The Rubik's Cubes in Space

When you think of satellites, you think of a big, complex machine orbiting the Earth that costs millions of dollars to construct. Satellites have various functions, including providing GPS, providing Internet, helping to broadcast TV, taking pictures of space, housing science experiments, and evening housing people. But not all satellites are enormous and expensive. With the development of CubeSats, satellites have been easier to build and put into orbit. CubeSats are 10cm by 10cm by 10cm and weigh less than 2.9lbs (1.33kg), and often use off the shelf components. These make them small and cheaper to manufacture. They are often put into orbit by deployers on the ISS or as secondary payloads on launch vehicles.

Ncube-2

The CubeSat was first proposed by Professor Jordi Puig-Surai of California Polytechnic State University and Professor Bob Twiggs of Stanford University in 1999. Their goal was to enable graduate students to design, build, test, and operate spacecraft similar to Sputnik's first satellite ever put into orbit. At first, the CubeSat wasn't popular. Still, over time, more and more people liked the idea, as it helped students understand satellites' functions and operations in space. The first CubeSats launched in 2003 on a Russian Eurockot. By 2012, there were 75 CubeSats in orbit. Eventually, NASA and other companies started to develop and launch CubeSats. As of January 1, 2021, more than 1350 CubeSats have been launched.

1U CubeSat Structure

The design of CubeSats accomplishes many goals that many engineers wanted to solve. The small size of the satellites helps reduce the cost of launching, help launch more payloads at one time, and use the excess capacity of launch vehicles. CubeSats are designed for low Earth orbit (LEO), where they could reenter the atmosphere in just weeks. Because most CubeSats are made from off the shelf components, space radiation often damages them quickly. The structure of CubeSats are mostly made up of an aluminum alloy and have different sizes that are scalable. Most CubeSats will founder vibration analysis to make sure they don't break during launch. CubeSats' use similar computing systems to those in larger satellites. CubeSats contain multiple computers that handle different tasks in parallel, including altitude control, power management, payload operation, and primary control tasks. CubeSats also can collect lots of data that scientists and engineers can use about space. 

Ion Thruster on a CubeSat

CubeSats have four propulsion systems: cold gas thrusters, chemical thrusters, electric propulsion, and the solar sail. In CubeSats, the propulsion system has to be small, light, and can only be used for short travel. The propulsion systems in CubeSats are mostly used to change orbit. Cold gas thrusters use Ipressurized gasses through a nozzle to produce thrust. Cold gas thrusters are the most simple propulsion system as they require a single valve. However, once all the gas is used, the CubeSat cannot be controlled again. Chemical propulsion uses a chemical reaction to produce a high-pressure, high-temperature gas that escapes through a nozzle. Chemical propulsion systems have very low power requirements, and their simplicity allows them to be small. Electric propulsion uses electric energy to accelerate propellant to high speeds. This results in a high specific impulse (a measure of how efficiently a rocket uses propellant or a jet engine uses fuel). Some examples of electric propulsion used in CubeSats are Hall-effect thrusters, ion thrusters, pulsed plasma thrusters, electrospray thrusters, and resistors. One problem with electric propulsion is that they require a high amount of power. Finally, there are solar sails. Solar sails are a foil that spread out and use the radiation pressure from the Sun to travel. Solar sails require no propellant. However, the solar sails have to be large relative to the CubeSat size to function correctly.

Winglet on CubeSat Expanding to Increase
Surface Area for Power Generation

For power, most CubeSats use solar cells that convert solar light to electricity stored in lithium-ion batteries that can provide power when sunlight is not available. Power is effectively shared with many other parts, such as antennas, optical sensors, camera lenses, propulsion systems, and access ports. Most CubeSats generate less than 10 watts of power. The only problem is that CubeSats have a tiny surface area. To solve this, many CubeSats increase their surface area in orbit by folding out. This same problem occurs with telecommunications. Most telecommunication dishes are large, which is a problem for CubeSats. The solution is for CubeSats to use a deployable high-gain mesh reflector. More complex designs use inflatable dishes. Most CubeSats use antennas for communications, but CubeSats that go deeper into space use larger antennas that are compatible with the Deep Space Network. CubeSats in orbit are heated by radiative heat emitted from the Sun. There are also many temperature sensors located all around the CubeSat to make sure that components are not overheating or freezing.

Antenna on CubeSat Opening Up

CubeSats are unique compared to other types of payloads, as CubeSats can be delivered and deployed as cargo to the ISS. From there, researchers on the ISS can deploy CubeSats into space or even work on a modified CubeSat in space. When launching, CubeSats hitch rides as secondary payloads on larger rockets, with most prices being $100,000 to launch each unit of a CubeSat. Currently, NASA is working on a new class of rockets that will be specifically designed to launch CubeSats and other small satellites. CubeSats are mounted inside Poly-PicoSatellite Orbital Deployers (P-PODs) when they are going to be deployed. P-PODs are mounted to a launch vehicle, which carries the CubeSats into orbit and deploys them. Most CubeSats are deployed using NanoRacks on the ISS. 

CubeSats in P-PODs

One important mission that used CubeSats was during the 2018 InSight mission. During the mission, two CubeSats, called Mars Cube One (Marco) A and B, relayed communications from the InSight stationary lander on Mars. This mission was the first time where CubeSats were deployed into deep space. Both MarCO A and B were able to provide real-time telemetry during the landing. In 2010, NASA created the CubeSat Launch Initiative. By creating this initiative, NASA hoped to provide CubeSat launch opportunities to educational institutions. Additionally, NASA started the Cube Quest Challenge in 2015 to foster innovation in the use of CubeSats beyond LEO. Many international projects are in the works that will utilize CubeSats.

CubeSats are an essential innovation that has helped revolutionize many parts of the space industry. CubeSats were first invented to help teach students the basics of operating and engineering satellites. Over time, the concept has evolved to where countries all over the world launch CubeSats. Now, CubeSats the future of space exploration and will eventually be used in more deep space exploration missions.

Artist's Rendering of MarCO A and B During the InSight Mission

Sources:

“CubeSat.” Wikipedia, Wikimedia Foundation, 25 Jan. 2021, en.wikipedia.org/wiki/CubeSat. 

“Specific Impulse.” Wikipedia, Wikimedia Foundation, 17 Jan. 2021, en.wikipedia.org/wiki/Specific_impulse.