Breakthrough Starshot was a research and engineering project by theBreakthrough Initiatives program to develop aproof-of-concept fleet oflight sailinterstellar probes namedStarchip,[1] to be capable of making the journey to theAlpha Centauri star system 4.34light-years away. It was founded in 2016 byYuri Milner,Stephen Hawking, andMark Zuckerberg.[2][3]
A flyby mission was proposed toProxima Centauri b, anEarth-sizedexoplanet in thehabitable zone of its host star,Proxima Centauri, in the Alpha Centauri system.[4] At a speed between 15% and 20% of thespeed of light,[5][6][7][8] it would take between 20 and 30 years to complete the journey, and approximately 4 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 ofUC Santa Barbara.[9][10] Sending the lightweight spacecraft involves a multi-kilometerphased array of beam-steerablelasers with a combined coherent power output of up to 100GW.[11]
In September 2025,Scientific American reported that the project was on hold indefinitely.[12] Philip Lubin estimates that the project had spent about $4.5 million of the proposed $100 million by this point.
The project was announced on 12 April 2016 in an event held inNew York City by physicist and venture capitalistYuri Milner, together with cosmologistStephen Hawking, who was serving as board member of the initiatives. Other board members include Facebook, Inc. (now known asMeta Platforms) CEOMark Zuckerberg. The project had an initial funding of US$100 million. Milner placed the final mission cost at $5–10 billion, and estimated the first craft could launch by around 2036.[6]Pete Worden is the project's executive director andHarvard ProfessorAvi Loeb chairs the advisory board for the project.[13]
The Breakthrough Starshot program aimed to demonstrate a proof-of-concept for ultra-fast, light-driven nano-spacecraft, and lay the foundations for a first launch toAlpha Centauri within the next generation.[14] The spacecraft would make a flyby, and possibly photograph, of any Earth-like worlds that might exist in the system. Secondary goals were Solar System exploration and detection ofEarth-crossing asteroids.[15]
TheEuropean Southern Observatory (ESO) announced the detection of a planet orbiting the third star in the Alpha Centauri system,Proxima Centauri in August 2016.[16][17] The planet, calledProxima Centauri b, orbits within thehabitable zone of its star. It could be a target for one of the Breakthrough Initiatives' projects.
In January 2017, Breakthrough Initiatives and the European Southern Observatory began collaborating to search forhabitable planets in the nearby star system Alpha Centauri.[18][19] The agreement involves Breakthrough Initiatives providing funding for an upgrade to the VISIR (VLT Imager and Spectrometer for mid-Infrared) instrument on ESO'sVery Large Telescope (VLT) inChile. This upgrade will increase the likelihood of planet detection in the system.
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The Starshot concept envisioned launching a "mothership" carrying about a thousand tiny spacecraft (on the scale of centimeters) to a high-altitude Earth orbit for deployment. Aphased array of ground-based lasers would then focus a light beam on the sails of these spacecraft 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 1TJ delivered to each sail. A preliminary sail model is suggested to have a surface area of 4 m × 4 m.[20][21] An October 2017 presentation of the Starshot system model[22][23] examined circular sails and finds that the beam director capital cost is minimized by having a sail diameter of 5 meters.
The Earth-sized planet Proxima Centauri b is within the Alpha Centauri system'shabitable zone. Ideally, the Breakthrough Starshot would aim its spacecraft within oneastronomical unit (150 million kilometers or 93 million miles) of that world. From this distance, a craft's cameras could capture an image of high enough resolution to resolve surface features.[24]
The fleet would have about 1000 spacecraft. Each one, called a StarChip, would be avery small centimeter-sized vehicle weighing a few grams.[1] They would be propelled by a square-kilometre array of 10 kW ground-basedlasers with a combined output of up to 100 GW.[25][26] A swarm of about 1000 units would compensate for the losses caused by interstellar dust collisionsen route to the target.[25][27] In a detailed study in 2016, Thiem Hoang and coauthors[28] found that mitigating the collisions withdust,hydrogen, andgalactic cosmic rays may not be as severe an engineering problem as first thought, although it will likely limit the quality of the sensors on board.[29]
