Batteries are used on both spacecraft and satellites as a means of power storage for various mission phases and operations. Compared to Earth batteries, space batteries undergo much more intensive testing, research, and development. Owing to the harsh conditions found in space, batteries must be specially designed to endure the intense vibrations, environment, and temperature while still being able to function well to protect personnel safety. So it is highly risky when batteries fail in these kinds of scenarios. Replacing batteries can also be an exhausting task. 

While there is some overlap in the technologies used, the specific requirements of spacecraft and satellites can lead to different battery choices. The following specifications should be considered when choosing batteries for space flight applications: ampere-hour capacity, rechargeability, longevity, temperature conditions, robustness, and weight.

• Ampere-hour capacity - The amount of current that a battery can deliver in one hour. Otherwise ampere-hour rating of a battery tells you how much electrical charge the battery can deliver over a specific period of time. It is a measure of the battery’s capacity. Higher Ah capacity is a crucial parameter for guaranteeing uninterrupted operation of spacecraft systems, instruments, and communication equipment since it enables the battery to deliver more energy over time.
• Rechargeability - A battery's rechargeability refers to its ability to be recharged and used repeatedly after its stored energy has been depleted.  Space missions often require batteries that can be recharged multiple times, especially for long-duration missions such as those aboard satellites or rovers. Rechargeable batteries, like lithium-ion types, are favored because they can be charged via solar panels or other energy sources during the mission. Rechargeability becomes crucial for sustainable energy management in space, where resupply is impossible, and power must be conserved and efficiently used over time.
• Depth of Discharge (DOD) - Indicates the percentage of the battery that has been discharged relative to the overall capacity of the battery. Otherwise Depth of Discharge measures the percentage of a battery’s capacity that has been depleted, with higher DOD values indicating more energy has been consumed which is beneficial in space applications. For instance, some batteries can be discharged up to 80-90% without degrading performance. A low DOD battery would require more frequent recharges, which could be less efficient for space applications.
• Lifetime (Cycle Life) - Number of charge and discharge cycles it can undergo before experiencing a noticeable decline in performance determines how long the battery can last. Space missions, especially long-duration ones, demand batteries with a high cycle life to ensure that the power source remains operational throughout the mission without requiring replacement. In many cases, mission success depends on the longevity of the battery. 
• Temperature Environments - Describes the range of temperatures that a battery needs to endure while functioning in the harsh environment of space. Space introduces severe thermal challenges that can greatly impact the performance, durability, and lifespan of batteries utilized in satellites, spacecraft, space probes, and other space-related missions.The battery needs to be able to function well in the vast temperature range that space experiences. Extreme heat and cold are commonplace for spacecraft, especially when they are traveling through areas of sunlight and darkness. Space batteries have to continue working in conditions with both high and low temperatures. It may also be essential to use specialized insulation and thermal management to shield the battery from temperature extremes that could harm the cells or impede its functionality. 
• Ruggedness - Refers to its ability to withstand the extreme and demanding conditions of space without losing functionality or performance. Space batteries must be designed with exceptional durability and resilience to ensure they can operate effectively under various challenging environments. Space environments can be harsh, not only because of the vacuum and radiation but also due to mechanical stress during launch, landing, or in-orbit maneuvers. Batteries must be rugged, meaning they can withstand physical vibrations, shocks, and impacts without performance loss. They should also be resistant to potential damage from cosmic radiation.
• Weight - It is a critical factor in its design because minimizing mass is essential for space missions. The battery's weight directly impacts the overall payload, fuel consumption, and cost of launching a spacecraft. As a result, space batteries are engineered to provide the maximum energy capacity with the minimum weight possible.

Numerous battery kinds exist, including alkaline, lithium-ion, carbon-zinc, lead-acid, nickel-cadmium, nickel-hydrogen, silver zinc, and nickel-cadmium. Different types of batteries are used in spacecraft and satellites. Spacecraft, ranging from manned vessels to robotic explorers, present a unique set of challenges for battery systems. These vehicles must support a diverse array of power-hungry systems, including life support, propulsion, scientific instruments, and communication arrays. The power requirements can vary dramatically across different mission phases, from launch to orbital operations, and potentially planetary landing or deep space exploration.   

Satellites, whether operating in Low Earth Orbit (LEO) or Geosynchronous Earth Orbit (GEO), present a different set of challenges for battery systems compared to exploratory spacecraft. These vehicles typically have more predictable power requirements but must withstand numerous charge-discharge cycles over operational lifetimes that can span decades. The reliability and longevity of battery systems are paramount in satellite applications, where replacement or servicing is often not feasible.

