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You might already be knowing that these batteries must be capable of withstanding severe launch environments (vibration, shock, acceleration) along with tolerance to high intensity radiations. Hence they should provide maximum electrical energy in minimum weight and volume. The most stringent requirement is maintaining the temperature of the battery. <br \>
In general, batteries that display higher gravimetric(higher mass) and volumetric energy densities(higher volume) can manifest in reduced mass and volume for the power subsystem and thus increased payload and mission capabilities. Batteries with tolerance to extreme environment can, on the other hand, be mission enabling and may facilitate increased scientific capabilities of the mission. <refname = "ieee">http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=4161575 </ref>
== Factors affecting battery performance ==
* '''History:''' Monitoring and storing the battery's history is another possible function of the BMS. This is needed in order to estimate the State of Health of the battery, but also to determine whether it has been subject to abuse. This does not have to necessarily be stored, it can as well be transmitted to the ground station.
* '''Communication:''' Most BMS systems incorporate some form of communication between the battery and the charger or test equipment. Communication interfaces are also needed to allow the user access to the battery for modifying the BMS control parameters or for diagnostics and test.
== Information about Available Batteries ==
=== Silver-Zinc batteries ===
The earliest use of a battery in an orbital spacecraft was the primary Ag-Zn battery used in the Russian spacecraft, Sputnik, launched October 4, 1956. This primary battery was used to provide power for communication and spacecraft operation. There were no solar cells available for charging, and thus when the energy was depleted, communication was terminated. <br \>
These have been used in several US spacecrafts.
=== Nickel-Cadmium Batteries ===
Intended for use where the battery will experience frequent charge/discharge cycles. Advantages include its low cost, flat discharge rate, its capacity to withstand deep discharges without damaging the cells and to remain sturdy for rough environments. <br \>
These have been successfully applied to LEO(low-earth orbit) microsatellite and minisatellite programs. It has performed some 70,000 charge/discharge cycles over a 14 year period and is still useful. <br \>
Disadvantages could be the memory effect (the condition that battery loses capacity to hold maximum energy when repeatedly overcharged after partial discharging) and its relatively low energy density compared with newer battery systems. <br \>
The “super” Ni-Cd cells, developed by Eagle-Picher, were the next step to enhance the Ni-Cd energy density and life. NASA utilized these in the late 80s on small satellites, such as the small Explorer series.
=== Nickel-Hydrogen Batteries ===
These have found wide use in high-reliability space applications that require extended service life. Replacement of Cd with hydrogen reduced weight and increased energy thus almost doubling the specific energy. The cells often appear capable of handling the stresses of inadvertent reversal or excessive overcharge with little evidence of the damage or performance degradation that had been the rule for nickel-cadmium cells. <ref>http://aerospace.wpengine.netdna-cdn.com/wp-content/uploads/2012/03/bk_ni-hyd-batteries-prin-pract_ch1.pdf <\ref>
=== Li-ion Batteries ===
High energy density, high specific energy and long cycle life make Li-ion batteries promising power sources for satellites. It offers significant advantages in terms of mass(almost half of nickel hydrogen batteries for the same stored energy), volume and temperature range. The batteries also display good tolerance to occasional deep discharge. Li-Ion cells also display impressive and adequate tolerance to radiation levels as high as 18 Mrad (1 rad=0.01 J/kg ; dose causing 100 ergs of energy to be absorbed by 1 gram of matter) and exhibit a loss of less than 10 % upon such high levels of radiation exposure. Furthermore, a portion of this loss can be attributed to the cycling or storage during this incremental radiation exposure. <ref name = "ieee"/> <\br \>
Significant advances have been made in the cathode materials and electrolytes for Li-ion cells and batteries. Several new cathodes with high specific capacity approaching 250 mAh/g, coupled with high voltage and improved thermal stability have been identified. Likewise, several new electrolytes for enabling operations at -60 °C have been demonstrated. These advances are expected to results in advanced lithium-ion cells and batteries with high specific energy and wide range of operating temperatures, as desired in future space missions. <ref name = "ieee"/> However, the polymer li-ion cells have an additional problem with electrolyte leakage under abusive conditions. <ref name = "nasa">https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090023862.pdf </ref>
