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Small satellites, or smallsats, are 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.
- 1 Rationales
- 2 History
- 3 Classification groups
- 4 Technical challenges
- 5 See also
- 6 References
- 7 External links
|Group name||Mass (kg)|
|Medium satellite||500 to 1000|
|Mini satellite||100 to 500|
|Micro satellite||10 to 100|
|Nano satellite||1 to 10|
|Pico satellite||0.1 to 1|
One rationale for miniaturizing satellites is to reduce the cost: heavier satellites require larger rockets with greater thrust that 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.
Another major reason for developing small 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, and was based on the Spanish low cost manufacturing for Commercial and Communication Satellites from the 1990s. Development activity in the 1–50 kg (2.2–110.2 lb) range has been significantly exceeding that in the 50–100 kg (110–220 lb) 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.
European analyst Euroconsult projects more than 500 smallsats being launched in the years 2015–2019 with a market value estimated at US$7.4 billion.
The term "small satellite", or sometimes "minisatellite", often refers to an artificial satellite with a wet mass (including fuel) between 100 and 500 kg (220 and 1,100 lb), but in other usage has come to mean any satellite under 500 kg (1,100 lb).
Small satellite launch vehicle
Although smallsats have traditionally been launched as secondary payloads on larger launch vehicles, there are a number of companies currently developing launch vehicles specifically targeted at the smallsat market. In particular, the secondary payload paradigm does not provide the specificity required for many small satellites that have unique orbital and launch-timing requirements.
Companies planning small sat launch vehicles include:
- Virgin Galactic's LauncherOne (100 kg)
- Firefly Space Systems' Alpha (400 kg).
- Rocket Lab's Electron (150 kg)
- PLD Space (150 kg) 
The term "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 those terms can refer to satellites larger than that, or smaller than that (e.g., 1–50 kg (2.2–110.2 lb)). Sometimes designs or proposed designs from some satellites of these types have microsatellites working together or in a formation. The generic term "small satellite" or "smallsat" is also sometimes used, as is "satlet".
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 that have unique orbital and launch-timing requirements.
In July 2012, Virgin Galactic announced LauncherOne, an orbital launch vehicle designed to launch "smallsat" primary payloads of 100 kg (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, and, as of 2015[update], is making it a larger part of Virgin's core business plan as the Virgin human spaceflight program has experienced multiple delays as well as a fatal accident in 2014.
In December 2012, DARPA announced that the Airborne Launch Assist Space Access program would provide the microsatellite rocket booster for another DARPA program that is intending to release a "constellation of 24 micro-satellites (~20 kg (44 lb) range) each with 1-meter imaging resolution." The program was cancelled in December 2015.
In April 2013, Garvey Spacecraft was awarded a US$200,000 contract to evolve their Prospector 18 suborbital launch vehicle technology into an orbital nanosat launch vehicle capable of delivering a 10 kg (22 lb) payload into a 250 km (160 mi) orbit to an even-more-capable clustered "20/450 Nano/Micro Satellite Launch Vehicle" (NMSLV) capable of delivering 20 kg (44 lb) payloads into 450 km (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 45 kg (100 lb) 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, as of 2012[update] could 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 kg (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 times: every area of the globe can be imaged every 3.5 hours rather than the once per 24 hours with the RapidEye constellation. More rapid revisit times are a significant improvement for nations performing 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.
Example satellites: ExoCube (CP-10)
In the ten years of nanosat launches prior to 2014, only 75 nanosats were launched. Launch rates picked up substantially when in the three-month period from November 2013–January 2014 94 nanosats were launched.
One challenge of using nanosats has been the economic delivery of such small satellites to anywhere beyond low-Earth orbit. By late 2014, proposals were being developed for larger spacecraft specifically designed to deliver swarms of nanosats to trajectories that are beyond Earth orbit for applications such as exploring distant asteroids.
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 (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)
- 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 kg (22 lb) payload into a 250 km (160 mi) orbit.
- Generation Orbit is developing an air-launched rocket to deliver both nanosats and sub-50 kg microsats to low Earth orbit.
- NASA launched three satellites on 21 April 2013 based on smart phones. Two phones use the PhoneSat 1.0 specification and the third used a beta version of PhoneSat 2.0
- ISRO launched 14 nanosatellites on 22 June 2016, 2 for Indian universities and 12 for the United States under the Flock-2P program. This launch was performed during the PSLV-C34 mission.
- ISRO launched 103 nanosatellites on 15 February 2017. This launch was performed during the PSLV-C37 mission.
The term "picosatellite" or "picosat" (not to be confused with the PicoSAT series of microsatellites) is usually applied to artificial satellites with a wet mass between 0.1 and 1 kg (0.22 and 2.2 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 kitbuilders. Picosatellites are currently commercially available across the full range of 0.1–1 kg (0.22–2.2 lb). 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.
The term "femtosatellite" or "femtosat" is usually applied to artificial satellites with a wet mass between 10 and 100 g (0.35 and 3.5 oz). Like picosatellites, some designs require a larger "mother" satellite for communication with ground controllers.
Three prototype "chip satellites" were launched to the ISS on Space Shuttle Endeavour on its final mission in May 2011. They were attached to the ISS external platform Materials International Space Station Experiment (MISSE-8) for testing. In March 2014, the nanosatellite KickSat was launched aboard a Falcon 9 rocket with the intention of releasing 104 femtosatellite-sized chipsats, or "Sprites". ThumbSat is another project intending to launch femtosatellites in 2016.
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Small satellites usually require innovative propulsion, attitude control, communication and computation systems.
Larger satellites usually use monopropellants or bipropellant combustion systems for propulsion and attitude control; these systems are complex and require a minimal amount of volume to surface area to dissipate heat. These systems may be used on larger small satellites, 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.
Small satellites can use conventional radio systems in UHF, VHF, 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 as 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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