS, and 30 or 60 s for Intermediate Rate LRS and Cal.
4.2.1.2 JADE-I Ion Data Resolution by Mode
Sweeping, species, and data collapsing are dependent on mode. In HRS and Burst modes, JADE-I’s inherent resolution is 32 energies×8 elevations×12 azimuths×256 TOF×4 s. Based on LUTs, ranges of TOF for each energy step are defined as species. Species 0 and 1 are predefined as being any events measured on any stop anode and any event with a valid TOF, respectively. Species 2 is for mass per charge of 1 amu/q, species 3 is for light components of the plasma (mass per charge between 2 and 5 amu/q), and species 4 is for heavy components of the plasma (mass per charge >5 amu/q). Up to 3 more species can be identified, and the values for species 2–7 can be redefined by upload of a table at any time.
In Burst there is no data collapse, and up to 6 species are stored configurable by command. In HRS the data is only collapsed in elevation by summing adjacent elevations; the data stored is 32 energies×4 elevations×12 azimuths for each transmitted species (default 2 species in HRS, configurable by command). An additional ‘optional’ species can be transmitted while in HRS. Our default configuration will be to transmit species 2 and 4, and have species 3 as the optional species while in HRS.
In LRS and Cal, the data is 32 energies×56 directions×1 species. Rather than 4 s resolution, the data are binned into histograms with 5 or 10 minute resolution for Low Rate LRS and Cal, and 30 or 60 s for Intermediate Rate LRS. JADE calculates the spin phase at each observation cycle boundary based on the time stamp of the spin phase provided by the spacecraft. JADE-I bins translate to 56 near-constant solid angle sectors. In LRS the data is mapped per spin, such that the counts in each anode are mapped over approximately equal solid angles. Since anodes 4 and 11 look nearly along the spin axis, in half a spin they sweep out about the same amount of solid angle as anodes 7 and 8 sweep out in about 15∘ of rotation, therefore in LRS, the count rates for each anode are mapped to different sized bins in spin phase (see Fig. 72). Anodes 0–3 are not used in LRS for the species data since they view the same region of space as anodes 4–7 out of phase by 180∘.
4.2.1.3 JADE-I TOF Resolution by Mode
JADE-I inherent TOF resolution is 32 energies×256 TOF×1 s over all available directions. In Burst science the TOF data is collapsed such that elements 0–83 are mapped one to one, and for TOF bins 84–255 the 4 consecutive bins are collapsed (i.e. bins 84, 85, 86, and 87 are collapsed and mapped to 84). In HRS, adjacent energies are collapsed to provide a resolution of 16 energies×128 TOF×4 s resolution. The same TOF collapsing as in burst is performed in HRS. In LRS and Cal, TOF data is collapsed into 16 energies×64 TOFs. In all modes, the TOF data is summed over all elevations and azimuths covered in the accumulation time.
Energy Sweeping by Mode
4.2.2.1 JADE-E Sweeping by Mode
JADE-E sweeps through its 64 ESA steps in 1 s, regardless of mode. A low-resolution, 32-step sweep is taken every 0.5 s, hitting every other energy step in the first half second where voltage is increasing, then filling in the skipped voltages during the second half of the second where the voltages are decreasing. ESA steps are 0,2,4,…,30,31,29,…,1 (Fig. 73). The reason for sweeping up then down is to minimize the largest single step taken and therefore minimizing the HVPS settling time. Because the intrinsic resolution of JADE data is 1 s, no additional temporal resolution is required.
There are 3 JADE-E sweep tables that can be updated; at launch, table 1 covered the full energy range from 0.1 to ∼100 keV, table 2 is a limited range solar wind sweep from 0.1–5 keV, and table 3 is a calibration table with 4 energies.
In HRS and Burst all 3 JADE-E sensors collect data, and deflectors are set to remain field-aligned according to the real-time magnetic field. The JADE software compensates for an ∼1 s latency in this vector by propagating from its last position to the time at the next sweep start, using the updated spin rate. In LRS only one sensor is operational. In Cal, all three sensors are active. Deflection is based on sweep tables, not magnetic field alignment.
4.2.2.2 JADE-I Sweeping by Mode
JADE-I makes use of low-resolution scans within the full ESA range to allow for greater temporal resolution over a large energy range. JADE-I has 32 ESA steps, but how long it remains in each step and how the voltages are ramped depend on the mode.
In HRS, one 32-step high-resolution ESA sweep is completed every 4 s, while each 8-step low-resolution ESA sweep is completed every 1 s. The low-resolution scans allow for greater temporal resolution than a sequential scan. ESA steps are 0,4,8,12,16,20,24,28,29,25,21,17,13,9,5,1,2,6,10,14,18,22,26,30,31,27,23,19,15,11,7,3 as shown in Fig. 74.
In HRS, the deflector is scanned 8 DFL steps for each ESA step (covering ±45∘ deflection), covering 64 ESA/DFL pairs per second. There are two sweep tables available for use in HRS that can be updated anytime by uploading new tables. The tables at launch are set to cover the full energy range. The first HRS sweep table sweeps the deflectors over 8 steps, spaced 11.25∘ apart, while the second sweeps the deflectors over 8 steps, spaced 6∘ apart.
In LRS and Cal, the ESA supply sweeps according to one of four sweep tables that command 32 voltage steps per second. The tables can be updated at anytime, with tables loaded at launch having 32 logarithmically spaced steps arranged in a pyramid sweep such that even numbered voltage steps ramp up in the first half second and the odd numbered voltage steps ramp down in the second half second (Fig. 75).
There are 4 sweep tables available in LRS that can also be updated. At launch, the first table covered the energy rang of 10 eV to 45 keV, and is the default table to be used at Jupiter, while the second covers the energy range from 350 eV to 7.7 keV to be used during cruise to measure the solar wind; this energy range will cover the most probable solar wind velocities (Gosling 2007). The third table covers energies from 125 eV to 45 keV, and the fourth, energies from 5 eV to 25 keV. The deflector supplies do not sweep in this mode.
