A nickel hydrogen battery (NiH2 or Ni-H2) is a rechargeable electrochemical power source based on nickel and hydrogen. The difference with a nickel-metal hydride battery is the use of hydrogen in a pressurized cell of up to 1200 psi (82.7 bar).
The cathode is made up of a dry sintered porous nickel plaque, which contains nickel hydroxide, the negative hydrogen electrode utilises a teflon-bonded platinum black catalyst, the separator is in general an asbestos paper or untreated knit zirconium oxide (Zircar) cloth.
NiH2 cells using 26% potassium hydroxide (KOH) as an electrolyte have shown a service life of 15 years or more at 80% depth of discharge (DOD)
The energy density for LEO and GEO is 75 Wh/kg, 60 Wh/dm3 specific power 220 W/kg. The open-circuit voltage is 1.55 V, discharge voltage 1.25 V, and the voltage under load 1.5 V. The cells handle more than 20,000 charge cycles on 85% efficiency.
NiH2 rechargeable batteries possess good electrical properties which make them attractive for the energy storage of electrical energy in satellites and space probes. For example, the ISS, Mars Odyssey and the Mars Global Surveyor[ are equipped with nickel-hydrogen batteries. The Hubble Space Telescope leads with the highest number of charge/discharge cycles of any NiH2 battery currently in low earth orbit.
Taken from - http://en.wikipedia.org/wiki/Nickel_hydrogen_battery
Batteries
Powering Hubble
When astronauts return to the Hubble Space Telescope during Servicing Mission 4 (SM4), they will replace all six of the telescope’s 125-pound nickel hydrogen batteries. These batteries provide all the electrical power to support Hubble operations during the night portion of its orbit.
The telescope’s orbit is approximately 97 minutes long, about 61 minutes of which are in sunlight and 36 minutes are in the Earth’s shadow (night). During Hubble’s sunlight or daytime period, the solar arrays provide power to the onboard electrical equipment. They also charge the spacecraft’s batteries, so that the batteries can power the spacecraft during the night portion of Hubble’s orbit.
All six batteries are normally used at the same time. Like the ones they replace, the six new batteries reside in two modules, each containing three batteries. Each module weighs 460 pounds and measures 36 inches long, 32 inches wide, and 11 inches high. Astronauts will remove the old battery modules from equipment bays #2 and #3, and will install the new modules in the same locations.
Each of the 6 batteries begins its life on the ground with approximately 88 amp-hrs of capacity. Each battery contains 22 individual cells wired together in series. Due to limitations of Hubble’s thermal control system, the batteries can only be charged to 75 amp-hrs when installed on Hubble. The 6 new batteries will begin their life on-orbit by delivering a total of over 450 amp-hrs of capacity to Hubble.
Durable and Reliable
Now more than 18 years into the mission, Hubble’s nickel hydrogen batteries have lasted more than 13 years longer than their design orbital life— longer than those in any other spacecraft located in low Earth orbit. This was possible partly because the batteries were built to very exacting standards using an extremely robust design. Nickel hydrogen battery chemistry is very stable and is known to exceed on-orbit performance requirements for long duration missions.
Another reason for the batteries’ longevity is that they are very carefully managed on a daily basis by Electrical Power System engineers at Goddard Space Flight Center (GSFC), which has resulted in improved long-term on-orbit performance. This is done by closely monitoring the amount of current that flows into the batteries and their temperature during each charging cycle. Due to aging and cycling, the batteries are showing a slow loss in capacity, a normal and expected trend. If not replaced, they will eventually be unable to support Hubble’s science mission.
The replacement batteries are superior to the old ones in several ways. The new batteries are made using a “wet slurry” process, in which powdered metallic materials mixed in a wet binder agent are poured into a mold and heated until the liquid boils off, leaving a porous solid. This process produces batteries which are physically stronger and better performing than the “dry sinter” batteries they are replacing. Metallic materials are mixed dry and pressed into a mold under high pressure in the “dry sinter” manufacturing process. Each new battery also has the added safety feature of a battery isolation switch that electrically dead-faces each connector. “Dead-face” means no electrical power is present at the connectors while the switch is in the “off” position. This creates a safer environment for astronauts installing the battery modules.
