COMMENT CYBERSECURITY The evidence SCI-FI What did Isaac Asimov NATURAL HISTORY The sisters FUNDING Rewarding that ‘weaponized rumours’ and L. Ron Hubbard have in who made exquisite swagger squeezes out hacked 2016 US election p.188 common? p.189 etchings of snails p.190 humility p.192 ESA/NASA-A. GERST ESA/NASA-A. Three miniature satellites — CubeSats — launching into orbit from the International Space Station in August 2018. Explore space using swarms of tiny satellites Sand-grain-sized computers, self-healing materials and constellations of craft would reboot our reach, explain Igor Levchenko, Michael Keidar and colleagues. he first trillionaire will be made back less than 1 gram of asteroid grains in bucks. Space hardware has not kept pace in space,” US Republican Senator 2010. The price tag for the whole mission with technology development and needs to Ted Cruz told scientists and entre­ was $250 million. be modernized. Satellites are still too bulky preneurs“ T in May at a Washington DC sum­ Still, space is big business. Globally, and expensive. Most perform only a limited mit on sending humans to Mars. He could be companies invested about $262 billion in set of predefined tasks. And, despite the skill right, but only if we rethink space technology. 2016, mostly on using satellites for tele­ and materials that went into them, they fail The cost of launching a satellite is communications, navigation and remote within decades — much more quickly than comparable with the value of its weight in sensing1 (see ‘Lift­off’). Governments, a Swiss watch. gold. It takes thousands of dollars to send too, spend billions — about $84 billion At this rate, humans will never venture far one kilogram into low Earth orbit, often ten worldwide in 2016. More than half that from Earth, let alone colonize the Moon and times more than that. Returning material is ($48 billion) was from the United States, Mars or capture asteroids. even more expensive: it cost the equivalent mainly for military, meteorological and Here we highlight three ways in which of US$250 billion per kilogram of sample communications purposes. space technology needs to advance. Costs for Japan’s Hayabusa spacecraft to bring No one is getting much bang for those must be slashed; satellites should be small, ©2018 Spri nger Nature Li mited. All ri ghts reserved.11 OCTOBER 2018 | VOL 562 | NATURE | 185 COMMENT nimble and able to repair themselves; and emissions that produce energetic ions; and ensure that they will keep working. A swarm they should operate in swarms. gas­fed systems, such as miniaturized Hall­ of unreliable satellites faulting like bulbs in effect thrusters, in which the propellant is a string of lights would hardly be efficient. MINIATURIZATION accelerated by an electric field. Longevity is crucial for colonizing the Moon Satellites are shrinking. More than Standard designs of tiny satellites will be and Mars, where equipment failure might 800 CubeSats are now in orbit. Made from needed to speed up development, produc­ mean life or death. palm­sized modules, these measure about tion and deployment, and to save money. Today’s satellites are typically designed to 10 centimetres across and weigh only a kilo­ But the designs must be customizable so last for between 1 and 15 years. Some space gram or so. And researchers could soon be that they can, for example, support bespoke technology survives for longer: the 41­year­ able to package the entire ‘brain’ of a satel­ scientific instruments and protect sensitive old Voyager 1 probe left our Solar System in lite into 1 cubic millimetre. For example, in components from heating or irradiation 2012, but it is unlikely to send us back a mes­ March, IBM demonstrated a computer the when necessary. Many design templates will sage 40,000 years from now, when it is due size of a grain of salt, containing 1 million need to be pursued at once. to pass near the star Gliese 445 in the con­ transistors. The smaller such devices become, Tiny satellites need small rockets to launch stellation Ursa Minor. Satellites disintegrate the less energy they need to run, and the them. Although industry interest remains quickly because space is hostile — extremely lighter and cheaper they are to launch. strong for large carriers such as the Falcon 9 cold, almost a vacuum and peppered with Satellites come in two types. Passive ones rocket (which is capable of carrying hun­ high­energy particles and ionizing radia­ need only orientation and stability con­ dreds of small satellites as well as big ones), tion. trol. Active ones can be manoeuvred using ‘microrockets’ are being developed by emerg­ Building in redundancy can only go so far. thrusters. Passive satellites are easiest to min­ ing companies such as Vector Launch in Tuc­ For example, the Curiosity rover on Mars iaturize. We anticipate that they could weigh son, Arizona (of which one of us, J.C., is chief was intended to work for about 500 Martian in at less than 100 grams if the hardware used