4.2.2.3. Histogram Binning
All histogram data is organized by spin phase. JADE calculates the spin phase at each observation cycle boundary based on the time stamp of the spin phase provided by the spacecraft. JADE-I bins translate to 56 near-constant solid angle sectors. In LRS the data is mapped per spin, such that the counts in each anode are mapped over approximately equal solid angles. Since anodes 4 and 11 look nearly along the spin axis, in half a spin they sweep out about the same amount of solid angle as anodes 7 and 8 sweep out in about 15∘ of rotation, therefore in LRS, the count rates for each anode are mapped to different sized bins in spin phase (see Fig. 72).
The JADE-E lookup tables controlling the ESA and DFL voltages in LRS are fixed. These tables contain 64 steps of ESA and DFL voltage combinations. For example, one can chose a table with 64 energies with zero voltage on the DFL. Alternately, one can chose a different table with 16 ESA voltages (e.g. 16 energies) and 4 DFL voltages for each energy step. The voltage sweep is different, but the total of ESA-DFL voltage combinations is the same. The LRS data products for JADE-E are independent of the lookup table and are always binned in an array of counts with dimension 64×24. We reconstruct the count rate versus energy by look direction using the lookup tables with ground processing.
4.2.2.4. Determining Count Rate
The ion species and electron products in LRS are in units of rates (counts per views) instead of counts. If a sector is viewed 2 times and has 1 count, the rate is 0.5, which is saved as 0 (losing data with integer truncation). So, rates are multiplied by 512 before being sent to the ground. Then the ground software then divides the rates by 512 into floating point numbers, and preserves decimal rates.
Operation and Processing by JSIB and Flight Software
The following sections describe which JADE functions are controlled directly by the JSIB and which are controlled by the Flight Software (FSW).
Electron Sensor Switched Power
The JSIB controls the power to the in-sensor processing electronics of the three JADE-Es. The power is individually switchable for each sensor. FSW controls which electron sensors are powered by setting power control bits in JSIB FPGA registers. FSW is commanded to enable/disable electron sensors based on the mode to conserve power. Commands nominally come from in-JADE stored sequences (macros).
High Voltage Control
Each high voltage power supply can also be individually switched on/off by the JSIB. FSW controls which supplies are enabled for each mode by setting power control bits in JSIB FPGA registers. FSW is commanded to enable/disable high voltage sources based on the mode to conserve power. Commands nominally come from onboard via stored sequences or macros. The ion sensor and electron sensors each have an MCP, an ESA, and two DFL voltages. Additionally, the ion sensor has a TOF voltage. Since JADE-E’s ESAs and deflectors both have positive polarity they use a single bulk power supply. However, because JADE-I’s ESA uses a negative voltage and the deflectors have a positive voltage, JADE requires separate bulk power supplies for the positive and negative voltages.
The JADE-I MCP and TOF are static supplies, staying at a fixed voltage during science data collection after being commanded to the appropriate voltage. FSW is commanded to the appropriate MCP and TOF voltages through macros and writes 12-bit raw digital values to the JSIB FPGA control registers.
The ESA and DFL are stepper supplies, designed to rapidly sweep through a range of voltages. The FSW retrieves voltage sweep tables stored in non-volatile memory (EEPROM), and writes these 13-bit raw digital values to arrays mapped into the JSIB FPGA memory. The sweep tables are selectable via command. The ESA and DFL are dual-range supplies. The 13th bit in each value is the range bit, selecting whether the 12-bit raw value should be mapped to hundreds of volts or thousands of volts. The FSW only calculates sweep tables on-the-fly during HRS and Burst science, and only for the electron sensor deflection; the electron sensors must deflect to view the magnetic field vector, which is not known in advance and must be retrieved on-board from the FGM (flux-gate magnetometer) instrument.
The JSIB controls the high voltage by using a digital to analog converter to convert the 12-bit raw voltage values into a scaled voltage interpreted by the high voltage control board. In LRS and MCP Cal, the JSIB sweeps the electron sensors with 64 ESA/DFL pairs in 1 s, and sweeps the ion sensor with 32 ESA steps (no deflection) in 1 s. In HRS and Burst science, the JSIB sweeps the electron sensors with 64 ESA/DFL pairs in 1 s, and sweeps the ion sensor every 4 s with 32 ESA steps each containing 8 DFL steps.
Analog Monitoring
The JSIB monitors voltages, currents, and temperatures from all parts of JADE, including high voltage, low voltage, sensors, and control boards (JSIB, IPB, HVPS, and LVPS). The JSIB uses an analog-to-digital converter to read the scaled monitor values as 12-bit digital values. The JSIB updates all 80 housekeeping monitors every 5.12 milliseconds, and arranges the values in an array in memory, where the FSW can read it 8 times per second. The FSW stores minimum, maximum, and average values for these monitored values and checks the values against red alarm minimum and maximum values, taking action (requesting a turnoff from the spacecraft) when monitors exceed limits for a persistent (selectable) number of samples. The software also performs rate limiting and auto safing, described below in Sects. 4.4.6 and 4.4.7.
Electron Sensor Data Products
The JSIB counts the number of electron detections in each ESA/DFL step for each sensor anode. As described above in Sect. 2.4.4.3, each electron sensor has 16 positional anodes covering a 120∘ FOV. Together, the three electron sensors ring the spacecraft to create a 360∘ FOV. Additionally, each electron sensor has a background anode to count penetrating radiation. The JSIB forms a matrix in FPGA memory representing the electron sensors as a two-dimensional array, with the ESA/DFL steps as the rows, and the 51 anodes (16⋅3 positional+3 background) as the columns. This data produces a histogram of counts.
