More than a decade of research and development in a battery that is expected to add years of life to spacecraft is ready for harvest.
New lines of Space and Communications Group satellites will be powered by nickel hydrogen (Ni-H₂) batteries, a hybrid that may outlive and outperform its predecessors.
By combining the nickel electrode from the commonly used nickel-cadmium batteries (Ni-Cd) with the hydrogen electrode from hydrogen-oxygen fuel cells, Hughes scientists have developed a battery that in its eighth year of real-time testing, has shown no signs of significant degradation.
“Compared with the 10-year life span of nickel cadmiums, we expect to get 15, possibly 20 years or more out of nickel hydrogens,” said senior scientist Howard Rogers of Space and Communications Group’s Power Sources department.
Dr. Rogers was hired by Hughes in 1973 to work on the development of Ni-H₂ batteries, an electrochemical system that was first suggested in 1961 by Frank Ludwig, who is now a senior scientist at Electro-Optical and Data Systems Group. Much of the development work has been sponsored by the Air Force.
The ongoing effort has produced a battery that will serve the high-power needs of the large, new spacecraft generation, such as the Intelsat VI series and the HS 393 family.
Batteries breathe life into satellites, storing energy that is collected in spacecraft solar cell arrays and providing full power during eclipses of the sun when solar-generated electricity is temporarily unavailable.
Although both Ni-H₂ and Ni-Cd batteries can power a spacecraft, the Ni-H₂ unit weighs less, a critical factor in determining space-bound payloads.
The beauty of the Ni-H₂ battery, said Dr. Rogers, is that it has the rechargeable quality of Ni-Cd batteries, but few of its disadvantages, such as high susceptibility to damage from electrical and thermal environments.
“Nickel-hydrogen batteries require less care and feeding than nickel cadmium, and are less likely to be damaged by unintentional abuse,” said Dr. Rogers.
Contained in pressurized containers, Ni- H₂ batteries do not bulge from pressure that builds up if one of the cells is completely discharged, a possible occurrence in Ni-Cd batteries. They also do not run the risk of severe damage from over-charging.
Another advantage is that, unlike Ni-Cd batteries, the amount of electricity stored in Ni-H₂ batteries can be monitored. “With a nickel cadmium, you can estimate the state of charge if you know how much electricity the battery should hold and its rate of discharge. But there’s no way to know for sure,” said Dr. Rogers.
The change in a Ni- H₂ battery can be assessed precisely by using a gauge that measures hydrogen pressure levels.
“Although a nickel-hydrogen cell can be discharged to 100 per cent of its capacity without adverse effects, the discharge limit has been set at 80 per cent to achieve at least a 10-year life,” said Dr. Rogers.
“The nickel-hydrogen battery, in its life test at the 80 per cent level,” he continued, “has been ‘cycled’ again and again, drained of its energy and recharged repeatedly many thousands of times without any significant decrease in performance.”