Future space missions aim to reach Mars and beyond, but many challenges must be overcome before this can be achieved – and nanomaterials will play a critical role. From bio-nano robot-laced spacesuits, to radiation shielding, to new means of travelling into space, research employing nanomaterials is underway.
At present, 95% of the weight of a spacecraft at launch is fuel, leaving only 5% for the craft itself, payload and astronauts. Launching – and manoeuvring in space – relies on a chemical propulsion. But is there an alternative?
Electric propulsion (EP) uses electrical power to accelerate the propellant and could significantly reduce the volume of the propellant required to get into space, offering a chance to increase the payload or decrease launch mass. NASA’s Deep Space 1 and the ESA’s SMART-1 launches successfully demonstrated EP as their primary propulsion system.
A nanotechnology EP concept could utilise electrostatically charged and accelerated nanoparticles as a propellant – such a method would consume less fuel than chemical rockets and utilise electricity gathered from solar cells to generate electrical fields that push ions away from the spacecraft. It would employ a microelectromechanical system (MEMS) to accelerate nanoparticles, helping to reduce the weight and complexity of the thrusters. Furthermore, millions on micron-sized nanoparticle thrusters could fit on a square centimetre, meaning highly scalable thruster arrays could be fabricated with the ability to vary the number of MEMS devices drawn on depending on the requirements of the spacecraft.
But there could be another way to get into space – a space elevator. Such a structure requires an incredibly long cable – approximately 90,000 km – and would need to be stronger than any cable found on Earth. Carbon nanotubes (CNTs) are a promising candidate. A CNT cable could be tethered to an asteroid in orbit and an anchor station on Earth while cars powered by solar cells travel up and down much like a vertical monorail. Many engineering challenges must be overcome before such an elevator could be established – namely how to get a 90,000km cable from A to B!
CNTs could also be used in lightweight sails that utilise the pressure of light reflecting on solar cells to propel spacecraft; this would negate the need to carry extra fuel for missions as only fuel for lift-off, docking and landing would be required. Such sails would need to be large yet light, and at present, how to unfold such a thin and fragile structure in space is proving challenging.
Protecting spacecraft and astronauts
NASA believes the risk of exposure to space radiation is the most significant issue restricting humans’ capacity for long-duration spaceflight. Nanotechnology could contribute to improving the spacecraft themselves, while also protecting both astronauts and equipment.
Nanotechnology could make spaceflight more practical: CNT composites could reduce the weight of spacecraft by providing a lightweight skin and internal structures while also maintaining or increasing structural strength. The future may also see self-healing spacecraft employing nanotechnology to repair damage sustained from meteors striking the craft, for example.
Multifunctional hulls are being designed that offer radiation protection and are low weight and structurally stable. Nanomaterials like boron nanotubes could be used in nanosensor-integrated hulls which, in addition to offering effective shielding and energy storage, could alert astronauts to stresses or damage in the spacecraft’s skin or improve onboard systems like life support by quickly reporting changes in levels of trace chemicals in the air.
Onboard electronic equipment also requires protection, and it’s been noted that electronic devices become more tolerant to radiation the smaller they are. Multi-quantum wells or dot devices are more radiation tolerant than larger, conventional devices. Quantum dots could be used in anti-satellite weapon countermeasures; a decoy of such dots of differing shapes and sizes engineered to emit radiation with a profile similar to that of the satellite could protect it from missile attacks.
Spacecraft and equipment aren’t the only things requiring protection – astronauts do too. Future spacesuits could feature layers of bio-nano robots which respond to damage in the suit, for example sealing a puncture in the outer layer. Robots in the inner layer could react if the astronaut is in trouble, providing drugs in a medical emergency for example.
There are still many other ways nanotechnology could help space travel – a network of nanosensors could explore large areas of planets like Mars for traces of water or other chemicals for example – but there many more challenges to overcome before we see some of these ideas launching into orbit.