Utilization of AGI STK and S-NPP Operational Data to Generate JPSS-1 Proxy Test Data

1. Introduction

NOAA’s next-generation environmental satellite system, Joint Polar Satellite System (JPSS), replaces the current Polar-orbiting Operational Environmental Satellites (POES). JPSS satellites carry sensors which collect meteorological, oceanographic, climatological, and solar-geophysical observations of the earth, atmosphere, and space. The first JPSS satellite, Suomi National Polar-orbiting Partnership (S-NPP), was launched in 2011 and is currently NOAA’s primary operational polar satellite for its operational weather forecasting mission. The second JPSS satellite, JPSS-1 is scheduled for launch in Oct’17. The JPSS ground system is the Common Ground System (CGS), and provides command, control, and communications (C3) and data processing (DP).

2. JPSS-1 Proxy Test data requirements and challenges

In order to be able to support the JPSS multi-mission (S-NPP and JPSS-1) system test needs for the various test events, two data streams are needed, one for each spacecraft and its sensor payload. For S-NPP, this would be the operational data stream “live data” during the test event timeframe. For JPSS-1, proxy test data would be needed. From functional testing perspective, JPSS-1 and its sensor payload is “similar” to S-NPP and its sensor payload, hence it’s logical to use S-NPP operational data as the JPSS-1 proxy test data. Logistically, however, this approach poses a challenge when accounting for routing the CCSDS packets “the atomic unit of the test data” through the two JPSS ground stations (GS) to mimic S-NPP download to Svalbard, Norway “North Pole,” GS and JPSS-1 download to both the Svalbard and McMurdo GS, Antarctica “South Pole,” GSs. The challenge is the synchronization of the JPSS-1 proxy “time-shifted” data stream to match, temporally, the S-NPP operational “live” data stream at the test event.

3. JPSS-1 Proxy Test data Generation TECHNIQUE

This paper presents a methodology of accurately generating JPSS-1 spacecraft attitude and ephemeris, A&E, proxy data to match its sensor payload geolocation needs for ATMS, CrIS, OMPS and VIIRS. Thus, ensures the completion of the more-complicated VIIRS chain product generation with proper functional quality “minimal to no fill” products. This technique can be used to generate the required JPSS-1 A&E proxy data for any test event to synchronize the JPSS-1 proxy test data with the S-NPP live stream data set for that test. Furthermore, this technique can be leveraged for the upcoming JPSS mission and satellite test data needs, e.g., JPSS-2.

The technique utilizes S-NPP operational TLE set as an input to AGI STK© propagator, e.g., SGP4, to create good-quality proxy A&E data for JPSS-1 that is used to populate the JPSS-1 proxy A&E CCSDS packets. These A&E packets are then used along with the sensor CAL/SCI/ENG proxy packets to drive the JPSS-1 various sensor products, e.g., Sensor Data Records (SDRs; calibrated science data; Level-1B) and Environmental Data Records (EDRs; Clouds, Aerosols, Land, Ocean, Cryosphere, etc. products; Level-1C). This technique ensured the generation of good-quality geolocation products for the sensor suite which is the main factor to drive the completion of the VIIRS chain product generation with proper functional quality “no fill” products.

This technique resulted in a convergence within 0.2-0.3% error for the generated proxy ephemeris when comparing SGP4 simulated ephemeris for 10 days against the generated ephemeris from the most recent S-NPP operational TLE set and continue to produce downstream products through 14 days.

The AGI STK© scenario is initially seeded by using the S-NPP operational TLE that was generated closest to the JPSS-1 proxy test data timestamp. The S-NPP operational TLE provides the initial starting point of the scenario. Once the starting point is determined, the JPSS-1 satellite attitude is forced to always be nadir-pointing. The JPSS-1 satellite sensor axis is forced to be nadir pointing (+z) and the velocity vector to be in-track (+x). These constraints ensure on-earth pointing. The JPSS-1 satellite attitude and ephemeris can now be simulated using the SGP4 propagator to cover the full range of the JPSS-1 proxy test data. Finally, AGI STK© is used to generate a report that provides the JPSS-1 attitude quaternion between spacecraft body frame and the ECI coordinate frame as well as position/velocity in ECEF coordinates. This report contains the A&E data that is used to populate the JPSS-1 proxy A&E CCSDS packets.

The generated JPSS-1 proxy attitude and ephemeris data needs to be aligned with the streamed JPSS-1 sensor CAL/SCI/ENG proxy packets. This allows for the sensor status to align with the orbital properties. Most important, aligning the geolocation-based day/night identification with the sensor mode that is based on the information contained in the CAL/SCI/ENG proxy packets. To accomplish this, the Repeat Ground Track (RGT) of S-NPP is leveraged. S-NPP has a known 16-day RGT. For example, if the JPSS-1 proxy test data is based on S-NPP operational data from April 4^th, 2014 @00:00:00 UTC, then this test data aligns with May 14^th, 2017 @00:000:00 UTC ground track. Using this information the AGI STK© generated data can be aligned with the timestamp of the JPSS-1 proxy test data.