Saft SOLUTIONS FOR FULL GEO ELECTRIC PROPULSION

Today, the full electric propulsion is becoming more commonly used on board geostationary satellites for the launch up to the Electrical Orbit Raising (EOR) and all on-orbit manoeuvres. This electrical propulsion induces additional cycles for the battery that may result in higher ageing. The Electrical Orbit Raising (EOR) is currently simulated by two additional GEO seasons up to 80%DoD while the Plasmic Propulsion System (PPS) cycles are carried out, at least 162 cycles up to 24%DoD or 198 cycles up to 20%DoD per solstice season and at least 52 cycles up to 15%DoD or 64 cycles up to 10%DoD per eclipse season for 15 years. The need for an appropriate demonstration by life-test was anticipated and addressed in collaboration with the primes and the agencies, in the frame of ARTES 3-4 contract with ESA for the VES180SA cell & CNES contract for the VES16 cell. The article will present the whole cycling results available, and will provide afterwards the correlation status of Saft Li-ion Model (SLIM) with the experimental data acquired.


VES180SA LI-ION CELL WITH & WITHOUT PPS GEO LIFE-TEST RESULTS
This chapter focuses on the analysis of the life-test results performed on VES180SA lithium-ion cells with and without PPS in semi-accelerated mode covering different mission profiles proposed by primes, as described in Tab. 1.The life time test performed without PPS is used as reference test in order to evaluate the impact of the Electrical Orbit Raising (EOR) and all on-orbit manoeuvres (PPS) on the cell ageing.The test set-ups applied to the NDTF 17 and 18 lifetime tests are similar, except for the base plate regulation temperature which varies respectively from 15 to 20 °C.

Test
For each lifetime test, three VES180SA cells were encapsulated "head down" in 3P cell-package and instrumented with two circumferential strain-gages, one thermocouple and one voltage telemetry in order to measure the PPS effect on the evolution of the temperature, the EOD voltage and the cell swelling.Then, they have undergone the specified mechanical and vacuum environmental tests without presenting leakage mark and abnormal degradations of their electrical performances.
Before starting the lifetime tests, the two cell-packages were assembled with a CHO-THERM layer on thermally regulated baseplate and insulated from ambient temperature by insulating box, as presented in the Fig. 1, 2 and 3.   -Also during cycling, no difference was identified on the evolution of the cell swelling at the end of charging (similar circumferential strains measured around 1000 ppm at the longest eclipse with or without PPS) and on the cell temperature increase at the end of discharge (similar temperature measured around 22°C at the longest eclipse with or without PPS), refer respectively to Fig. 7 and 8, then Fig. 9 and 10.       -The evolution of the cell characteristics, such energy, IR20%DoD and IR60%DoD is measured every two seasons through a check-up sequence, involving a residual discharge and a reference test performed at EOCV=4.1V @20°C.This reference test is based on charge up to 4.1V, then discharge down to 2.7V under C/2 discharge rate @20°C with pulses 1.5C-30seconds at 20% and 60%DoD.
After 18 GEO seasons, no significant impact of PPS is visible on the energy variation slopes.That should permit to maintain energy loss under the expected value DIWHU VHDVRQV ZLWK 336 LH 1.2%), as presented in Fig. 23.The changes noticeable on the energy evolution are mainly induced by EoD temperature variation, as presented in Fig. 22.

Conclusion
The effect of PPS discharge on those GEO cycling tests @ 4.075V are negligible in term of energy loss, EoDV drop and internal resistance increase, which confirm the excellent ability of VES180 cell to sustain GEO PPS missions.
As of today after respectively 16 and 18 seasons, the expended EoL PPS trends are in line with SLIM predictions on the two experimented PPS profiles, including some margin as the results are better than prediction so far.

VES16 LI-ION CELL WITH & WITHOUT PPS GEO LIFE-TEST RESULTS
This chapter focuses on the analysis of the life-test results performed on VES16 lithium-ion cells with and without PPS in semi-accelerated mode, as described in Tab. 2. The life time test performed without PPS is used as reference test in order to evaluate the impact of the Electrical Orbit Raising (EOR) and all on-orbit manoeuvres (PPS) on the cell ageing.The test set-ups applied to the G10a and G10b lifetime tests are similar.All VES16 cells were instrumented with one thermocouple and one voltage telemetry in order to measure the PPS effect on the evolution of the temperature and the EOD voltage.Before starting the lifetime tests, all VES16 cells were located in a ventilated thermal chamber set at 20°C.

G10a and G10b Lifetime Test Results
-In cycling, we have not observed significant impact of PPS on EoD voltage at the longest eclipse (cycle 23), as presented in Fig. 26 and 27.60%DoD.After 14 GEO seasons, no significant impact of PPS is visible on the energy variation slopes.That should permit to maintain energy loss under the expected value after 30 seasons with PP6 LH 9.9%), as presented in Fig. 30.

Conclusion
The effect of PPS discharge on those GEO cycling tests @ 4.05V are negligible in term of energy loss, EoDV drop and internal resistance increase, which confirm the excellent ability of VES16 cell to sustain GEO PPS missions.
As of today after respectively 14 seasons, the expended EoL PPS trends are in perfectly line with SLIM predictions.

Figure 1 .
Figure 1.Cell-Package instrumented and mounted on baseplate

Figure 11 .
Figure 11.Energy & Temperature evolution in GEO cycling with & without PPS

Figure 17 .
Figure 17.EoD Voltage at cycle 23 evolution vs. season -Also during cycling, no significant difference was identified on the evolution of the cell swelling at the end of charging and on the cell temperature at the end of discharge, respectively about 100 ppm increase and 1°C decrease were measured in GEO cycling with PPS at the longest eclipse, refer respectively to Fig.18 and 19, then Fig.20 and 21.

Table 2 :
VES16 Li-ion cells On-Going GEO with & without PPS Life-Tests Program 2.1 G10a and G10b Test Set-Ups

Figure 28 .
Figure 28.EoD Voltage at cycle 23 evolution vs. season -Also during cycling, no difference was identified on the evolution of the cell temperature increase at the end of discharge (similar temperature measured around 24°C at the longest eclipse with or without PPS), refer to Fig.29.

Figure 29 .
Figure 29.Cell Temperature evolution at cycle 23 with & without PPS vs. season

Figure 30 .
Figure 30.Energy variation in GEO Cycling with & without PPS Also, no significant difference was identified on the evolution of Internal Resistance at 20% & 60%DoD after 14 GEO seasons with or without PPS, as presented respectively in Fig.31 and 32.