WISPR Science

Calibration

Lakin Jones — Wed, 16 May 2018 21:04:26 +0000

We plan a limited set of observations for instrument checkout and calibration following instrument turn-on on the approach to each solar encounter. A few images per day will be taken for up to ten days while the spacecraft distance from the Sun is less than 0.5 AU on the inbound segment of each orbit. Some of these images may involve small off-points of the spacecraft from the Sun (up to a few arc minutes) to verify the stray light performance of the instrument. These data would need to be downlinked prior to the solar encounter period to be useful for planning purposes.

For photometric calibration, WISPR compares selected background stars in the images to star catalog positions and magnitudes. Thanks to the wide FOV of WISPR, no spacecraft maneuver is required to capture a standard set of calibration stars. These calibrations are used to verify the pre-launch ground photometric calibration and to monitor the WISPR telescope throughput loss during the mission. The final photometric calibration accuracy using standard stars is ∼3 %, based on procedures developed and used for SOHO/LASCO and STEREO/SECCHI. Between perihelion passes, a three-phase calibration sequence must be performed: (1) to determine if any degradation of the detector and/or the lenses occurred during the perihelion pass, where the instrument might be subjected to high radiation exposure, (2) to anneal the APS detector, and (3) to perform a calibration sequence to determine the pre-perihelion calibration. Photometry changes are fixed by the stellar transits combined with LED calibration lamp images.

WISPR Example Observing Program for SPP Orbit 24

WISPR Pub Number 1

WISPR Science

Nominal Science

Lakin Jones — Wed, 16 May 2018 20:45:49 +0000

Routine observations to meet the science objectives occur during a window of ∼10 days duration centered on perihelion when the spacecraft is within 0.25 AU of the Sun (see Table 6). The standard image capture method takes short exposures (<20 seconds) and sums up to ‘N’ individual exposures to achieve the required integration time using on-board processing for image summing and “cosmic ray” scrubbing techniques that were developed and used on SECCHI/HI. The instrument is operated primarily in a synoptic observing mode, and similar observations are conducted each orbit using preplanned schedule blocks uploaded in advance of each encounter. Special observations tailored to specific science objectives are conducted on selected orbits (e.g. close to the minimum perihelion or with favorable geometries of Earth or other missions). Data are stored on the SPP solid state recorder (SSR) for transmission to the ground. A subset of the SSR data is transmitted at higher priority to facilitate planning for the next orbit.

Table 7 shows an observing program that is designed to fulfill the mission requirements for the final orbit in the nominal mission (Orbit 24). Many of the baseline science measurement requirements (including radial scene coverage, photometric accuracy, image cadence, and science observation days for the orbit and mission) depend on the instrument distance from the Sun. For this reason, the observing program over the solar encounter period is divided into the following four regions based on spacecraft distance from the Sun: Perihelion: <0.07 AU; Inner: 0.07–0.11 AU; Mid: 0.11–0.18 AU; Outer: 0.18–0.25 AU.

WISPR Operational Timelines

Mission Event	Duration	WISPR Operations
Launch and Early Operations	Launch to first Venus encounter (L + 6 weeks)	Initial power on, IDPU, camera and FSW checkout, door-closed commissioning
Approach to First Solar Encounter	First Venus Encounter to First Solar Encounter (L + 6 weeks to L + 3 months)	Checkout/commissioning to prepare for science observations
Approach to Subsequent Solar Encounters	10 days per orbit for 23 orbits (spacecraft to Sun distance <0.5 AU) on inbound segment of orbit	Checkout, detector annealing, and on-orbit calibration to prepare for science observations
Solar Encounters	10 days per orbit for 24 orbits (spacecraft to Sun distance <0.25 AU)	Synoptic and tailored science observations
Aphelion Orbit Segment	68–130 days per orbit for 24 orbits (spacecraft to Sun distance >0.25 AU)	None (data downlinked when spacecraft to Sun distance >0.59 AU)

The highest cadence, full-FOV and partial-FOV observations are taken over a 36-hour period centered on perihelion. At larger distances from the Sun, the image cadence is reduced to satisfy the Level 1 photometric accuracy requirement. The observing program, including science data, housekeeping data, and CCSDS packet overhead, is constrained to fit within the WISPR data volume allocation of 23 Gbits for each orbit.

