In 2016, Russian-American billionaire Yuri Milner founded Breakthrough Initiatives, a non-profit organization dedicated to investigating some of the most enduring mysteries of the Universe. Chief among their scientific efforts is Breakthrough Starshot, a proof-of-concept prototype that combines a lightsail, a nanocraft, and directed energy (aka. laser) propulsion to create a spacecraft capable of reaching the nearest star (Alpha Centauri) in our lifetimes.
Naturally, this presents all sorts of technical and engineering challenges, not the least of which is the amount of power needed to accelerate the spacecraft to relativistic speeds (a fraction of the speed of light). Luckily, scientists from the Australian National University (ANU) recently came up with a design for a directed-energy array made up of millions of individual lasers positioned across the Earth’s surface.
Last week (Friday. Feb. 14th), the Breakthrough Listen Initiative released about 2 petabytes of optical and radio data that they have accumulated over the past four years. This is the second data release by the non-profit effort (as part of Breakthrough Initiatives) and the public is once again invited to search through the data for possible signs of extraterrestrial communications.
Alpha Centauri is the closest star system to us, at 4.37 light-years (about 25 trillion miles) away. In 2016, astronomers discovered an exoplanet orbiting one of the three stars in the Alpha Centauri system. Spurred on by that discovery, the European Southern Observatory (ESO) has developed a new instrument to find any other planets that might be in the Alpha Centauri system, and it’s busy looking right now.
In 2015, Russian billionaire Yuri Milner established Breakthrough Initiatives, a non-profit organization dedicated to enhancing the search for extraterrestrial intelligence (SETI). In April of the following year, he and the organization be founded announced the creation of Breakthrough Starshot, a program to create a lightsail-driven “wafercraft” that would make the journey to the nearest star system – Proxima Centauri – within our lifetime.
In the latest development, on Wednesday May 23rd, Breakthrough Starshot held an “industry day” to outline their plans for developing the Starshot laser sail. During this event, the Starshot committee submitted a Request For Proposals (RFP) to potential bidders, outlining their specifications for the sail that will carry the wafercraft as it makes the journey to Proxima Centauri within our lifetimes.
As we have noted in severalpreviousarticles, Breakthrough Starshot calls for the creation of a gram-scale nanocraft being towed by a laser sail. This sail will be accelerated by an Earth-based laser array to a velocity of about 60,000 km/s (37,282 mps) – or 20% the speed of light (o.2 c). This concept builds upon the idea of a solar sail, a spacecraft that relies on solar wind to push itself through space.
At this speed, the nanocraft would be able to reach the closest star system to our own – Proxima Centauri, located 4.246 light-years away – in just 20 years time. Since its inception, the team behind Breakthrough Starshot has invested considerable time and energy addressing the conceptual and engineering challenges such a mission would entail. And with this latest briefing, they are now looking to move the project from concept to reality.
In addition to being the Frank B. Baird, Jr. Professor of Science at Harvard University, Abraham Loeb is also the Chair of the Breakthrough Starshot Advisory Committee. As he explained to Universe Today via email:
“Starshot is an initiative to send a probe to the nearest star system at a fifth of the speed of light so that it will get there within a human lifetime of a couple of decades. The goal is to obtain photos of exo-planets like Proxima b, which is in the habitable zone of the nearest star Proxima Centauri, four light years away. The technology adopted for fulfilling this challenge uses a powerful (100 Giga-watt) laser beam pushing on a lightweight (1 gram) sail to which a lightweight electronics chip is attached (with a camera, navigation and communication devices). The related technology development is currently funded at $100M by Yuri Milner through the Breakthrough Foundation.”
“The scope of this RFP addresses the Technology Development phase – to explore LightSail concepts, materials, fabrication and measurement methods, with accompanying analysis and simulation that creates advances toward a viable path to a scalable and ultimately deployable LightSail.”
As Loeb indicated, this RFP comes not long after another “industry day” that was related to the development of the technology of the laser – termed the “Photon Engine”. In contrast, this particular RFP was dedicated to the design of the laser sail itself, which will carry the nanocraft to Proxima Centauri.
