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Power System and Sources For Spacecrafts

Power System And Sources For Spacecrafts


Image Credit:NASA

One of the key elements in any spacecraft which keeps the components alive is the power source. The spacecraft is dead with no ability to communicate with the ground station without any on-board power source. However, the process of powering a spacecraft is a challenging task for different missions with different use cases.


The power source for any space bound mission is in itself a vast research topic with different techniques being proposed regularly. However, the most of the research topics falls under these broad categories. They are,

  • Solar
  • Nuclear
  • Fuel cell
  • Battery

 

 

Solar power
This is the mostly commonly used power source in most of the near earth missions and missions inside our solar system. The spacecraft will be equipped with a large array of solar panels pointing directly towards to the sun. The solar panel consists of array of solar cell each converting sun light into electricity using the photovoltaic mechanism.


Chandrayaan-1 had a single solar panel projecting from one-side of the spacecraft. It could generate maximum of 700 watts of power. It was also used to recharge the Lithium-ion battery which was used whenever solar panel was not completely exposed or partially exposed to the sun.

 


Image Credit: ISRO


Similarly, Mangalyaan has an array of 3 solar panels projecting from one side of the spacecraft. The reason for using 3 solar panels is due to low exposure to sun light near Mars atmosphere. The 3 solar panels are capable of producing a maximum of 840W in total. Again, it uses rechargeable Lithium-ion battery as a backup.

NASA always preferred to have non-solar power source for deep solar exploration missions due to less availability of sunlight. However, Juno is the first deep solar exploration (mission to Jupiter) mission from NASA to use solar panel for generating electricity instead of other methods (RTGs). It uses 18,000 solar cells for producing about 405 watts of power.

Image Credit:NASA


The international space station has an array of 8 large solar panels consisting of 2, 62,400 solar cells (Si based) producing maximum of 120kilo watts of power. These solar arrays are so large that it occupies an area of 27,000 square feet in space.


Solar cell
A solar panel is a collection of solar cell. The solar cells used in the array of solar panels could be made from variety of materials. As of today, there are broadly 4 flavors of the solar cells as mentioned below.


Silicon

  • Practical efficiency 14%

Gallium arsenide

  • Practical efficiency 19%
  • Expensive than silicon based
  • Extremely radiation resistant and suited for space applications

Indium phosphide

  • Practical efficiency 18%
  • Expensive of all
  • Extremely radiation resistant and suited for space applications

Multijunction GaAs

  • Practical efficiency 22% (maximum of 29% under ideal conditions)
  • Expensive than silicon and Gallium arsenide based

Thin-film cell

  • Production quality cell is not available
  • Low cost
  • Low efficiency

 

Most of the solar powered space missions either use the multijunction GaAs or silicon based solar cells for generating electricity.  The solar array to be used in a space bound mission is decided based on the cost, mass, area and risk of failure. The silicon solar cells are popular because of their low cost and high reliability but they have a disadvantage of larger mass and area for a given power requirement. However, GaAs based solar cells are expensive but they present less area and mass.


From the above, it is clear that one of the main issues with the current solar cells is the efficiency of converting the sun light into electricity. At ideal conditions, the present day solar cell could be efficient only up to 29% to convert light into electricity. So, there is a portion of the sun light which goes unused. To give more data, the solar panels used at home are close to 14% efficient only.


This is one of the major concerns for considering the solar powered mode for deep space missions where the sunlight might be even less.  So, there is a need to put more solar panels to compensate for the reduced sunlight. However, the increased solar panel weight adds to the fuel cost and eventually overall cost of the mission. In this direction, there are a lot of researchers working in the area of solar cell to improve the efficiency further. In fact, there are proposals for newer type of solar cells like light absorbing dyes, Quantum dot solar cells and organic/polymer solar cells however they are not feasible as of now for space bound missions.


Author
Vasanth

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