Basic knowledge of batteries used in aerospace and communication satellites

Basic knowledge of batteries used in aerospace and communication satellites

Spacecraft and communication satellites have very strict requirements on rechargeable batteries. Reliability, weight, size, and longevity are necessary performance requirements for rechargeable batteries deployed on spacecraft and communication satellites. In addition, redundancy may be another important performance requirement. The performance requirements of low earth orbit (LEO) satellites are strict, and the requirements for synchronous orbit satellites will be more stringent. Due to the launch cost and the complexity of the system, the demand for battery life will exceed 10 to 15 years. Space batteries must be able to provide electricity for lights, rotation control stability sensors, space monitoring systems, air conditioning systems, drinking water products, and a range of other key equipment that provide astronauts’ comfort and safety.

The electrical system of communication satellites, covert reconnaissance and surveillance satellites, and spacecraft for astronauts conducting scientific research activities include energy conversion equipment, (solar cells) combined with energy storage devices (batteries) and power conditioning components (PC), that is, pulse duration regulator (PVR), PVR maintains a constant voltage during the pulse period, which plays a key role in achieving the best performance. All these parts of weight, size and power consumption must be kept to a minimum in order to minimize the cost of launching satellites and spacecraft.

Nickel-cadmium (Ni-Cd) batteries were widely used by early communication satellites and spacecraft from 1960 to 1995. When advanced designs of nickel-metal hydride (Ni-H2) batteries became available in the early 2000s, most satellites and spacecraft gave priority to using Ni-H2 batteries. The reliability and improved electrical performance of these batteries will be explained in detail. For short-term mission satellites and low-orbit communication satellites, nickel-cadmium Ni-Cd and nickel-hydrogen Ni-H2 batteries are still in use.

Basic knowledge of batteries used in aerospace and communication satellites
Nickel-cadmium batteries

During the dark period experienced by the satellite, the onboard battery must meet the power consumption requirements of all the electronic sensors and electrical equipment operating on the satellite or spacecraft. During the dark period, neither electronic nor electrical components can obtain any electrical energy from the satellite-based solar cells. Once the dark period is over, the onboard electronic sensors and electrical components will receive power from the solar array connected to the satellite or spacecraft. As mentioned, the solar cell array and the battery are interconnected by the regulator bus, as shown in Figure 1.

Basic knowledge of batteries used in aerospace and communication satellites
Figure 1 The concept of controlled and uncontrolled power buses for potential applications such as satellite power systems

The dark period experienced by the satellite is called the “satellite eclipse”. During this period, the local time must be carefully considered in order to receive audio and video signals from the satellite. When the moon on the spring and autumn equinox is in the shadow of the earth, the maximum eclipse duration is usually 72 minutes.

The peak started about 36 minutes ago, and there is an 8 minute correction due to the difference between apparent and average solar time. This makes the television report of the eclipse at the satellite projection point appear at about 11:15P.M. As the area covered by the satellite projection point moves east or west, the eclipse starts 2 hours earlier or later than local time. The impact of this on spacecraft design should not be underestimated. During a eclipse, a high-power TV transponder requires a large number of batteries to operate, and the battery must be able to provide all the power requirements during a eclipse or dark period. This is the most important design requirement for satellite batteries.