In Burst science, the FSW transmits the raw histogram from the JSIB each second as the data product, providing JADE’s highest rate science data for selected intervals in the auroral zones. Owing to telemetry limitations, this product can only be provided for a small fraction of the time.
In HRS, which is available throughout the entire perijove intervals, including all auroral zone crossings, the FSW reduces the data product size by summing adjacent rows into 32 ESA/DFL steps, and prioritizing resolution in the positional anodes. The 8 anodes closest to being parallel and anti-parallel to the magnetic field vector are preserved as individual bins, creating high resolution for particle pitch angles around the field vector. The anodes furthest from the magnetic field vector are summed with 4 anodes into coarse bins (see Fig. 71). Over a spacecraft rotation, the magnetic field vector traverses around all three electron sensors, and all anodes fall into high-resolution (fine) bins. From this, a complete 360∘ map can be created by combining the high-resolution histogram pieces on the ground. The FSW collapses each background count into a single counter, preserving total counts. The FSW produces this data product each second.
During LRS, over the rest of Juno’s orbit away from the polar regions, the FSW reads the histograms from the JSIB each second and further accumulates them over a commendable amount of time depending on telemetry allocation. For most of the mission this resolution is nominally 10 minutes. This accumulation interval must be an even multiple of spacecraft spins (2 rpm).
The spin dependency is a result of the data product binning in the FSW by spin sectors. Each positional anode is mapped into a particular solid angle sector based on the orientation of the spacecraft. As the spacecraft rotates, different positional anodes fall into that sector. The FSW creates a histogram of count rates for 24 spin sectors, preserving the 64 ESA/DFL step resolution. The background count is summed into a single counter, independent of energy step. The units of count rates are created by dividing the total counts by the number of times each sector was viewed.
In MCP Calibration mode, the FSW creates a separate data product for each electron sensor, preserving the complete 64 ESA/DFL steps and 17 anodes (16 positional and 1 background). The FSW reads this histogram from the JSIB each second and accumulates it over a commendable time period (nominally 30-s integrations).
Ion Sensor Data Products
The ion sensor contains 12 position anodes, and a background anode for penetrating radiation. JADE-I also measures the TOF for each particle. This measurement begins when the JSIB receives a start pulse, and ends either with reception of a stop pulse from an anode, or a timeout with no stop pulse. During the measurement interval, new start pulses are locked out. The JSIB stores data products for these particles at 1-s intervals in LRS and Cal, and at 4-s intervals in HRS and Burst, which have a longer sweep time to accommodate elevation deflection not used in low rate scans.
The JSIB represents each particle as a direct event, which contains the ESA/DFL step, the TOF, anode, and quality information. A certain number of direct events are stored in a two-dimensional buffer (ESA step by event) in LRS and Cal, and three-dimensional buffer (ESA step by DFL step by event) in HRS and Burst. The FSW reads the direct events from the JSIB as an array mapped into JSIB FPGA memory and transmits them over a selectable interval (nominally 10 minutes in HRS and Burst, and 10 hours in LRS).
The JSIB histograms the TOF measurements into a data product with 32 ESA steps (all 8 DFL summed together in HRS and Burst) and 128 TOF bins (256 for Direct Event data only). The TOF information is represented in digital values corresponding to asserted delay line taps and coarse ticks, which the ground processing converts into nanoseconds. The FSW transmits this data product in Burst mode, and reduces resolution in HRS mode by summing adjacent energy rows into 16 ESA steps, preserving the 128-bin TOF resolution. In LRS and Cal modes, the FSW accumulates this product over a selectable number of seconds (nominally 5 or 10 minutes for LRS, and 30 s for Cal), and reduces row and column resolution by summing adjacent rows and columns to form a 16 ESA by 64 TOF histogram.
The JSIB classifies each particle with a valid TOF as a specific ion species via a lookup table provided by FSW. The FSW generates this table on-the-fly by retrieving the ESA voltage and comparing it against a stored table in non-volatile memory (EEPROM) to determine which TOF ranges map to which species for each ESA step. The FSW writes this table to the JSIB as an array in the JSIB FPGA memory space, so the JSIB can use the energy step and TOF as a lookup table to determine the correct species. The JSIB produces a data product with 32 ESA steps by 8 DFL steps by 12 positional anodes. The FSW produces this data product in Burst mode. In HRS mode, the FSW reduces DFL resolution by summing adjacent DFL steps to create a data product of 32 ESA steps by 4 DFL steps by 12 positional anodes. During LRS and Cal modes, away from the polar regions and away from the prime science, the FSW reads the histograms from the JSIB and further accumulates them over a commendable number of seconds, nominally 10 minutes in LRS and 30 s during Cal. This accumulation is an even multiple of spacecraft spins (30-s spin at 2 rpm). The reason for the spin dependency is because the data product is binned in FSW by spin sectors. Each positional anode is mapped into a solid angle sector, based on the orientation of the spacecraft. As the spacecraft rotates, different positional anodes will fall into that sector. The FSW creates a histogram of count rates for 56 spin sectors, preserving the 32 ESA step resolution. As for JADE-E, the JADE-I units of count rates are created by dividing the total counts by the number of times each sector was viewed.