=== Comparison between the batteries ====
{| class="wikitable"
|-
|'''System'''
|'''Specific Energy (Wh/kg)'''
|'''Energy Density (W/L)'''
|'''Operating Temperature (°C)'''
|'''Lifetime (in Years)'''
|'''Cycle life (* @partial Depth of Discharge)'''
|-
|'''Silver-Zinc'''
|100
|200
| -10 to +25
|<1
|<100
|-
|'''Nickel Cadmium'''
|35
|100
| -10 to 25
|>5
| >30,000*
|-
|'''Nickel-Hydrogen'''
|40
|80
| -10 to 30
|5-10
|>40,000*
|-
|'''Li-ion'''
|100
|240
| -30 to 40
|4
|1000
|}
Traditionally used batteries use aqueous electrolyte (eg. Ni-Cd, Ni-H2, lead-acid) mainly because water is the best and cheapest chemical solvent for most ionic compounds and such solutions can have very good ionic conductivity. However water decomposes at a relatively low voltage limiting the cell voltage of aqueous cells to a maximum in the region of 1.5 to 2.0 V. For satellites requiring more than 3 years of operation, batteries used must achieve 1000 to 33000 cycles without the requirement of maintenance. This is considerably in excess of the cycle lives demanded by most terrestrial battery applications and it is the cycle life requirement that has confined spacecrafts to the use of well-proven alkaline battery technologies- Ni-Cd and Ni-H2. However, when used to 80% of their available capacity, these technologies offer useful mass energy densities of no more than 24 and 36 watt-hours/kg respectively at battery level( taking into account mass of battery packaging). Provided life-cycle requirements can be met, lithium ion technology provided for better in terms of cost/performance factor.<ref> http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1998ESASP.416...17D&db_key=AST&page_ind=0&data_type=GIF&type=SCREEN_VIEW&classic=YES </ref>
== Hazards and Prevention ==
Risk regarding batteries are broadly due to: <ref name = "nasa"/>
* Overcharging
* Over-discharge
* External and internal short circuits
* High temperatures - ambient as well as cell temperature limit
* Under voltage- Exceeding depth of discharge (DOD) limits
* Pressure build up in the cell
The individual cells should be able to survive a short circuit with an opening to release gaseous products, to prevent pressure build-up in the cell . Circuit should be designed keeping overcharge, over-discharge, short circuits and temperature considerations in mind. Battery designing must have a significant safety factor. <br \>
Lithium cells shouldn't be kept on conducting surfaces unless they have appropriate conduction protection. Spot welding, and not soldering, should be used to attach leads directly to a cell.<ref name = "nasa"/> Caution also has to be taken against radiation - via either MLI (Multi-Layer Insulation) or a black coating. Internal short prevention in lithium-ion batteries effectively opens the battery circuit, shutting off current flow through the battery.<br \>
A PTC (Positive Temperature Coefficient) switch can also be used to prevent short-circuiting by inhibiting high currents. As temperature increases above a limit, material resistance faces a large increase and being reversible they cycle back to conductive state when we have normal condition again.
CIDs (Current Interrupter Devices) can prevent further charging of a battery until internal pressure(of battery) is alleviated. These devices prevent venting of hazardous electrolytes and bursting due to buildup of high pressures.<ref name = "nasa2">https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150020899.pdf </ref> However, both PTCs and CIDs may fail when exposed to high voltages due to other failures. The use of bypass diodes is recommended to prevent these failures.<br \>
The surfaces of battery terminals that extend inside the battery case need to be insulated with potting materials to prevent unintentional contact with other conductors inside the case and also to prevent bridging by electrolyte leaks. Wires inside the battery case should be insulated, restrained from contact with cell terminals, protected against chafing and physically constrained from movement due to vibration or bumping.<ref name = "nasa">
Certification of the crimp is critical for ensuring that individual cells will not leak after launching.<ref name = "nasa2"/> Cell terminals need to be protected from contact with other conductive surfaces. <br \>
For example, in lithium energy cells,
[[File:Licells.png|frame|center]]
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==References==