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Thread: The Interstellar Travel thread

  1. #1
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    Lightbulb The Interstellar Travel thread

    There does not seem to be a recent general thread on interstellar travel, given my searches, so here is one.

    The problems in sending a fleet of very small interstellar probes to Proxima Centauri are discussed in the paper below.

    https://arxiv.org/abs/2001.09987

    Technological Challenges in Low-mass Interstellar Probe Communication
    David Messerschmitt, Philip Lubin, Ian Morrison
    (Submitted on 24 Jan 2020)

    Building on a preliminary paper design of a downlink from a swarm of low-mass interstellar probes for returning scientific data from the vicinity of Proxima Centauri, the most critical technology issues are summarized, and their significance is explained in the context of the overall system design. The primary goal is to identify major challenges or showstoppers if such a downlink were to be constructed using currently available off-the-shelf technology, and thereby provide direction and motivation to future research on the constituent design challenges and technologies. While there are not any fundamental physical limits that prevent such communication systems, currently available technologies fall significantly short in several areas and there are other major design challenges with uncertain solutions. The greatest identified challenges are in mass constraints, multiplexing simultaneous communication from multiple probes to the same target exoplanet, attitude control and pointing accuracy, and Doppler shifts due to uncertainty in probe velocity. The greatest technology challenges are electrical power, high power and wavelength-agile optical sources, very selective and wavelength-agile banks of optical bandpass filters, and single-photon detectors with extremely low dark-count rates. For a critical subset of these, we describe the nature of the difficulties we encounter and their origins in the overall system context. A receiver that limits reception to a single probe is also considered and compared to the swarm case.
    Do good work. —Virgil Ivan "Gus" Grissom

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    Getting to relativistic speeds using light sails powered by... Active Galactic Nuclei ? Supernovae ?

    https://arxiv.org/abs/2002.03247

    Propulsion of Spacecrafts to Relativistic Speeds Using Natural Astrophysical Sources
    Manasvi Lingam and Abraham Loeb
    February 11, 2020

    In this paper, we explore the possibility of using natural astrophysical sources to accelerate spacecrafts to relativistic speeds. We focus on light sails and electric sails, which are reliant on momentum transfer from photons and protons, respectively, because these two classes of spacecrafts are not required to carry fuel on board. The payload is assumed to be stationed near the astrophysical source, and the sail is subsequently unfolded and activated when the source is functional. By considering a number of astrophysical objects such as massive stars, microquasars, supernovae, pulsar wind nebulae, and active galactic nuclei, we show that speeds approaching the speed of light might be realizable under broad circumstances. We also investigate the constraints arising from the ambient source environment as well as during the passage through the interstellar medium. While both of these considerations pose significant challenges to spacecrafts, we estimate that they are not insurmountable. Finally, we sketch the implications for carrying out future searches for technosignatures.
    Do good work. —Virgil Ivan "Gus" Grissom

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    Quote Originally Posted by Roger E. Moore View Post
    Getting to relativistic speeds using light sails powered by... Active Galactic Nuclei ? Supernovae ?
    There was a science fiction story (might have been from Larry Niven) about an alien race that comes to visit our solar system on a light sail craft. They offer to give us the technology to build the giant laser necessary for powering such a craft out of the solar system and to help us build it. They would be the first users of it when they leave our solar system.

    They also point out that if we don't accept their gift and build the device, that they have a different device that they can use to make a star go nova, and use that to power their light sail.

    Astronomers note that the alien craft came from the direction of a star that had recently gone nova.
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    Quote Originally Posted by Swift View Post
    There was a science fiction story (might have been from Larry Niven) about an alien race that comes to visit our solar system on a light sail craft. They offer to give us the technology to build the giant laser necessary for powering such a craft out of the solar system and to help us build it. They would be the first users of it when they leave our solar system.

    They also point out that if we don't accept their gift and build the device, that they have a different device that they can use to make a star go nova, and use that to power their light sail.