The JSIB creates a singles/logicals histogram with 32 ESA steps and 25 counters in LRS and Cal, and 32 ESA steps by 8 DFL steps by 25 counters in High Rate and Burst. The 25 counters represent the 12 positional anodes, background anodes, and coincidence logic. Coincidence logic represents events such as adjacent anodes being hit, non-adjacent anodes being hit, TOF underflow and overflow, starts without stops, stops without starts, invalid events, and multiple starts before a stop. In Burst mode, the FSW preserves full 32 ESA by 8 DFL resolution, but only keeps the counters for all starts, all stops, background, and invalid events. In High Rate mode, the FSW creates the same product as Burst, but with a reduced DFL resolution (summing adjacent DFL steps), for a data product of 32 ESA steps by 4 DFL steps by 4 counters. Additionally during HRS mode, the FSW produces a data product with the remaining 21 counters, but with no ESA/DFL resolution (all ESA and DFL steps summed together). During LRS and Cal modes, the FSW sums the histogram over a selectable number of seconds (nominally 5 or 10 minutes in LRS, and 30 s in Cal) then reduces the product to 25 individual counters, preserving no energy resolution (summing all ESA steps together).
Software and Instrument Modes
JADE has only two basic sets of modes: Boot Program and Science Program.
Boot Program Mode
Upon initial power on, JADE is in Bootup mode. The Boot Program starts execution of the Science Program from one of the two code images stored in the EEPROM (whichever has the first valid checksum). A number of checksums and memory tests are performed in Bootup mode. If all tests are passed, JADE autonomously transitions into the Low Voltage Engineering (LVENG) mode. Upon initial Bootup, JADE-I is powered on but all three JADE-Es remain off until commanded on.
If any of the conditions to enter the Science Program are not met, JADE enters Boot Maintenance mode rather than autonomously booting into LVENG. The following conditions result in entering Boot Maintenance mode: command sent and received, EDAC error, memory test error, bad checksum of both Science code images. JADE remains in Boot Maintenance until power cycled or explicitly commanded into the Science Program, where it enters LVENG.
Science Program Modes
JADE has 6 Science Program modes: LVENG, HVENG, MCP Calibration, LRS, HRS, Burst Science. Figure 76 shows the acceptable transition paths between the various modes.
4.4.2.1 Low Voltage Engineering (LVENG)
LVENG is entered immediately following successful Bootup and in this mode, the FSW first validates the Science Program Lookup Tables and then checks for the presence of the JSIB. If the JSIB is not present, or the Lookup Tables are corrupted, the Science Program stays in this mode and refuses to enter any other Science modes. In LVENG, all power supply voltages are set to 0, all JADE-E sensors are powered off (JADE-I low voltage remains powered), stims are disabled, and data buffers are cleared. Once in LVENG, the FSW produces housekeeping data and waits for commanding to one of the other modes.
4.4.2.2 High Voltage Engineering (HVENG)
Once commanded into HVENG, JADE-I is, and any number of the three JADE-E sensors can be, powered on. Default consists of all 3 JADE-E powered off, and macros enable the sensors for transition into the next mode. Upon initial entry into HVENG no voltages are changed. In each subsequent return to HVENG, the ESA and DFL are returned to the last values commanded while in HVENG. This ensures photoelectron rejection voltages are retained after the MCP voltages have been brought up after initial turn-on. Science and housekeeping data are produced in HVENG and JADE can only enter and leave this mode by command or autosafing.
4.4.2.3 MCP Calibration (Cal)
In Cal mode, JADE-I is on and any number of the three JADE-E sensors can be on, with a default is all three JADE-Es powered on. All prior MCP and TOF voltages from HVENG are retained and MCP voltages are stepped via command or macro to generate a gain curve (counts vs MCP voltage).
4.4.2.4 Low Rate Science (LRS)
Low rate science mode is used for the large portions (>90 %) of the Juno orbit away from Jupiter, where power needs to be conserved. In LRS, JADE-I and only one of the three JADE-E sensors is powered on. Deflector voltages are 0 for JADE-I and are swept via DFL sweep table for JADE-E. The inertial spin phase and inertial spin rate provided by spacecraft Attitude Control System (ACS) are used to map the JADE-I and JADE-E anodes into spin sectors (if no ACS message is received, the default spin phase is 0 and the default spin rate is set to the nominal spin rate of 2 rpm). These spin phase ordered observations are collapsed, saved and telemetered down at a low cadence, depending on the available telemetry (typically providing 5 or 10 minute temporal resolution for standard LRS but increasing temporal resolution to 30 or 60 s accumulation for intermediate rate LRS.
4.4.2.5 High Rate Science (HRS)
High rate science is the primary science mode for JADE, and is the mode that JADE is in for each of the critical perijove intervals, which includes the critical auroral crossings. In HRS, JADE-I and all three JADE-E sensors are nominally on with the DFL and ESA voltages sweeping at high rate to attain high temporal resolution observations. The broadcast magnetic field vector onboard Juno is received by JADE and used to determine which of the three JADE-E sensors has positive deflection, which has negative deflection, and which remains undeflected. Deflector voltages are swept via table.
4.4.2.6 Burst Science (Burst)
Burst science mode is simply an extension of HRS, but at higher resolution (no collapsing of dimensions and no accumulation of multiple samples). Data products are sent directly to the spacecraft over dedicated serial lines and include all ion species. Owing to the very large data content, only short intervals of Burst can be stored and fit into the JADE telemetry allocation.
Tables and Macros
The bulk of JADE operations are controlled by internally stored tables and macros to minimize the need for ground commanding. These allow the sensors to operate under a series of operating regimes within an orbit based on a small number of stored commands loaded once per orbit.
4.4.3.1 JADE Tables
JADE Lookup Table (LUT)
The JADE Lookup Table (LUT) is a partition in JADE memory that contains the definitions of tables, macros and parameters. The LUT contains default parameters, hidden parameters, ion species TOF definitions, voltage sweep tables, compression definition, MCP rate limiting definitions, macros, autosafing definitions, and the magnetometer parameters.
Upon transition from Bootup to LVENG, the Science Program performs a checksum and EDAC check of the table images stored in EEPROM. If table image 1 has no errors, it is used. If image 1 of a table has errors and image 2 does not, image 2 is used. If both table images have errors, JADE remains in LVENG mode. The error-free table is stored in SRAM, where it is used to define and execute Science Program tasks. The contents of the LUT can be updated in LVENG or HVENG modes. These updates can be temporary (written to SRAM; reverts to default upon power cycle) or permanent (written to EEPROM; establishes new default).
