CubeSat

A CubeSat (U-class spacecraft^[1]) is a type of miniaturized satellite for space research that is made up of multiples of 10×10×11.35 cm cubic units, has a mass of no more than 1.33 kilograms per unit,^[2] and often sees the use of commercial off-the-shelf (COTS) components for its electronics and structure. CubeSats are most commonly put in orbit by deployers on the International Space Station, or launched as secondary payloads on a launch vehicle.^[3]

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, manufacture, and testing of small satellites intended for low Earth orbit (LEO) that perform a number of scientific research functions and explore new space technologies. Academia accounted for the majority of CubeSat launches until 2013, when over half of launches were for non-academic purposes, and by 2014 most newly deployed CubeSats were for commercial or amateur projects.^[3] CubeSats have been built by large and small companies alike, while other projects have been the subject of Kickstarter campaigns.^[4]

Uses typically involve experiments which can be miniaturized or serve purposes such as Earth observation or amateur radio. Many CubeSats are used to demonstrate spacecraft technologies that are targeted for use in small satellites or that present questionable feasibility and are unlikely to justify the cost of a larger satellite. Scientific experiments with questionable underlying theory may also find themselves aboard CubeSats as their low cost could justify riskier experiments. Biological research payloads have been flown on several missions, with more planned.^[5] Several missions to the Moon and Mars are planned to use CubeSats.^[6]

Some CubeSats became the first national satellites of their countries, being launched by universities, state, or private companies.

History

The CubeSat reference design was proposed in 1999 by professors Jordi Puig-Suari of California Polytechnic State University and Bob Twiggs of Stanford University.^[7][8]: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.^[9]

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.^{[8]: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.^{[8]: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.^[10] 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.^[11] His efforts have focused on CubeSats from educational institutions.^[12] The specification does not apply to other cube-like nanosatellites such as the NASA "MEPSI" nanosatellite, which is slightly larger than a CubeSat.

Design

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.

Standard CubeSats are made up of 10×10×11.35 cm units designed to provide 10×10×10 cm or 1 liter of useful volume while weighing no more than 1.33 kg (2.9 lb) per unit. The smallest standard size is 1U, while 3U+ is the largest being composed of three units stacked lengthwise with an additional 6.4 cm diameter cylinder centered on the long axis and extending 3.6 cm beyond one face.^[2] The Aerospace Corporation has constructed and launched two smaller form CubeSats of 0.5U for radiation measurement and technological demonstration.^[13] In recent years larger CubeSat platforms have been proposed, most commonly 6U (10×20×30 cm or 12×24×36 cm^[14]) and 12U (20x20x30 cm or 24x24x36 cm^[14]), to extend the capabilities of CubeSats beyond academic and technology validation applications and into more complex science and national defense goals. In 2014 two 6U Perseus-M CubeSats were launched for maritime surveillance, those two CubeSats represent the largest CubeSats flown as of 2015. The 2016 launch of the InSight lander to Mars, will include two 6U CubeSats called Mars Cube One (MarCO).

Since nearly all CubeSats are 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), developed and built by Cal Poly.^[15]

No electronics form factors or communications protocols are specified or required by the CubeSat Design Specification, but COTS hardware has consistently utilized certain features which many treat as standards in CubeSat electronics. Most COTS and custom designed electronics fit the form of PC/104, which was not designed for CubeSats but presents a 90 × 96 mm profile that allows most of the spacecraft's volume to be occupied. Technically, the PCI-104 form is the variant of PC/104 used^[16] and the actual pinout used does not reflect the pinout specified in the PCI-104 standard. Stackthrough connectors on the boards allow for simple assembly and electrical interfacing and most manufacturers of CubeSat electronics hardware hold to the same signal arrangement, but some products do not, so care must be taken to ensure consistent signal and power arrangements to prevent damage.^[17]

Care must be taken in electronics selection to ensure the devices can tolerate the radiation present. For very low Earth orbits (LEO) in which atmospheric reentry would occur in just days or weeks, radiation can largely be ignored and standard consumer grade electronics may be used. Consumer electronic devices can survive LEO radiation for that time as the chance of a single event upset (SEU) is very low. Spacecraft in a sustained low Earth orbit lasting months or years are at risk and only fly hardware designed for and tested in irradiated environments. Missions beyond low Earth orbit or which would remain in low Earth orbit for many years must use radiation-hardened devices.^[18] Further considerations are made for operation in high vacuum due to the effects of sublimation, outgassing, and metal whiskers, which may result in mission failure.^[19]

Different classifications are used to categorize such miniature satellites based on mass.^[20] 1U CubeSats belong to the genre of picosatellites.