“The Industry Day was intended to inform potential partners about the project and request for proposals (RFP) associated with research on the sail materials and design,” added Loeb. “Within the next few years we hope to demonstrate the feasibility of the required sail and laser technologies. The project will allocate funds to experimental teams who will conduct the related research and development work. ”
The RFP also addressed Starshot’s long-term goals and its schedule for research and development in the coming years. These include the investment in $100 million over the next five years to determine the feasibility of the laser and sail, to invest the value of the European Extremely Large Telescope (EELT) from year 6 to year 11 and build a low-power prototype for space testing, and invest the value of the Large Hardon Collider (LHC) over a 20 year period to develop the final spacecraft.
“The European Extremely Large Telescope (EELT) will cost on order of a billion [dollars] and the Large Hadron Collider cost was ten times higher,’ said Loeb. “These projects were mentioned to calibrate the scale of the cost for the future phases in the Starshot project, where the second phase will involve producing a demo system and the final step will involve the complete launch system.”
The research and development schedule for the sail was also outlined, with three major phases identified over the next 5 years. Phase 1 (which was the subject of the RFP) would entail the development of concepts, models and subscale testing. Phase 2 would involve hardware validation in a laboratory setting, while Phase 3 would consist of field demonstrations.
With this latest “industry day” complete, Starshot is now open for submissions from industry partners looking to help them realize their vision. Step A proposals, which are to consist of a five-page summary, are due on June 22nd and will be assessed by Harry Atwater (the Chair of the Sail Subcommittee) as well as Kevin Parkin (head of Parkin Research), Jim Benford (muWave Sciences) and Pete Klupar (the Project Manager).
Step B proposals, which are to consist of a more detailed, fifteen-page summary, will be due on July 10th. From these, the finalists will be selected by Pete Worden, the Executive Director of Breakthrough Starshot. If all goes according to plan, the initiative hopes to launch the first lasersail-driven nanocraft in to Proxima Centauri in 30 years and see it arrive there in 50 years.
So if you’re an aerospace engineer, or someone who happens to run a private aerospace firm, be sure to get your proposals ready! To learn more about Starshot, the engineering challenges they are addressing, and their research, follow the links provided to the BI page. To see the slides and charts from the RFP, check out Starshot’s Solicitations page.
Dr. Emilio Enriquez is a Post Doc at the Berkeley SETI Research Center and a member of the Breakthrough Listen Initiative (http://seti.berkeley.edu/listen/). Emilio is the lead author of two recent SETI Research Center publications about Ross 128 b, the nearby exoplanet that researchers feel may have conditions that are conducive to life.
His expertise is in modelling of physical processes in galaxies, such as gas accretion onto galaxies, star formation, stellar feedback, gas accretion onto black holes, among other similar mechanisms. He also works with large multi-wavelength surveys of galaxies to study the connection between galaxies and their central super-massive black holes.
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On October 19th, 2017, the Panoramic Survey Telescope and Rapid Response System-1 (Pan-STARRS-1) in Hawaii announced the first-ever detection of an interstellar asteroid, named 1I/2017 U1 (aka. ‘Oumuamua). Based on subsequent measurements of its shape (highly elongated and thin), there was some speculation that it might actually be an interstellar spacecraft (the name “Rama” ring a bell?).
For this reason, there are those who would like to study this object before it heads back out into interstellar space. While groups like Project Lyra propose sending a mission to rendezvous with it, Breakthrough Initiatives (BI) also announced its plans to study the object using Breakthrough Listen. As part of its mission to search for extra-terrestrial communications, this project will use the Greenbank Radio Telescope to listen to ‘Oumuamua for signs of radio transmissions.
Observations of ‘Oumuamua’s orbit revealed that it made its closest pass to our Sun back in September of 2017, and has been on its way back to interstellar space ever since. When it was observed back in October, it was passing Earth at a distance of about 85 times the distance between Earth and the Moon, and was traveling at a peak velocity of about 315,430 km/h (196,000 mph).
