Breakthrough Starshot

Breakthrough Starshot is a research and engineering project by the Breakthrough Initiatives to develop a proof-of-concept fleet of light sail spacecraft named StarChip,[1] to be capable of making the journey to the Alpha Centauri star system 4.37 light-years away.

A flyby mission has been proposed to Proxima Centauri b, an Earth-sized exoplanet in the habitable zone of its host star, Proxima Centauri, in the Alpha Centauri system.[2] At a speed between 15% and 20% of the speed of light,[3][4][5][6] it would take between twenty and thirty years to complete the journey, and approximately four years for a return message from the starship to Earth.

The conceptual principles to enable this interstellar travel project were described in "A Roadmap to Interstellar Flight", by Philip Lubin of UC Santa Barbara.[7][8] Sending the lightweight spacecraft involves a multi-kilometer phased array of beam-steerable lasers with a combined coherent power output of up to 100 GW.[9]

Press Conference at ESO HQ2
On 24 August 2016, ESO hosted a press conference to discuss the announcement of exoplanet Proxima b at its headquarters in Germany. In this picture, Pete Worden giving a speech.

General

The project was announced on 12 April 2016 in an event held in New York City by physicist and venture capitalist Yuri Milner, together with cosmologist Stephen Hawking, who was serving as board member of the initiatives. Other board members include Facebook CEO Mark Zuckerberg. The project has an initial funding of US$100 million to initialize research. Milner places the final mission cost at $5–10 billion, and estimates the first craft could launch by around 2036.[4] Pete Worden is the project's executive director and Professor Avi Loeb (Harvard University) chairs the Advisory Board for the project.[10]

In 2017 Stephen Hawking told the audience at Starmus Festival:

Our physical resources are being drained at an alarming rate. We have given our planet the disastrous gift of climate change. Rising temperatures, reduction of the polar ice caps, deforestation and decimation of animal species. We can be an ignorant, unthinking lot. We are running out of space and the only places to go to are other worlds. It is time to explore other solar systems. Spreading out may be the only thing that saves us from ourselves. I am convinced that humans need to leave Earth.[11]

Objectives

The Breakthrough Starshot program aims to demonstrate a proof-of-concept for ultra-fast, light-driven nano-spacecraft, and lay the foundations for a first launch to Alpha Centauri within the next generation.[12] Secondary goals are: Solar System exploration and detection of Earth-crossing asteroids.[13] The spacecraft would make a flyby of, and, possibly photograph any Earth-like worlds that might exist in the system.

Target planet

In August 2016, the European Southern Observatory (ESO) announced the detection of a planet orbiting the third star in the Alpha Centauri system, Proxima Centauri.[14][15] The planet, called Proxima Centauri b, is orbiting within the habitable zone of its star, and it could be a potential target for one of the projects of Breakthrough Initiatives.

In January 2017, Breakthrough Initiatives and the European Southern Observatory entered a collaboration to search for habitable planets in the nearby star system, Alpha Centauri.[16][17] The agreement involves Breakthrough Initiatives providing funding for an upgrade to the VISIR (VLT Imager and Spectrometer for mid-Infrared) instrument on ESO’s Very Large Telescope (VLT) in Chile. This upgrade will greatly increase the likelihood of planet detection in the system.

Concept

Solar Sail (14914129324)
A solar sail concept

The Starshot concept envisions launching a "mothership" carrying about a thousand tiny spacecraft (on the scale of centimeters) to a high-altitude Earth orbit and then deploying them. A phased array of ground-based lasers would then focus a light beam on the crafts' sails to accelerate them one by one to the target speed within 10 minutes, with an average acceleration on the order of 100 km/s2 (10,000  ɡ), and an illumination energy on the order of 1 TJ delivered to each sail. A preliminary sail model is suggested to have a surface area of 4 m × 4 m.[18][19] An October 2017 presentation of the Starshot system model[20][21] examines circular sails and finds that the beam director capital cost is minimized by having a sail diameter of 5 meters.