1. Minisatellite (100–500 kg)
2. Microsatellite (10–100 kg)
3. Nanosatellite (1–10 kg)
4. Picosatellite (0.1–1 kg)
5. Femtosatellite (0.01–0.1 kg)

Most CubeSats carry one or two scientific instruments as their primary mission payload.

Structure

The number of joined units classifies the size of CubeSats and according to the CubeSat Design Specification and are scalable along only one axis to fit the forms of 0.5U, 1U, 1.5U, 2U, or 3U. All the standard sizes of CubeSat have been built and launched, and represent the form factors for nearly all launched CubeSats as of 2015.^[22] Materials used in the structure must feature the same coefficient of thermal expansion as the deployer to prevent jamming. Specifically, allowed materials are four aluminum alloys: 7075, 6061, 5005, and 5052. Aluminum used on the structure which contacts the P-POD must be anodized to prevent cold welding, and other materials may be used for the structure if a waiver is obtained.^[2] Beyond cold welding, further consideration is put into material selection as not all materials can be used in vacuums. Structures often feature soft dampers at each end, typically made of rubber, to lessen the effects of impacting other CubeSats in the P-POD.

Protrusions beyond the maximum dimensions are allowed by the standard specification, to a maximum of 6.5 mm beyond each side. Any protrusions may not interfere with the deployment rails and are typically occupied by antennas and solar panels. In Revision 13 of the CubeSat Design Specification an extra available volume was defined for use on 3U projects. The additional volume is made possible by space typically wasted in the P-POD Mk III's spring mechanism. 3U CubeSats which utilize the space are designated 3U+ and may place components in a cylindrical volume centered on one end of the CubeSat. The cylindrical space has a maximum diameter of 6.4 cm and a height no greater than 3.6 cm while not allowing for any increase in mass beyond the 3U's maximum of 4 kg. Propulsion systems and antennas are the most common components that might require the additional volume, though the payload sometimes extends into this volume. Deviations from the dimension and mass requirements can be waived following application and negotiation with the launch service provider.^[2]

CubeSat structures do not have all the same strength concerns as larger satellites do, as they have the added benefit of the deployer supporting them structurally during launch. Still, some CubeSats will undergo vibration analysis or structural analysis to ensure that components unsupported by the P-POD remain structurally sound throughout the launch.^[23] Despite rarely undergoing the analysis that larger satellites do, CubeSats rarely fail due to mechanical issues.^[24]

Computing

Like larger satellites, CubeSats often feature multiple computers handling different tasks in parallel including the attitude control, power management, payload operation, and primary control tasks. COTS attitude control systems typically include their own computer, as do the power management systems. Payloads must be able to interface with the primary computer to be useful, which sometimes requires the use of another small computer. This may be due to limitations in the primary computer's ability to control the payload with limited communication protocols, to prevent overloading the primary computer with raw data handling, or to ensure payload's operation continues uninterrupted by the spacecraft's other computing needs such as communication. Still, the primary computer may be used for payload related tasks, which might include image processing, data analysis, and data compression. Tasks which the primary computer typically handles include the delegation of tasks to the other computers, attitude control, calculations for orbital maneuvers, scheduling, and activation of active thermal control components. CubeSat computers are highly susceptible to radiation and builders will take special steps to ensure proper operation in the high radiation of space, such as the use of the ECC RAM. Some satellites may incorporate redundancy by implementing multiple primary computers, this could be done on valuable missions to lessen the risk of mission failure. Consumer smartphones have been used for computing in some CubeSats, such as NASA's PhoneSats.