This indicated that, unlike the many Near-Earth Objects (NEOs) that periodically cross Earth’s orbit, this asteroid was not gravitationally bound to the Sun. In November, astronomers using the ESO’s Very Large Telescope (VLT) at the Paranal Observatory in Chile were also able to determine the brightness and color of the asteroid, which allowed for precise calculations of its size and shape.
Basically, they determined that it was 400 meters (1312 ft) long and very narrow, indicating that it was shaped somewhat like a cigar. What’s more, the idea of a cigar or needle-shaped spacecraft is a time-honored concept when it comes to science fiction and space exploration. Such a ship would minimize friction and damage from interstellar gas and dust, and could rotate to provide artificial gravity.
For all of these reasons, it is understandable why some responded to news of this asteroid by making comparisons to a certain science fiction novel. That would be Arthur C. Clarke’s Rendezvous with Rama, a story of a cylindrical space ship that travels through the Solar System while on its way to another star. While a natural origin is the more likely scenario, there is no consensus on what the origin this object might be – other than the theory that it came from the direction of Vega.
Hence why Breakthrough Listen intends to explore ‘Oumuamua to determine whether it is truly an asteroid or an artifact. Established in January of 2016, Listen is the largest scientific research program aimed at finding evidence of extra-terrestrial intelligence with established SETI methods. These include using radio observatories to survey 1,000,000 of the closest stars (and 100 of the closest galaxies) to Earth over the course of ten years.
Listen’s observation campaign will begin on Wednesday, December 13th, at 3:00 pm EST (12:00 PST), using the Greenbank Radio Telescope. This 100-meter telescope is the world’s premiere single-dish radio telescope and is capable of operating at millimeter and submillimeter wavelengths. It is also the mainstay of the NSF-funded Green Bank Observatory, located in West Virginia.
The first phase of observations will last a total of 10 hours, ranging from the 1 to 12 GHz bands, and will broken down into four “epochs” (based on the object’s rotational period). At present, ‘Oumuamua is about 2 astronomical units (AUs) – or 299,200,000 km; 185,900,000 mi – away from Earth, putting it at twice the distance between the Earth and the Sun. This places it well beyond the orbit of Mars, and over halfway between Mars and Jupiter.
At this distance, the Green Bank Telescope will take less than a minute to detect an omni-directional transmitter with the power of a cellphone. In other words, if there is a alien signal coming from this object, Breakthrough Listen is sure to sniff it out in no time! As Andrew Siemion, Director of Berkeley SETI Research Center and a member of Breakthrough Listen, explained in a BI press statement:
“‘Oumuamua’s presence within our solar system affords Breakthrough Listen an opportunity to reach unprecedented sensitivities to possible artificial transmitters and demonstrate our ability to track nearby, fast-moving objects. Whether this object turns out to be artificial or natural, it’s a great target for Listen.”
Even if there are no signals to be heard, and no other evidence of extra-terrestrial intelligence is detected, the observations themselves are a opportunity for scientists and the field of radio astronomy in general. The project will observe ‘Oumuamua in portions of the radio spectrum that it has not yet been observed at, and is expected to yield information about the possibility of water ice or the presence of a “coma” (i.e. gaseous envelop) around the object.
During the previous survey, data gathered using the VLT’s FOcal Reducer and low dispersion Spectrograph (FORS) indicated that ‘Oumuamua was likely a dense and rocky asteroid with a high metal content and little in the way of water ice. Updated information provided by the Greenbank Telescope could therefore confirm or cast doubt on this, thus reopening the possibility that it is actually a comet.
Regardless of what it finds, this survey is likely to be a feather in the cap of Breakthrough Listen, which already demonstrated it’s worth in terms of non-SETI astronomy this past summer. At that time, and using the Green Bank Radio Telescope, the Listen science team at UC Berkeley observed 15 Fast Radio Bursts (FRBs) for the fist time coming from a dwarf galaxy three billion light-years from Earth.
Still, I think we can all agree that an extra-terrestrial spaceship would be the most exciting possibility (and perhaps the most frightening!). And it is very safe to say that some of us will be awaiting the results of the survey with baited breath. Luckily, we’ll only have to wait two more days to see if humanity is still alone in the Universe or not! Stay tuned!