Earth-size planet Proxima Centauri b was discovered in 2016 orbiting within the Alpha Centauri system habitable zones, compelling the Breakthrough Starshot to try to aim its spacecraft within 1 astronomical unit (150 million kilometers or 93 million miles) of it. From this distance, a craft's cameras could potentially capture an image of high enough quality to resolve surface features.[22]

The fleet would have about 1000 spacecraft, and each one (dubbed a StarChip), would be a very small centimeter-sized vehicle weighing a few grams.[1] They would be propelled by a square-kilometre array of 10 kW ground-based lasers with a combined output of up to 100 GW.[23][24] A swarm of about 1000 units would compensate for the losses caused by interstellar dust collisions en route to the target.[23][25] In a detailed study in 2016 Thiem Hoang and coworkers[26] found that mitigating the collisions with dust, hydrogen and galactic cosmic rays may not be quite as severe an engineering problem as first thought.[27]

Technical challenges

Light propulsion requires enormous power: a laser with a gigawatt of power (approximately the output of a large nuclear plant) would provide only a few newtons of thrust.[24] The spaceship will compensate for the low thrust by having a mass of only a few grams. The camera, computer, communications laser, a plutonium power source, and the solar sail must be miniaturized to fit within a mass limit.[24][28] All components must be engineered to endure extreme acceleration, cold, vacuum, and protons.[25] The spacecraft will have to survive collisions with space dust; Starshot expects each square centimeter of frontal cross-section to collide at high speed with about a thousand particles of size at least 0.1 μm.[24][29] Focusing a set of lasers totaling one hundred gigawatts onto the solar sail will be difficult, due to atmospheric turbulence. According to The Economist, at least a dozen off-the-shelf technologies will need to improve by orders of magnitude.[24]

StarChip

StarChip is the name used by Breakthrough Initiatives for a very small, centimeter-sized, gram-scale, interstellar spacecraft envisioned for the Breakthrough Starshot program,[1][30] a proposed mission to propel a fleet of a thousand StarChips on a journey to the Alpha Centauri star system, the nearest extrasolar stars, about 4.37 light-years from Earth.[31][4][32][3][33][34] The journey may include a flyby of Proxima Centauri b, an Earth-sized exoplanet that is in the habitable zone of its host star.[2] The ultra-light StarChip robotic nanocrafts, fitted with lightsails, are planned to travel at speeds of 20%[1][4][32][3] and 15%[3] of the speed of light, taking between 20 and 30 years to reach the star system, respectively, and about 4 years to notify Earth of a successful arrival.[4] The conceptual principles to enable practical interstellar travel were described in "A Roadmap to Interstellar Flight", by Philip Lubin of UC Santa Barbara,[7] who is an advisor for the Starshot project.

In July 2017, scientists announced that precursors to StarChip, named Sprites, were successfully launched and flown through Polar Satellite Launch Vehicle by ISRO from Satish Dhawan Space Centre.[35] Sprites will also be flown on the KickSat-2 mission scheduled for November 2018.

Components

Each StarChip nanocraft is expected to carry miniaturized cameras, navigation gear, communication equipment, photon thrusters and a power supply. In addition, each nanocraft would be fitted with a meter-scale lightsail, made of lightweight materials, with a gram-scale mass.[1][30][31][4][33][34][36][37]

Cameras

Four sub-gram scale digital cameras, each with a minimum 2-megapixels resolution, are envisioned.[1][38]

Processors

Four sub-gram scale processors are planned.[33][39]

Photon thrusters

Four sub-gram scale photon thrusters, each minimally capable of performing at a 1W diode laser level, are planned.[30][40][41]

Battery

A 150 mg atomic battery, powered by plutonium-238 or americium-241, is planned.[4][34][42]

Protective coating

A coating, possibly made of beryllium copper, is planned to protect the nanocraft from dust collisions and atomic particle erosion.[34][43]

Lightsail

The lightsail is envisioned to be no larger than 4 by 4 meters (13 by 13 feet),[1][44] possibly of composite graphene-based material.[1][31][4][34][37][45] The material would have to be very thin and be able to reflect the laser beam while absorbing only a small fraction of the incident energy, or it will vaporize the sail.[1][4][46]

Other potential destinations

The table below lists possible target stars for similar photogravitational assist travel.[47] The travel times are for the spacecraft to travel to the star and then enter orbit around the star (using photon pressure in maneuvers similar to aerobraking).