NASA uses nickel hydrogen batteries because they are highly reliable and are able to handle deep discharging better than other types of batteries. Nickel hydrogen batteries also can store more energy than other types of similar size. They perform very well over long missions in low Earth orbit, and have been used on many NASA missions in the past decade.
For more information, contact:
Susan Hendrix,
Office of Public Affairs.
301-286-7745
Or visit the Hubble website at:
www.nasa.gov/hubble
Battery Module Assembly with lid removed, showing the cells and power isolation switches.
Credit: NASA
Original Battery Module Assembly installed on Hubble in Bay 2.
Credit: NASA
Taken from - http://www.nasa.gov/mission_pages/hubble/servicing/SM4/main/Battery_FS_HTML.html
Over the years disposable and rechargeable batteries for electronics have made life easier for millions of consumers, running everything from smoke detectors to digital cameras to computer laptops.
Hubble’s Rechargeable Batteries
The famed Hubble Space Telescope relies on specially formulated rechargeable batteries that provide power to the telescope’s science instruments and critical components during each night orbit.
During Hubble’s sunlight (or daytime) orbit, its solar arrays provide power to the electrical components and charge the batteries so they have enough power to support Hubble during its night orbit. Since Hubble spends about one third of its 97 minute orbit around the Earth “in the dark” it must rely on the energy that is stored in its onboard batteries to supply power to the entire telescope.
The six, 125-lb nickel hydrogen batteries on Hubble have provided electrical power to the telescope during its night orbit since the telescope launched in 1990. That means they have been operating for more than 18 years and counting. How is this possible?
Engineers on the ground carefully manage the charging of Hubble’s batteries, enabling the spacecraft to function efficiently during the entire orbit. “Hubble’s batteries have far exceeded our expectations,” said Mike Weiss, Hubble’s Deputy Program Manager at NASA’s Goddard Space Flight Center. “They have made possible all of the improvements we have made to Hubble over the course of four servicing missions. On SM4, after 18 years of remarkable performance, the time has finally come to renew Hubble’s lease on life with new batteries.”
Unlike a small digital camera battery that weighs only a few ounces, Hubble’s batteries are much larger and heavier. Collectively they weigh 460 pounds and measure 36 inches long, 32 inches wide, and 11 inches high.
A battery’s ability to store energy and supply this energy over time is measured in terms of battery storage capacity. Engineers measure such capacity in terms of ampere-hours or amp-hours. Each Hubble battery begins its life in space with about 75 amp-hours of capacity. By comparison, the typical modern digital camera battery has about 1 amp-hour of capacity. And while digital camera batteries deliver their power around 6 volts, Hubble’s power is delivered at 24 volts. This means Hubble batteries store about 2,000 times the amount of energy that is stored in a digital camera battery.
What Lies Ahead
The batteries on Hubble are original equipment. Not bad for components that were originally tagged with a five-year mission life. Their extended useful life is due largely to a team of electrical power system engineers at Goddard who constantly monitor the amount of current flowing into the batteries, along with their temperature during charging cycles. Small tweaks to the charging cycles are made when needed to ensure optimal performance.
However, due to normal aging and cycling, the telescope’s batteries are showing an expected slow loss in capacity, or their ability to hold a charge. So during the next Hubble servicing mission in 2009, astronauts will replace the existing batteries with new and improved ones that will enable Hubble to continue its amazing scientific journey for years to come.
Susan Hendrix
NASA's Goddard Space Flight Center
Related link:
Read the other stories in the "Next Stop: Hubble" series
This image shows a close up of the two nickel hydrogen battery modules, containing three batteries each, destined for Hubble.
Mission specialist Michael Good practices installing a battery module into the Hubble High Fidelity Mechanical Simulator, located in the cleanroom at NASA’s Goddard Space Flight Center. Astronauts will install new batteries into the Hubble Space Telescope during SM4 in early 2009. Credit: NASA
Taken from - http://www.nasa.gov/mission_pages/hubble/servicing/series/battery_story.html