CubeSats

CubeSats are a class of research spacecraft called nanosatellites. CubeSats are built to standard dimensions of 4 in x 4 in x 4 in. They typically weigh less than (3 lbs). NASA’s CubeSats are deployed from a Poly-Picosatellite Orbital Deployer, or P-POD.

The P-POD is a standard deployment system that
ensures all CubeSat developers conform to common physical requirements. The P-POD
plays a critical role as the interface between the launch vehicle and CubeSats.

It utilizes a tubular design and can hold up to 12 in x 4 in x 4 in of deployable hardware. The most common configuration is three picosatellites of equal size; however, CubeSats of
different lengths can be accommodated in the same P-POD. Started in 1999, the CubeSat program was a joint effort between Cal Poly and Stanford University to develop a new class of picosatellites: the CubeSat standard. This standard is defined in the CubeSat Design Specification (CDS).

It includes information regarding nominal
dimensions of the standard, the dimension tolerances, acceptable materials, the reference coordinate system, accessible areas once inside the P-POD, and other general information.

Professors Jordi Puig-Suari and Bob Twiggs wanted their students to design, build, test, and operate a low-cost, low-mass (for reduced launch costs) satellite in space, within a timeframe of a year or two. The first CubeSats were launched in June 2003, and there are now currently 461 CubeSat missions in space.

The communications system (COM) is severely limited by the amount of power available, which is usually around 2W. Compared to Boeing’s 702SP Spacecraft, which uses a Xenon Electrostatic ion thruster system (XIPS), operates in the low-to mid-power range of satellites, and has three to eight kilowatts of power, CubeSats’ power is exponentially less.

CubeSats use radio-communication systems in VHF, UHF, F-, S-, C- and X-band. The satellite uses an antenna, usually deployed once in orbit to help with communication. Antennas range from commercial measuring tape to more complicated inflatable dish antennas. The electrical power system (EPS) consists of solar panels and batteries.

Solar panels hold solar cells that convert the solar light from the sun to electricity. Batteries take up a lot of mass and volume on the already tightly packed CubeSat. A major design challenge is placing the solar panels, either on the sides of the CubeSat itself or having to deploy solar panels.

Having deployable panels adds solar cell area but also an extra mechanical complexity. For the panels to deploy, they need a burn wire release mechanism (the wire being fishing line), and every mechanical system adds the possibility of failure. If the panel does not deploy properly, the CubeSat will not have any power and even if everything else is functioning properly, the CubeSat will fail due to the lack of power. The attitude determination and control system (ADCS) controls the orientation of the CubeSat with respect to an inertial frame of reference and includes reaction wheels, magnetorquers, thrusters, star trackers, sun, and Earth sensors, angular rate sensors, and GPS receivers and antennas.

This complex system is needed because when the satellite is first deployed, for example via NanoRacks from the International Space Station, it is tumbling. Some CubeSats can operate in this state, but others require pointing accuracy and location knowledge.

They can be quite inexpensive to build and launch, in many cases within the budget of university science and engineering departments. They are less complex and smaller than the typical satellite launched into space.

In addition, under the right circumstances, they can be built with commercial off-the-shelf components (COTS) rather than expensive, radiation-hardened electronics. Even these components can survive space radiation for a limited amount of time, long enough for missions of short duration. MarCo, short for Mars Cube One, was the first interplanetary mission to use a class of mini-spacecraft called CubeSats.

The MarCOs — nicknamed EVE and WALL-E, after characters from a Pixar film — served as communications relays during InSight’s November 2018 Mars landing, beaming back data at each stage of its descent to the Martian surface in near-real-time, along with InSight’s first image. WALL-E sent back stunning images of Mars as well, while EVE performed some simple radio science.