CubeSats are in Earth orbit and about to make the great leap into interplanetary space. No, we aren't about to experience an invasion by the Borg, though, to some degree, CubeSats resemble miniature versions of the massive Borg Cubes—but the resemblance is merely cosmetic. Modern CubeSats are technologically sophisticated by our standards, but extremely primitive compared to their science fictional cousins. They do have one big advantage over their Borg counterparts—they're real.
A CubeSat is a nothing more than a very small spacecraft built on a modular design architecture of 10 cm x 10 cm x 10 cm cubes—sort of like square Legos. Each cube is called a “U” and is typically allocated 1-2 kg of total mass. A spacecraft can then be built by combining these cubes together, typically into 3U and, more recently, 6U configurations as seen in Figure 1. The more U's, the more available volume allowing more complexity. But as the U's grow, so does their total mass and the associated launch cost.
So why build a CubeSat? Aren't they too small to do significant science? The answer to the first question is, to no great surprise, cost. With the electronics revolution we've seen over the last 25 years, the mass, volume and power requirements of electronic systems have dramatically decreased, allowing the average person to carry in their pockets or purses a sophisticated computer more powerful than was used to first guide people to the Moon. And the phone doesn't just contain a relative supercomputer, it also contains a very sensitive camera, accelerometers, and other sensors that are now lightweight and low cost due to mass production and commercial consumption. The "innards" of your iPhone or Android are very similar to the electronics being stuffed into CubeSats to provide all the necessary spacecraft control functions previously performed by much larger, less robust and much more expensive space flight computers.
The answer to the second question is a bit tougher. Though CubeSats are now priced so that small businesses and universities can purchase the piece parts and build them, they are still very limited in what they can carry. After all, you cannot mount a 1 meter diameter space telescope lens in a 10 cm wide Cube! Did I say that CubeSats are cheap to build? When faced with flying small scale modest science experiments frequently and at low cost versus maybe flying a full-size, science-driven spacecraft at high cost and once in your career, sometimes the best answer is to take what you can get and afford. Often there is no choice to be made—large, expensive science missions are difficult to get funded and are all-too-often canceled before they get to fly in space.
CubeSats are inexpensive because they are made of parts that are mass produced, taking advantage of the economies of scale afforded by a consumer oriented marketplace. Before CubeSats, only a few vendors made spacecraft parts. And, if you are only flying 1 or 2 spacecraft per year, a vendor has to charge a high price for each piece part in order to break even, let alone turn a profit. But with CubeSats, components come from an industrial base where thousands to millions of each are made annually, the cost can be dramatically reduced. Adapting them for flight in space, in some cases, adds cost due to the time an engineer has to spend redesigning them. But even this expense is typically much smaller than more traditional spacecraft engineering companies can attain.
Fortunately, the space environment of Low Earth Orbit (LEO), at least from a radiation point of view, isn't that much more hostile to spacecraft electronics than the environment here on the ground. This is because of the Earth's magnetic field acting like a large and very powerful charged particle (a form of radiation) deflector screen—another Star Trek allusion (Figure 2). Much of the harmful radiation that would otherwise pummel the Earth and its residents is shunted safely away from the surface by the magnetic field and the streams of trapped radiation that surrounds us. Those who follow current human spaceflight will now understand how we can send astronauts for months at a time to live on the International Space Station. Crews there are still exposed to the very high energy cosmic rays coming from outside the solar system, but are mostly shielded from the harmful radiation coming from the Sun. If astronauts can use commercial laptops in the radiation protected ISS, then why can't CubeSats use similar technologies? (They can.)
The CubeSat was initially developed by California Polytechnic State University and Stanford University in the late 1990s. Once the spacecraft form factor (size and weight) was standardized, companies began developing ways to inexpensively launch them by riding piggyback into space with other, more expensive or "primary" satellites (often called "payloads"). This secondary ride to space market has grown dramatically, as have the number of organizations and institutions developing CubeSats. Each year there are now multiple inexpensive opportunities to get a CubeSat launched into Earth orbit by riding there with something else and allowing the primary payload to pay the lion's share of the launch cost.
Until recently, CubeSats were restricted to missions in Low Earth Orbit (LEO), the region of near-space that reaches up to a few hundred kilometers. There are many reasons for this. First of all, rides to LEO are plentiful. Countries and companies all over the world launch spacecraft into LEO for Earth observation, communications and military purposes. It's also the region in which the ISS flies; from there many CubeSats have been deployed.
Flying multiple CubeSats in LEO can also create problems. Big problems. CubeSats aren’t designed for long life and only about half that are launched actually live long enough to complete their primary missions. (CubeSats are cheap, and that, unfortunately, often means more than that they are inexpensive to build.) Those that complete their mission often don’t continue functioning very long thereafter. This, combined with the fact that CubeSats almost always don’t come with a method of removing themselves from orbit after they die, makes them inevitably become yet more space junk. Space junk is a growing problem—and one day it might threaten our ability to productively use near-Earth space for any length of time. For more information about space junk and how it might adversely affect our future in space, please refer to my Baen essay, Living without Satellites.
Most of Low Earth Orbit is safely within the Earth's magnetosphere, allowing unshielded electronics there to remain operational for longer periods of time (as discussed above). Being only a few hundred miles overhead, it is also relatively easy to communicate with CubeSats in LEO using an extensive network provided by volunteer amateur radio enthusiasts from around the globe. Communications highlights one of the biggest problems facing CubeSats—the limited power they can generate. Sending data home requires power. To send more data, you need either yet more power, or a larger antenna, or both, requiring yet more hardware be included in the CubeSat.