Attitude control

Attitude control for CubeSats relies on miniaturizing technology without significant performance degradation. Tumbling typically occurs as soon as a CubeSat is deployed, due to asymmetric deployment forces and bumping with other CubeSats. Some CubeSats operate normally while tumbling, but those that require pointing in a certain direction or cannot operate safely while spinning, must be detumbled. Systems that perform attitude determination and control include reaction wheels, magnetorquers, thrusters, star trackers, Sun sensors, Earth sensors, angular rate sensors, and GPS receivers and antennas. Combinations of these systems are typically seen in order to take each method's advantages and mitigate their shortcomings. Reaction wheels are commonly utilized for their ability to impart relatively large moments for any given energy input, but reaction wheel's utility is limited due to saturation, the point at which a wheel cannot spin faster. Examples of CubeSat reaction wheels include the Maryland Aerospace MAI-101^[25] and the Sinclair Interplanetary RW-0.03-4.^[26] Reaction wheels can be desaturated with the use of thrusters or magnetorquers. Thrusters can provide large moments by imparting a couple on the spacecraft but inefficiencies in small propulsion systems cause thrusters to run out of fuel rapidly. Commonly found on nearly all CubeSats are magnetorquers which run electricity through a solenoid to take advantage of Earth's magnetic field to produce a turning moment. Attitude-control modules and solar panels typically feature built-in magnetorquers. For CubeSats that only need to detumble, no attitude determination method beyond an angular rate sensor or electronic gyroscope is necessary.

Pointing in a specific direction is necessary for Earth observation, orbital maneuvers, maximizing solar power, and some scientific instruments. Directional pointing accuracy can be achieved by sensing Earth and its horizon, the Sun, or specific stars. Sinclair Interplanetary's SS-411 sun sensor^[27] and ST-16 star tracker^[28] both have applications for CubeSats and have flight heritage. Pumpkin's Colony I Bus uses an aerodynamic wing for passive attitude stabilization.^[29] Determination of a CubeSat's location can be done through the use of on-board GPS, which is relatively expensive for a CubeSat, or by relaying radar tracking data to the craft from Earth-based tracking systems.

Propulsion

CubeSat propulsion has made rapid advancements in the following technologies: cold gas, chemical propulsion, electric propulsion, and solar sails. The biggest challenge with CubeSat propulsion is preventing risk to the launch vehicle and its primary payload while still providing significant capability.^[30] Components and methods that are commonly used in larger satellites are disallowed or limited and the CubeSat Design Specification (CDS) requires a waiver for pressurization above 1.2 standard atmospheres, over 100 Wh of stored chemical energy, and hazardous materials.^[2] Those restrictions pose great challenges for CubeSat propulsion systems, as typical space propulsion systems utilize combinations of high pressures, high energy densities, and hazardous materials. Beyond the restrictions set forth by launch service providers, various technical challenges further reduce the usefulness of CubeSat propulsion. Gimbaled thrust cannot be used in small engines due to the complexity of gimbaling mechanisms, thrust vectoring must instead be achieved by thrusting asymmetrically in multiple-nozzle propulsion systems or by changing the center of mass relative to the CubeSat's geometry with actuated components.^[31] Small motors may also not have room for throttling methods that allow smaller than fully-on thrust, which is important for precision maneuvers such as rendezvous.^[32] CubeSats which require longer life also benefit from propulsion systems, when used for orbit keeping a propulsion system can slow orbital decay.

Cold gas thrusters

A cold gas thruster typically stores inert gas, such as nitrogen, in a pressurized tank and releases the gas through a nozzle to produce thrust. Operation is handled by just a single valve in most systems, which makes cold gas the simplest useful propulsion technology.^[33] Cold gas propulsion systems can be very safe since the gases used do not have to be volatile or corrosive, though some systems opt to feature dangerous gases such as sulfur dioxide.^[34] This ability to use inert gases is highly advantageous to CubeSats as they are usually restricted from hazardous materials. Unfortunately, only low performance can be achieved with them,^[33] preventing high impulse maneuvers even in low mass CubeSats. Due to this low performance, their use in CubeSats for main propulsion is limited and designers choose higher efficiency systems with only minor increases in complexity. Cold gas systems more often see use in CubeSat attitude control.