Types Of Batteries

Batteries in Spacecraft 

In spacecraft, the major type of batteries used are Lithium-Ion (Li-ion) Batteries, Silver-Zinc (AgZn) Batteries, and Lithium-Sulfur (Li-S) Batteries  

Lithium-Ion (Li-ion) Batteries 

Lithium-ion battery's basic operating principle is ions travel between the anode and cathode via an electrolyte in these batteries' primary operating principle, which results in a portable and effective energy storage option. In spacecraft applications, Li-ion batteries excel due to their high specific energy, typically ranging from 150 to 250 Wh/kg. 

This high energy density is crucial for space missions where every gram of payload comes at a premium. Moreover, Li-ion batteries exhibit a low self-discharge rate, generally less than 5% per month, ensuring that energy is available when needed, even during extended periods of low activity.  

The absence of the memory effect in Li-ion batteries is another significant advantage for spacecraft operations.  Li-ion batteries offer flexibility in power management methods because, in contrast to previous battery technologies, they may be charged at any point throughout their discharge cycle without experiencing capacity deterioration. 

Recent space missions have showcased the capabilities of Li-ion batteries. The Mars rovers, including Curiosity and Perseverance, rely on Li-ion batteries to supplement their solar power systems during Martian nights and dust storms. These batteries have demonstrated remarkable resilience, operating in the extreme temperature fluctuations and radiation environment of the Martian surface. 

However, the implementation of Li-ion batteries in spacecraft is not without challenges. Thermal management is critical Because these batteries might be susceptible to temperature extremes. Sophisticated battery management systems are deployed to monitor cell voltages, temperature, and state of charge, assuring safe and optimal performance. Additionally, while the risk is low with proper design, the potential for thermal runaway in Li-ion cells necessitates careful consideration in spacecraft architecture to mitigate any safety concerns.

Silver-Zinc (AgZn) Batteries 

Silver-zinc batteries, batteries are known for their exceptionally high energy density, surpassing even that of lithium-ion in some metrics, with specific energies reaching up to 300 Wh/kg. The AgZn battery operates using a silver oxide cathode and a zinc anode, with an aqueous potassium hydroxide electrolyte. Because of this chemistry, the battery has a very low internal resistance and can deliver strong current pulses, which can be highly useful for some spacecraft tasks. 

Perhaps the most famous application of AgZn batteries was in the Apollo program. These batteries powered critical systems in the lunar landers, providing reliable energy during the most crucial phases of the moon landings. The space shuttle program also utilized AgZn batteries for specific applications where high-power density was required. 

Despite their impressive performance characteristics, the use of AgZn batteries in spacecraft has declined in recent years. The primary limitations include a relatively short cycle life and high cost due to the silver content. However, for specific short-duration missions or applications requiring extremely high power density, AgZn batteries remain a viable option in the spacecraft designer's toolkit.

Lithium-Sulfur (Li-S) Batteries 

Lithium-sulfur batteries represent the cutting-edge energy storage technology for space applications. While still largely in the research and development phase, Li-S batteries hold immense promise for future space missions due to their theoretical energy density of up to 500 Wh/kg – significantly higher than current Li-ion technologies. 

The Li-S battery employs a lithium metal anode and a sulfur-carbon composite cathode. During discharge, lithium ions react with sulfur to form various lithium sulfides, storing a large amount of energy in the process. This chemistry not only offers high energy density but also utilizes sulfur, an abundant and low-cost material. 

Li-S technology is being invested in by several space organizations and commercial businesses for upcoming long-duration space missions, such as possible Mars exploration. These batteries' lightweight design has the potential to significantly lower launch expenses and boost payload capacity for deep space missions.   

Before Li-S technology is widely used in spacecraft, there are still several obstacles to overcome. Current iterations suffer from rapid capacity fade due to the dissolution of lithium polysulfides in the electrolyte. Researchers are exploring diverse approaches to address this problem, such as advanced electrolyte formulations and cathode architectures. 

Moreover, the integration of Li-S batteries into spacecraft power systems will require the development of new battery management systems tailored to the unique characteristics of this chemistry. Despite these challenges, the potential benefits of Li-S batteries make them a technology to watch in the coming years of space exploration.

Fuel Cells 

While not batteries in the traditional sense, fuel cells deserve mention in any comprehensive discussion of spacecraft power systems. Fuel cells generate electricity through an electrochemical reaction between hydrogen and oxygen, producing water as a byproduct – a valuable resource in space missions. 

The use of fuel cells in spacecraft dates back to the Gemini and Apollo missions, where they provided primary electrical power. The space shuttle program also utilized fuel cells, leveraging their high energy density and the useful byproduct of potable water. 