Parameter Tables
All default parameters are captured within the LUT. Examples of these parameters are default sweep table for JADE-E and JADE-I, default JADE-E for LRS, and default additional ion species. These parameters can be updated individually using the Set Parameter command or as part of a LUT upload. Updates can be either temporary or permanent.
ESA & DFL Sweep Tables
When in specified science modes, the ESA and DFL voltages sweep according to predefined sweep tables stored in the LUT. In LRS, JADE-I has 4 ESA sweep tables available and JADE-E has 3. In LRS JADE-E also sweeps their DFL using one of their 3 available DFLs tables. In HRS and Burst, JADE-I has 2 sweep tables that define ESA+DFL voltages. JADE-E has 3 ESA sweep tables available, and the DFL voltages are set according to the Mag parameters table in order to track the magnetic field direction. Large tables like the ESA and DFL sweep tables are updated by either overwriting the whole sweep table or the entire LUT. Updates can be either temporary or permanent.
Ion TOF Tables
The TOF of an ion is measured between the START and STOP signals generated by JADE-I electronics. For each of the 32 JADE-I energy steps, the JSIB converts the time between the START and STOP into digital numbers, and uses it for the subsequent ion data processing. The delta time between the START and STOP signals is proportional to the M/q of the ion and is used to distinguish ion species. See Sect. 3.3.2 for more detail. Large tables like the Ion TOF table can be updated by either replacing the whole sweep table or the entire LUT. Updates can be either temporary or permanent.
4.4.3.2 JADE Macros
JADE macros are a series of relative-timed commands stored in the LUT. These macros are called using the Execute Macro commands. When JADE receives an Execute Macro command, it sends the series of time-tagged commands stored in SRAM. Note that these macros are completely internal to JADE and are different from spacecraft command blocks, although the concept behind spacecraft blocks and JADE macros is the same.
There are 40 macro “slots” available for use in JADE; half contain at least one interactive command and half contain only non-interactive commands. A non-interactive command does not change power draw by any more than 1 W. The first 20 macros are dedicated to interactive commands and contain commanding to change Science modes, decrease voltage prior to an orbital maneuver, increase voltages after an OTM, and prepare JADE to be turned off by the spacecraft. The second 20 macros contain only non-interactive commands that contain commanding to configure settings within a mode, i.e. change the LRS histogram accumulate rate, change the optional ion species transmitted. Large tables like the macros can be updated by either replacing the whole macro table or the entire LUT. Updates can be either temporary or permanent.
Data Compression
4.4.4.1 Lossy Compression
Most JADE products are lossy compressed by JADE except for Ion Direct Events, HVENG products, and housekeeping telemetry. Burst products transmitted over the high speed interface are also not compressed by JADE although they are subsequently compressed by the spacecraft.
Two 32–8 bit compression tables are provided for LRS and Cal Science products. This compression is implemented as a binary search through a step table of 256 values, where at most 8 comparisons are made before determining the compressed value. In contrast, HRS utilizes two 16–8 bit LUT compression tables where the value to be compressed is treated as an index into the table. Before each data product gets lossy compressed to 8 bits, the Science Program subtracts the minimum data value from each product element and reports the subtracted value in telemetry.
The JADE compression cuts the data volume in half, while maintaining losses below 14 % across the entire range of fluxes measured. Steps are spaced such that there is ∼4 % error in 16–8 compression and up to 14 % error in 32–8 compression. The data processing software assigns a value to the data that is the average value of the compression bin; for example, if data with original values of 1000–1040 were compressed together, the data processing software could output 1020±20 as the value of the original data.
4.4.4.2 Lossless Rice Compression
In addition to the lossy compression, most products are also subsequently lossless compressed using the Rice algorithm (exceptions are Ion Direct Events, HVENG products, and housekeeping). Burst products are not lossless compressed by JADE although they may subsequently be lossless compressed by the spacecraft. Lossless compression can be enabled/disabled via the Set Parameter command.
4.4.4.3 Internal Data Policing
The JADE instrument can produce far more telemetry than the spacecraft can store for transmission to the ground. JADE uses lossless compression techniques to reduce data size, but the compression ratio varies. Once JADE reaches a predefined orbit data limit in the spacecraft, all remaining data in the orbit is lost. To avoid losing high-priority data, JADE monitors data volume and omits low priority data as needed.
The orbit is broken into time intervals with a data limit set for each interval. A priority mask, configurable as a table parameter, designates each data product as high or low priority. While data volume for an interval is below the limit, all products are produced. Once the limit has been reached, only the high-priority products are produced. This ensures high-priority products are transmitted regardless of how well they compress. If an interval ends up below the data limit, the excess data allocation is saved for future use.
Burst Data Flow
There are two ways to record JADE Burst data: bin recording and continuous recording. JADE must be commanded into and out of these Burst modes. The time spent in Burst mode is called a record session.
4.4.5.1 Bin Recording Burst
JADE records data as a series of bins, which are regions of memory designed to hold N words of recorded burst data. The number of bins, size of bins, and amount of data recorded in the bin leading up to the quality factor data is configurable by command. During any one record session, all bins are the same size, with the number and size configurable via command, subject to a minimum of 10 s of data. Once the bin is no longer being written to, it is a “saved bin” and is typically associated with a Waves quality factor. If no Waves quality factors are received with empty bins remaining, JADE data fills them with high-rate data, and those bins are saved without an associated quality factor. When there are no remaining empty bins the spacecraft first records over any bins without an associated Waves quality factor in a circular manner. If there are no empty bins and no bins without an associated Waves quality factor, data with an associated higher Waves quality factor overwrites the lowest quality factor data.