Early Operations and Commissioning

During launch and early operations (until the first Venus flyby, ∼6 weeks after launch), WISPR anticipates only door-closed operations, consisting of initial turn-on of camera subsystems, flight software (FSW) checkout and a few calibration lamp images (see table above). The door remains closed during this time and throughout the SWEAP commissioning slew to permit outgassing of the instrument and spacecraft and to maintain survival temperature with minimal heater power. WISPR door-open commissioning operations are conducted in the interval between the first Venus flyby and the first solar encounter 6 weeks duration.

WISPR Pub Number 1

WISPR Science

Flight Software

Lakin Jones — Wed, 16 May 2018 19:09:39 +0000

The WISPR Flight Software (FSW) is developed by the APL IDPU team. It incorporates considerable heritage/commonality from other missions such as MESSENGER, MRO/CRISM, New Horizons, and Solar Orbiter/SIS. The common software makes use of heritage boot code, telemetry and command packet handling, macro (stored command script) implementation, memory management, autonomy, and reporting modules. The data interface with the spacecraft is SpaceWire and has a SPP-specific protocol with static bus schedule and Instrument Transfer Frames. Telemetry packets may be up to 4096 bytes and there are 64 APIDs available for WISPR to use for addressing destination. There is a critical status packet monitored by the spacecraft, which can request power off or power cycle. WISPR receives time and status from SPP at 1 Hz.

Software that is WISPR-specific includes camera control, image processing, observation scheduling including autonomous operations, and instrument health. There are 12 independently controlled operational heaters. The observation schedule time line is loaded prior to the start of the encounter. The concept is similar to the time line developed for the STEREO/SECCHI instrument. All the parameters of the time line are loaded—image time, exposure duration, number of images in the sum, subimage coordinates, image compression, etc. To smooth out the telemetry flow to the spacecraft a large memory buffer has been included on the instrument side of the interface. The size of the buffer is sufficient to store the data from more than one orbit. No ability to perform selective data transfers to the spacecraft data recorder is envisioned.

Camera operation involves loading, starting, and stopping various instances of “microcode”, and setting various registers which determine certain observations parameters. There are also calibration LEDs which need control. Most of the image processing is done in hardware (FPGA) and is orchestrated by the FSW. The possible image processing steps are: bias subtraction, clipping (max/min), cosmic ray scrub, divide by 2°ø, autonomous exposure control, pixel binning, image data compression (lossy or lossless), apply mask, and sum multiple images.

Image files received from the FPGA, including headers, are put in packets and assigned ApIDs to specify destination and downlink priority. The FSW must also manage 3 areas of image memory: (1) 156 Mb SRAM serves as an image output buffer (2) ∼3 Gb of SDRAM is available for image processing and secondary image output buffer (3) 64 Gb of Flash memory is available as tertiary image output buffer, if required. The SpaceWire output to spacecraft is limited to 350 kbps. For observation scheduling, the FSW must conduct activities such as load microcode, specify to FPGA what processing is to be done with each image received from the camera, implementing post-FPGA processing, and handle image telemetry priorities. Since this is an encounter mission with limited contact, the scheduling must be tolerant of instrument power cycles. Hence, the nominal mode of operations is “Autonomous Mode” where observations are resumed at the current mission experiment time. It is possible to specify that WISPR boot into “Manual Mode” where commanding is required to conduct operations.

WISPR Pub Number 1

WISPR Science

Data Products

Lakin Jones — Fri, 16 Mar 2018 21:26:32 +0000

NASA categorizes Data Products based on a system of Levels starting with Level zero. A level zero data product is usually defined as representing raw, but cleaned spacecraft telemetry. Subsequent data levels represent successive levels of data processing involving calibration and the application of science algorithms. The SPP mission has defined five data levels that are described elsewhere.

After generation of the Level-1 FITS files, selected Level-3 products (mostly browse data) will also be generated in the IPP. Level-2 (calibrated) products will be generated onthe- fly by using routines in the Solarsoft library. The best-available calibration will be made available to users as it is obtained via Solarsoft. Most of the code in the IPP will be available in the Solarsoft library. This data product philosophy follows closely the SECCHI data model. The table below summarizes the various WISPR data products.

TheWISPR L1 quick-look data comprises two parts. Part 1 will be a subset of the images (such as subfields) sent down with low-latency to assist in planning selective downlink for other instruments and for planning WISPR observations for the next orbit. Part 2 of the quick-look data will be the remainder of the science telemetry, which is processed as it is played back. The L1 “Final” data set will replace the quick-look Part 2.