Chemical propulsion

Chemical propulsion systems use a chemical reaction to produce a high-pressure, high-temperature gas that accelerates out of a nozzle. Chemical propellant can be liquid, solid or a hybrid of both. Liquid propellants can be a monopropellant passed through a catalyst, or bipropellant which combusts an oxidizer and a fuel. The benefits of monopropellants are relatively low-complexity/high-thrust output, low power requirements, and high reliability. Monopropellant motors tend to have high thrust while remaining comparatively simple, which also provides high reliability. These motors are practical for CubeSats due to their low power requirements and because their simplicity allows them to be very small. Small hydrazine fueled motors have been developed,^[35] but may require a waiver to fly due to restrictions on hazardous chemicals set forth in the CubeSat Design Specification.^[2] Safer chemical propellants which would not require hazardous chemical waivers are being developed, such as AF-M315 (hydroxylammonium nitrate) for which motors are being or have been designed.^[35][36] A "Water Electrolysis Thruster" is technically a chemical propulsion system, as it burns hydrogen and oxygen which it generates by on-orbit electrolysis of water.^[37]

Electric propulsion

CubeSat electric propulsion typically uses electric energy to accelerate propellant to high speed, which results in high specific impulse. Many of these technologies can be made small enough for use in nanosatellites, and several methods are in development. Types of electric propulsion currently being designed for use in CubeSats include Hall-effect thrusters,^[38] ion thrusters,^[39] pulsed plasma thrusters,^[40] electrospray thrusters,^[41] and resistojets.^[42] Several notable CubeSat missions plan to use electric propulsion, such as NASA's Lunar IceCube.^[43] The high efficiency associated with electric propulsion could allow CubeSats to propel themselves to Mars.^[44] Electric propulsion systems are disadvantaged in their use of power, which requires the CubeSat to have larger solar cells, more complicated power distribution, and often larger batteries. Furthermore, many electric propulsion methods may still require pressurized tanks to store propellant, which is restricted by the CubeSat Design Specification.

The ESTCube-1 used an electric solar-wind sail, which is nothing like a solar sail, despite its name. This technology used an electric field to deflect protons from solar wind to produce thrust. It is similar to an electrodynamic tether in that the craft only needs to supply electricity to operate.

Solar sail

Solar sails (also called light sails or photon sails) are a form of spacecraft propulsion using the radiation pressure (also called solar pressure) from stars to push large ultra-thin mirrors to high speeds, requiring no propellant. Force from a solar sail scales with the sail's area, this makes sails well suited for use in CubeSats as their small mass results in the greater acceleration for a given solar sail's area. However, solar sails still need to be quite large compared to the satellite, which means useful solar sails must be deployed, adding mechanical complexity and a potential source of failure. This propulsion method is the only one not plagued with restrictions set by the CubeSat Design Specification, as it does not require high pressures, hazardous materials, or significant chemical energy. Few CubeSats have employed a solar sail as its main propulsion and stability in deep space, including the 3U NanoSail-D2 launched in 2010, and the LightSail-A in May 2015. LightSail-1 is scheduled for launch in April 2016,^[45][46] while at least two CubeSats that plan to launch on the Space Launch System's first flight in September 2018 are set to use solar sails, the proposed Near-Earth Asteroid Scout (NEA Scout)^[47] and the Lunar Flashlight.

Power

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.^[48] 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, propulsion systems, and access port. Lithium-ion batteries feature high energy-to-mass ratios, making them well suited to use on mass-restricted spacecraft. Battery charging and discharging is typically handled by a dedicated electrical power system (EPS). Batteries sometimes feature heaters^[49] to prevent the battery from reaching dangerously low temperatures which might cause battery and mission failure.^[50] Missions with higher power requirements can make use of attitude control to ensure the solar panels remain in their most effective orientation toward the Sun, and further power needs can be met through the addition and orientation of deployed solar arrays. Recent innovations include additional spring-loaded solar arrays that deploy as soon as the satellite is released, as well as arrays that feature thermal knife mechanisms that would deploy the panels when commanded. CubeSats may not be powered between launch and deployment, and must feature a remove-before-flight pin which cuts all power to prevent operation during loading into the P-POD. Additionally, a deployment switch is actuated while the craft is loaded into a P-POD, cutting power to the spacecraft and is deactivated after exiting the P-POD.^[2]

Telecommunications

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.^[20][51] They can use radio-communication systems in the VHF, UHF, L-, S-, C- and X-band.^[20] For UHF/VHF transmissions, a single helical antenna or four monopole antennae are deployed by a spring-loaded mechanism.^[20][51]

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.^[20][51] For example, MIT and JPL are developing an inflatable dish antenna with a useful range to the Moon.^[52]

Thermal management

Different CubeSat components possess different acceptable temperature ranges, beyond which they may become temporarily or permanently inoperable. Satellites in orbit are heated by radiative heat emitted from the Sun, Earth, sunlight reflected off Earth, as well as heat generated by the craft's components. CubeSats must also cool by radiating heat either into space or into the cooler Earth's surface, if it is cooler than the spacecraft. All of these radiative heat sources and sinks are rather constant and very predictable, so long as the CubeSat's orbit and eclipse time are known.