Light propulsion requires enormous power: a laser with a gigawatt of power (approximately the output of a large nuclear plant) would provide only a fewnewtons ofthrust.[26] The spaceship will compensate for the low thrust by having a mass of only a few grams. The camera, computer, communications laser, anuclear power source, and the solar sail must be miniaturized to fit within a mass limit.[26][30] All components must be engineered to endure extremeacceleration, cold, vacuum, and interstellar particles such as stray protons.[27] The spacecraft will have to survive collisions withspace 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.[26][31] Focusing a set of lasers totaling one hundred gigawatts onto the solar sail will be difficult due toatmospheric turbulence, so there is the suggestion to use space-based laser infrastructure.[32] In addition, due to the size of the light sail and distance the light sail will be from the laser at the end of the acceleration, very large coherent combining optics would be required to focus the laser.[33][34] The diffraction limit of the laser light used sets the minimum diameter of the coherently focused laser beam at the source. For example, to accelerate the previously mentioned 4m sail at 10,000Gs to 0.2c requires combining optics which are approximately 3 kilometers in diameter to focus the laser light on the sail. This could be implemented using a phased array system which is being researched at The University of California Santa Barbara.[35][36] According toThe Economist, at least a dozen off-the-shelf technologies will need to improve byorders of magnitude.[26]
StarChip was the name used byBreakthrough Initiatives for a very small, centimeter-sized, gram-scale,interstellarspacecraft envisioned for the Breakthrough Starshot program,[1][37] a proposed mission to propel a fleet of a thousandStarChips on a journey toAlpha Centauri, the neareststar system, about 4.37light-years fromEarth.[38][6][39][5][40][41] The ultra-lightStarChip robotic nanocraft, fitted withlight sails, are planned to travel at speeds of 20%[1][6][39][5] and 15%[5] of thespeed 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.[6]
In July 2017, scientists announced that precursors toStarChip, called Sprites, were successfully launched and flown throughPolar Satellite Launch Vehicle byISRO fromSatish Dhawan Space Centre.[42] 105 Sprites were also flown to the ISS on theKickSat-2 mission that launched on 17 November 2018, from where they were deployed on 18 March 2019. They successfully transmitted data before reentering the atmosphere and burning up on 21 March.[43][44][45][46]
EachStarChip nanocraft was 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-scalelight sail, made of lightweight materials, with a gram-scale mass.[1][37][38][6][40][41][47][48] The envisioned technical specifications for the nanocrafts included:
Thelight sail was envisioned to be no larger than 4 by 4 meters (13 by 13 feet),[1][55] possibly of compositegraphene-based material.[1][38][6][41][48][56] 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][6][57] The light sail was also proposed to double as a power source during cruise, because collisions with atoms of interstellar medium would deliver 60 watt/m2 of power.[53]
A laser communicator, utilizing the light sail as the primary reflector, would be capable of data rates of 2.6-15baud per watt of transmitted power at the distance to Alpha Centauri, assuming a 30 m diameter receiving telescope on Earth.[58]
The Starshot project was a fly-by mission, which pass the target at high velocity. Helleret al.[59] proposed that a photo-gravitational assist could be used to slow such a probe and allow it to enter orbit (using photon pressure in maneuvers similar toaerobraking). This requires a sail that is both much lighter and much larger than the proposed Starshot sail. The table below lists possible target stars for photogravitational assist rendezvous.[59] The travel times are the calculated times for an optimized spacecraft to travel to the star and then enter orbit around the star.
| 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 | TBD | 8.58 | 24.20 |
| Epsilon Eridani | 363.35 | 10.50 | 0.50 |
| Procyon A | 154.06 | 11.44 | 6.94 |
| Altair | 176.67 | 16.69 | 10.70 |
| Vega | 167.39 | 25.02 | 50.05 |
| Fomalhaut A | 221.33 | 25.13 | 16.67 |
| Denebola | 325.56 | 35.78 | 14.66 |
| Castor A | 341.35 | 50.98 | 49.85 |
The German physicistClaudius Gros has proposed that the technology of the Breakthrough Starshot initiative may be used in a second step to establish abiosphere ofunicellular microbes on otherwise only transientlyhabitableexoplanets.[60][61] A Genesis probe would travel at lower speeds, at a speed 4.6% of the speed of light, which would take at least 90 years to get to Alpha Centauri A. The sail could be configured so that the stellar pressure from Alpha Centauri A brakes and deflects the probe toward Alpha Centauri B, where it would arrive after a few days. The sail would then be slowed again to 0.4% of the speed of light and catapulted towards Proxima Centauri. At that speed it will arrive there after another 46 years – about 140 years after its launch. It could hence be decelerated using amagnetic sail.[62]
In 2025, researchers fromBrown University andTU Delft developed a cutting-edge, ultra-thin light sail optimized withartificial intelligence. This light sail, designed for interstellar missions, was only 200 nanometers thick, with a surface covered in billions of nanoscale holes. These microscopic holes reduced weight while significantly increasing reflectivity, making the light sail more efficient for light-driven propulsion. This breakthrough could play a crucial role in advancing interstellar travel, allowing spacecraft to reach distant stars within a human lifetime.[63]
NASA is pleased to hear that Professor Lubin has received external funding to continue the work started in his NIAC study.
TheAlpha Centauri system | ||
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| Planets | ||
| Proposed mission concepts | ||
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