A CubeSat (U-class spacecraft) is a type of miniaturized satellite for space research that usually has a volume of exactly one liter (10 cm cube), has a mass of no more than 1.33 kilograms, and typically uses commercial off-the-shelf components for its electronics.
Beginning in 1999, California Polytechnic State University (Cal Poly) and Stanford University developed the CubeSat specifications to promote and develop the skills necessary for the design, manufacturing, and testing of small satellites intended for low Earth orbit (LEO) that perform a number of scientific research and explore new space technologies. Although the bulk of development and launches comes from academia, several companies build CubeSats such as large-satellite-maker Boeing, and several small companies. CubeSat projects have also been the subject of Kickstarter campaigns. The CubeSat format is also popular with amateur radio satellite builders.
The CubeSat reference design was proposed in 1999 by professors Jordi Puig-Suari of California Polytechnic State University and Bob Twiggs of Stanford University.:159 The goal was to enable graduate students to be able to design, build, test and operate in space a spacecraft with capabilities similar to that of the first spacecraft, Sputnik. The CubeSat as initially proposed did not set out to become a standard; rather, it became a standard over time by a process of emergence. The first CubeSats were launched in June 2003 on a Russian Eurockot, and approximately 75 CubeSats had been placed into orbit by 2012.
The need for such a small-factor satellite became apparent in 1998 as a result of work done at Stanford University's Space System Development Laboratory. At SSDL students had been working on the OPAL (Orbiting Picosatellite Automatic Launcher) microsatellite since 1995. OPAL's mission to deploy daughter-ship "picosatellites" had resulted in the development of a launcher system that was "hopelessly complicated" and could only be made to work "most of the time". With the project's delays mounting, Twiggs sought out DARPA funding that resulted in the redesign of the launching mechanism into a simple pusher plate concept with the satellites held in place by a spring-loaded door.:151–157
Desiring to shorten the development cycle experienced on OPAL and inspired by the picosatellites OPAL carried, Twiggs set out to find "how much could you reduce the size and still have a practical satellite". The picosatellites on OPAL were 10.1×7.6×2.5 cm, a size that was not conducive to covering all sides of the spacecraft with solar cells. Inspired by a 4-inch cubic plastic box used to display Beanie Babies in stores, Twiggs first settled on the larger 10-centimeter cube as a guideline for the new (yet-to-be-named) CubeSat concept. A model of a launcher was developed for the new satellite using the same pusher plate concept that had been used in the modified OPAL launcher. Twiggs presented the idea to Puig-Suari in the summer of 1999 and then at the Japan-U.S. Science, Technology, and Space Applications Program (JUSTSAP) conference in November 1999.:157–159
The term "CubeSat" was coined to denote nanosatellites that adhere to the standards described in the CubeSat design specification. Cal Poly published the standard in an effort led by aerospace engineering professor Jordi Puig-Suari. Bob Twiggs, of the Department of Aeronautics & Astronautics at Stanford University, and currently a member of the space science faculty at Morehead State University in Kentucky, has contributed to the CubeSat community. His efforts have focused on CubeSats from educational institutions. The specification does not apply to other cube-like nanosatellites such as the NASA "MEPSI" nanosatellite, which is slightly larger than a CubeSat.
The CubeSat specification accomplishes several high-level goals. The main reason for miniaturizing satellites is to reduce the cost of deployment and are often suitable for launch in multiples, using the excess capacity of larger launch vehicles. The CubeSat design specifically minimizes risk to the rest of the launch vehicle and payloads. Encapsulation of the launcher–payload interface takes away the amount of work that would previously be required for mating a piggyback satellite with its launcher. Unification among payloads and launchers enables quick exchanges of payloads and utilization of launch opportunities on short notice.
The standard 10×10×10 cm basic CubeSat is often called a "one unit" or 1U CubeSat, has a volume of one liter, and weighs no more than 1 kg (2.2 lb). They are scalable along only one axis, by 1U increments. CubeSats such as a 2U CubeSat (20×10×10 cm) and a 3U CubeSat (30×10×10 cm) have been built and launched. In recent years larger CubeSat platforms have been proposed, most commonly 6U (10×20×30 cm or 12×24×36 cm) and 12U (20x20x30 cm or 24x24x36 cm), to extend the capabilities of CubeSats beyond academic and technology validation applications and into more complex science and national defense goals.
Since CubeSats are all 10×10 cm (regardless of length) they can all be launched and deployed using a common deployment system called a Poly-PicoSatellite Orbital Deployer (P-POD), also developed and built by Cal Poly. P-PODs are mounted to a launch vehicle and carry CubeSats into orbit and deploy them once the proper signal is received from the launch vehicle. P-PODs have deployed over 90% of all CubeSats launched to date, and 100% of all CubeSats launched since 2006. The P-POD Mk III has capacity for three 1U CubeSats, or other 1U, 2U, or 3U CubeSats combination up to a maximum volume of 3U.
