In the past decade, thousands of planets have been discovered beyond our Solar System. This has had the effect of renewing interest in space exploration, which includes the possibility of sending spacecraft to explore exoplanets. Given the challenges involved, a number of advanced concepts are currently being explored, like the time-honored concept of a light sail (as exemplified by Breakthrough Starshot and similar proposals).
However, in more recent years, scientists have proposed a potentially more-effective concept known as the electric sail, where a sail composed of wire mesh generates electrical charges to deflect solar wind particles, thus generating momentum. In a recent study, two Harvard scientists compared and contrasted these methods to determine which would be more advantageous for different types of missions.
At the University of California, Santa Barbara, researchers with the UCSB Experimental Cosmology Group (ECG) are currently working on ways to achieve the dream of interstellar flight. Under the leadership of Professor Philip Lubin, the group has dedicated a considerable amount of effort towards the creation of an interstellar mission consisting of directed-energy light sail and a wafer-scale spacecraft (WSS) “wafercraft“.
If all goes well, this spacecraft will be able to reach relativistic speeds (a portion of the speed of light) and make it to the nearest star system (Proxima Centauri) within our lifetimes. Recently, the ECG achieved a major milestone by successfully testing a prototype version of their wafercraft (aka. the “StarChip“). This consisted of sending the prototype via balloon into the stratosphere to test its functionality and performance.
On July 14th, 2015, theNew Horizons mission made history when it became the first robotic spacecraft to conduct a flyby of Pluto. On December 31st, 2018, it made history again by being the first spacecraft to rendezvous with a Kuiper Belt Object (KBO) – Ultima Thule (2014 MU69). In addition, the Voyager 2probe recently joined its sister probe (Voyager 1) in interstellar space.
Given these accomplishments, it is understandable that proposals for interstellar missions are once again being considered. But what would such a mission entail, and is it even worth it? Kelvin F. Long, the co-founder of the Initiative for Interstellar Studies (i4iS) and a major proponent of interstellar flight, recently published a paper that supports the idea of sending robotic missions to nearby star systems to conduct in-situ reconnaissance.
The dream of traveling to another star system, and maybe even finding populated worlds there, is one that has preoccupied humanity for many generations. But it was not until the era of space exploration that scientists have been able to investigate various methods for making an interstellar journey. While many theoretical designs have been proposed over the years, a lot of attention lately has been focused on laser-propelled interstellar probes.
The first conceptual design study, known as Project Dragonfly was hosted by the Initiative for Interstellar Studies (i4iS) in 2013. The concept called for the use of lasers to accelerate a light sail and spacecraft to 5% the speed of light, thus reaching Alpha Centauri in about a century. In a recent paper, one of the teams that took part in the design competition assessed the feasibility of their proposal for a lightsail and magnetic sail.
On October 19th, 2017, the first interstellar object – named 1I/2017 U1 (aka. ‘Oumuamua) – to be observed in our Solar System was detected. In the months that followed, multiple follow-up observations were conducted to gather more data on its composition, shape, and possible origins. Rather than dispel the mystery surrounding the true nature of ‘Oumuamua – is a comet or an asteroid? – these efforts have only managed to deepen it.
In a recent study, Harvard Professor Abraham Loeb and Shmuel Bialy – a postdoctoral researcher from the Smithsonian Center for Astrophysics (CfA) – addressed this mystery by suggesting that ‘Oumuamua may be an extra-terrestrial solar sail. Building on this, Loeb and Amir Siraj (a Harvard undergraduate student) conducted a new study that indicated that hundreds of “‘Oumuamua-like” objects could be detectable in our Solar System.
Interestingly enough, there has also been some speculation that based on its shape, ‘Oumuamua might actually be an interstellar spacecraft (Breakthrough Listen even monitored it for signs of radio signals!). A new study by a pair of astronomers from the Harvard Smithsonian Center for Astrophysics (CfA) has taken it a step further, suggesting that ‘Oumuamua may actually be a light sail of extra-terrestrial origin.
A team of researchers from the University of Nebraska–Lincoln recently conducted an experiment where they were able to accelerate plasma electrons to close to the speed of light. This “optical rocket”, which pushed electrons at a force a trillion-trillion times greater than that generated by a conventional rocket, could have serious implications for everything from space travel to computing and nanotechnology.
In April of 2016, Russian billionaire Yuri Milner announced the creation of Breakthrough Starshot. As part of his non-profit scientific organization (known as Breakthrough Initiatives), the purpose of Starshot was to design a lightsail nanocraft that would be capable of achieving speeds of up to 20% the speed of light and reaching the nearest star system – Alpha Centauri (aka. Rigel Kentaurus) – within our lifetimes.
At this speed – roughly 60,000 km/s (37,282 mps) – the probe would be able to reach Alpha Centauri in 20 years, where it could then capture images of the star and any planets orbiting it. But according to a recent article by Professor Bing Zhang, an astrophysicist from the University of Nevada, researchers could get all kinds of valuable data from Starshot and similar concepts long before they ever reached their destination.