Level 2 data is calibrated data. Our experience suggests that it is more efficient to let the user generate the Level 2 data using standard software provided by the WISPR team as part of the Solarsoft library. Users are assured of having the latest calibration factors, and the operations team does not have to generate a new set of data every time calibrations are updated. A best and final Level 2 dataset will be provided when final calibrations are available, or after the end of the mission.

Data Level	Product Title	Contents	Format	Latency	Frequency
L1	Level-1 quick-look	uncalibrated image data	FITS	T₀+minutes	as received; track-dependent
L1	Level-1 final	uncalibrated image data	FITS	T₀ +7 days	per orbit
L3	Browse images (quick-look and final)	uncalibrated binned images with background removed, and compressed	PNG, JPG	L1+ minutes	same as L1
L3	Browse movies	browse images	MPG	L1+hours	same as L1
L3	Jmaps	time-elongation plots, uncalibrated	PNG	L1+hours	same as L1
L3	Syncronic or Carrington maps	heliospheric brightness at selected elongation angles	PNG	L1+hours	same as L1
L2	Level-2	calibrated L1, user-generated	FITS	User-depended	as needed
L4	CME masses		FITS	T₀ +one year	Annually

Data Archive

In addition, theWISPR team will provide the final instrument calibration and a complete best and final Level-2 calibrated data set from the entire mission to an appropriate NASA archive at the end of Phase F or the end of the extended mission. The WISPR data policy dictates completely open access to all data, including: Planning, Quick-look, and Final data products, the calibration data, and all procedures to calibrate and perform high-level processing of the data. NRL will maintain a web interface to a database of all science and housekeeping data that will permit users to search for data corresponding to time periods or events of interest using selected values from the image header, as well as to perform trend analysis of instrument housekeeping parameters such as temperatures and voltages. Validated science data will be distributed directly from NRL to requesters based on the results of a database query. Requests for larger amounts of data will be handled through the SPP Science Data Portal or the Virtual Solar Observatory (VSO).

The WISPR data policy dictates completely open access to all data, including: Planning, Quick-look, and Final data products, the calibration data, and all procedures to calibrate and perform high-level processing of the data. NRL will maintain a web interface to a database of all science and housekeeping data that will permit users to search for data corresponding to time periods or events of interest using selected values from the image header, as well as to perform trend analysis of instrument housekeeping parameters such as temperatures and voltages. Validated science data will be distributed directly from NRL to requesters based on the results of a database query. Requests for larger amounts of data will be handled through the SPP Science Data Portal or the Virtual Solar Observatory (VSO).

Data Release Schedule

There will be two versions of WISPR processed science data: quick-look data produced immediately upon receipt of any image telemetry from the spacecraft (including a lowlatency "planning" subset), and final data incorporating any telemetry packets that may be missing or corrupted in the quick-look telemetry and that are later recovered. (See Sect. 4.4.) Quicklook L1 data may be used for mission operations planning purposes and will be made public as soon as it is processed. Final L1 data will replace the quicklook data and will be differentiated from the quicklook L1 data product in the FITS image header via the VERSION keyword. The Final L1 and resulting visualization data products will be (re-)generated after each orbit. These will be suitable for archiving and distribution. Both quick-look and final data will be processed in the same way and will have the same file formats.

Data Catalogues

The WISPR project will use an open source database program such as MYSQL, which is currently being used to manage the housekeeping and image header information on both SECCHI and LASCO. A web-based tool enables searches of the image header database with the ability to select FITS files for download using FTP to the user's computer. The table structures will be similar to the existing tables. For example, the existing IDL tools include the ability to extract any parameter(s) of interest and to generate plots against time or to correlate one parameter against another. It is our intention that the FITS header will mirror the SPASE catalog. To the extent that the required keywords are known, they will be incorporated into the image FITS headers.

WISPR Pub Number 1

WISPR Science

Mission Operations

Lakin Jones — Wed, 14 Feb 2018 22:11:53 +0000

The detailed observing schedule will be uploaded prior to the beginning of each perihelion pass. However, there may not be sufficient time to modify the detailed schedule for the upcoming perihelion passage after the download of the SRR from the preceding pass. For this reason, the observing objectives are defined for the next two perihelia.

The cruise/downlink portion of each orbit is broken into either cruise operations or science downlink operations. For cruise operations, the instruments may be powered on if the Sun-spacecraft distance is less than 0.82 AU. Periodically, during cruise operations the instruments may be powered off to support routine and special spacecraft activities. During cruise operations the fanbeam antenna (via X-band) will be used for spacecraft communications. Downlink rates will be limited and there is no plan to playback the SSR data.

