arXiv subjects

Kevin L. G. Parkin

Publications and source records attributed to Kevin L. G. Parkin.

3 recordsLinked to original sources

arXiv2024

Cost-Optimal Laser-Accelerated Lightsails

Laser-accelerated lightsails enable new types of missions that are very different from the Breakthrough Starshot mission to the Centauri system that aims to send 1 gram of payload at 0.2 c. The present work widens the mission design space to 0.1 mg to 100 kt payload and 0.0001-0.99 c cruise velocity. Drawing up to 5 GW directly from the grid (to augment power drawn from local energy storage) turns out to be the key to making small missions affordable: It collapses the accelerating laser's capital cost by up to 5 orders of magnitude, enabling new possibilities such as a 10 kg Solar system cubesat that accelerates to 0.001 c (63 au/yr) using a 77 m sail and \$610M laser, costing \$58M worth of energy per mission. Trajectory equations describing lightsail acceleration are derived in closed form and used instead of numerical integration. Consequently, analyses have progressed from single point designs to whole performance maps comprised of thousands of cost-optimized point designs. The performance maps reveal qualitatively different regimes characterized by the particular constraint that drives cost, and these driving constraints change depending on mission payload mass and cruise velocity. The performance maps also reveal a family of cost-optimal missions that accelerate at Earth gravity: The heaviest such mission is a 7.4 km diameter 100 kt vessel (equivalent to 225 International Space Stations) that is accelerated for 21 days to achieve 0.07 c, reaching the Centauri system within a human lifetime. While unthinkable at this time, the required 380 PW peak radiated power (twice terrestrial insolation) might be generated by space solar power or fusion within a few centuries. Regardless, it is now possible to contemplate such missions using laser-accelerated lightsails.

astro-ph.IM↗

arXiv2020

A Starshot Communication Downlink

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 μm, 100 Watt laser that is received at 1.25 μm 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.

astro-ph.IM↗

arXiv2018

The Breakthrough Starshot System Model

Breakthrough Starshot is an initiative to prove ultra-fast light-driven nanocrafts, and lay the foundations for a first launch to Alpha Centauri within the next generation. Along the way, the project could generate important supplementary benefits to solar system exploration. A number of hard engineering challenges remain to be solved before these missions can become a reality. A system model has been formulated as part of the Starshot systems engineering work. This paper presents the model and describes how it computes cost-optimal point designs. Three point designs are computed: A 0.2 c mission to Alpha Centauri, a 0.01 c solar system precursor mission, and a ground-based test facility based on a vacuum tunnel. All assume that the photon pressure from a 1.06 μm wavelength beam accelerates a circular dielectric sail. The 0.2 c point design assumes \$0.01/W lasers, \$500/m$^2$ optics, and \$50/kWh energy storage to achieve \$8.0B capital cost for the ground-based beam director. In contrast, the energy needed to accelerate each sail costs \$6M. Beam director capital cost is minimized by a 4.1 m diameter sail that is accelerated for 9 min. The 0.01 c point design assumes \$1/W lasers, \$10k/m$^2$ optics, and \$100/kWh energy storage to achieve \$517M capital cost for the beam director and \$8k energy cost to accelerate each 19 cm diameter sail. The ground-based test facility assumes \$100/W lasers, \$1M/m$^2$ optics, \$500/kWh energy storage, and \$10k/m vacuum tunnel. To reach 20 km/s, fast enough to escape the solar system from Earth, takes 0.4 km of vacuum tunnel, 22 kW of lasers, and a 0.6 m diameter telescope, all of which costs \$5M. The system model predicts that, ultimately, Starshot can scale to propel probes faster than 0.9 c.

astro-ph.IM↗