Name Travel time
(yr)
Distance
(ly)
Luminosity
(L)
Proxima Centauri 121 4.2 0.00005
α Centauri A 101.25 4.36 1.52
α Centauri B 147.58 4.36 0.50
Sirius A 68.90 8.58 24.20
Procyon A 154.06 11.44 6.94
Vega 167.39 25.02 50.05
Altair 176.67 16.69 10.70
Fomalhaut A 221.33 25.13 16.67
Denebola 325.56 35.78 14.66
Castor A 341.35 50.98 49.85
Epsilon Eridani 363.35 10.50 0.50
  • Successive assists at α Cen A and B could allow travel times to 75 yr to both stars.
  • Lightsail has a nominal mass-to-surface ratio (σnom) of 8.6×10−4 gram m−2 for a nominal graphene-class sail.
  • Area of the Lightsail, about 105 m2 = (316 m)2
  • Velocity up to 37,300 km s−1 (12.5% c)

Other applications

The German physicist Claudius Gros has proposed that the technology of the Breakthrough Starshot initiative may be utilized in a second step to establish a biosphere of unicellular microbes on otherwise only transiently habitable exoplanets.[48][49] A Genesis probe would travel at lower speeds, about 0.3% of the speed of light. It could hence be decelerated using a magnetic sail.[50]