Fuel cells offer several advantages for spacecraft applications. They can provide continuous power as long as fuel is supplied, offering high energy density for long-duration missions. The efficiency of fuel cells can exceed 60%, significantly higher than many traditional power generation methods. 

Current research in fuel cell technology for space applications focuses on improving durability, reducing system complexity, and exploring regenerative systems that can recharge using solar power. While not suitable for all spacecraft applications, fuel cells remain an important consideration for specific mission profiles, particularly those requiring sustained high power output.

Batteries in Satellites 

In satellites, the major types of batteries used are Nickel-Cadmium (NiCd) Batteries, Nickel-Hydrogen (NiH2) Batteries, Lithium-Ion (Li-ion) Batteries, and Lithium Polymer (Li-Po) Batteries.

Nickel-Cadmium (NiCd) Batteries 

Nickel-cadmium batteries were the workhorses of satellite power systems for many years, valued for their robustness and reliability in the space environment. While it's commonly believed that Ni-Cd batteries are being replaced by NiH2 and Lithium-based batteries in more recent systems, this format has been a reliable storage solution for many years, offering a fair capacity and sufficient lifetime to meet the needs of space missions in the past. These batteries operate using a nickel oxide hydroxide cathode and a cadmium anode, with an alkaline electrolyte most of the time it is potassium hydroxide. 

In satellite applications, NiCd batteries proved their worth through their ability to withstand the harsh radiation environment of space and their tolerance for the repeated deep discharge cycles typical of orbital operations. With proper thermal management, NiCd batteries can operate effectively across a wide temperature range, a crucial factor in the variable thermal conditions experienced by satellites. Both LEO and GEO spacecraft have used these batteries. 

The cycle life of NiCd batteries, which can exceed 20,000 cycles under optimal conditions, made them particularly suitable for LEO satellites that experience frequent charge-discharge cycles as they move in and out of Earth's shadow. Additionally, their ability to handle high discharge rates was beneficial for satellites requiring occasional bursts of high power. One of the main benefits of the batteries is their potential to discharge at a high pace while still delivering their full capacity. 

However, the use of NiCd batteries in new satellite designs has declined significantly in recent years. These batteries have certain notable drawbacks, including the possibility of overcharging and overheating due to the rapid charging rate, which might harm the battery. Additionally, if these batteries are used for an extended period, the insulator material may develop holes where crystalline "shorts" emerge. When this happens, an intense pulse current must open these crystallines for the cell to charge. 

The primary drivers for this shift include the lower energy density of NiCd compared to newer technologies (typically around 40-60 Wh/kg) and environmental concerns related to cadmium toxicity. While still in service on some older satellites, NiCd batteries have largely been superseded by more advanced technologies in modern satellite designs.

Nickel-Hydrogen (NiH2) Batteries 

Nickel-hydrogen batteries represented a significant advancement in satellite energy storage when they were introduced in the 1970s. These batteries were developed specifically for aerospace applications, combining the proven nickel electrode technology from NiCd batteries with hydrogen gas storage, eliminating the need for a solid metal anode. 

The primary benefit of using Nickel-Hydrogen batteries is that overcharging or over-discharging them doesn't endanger user safety. In addition, their specific energy is higher than that of Ni-Cd batteries. Their high rate of self-discharge, low volumetric energy density, and need for high-pressure storage to contain the hydrogen gas produced while charging are their primary drawbacks. 

The most notable characteristic of NiH2 batteries is their exceptional cycle life, often exceeding 20,000 cycles with minimal degradation. This longevity made them ideal for GEO satellites, which typically have a design life of 15 years or more. The ability to withstand repeated deep discharges without significant capacity loss was a key factor in their widespread adoption. 

NiH2 batteries also offer improved energy density compared to NiCd, typically in the range of 45-75 Wh/kg. While not as high as some newer technologies, this energy density, combined with their proven reliability, made NiH2 batteries a preferred choice for many satellite manufacturers. 

An outstanding example of NiH2 battery technology in operation is the International Space Station (ISS). NiH2 batteries were the foundation of the initial ISS power system, and they functioned wonderfully for many years despite the demanding LEO environment. Another prime example is the Nickel-Hydrogen batteries that ran the Hubble Telescope in low-Earth orbit from 1990 until 2009. Later, upgraded models of the same system took their place. 

Despite their advantages, NiH2 batteries have some drawbacks. Compared to other battery types, they are typically more expensive to construct, and integrating their cylindrical pressure vessel design into satellite structures can be difficult. Similar to NiCd batteries, more sophisticated lithium-ion systems are gradually replacing NiH2 technology in many current satellite designs.