To generate power in space, you need to use solar cells to capture sunlight and turn it into electricity. The amount of power you can generate depends upon the area available to mount solar cells. With cell efficiencies hovering below 25%, this means you need four times the total area you would otherwise need to generate a specific amount of power if your cells were 100% efficient. At the Earth, the amount of energy contained in sunlight is 1368 Watts per square meter. If you only have the area of 1U (1 square cm per side) to mount solar cells, then you cannot generate much power. Earth orbiting CubeSats can generate a few tens of watts from today’s commercially available solar arrays.
Compare this with the energy output of a traditional incandescent lightbulb used to read your favorite Baen book: 75W. This is not much power—but is far more than is available to your average CubeSat. Creative engineers have found ways to add deployable panels to the CubeSats, allowing them to increase the available surface area, hence area for generating power, thus increasing the total power available for the CubeSat upward by a few more tens of Watts. Needless to say, limited power highly constrains what missions can be accomplished by CubeSats and limits how far they can operate away from home since the power available limits the distance from which they can communicate and the rate at which they can send home scientific data.
To increase the power available for such small spacecraft, engineers are working on various forms of deployables to which solar cells can be affixed. When stowed, the deployable solar arrays take up much less volume, allowing them to be packed in the limited available space on a CubeSat. From simple panels that store flat against the sides of the CubeSat and deploy once in space (Figure 3) to more exotic concepts such as NASA’s Lightweight Integrated Solar Array (LISA). In just a few years there will likely be a tripling of the power available.
Remember what I said about creative engineers? Engineers don't like hearing what they cannot do. They like challenges and to meet the power challenge (and associated operational constraints), they've come up with creative missions and applications for CubeSats. Here are a few examples:
NASA's GeneSat 1 studied the growth of biological samples in microgravity and possible genetic changes therein.
QuakeFinder LLC and Stanford University's QuakeSat consisted of 3 CubeSats flown at the same time to test a theory of earthquake prediction.
The National Science Foundation sponsored the ExoCube to study space weather and charged particle populations in the upper ionosphere and LEO.
NASA's PhoneSat quite literally flew smartphones to see whether their unaltered, unshielded electronics would work in space. They did.
The Planetary Society's LightSail-A showed the deployment of a 32 square meter solar sail in orbit; LightSail-B is scheduled to fly in late 2016.
The future will see more ambitious Earth orbiting CubeSats and the first-ever use of them for missions in interplanetary space. Many of these next generation CubeSats will have a 6U form factor (10cm X 20cm X 30cm) or larger to allow more science, electronics and power generation capability, greatly expanding the reach of these recent space interlopers. The Mars Cube One (MarCO) dual spacecraft will ride to Mars in 2016 with the NASA InSight mission and provide additional communications capability for it. Since the mission will fly beyond LEO, its electronics will be somewhat hardened compared to its LEO spacecraft comrades and it will have much larger deployable solar panels to increase the power available at Mars. NASA’s IceCube will be launched in 2016 and help scientists to better understand the role of cloud ice in climate change and the similarly named Lunar IceCube (cute "cube" names will soon be all used up) will be among the first CubeSats to use highly efficient electric propulsion as it searches for water on the Moon.
The European Space Agency plans to launch 50 CubeSats on one rocket in a mission creatively called, "QB-50." The launch date is to be determined and the countries contributing spacecraft reads like a meeting of the United Nations: Austria, South Africa, Belgium, Brazil, Canada, China, Czech Republic, Greece, Ukraine, the United States and others. NASA will continue deploying CubeSats from the ISS and expendable rockets, as will Russia and private companies such as SpaceX. Among those launched will be 1) Belgium’s SIMBA, a 3U to provide measurements of the amount of sunlight impinging the Earth’s biosphere, 2) Belgium’s QARMAN, which will be testing systems that can provide data during a spacecraft’s entry into the atmosphere, and 3) Picasso, another Belgian satellite that will take measurements of ozone in the stratosphere.
In 2018, NASA will launch eleven 6U CubeSats into interplanetary space for missions to the Moon, in deep space, and to an asteroid. The Near Earth Asteroid Scout mission will use an 86 square meter solar sail, a big brother to the LightSail-A developed by The Planetary Society and mentioned above, to propel the spacecraft to rendezvous with an asteroid 2 years into the mission. An artist concept of the mission can be seen in Figure 4. Note the scale of the deployed solar sail compared to the 6U CubeSat from which it will be deployed.
The University of Illinois, The University of Alaska, and others have been selected to look at the feasibility of deploying CubeSats from larger primary mission spacecraft studying Europa. If successful, it is possible CubeSats will become commonplace in deep space exploration and science missions of the future.
CubeSats have democratized space, allowing amateurs, small businesses and universities to fly real engineering and science missions in Earth orbit and may soon enable more affordable science and exploration of the solar system by NASA and other space organizations. Their future is bright and I personally expect to see them flying in ever greater numbers and throughout the solar system. The Borg better watch their backs!
Copyright © 2015 Les Johnson
Les Johnson is a Baen science fiction author, popular science writer, and NASA technologist. His most recent science fiction novel, Rescue Mode, coauthored with Ben Bova, was released in paperback in 2015. To learn more about Les, please visit his website at www.lesjohnsonauthor.com.