The solar photon pressure provides a viable source of thrust for spacecraft in the solar system. Theoretically it could also enable interstellar missions, but an extremely small mass per cross section area is required to overcome the solar gravity. We identify aerographite, a synthetic carbon-based foam with a density of 0.18 kg/m^3 (15,000 times more lightweight than aluminum) as a versatile material for highly efficient propulsion with sunlight. A hollow aerographite sphere with a shell thickness eps_shl = 1 mm could go interstellar upon submission to the solar radiation in interplanetary space. Upon launch at 1 AU from the Sun, an aerographite shell with eps_shl = 0.5 mm arrives at the orbit of Mars in 60 d and at Pluto's orbit in 4.3 yr. Release of an aerographite hollow sphere, whose shell is 1 micrometer thick, at 0.04 AU (the closest approach of the Parker Solar Probe) results in an escape speed of nearly 6900 km/s and 185 yr of travel to the distance of our nearest star, Proxima Centauri. The infrared signature of a meter-sized aerographite sail could be observed with JWST up to 2 AU from the Sun, beyond the orbit of Mars. An aerographite hollow sphere with eps_shl = 100 micrometer and a radius of 1 m (5 m) weighs 230 mg (5.7 g) and has a 2.2 g (55 g) mass margin for interstellar escape. The payload margin is ten times the mass of the spacecraft, whereas the payload on chemical interstellar rockets is typically a thousandth of the weight of the rocket. Simplistic communication would enable studies of the interplanetary medium and a search for the suspected Planet Nine, and would serve as a precursor mission to alpha Centauri. We estimate prototype developments costs of 1 million USD, a price of 1000 USD per sail, and a total of <10 million USD including launch for a piggyback concept with an interplanetary mission.
The Feasibility of a Spacecraft Flyby with the Third Interstellar Object 3I/ATLAS from Earth or Mars
Michigan State University（密歇根州立大学）；NASA Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；University of Arizona（亚利桑那大学）；Politecnico di Milano（米兰理工大学）；University of Michigan（密歇根大学）
Interstellar Object Accessibility and Mission Design
Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；California Institute of Technology（加州理工学院）；Division of Engineering and Applied Science, California Institute of Technology（加州理工学院工程与应用科学学院）；Institute for Astronomy, University of Hawaii at Manoa（夏威夷大学马诺阿分校天文研究所）；University of Hawaii at Manoa（夏威夷大学马诺阿分校）
