A couple of weeks ago, Elon Musk’s company SpaceX launched the Starlink app to help people connect with their Starlink satellite. But the app made an interesting claim in its terms of service: any future Mars colonizers will not be subject to the authority of “Earth-based government.” There is a lot to unpack there, from the implications of unchecked capitalistic imperialism to the questionable legality of ignoring established space law (yes, there are already laws in space). But before we consider the governing of space colonies, we have to determine if they are even possible. There are many practical considerations that could make space imperialism difficult or near-impossible. One of the hardest problems to overcome may end up being humans themselves. From the unknown health impacts of long-term space travel to the psychological consequences of being uprooted from all you’ve ever known, there is a lot we cannot predict about how humans will cope on Mars. But, setting aside these human concerns, what are the practical limitations for setting up a Mars colony? One of the biggest practical concerns is power. Power is comparatively plentiful on Earth. Even once fossil fuels on Earth run out, we will have seemingly limitless access to renewable energy—wind, solar energy, and hydroelectric power—provided that we have the infrastructure to access it. Power in other regions of space, however, can be much harder to come by.
One of the most plentiful power resources in space, and on Earth, is the Sun. In the US, roughly 9% of energy consumption in 2019 came from solar energy—and this is only a fraction of what could be possible if enough infrastructure was built to harness solar energy. The Sun itself is a massive nuclear fusion reactor, using the immense temperature (roughly 28.3 million degrees Fahrenheit) and pressure (over 5,000 times the pressure needed to make a diamond) in its core to crush hydrogen atoms together into helium atoms—releasing energy. That energy radiates out from the Sun’s core until it reaches the outer photosphere (which is a relatively chilly 7–10 thousand degrees Fahrenheit), where it disperses into space as light and heat.
Technically speaking, the Sun is not a limitless resource. Within the next roughly 5.5 billion years, the Sun will deplete its finite store of hydrogen atoms and expand out into a red giant—with a radius large enough to completely swallow Mercury and Venus (and possibly Earth). Eventually, it will begin fusing heavier elements, which don’t produce enough energy to keep the core stable against the crushing force of gravity and collapse into a dim, cool white dwarf star.
Despite this, the Sun is still one of the most reliable and renewable energy sources in space. For comparison, experts estimate we may have 50–100 years of fossil fuels left on Earth. On Earth, solar energy can be harnessed most efficiently through the use of photovoltaic panels or arrays. These devices utilize the photoelectric effect in metals—where light knocks electrons off of the metal atoms creating an electrical current. The first practical photovoltaic cell was made in 1954, but at the time it was too expensive to replace existing power sources. In the 60s, NASA began utilizing photovoltaic cells to provide power aboard spacecraft. NASA scientists made major advancements in photovoltaic technology, which made them cheaper and more efficient and enabled the eventual widespread use of solar panels.
Today, the International Space Station (ISS)—which orbits 220 miles above Earth—is powered by massive solar arrays that extend off the space station like wings. There are eight solar arrays attached to the ISS and each solar array is 112 feet long (roughly a third of the length of a football field) and 39 feet wide. These solar arrays generate roughly enough power for 40 average American homes (84–120 kilowatts). To ensure maximum power collection, solar arrays are attached to specialized gimbals that rotate them to an optimal orientation relative to the Sun as the space station orbits Earth. In addition to providing power to the station, the solar arrays charge batteries that power the station when it is in the shadow of Earth.
The farther you get from the Sun, the more dilute solar energy gets (that’s why the outer planets are so icy and cold). For this reason, solar arrays are often not ideal for distant space travel. The record for most-distant solar power spacecraft is currently held by NASA’s Juno spacecraft, which started orbiting Jupiter in 2016. Jupiter is about 5 times as far from the Sun as Earth (43,440 miles), and light from the Sun takes 43 minutes to get there. At this distance, 25 times less energy can be collected and used by solar arrays. Juno is still able to operate on these meager supplies of light because of massive advancements in solar panel efficiency. The spacecraft has 3 massive solar arrays, with a total of 18,698 individual solar cells. The solar arrays still only manage to produce a measly 500 watts (less power than is used by a small refrigerator), but Juno’s efficient design allows it to carry out all its necessary tasks on this power.
But what about Mars? Mars is only 1.5 times as far from the Sun as Earth, so it is certainly possible to harvest solar energy on the red planet. In fact, in the past, both the Spirit and Opportunity Mars rovers were primarily powered by solar panels. These solar panels collected and used solar energy during the Martian days and stored some of it in batteries to hunker down at night. This system worked fairly well for a while. In 2010, 7 years after its launch, Spirit got caught in a sand trap at the start of the Martian winter. Unable to catch sunlight on its solar panels, Spirit froze to death. Opportunity ended up running for a total of 15 years, until May of 2018, when a massive sandstorm buried the rover and cut off communication. NASA attempted to reestablish communication for eight months before ultimately declaring Opportunity dead in February 2019. If descriptions of Mars rovers dying is making you sad, then you can imagine how tragic an event like this would be if it happened to human Mars colonists. The unpredictable weather and frigid temperatures on Mars make solar energy an unreliable solution for a Mars colony.
After the deaths of Spirit and Opportunity, more recent NASA rovers, Curiosity and Perseverance, were designed to run completely on energy generated by radioisotope thermoelectric generators (RTGs)—the same power generator used aboard the Voyager probes. Next week, I’ll talk more about how these RTGs work, and whether they could reasonably be power sources for a Martian colony.
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