Functional and Performance Verification of the Space Weather Sensor on GEO-KOMPSAT-2A Satellite

Abstract

GK2A(GEO-KOMPSAT-2A)satellite has been operating excellently since its launch in Dec 2018. The secondary payload called KSEM (Korean Space Environment Monitor) was equipped into the GK2A satellite along with AMI (Advanced Meteorological Imager) sensor. KSEM is the Korea's first operational geostationary space weather sensor and has been developed collaboratively by KHU (Kyung Hee University) and KARI (Korea Aerospace Research Institute). The interface works between KSEM and GK2A were conducted by KARI. Various interface tests, which aim for evaluating effective functionality of KSEM with the spacecraft, were intensively conducted at KARI facilities. Main tests consisted of mechanical and electrical check-up activities between the KSEM and GK2A. Interface tests of KSEM, which involve pre-launch tests such as ETB and GK2A system level tests, were conducted to evaluate functional and performance of KSEM before the launch. The tests carried out during the GK2A LEOP (Launch and Early Orbit Phase) and IOT (In Orbit Test) period (Dec 2018 ~ June 2019) showed excellent in-orbit performance of KSEM data.

1. Introduction

KSEM (Jin et al., 2014) equipped on GK2A(Jin and Yang, 2013) is comprised of three different sensors: PD (Particle Detector), MG (Magnetometer) and CM (Charging monitor). PD is an enhanced energetic particle detector, which adopted a heritage design by THEMIS SST (Solid State Telescope) (Ni et al., 2011) and MAVEN SEP(Solar Energetic Particle)(Larson et al., 2015; Lee et al., 2017). The electron measurement range of PD is from 100keV up to 2MeV. MG called SOSMAG (Service Oriented Space Magnetometer) (Leitner et al., 2015) developed cooperatively withESA (EuropeanSpaceAgency) consists of four magnetometers and a 1-m deployable boom, which measures Earth magnetic field disturbances at three axes. CM sensor has a function to monitor currents driven by energetic particles.The electronicbox of KSEM, IDPU(Instrument Data Processing Unit) is a main control unit, which integrates and controls all of three sensors. To achieve sufficient credibility forthe functional and performance of KSEM instrument in the GEO orbit, various prelaunch interface tests of KSEM payload between GK2A satellite during the EQM (Engineering Qualification Model) & FM (Flight Model) development phases, ETB (Electrical Test Bed) and GK2A System Level Interface Tests were conducted at the KARI (Korea AerospaceResearch Institute)AIT(Assembly Integration and Test) facilities from 2016 to 2018. To confirm the final performance of KSEM data in space, LEOP and IOTtests were carried outfrom Dec 2018 to June 2019 after the GK2A satellite launch (Dec 2018).

2. Methods

1) KSEM EQM Environmental Tests

Payload level environmental tests aim for verifying functionality of KSEM instrument under launch and space environments. The tests are comprised of mechanical (vibration and shock tests), thermalvacuum tests and EMI/EMC (Electro Magnetic Interference/Electro Magnetic Compatibility) tests. KSEM environmental tests were conducted at the KARI AIT facilities from March 2016 to Sept 2016 (Fig. 1). First, EQM vibration tests, which simulate conditions during the S/Claunch time, were conducted. Some anomaliesfound on the electronic board in IDPU and the PD structure during the 1st test (2016.3.17~3.18) and thus updated designs were adopted on the PD and the IDPU.The 2nd test wassuccessfully conducted (2016.5.23 ~6.1). The thermal-vacuum tests using the EQM, which is underthe simulated space environments after the satellite launch, was conducted in KHU (2016.6.15~6.18). Temperature ranges(-30°Cto +60°C for Operation; -40°C to +75°C for Non-Operation) for KSEM were set up as worst limits for PD and CM sensors. The EMI/EMC tests, which verify electro magnetic influences from/into the KSEM instrument into/from GK2A S/C were completed at the KARI EMC Shielded Room: 1st test (2016.6.22~6.29); 2nd test (2016.7.18~7.28). Total seven NCR (NonConformance Report) items were identified during the KSEM EQM environmental tests and resolutions were established in the EQM MRB(MaterialReview Board). EQM was delivered finally at KARI in Sept 28, 2016.

Fig. 1. KSEM EQM Environmental Tests: (a) Vibration Test, (b) Shock Test, and (c) Thermal-Vac. Test.

2) Electrical Test Bed Tests

The ETBtests using KSEM EQM were divided into three phases (Fig. 2). First, Phase I test focused on a payload level. Full functional and performance tests between KSEM EQM and KSEM EGSE (Electrical Ground Support Equipment) were conducted. Test procedures(including KSEM EGSE procedure), which contains the communication between the instrument and the EGSE via TM (Telemetry) and TC (Telecommand), were verified through the Phase I test (conducted in May 2016). Second, Phase II test (2016.5.23~5.24) was carried out using the S/W based simulators. KSEM DB and TC were validated from the GK2A FSW (Flight Software) simulator. Based on a virtual platform, TC written by SOP (Satellite Operation Procedure) were uploaded into the GMU simulator using the ITOS simulator. Test results were verified based on an event log, which contains the performed procedures (STEP1: Run Application SW; STEP2: Verification of PPS (Pulse Per Second) signal & 1553B command; STEP3: Mode Change, Start Up and Sensor Power On; STEP4: verification of a safe signal). Finally, Phase III test (1st: Oct 2016) were performed using the H/W basis simulators. The DC & Electrical integration were verified first. Basic functional tests of KSEM combined with the ETB platform were also conducted. KSEM TM/TC and KSEMDB were validated from the GK2ETB(Satellite System Simulator), KSEM EQM (Payload System) and GK2 ETB EGSE (Ground System Simulator). Main issues driven by the KSEM Flight S/Wdeficiencies for MG commissioning mode for calibration; PD calibration, PD Sun Avoidance Operation, unstable data transmitting and receiving with the S/C were corrected by updated new functionalities and related rigoroustests.

