PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "Brad Trantham, 2014-10-23" RECORD_TYPE = STREAM OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = "JNO" INSTRUMENT_ID = "UVS" OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "ULTRAVIOLET SPECTROGRAPH" INSTRUMENT_TYPE = "ULTRAVIOLET SPECTROMETER" INSTRUMENT_DESC = " Instrument Overview =================== Juno-UVS, the ultraviolet instrument on the Juno mission to Jupiter, is primarily based on the Alice instrument on the New Horizons (NH) mission to the Pluto system and on the Lyman Alpha Mapping Project (LAMP) instrument on the Lunar Reconnaissance Orbite(LRO) mission currently in orbit around the Moon. Juno-UVS is an imaging spectrograph with a spectral range in the extreme-ultraviolet (EUV) and far ultraviolet (FUV) of 68-210 nm. This wavelength range was chosen to cover all important UV emissions from the H2 bands and the H Lyman series produced in Jupiter's auroras, while also including longer wavelengths sensitive to the absorption signatures of aurora -produced hydrocarbons. Juno-UVS will remotely sense Jupiter's auroral morphology and brightness, providing context for in-situ measurements, and will map the mean energy and flux of precipitating auroral particles. The Juno-UVS instrument was developed at SwRI and delivered to Lockheed Martin for integration onto the Juno spacecraft before launch on August 5, 2011. The instrument consists of two main assemblies: (1) a shoebox sized sensor, which includes a telescope section and a spectrograph & detector section, and (2) an electronics box housed in the spacecraft vault. Besides this changed configuration (LRO-LAMP and the Alices each consisted of a single assembly), a number of changes have been incorporated to adapt the instrument to the Juno mission. A main design driver for these differences is Jupiter's harsh radiation environment.Another major change is the addition of a scan mirror, which allows the targeting of specific areas of interest when the spinning spacecraft is close to Jupiter. In the following sections we present the design and operation, the key changes from earlier designs, calibration results, and initial in-flight results for Juno-UVS, but we first begin with an overview of the science planned for Jupiter. 2 Scientific Much of the information in this instrument description is taken from the UVS mission paper [GLADSTONEETAL2014]. See this paper for more details. Scientific Objectives ===================== Juno-UVS-s main objective is to provide context for the particles and fields instruments(i.e., JADE, JEDI, Waves, and MAG) in the investigation of Jupiter's polar magnetosphere(Fig. 1). During the typically 6-hour near- perijove period of auroral observations, Juno-UVS will scan Jupiter's auroral regions once per 30-s spacecraft spin to observe the morphology, brightness, and spectral characteristics of Jupiter's far-ultraviolet (FUV) auroral emissions, which are primarily comprised of the Lyman series of H and the Lyman, Werner, and Rydberg band systems of H2. By obtaining time- tagged pixel list data (where each photon event is assigned a unique location, wavelength, and time), images and maps of the northern and southern auroral regions will be reconstructed on the ground at a resolution appropriate for the signal-to-noise ratio (SNR) of the spectral feature of interest. Near the beginning and end of the near-perijove observation period Juno-UVS will provide global snapshots of the northern and southern auroral morphology from a range of several Jovian radii. Closer to Jupiter, a scan mirror will be used to target the atmospheric region near the expected location of the Juno magnetic field line footprint (based on magnetic field models and the spacecraft orbit and spin axis). This will allow a direct comparison of the precipitating particle fluxes measured by JADE and JEDI with the FUV emissions they produce upon impacting Jupiter's upper atmosphere, and how the particular region sampled by the spacecraft relates to the rest of the magnetosphere. Other frequent targets will be the magnetic field line footprints of the Galilean satellites (at a variety of local times and from near nadir to positions near the limb),the polar flares, and the main oval ansae (i.e., the locations where the main oval emission cross the limb). During MWR orbits (when the Juno spin and orbit planes coincide), the Juno-UVS scan mirror will be used much less, so that simultaneous FUV data will be acquired from the same auroral regions observed by the JIRAM near-IR instrument. Calibration =========== After it was assembled and through with environmental testing, just prior to delivery to Lockheed Martin for integration on the Juno spacecraft, Juno- UVS underwent a series of tests to characterize its radiometric performance. Specifically, the Juno-UVS flight instrument was tested in SwRI's vacuum radiometric calibration chamber in order to determine the best pre-launch values for: (1) dark count rate; (2) PSF and wavelength calibration; (3) off-axis light scatter, and (4) effective area. Note that some of these attributes (e.g., effective area) can be measured much more accurately in flight (through stellar calibration), while other important calibration data (e.g., flat field measurements) are obtained only after launch. Table 3 shows a summary of the results for each of the ground