- Minisatellite (100–500 kg)
- Microsatellite (10–100 kg)
- Nanosatellite (1–10 kg)
- Picosatellite (0.1–1 kg)
- Femtosatellite (0.01–0.1 kg)
Propulsion and attitude control
For mission safety, only a few CubeSats are equipped with a propulsion system that enables orbit correction or attitude control. Attitude control (or pointing control) has always been challenging due primarily to volumetric constraints and lack of small attitude sensors. Hence, most CubeSat control designs rely on general tumbling or, at best, magnetic rate control with large attitude errors. New proposals, for instance, may use solar-electric propulsion (ion thrusters), compressed gas, vaporizable liquids, such as butane or carbon dioxide, or other innovative propulsion systems that are simple, cheap and scalable. One such example was the Illinois Observing Nanosatellite (ION) 2U CubeSat, which used three magnetic torque coils for 3-axis control of the satellite. It was built by the University of Illinois and destroyed at launch. Another example is hydrogen propulsion by on-orbit electrolysis of water.
Other innovations employ a solar sail as its main propulsion and stability in deep space; three examples are the 3U NanoSail-D2 launched in 2010, the LightSail-1 scheduled for launch in April 2016, and the proposed Near-Earth Asteroid Scout (NEA Scout). The ESTCube-1 used an electric solar-wind sail. The ambitious 'Time Capsule to Mars' is a student-led project at the Duke University that proposes to use an electric propulsion concept under development at MIT called ion electrospray propulsion, a miniature form of electric propulsion and attitude control.
CubeSats use solar cells to convert solar light to electricity that is then stored in rechargeable lithium-ion batteries that provide power during eclipse as well as during peak load times. These satellites have a limited surface area on their external walls for solar cells assembly, and has to be effectively shared with other parts, such as antennas, optical sensors, camera lens, and access port. Recent innovations include additional spring-loaded solar arrays that deploy as soon as the satellite is released.
The low cost of CubeSats has enabled unprecedented access to space for smaller institutions and organizations but, for most CubeSat forms, the range and available power is limited to about 2W for its communications antennae. They can use radio-communication systems in the VHF, UHF, L-, S-, C- and X-band. For UHF/VHF transmissions, a single helical antenna or four monopole antennae are deployed by a spring-loaded mechanism.
Because of tumbling and low power range, radio-communications are a challenge. Many CubeSats use an omnidirectional monopole or dipole antenna built with commercial measuring tape. For more demanding needs, some companies offer high-gain antennae for CubeSats, but their deployment and pointing systems are significantly more complex. For example, MIT and JPL are developing an inflatable dish antenna with a useful range to the Moon.
CubeSat forms a cost-effective independent means of getting a payload into orbit. With their relatively small size, 1U CubeSats could each be made and launched to low Earth orbit (LEO) for an estimated cost (2014) of $65,000 to $80,000. After delays from low-cost launchers such as Interorbital Systems, by 2015 launch prices have been $100,000–$125,000, plus approximately $10,000 to construct the CubeSat. This price tag, far lower than most satellite launches, has made CubeSat a viable option for schools and dozens of universities and some companies around the world to develop their own CubeSats.
Notable past missions
One of the earliest CubeSat launches was on 30 June 2003 from Plesetsk, Russia, with Eurockot Launch Services's Multiple Orbit Mission. CubeSats were put into a Sun-synchronous orbit and included the Danish AAU CubeSat and DTUSat, the Japanese XI-IV and CUTE-1, the Canadian Can X-1, and USA's Quakesat.
On February 13, 2012, three PPODs containing seven CubeSats were placed into orbit along with the Lares satellite aboard an Avio Vega rocket launched from French Guyana. The CubeSats launched were e-st@r (Politecnico di Torino, Italy), Goliat (University of Bucarest, Romania), Masat-1 (Budapest University of Technology and Economics, Hungary), PW-Sat (Warsaw University of Technology, Poland), Robusta (University of Montpellier 2, France), UniCubeSat-GG (University of Rome La Sapienza, Italy), and XaTcobeo (University of Vigo and INTA, Spain).
On September 13, 2012, eleven CubeSats were launched from eight P-PODs, as part of the "OutSat" secondary payload aboard a United Launch Alliance Atlas V rocket. This was the largest number of CubeSats (and largest volume of 24U) successfully placed to orbit on a single launch, this was made possible by use of the new NPS CubeSat Launcher system (NPSCuL) developed at the Naval Postgraduate School (NPS). The following CubeSats were placed in orbit: SMDC-ONE 2.2 (Baker), SMDC-ONE 2.1 (Able), AeroCube 4.0(x3), Aeneas, CSSWE, CP5, CXBN, CINEMA, and Re (STARE).
Five CubeSats (Raiko, Niwaka, We-Wish, TechEdSat, F-1) were placed into orbit from the International Space Station on October 4, 2012, as a technology demonstration of small satellite deployment from the ISS. They were launched and delivered to ISS as a cargo of Kounotori 3, and an ISS astronaut prepared the deployment mechanism attached to Japanese Experiment Module's robotic arm.