Fig. 2. KSEM ETB test flowchart for Phase I, Phase II and Phase III.

3) KSEM FM Environmental Tests

Based on complete EQM, FM was developed and intensive tests to verify all units of KSEM FM were conducted. In particular, KSEM electronic box, IDPU (Instrument Data Processing Unit), which plays a key role of controlling the space weathersensors(PD/MG/ CM), was heavily tested with a burn-in test (long time stability check). The burn-in test (> 100 hours) was employed with an augmented way, which integrates each FM components of IDPU according to the completion of each unit. This augmented strategy was very effective to reduce the manufacturing/testing periodsforthe key FMcomponents of KSEM.Afterthe complete development of entire KSEM sub-systems, environmental tests for KSEM FM were carried out. Those tests(vibrational tests: 2017.7.10~7.14), thermalvacuum tests: 2017.7.17~7.21) and EMI/EMC tests:2017.7.24~7.28) were completed successfully.

4) Electrical Interface Tests before the S/C Assembly

The KSEM payload and the KSEM-GK2Asatellite ElectricalInterfaceTests(2017.8.24~8.25)wereconducted before the GK2AS/Cpanel assembly (Fig. 3).The tests verified that electrical communications between all sub-systems of KSEM and GK2A S/C are normal.

Fig. 3. KSEM-GK2A electrical interface test before the S/C panel assembly.

5) KSEM Functional and Environmental Tests after the S/C Assembly

After the installation of KSEM payload into the GK2A S/C (Fig. 4), GK2A dynamic test (vibrational and acoustic tests) was conducted fromJan 2018 to Mar 2018. Electrical functional tests between the satellite and KSEM instrument were carried out(2018.3.6~3.7) after the System dynamic test. Key functional tests of KSEM were carried out during the GK2A thermalvacuum test(2018.4.16~5.8)in orderto verify effective functionalityofthe instrumentunder a space environment. Afterthe thermal-vacuumtest, electrical tests of KSEM were conducted again to double check the status of the payload.Comprehensive MG verification activities (Frangibolt gap check, SOSMAG boom MLI inspection, harness foil repair and tether cable repair) were also conducted by ESA and KARI. Before and during the GK2AEMI/EMCtests(2018.7.9~7.18),KSEMfunctional tests were carried out to verify the compliance of the instrument affected by satellite electromagnetic interferences.

Fig. 4. KSEM instrument assembly on the GK2A spacecraft.

6) Final Function Test and Inspection for KSEM

After the transport of GK2A satellite into a launch site, the electrical function test of KSEM was carried out to verify the status of the instrument during the transportation. Under KSEM A-side (primary side), final functional tests for PD1/2/3, MG and CM were carried out in Oct 2018.

7) GK2A Satellite Launch and KSEM LEOP and IOT

After GK2A satellite launch (2018.12.5, KST), KSEM LEOPactivities were carried outfrom Jan 2019 to June 2019. About a month period of GK2A outgassing, which eliminate any remnant water vapors or contaminants, the payloads were turned off as a survival mode.With turning on the KSEM instrument, IAC (InitialActivation and Check Out) and functional IOT were started in Jan 2019. Main activities were KSEM power on, MG boom deployment and PD/ MG/CM normal mode entry and commissioning start. After the MG boom deployment, the change of the magnetic fields measured on three axes of the four fluxgate magnetometers(inner and outer) were clearly observed in Fig. 5. Fundamental status and health of KSEM were examined and communications between the instrument and the satellite were verified. The telemetries and science data from KSEM were also analyzed. Key results are shown in Figs. 5-8.After the successful completion of KSEM IAC and functional IOT, performance IOT was conducted from Jan 2019 to June 2019. To improve data quality of the payload, baseline and LLD (Low Level Discrete) adjustmentfor PD sensors were employed. As a result, detectable energy ranges of electrons and protons by PD sensor were extended to amuch lower one (Fig. 6).In addition, EEPROM (Electrically Erasable ProgrammableReadonly Memory) parameters of MG were uploaded two times to improve the MG data by eliminating noise components from the S/C (Fig. 7). It was observed that the onboard data matched the computed data after the new EEPROM parameter upload. Fig. 8 shows comparison ofCM science data with the GK2APD and GEOS-16 E4 data, which are consistent one another. After the completion of GK2A IOT, high quality of nearreal-time KSEMscience data have been distributed to the public by KMA (Korea Meteorological Administration) since July 2019 (Fig. 9).

Fig. 5. KSEM MG boom deployment activation/confirmation analysis (Image courtesy of ESA).

Fig. 6. KSEM PD science data acquisition and analysis: before (left) and after(right) the new PD parameter upload (Image courtesy of KHU).

Fig. 7. KSEM MG science data acquisition and analysis (Image courtesy of KHU)

Fig. 8. KSEM CM science data acquisition and analysis (Image courtesy of KHU).

Fig. 9. KSEM near real-time data (from http://nmsc.kma.go.kr).

3. Summary and Conclusion

KSEM instrument equipped on GK2Aisthe Korea’s first geostationary operational space weather sensor suite. To accomplish its requirements in terms of function and performance of KSEM, intensive tests are conducted through the GK2Aand KSEM development milestones. Primary verifications of KSEM performances with GK2A spacecraft are conducted after the completion of KSEM EQM. Major functional tests and electrical interface tests between KSEM and GK2Awere carried out according to KSEM development phases. After the launch of GK2A satellite and completion of KSEM LEOP/IOT tests, the instrument has been providing valuable science data for a space weather monitoring and associated researches.