Explore Space Using Swarms of Tiny Satellites

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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 ‘Lift-off’). 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,

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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. gas-fed 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. palm-sized 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 41-year- 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 high-energy 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 500-tonne If satellites are to remain functional for to shrink. As Russian poet Vladimir Falcon 9 or 733-tonne 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 more-complex 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 self-healing 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 self-repairing 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 re-entering the atmosphere of Earth or Manufacturing $13.9 Number of satellite launches (1–10 kg) Launch services $5.5 other planets. Carbon-nanotube 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

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NEXT STEPS Experts in advanced nano- and metamateri als and propulsion need to collaborate more to develop self-healing, regenerative materi als for space applications. These range from composite materials for human habitats and large inflatable structures, to ultra-hard ceramics for thrusters. Micro-thrusters need to be more efficient and reliable. Uncon ventional systems, such as thin-film and 3D-printable 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. signals and perform basic logic operations lions of dollars the research teams will need. Researchers need to explore adaptation. could be combined with clusters of fewer, Mass-production methods must be Spacecraft might have to deal with the larger, more-complicated and manoeuvrable optimized for delivering constellations of unexpected, such as grabbing irregu satellites that act as communications or thousands of satellites. Additive manufactur larly shaped asteroids or handling other analysis hubs. ing techniques such as 3D printing are lower satellites for repair missions. Adaptable Ultimately, constellations might behave ing the costs of custom satellites. Production grippers, made from elastic or intelligent like a neural network or artificial intel methods must be factored in when design NASA/DIMITRI GERONDIDAKIS materials, need to be designed. Eventu ligence. Collective properties could be ing space technologies. Designs of auxiliary ally, we’ll need fully self-repairing space exploited, such as self-organization, trans systems such as launch pads, thruster plat platforms, including propulsion systems, formability, self-learning and simultaneous forms and power and control systems must power plants, life-support systems and sensing over a large area — as in the clouds be standardized. scientific instruments. Building even a of microscopic, interacting robots envisaged In addition, policymakers and lawyers prototype demands major breakthroughs by Polish science-fiction writer Stanisław need to develop an international legal and new ways of working. Lem in his 1964 book The Invincible. framework for operating large constella So far, only tens of satellites have been tions. For example, licences and permissions NETWORKING strung together. The Global Positioning are needed to launch craft. Communication Instead of building one satellite to perform System (GPS) satellite constellation, for frequencies and orbits need to be assigned. a single task, constellations of thousands example, requires about 30 operational sat The de-commissioning and removal of of satellites have much broader potential. ellites for reliable global coverage. Efforts satellites at the end of their working lives Their instruments can operate together are afoot to increase the numbers. In Japan, must be coordinated internationally. Insur as if they were on a much larger platform. Hokkaido and Tohoku universities have ance needs to be established for losses from For example, the five satellites that now partnered with other organizations to send delays in the deployment of satellites, as make up the Afternoon Train constellation 50 microsatellites into space by 2050 (each happened for the Iridium NEXT mission to monitor clouds, aerosols and greenhouse weighing about 50 kg) to trace the after upgrade its constellation. and other gases in Earth’s atmosphere to maths of natural disasters. The Iridium It is too soon to say whether the space provide 3D reconstructions of climate telecommunications network is being economy will become profitable. But cen and weather patterns and atmospheric boosted to contain around 80 satellites. tral to that economy will be the coming pollution. In the CANYVAL-X mission, By the mid-2020s, the company SpaceX constellations of tiny satellites. ■ two CubeSats fly in formation to develop intends to launch 12,000 small satellites techniques that will help to study the Sun to set up Starlink, a space-based Internet Igor Levchenko is a research scientist at the (one is equipped with a microcathode arc network. Two prototype Starlink satellites National Institute of Education, Nanyang thruster). were launched in February, and the net Technological University, Singapore. Many configurations are possible — work may begin operating as soon as 2020. Michael Keidar is professor of engineering from trains of satellites following one The communications company OneWeb and founding director of the Micropropulsion another along the same orbit, to evenly aims to ensure affordable global access to and Nanotechnology Laboratory at George spread networks watching Earth’s entire Internet services through a constellation Washington University, Washington DC, surface (and, in future, maybe also those of 600–2,000 small satellites (up to 200 kg), USA. Jim Cantrell, Yue-Liang Wu, Hitoshi of the Moon and Mars). The constellation’s with the first slated to be launched as early as Kuninaka, Kateryna Bazaka, Shuyan Xu. shape can be adjusted. Several networks December. Boeing’s proposed constellation e-mail: [email protected] can be linked together virtually, to increase of 1,300–3,000 communications satellites is 1. Bryce Space and Technology. Global Space their power, resilience and responsiveness. another example. Industry Dynamics: Research Paper for Australian Some satellites might be tooled to repair However, the satellites in most of these Government, Department of Industry, Innovation and Science (Bryce Space and Technology, 2017). and adjust others. constellations are controlled from the 2. Bauer, S. & Kaltenbrunner, M. Nature 539, Swarms of miniature satellites should ground. To operate efficiently, constellation 365–367 (2016). be cheap and quick to deploy. Thousands units need to be able to communicate with 3. Kim, J. T. et al. Sci. Rep. 8, 2120 (2018). 4. Oh, J. Y. et al. Nature 539, 411–415 (2016). could be released from a large central satel each other and to adjust their positions and 5. NASA. NASA Strategic Technology Investment Plan lite in orbit. Swarms able to receive and send orientations in real time. 2017 (NASA, 2017).