skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Relativistic Light Sails

Abstract

One proposed method for spacecraft to reach nearby stars is by accelerating sails using either solar radiation pressure or directed energy. This idea constitutes the thesis behind the Breakthrough Starshot project, which aims to accelerate a gram-mass spacecraft up to one-fifth the speed of light toward Proxima Centauri. For such a case, the combination of the sail’s low mass and relativistic velocity renders previous treatments incorrect at the 10% level, including that of Einstein himself in his seminal 1905 paper introducing special relativity. To address this, we present formulae for a sail’s acceleration, first in response to a single photon and then extended to an ensemble. We show how the sail’s motion in response to an ensemble of incident photons is equivalent to that of a single photon of energy equal to that of the ensemble. We use this principle of ensemble equivalence for both perfect and imperfect mirrors, enabling a simple analytic prediction of the sail’s velocity curve. Using our results and adopting putative parameters for Starshot , we estimate that previous relativistic treatments underestimate the spacecraft’s terminal velocity by ∼10% for the same incident energy. Additionally, we use a simple model to predict the sail’s temperature and diffractionmore » beam losses during the laser firing period; this allows us to estimate that, for firing times of a few minutes and operating temperatures below 300°C (573 K), Starshot will require a sail that absorbs less than one in 260,000 photons.« less

Authors:
 [1]
  1. Department of Astronomy, Columbia University, 550 W. 120th St., New York, NY 10027 (United States)
Publication Date:
OSTI Identifier:
22663536
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 153; Journal Issue: 6; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; DIAGRAMS; DIFFRACTION; LASERS; MASS; MIRRORS; PHOTONS; RADIATION PRESSURE; RELATIVISTIC RANGE; RELATIVITY THEORY; SAILS; SOLAR RADIATION; SPACE; SPACE VEHICLES; STARS; VELOCITY; VISIBLE RADIATION

Citation Formats

Kipping, David, E-mail: dkipping@astro.columbia.edu. Relativistic Light Sails. United States: N. p., 2017. Web. doi:10.3847/1538-3881/AA729D.
Kipping, David, E-mail: dkipping@astro.columbia.edu. Relativistic Light Sails. United States. doi:10.3847/1538-3881/AA729D.
Kipping, David, E-mail: dkipping@astro.columbia.edu. Thu . "Relativistic Light Sails". United States. doi:10.3847/1538-3881/AA729D.
@article{osti_22663536,
title = {Relativistic Light Sails},
author = {Kipping, David, E-mail: dkipping@astro.columbia.edu},
abstractNote = {One proposed method for spacecraft to reach nearby stars is by accelerating sails using either solar radiation pressure or directed energy. This idea constitutes the thesis behind the Breakthrough Starshot project, which aims to accelerate a gram-mass spacecraft up to one-fifth the speed of light toward Proxima Centauri. For such a case, the combination of the sail’s low mass and relativistic velocity renders previous treatments incorrect at the 10% level, including that of Einstein himself in his seminal 1905 paper introducing special relativity. To address this, we present formulae for a sail’s acceleration, first in response to a single photon and then extended to an ensemble. We show how the sail’s motion in response to an ensemble of incident photons is equivalent to that of a single photon of energy equal to that of the ensemble. We use this principle of ensemble equivalence for both perfect and imperfect mirrors, enabling a simple analytic prediction of the sail’s velocity curve. Using our results and adopting putative parameters for Starshot , we estimate that previous relativistic treatments underestimate the spacecraft’s terminal velocity by ∼10% for the same incident energy. Additionally, we use a simple model to predict the sail’s temperature and diffraction beam losses during the laser firing period; this allows us to estimate that, for firing times of a few minutes and operating temperatures below 300°C (573 K), Starshot will require a sail that absorbs less than one in 260,000 photons.},
doi = {10.3847/1538-3881/AA729D},
journal = {Astronomical Journal (Online)},
number = 6,
volume = 153,
place = {United States},
year = {Thu Jun 01 00:00:00 EDT 2017},
month = {Thu Jun 01 00:00:00 EDT 2017}
}
  • The primary challenge of rocket propulsion is the burden of needing to accelerate the spacecraft’s own fuel, resulting in only a logarithmic gain in maximum speed as propellant is added to the spacecraft. Light sails offer an attractive alternative in which fuel is not carried by the spacecraft, with acceleration being provided by an external source of light. By artificially illuminating the spacecraft with beamed radiation, speeds are only limited by the area of the sail, heat resistance of its material, and power use of the accelerating apparatus. In this paper, we show that leakage from a light sail propulsionmore » apparatus in operation around a solar system analogue would be detectable. To demonstrate this, we model the launch and arrival of a microwave beam-driven light sail constructed for transit between planets in orbit around a single star, and find an optimal beam frequency on the order of tens of GHz. Leakage from these beams yields transients with flux densities of Jy and durations of tens of seconds at 100 pc. Because most travel within a planetary system would be conducted between the habitable worlds within that system, multiply transiting exoplanetary systems offer the greatest chance of detection, especially when the planets are in projected conjunction as viewed from Earth. If interplanetary travel via beam-driven light sails is commonly employed in our galaxy, this activity could be revealed by radio follow-up of nearby transiting exoplanetary systems. The expected signal properties define a new strategy in the search for extraterrestrial intelligence (SETI)« less
  • We examine the possibility that fast radio bursts (FRBs) originate from the activity of extragalactic civilizations. Our analysis shows that beams used for powering large light sails could yield parameters that are consistent with FRBs. The characteristic diameter of the beam emitter is estimated through a combination of energetic and engineering constraints, and both approaches intriguingly yield a similar result that is on the scale of a large rocky planet. Moreover, the optimal frequency for powering the light sail is shown to be similar to the detected FRB frequencies. These “coincidences” lend some credence to the possibility that FRBs mightmore » be artificial in origin. Other relevant quantities, such as the characteristic mass of the light sail, and the angular velocity of the beam, are also derived. By using the FRB occurrence rate, we infer upper bounds on the rate of FRBs from extragalactic civilizations in a typical galaxy. The possibility of detecting fainter signals is briefly discussed, and the wait time for an exceptionally bright FRB event in the Milky Way is estimated.« less
  • The 2400-mile ocean tow of Rowan Cos., Inc.'s Rowan-Juneau jack-up drilling rig has verified the economic feasibility of using rig-mounted sails to assist tows. Proven technically feasible in earlier trials in the Gulf of Mexico, the use of sails increases the towing speed by an estimated 1/2-1 knot, stabilizes the rig, and ultimately cuts travel cost by $6000-$9500/day. Because it takes 4-5 days to install and remove the rigging and sails en route, profitable utilization is limited to fairly long moves.
  • Nippon Kokan K.K. determined that motor power supplemented by sail power would result in at least 10% fuel savings. Sails were tested first with a 1/15-scale model of a 480,000-dwt oil tanker, then the 1600-dwt Shin Aitoku Maru was built with computer-controlled sails. 4 figures. (DLC)
  • This article discusses the possibilities and politics of reorganizing US DOE, after two years of non-action in the Congress.