Components used to ensure the temperature requirements are met in CubeSats include multi-layer insulation and heaters for the battery. Other spacecraft thermal control techniques in small satellites include specific component placement based on expected thermal output of those components and, rarely, deployed thermal devices such as louvers. Analysis and simulation of the spacecraft's thermal model is an important determining factor in applying thermal management components and techniques. CubeSats with special thermal concerns, often associated with certain deployment mechanisms and payloads, may be tested in a thermal vacuum chamber before launch. Such testing provides a larger degree of assurance than full-sized satellites can receive, since CubeSats are small enough to fit inside of a thermal vacuum chamber in their entirety. Temperature sensors are typically placed on different CubeSat components so that action may be taken to avoid dangerous temperature ranges, such as reorienting the craft in order to avoid or introduce direct thermal radiation to a specific part, thereby allowing it to cool or heat.

Costs

CubeSat forms a cost-effective independent means of getting a payload into orbit.^[10] 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,^[53] by 2015 launch prices have been about $100,000 per unit,^[54][55] plus about $50,000 to construct a basic 1U CubeSat.^[56] These low launch costs have rendered CubeSats a viable option for schools and dozens of universities, as well as small businesses which develop their own CubeSats for commercial purposes. Some CubeSats have complicated components or instruments, such as LightSail-1, that pushes their construction cost into the millions.^[57]

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.^[58]

On February 13, 2012, three PPODs deployers 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).^[59]

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.^[60] 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).^[61]

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.^[62][63][64]

Four CubeSats were deployed from the Cygnus Mass Simulator, which was launched April 21, 2013 on the maiden flight of Orbital Sciences' Antares rocket.^[65] 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 on 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.^[66] To control the E-Sail element's interaction with both the plasma surrounding 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.^[67]

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.^[68]

Future projects

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 (2U) 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.^[69] The Request for Proposals (RFP) for the QB50 CubeSat was released on February 15, 2012.

2018 InSight mission: MarCO CubeSats

The 2018 launch, previously scheduled for 2016,^[70] of the InSight stationary lander to Mars, will include two CubeSats to flyby Mars to provide additional relay communications from InSight to Earth during entry and landing. This will be the first flight of CubeSats in deep space. The mission CubeSat technology is called Mars Cube One (MarCO), 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 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.

MarCO will launch in May 2018 with the InSight lander and will separate after launch and 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 their own course adjustments on the flight.

During InSight's planned entry, descent and landing (EDL) in September 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 on Earth several hours after, so MarCO would be a technology demonstration of real-time telemetry during the landing.^[71][72][73]

Cubesat Launch Initiative

NASA created in 2010 the 'Cubesat Launch Initiative' that aims to provide access to space for CubeSats developed by educational institutions and non-profit organizations.^[74] Selected experiments fly as auxiliary payloads on NASA rocket launches or are deployed from the International Space Station.^[75]

NASA’s Cube Quest Challenge

NASA initiated its Cube Quest Challenge in 2015, a competition to foster innovation in the use of cubesats beyond low-earth orbit. Teams compete for the opportunity to launch their cubesat design into orbit around the moon in 2018.^[76]

Launch and deployment

Unlike full-sized spacecraft, CubeSats have the ability to be delivered into space as cargo and then deployed by the International Space Station. This presents an alternative method of achieving orbit apart from launch and deployment by a launch vehicle. NanoRacks and Made in Space are developing means of constructing CubeSats on the International Space Station.^[77]

Current launch systems

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.^[78] 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.^[78] Since CubeSats are deployed by P-PODs and similar deployment systems, they can be integrated and launched into virtually any launch vehicle. However, some launch service providers refuse to launch CubeSats, whether on all launches or only on specific launches, two examples are ILS and Sea Launch.^[79]

