What’s the Most Effective Way to Explore our Nearest Stars?

Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity's first interstellar voyage. Credit: breakthroughinitiatives.org

It was 1903 that the Wright brothers made the first successful self-propelled flight. Launching themselves to history, they set the foundations for transatlantic flights, supersonic flight and perhaps even the exploration of the Solar System. Now we are on the precipice of travel among the stars but among the many ideas and theories, what is the ultimate and most effective way to explore our nearest stellar neighbours? After all, there are 10,000 stars within a region of 110 light years from Earth so there are plenty to choose from. 

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Starshot … Not? Get a Reality Check on the Search for Alien Civilizations

Zine Tseng as Chinese radio astronomer, sitting at control panel for antenna
Zine Tseng plays a Chinese radio astronomer in "3 Body Problem." (Credit: Ed Miller / Netflix © 2024)

Fortunately, the real-world search for signs of extraterrestrial civilizations doesn’t have to deal with an alien armada like the one that’s on its way to Earth in “3 Body Problem,” the Netflix streaming series based on Chinese sci-fi author Cixin Liu’s award-winning novels. But the trajectory of the search can have almost as many twists and turns as a curvature-drive trip from the fictional San-Ti star system.

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Ground-Based Lasers Could Accelerate Spacecraft to Other Stars

An artist's illustration of a light-sail powered by a radio beam (red) generated on the surface of a planet. The leakage from such beams as they sweep across the sky would appear as Fast Radio Bursts (FRBs), similar to the new population of sources that was discovered recently at cosmological distances. Credit: M. Weiss/CfA

The future of space exploration includes some rather ambitious plans to send missions farther from Earth than ever before. Beyond the current proposals for building infrastructure in cis-lunar space and sending regular crewed missions to the Moon and Mars, there are also plans to send robotic missions to the outer Solar System, to the focal length of our Sun’s gravitational lens, and even to the nearest stars to explore exoplanets. Accomplishing these goals requires next-generation propulsion that can enable high thrust and consistent acceleration.

Focused arrays of lasers – or directed energy (DE) – and lightsails are a means that is being investigated extensively – such as Breakthrough Starshot and Swarming Proxima Centauri. Beyond these proposals, a team from McGill University in Montreal has proposed a new type of directed energy propulsion system for exploring the Solar System. In a recent paper, the team shared the early results of their Laser-Thermal Propulsion (LTP) thruster facility, which suggests that the technology has the potential to provide both high thrust and specific impulse for interstellar missions.

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NASA Selects Bold Proposal to “Swarm” Proxima Centauri with Tiny Probes

Swarm of laser-sail spacecraft leaving the solar system. Credit: Adrian Mann

Humans have dreamed about traveling to other star systems and setting foot on alien worlds for generations. To put it mildly, interstellar exploration is a very daunting task. As we explored in a previous post, it would take between 1000 and 81,000 years for a spacecraft to reach Alpha Centauri (of which Proxima Centauri is considered a companion) using conventional propulsion (or those that are feasible using current technology). On top of that, there are numerous risks when traveling through the interstellar medium (ISM), not all of which are well-understood.

Under the circumstances, gram-scale spacecraft that rely on directed-energy propulsion (aka. lasers) appear to be the only viable option for reaching neighboring stars in this century. Proposed concepts include the Swarming Proxima Centauri, a collaborative effort between Space Initiatives Inc. and the Initiative for Interstellar Studies (i4is) led by Space Initiative’s chief scientist Marshall Eubanks. The concept was recently selected for Phase I development as part of this year’s NASA Innovative Advanced Concepts (NIAC) program.

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Communicating With a Relativistic Spacecraft Gets Pretty Weird

Artistic rendition of an interstellar spacecraft traveling near the speed of light. Credit: Made with ChatGPT

Someday, in the not-too-distant future, humans may send robotic probes to explore nearby star systems. These robot explorers will likely take the form of lightsails and wafercraft (a la Breakthrough Starshot) that will rely on directed energy (lasers) to accelerate to relativistic speeds – aka. a fraction of the speed of light. With that kind of velocity, lightsails and wafercraft could make the journey across interstellar space in a matter of decades instead of centuries (or longer!) Given time, these missions could serve as pathfinders for more ambitious exploration programs involving astronauts.

Of course, any talk of interstellar travel must consider the massive technical challenges this entails. In a recent paper, a team of engineers and astrophysicists considered the effects that relativistic space travel will have on communications. Their results showed that during the cruise phase of the mission (where a spacecraft is traveling close to the speed of light), communications become problematic for one-way and two-way transmissions. This will pose significant challenges for crewed missions but will leave robotic missions largely unaffected.