Another key aspect of Burst is the “quality point,” which is where the recorded data associated with the quality factor resides. As part of the configuration of bins (number of bins, size of bins, etc.), the number of 32-bit words desired before the quality point is specified. If, at the time the quality factor is received from Waves, the scratch bin contains the specified number of words or more, the recording is allowed to continue until exactly the number of specified words precedes the quality point. If there are less than the specified points, the scratch bin is allowed to fill, and the resulting quality point will not have the specified number of 32-bit words preceding the event. It is important to note that the timestamp associated with the quality factor is not where the quality point nominally resides.
4.4.5.2 Continuous Burst
The second mechanism, continuous recording, is independent of the Waves instrument. This recording is used to turn on recording and record up to a commanded number of data words.
MCP Rate Limiting
MCPs may be damaged by very large count rates. To protect against this, a rate-limiting algorithm has been implemented (see Fig. 77). When a consecutive number of count rates (Persistence Count) exceed a specified threshold (Critical Maximum), the MCP supply voltage is reduced by a specified “Delta Voltage.” As long as count rates exceed the threshold, the voltage continues to be reduced until count rates are at an acceptable level. Once acceptable, supply voltage remains reduced for a specified amount of time (Down Time). After the Down Time, the supply voltage is incremented by Delta Voltage to the original voltage. The controlling parameters for MCP rate limiting: Persistence Count, Critical Maximum, Delta Voltage, and Down Time are commendable, and held within the LUT. All parameters in the rate limiting algorithm are changeable/settable in an onboard parameter table.
JADE Autosafing
The vast majority of JADE operations occur while the spacecraft is not in contact. As such, it is necessary for JADE software to internally monitor housekeeping telemetry and enter a safe state if conditions suggest the possibility of hardware damage. Autosafing limits are set higher than the yellow and red limits monitored on the spacecraft in the real-time telemetry stream.
Within the LUT, all JSIB monitors have associated critical minimum and critical maximum values. JADE Autosafes if a telemetry point is consistently outside the region bracketed by these values over a specified persistence. Each monitored telemetry point also has an associated subsystem to be safed. For example if a telemetry point associated with safing JADE-E180 only is out of limits for the required persistence, only E180 is safed, and the rest of JADE continues taking data unaffected. Since JADE-I cannot be powered off without powering all of JADE off, when a JADE-I only telemetry point is tripped, it’s high voltage is disabled.
EDAC and Table Checksums
Once the Science Program is running, JADE is very robust against bit errors. Error Detection and Correction (EDAC) scrubbing is performed continuously, which corrects single-bit errors. JADE is therefore not sensitive to single event upsets (SEUs). A double-bit error in SRAM causes a watchdog reset, and JADE reboots into LVENG. If a multiple-bit EDAC error in SRAM occurs, the Science Program writes the contents of the processor trace buffer into the EDAC Log before performing the watchdog reset.
JADE Data Products
JADE data files follow the Committee on Data Management and Computation (CODMAC) level descriptions, which are generic for use on science missions and not Juno-specific. The process follows level 1 (the raw data telemetered to Earth from Juno) to level 8 where user-orientated information is provided, explaining why particular data is taken at a given time, and if there is any ancillary information associated with the dataset. Table 17 shows the CODMAC levels (different from NASA levels); not all levels are relevant to JADE, e.g. JADE does not provide any level 4 data products since there is no resampling of data.
Table 17 CODMAC level descriptions
For JADE, the data at different CODMAC levels is as:
-
Level 1 Raw: All JADE instrument data delivered to Earth in Juno’s telemetry stream, exactly as telemetered down.
-
Level 2 Edited: Reformatted Engineering Data Records. Raw level 1 data is unpacked to separate science/engineering products and decompressed if required. Data are time-ordered, redundant data packets are removed, and missing expected data flagged. No other calibration is carried out, e.g. data are left as counts per accumulation period for energy step i and deflection step j.
-
Level 3 Calibrated: Counts are converted to scientific units (i.e. counts per second, electron flux, energy is given in eV and deflection direction in degrees).
-
Level 4 Resampled data: not relevant to JADE, data will not be resampled.
-
Level 5 Derived: Pitch-angle distributions, electron/ion plasma parameters such as density, temperature and velocity. This may require additional calibrated information from other Juno instruments, i.e. magnetometer data for pitch angles.
-
Level 6 Ancillary: Spacecraft position, velocity, orientation, spin-phase, quality flags, efficiency/voltage/energy tables used for level 3 products.
Figure 78 shows the planned data flow of the data from level 1 data from JPL (where the level 1 JADE data from Juno is gathered and transferred to the instrument team) through to level 3. The following subsections discuss currently planned data products at each level.
Level 2 Reformatted Engineering Data Records
4.5.1.1 Science Data
Reformatted Engineering Data Records (REDRs) take the raw data and divide it into separate files depending on the JADE Data Product IDentifier (DPID) number. Table 18 separates these out by data type (rows) and telemetry mode (columns).
Table 18 All JADE science products
In addition to the above science data there are five operations-related data products concerning the whole JADE instrument suite: (1) BOOT_HK—Engineering/Housekeeping packet of the Boot Program (i.e. General monitors and power status’), (2) BOOT_MEM_STAT—Memory Status packet of the Boot Program (i.e. checksums and counts of single/double-bit errors), MEM_DMP—Memory Dump packet (a complete dump of the memory), SCI_ENG—Engineering/Housekeeping packet of the Science Program (i.e. General monitors and power status), SCI_EVENT—Event Message packet of the Science Program (describes an unusual or unexpected occurrence, i.e. a command rejection).