    Astronomers note that the alien craft came from the direction of a star that had recently gone nova.
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    That different device would probably be a gamma ray laser:
    --from the discussion section here:
    https://www.centauri-dreams.org/2020...nd-supernovae/

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    The communications aspect of a Starshot at Alpha Centauri

    https://arxiv.org/abs/2005.08940
    A Starshot Communication Downlink
    Kevin L. G. Parkin
    [Submitted on 15 May 2020]
    Breakthrough Starshot is an initiative to propel a sailcraft to Alpha Centauri within the next generation. As the sailcraft transits Alpha Centauri at 0.2 c, it looks for signs of life by imaging planets and gathering other scientific data. After the transit, the 4.1-meter diameter sailcraft downlinks its data to an Earth-based receiver. The present work estimates the raw data rate of a 1.02 {\mu}m, 100 Watt laser that is received at 1.25 {\mu}m by a 30-meter telescope. The telescope receives 288 signal photons per second (-133 dBm) from the sailcraft after accounting for optical gains (+296 dBi), conventional losses (-476 dB), relativistic effects (-3.5 dB), and link margin (-3.0 dB). For this photon-starved Poisson channel with 0.1 nm equivalent noise bandwidth, 90% detector quantum efficiency, 1024-ary PPM modulation, and 10^-3 raw bit error rate, the raw data rate is 260 bit/s (hard-decision) to 1.5 kbit/s (ideal) raw data rate, which is 8-50 Gbit/year. This rate is slowed by noise, especially starlight from Alpha Centauri A scattered into the detector by the atmosphere and receiver optics as sailcraft nears the star. Because this is a flyby mission (the sailcraft does not stop in the Centauri system), the proper motion of Alpha Centauri relative to Earth carries it away from the sailcraft after transit, and the noise subsides over days to weeks. The downlink can resume as soon as a day after transit, starting at 7-22 bit/s and reaching nearly full speed after 4 months. By using a coronagraph on the receiving telescope, full-rate downlink speed could be reached much sooner.
    Do good work. —Virgil Ivan "Gus" Grissom

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    Two proposals for interstellar spacecraft that just popped out.


    https://arxiv.org/abs/2007.11474

    Solar One: A Proposal for The First Crewed Interstellar Spacecraft

    Alberto Caballero

    In this paper it is presented the concept and design of a new type of spacecraft that could be used to make the first manned interstellar travel. Solar one would integrate three near-term technologies, namely: the US Navy CFR fusion reactor, a larger version of NASA Sunjammer light sail, and an array of DE-STAR laser systems. A system of Fresnel lenses and flexible mirrors to propel the sail with sunlight is suggested as an alternative to this array. With a mile-long light sail, Solar One could reach an average of 22% the speed of light, arriving to the closest potentially habitable exoplanet in less than 19 years with the help of a Bussard scoop. Key challenges are reducing the weight of continuous-wave lasers and compact fusion reactors as well as achieving cryo-sleep and artificial gravity.

    ======

    https://arxiv.org/abs/2007.12814

    Low-cost precursor of an interstellar mission

    René Heller (1), Guillem Anglada-Escudé (2,3), Michael Hippke (4,5), Pierre Kervella (6) ((1) Max Planck Institute for Solar System Research, Göttingen (GER), (2) Institut de Ciències de l'Espai, Bellaterra (ESP), (3) Institut d'Estudis Espacials de Catalunya, Barcelona (ESP), (4) Sonneberg Observatory (GER), (5) Visiting Scholar, Breakthrough Listen Group, Astronomy Department, UC Berkeley (USA), (6) LESIA, Observatoire de Paris (FRA))

    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.
    Do good work. —Virgil Ivan "Gus" Grissom

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    Here is another paper on the subject—the meson drive
    https://doi.org/10.1016/j.actaastro.2020.05.034

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