Today, many space agencies are looking at cutting-edge propulsion ideas that would allow rapid transfer to other bodies in the solar system.
They include NASA concepts of thermonuclear or electric propulsion (NTP/NEP) that could enable transit times to Mars in 100 days (or even 45) and a Chinese nuclear-powered spacecraft that could explore Neptune and its largest moon, Triton.
While these and other ideas may allow for interplanetary exploration, going beyond the solar system presents some major challenges.
As we discovered in a previous article, it would take a spacecraft using conventional propulsion anywhere from 19,000 to 81,000 years to reach even the nearest star, Proxima Centauri (4.25 light-years from Earth). To this end, engineers have been looking at proposals for uncrewed spacecraft that rely on beams of directed energy (lasers) to accelerate light sails to a fraction of the speed of light.
A new idea proposed by UCLA researchers envisions an evolution of the beam sail idea: a pellet beam concept that could accelerate a one-ton spacecraft to the edge of the solar system in less than 20 years.
The concept, titled “Particle Beam Propulsion for Supersonic Space Exploration,” was proposed by Artur Davoyan, assistant professor of mechanical and aerospace engineering at the University of California, Los Angeles (UCLA).
The proposal was one of fourteen selected by the NASA Innovative Advanced Concepts (NIAC) program as part of their 2023 selections, which awarded a total of $175,000 in grants to further develop technologies. Davoyan’s proposal builds on recent work with directed energy propulsion (DEP) and photosail technology to achieve solar gravitational lensing.
As Professor Davoyan told Universe Today via email, the problem with spacecraft is that they still owe a debt to the rocket equation:
“All current spacecraft and rockets fly by boosting fuel. The faster the fuel is eliminated, the more efficient the rocket is. However, there is a finite amount of fuel that we can carry on board. As a result, the speed of the spacecraft can be accelerated to a finite “This fundamental limitation is dictated by the rocket equation. The limitations of the rocket equation translate into relatively slow and expensive space exploration. Such missions as solar gravitational lensing are not feasible with current spacecraft.”
The Solar Gravitational Lens (SGL) is a revolutionary proposal that would be the most powerful telescope ever built. Examples include the solar gravitational lens, which was selected in 2020 for NIAC’s third phase development.
The concept is based on a phenomenon predicted by Einstein’s theory of general relativity known as Gravitational Lensing, in which massive objects alter the curvature of space-time, amplifying light from background objects. This technology allows astronomers to study distant objects with greater accuracy and precision.
By placing a spacecraft in the sun’s region (about 500 astronomical units from the sun), astronomers can study exoplanets and distant objects with a primary mirror resolution of about 100 kilometers (62 miles) in diameter. The challenge is to develop a propulsion system that can get the spacecraft that far in a reasonable amount of time.
To date, the only spacecraft to have reached interstellar space have been the Voyager 1 and 2 probes, which were launched in 1977 and are currently about 159 and 132 AUs from the Sun (respectively).
When it left the solar system, the Voyager 1 probe was traveling at a record speed of about 17 km/s (38,028 mph), or 3.6 AU per year. However, it still took 35 years for this probe to reach the boundary between the sun’s solar wind and the interstellar medium (heliosphere).
At its current speed, Voyager 1 will take more than 40,000 years to pass by another star system – AC+ 79 3888, a mysterious star in the constellation Ursa Minor. For this reason, scientists are looking at directed energy propulsion to accelerate light sails, which could reach another star system in a matter of decades.
As explained by Professor Davoyan, this method offers some distinct advantages but also has its share of disadvantages:
“Laser sailing, unlike conventional spacecraft and rockets, does not require fuel on board for acceleration. Here the acceleration comes from the laser propelling the spacecraft with radiation pressure. In principle, speeds approaching the speed of light can be reached in this way. However, the lasers diverge over long distances, which means that there is only a limited distance range over which a spacecraft can be accelerated This limitation of laser navigation either leads to the need for extremely high laser power, gigawatts, and in some proposals, terawatts, or places a limitation on the mass of the spacecraft “.
Examples of the laser beam concept include Project Dragonfly, a feasibility study by the Institute for Interstellar Studies (i4is) for a mission that could reach a nearby star system within a century.
Then there’s Breakthrough Starshot, which proposes a 100-gigawatt (Gw) laser array that would accelerate the manufacture of nanocomposites (Starchip) on the gram-scale.
At a top speed of 161 million kilometers (100 million miles) or 20 percent of the speed of light, Starshot will be able to reach Alpha Centauri in about 20 years. Inspired by these concepts, Professor Davoyan and his colleagues proposed a new development of the idea: the pellet beam concept.
This mission concept could be an introductory fast-traveling interstellar mission, such as Starshot and Dragonfly.
But for their purposes, Davoyan and his team investigated a pellet beam system that would propel a 900 kg (1 US ton) payload a distance of 500 astronomical units in less than 20 years. Davoyan said:
“In our case, the beam propelling the spacecraft is made of tiny grains, and therefore [we call it] pellet beam. Each pellet is accelerated to very high speeds by laser ablation, and then the pellet carries its own momentum to propel the spacecraft.
Unlike a laser beam, the grains do not diverge quickly, allowing us to accelerate heavier spacecraft. The spherules are much heavier than photons, carry more momentum and can impart a higher force to a spacecraft. “
In addition, the small size and low mass of the grains means that they can be propelled by relatively low-energy laser beams. Overall, Davoyan and his colleagues estimate that a one-ton spacecraft could be accelerated to speeds of up to 30 astronomical units per year using a 10-megawatt laser beam.
For the Phase 1 effort, they will demonstrate the feasibility of the granular beam concept through detailed modeling of the various subsystems and proof-of-concept experiments. They will also explore the usefulness of the Beam System for interstellar missions that could explore neighboring stars in our lives.
“The pellet package aims to change the way deep space is explored by enabling fast transit missions to distant destinations,” Davoyan said. “With a pellet beam, exoplanets can be reached in less than a year, 100 astronomical units in about three years, and solar gravitational lensing at 500 astronomical units in about 15 years. Most importantly, unlike other concepts, a pellet beam can Heavy (~1 ton) spacecraft pushes, which greatly increases the range of possible missions.
If this is achieved, the SGL spacecraft will allow astronomers to directly image neighboring exoplanets (such as Proxima b) at multi-pixel resolution and obtain spectra of their atmospheres. These observations will provide direct evidence of the atmosphere, biosignatures, and possibly even technical fingerprints.
In this way, the same technology that allows astronomers to directly image exoplanets and study them in exhaustive detail will also enable interstellar missions to explore them directly.
This article was originally published by Universe Today. Read the original article.