In 2015, Russian billionaire Yuri Milner established Breakthrough Initiatives, a non-profit organization dedicated to enhancing the search for extraterrestrial intelligence (SETI). In April of the following year, he and the organization be founded announced the creation of Breakthrough Starshot, a program to create a lightsail-driven “wafercraft” that would make the journey to the nearest star system – Alpha Centauri – within our lifetime.
This past June, the organization took a major step towards achieving this goal. After hitching a ride on some satellites being deployed to Low Earth Orbit (LEO), Breakthrough conducted a successful test flight of its first spacecraft. Known as “Sprites”, these are not only the smallest spacecraft ever launched, but prototypes for the eventual wafercraft Starshot hopes to send to Alpha Centauri.
The concept for a wafercraft is simple. By leveraging recent developments in computing and miniaturization, spacecraft that are the size of a credit card could be created. These would be capable of carrying all the necessary sensors, microprocessors and microthrusters, but would be so small and light that it would take much less energy to accelerate them to relativistic speeds – in the case of Starshot, up to 20% the speed of light.
As Pete Worden – Breakthrough Starshot’s executive director and the former director of NASA’s Ames Research Center – said in an interview with Scientific American:
“This is a very early version of what we would send to interstellar distances. In addition, this is another clear demonstration that it is possible for countries to work together to do great things in space. These are European spacecraft with U.S. nanosatellite payloads launching on an Indian booster—you can’t get much more international than that.”
Professor Abraham Loeb also has some choice words to mark this historic occasion. In addition to being the Frank B. Baird Jr. Professor of Science, the Chair of the Astronomy Department and the Director of the Institute for Theory and Computation at Harvard University, Prof. Loeb is also the chairman of the Breakthrough Starshot Advisory Committee. As he told Universe Today via email:
“The launch of the Sprite satellites marks the first demonstration that miniaturized electronics on small chips can be launched without damage, survive the harsh environment of space and communicate successfully with earth. The Starshot Initiative aims to launch similar chips attached to a lightweight sail that it being pushed by a laser beam to a fifth of the speed of light, so that its camera, communication and navigation devices (whose total weight is of order a gram) will reach the nearest planet outside the solar System within our generation.”
The craft were deployed on June 23rd, piggybacking on two satellites belonging to the multinational technology corporation OHB System AG. Much like the StarChips that Starshot is proposing, the Sprites represent a major step in the evolution of miniature spacecraft that can do the job of larger robotic explorers. They measure just 3.5 by 3.5 cm (1.378 x 1.378 inches) and weight only four grams (0.14 ounces), but still manage to pack solar panels, computers, sensors and radios into their tiny frames.
The Sprite were originally conceived by Zac Manchester, a postdoctorate researcher and aerospace engineer at Cornell University. Back in 2011, he launched a Kickstarter campaign (called “KickSat“) to raise funds to develop the concept, which was his way of bringing down the associated costs of spaceflight. The campaign was a huge success, with Manchester raising a total of $74,586 of his original goal of $30,000.
“The Sprites project is led by Zac Manchester, a Harvard postdoc who started working on this during his PhD at Cornell. Sprites are chip-size satellites powered by sunlight, intended to be released in space to demonstrate a new technology of lightweight (gram-scale) spacecrafts that can communicated with Earth.”
The purpose of this mission was to test how well the Sprites’ electronics systems and radio communications performed in orbit. Upon deployment, the Sprites remained attached to these satellites (known as “Max Valier” and “Venta”) and began transmitting. Communications were then received from ground stations, which demonstrated that the Sprites’ novel radio communication architecture performed exactly as it was designed to.
With this test complete, Starshot now has confirmation that a waferocraft is capable of operating in space and communicating with ground-based controllers. In the coming months and years, the many scientists and engineers that are behind this program will no doubt seek to test other essential systems (such as the craft’s microthrusters and imagers) while also working on the various engineering concerns that an instellar mission would entail.
In the meantime, the Sprites are still transmitting and are in radio contact with ground stations located in California and New York (as well as radio enthusiasts around the world). For those looking to listen in on their communications, Prof. Loeb was kind enough to let us know what frequency they are transmitting on.