During science downlink operations all instruments will be powered off and the high-gain antenna (via Ka-Band) will be used for playing back the SSR and retrieving all of the science data collected in the previous encounter(s). During both the cruise and science downlink periods, real-time spacecraft commanding will be done as needed to support routine and special spacecraft activities.

The table below outlines the planned DSN contact frequency for all phases of the SPP mission. Part of the planning process entails assigning downlink priority to telemetry. The SPP supports up to 10 levels of priority for downlink; a small percentage of science data comes down relatively quickly (days) after an observing window. The majority of science data comes down at lower priority and could take months to reach the ground. These priorities may vary from orbit to orbit and are managed by the SWG.

Mission Phase	Contact Frequency	Duration
Launch & Initial C/O Spacecraft	Continuous	2 weeks
Early Commissioning	5 × 10 hr (per week)	4 weeks
Cruise Operations	3 × 8 hr (per week)	Weekly
Science Downlink	10 hr/day	Entire science downlink period (Varies in each orbit leg, ∼4–21 days)
Solar Encounter Phase	3 × 4 hr (per week)	Entire encounter period (∼2 weeks)
Venus Fly-Bys	5 × 10 hr (per week) 10 hr/day	V−5 to V− 1 weeks V−1 to V+ 1 weeks

Science Operations Center

The WISPR Science Operations Center (SOC) at NRL utilizes the GSEOS software suite provided through APL to send command files to the SPP Mission Operations Center (MOC) for uplink to the spacecraft. At the SOC, WISPR personnel utilize a Heliospheric Imager Planning Tool (HIPT) to model observation plans and translate them to schedule files that are uploaded to the WISPR IDPU.

WISPR Pub Number 1

WISPR Science

Documentation

Lakin Jones — Tue, 16 Jan 2018 22:44:01 +0000

Documentation necessary for data analysis and interpretation is made available through the WISPR website. These include:

Instrument description. Descriptions of the instrument can be found on the main WISPR design page. Additional details can be found in the various papers listed in the WISPR Bibliography.
Calibration and validation methodology. Work is ongoing regarding the calibration of the WISPR instruments, with publications under peer review at this time.
Validation through cross-calibration with other instruments or other assets. This is an ongoing process that will evolve as the mission evolves and more observations are recorded.
Dataset description including FITS header definition. The WISPR data and data descriptions are fully available on the WISPR Data pages.
Meta-data products. The WISPR data and data descriptions are fully available on the WISPR Data pages.
List of special events such as CMEs, comets, etc. We provide a list of events, including CMEs, comets, and operational events, on the Encounter Summary pages of this site.

WISPR Pub Number 1

WISPR Science

Processing and Analysis Tools

Lakin Jones — Mon, 01 Jan 2018 22:45:31 +0000

The radiometric calibration of the data will be performed using the pre-flight laboratory calibration data and calibration updates using observations of an ensemble of stable stars as used for SOHO/LASCO and STEREO/SECCHI. The calibration team monitors the detector telemetry and the images and provides periodic updates to the science calibration routines. IDL procedures will be provided in the Solarsoft library to convert the Level-1 FITS image files into higher-level calibrated data products. These procedures will permit the user to perform standard corrections such as removal of geometric distortion, vignetting and stray light, and photometric calibration, on-the-fly for the data of interest. All calibration data necessary for these corrections will be included as part of the Solarsoft distribution which is publicly available at http://sohowww.nascom.nasa.gov. This approach has been used successfully for both LASCO and SECCHI, and ensures that the user has access to the most up-to-date calibrations while avoiding repeated processing and redistribution of large amounts of data.

Software tools for common analysis tasks that are in use for LASCO, SECCHI, and SoloHI will be extended to incorporate WISPR data. These include image visualization, generation of movies, feature tracking, structure measurement, and combining datasets from multiple remote-sensing and in-situ instruments and spacecraft. Forward fitting of threedimensional models to heliospheric features such as streamers and CMEs will also be provided in Solarsoft. NRL will work with the Community Coordinated Modeling Center (CCMC) at NASA Goddard Space Flight Center to produce appropriate heliospheric model calculations for comparison with the WISPR data for each Carrington rotation, as well as for selected events of interest. The results of these model calculations will be made publicly available on the WWW.

WISPR Pub Number 1

WISPR Science