Tuesday, December 7, 2010

UNIVERSE- Miniaturized satellite


Miniaturized satellites or small satellites are artificial satellites of unusually low weights and small sizes, usually under 500 kg (1,100 lb).[1] While all such satellites can be referred to as small satellites, different classifications are used to categorize them based on mass (see below).
One reason for miniaturizing satellites is to reduce the cost: heavier satellites require larger rockets of greater cost to finance; smaller and lighter satellites require smaller and cheaper launch vehicles and can sometimes be launched in multiples. They can also be launched 'piggyback', using excess capacity on larger launch vehicles. Miniaturized satellites allow for cheaper designs as well as ease of mass production, although few satellites of any size other than 'communications constellations' where dozens of satellites are used to cover the globe, have been mass produced in practice.
        Besides the cost issue, the main rationale for the use of miniaturized satellites is the opportunity to enable missions that a larger satellite could not accomplish, such as:
    


  • Constellations for low data rate communications

  • Using formations to gather data from multiple points

  • In-orbit inspection of larger satellites.

  • Minisatellite

    The term "minisatellite" usually refers to an artificial satellite with a "wet mass" (including fuel) between 100 and 500 kg (220 and 1,100 lb), though these are usually simply called "small satellites". Minisatellites are usually simpler but use the same technologies as larger satellites.
          

    Microsatellite

    Microsatellite or "microsat" is usually applied to the name of an artificial satellite with a wet mass between 10 and 100 kg (22 and 220 lb). However, this is not an official convention and sometimes microsats can refer to satellites larger than that. Sometimes designs or proposed designs of these types have microsatellites working together or in a formation. The generic term "small satellite" is also sometimes used.

        

    Nanosatellite

    The term "nanosatellite" or "nanosat" is usually applied to the name of an artificial satellite with a wet mass between 1 and 10 kg (2.2 and 22 lb). Again designs and proposed designs of these types usually have multiple nanosatellites working together or in formation (sometimes the term "swarm" is applied). Some designs require a larger "mother" satellite for communication with ground controllers or for launching and docking with nanosatellites.

      

    Picosatellite

    Picosatellite or "picosat" (not to be confused with the PICOSat series of microsatellites) is usually applied to the name of an artificial satellite with a wet mass between .1 and 1 kg (0.22 and 2.2 lb). Again designs and proposed designs of these types usually have multiple picosatellites working together or in formation (sometimes the term "swarm" is applied). Some designs require a larger "mother" satellite for communication with ground controllers or for launching and docking with picosatellites. The CubeSat design, with 1 kg maximum mass, is an example of a large picosatellite (or minimum nanosat).

              

    Technical challenges

    Micro/nanosats usually require innovative propulsion, attitude control, communication and computation systems.
    Larger satellites usually use monopropellants or bipropellant combustion rockets for propulsion and attitude control; these systems are complex and require a minimal amount of volume to surface area to dissipate heat. These systems are used on larger microsats, while other micro/nanosats have to use electric propulsion, compressed gas, vaporizable liquids such as butane or carbon dioxide or other innovative propulsion systems that are simple, cheap and scalable.
    Microsats can use conventional radio systems in UHF, VHF, the S-band and X-band, although often miniaturized using more up-to-date technology as compared to larger satellites. Tiny satellites such as nanosats and small microsats may lack the power supply or mass for large conventional radio transponders, and various miniaturized or innovative communications systems have been proposed, such a laser receivers, antenna arrays and satellite to satellite communication networks. Few of these have been demonstrated in practice.
    Electronics need to be rigorously tested and modified to be "space hardened" or resistant to the outer space environment (vacuum, microgravity, thermal extremes, and radiation exposure). Miniaturized satellites allow for the opportunity to test new hardware with reduced expense in testing. Furthermore, since the overall cost risk in the mission is much lower, more up-to-date but less space-proven technology can be incorporated into micro and nanosats than can be used in much larger, more expensive missions with less appetite for risk.
    Manufacturers of microsatellites include SpaceDev and Surrey Satellite Technology Ltd.
    Manufacturers of nanosatellites include GomSpace, ISIS and UTIAS-SFL.
    SuitSat, a retired spacesuit fitted with some basic instrumentation and radio transmitting equipment and released into orbit in 2006, was an unconventional example of a low-cost microsatellite test platform.

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