4.5.1.2 Ion Species Identification
The JADE-I sensor uses a loadable LUT to separate the measured events on the anodes to different species mappings. Events that register on a single or two adjacent STOP anodes get mapped to a species. Events that result in only a START event, Background events, or any events that get mapped to non-adjacent STOP anodes are not mapped to a species.
There are 8 potential species, numbered 0 through 7. Species 0 is defined as any event that is seen on either a single or two adjacent STOP anodes. No START is required, so species 0 includes events that do not have a valid TOF measurement (a valid TOF measurement includes a valid START and STOP within a defined time range). For species 1–7 there is additional event masking possible so that events that have a ‘bad’ TOF can be masked out. Bad TOF events are durations shorter than 1 ns or longer than 330 ns. Also, events that have multiple starts prior to the stop signal, or events that result in STOPS in adjacent anodes can be masked out of species 1–7. In the case of measuring STOPS in adjacent anodes, the event is mapped to the lower anode number in addition to incrementing a counter of the number of adjacent events. The mask setting is adjustable based on table values. At launch, adjacent events are included in species 1–7, but bad TOF events and events with multiple starts are not.
Species 1 are all events that do have a valid TOF measurement. Species 1 is a subset of the species 0 events. Species 2–7 are reserved for specific mass ranges and each of species 2–7 are a subset of the species 1 data. Events are mapped to species 2–7 based on a LUT that defines a TOF range for each species and each ESA step. The TOF table in the LUT can be updated by uploading a new table or a new LUT. The species TOF table is currently defined to have species 2 for M/q of 1 amu/q, species 3 for M/q between 2 and 5, and species 4 to be for M/q greater than 5 amu/q.
4.5.1.3 Ion Direct Events
There are two types of primary Science data products: histograms and direct events. Histograms are binned data and retain a complete history of the number of events that occurred within a given bin during an accumulation period. The duration of the accumulation period can be commanded, as noted earlier; low accumulation LRS has histograms that cover 300 or 600 s periods while intermediate accumulation LRS has histograms that cover 30 or 60 s periods. Because these events are simply counted, you can derive the number of particles from a given region from histograms but have no data on the order in which the particles were collected (i.e. if one section of the sky filled in preferentially earlier in the accumulation period and another section filled in later).
Direct events are individual events stored with time of collection, TOF, ESA and DFL information associated with them. A direct event carries with it all relevant information to describe the stored event, and thus is a much more detailed data product. Because the level of detailed information associated with just one direct event is large, telemetering many direct events quickly becomes a bandwidth issue. Juno is a telemetry-limited mission, so histograms are given priority storage. Direct events are stored on a low-priority basis and are transmitted when downlink allows.
4.5.1.4 Electron Data
The electron data are returned as histograms of energy vs. pitch angle, as described in Sect. 4.3.4. For electrons, there is no complexity of TOF data, nor species separation, as there is for JADE-I.
Level 3 Calibrated Data
The measurements need to be converted to scientific units, which often requires knowing which plasma species is being measured. This is straightforward for electrons (negative ions are not expected at Jupiter). However, the ion detectors measure a variety of positively charged ions with different masses and different charges, i.e. O+, S++, S+, O++S+++, H+, in order of decreasing abundance. Therefore, the user must first partition the counts into their separate species, which is not possible if, as is usually the case, the velocity distributions overlap.
4.5.2.1 Conversion of Counts per Accumulation to Counts per Second
The first level of calibration is to convert the counts per accumulation (C
Accum.) into counts per second (C
s
). This is a simple division of:
$$ C _{s} = \frac{C _{Accum.}}{dt} $$
(4.1)
where dt is the accumulation period, which is provided in each data file. Note this unit is independent of ion species or charge.
4.5.2.2 Convert to Differential Energy Flux
Differential energy flux, DEF, is counts per second of a particular species (i.e. electrons or protons) divided by the geometric factor (see Sects. 3.2.1.3, 3.3.1.1 and Table 6) and has units of cm−2 sr−1 s−1.
$$ \mathit{DEF}= \frac{C _{s}}{G} = \frac{C _{Accum.}}{G\ dt} $$
(4.2)
where the MCP efficiencies are already included in the effective geometric factors as they were derived from laboratory calibration measurements.
4.5.2.3 Convert to Differential Number Flux
Differential number flux, DNF, of a particular species is DEF divided by the energy (E, in eV) and modulus of charge (q, in Coulombs) of the particle and has units of cm−2 sr−1 s−1 J−1. For electrons or singularly charged ions, q=1.602×10−19 C.
$$ \mathit{DNF}= \frac{\mathit{DEF}}{E | q|} = \frac{C _{Accum.}}{E | q|G dt} $$
(4.3)
4.5.2.4 Convert to Phase Space Density
If the mass and charge of the species is known (or assumed), the Phase Space Density, PSD, is calculated from dividing the DEF by v
4 (where v is found from \(E/q = \frac{1}{2} mv^{2}\)),
$$ \mathit{PSD}= \frac{\mathit{DEF}}{ ( {2E} / {mq} ) ^{2}} = \frac{m ^{2} q ^{2} C _{Accum.}}{4 E ^{2} G dt} $$
(4.4)
Note that this equation assumes there is zero spacecraft potential accelerating/decelerating the incident electrons/ions. This equation also shows the necessity of partitioning the ion counts into separate ion species. Note the strong dependence of this conversion of DEF to phase space density on the mass and charge of the particles: H+ has an (mq)2=1 amu2e2, O+ has (mq)2=256 (=162) amu2e2, while S++ has (mq)2=4096 amu2e2. The net effect is that the resulting PSD, the desired scientific measurement, is very sensitive to assumption of what species is being detected.
Level 5 Derived Data
Once level 3 calibrated data exists; other data products may be derived. Examples include plasma density, flow velocity, isotropic temperatures, anisotropic temperatures and temperature anisotropies, and plasma β. Many methods for these derivations exist, however a few are discussed below.