“The radio frequency at which the Sprites that were just launched operate is 437.24 MHz, corresponding to a wavelength of roughly 69 cm,” he said. So if you’ve got a ham radio and feel like tuning in, this is where to set your dials!
And be sure to check out Zac Manchester’s Kickstarter video, which showcases the technology and inspiration for the KickSat:
In July of 2015, Breakthrough Initiatives – a non-profit dedicated to the search for extra-terrestrial intelligence, founded by Yuri Milner – announced the creation of Breakthrough Listen. A ten-year initiative costing $100 million, this program was aimed at using the latest in instrumentation and software to conduct the largest survey to date for extraterrestrial communications, encompassing the 1,000,000 closest stars and 100 closest galaxies.
On Thursday, April. 20th, at the Breakthrough Discuss conference, the organization shared their analysis of the first year of Listen data. Gathered by the Green Bank Radio Telescope, this data included an analysis of 692 stars, as well as 11 events that have been ranked for having the highest significance. The results have been published on the project’s website, and will soon be published in the Astrophysical Journal.
While the results were not exactly definitive, this is just the first step in a program that will span a decade. As Dr. Andrew Siemion, the Director of the BSRC, explained in a BI press release:
“With the submission of this paper, the first scientific results from Breakthrough Listen are now available for the world to review. Although the search has not yet detected a convincing signal from extraterrestrial intelligence, these are early days. The work that has been completed so far provides a launch pad for deeper and more comprehensive analysis to come.”
The Green Bank Telescope searched for these signals using its “L-band” receiver, which gathers data in frequencies ranging from 1.1 to 1.9 GHz. At these frequencies, artificial signals can be distinguished from natural sources, which includes pulsars, quasars, radio galaxies and even the Cosmic Microwave Background (CMB). Within these parameters, the BSRC team examined 692 stars from its primary target list.
For each star, they conducting three five-minutes observation periods, while also conducting five-minute observations on a set of secondary targets. Combined with a Doppler drift search – a perceived difference in frequency caused by the motion of the source or receiver (i.e. the star and/or Earth) – the Listen science team identified channels where radio emission were seen for each target (aka. “hits”).
This led to a combined 400 hours and 8 petabytes worth of observational data. All together, the team found millions of hits from the sample data as a whole, and eleven events that rose above the threshold for significance. These events (which are listed here) took place around eleven distant stars and ranged from to 25.4 to 3376.9 SNR (Signal-to-Noise Ratio).
However, the vast majority of the overall hits were determined to be the result of radio frequency interference from local sources. What’s more, further analysis of the 11 events indicated that it was unlikely that any of the signals were artificial in nature. While these stars all exhibited their own unique radio “fingerprints”, this is not necessarily an indication that they are being broadcast by intelligent species.
But of course, finding localized and unusual radio signals is an excellent way to select targets for follow-up examination. And if there is evidence to be found out there of intelligent species using radio signals to communicate, Breakthrough Listen is likely to be the one that finds them. Of all the SETI programs mounted to date, Listen is by far the most sophisticated.
Not only do its radio surveys cover 10 times more sky than previous programs, but its instruments are 50 times more sensitive than telescopes that are currently engaged in the search for extra-terrestrial life. They also cover 5 times more of the radio spectrum, and at speeds that are 100 times as fast. Between now and when it concludes in the coming decade, the BSRC team plans to release updated Listen data once every six months.
In the meantime, they are actively engaging with signal processing and machine learning experts to develop more sophisticated algorithms to analyze the data they collect. And while they continue to listen for extra-solar sources of life, Breakthrough Starshot continues to develop the first concept for a laser-driven lightsail, which they hope will make the first interstellar voyage in the coming years.
And of course, we here in the Solar System are looking forward to missions in the coming decade that will search for life right here, in our own backyard. These include missions to Europa, Enceladus, Titan, and other “ocean worlds” where life is believed to exist in some exotic form!