executive), Firefly Aerospace in Cedar Park, solar days (sols). It celebrated sol 2,000 in for controlling stability could be made less Texas, and Gilmour Space Technologies in March — although it has small breaks on bulky. Together, thousands of these ‘femto­ Queensland, Australia. Microrockets are rel­ at least one of its six wheels. Adding spare satellites’ could operate as a network. atively cheap and quick to make. They weigh wheels is an obsolete approach. Active satellites would take longer a few tonnes — much less than the 500­tonne If satellites are to remain functional for to shrink. As Russian poet Vladimir Falcon 9 or 733­tonne Delta IV Heavy. Small a century or more, they need to be able to Mayakovsky said (of mining radium), “For rockets fitted with small, simple engines (that regenerate — as living organisms do. For every gram you work a year.” They would use solid propellants) could deliver dozens of example, the jellyfish Turritopsis dohrnii need minute propulsion systems. Electri­ CubeSats at once to low Earth orbit, poten­ can rejuvenate almost indefinitely. When­ cal techniques are most efficient. These tially daily. ever it feels threatened or is injured, it include: microcathode arc thrusters that use reverts from its mature medusa state to the electrical arcs to convert solids into plasma; LONGEVITY polyp state, thus beginning its life again. It electrospray systems that generate micro­ Before we blast thousands of small satellites can do this several times a year, depending droplets or ions; thrusters based on field or interplanetary probes into space, we must on the environment. Some more­complex animals, such as axolotls (Ambystoma mexi- canum), can grow new limbs, and micro­ LIFT-OFF scopic tardigrades can survive in outer Satellites make up three-quarters of the global space economy. They are being launched in space. record numbers as the costs of building and putting them into orbit come down. Likewise, in space, human habitats, as well as tanks containing fuel and air, must SPACE SPENDING HIGH LAUNCHES SET TO RISE be able to plug punctures and cracks auton­ Companies spend billions of dollars on satellites for Hundreds of small satellites are now in orbit; many television, communications and remote sensing. more should join them in the next 5 years. omously. Batteries, electric generators and sensors should repair themselves when they US$344.5 $260.5 400 are damaged. Some materials capable of total total More nanosatellites were self­healing have been developed in the lab, launched in 2017 than including flexible laminates, polyurethane 10 kg+ satellites and other composites, metallic materials and semi­ spacecraft combined (175). conducting polymers2–4. NASA recognized Communications 300 this need in its 2017 technology investment and other services 5 (RIGHT PANEL) SPACEWORKS 1 (LEFT PANEL); REF. SOURCES: $127.7 plan . But a lack of collaboration between materials scientists and space technologists Satellite is slowing development. industry Other types of advanced materials that $260.5 Satellite ground 200 are ripe for exploitation in space include equipment $60.8 durable and self­repairing lightweight and flexible structures for exploration and col­ Global navigation onization missions. Materials with special and related technology $52.6 heat properties are needed for spacecraft 100 re­entering the atmosphere of Earth or Manufacturing $13.9 Number of satellite launches (1–10 kg) Launch services $5.5 other planets. Carbon­nanotube scaffolds, 2016 global space economy (billions) mimicking the nanoscale structures of sea Non-satellite shells, might increase the toughness of industry Small rockets will cut materials and improve ceramics. Strategies $84 costs and raise demand 0 are also needed to stop cracks propagat­ for small satellites. 2011 2013 2015 2017 ing and to prevent fatigue damage from accumulating. Environmentally friendly 186 | NATURE | VOL 562 | 11 OCTOBER 2018 ©2018 Spri nger Nature Li mited. All ri ghts reserved. ©2018 Spri nger Nature Li mited. All ri ghts reserved. COMMENT NEXT STEPS Experts in advanced nano­ and metamateri­ als and propulsion need to collaborate more to develop self­healing, regenerative materi­ als for space applications. These range from composite materials for human habitats and large inflatable structures, to ultra­hard ceramics for thrusters. Micro­thrusters need to be more efficient and reliable. Uncon­ ventional systems, such as thin­film and 3D­printable thrusters, also need atten­ tion. This will require a continuing dialogue between materials scientists, propulsion experts and robotics specialists, which should begin in conferences on material advances in space technology, such as the International Conference on Micropropul­ sion and CubeSats (www.micropropulsion. A rocket built by US firm Garvey Spacecraft (now part of Vector Launch) carried four CubeSats in 2013. org). Commercial companies will reap the benefits, and should contribute to the mil­ materials are desirable.