No outlets in outer space

On May 15th, Mars welcomed its first Chinese visitor. The Martian rover Tianwen 1 successfully landed, joining the NASA Curiosity rover on the red planet.

The design life of Tianwen 1 is 90 days but is expected to work longer. The NASA rover Opportunity, intended to have a 90-day life, ultimately survived for 14 years, thanks to the careful management of its power. Power supply has always been an extremely crucial issue for unmanned exploration of distant planets.

At present, the electric energy of these robots comes primarily from two sources: nuclear heat and solar energy.

NASA, as an example, mainly uses a plutonium-238 isotope heat source (Plutonium-238) to generate heat, then convert it into electrical energy. Despite continuous decay, it can steadily output about 110 watts of power, according to NASA. But this method is not without disadvantages – it is an expensive, and heavy (about 5kg) method of providing power.

Figure 1 The nuclear battery on the NASA Curiosity rover (the yellow circled part)

In contrast, Tianwen 1 uses traditional solar panels, as does NASA’s Ingenuity helicopter. Generally, the charging performance of solar energy would be less robust than nuclear energy. Even on Earth, the average conversion efficiency of solar panels is about 20%. Wind and sand make it even worse. We know that on Mars sandstorms are common. Furthermore, solar panels may not be helpful on distant planets away from the sun.

Figure 2 NASA's Ingenuity helicopter and its solar panel on top

Figure 3 China Tianwen 1 (Zhurong) and four solar panels

As the number of rovers and drones increases, how to power them may become a thorny issue. After all, it is no longer economical to carry a Pu-238 or solar panel on each robot.

In fact, wireless power transmission technology has long been considered by the aerospace industry. In the past decade, with the increasing commercialization of wireless charging products, the possibility of their application in the aviation field has further been accelerated.

In short, would it be possible to use nuclear charging stations equipped with wireless charging to charge robots or drones? Considering weight, implementation cost, reliability and safety, wireless power transmission becomes undoubtedly an ideal solution.

The environment of Mars makes it impossible for metal-contact-based charging methods. Also, without heavy nuclear heat sources or huge solar panels, robots and drones can save space and weight for other equipment, relying on a base station, i.e., charging station to power up.

The charging station can still use the Plutonium-238 to generate power and have wireless charging transmitters on top and/or on the side, in order to recharge drones and the Mars rover, respectively. With some coordination of charge sequence, multiple rovers or drones can be charged.

As more and more areas of Mars are explored in the future, these areas can be connected to create a network with charging stations scattered along the route to enable more distant explorations. Similar to highway gas stations, we can place charging stations at intervals on this main “road”. In the future, electric power can even be provided to unmanned mining vehicles using a similar network of charging stations.

It is believed that in the near future, humans will send more machines and equipment to Mars. Wireless charging will enable these man-made devices to expand explorations of Mars and even deeper space.