Solar propulsion can make space travel cheaper and more efficient: NASA researchers

Solar has long been used for unmanned space missions, but advances in the technology could spell great things human space flight

Ever since NASA popularised the solar panel way back in the 1970s, solar has proved crucial to expanding our knowledge of space.

Space exploration has long utilised solar to power probes that have been sent to the depths of space. A lot of man-made objects that are far from the surface of this planet have used solar: Rosetta and Philae which reached and landed on the comet 67P rely on solar; Mars Rovers have solar arrays that keep them powered and the MESSENGER mission to Mercury used solar panels as its main source of power.

solar-roverFor long distance manned missions into space, the agency is working on electromagnetic space technology called the EmDrive, which it has recently said is functional. It almost goes without saying that solar isn’t perfect for every mission into space; the probe still has to be in sight of the sun’s rays. A 1996 NASA fact sheet, which was produced in advance of the Cassini mission to Saturn, said Radioisotope Thermoelectric Generators were more suitable: “RTGs enable spacecraft to operate at significant distances from the Sun or in other areas where solar power systems would not be feasible.

“They remain unmatched for power output, reliability and durability by any other power source for missions to the outer solar system and are very safe.”

However despite all this, solar is still going to play a big part of the future of exploration, as power is crucial.

“Power availability can limit almost all aspects of a space mission from payloads, propulsion and communication systems to life support and surface mobility for human space missions,” says a NASA research paper recently published online.

The paper Solar Power For Future NASA Missions, written by researchers at Glenn Research Center, says that solar power in space may have a more influential future than you would imagine.

“With continued incremental development via new materials and manufacturing techniques, solar cells may become relatively inexpensive, light, and versatile enough to be integrated into all structures, fabric, vehicles, sensors, and other exploration systems – serving a multifunctional purpose of providing primary power as well as other possible applications.”

Solar space travel

Further trips to Mars or asteroids are always being considered, and one way that makes them cheaper – essential for when we want to inhabit other parts of the galaxy – is using solar to power the travel.

The Solar Electric Propulsion (SEP) project that’s being run is looking at developing “critical technologies” that will make difficult missions easier.

“High power and high efficiency SEP systems will require much less propellant to meet those requirements,” the researchers write.

Images courtesy of NASA

Images courtesy of NASA

“The new system will use xenon propellant energized by electric power from solar arrays and use 10 times less propellant than a chemical propulsion system like the engines on the space shuttle.”

They go on to say that large solar arrays and “high power thrusters” are being created for future launches. These arrays must be able to fit into small loads when they are packed for launch and once they are in space must be able to unfurl and capture as much solar energy as possible. Flexible solar technology is likely to be part of the key to unlocking a maximum solar surface area and there have been recent breakthroughs in the field by MIT researchers.

NASA researchers are already creating two “20kW-sized deployable solar arrays”, and one research project is building solar arrays of around 1500m2 that can be stored and unfurled in space.

“The project addresses the most challenging aspects of developing deployable solar array structures, including aspects related to: compact stowage, reliable deployment, high deployed strength and stiffness, robustness to dynamic docking and manoeuvre loads, modularity, reusability, and ground validation,” the researchers Sheila Bailey and Geoffrey Landis write.

The benefits, in the eyes of the researchers, are worth the development costs: “Compared with current systems, they will launch one-half the weight with one-quarter of the storage for electricity produced, and will be able to withstand four times the radiation.”

Sailing into the future

If any of the above sounds like it is ringing any bells that might be because you’re thinking of the LightSail – dreamed up by Bill Nye, funded by citizens, and run by the Planetary Society.

In June, a sail measuring 32 square meters was sent to Earth’s orbit where successfully unfurled its solar array and flew using the sun’s energy.

It even had time to snap a selfie before it was dragged back by the Earth’s gravity and burned up in the atmosphere.

Although the LightSail is the most well-known unfurling solar array of its kind – party due to being in close memory – it isn’t the only creation of its kind. NASA’s NanoSail-D2, measuring just 30 x 10 x 10cm at launch with a sail area of 10 square meters, was in space in 2011 and deployed its own sail. It stayed in orbit for 240 days and was part proving that solar propulsion will one day be possible.

Image and featured image courtesy of the Planetary Society

Image and featured image courtesy of the Planetary Society

The NASA researchers who published the recent study are primary concerned with the development of solar technology, and don’t give any details of what space travel by solar power would look like.

There’s no indication of timescales for travelling to Mars or asteroids compared to traditionally fuelled spacecraft, but there is optimism for the potential of solar in space.

“It is difficult to predict the ultimate efficiencies for hybrid organic/inorganic and perovskite cells, for example,” the study concluded.

“We also find ourselves re-examining old materials in new ways and combining materials in new ways.

“Breathtaking new materials processing and device design options have re-invigorated space photovoltaics for future space exploration.”

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