radiometric tests performed, along with the performance requirement. As shown in this table, all the specified radiometric requirements measured during the vacuum radiometric tests were met. Figure 7 shows Juno-UVS in the test chamber just before starting radiometric calibration (during 2010 October 12-17). Design Overview ========================== The scan mirror, OAP mirror, and diffraction grating are each constructed from monolithic pieces of aluminum, coated with electroless nickel and polished using low-scatter polishing techniques. The aluminum optics, in conjunction with the aluminum housing, form an athermal optical design. The scan mirror, OAP mirror, and diffraction grating are also each overcoated with sputtered Al/MgF2 for optimum reflectivity within the Juno-UVS spectral bandpass. Besides using low-scatter optics, additional control of internal stray light is achieved using internal baffle vanes within both the telescope and spectrograph sections of the housing, a holographic diffraction grating with low scatter and near-zero line ghost problems, and an internal housing with alodyned aluminum surfaces (Jelinsky and Jelinsky 1987; Moldosanov et al. 1998). In addition, a zero order light trap has a black anodized Al coating with very low surface reflectance at EUV/FUV wavelengths. Figure 4 shows a labeled opto-mechanical schematic of the interior of the Juno-UVS instrument, with light rays illustrating the optical path. Detector and Detector Electronics ================================= The Juno-UVS detector configuration includes an XDL microchannel plate (MCP) detector scheme housed in a vacuum enclosure with a one-time opening door containing a UV-grade fused-silica window (for limited UV throughput during testing). The door was spring loaded for opening with a wax-pellet- type push actuator. The vacuum enclosure has a vacuum pump port and a small, highly polished region which functions as a zero-order reflector (directing zero-order light from the instrument grating into the zero-order trap on the side of the instrument housing). The vacuum enclosure also utilizes four female connectors for the anode signals, and two high-voltage (HV) connectors for the MCP and anode gap voltages. The detector's MCP configuration uses a Z-stack that is cylindrically curved to match the 150-mm Rowland circle diameter to optimize spectral and spatial focus across the Juno-UVS bandpass. The detector electronics provide two stimulation pixels that can be turned on to check data throughput and acquisition modes without the need to apply high voltage to the MCP stack or to have light on the detector. The MCP pulse-height information is output as 5 bits, which, together with the 11 bits of spectral and 8 bits of spatial information,results in the 3-byte output for every photon. The input surface of the Z-stack is coated with an opaque photocathode of CsI (Siegmund 2000). A repeller grid above the curvedMCP Z-stack enhances the detective quantum efficiency(DQE). Each of the three nested MCPs has a cylindrical 7.5-cm radius of curvature matching the instrument's Rowland circle radius (i.e., 15.0 cm diameter). The approximate resistance per MCP plate is 130 MCP. The MCP format is 4.6 cm wide in the spectral axis by 3.0 cm height in the spatial axis with 12 mm diameter pores and a length-to-diameter (L/D) ratio of 80:1 per plate. The XDL anode is a rectangular format of 4.4 cm x 3.0 cm. The combination anode array and MCP sizes gives an active array format of 3.5 cm x 1.8 cm necessary to capture the entire 68nm x 210 nm instrument bandpass. The pixel readout format is 2048 pixels(spectral dimension) 256 pixels (spatial dimension). The active area is 3.5 cm x 1.8 cm, with 1500 spectral pixels and 230 spatial pixels. The XDL anode uses two orthogonal serpentine conductive strips for encoding an event's X-position and Y-position. Each event(i.e., a cloud of electrons exiting the MCP) is collected in equal amounts by the two strips, Charge is collected at each end of each strip, and the difference in arrival time at each end of a given strip is used to determine the event position (e.g., Siegmund et al. 1999). The detector electronics are composed of a separate electronics package mounted directly behind the detector vacuum enclosure within the sensor housing. Power to the detector electronics is supplied by the Juno-UVS low voltage power supply (LVPS) and commandand-data handling electronics (C&DH), both located in the electronics box (Ebox) in the spacecraft vault (several meters of cable away from the Juno-UVS sensor housing). The detector electronics are composed of five boards: (1) the amplifier board with two fast amps for the X direction (spectral dimension) and two fast amps for the Y direction (spatial dimension) and two charge amps for total event charge; (2 & 3) a time amplitude converter(TAC) board for each axis, X and Y , that encodes 2048 pixels in the X-axis and 256 pixels in the Y -axis by event arrival time differences; (4) the digital board (DIG) that provides the control signals and interface logic, and (5) a delay line board to delay the End signals. The detector electronics also generate a 5-bit analog sum signal for each detected photon event that can be used for generating a pulse -height distribution (PHD) via ground test or flight analysis software. Pixel list data (i.e., a list of pixel x, y