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Tiny Swarming Spacecraft Could Establish Communications with Proxima Centauri

Swarm of laser-sail spacecraft leaving the solar system. Credit: Adrian Mann

Achieving interstellar travel has been the dream of countless generations, but the challenges remain monumental. Aside from the vast distances involved, there are also the prohibitive energy requirements and the sheer cost of assembling spacecraft that could survive the trip. Right now, the best bet for achieving an interstellar mission within a reasonable timeframe (i.e., a single person’s lifetime) is to build gram-scale spacecraft paired with lightsails. Using high-power laser arrays, these spacecraft could be accelerated to a fraction of the speed of light (relativistic speeds) and reach nearby stars in a few decades.

There are a handful of major projects, like Breakthrough Starshot, that hope to leverage this technology to create spacecraft that could reach Alpha Centauri in a few decades (instead of centuries). This technology also presents other opportunities, like facilitating communications across interstellar distances. This is the idea recently by a team of researchers led by the Initiative for Interstellar Studies (i4is). In a recent paper, they recommended that a swarm of gram-scale spacecraft could rely on their launch laser to maintain optical communications with Earth.

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Lightweight Picogram-Scale Probes Could be the Best way to Explore Other Star Systems

Inspiration for space exploration can come from all corners. One of the most inspiring, or terrifying, sources of inspiration for some in space exploration came from computer science expert John von Neumann, who laid out a framework for self-replicating machines in a series of lectures he gave in 1948. Ever since then, scientists and engineers have been debating the advantages, and the perils, of such a system.

However, while technology has indeed advanced a long way since the 1940s, it still seems like we are still a long way from having a fully functional von Neumann machine. That is unless you turn to biology. Even simple biological systems can perform absolutely mind-blowing feats of chemical synthesis. And there are few people in the world today who know that better than George Church. The geneticist from Harvard has been at the forefront of a revolution in the biological sciences over the last 30 years. Now, he’s published a new paper in Astrobiology musing about how biology could aid in creating a pico-scale system that could potentially explore other star systems at next to no cost.

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Laser-Powered Sails Would be Great for Exploring the Solar System too

Swarm of laser-sail spacecraft leaving the solar system. Credit: Adrian Mann

Between the exponential growth of the commercial space industry (aka. NewSpace) and missions planned for the Moon in this decade, it’s generally agreed that we are living in the “Space Age 2.0.” Even more ambitious are the proposals to send crewed missions to Mars in the next decade, which would see astronauts traveling beyond the Earth-Moon system for the first time. The challenge this represents has inspired many innovative new ideas for spacecraft, life-support systems, and propulsion.

In particular, missions planners and engineers are investigating Directed Energy (DE) propulsion, where laser arrays are used to accelerate light sails to relativistic speeds (a fraction of the speed of light). In a recent study, a team from UCLA explained how a fleet of tiny probes with light sails could be used to explore the Solar System. These probes would rely on a low-power laser array, thereby being more cost-effective than similar concepts but would be much faster than conventional rockets.

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Lasers Could Send Missions to Mars in Only 45 Days

Swarm of laser-sail spacecraft leaving the solar system. Credit: Adrian Mann

NASA and China plan to mount crewed missions to Mars in the next decade. While this represents a tremendous leap in terms of space exploration, it also presents significant logistical and technological challenges. For starters, missions can only launch for Mars every 26 months when our two planets are at the closest points in their orbit to each other (during an “Opposition“). Using current technology, it would take six to nine months to transit from Earth to Mars.

Even with nuclear-thermal or nuclear-electric propulsion (NTP/NEP), a one-way transit could take 100 days to reach Mars. However, a team of researchers from Montreal’s McGill University assessed the potential of a laser-thermal propulsion system. According to their study, a spacecraft that relies on a novel propulsion system – where lasers are used to heat hydrogen fuel – could reduce transit times to Mars to just 45 days!

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If Launched by 2028, a Spacecraft Could Catch up With Oumuamua in 26 Years

Laser sail spacecraft arriving at 'Oumuamua, the interstellar asteroid (Credit: Maciej Rebisz)

In October 2017, the interstellar object ‘Oumuamua passed through our Solar System, leaving a lot of questions in its wake. Not only was it the first object of its kind ever to be observed, but the limited data astronomers obtained as it shot out of our Solar System left them all scratching their heads. Even today, almost five years after this interstellar visitor made its flyby, scientists are still uncertain about its true nature and origins. In the end, the only way to get some real answers from ‘Oumuamua is to catch up with it.

Interestingly enough, there are many proposals on the table for missions that could do just that. Consider Project Lyra, a proposal by the Institute for Interstellar Studies (i4is) that would rely on advanced propulsions technology to rendezvous with interstellar objects (ISOs) and study them. According to their latest study, if their mission concept launched in 2028 and performed a complex Jupiter Oberth Manoeuvre (JOM), it would be able to catch up to ‘Oumuamua in 26 years.

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