4.5.3.1 Pitch-Angle Distributions
In order to calculate pitch-angle distributions with respect to the magnetic field, one must know the magnetic field direction at the time of the particle measurement as accurately as possible, ideally with level 3 data from Juno’s magnetometer. Calculating pitch-angle distributions requires reordering the data to refer to the particle’s (ion or electron) direction of motion relative to the magnetic field direction, such that 0∘ is parallel to the magnetic field, 90∘ is perpendicular, and 180∘ is anti-parallel. A dot product between the particle’s flow direction and the magnetic field vector (in the same co-ordinate system) is then used to find the pitch angle. Note that the instrument FOV measures incoming particles, so that the flow FOV is the opposite direction (i.e. the instrument aperture must include the direction opposite to the particle motion).
4.5.3.2 Methods of Calculating Plasma Moments
Methods of calculating single species moments of the velocity distribution function, f(v), are well known (Baumjohann and Treumann 1999; Boyd and Sanderson 1969; Paschmann and Daly 1998) and particularly well suited to spinning spacecraft and electron data.
The ith moment, M
i
, of a given species is:
$$ M _{i} = \int f ( v ) v ^{i} d ^{3} v $$
(4.5)
As such density, n, may be calculated by setting i=0:
$$ n= M _{0} = \int f ( v ) d ^{3} v $$
(4.6)
i=1 provides M
1, which is equal to n
V:
$$ n \boldsymbol{V} = M _{1} = \int f ( v ) v d ^{3} v $$
(4.7)
Since n was found from the previous equation we can divide to obtain velocity, V. Continuing to higher orders of i can provide temperatures and pressures.
This technique is excellent for electron data where the plasma species has a known mass and charge (at Jupiter we do not expect to find the negative ions that are found near Titan or Enceladus at Saturn), and can give a cadence of one set of moments values per spin per sensor. Another benefit is that no plasma distribution (Maxwellian, Kappa, or other) is assumed.
However it is more complicated to use this technique for ion data because of the multiple species with differing masses and charges. Partitioning the ion data into single species to calculate f(v) is complicated because the different species often overlap in velocity space. Therefore, a forward modeling method is generally preferred for magnetospheric ions.
4.5.3.3 Methods of Calculating Plasma Parameters via Forward Modeling
If multiple plasma species exist and overlap in velocity space, then plasma parameters can also be obtained by a forward modeling. This requires assuming which plasma species are present and the nature of their velocity distribution (i.e. Maxwellian, kappa, etc.). These assumptions are then used to create a virtual model of the instrument response for a specified density, temperature and velocity of each plasma species. The simulated histogram (for a given density, temperature and velocity per plasma species) is then compared with the measured histogram from JADE, and the model plasma properties adjusted until the model matches the measured data (e.g. as quantified by a reduced Chi-square measure of goodness of fit).
This technique is computationally expensive, but does not require partitioning of the data in to separate species, allows exploration of the parameter space (usually not unique) that reasonably fit the data, and estimates statistical uncertainties of the output plasma properties. The disadvantage is it is necessary to assume the plasma species and distributions to use for the calculation; a poor assumption will give poor values.
4.5.3.4 Temperature Anisotropies and Plasma-β
Once densities and temperatures have been deduced by either moment summation or forward modeling, further values can be derived. For instance temperature anisotropy is the ratio of the perpendicular temperature to the parallel temperature. Likewise plasma β is calculated as the ratio of plasma pressure to the magnetic pressure. Level 3 Juno magnetometer data provides B, and combined with the level 5 JADE data of density, n, and temperature, T to compute:
$$ \beta= \frac{n k _{B} T}{{B ^{2}} / {2 \mu_{0}}} $$
(4.8)
where k
B
is the Boltzmann constant and μ
0 is the permeability of free space. Further plasma properties such as Mach numbers, scale lengths, wave and collision frequencies can be calculated from the JADE ion and electron plasma parameters.
Level 6 Ancillary Data
Level 6 data aid in understanding JADE data, but are not measured by JADE. For example, JADE data are time-stamped from the onboard Juno spacecraft clock and values included within all level 1 data records. For level 2 data, time is converted to UTC using NASA’s Navigation and Ancillary Information Facility (NAIF) SPICE software suite (http://naif.jpl.nasa.gov). NAIF SPICE software is also used to generate all spacecraft orientation, position and velocity data. In addition, data from the magnetometer on Juno is used to convert JADE counting data in to pitch-angle distributions.
4.5.4.1 Time
Time is expressed as a UTC string (yyyy-dddTHH:MM:SS.sss) and the corresponding Spacecraft clock time. Additionally, time to/since perijove is provided. These times and conversions are calculated using NAIF SPICE.
4.5.4.2 Spacecraft Position/Orientation
Spacecraft position and velocity is provided in a variety of co-ordinate systems, including (but not limited to) Jupiter-centered radial distance, latitude and local time, SYS3 (with west longitude), RTN and J2000. The spacecraft’s orientation is provided along with transformation matrices to convert this in to several other co-ordinate systems. Finally, the spacecraft spin rate and a spin phase are given, where zero spin phase is when Juno scans past ecliptic north. All this information originates from NAIF SPICE routines, so the particular SPICE kernels used are also noted.
4.5.4.3 JADE Instrument Information
JADE can take a variety of data products, but often runs a subset in order to meet telemetry bandwidth allowances, therefore the data products “on” at any given time are listed. In addition, quality and warning flags are provided to help give context to the data. Magnetic field information is provided, along with a flag describing its source (i.e. onboard uncalibrated or ground-calibrated CODMAC level 3 data from the Juno MAG team).
Different energy tables can be used for each of the JADE instruments. This information includes which table is used, and efficiency parameters required to convert raw data in to calibrated units for CODMAC level 3 products.