Breakthrough Listen‘s data analysis can be found here. Director Andrew Siemion also took to Facebook Live on Thursday, April 20th, to presents the results of Listen’s first year of study.And be sure to check out this video that marked the launch of Breakthrough Initiatives:
Ever since the European Southern Observatory (ESO) announced that they had discovered an exoplanet in the nearby system of Proxima Centauri, there have been a lot of questions about this exoplanet. In addition to whether or not this planet could actually support life, astronomers have also been eager to see if its companion stars – Alpha Centauri A and B – have exoplanets too.
Prior to the discovery of Proxima b, Alpha Centauri was thought to host the closest exoplanets to Earth (Alpha Bb and Bc). However, time has cast doubt on the existence of the first, while the second’s existence remains unconfirmed. But thanks to a recent agreement between the ESO and Breakthrough Initiatives, we may yet find out if there are exoplanets in Alpha Centauri – which will come in handy when it comes time to explore there!
This includes a new instrument module that will allow the VLT to use a technique known as coronagraphy – a form of adaptive optics that corrects for a star’s brightness, thus making it easier for a telescope to spot the thermal glow of orbiting planets around them. While the Breakthrough Prize Foundation will pay a large fraction of the upgrade costs, the ESO will be making the VLT and its staff available to conduct the survey – which is scheduled for 2019.
Such an agreement is truly a win-win scenario. For the ESO, this will not only improve the VLT’s imaging abilities, but will also assist with the development of the European Extremely Large Telescope (E-ELT). This proposed array, which is scheduled for completion by 2024, will rely on the Mid-infrared E-ELT Imager and Spectrograph (METIS) instrument to hunt for potentially habitable exoplanets.
Any lessons learned from the upgrade of VISIR will allow them to develop the necessary expertise to run METIS, and will also allow them to test the effectiveness of the technology beforehand. For Breakthrough Initiatives, determining if there are any planets in the Alpha Centauri system will go a long way towards helping them mount their historic mission to this star.
In the coming years, Breakthrough Initiatives hopes to mount the first interstellar voyage in history using a lightsail and nanocraft that would rely on lasers to push it up to relativistic speeds (20% the speed of light). Known as Breakthrough Starshot, this craft could be ready to launch in a few years time, and would reach Alpha Centauri in just 20 years time.
Once there, the nanocraft (using a series of microsensors) would relay information back to Earth about the Alpha Centauri system – which would include any information on its system of planets, and whether or not they are habitable. Hence, determining if there’s anything there to study in the first place will help lay the groundwork for the mission.
As Professor Avi Loeb – the Frank B. Baird, Jr. Professor of Science at Harvard and a member of the Breakthrough Starshot Advisory Committee – told Universe Today via email:
“We hope that the partnership between the Breakthrough Prize Foundation and ESO will lead to the discovery of new habitable planets around the nearest stars. Once discovered, we could search for the molecular signatures of life in the atmosphere of these planets, and potentially even send a spacecraft that will reach them within our lifetime. The latter is the driver for the Starshot Initiative. The discovery of habitable nearby planets will provide us with targets for photography by gram-scale spacecrafts, launched at a fraction of the speed of light and equipped with cameras. For example, we would like to find out whether such planets are covered by blue oceans, green vegetation or yellow deserts.”
It’s one of the hallmarks of the new space age: a private and public organization coming together for the sake of mutual benefit. But when those benefits include advancing scientific research, space exploration, and the hunt for habitable planets other than our own, it truly is a win-win situation!
In the meantime, enjoy this video provided by ESO about their new partnership with Breakthrough Initiatives:
In 2015, Russian billionaire Yuri Milner founded Breakthrough Initiatives with the intention of bolstering the search for extra-terrestrial life. Since that time, the non-profit organization – which is backed by Stephen Hawking and Mark Zuckerberg – has announced a number of advanced projects. The most ambitious of these is arguably Project Starshot, an interstellar mission that would make the journey to the nearest star in just 20 years.
This concept involves an ultra-light nanocraft that would rely on a laser-driven sail to achieve speeds of up to 20% the speed of light. Naturally, for such a mission to be successful, a number of engineering challenges have to be tackled first. And according to a recent study by a team of international researchers, two of the most important issues are the shape of the sail itself, and the type of laser involved.
