Inside Unmanned Systems

APR-MAY 2018

Inside Unmanned Systems provides actionable business intelligence to decision-makers and influencers operating within the global UAS community. Features include analysis of key technologies, policy/regulatory developments and new product design.

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30 April/May 2018 unmanned systems inside SPECIAL REPORT NASA TECHNOLOGY For decades, researchers have sug- gested launching many tiny space- craft into orbit that can then assemble themselves into large structures. Now scientists are on the verge of launch- ing tiny satellites they propose could one day converge to form a Giant Orbiting A stronomical Telescope (GOAT) more than 100 metric tons in size. In comparison, the Hubble Space Telescope is about 11 metric tons, and the International Space Station has a mass of roughly 420 metric tons. GO BIG The GOAT's design comprises two ring-shaped mirrors that can work in sync to act like a single mirror 25 meters wide for gathering visible and near-infrared light. The Hubble Space Telescope's primary mirror is only 2.4 meters wide, while NASA's upcom- ing James Webb Space Telescope will have a primary mirror 6.5 meters wide made from 18 hexagonal segments. G OAT could potentially image structures on Jupiter that are just 10 to 20 kilometers in size and features 200 kilometers wide in the Kuiper Belt some 50 times farther from the sun than Earth. Similar platforms could watch Earth for continuous, re- al-time, high-resolution observations, said Craig Underwood, head of the planetary environments group at the Surrey Space Centre at the University of Surrey in England. One strategy for constructing GOAT would use a hub satellite with a robot- ic arm to assemble relatively "dumb" mirror elements together. Another would have relatively "smart" mirror segments, each capable of f lying au- tonomously to assemble around a hub satellite. The scientists said smart mirrors might prove wasteful, in that each would spend most of its life as part of a whole instead of as an autonomous spacecraft, making its propulsion, power and computational systems largely dead weight in the finished space telescope. However, they noted that because smart mirrors are more independent, launches of them could be distributed over time to spread out costs. Ultimately, they suggested building GOAT might incorporate a combination of these approaches. If each of GOAT's mirror segments is an autonomous hexagonal space- craft 10 centimeters wide and 6 kilo- grams in mass—about the size of the CubeSats now frequently deployed in orbit—the researchers imagined that about 14,000 smart mirrors would be needed for the space telescope. In addition to a central hub satellite that holds GOAT's lenses as well as power and other key systems, several mobile "helper satellites" would be needed to assemble elements such as the trusses holding everything together. The researchers plan to employ a ra- dio-frequency WiFi-like wireless com- munication network to help coordinate smart mirror activity during assembly and operations. Getting many small mirrors to act like a single big mirror re- quires scientists to control the shape and position of each small mirror to a preci- sion of about 10 nanometers, or roughly ten thousand times thinner than the av- erage width of a human hair. "To do this with a large number of mirror elements is no easy task!" Underwood said. All in all, the researchers said GOAT would have a mass of roughly 112 met- ric tons, requiring 17 launches with United Launch A lliance Delta-IV Heavy rocket, with launch costs alone reaching about $5 billion. However, the scientists added that using SpaceX's new Falcon Heavy rocket might slash launch costs by two-thirds, based on current price estimates. The scientists envision that GOAT would orbit at geostationary altitudes of roughly 35,800 kilometers. This would make GOAT close enough to Earth to enable potential repair, up- grade and refueling missions. Many research teams have previ- ously suggested assembling large space telescopes from smaller modules in or- bit. For example, in 2006, scientists at NASA's Goddard Space Flight Center suggested the Thirty Meter Space Telescope, which would be assembled by robots, astronauts or a combina- tion of both. In 2016 researchers at the California Institute of Technology and NASA's Jet Propulsion Laboratory pro- posed a 100-meter-wide, robotically assembled space telescope. However, GOAT has an advantage over those past concepts; there is already a project in the works that could make it a reality—the AAReST (Autonomous Assembly of a Reconfigurable Space Tele sc ope) m ission, sa id Serg io Pellegrino, a senior research scientist at NASA's Jet Propulsion Laboratory. NASA's AAReST Mission Underwood, one of the principal inves- tigators behind AAReST, has worked on small satellites for more than 30 years and has had "a long-term inter- est in investigating how small-satellite technology can be used to sense our world and to look beyond, out into the solar system." He was the chief architect of the SNAP-1 mission, the United Kingdom's first nano-satellite,

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