To recap, Breakthrough Starshot seeks to leverage recent technological developments to mount an interstellar mission that will reach another star within a single generation. The spacecraft would consist of an ultra-light nanocraft and a lightsail, the latter of which would accelerated by a ground-based laser array up to speeds of hundreds of kilometers per second.
Such a system would allow the tiny spacecraft to conduct a flyby mission of Alpha Centauri in about 20 years after it is launched, which could then beam home images of possible planets and other scientific data (such as analysis of magnetic fields). Recently, Breakthrough Starshot held an “industry day” where they submitted a Request For Proposals (RFP) to potential bidders to build the laser sail.
According to Zhang, a lightsail-driven nanocraft traveling at a portion of the speed of light would also be a good way to test Einstein’s theory of Special Relativity. Simply put, this law states that the speed of light in a vacuum is constant, regardless of the inertial reference frame or motion of the source. In short, such a spacecraft would be able to take advantage of the features of Special Relativity and provide a new mode to study astronomy.
Based on Einstein’s theory, different objects in different “rest frames” would have different measures of the lengths of space and time. In this sense, an object moving at relativistic speeds would view distant astronomical objects differently as light emissions from these objects would be distorted. Whereas objects in front of the spacecraft would have the wavelength of their light shortened, objects behind it would have them lengthened.
This phenomenon, known as the “Doppler Effect”, results in light being shifted towards the blue end (“blueshift”) or the red end (“redshift”) of the spectrum for approaching and retreating objects, respectively. In 1929, astronomer Edwin Hubble used redshift measurements to determine that distant galaxies were moving away from our own, thus demonstrating that the Universe was in a state of expansion.
Because of this expansion (known as the Hubble Expansion), much of the light in the Universe is redshifted and only measurable in difficult-to-observe infrared wavelengths. But for a camera moving at relativistic speeds, according to Prof. Zhang, this redshifted light would become bluer since the motion of the camera would counteract the effects of cosmic expansion.
This effect, known as “Doppler boosting”, would cause the faint light from the early Universe to be amplified and allow distant objects to be studied in more detail. In this respect, astronomers would be able to study some of the earliest objects in the known Universe, which would offer more clues as to how it evolved over time. As Prof. Zhang explained to Universe Today via email, this would allow for some unique opportunities to test Special Relativity:
“In the rest frame of the camera, the emission of the objects in the hemisphere of the camera motion is blue-shifted. For bright objects with detailed spectral observations from the ground, one can observe them in flight. By comparing their blue-shifted flux at a specific blue-shifted frequency with the flux of the corresponding (de-blueshifted) frequency on the ground, one can precisely test the Doppler boosting prediction in Special Relativity.”
In addition, the frequency and intensity of light – and also the size of distant objects – would also change as far as the observer was concerned. In this respect, the camera would act as a lens and a wide-field camera, magnifying the amount of light it collects and letting astronomers observe more objects within the same field of view. By comparing the observations collected by the camera to those collected by a camera from the ground, astronomers could also test the probe’s Lorentz Factor.
This factor indicates how time, length, and relativistic mass change for an object while that object is moving, which is another prediction of Special Relativity. Last, but not least, Prof. Zhang indicates that probes traveling at relativistic speeds would not need to be sent to any specific destination in order to conduct these tests. As he explained:
“The concept of “relativistic astronomy” is that one does not really need to send the cameras to specific star systems. No need to aim (e.g. to Alpha Centauri system), no need to decelerate. As long as the signal can be transferred back to earth, one can learn a lot of things. Interesting targets include high-redshift galaxies, active galactic nuclei, gamma-ray bursts, and even electromagnetic counterparts of gravitational waves.”
However, there are some drawbacks to this proposal. For starters, the technology behind Starshot is all about accomplishing the dream of countless generations – i.e. reaching another star system (in this case, Alpha Centauri) – within a single generation.
And as Professor Abraham Loeb – the Frank B. Baird Jr. Professor of Science at Harvard University and the Chair and the Breakthrough Starshot Committee – told Universe Today via email, what Prof. Zhang is proposing can be accomplished by other means:
>“Indeed, there are benefits to having a camera move near the speed of light toward faint sources, such as the most distant dwarf galaxies in the early universe. But the cost of launching a camera to the required speed would be far greater than building the next generation of large telescopes which will provide us with a similar sensitivity. Similarly, the goal of testing special relativity can be accomplished at a much lower cost.”
Of course, it will be many years before a project like Starshot can be mounted, and many challenges need to be addressed in the meantime. But it is exciting to know that in meantime, scientific applications can be found for such a mission that go beyond exploration. In a few decades, when the mission begins to make the journey to Alpha Centauri, perhaps it will also be able to conduct tests on Special Relativity and other physical laws while in transit.
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.
It’s a staple of science fiction, and something many people have fantasized about at one time or another: the idea of sending out spaceships with colonists and transplanting the seed of humanity among the stars. Between discovering new worlds, becoming an interstellar species, and maybe even finding extra-terrestrial civilizations, the dream of spreading beyond the Solar System is one that can’t become reality soon enough!