SpaceX^[80][81] and Japan Manned Space Systems Corporation (JAMSS)^[82][83] are two recent companies that offer commercial launch services for CubeSats as secondary payload, but a launch backlog still exists. Additionally, India's ISRO has been commercially launching foreign CubeSats since 2009 as secondary payloads.^[84] ISC Kosmotras and Eurockot also offer launch services for CubeSats.^[85]

Future and proposed launch systems

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),^[78][86][87] which will offer a payload mass of 30 kg to 60 kg for each launcher.^[86][88] Five months later, in October 2015, NASA awarded a total of $17.1 million to three separate startup launch companies for one flight each: $6.9 million to Rocket Lab (Electron rocket); $5.5 million to Firefly Space Systems (Alpha rocket); and $4.7 million to Virgin Galactic (LauncherOne rocket).^[89] The payloads for the three flights under the VCLS contract have not yet been assigned.^[89] Other small satellite launch systems are under development that would carry CubeSats alongside a small payload, including the Neptune series of rockets by Interorbital Systems, Garvey Spacecraft's Nanosat Launch Vehicle,^[90] and the Super Strypi. In addition to conventional launch vehicles, several air launch to orbit vehicles are in the works by Swiss Space Systems, Generation Orbit Launch Services, and Boeing (in the form of their Small Launch Vehicle).

As of December 2015, only one launch vehicle that emphasizes small CubeSat payloads has made a launch attempt, the Super Strypi, broke up shortly after launch on 4 November 2015. The rocket was carrying 12 CubeSats of various sizes along with its 55 kilogram primary payload.^[91]

Rocket Lab plans to launch cubesat's in New Zealand after the Mahia launch site is completed in the first quarter of 2016^[92][93]

Deployment

P-PODs were designed with CubeSats to provide a common platform for secondary payloads. 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. The P-POD Mk III has capacity for three 1U CubeSats, or other 0.5U, 1U, 1.5U, 2U, or 3U CubeSats combination up to a maximum volume of 3U.^[94] Other CubeSat deployers exist, with the NanoRacks CubeSat Deployer (NRCSD) on the International Space Station being the most popular method of CubeSat deployment as of 2014.^[3] Some CubeSat deployers are created by companies, such as the ISIPOD (Innovative Solutions In Space BV) or SPL (Astro und Feinwerktechnik Adlershof GmbH), while some have been created by governments or other non-profit institutions such as the X-POD (University of Toronto), T-POD (University of Tokyo), or the J-SSOD (JAXA) on the International Space Station.^[95] While the P-POD is limited to launching a 3U CubeSat at most, the NRCSD can launch a 6U (10×10×68.1 cm) CubeSat and the ISIPOD can launch a different form of 6U CubeSat (10×22.63×34.05 cm).

While nearly all CubeSats are deployed from a launch vehicle or the International Space Station, some are deployed by the primary payloads themselves. For example, FASTSAT deployed the NanoSail-D2, a 3U CubeSat designed by the same contractor as FASTSAT, Orbital Sciences Corporation. This was done again with the Cygnus Mass Simulator as the primary payload launched on the maiden flight of the Antares rocket, carrying and later deploying four CubeSats. For CubeSat applications beyond Earth's orbit, the method of deploying the satellites from the primary payload will also be adopted. Eleven CubeSats are planned to be launched on the Space Launch System's Exploration Mission 1, which would place them in the vicinity of the Moon. Insight, a planned Mars lander, will also bring CubeSats beyond Earth orbit to use them as relay communications satellites. Known as MarCO A and B, they would be the first CubeSats sent beyond the Earth-Moon system.

Chasqui I saw a very unique deployment process, when it was deployed by hand during a spacewalk on the International Space Station in 2014.

See also

• AMSAT
• Canadian Advanced Nanospace eXperiment Program
• Cubesat Space Protocol
• Israeli Nano Satellite Association
• Lunar IceCube
• Nanosatellite Launch System
• OSCAR

References

External links

Wikimedia Commons has media related to CubeSat satellites.

• Cubesat introduction, 2-minute video at DIY Space Exploration
• CubeSat Program official website Contains information about upcoming launches
• Amsat's list of CubeSats (generally kept well up to date)