Jeffrey C. Brewer

AXAF-I Electrical Power System breadboard simulation testing

Electrical Power System (EPS) breadboard simulation testing for the Advanced X-ray Astrophysics Facility-Imaging (AXAF-I) spacecraft is being performed at NASAs Marshall Space Flight Center (MSFC). This real-time testing will verify functionality of software control routines and where possible, operation of flight type hardware. The breadboard completely encompasses the AXAF-I EPS allowing contingency simulation and planning. The planned cycling operation of the breadboard will provide a real-time orbital cycle lead over the flight vehicle and hopefully identify any chronologically induced anomalies while sufficient time remains to take corrective action or make preventative moves on the flight vehicle. The breadboard system will also offer a platform for analysis of the EPS of the flight vehicle to investigate the source of anomalies observed during flight. The AXAF-I EPS testbed utilizes three Ni-H/sub 2/ batteries composed of cells from the same build lot as the cells in the batteries on the flight vehicle. Operation of the breadboard EPS with the flight type Ni-H/sub 2/ batteries is scheduled to begin early June 1997; the launch of the AXAF-I spacecraft is scheduled for summer 1998. This paper discusses the design and assembly of the AXAF-I EPS breadboard testbed with an emphasis on the design and performance of the Ni-H/sub 2/ batteries.

Real-time mission simulation test for AXAF-I

The mission profile for the Advanced X-ray Astrophysics Facility-Imaging (AXAF-I) vehicle is characterized by long solstice seasons and short eclipse seasons. This type of cycle profile is ideal for accelerating real-time testing by shortening the solstice seasons while maintaining real-time cycling during eclipse seasons. Because of the benign operation of the nickel-hydrogen (Ni-H/sub 2/) cells during the solstice seasons, this acceleration can be done without significantly decreasing the validity of the test results. The accelerated testing profile was used here on a five-cell pack of AXAF-I flight-design 30 ampere-hour (Ah) Ni-H/sub 2/ cells (designated as RNH 30-9). It was used to verify that the proposed design is capable of meeting mission life requirements. The accelerated testing began in March 1994 and was completed in August 1995. The results showed that all program battery requirements were met with significant margin remaining. Following completion of the accelerated portion of the test, the cells were once again subjected to identical pre-launch/launch profiles as they were leading into the accelerated mission simulation. From that, they were placed in a real-time mission simulation profile. This paper discusses conclusions from the accelerated mission simulation, a comparison of the characterization and prelaunch/launch profile data generated at the beginning of the test with that generated during a repeat of those profiles following completion of the accelerated mission simulation, and a comparison of the data from the first 6 months of real-time mission simulation testing with earlier data.

Low rate trickle charging of nickel-hydrogen batteries

Nickel-hydrogen battery management, during spacecraft prelaunch activities, traditionally includes active cooling if high state of charge is required at launch. The NASA AXAF-I Program has been investigating techniques for managing nickel-hydrogen battery state of charge, during prelaunch and launch operations, in the absence of active cooling. These investigations demonstrate that high states of charge can be achieved and maintained, in the absence of active cooling, utilizing adiabatic charging and low rate trickle charging techniques. This paper describes the experimental determination of steady state battery capacity and temperature, during low rate trickle charging, in a simulated prelaunch ambient environment. Initial parametric data was obtained with individual cells. Subsequently a six-cell battery module, simulating the 22-cell flight battery thermal characteristics, was designed and fabricated. The module was mounted in a structure simulating the thermal environment the battery would experience in the spacecraft, during prelaunch operations. The test set up was fully instrumented. The six-cell module was trickle charged at rates in the range C/100 to C/1000. Steady state capacities and temperatures were determined. Test results indicate that trickle charge rates less than or equal to the self discharge rate (/spl sim/C/750) do not significantly increase dissipation beyond that due to the self discharge. Accordingly, significant trickle charge rates (/spl sim/C/500) result in battery temperatures only a few degrees (F) higher than observed during periods of open circuit stand.

Hubble Space Telescope Nickel-Hydrogen Battery and Cell Testing - An Update

NASAs HST uses Ni-H2 batteries. NASA-Marshall has been conducting developmental tests of such batteries in both six-battery and 22-cell single battery arrays. Tests have recently been conducted on such batteries with a view to the possible need to free additional memory in the HST onboard computer; the electrical power system could contribute to this end by eliminating its software control charge mode capability, which requires significant computer memory capacity.

Life Testing Of Secondary Silver-zinc Cells For The Orbiting Maneuvering Vehicle

Over the past 5 years, extensive testing has been performed at the Marshall Space Flight Center (MSFC) on a variety of secondary (rechargeable) silver-zinc (Ag-Zn) cells for the Orbital Maneuvering Vehicle (OMV). The first tests performed were to determine the feasibility of using such a cell in a long-life (18-month), low-Earth-orbit (LEO) application. Results from these tests were promising, so testing continued with a 250-Ah cell that was specifically designed for this type of application. Once again, results from the tests were promising. Following a review of the data from these previous tests, slight modifications to the 250-Ah design were necessary to alleviate problem areas. Currently, MSFC is testing a 350-Ah design that has incorporated these changes and is the baseline design for the OMV. This test began in mid-November, 1989, and will be complete in the spring of 1991, barring any substantial offline time. A report is presented on the preliminary results from the first few months of this test and they are compared to results obtained in previous tests done at MFSC.

Characterization testing of a 40 ampere hour bipolar nickel-hydrogen battery

Abstract Extensive characterization testing has been done on a second 40 ampere hour (A h), 10-cell, bipolar nickel—hydrogen (Ni—H 2 ) battery to study the effects of operating parameters such as charge and discharge rates, temperature, and pressure on capacity, A h and watt hour (W h) efficiencies, end-of-charge (EOC), and mid-point discharge voltages. Testing to date has produced many interesting results, with the battery performing well throughout the test matrix except during the high-rate (5 C and 10 C ) discharges, where poorer than expected results were observed. The exact cause of this poor performance is, as yet, unknown. Small scale 2 in. × 2 in. battery tests are to be used in studying this problem. Low earth orbit (LEO) cycle life testing at a 40% depth of discharge (DOD) and 10 °C is scheduled to follow the characterization testing.