Lithium-Ion (Li-ion) Batteries 

The lithium-ion battery technology has had a profound impact on satellite power systems, much as it has on terrestrial applications. The high energy density, low self-discharge rate, and absence of memory effect that make Li-ion batteries attractive for consumer electronics translate well to the demands of satellite operations. 

In satellite applications, Li-ion batteries typically achieve energy densities of 150-200 Wh/kg, significantly higher than their NiCd or NiH2 predecessors. This increased energy density allows satellite designers to allocate more mass to payload or reduce overall satellite mass, both of which can lead to significant cost savings in launch and operations. 

The performance of Li-ion batteries in the space environment has been extensively validated through numerous satellite missions. Modern LEO communication constellations, Earth observation satellites, and even some GEO satellites now rely on Li-ion technology for their energy storage needs. 

The key highlights of Li-ion batteries are their large working cycle and broad operating temperature range. Additionally, the systems may produce high- and short-wavelength energy peaks without damaging the cell. While the anode is usually made of carbon, the properties of Li-ion cells vary depending on the cathode material. 

Among Li-ion cells, lithium manganese oxide (LMO) and lithium manganese nickel (NMC) cells are inexpensive and have respectable safety ratings. While NMC cells have low resistance, low specific energy, and low discharge rate capability, LMO cells have low specific energy and high discharge rate capability. 

Li-ion batteries' adaptability is one of its main benefits for satellite applications. The limited space inside a satellite structure can be better utilized by arranging the cells in a variety of sizes and shapes. Li-ion batteries are especially well-liked for small satellite and CubeSat applications, where volume and mass are limited, due to their flexibility and high energy density.

Li-ion battery use in satellites is not without its difficulties, though. Because high temperatures can shorten battery life, thermal control is essential. Throughout the satellite's operating life, sophisticated battery management systems are used to monitor temperature, state of charge, and cell voltages, guaranteeing safe and optimal performance. 

Among the Li-ion cells, Lithium nickel cobalt aluminum oxide (NCA) cells have the highest cycle life and specific energy. Lithium nickel cobalt oxide (NCO) cells are rarely used. The drawbacks of lithium cobalt oxide (LCO) cells include their high cost, low specific energy, inadequate safety, and limited capacity for discharge rate. The low specific energy and high discharge rate capabilities of lithium iron phosphate (LFP) cells, along with their superior safety ratings, define them. 

Radiation tolerance is another crucial factor in the space environment. While Li-ion batteries have generally shown good radiation resistance, long-term exposure can lead to degradation. Satellite designers must carefully consider radiation shielding and cell selection to ensure the longevity of Li-ion battery systems in orbit.

Lithium Polymer (Li-Po) Batteries 

Lithium polymer batteries have a more flexible form factor because they use a polymer electrolyte rather than the liquid electrolyte present in conventional Li-ion cells. It is a Li-ion technology variation that has proven very useful for small satellite and CubeSat applications.

The key advantage of Li-Po batteries in satellite applications is their ability to be shaped to fit available spaces within the satellite structure. This flexibility is particularly valuable in small satellites, where every cubic centimeter of volume is precious. Li-Po batteries can be made in thin, flat packages that can be integrated into solar panels or other structural elements of the satellite. 

In terms of performance, Li-Po batteries offer energy densities comparable to or slightly higher than traditional Li-ion cells, typically in the range of 150-200 Wh/kg. They also share many of the other advantages of Li-ion technology, including low self-discharge rates and the absence of memory effect. 

However, Li-Po batteries do have some limitations that must be considered in satellite applications. They can be more sensitive to physical damage than cells in rigid casings, which can be a concern during launch or deployment. Additionally, they require careful charging and discharging management to prevent swelling or damage to the polymer electrolyte. 

Despite these challenges, Li-Po batteries have found a niche in the rapidly growing small satellite market. Their use in CubeSats and other miniaturized satellite platforms has enabled new possibilities in Earth observation, communications, and scientific research, demonstrating the impact that advances in battery technology can have on space exploration and utilization. 

The evolution of battery technology has been essential to advancements in spacecraft and satellite capabilities, from early silver-zinc batteries to today’s lithium-ion dominance and promising next-generation chemistries like lithium-sulfur. As space exploration continues, battery innovation will focus on higher energy density, longer life cycles, improved safety, and performance in extreme environments, supporting everything from global communication satellites to Mars rovers and human space travel. These advancements not only expand space exploration possibilities but also have a significant impact on terrestrial technologies, underscoring the broader benefits of space-related research.