Four CubeSats were deployed from the Cygnus Mass Simulator, which was launched April 21, 2013 on the maiden flight of Orbital Sciences' Antares rocket. Three of them are 1U PhoneSats built by NASA's Ames Research Center to demonstrate the use of smart phones as avionics in CubeSats. The fourth was a 3U satellite, called Dove-1, built by Planet Labs.
The working principles of the theoretical electric solar wind sail (E-Sail) propulsion underwent successful testing in 7 May 2013 with the ESTCube-1, developed as part of the Estonian Student Satellite Program. During the ESTCube-1 flight, 10 meters of 20–50 micrometer thick E-Sail wire were deployed from the satellite to affect the attitude control. To control the E-Sail element's interaction with both the plasma surrounding the Earth and the effect it has on the spacecraft's spinning speed, the students adapted two miniaturized electron emitters connected to the E-Sail element which it loads positively to 500 volts by shooting out electrons. The positive ions in the plasma push the E-Sail element and influence the satellite's rotation speed.
A total of thirty-three CubeSats were deployed from the ISS on February 11, 2014. Of those thirty-three, twenty-eight were part of the Flock-1 constellation of Earth-imaging CubeSats. Of the other five, two are from other US-based companies, two from Lithuania, and one from Peru.
The LightSail-A is a 3U CubeSat prototype propelled by a solar sail. It was launched on 20 May 2015 from Florida. Its four sails are made of very thin Mylar and have a total area of 32 m2. This test will allow a full checkout of the satellite's systems in advance of the main 2016 mission.
An ambitious project is the QB50, an international network of 50 CubeSats for multi-point, in-situ measurements in the lower thermosphere (90–350 km) and re-entry research. QB50 is an initiative of the Von Karman Institute and is funded by the European Union. Double-unit (2-U) CubeSats (10×10×20 cm) are foreseen, with one unit (the 'functional' unit) providing the usual satellite functions and the other unit (the 'science' unit) accommodating a set of standardised sensors for lower thermosphere and re-entry research. 35 CubeSats are envisaged to be provided by universities in 19 European countries, 10 by universities in the US, 2 by universities in Canada, 3 by Japanese universities, 1 by an institute in Brazil, and others. Ten 2U or 3U CubeSats are foreseen to serve for in-orbit technology demonstration of new space technologies. All 50 CubeSats will be launched together on a single Cyclone-4 launch vehicle in February 2016. The Request for Proposals (RFP) for the QB50 CubeSat was released on February 15, 2012.
2016 InSight mission: MarCO CubeSats
The 2016 launch of the InSight stationary lander to Mars, will include two CubeSats to flyby Mars and provide communications from InSight to Earth during entry and landing. This will be the first flight of CubeSats in deep space. The mission CubeSats technology is called Mars Cube One (MarCO). The basic CubeSat unit is a box roughly 4 inches (10 centimeters) square. MarCO's design is a six-unit CubeSat, 14.4 inches (36.6 centimeters) by 9.5 inches (24.3 centimeters) by 4.6 inches (11.8 centimeters).
MarCO will launch in March 2016 from Vandenberg Air Force Base, California on the same Atlas V rocket as the InSight lander. Insight is NASA’s first mission to understand the interior of Mars. MarCO will fly by Mars while InSight is landing, September 2016. The two CubeSats will separate from the Atlas V booster after launch then travel in their own trajectories to Mars. After separation, MarCO will deploy two radio antennas and two solar panels. The high-gain, X-band antenna is a flat panel to direct radio waves. MarCO will navigate to Mars independently from the InSight lander, making its own course adjustments on the flight. Marco is an experiment, but not necessary for the InSight mission, to add relay communications to space missions in important time durations, in this landing from the time of InSight atmospheric entry and landing.
During InSight’s planned entry, descent and landing(EDL) Sept. 28, 2016, the lander will transmit information in the UHF radio band to NASA's Mars Reconnaissance Orbiter (MRO) flying overhead. MRO will forward EDL information to Earth using a radio frequency in the X band, but cannot simultaneously receive information in one band if transmitting on another. Confirmation of a successful landing could be received by the MRO an hour before it’s relayed to Earth. MarCO’s radio provides both UHF (receive only) and X-band (receive and transmit) functions capable of immediately relaying information received over UHF, not capable with MRO.
NASA has launched more than 30 CubeSats over the last several years, and as of 2015, it has a backlog of more than 50 awaiting launch. No matter how inexpensive or versatile CubeSats may be, they must hitch rides as secondary payload on large rockets launching much larger spacecraft, at prices starting around $100,000.
SpaceX and Japan Manned Space Systems Corporation (JAMSS) are two recent companies that offer commercial launch services for CubeSats as secondary payload, but a launch backlog still exists. Meanwhile, India's ISRO has been commercially launching foreign CubeSats since 2009 as secondary payloads.
On 5 May 2015, NASA announced a program based at the Kennedy Space Center dedicated to develop a new class of rockets designed specifically to launch very small satellites: the NASA Venture Class Launch Services (VCLS), which will offer a payload mass of 30 kg to 60 kg for each launcher.
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