As they indicate in their study, titled “On the Stability of a Space Vehicle Riding on an Intense Laser Beam“, the team ran stability simulations 0n the concept, taking into account the nature of the wafer-sized craft (aka. StarChip), the sail (aka. Lightsail) and the nature of the laser itself. For the sake of these simulations, they also factored in a number of assumptions about Starshot’s design.
These included the notion that the StarChip would be a rigid body (i.e. made up of solid material), that the circular sail would either be flat, spherical or conical (i.e. concave in shape), and that the surface of the sail would reflect the laser light. Beyond this, they played with multiple variations on the design, and came up with some rather telling results.
As Dr. Elena Popova, the lead author on the paper, told Universe Today via email:
“We considered different shapes of sail: a) spherical (coincides with parabolic for small sizes) as most appropriate for final configuration of nanocraft en route; b) conical; c) flat (simplest) (will be seen to be unstable so that even spinning of craft does not help).”
What they found was that the simplest, stable configuration would involve a sail that was spherical in shape. It would also require that the StarChip be tethered at a sufficient distance from the sail, one which would be longer than the curvature radius of the sail itself.
“For the sail with almost flat cone shape we obtained similar stability condition,” said Popova. “The nanocraft with flat sail is unstable in every case. It simply corresponds to the case of infinite radius of curvature of the sale. Hence, there is no way to extend center of mass beyond it.”
As for the laser, they considered several how the two main types would effect stability. This included uniform lasers that have a sharp boundary and “Gaussian” beams, which are characterized by high-intensity in the middle that declines rapidly towards the edges. As Dr. Popova stated, they determined that in order to ensure stability – and that the craft wouldn’t be lost to space – a uniform laser was the way to go.
“The nanocraft driven by intense laser beam pressure acting on its Lightsail is sensitive to the torques and lateral forces reacting on the surface of the sail. These forces influence the orientation and lateral displacement of the spacecraft, thus affecting its dynamics. If unstable the nanocraft might even be expelled from the area of laser beam. The most dangerous perturbations in the position of nanocraft inside the beam and its orientation relative to the beam axis are those with direct coupling between rotation and displacement (“spin-orbit coupling”).”
In the end, these were very similar to the conclusions reached by Professor Abraham Loeb and his colleagues at Starshot. In addition to being the Frank B. Baird, Jr. Professor of Science at Harvard University, Prof. Loeb is also the chairman of the Breakthrough Foundation’s Advisory Board. In a study titled “Stability of a Light Sail Riding on a Laser Beam” (published on Sept, 29th, 2016), they too examined what was necessary to ensure a stable mission.
This included the benefits of a conical vs. a spherical sail, and a uniform vs. a Gaussian beam. As Prof. Loeb told Universe Today via email:
“We found that a parachute-shaped sail riding on a Gaussian laser beam is unstable… We show in our paper that a sail shaped as a spherical shell (like a large ping-pong ball) can ride in a stable fashion on a laser beam that is shaped like a cylinder (or 3-4 lasers that establish a nearly circular illumination).”
As for the recommendations about the StarChip being at a sufficient distance from the LightSail, Prof. Loeb and his colleagues are of a different mind. “They argue that in case you attach a weight to the sail that is sufficiently well separated from the parachute, you might make it stable.” he said. “Even if this is true, it is unclear that their proposal is useful because such a configuration is rather complicated to build and launch.”
These are just a few of the engineering challenges facing an interstellar mission. Back in September, another study was released that assessed the risk of collisions and how it might effect the Starshot mission. In this case, the researchers suggested that the sail have a layer of shielding to absorb impacts, and that the laser array be used to clear debris in the LightSail’s path.
When Milner and the science team behind Starshot first announced their intention to create an interstellar spacecraft (in April 2016), they were met with a great deal of enthusiasm and skepticism. Understandably, many believed that such a mission was too ambitious, due to the challenges involved. But with every challenge that has been addressed, both by the Starshot team and outside researchers, the mission architecture has evolved.
At this rate, barring any serious complications, we may be seeing an interstellar mission taking place within a decade or so. And, barring any hiccups in the mission, we could be exploring Alpha Centauri or Proxima b up close within our lifetime!