addresses) is sent from the detector electronics to the C&DH electronics for further processing. A commandable stimulation pulse generator is also included that provides two stim pixels at two locations in the array; these are useful in checking data throughput without HV and in correcting for temperature effects on the wavelength scale. A UV photon impinging on the photocathode generates a charge that is amplified by the microchannel plate Z-stack. The amplified charge cloud leaves the back end of the microchannel plate and is accelerated across the MCP-anode gap, impinging on the anode and generating pulses that propagate in both the +X and -X directions and +Y and -Y directions along separate integral delay lines to the detector electronics. The detector electronics then output the X and Y pixel locations to the C&DH based on the time delay between the two opposing pulses in each axis. The detector electronics require input DC voltages of 7.3 V and +5.0 V. The detector MCP high voltage is raised to a room temperature operational voltage of about 4.2 kV.The gap between the MCP output and the anode array requires a voltage drop of approximately .600 V. Both the MCP and the anode gap voltages are supplied by the instrument's two redundant high voltage power supplies (HVPS) located in the Ebox. The overall detector gain is 2E7 (25%). At an expected average count rate of 2000 count/s, the amount of charge pulled from the MCP as a function of time is 0.2 Coulomb/year. Telecommanding ================= Juno-UVS operations are commanded using a set of 30 separate telecommands. Telecommand processing handles the redundant telecommand channels and includes error detection and recovery. Nominally, the spacecraft may send up to two telecommand transactions to the instrument every 2 s cycle. These are formatted as separate Internet Protocol/User Datagram Protocol (IP/UDP) Packets, and include (among other items) time and nadir messages. The acceptance and completion status of the command execution is reported in the housekeeping data. The instrument verifies incoming telecommands before they can be executed; this basic verification includes a format and checksum check of the telecommand. As mentioned, Juno-UVS has two redundant telecommand interfaces, but after power-up, the active interface will be determined and operations from that point on will only use that single interface. In addition to the command verification mechanism, the instrument implements two additional mechanisms to protect the instrument from anomalous telecommands. Some commands are only allowed when the instrument is in a specific state. In addition to this, a number of commands have been declared 'critical'. For Juno-UVS, this means that within a nominal 30-second timeout period, a specific confirmation command has to be received before the actual (critical) command execution starts. During most of the in-flight operations, this timeout is short compared with the light travel time to the spacecraft, meaning that the confirmation already has to be issued before confirmation of the acceptance of the command has been received on the ground. Still, this mechanism provides protection against accidental execution of commands. The set of telecommands can be divided into three categories: General operations-These allow for the complete basic operational commanding of the instrument. This includes setting and storing of parameters and starting and stopping of the science acquisitions. This set of seven commands allows for the full science operations of the instrument. Manual operations-Additional capabilities needed during commissioning and instrument verification are provided by 15 additional telecommands that allow for extended command options. Some of these commands may be used for science operations depending on the situation. Memory functions-Software code management and maintenance and additional debugging functions are provided by three general-purpose memory functions that allow for verification, load, and dump of memory blocks. Whenever Juno-UVS detects errors while accepting or executing commands, an error will be reported in the generated telemetry packet. This includes an identifier for the telecommand (if available) and a general error code. The error code continues to be reported in the telemetry data until another error is detected or the instrument is reset. This simple form of error reporting is limited to reporting a single error per HK cycle (i.e., at most once per 2 s). An additional mechanism implementing a small error log is available for more extensive problem investigation. The command code for any successful command is also reported in the telemetry data, so the telemetry registration can be used to reconstruct the received telecommands. Note that the parameters of a telecommand are not included in this reporting." END_OBJECT = INSTRUMENT_INFORMATION /* */ /* The INSTRUMENT_REFERENCE_INFO object provides a pointer to */ /* related reference publications or private communications. Only */ /* the key is provided in this file. The catalog object which */ /* provides the full citation is delivered separately. */ /* */ /* The INSTRUMENT_REFERENCE_INFO object is repeated once for */ /* each reference. */ /* */ OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "GLADSTONEETAL2014" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END