This week saw the launch of the X-37B, the US Air Force’s ultra high-tech, small-scale “space plane” project. No one is entirely sure of its overall mission, as its operations are often veiled in secrecy and deemed classified, however we do know of at least one of the technologies it is trialling – and it could revolutionise the solar power industry.
The unmanned spacecraft, which launched for the sixth time this week, features a payload bay that operates as an experimental testbed for a variety of technologies. This time it launched with a Photovoltaic Radio-frequency Antenna Module (PRAM) developed by the US Naval Research Laboratory (NRL). This piece of technology hopes to gain important insights into the possibility of beaming solar energy back to Earth – a concept that has been long theorised about but only partially explored.
Solar energy is of course no stranger to space travel, as solar arrays have been used to power spacecraft and satellites since the 1950s. Not only is solar energy hugely abundant in our solar system, but the technology required tends to also be relatively lightweight making it the ideal tool for powering humanity’s space endeavours.
The concept of beaming this outer-space solar energy back to Earth actually predates space travel itself, emerging in science fiction stories in the 1940s. In the 1970s in particular, it received considerable attention in the wake of concerns surrounding access to reliable oil supplies. However, only in the 1990s did serious work begin to develop the concept feasibly by various space agencies and organisations. Most recently, we have heard of Chinese hopes to build space solar farms.
Powering Earth From Space
The PRAM itself is a 30 centimetre square tile consisting of a solar panel and microwave transmitter, which can generate electricity and then beam it back to Earth to receiving stations in the form of microwave energy waves. The technology itself builds on already well-understood concepts, but this is the first time such an apparatus has been tested in a space environment. According to Paul Jaffe, PRAM’s principal investigator:
“To our knowledge, this experiment is the first test in orbit of hardware designed specifically for solar power satellites, which could play a revolutionary role in our energy future.”
Generating solar power in space comes with a range of advantages over its terrestrial version. Firstly, space-based solar arrays are not subject to the day-night cycle or atmospheric and weather conditions, meaning they can continue to generate power over their entire lifetime – if they remain in the light of the sun.
Additionally, they can generate much more power than Earth-based solar panels as the light they receive is not filtered through the Earth’s environment. As sunlight passes through our atmosphere, parts of its spectrum – especially blue light – are heavily filtered out, reducing the output of the solar plant. In space, all parts of the spectrum are used, while the microwave emitters allow this energy to be passed back to the surface through the atmosphere. Ultimately, the only limit to the power output of a theoretical orbital power plant is the size of the solar array deployed.
The PRAM project is only the first small steps towards making the technology a reality, and the amount of power generated is expected to be negligible. Despite this, it is hoped the experiment will provide valuable information in how to further refine the process. If successful, the next step will be to create a specially-designed space vehicle prototype to expand upon the project.
Some also suggest the technology could also be used to power permanent research stations on the Moon, although this is, for the time being, perhaps the realms of science fiction. Even developing a workable space-based solar plant is expected to be decades away.
A Giant Leap… But for Whom?
The X-37B project is not without criticism – especially in relation to the ongoing militarisation of space. Although the project originated with NASA in the 1990s, it was handed over to the US military, specifically the Defense Advanced Research Projects Agency (DARPA), in 2004. It has since then faced accusations that it is being used as a testbed for purely military technologies, including as a space fighter or anti-satellite tool; a theory which is naturally fuelled by the secrecy surrounding the project.
In reality, it is likely too small for such a role, while anti-satellite missiles are a much cheaper and already available technology. Regardless, it is almost certainly being used to research the military applications of new technologies and develop space as an area of operations, although most likely in the support of traditional Earth-based forces.
Although the PRAM project could have major implications for commercial power generation, the US military is more likely interested in its ability to continually power unmanned drones for unlimited flight or supply electricity to isolated military bases without the need of costly and vulnerable diesel supply routes.
While it is an unfortunate fact that US military scientific research is often one of the few research sectors which receives generous and continual funding and governmental support, it should also be noted that many important civilian technologies, such as radio, satellite navigation and the internet derived originally from military applications. In 2016, around 57 percent of all US government research grants went to defence-related projects.