See also

References

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  2. ^ a b Chang, Kenneth (24 August 2016). "One Star Over, a Planet That Might Be Another Earth". New York Times. Retrieved 24 August 2016.
  3. ^ a b c d Staff (12 April 2016). "Breakthrough Starshot". Breakthrough Initiatives. Retrieved 12 April 2016.
  4. ^ a b c d e f g h i Overbye, Dennis (12 April 2016). "Reaching for the Stars, Across 4.37 Light-Years; A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away". New York Times. Retrieved 12 April 2016.
  5. ^ Stone, Maddie (12 April 2016). "Stephen Hawking and a Russian Billionaire Want to Build an Interstellar Starship". Gizmodo. Retrieved 12 April 2016.
  6. ^ Staff (12 April 2016). "Breakthrough Initiatives - Breakthrough Starshot". Breakthrough Initiatives. Retrieved 14 April 2016.
  7. ^ a b Lubin, Philip (2016). "A Roadmap to Interstellar Flight". Journal of the British Interplanetary Society. 69: 40. arXiv:1604.01356. Bibcode:2016arXiv160401356L.(file available at University of California, Santa Barbara here Archived 17 April 2016 at the Wayback Machine. Accessed 16 April 2016)
  8. ^ Hall, Loura (7 May 2015). "DEEP IN Directed Energy Propulsion for Interstellar Exploration". NASA News. Retrieved 2016-04-22. NASA is pleased to hear that Professor Lubin has received external funding to continue the work started in his NIAC study.
  9. ^ "Breakthrough Initiatives". breakthroughinitiatives.org. Retrieved 2017-12-25.
  10. ^ "Starshot Leadership".
  11. ^ "Stephen Hawking Says Earth Is Under Threat And Humans Need To Leave". Newsweek. October 20, 2017.
  12. ^ "Breakthrough Initiatives". breakthroughinitiatives.org. Retrieved 10 January 2017.
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  14. ^ "Planet Found in Habitable Zone Around Nearest Star - Pale Red Dot campaign reveals Earth-mass world in orbit around Proxima Centauri". www.eso.org. Retrieved 10 January 2017.
  15. ^ Witze, Alexandra (25 August 2016). "Earth-sized planet around nearby star is astronomy dream come true". Nature. 536 (7617): 381–382. Bibcode:2016Natur.536..381W. doi:10.1038/nature.2016.20445.
  16. ^ "VLT to Search for Planets in Alpha Centauri System - ESO Signs Agreement with Breakthrough Initiatives". www.eso.org. Retrieved 10 January 2017.
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  18. ^ Lightsail, Integrity under thrust.
  19. ^ Lightsail | Stability on the beam.
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  21. ^ Parkin, Kevin. "Starshot System Model".
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  25. ^ a b Emspak, Jesse (15 April 2016). "No Breakthrough Yet: Stephen Hawking's Interstellar 'Starshot' Faces Challenges". Space. Retrieved 15 April 2016.
  26. ^ Hoang (2017). "The Interaction of Relativistic Spacecrafts with the Interstellar Medium". The Astrophysical Journal. 837: 5. arXiv:1608.05284. Bibcode:2017ApJ...837....5H. doi:10.3847/1538-4357/aa5da6.
  27. ^ Timmer, John (24 August 2016). "Just how dangerous is it to travel at 20% the speed of light?". Science. Ars Technica. Retrieved 2016-08-28.
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  29. ^ "Interstellar Dust". Breakthrough Initiatives. Retrieved 15 April 2016.
  30. ^ a b c Greene, Kate (13 April 2016). "What Will Make Interstellar Travel a Reality?". Slate. Retrieved 16 April 2016.
  31. ^ a b c Clery, Daniel (12 April 2016). "Russian billionaire unveils big plan to build tiny interstellar spacecraft". Science. doi:10.1126/science.aaf4115. Retrieved 15 April 2016.
  32. ^ a b Stone, Maddie (12 April 2016). "Stephen Hawking and a Russian Billionaire Want to Build an Interstellar Starship". Gizmodo. Retrieved 12 April 2016.
  33. ^ a b c Domonoske, Camila (12 April 2016). "Forget Starships: New Proposal Would Use 'Starchips' To Visit Alpha Centauri". NPR. Retrieved 15 April 2016.
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  35. ^ Staff (26 July 2017). "In Quest To Reach Alpha Centauri, BreakThrough Starshot Launches World's Smallest Spacecraft - First Prototype 'Sprites' – Precursors to Eventual 'StarChip' Probes – Achieve Low Earth Orbit". BreakThroughInitiatives.org. Retrieved 28 July 2017.
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  38. ^ Staff (12 April 2016). "Breakthrouth Starshot: Gram-Scale Starchip Components - 4 Cameras". Breakthrough Initiatives. Retrieved 15 April 2016.
  39. ^ Staff (12 April 2016). "Breakthrouth Starshot: Gram-Scale Starchip Components - 4 Processors". Breakthrough Initiatives. Retrieved 15 April 2016.
  40. ^ Staff (12 April 2016). "Breakthrouth Starshot: Gram-Scale Starchip Components - 4 Photon Thrusters". Breakthrough Initiatives. Retrieved 15 April 2016.
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  43. ^ Staff (12 April 2016). "Breakthrouth Starshot: Gram-Scale Starchip Components - Protective Coating". Breakthrough Initiatives. Retrieved 15 April 2016.
  44. ^ Staff (12 April 2016). "Breakthrough Starshot: Lightsail, Integrity under thrust". Breakthrough Initiatives. Retrieved 16 April 2016.
  45. ^ Staff (12 April 2016). "Breakthrouth Starshot: Gram-Scale Starchip Components - Lightsail - Structure". Breakthrough Initiatives. Retrieved 15 April 2016.
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  47. ^ Heller, René; Hippke, Michael; Kervella, Pierre (2017). "Optimized trajectories to the nearest stars using lightweight high-velocity photon sails". The Astronomical Journal. 154 (3): 115. arXiv:1704.03871. Bibcode:2017AJ....154..115H. doi:10.3847/1538-3881/aa813f.
  48. ^ Claudius Gros: Developing Ecospheres on Transiently Habitable Planets: The Genesis Project, Astrophysics and Space Science, Vol. 361, pp 1-14 (2016).
  49. ^ Jessica Boddy: Q&A: Should we seed life on alien worlds?, Science, 9. September 2016.
  50. ^ James Romero, "Should we seed life through the cosmos using laser-driven ships?", New Scientist, 13 November (2017).

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