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Miniaturized satellites or small satellites are artificial satellites of low mass and size, usually under 500 kg (1,100 lb). 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 with greater thrust which also has greater cost to finance. In contrast, 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
- University-related research
The nanosatellite and microsatellite segments of the satellite launch industry have been growing rapidly in recent years. Development activity in the 1–50 kg range has been significantly exceeding that in the 50–100 kg range.
In the 1–50 kg range alone, there were fewer than 15 satellites launched annually in 2000 to 2005, 34 in 2006, then fewer than 30 launches annually during 2007 to 2011. This rose to 34 launched in 2012, and 92 launched in 2013.
The term "small satellite", or sometimes "minisatellite," usually refers to an artificial satellite with a "wet mass" (including fuel) between 100 and 500 kg (220 and 1,100 lb),. Small satellites are usually simpler but use the same technologies as larger satellites.
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, or smaller than that (e.g., 1 and 50 kg (2.2 and 110.2 lb)). Sometimes designs or proposed designs from some sats of these types have microsatellites working together or in a formation. The generic term "small satellite" or "smallsat" is also sometimes used.
Except the mass,[clarification needed] the size of satellite is important too.
Microsatellite launch vehicle
A number of commercial and military-contractor companies are currently developing microsatellite launch vehicles to perform the increasingly-targeted launch requirements of microsatellites. While microsatellites have been carried to space for many years as secondary payloads aboard larger launchers, the secondary payload paradigm does not provide the specificity required for many increasingly sophisticated small satellites which have unique orbital and launch-timing requirements.
In July 2012, Virgin Galactic announced LauncherOne, an orbital launch vehicle designed to launch "smallsat" payloads of 100 kilograms (220 lb) into low-Earth orbit, with launches projected to begin in 2016. Several commercial customers have already contracted for launches, including GeoOptics, Skybox Imaging, Spaceflight Services, and Planetary Resources. Both Surrey Satellite Technology and Sierra Nevada Space Systems are developing satellite buses "optimized to the design of LauncherOne." Virgin Galactic has been working on the LauncherOne concept since late 2008.
In December 2012, DARPA announced that the DARPA ALASA program would provide the microsat launch vehicle booster for another DARPA program that is intending to release a "constellation of 24 micro-satellites (~20 kilograms (44 lb) range) each with 1-meter imaging resolution."
In April 2013, Garvey Spacecraft was awarded a USD$200,000 contract to evolve their Prospector 18 suborbital launch vehicle technology into an orbital nanosat launch vehicle capable of delivering a 10 kilograms (22 lb) payload into a 250 kilometres (160 mi) orbit to an even-more-capable clustered "20/450 Nano/Micro Satellite Launch Vehicle" (NMSLV) capable of delivering 20 kilograms (44 lb) payloads into 450 kilometres (280 mi) circular orbits.
The Boeing Small Launch Vehicle is an air-launched three-stage-to-orbit launch vehicle concept aimed to launch small payloads of 100 pounds (45 kg) into low-Earth orbit. The program is proposed to drive down launch costs for U.S. military small satellites to as low as US$300,000 per launch ($7,000/kg) and, if the development program was funded, could be as of 2012[update] be operational by 2020.
The Swiss company Swiss Space Systems (S3) has announced plans in 2013 to develop a suborbital spaceplane named SOAR that would launch a microsat launch vehicle capable of putting a payload of up to 250 kilograms (550 lb) into low-Earth orbit.
The term "nanosatellite" or "nanosat" is applied to an artificial satellite with a wet mass between 1 and 10 kg (2.2 and 22.0 lb). Designs and proposed designs of these types may be launched individually, or they may have multiple nanosatellites working together or in formation, in which case, sometimes the term "satellite swarm"  or "fractionated spacecraft" may be applied. Some designs require a larger "mother" satellite for communication with ground controllers or for launching and docking with nanosatellites.
With continued advances in the miniaturization and capability increase of electronic technology and the use of satellite constellations, nanosatellites are increasingly capable of performing commercial missions that previously required microsatellites. For example, a 6U CubeSat standard has been proposed to enable a constellation of 35 8 kg (18 lb) Earth-imaging satellites to replace a constellation of five 156 kg (344 lb) RapidEye Earth-imaging satellites, at the same mission cost, with significantly increased revisit time: every area of the globe can be imaged every 3.5 hours rather than the once per 24 hours with RapidEye constellation. More rapid revisit time is a significant improvement for nations doing disaster response, which was the purpose of the RapidEye constellation. Additionally, the nanosat option would allow more nations to own their own satellite for off-peak (non-disaster) imaging data collection.
Nanosatellite launch vehicle
With the emergence of the technological advances of miniaturization and increased capital to support private spaceflight initiatives in the 2010s, several startups have been formed to pursue opportunities with developing a variety of small-payload Nanosatellite Launch Vehicle or NLV technologies.
NLVs proposed or under development include:
- Virgin Galactic LauncherOne upper stage, intended to be air-launched from WhiteKnightTwo similar to how the SpaceShipTwo spaceplane is launched.
- Ventions Nanosat upper stage.
- Nammo/Andøya North Star (polar orbit-capable launcher for a 10 kg (22 lb) payload)
- The United States Army is developing the SWORDS launcher, aimed to deploy nanosatellites into "precise orbits from almost any location at an ultra-low cost." SWORDS is an acronym for Soldier-Warfighter Operationally Responsive Deployer for Space. Design payloads could be as large as 25 kg (55 lb). The Army expects to make the initial orbital test flight during the summer of 2013.
- As of April 2013[update], Garvey Spacecraft is evolving their Prospector 18 suborbital launch vehicle technology into an orbital nanosat launch vehicle capable of delivering a 10 kilograms (22 lb) payload into a 250 kilometres (160 mi) orbit.
- NASA launched three satellites on April 21, 2013 based on smart phones. Two phones use the PhoneSat 1.0 specification and third used a beta version of PhoneSat 2.0
Picosatellite or "picosat" (not to be confused with the PicoSAT series of microsatellites) is usually applied as the name of an artificial satellite with a wet mass between 0.1 and 1 kg (0.22 and 2.20 lb), although it is sometimes used to refer to any satellite that is under 1 kg in launch mass. 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 approximately 1 kilogram (2.2 lb) mass, is an example of a large picosatellite (or minimum nanosat).
Picosatellites are emerging as a new alternative for Do It Yourself (DIY) kitbuilders. Picosatellites are currently commercially available across the full range of 0.1–1 kilogram (3.5–35.3 oz). Launch opportunities are now available for $12,000 to $18,000 for sub-1 kg picosat payloads that are approximately the size of a soda can. as well as for the much smaller "Sprite" picosatellite whose builder, KickSat, plans to launch 250 of the "cracker-size satellites" into low-Earth orbit (LEO) on a SpaceX Falcon 9 launch vehicle in March 2014.
Femtosatellite or "femtosat" is usually applied as the name of an artificial satellite with a wet mass between 10 and 100 g (0.35 and 3.53 oz). Like picosatellites, some designs require a larger "mother" satellite for communication with ground controllers. KickSat Sprites "chipsats" would be in this weight class.
Three prototype "chip satellites" were launched to the ISS on Space Shuttle Endeavor on its final mission in May 2011. They were attached to the ISS external platform Materials International Space Station Experiment (MISSE-8) for testing.
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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.
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