Today, several space agencies are investigating advanced concepts that would allow fast travel to other bodies in the Solar System.
These include NASA’s Nuclear-Thermal or Nuclear-Electric Propulsion (NTP/NEP) principles that would allow the time to go to Mars in 100 days (or even 45) and a Chinese nuclear spacecraft that could explore Neptune and its largest moon, Triton.
While these and other concepts may allow for interplanetary exploration, crossing the Sun poses significant challenges.
As we discussed in a previous article, it would take a space shuttle using normal speed anywhere from 19,000 to 81,000 years to reach even the nearest star, Proxima Centauri (4.25 light-years from Earth). In order to achieve this, engineers have been researching how to use non-destructive aircraft that rely on direct-energy light (lasers) to guide sails that are slightly lighter than the speed of light.
A new idea presented by UCLA researchers sees a twist on the idea of the cost of a ship: the idea of a pellet cost that can accelerate a 1 ton ship to the edge of the Solar System in less than 20 years.
The idea, called “Pellet-Beam Propulsion for Breakthrough Space Exploration,” was proposed by Artur Davoyan, Assistant Professor of Mechanical and Aerospace Engineering at the University of California, Los Angeles (UCLA).
The concept was one of fourteen ideas selected by the NASA Innovative Advanced Concepts (NIAC) program as part of their 2023 decisions, which provided a total of US $ 175,000 to advance the technology. Davoyan’s proposal builds on recent work with Directed-energy propulsion (DEP) and light-sea technology to locate the Solar Gravitational Lens.
As Prof. Davoyan told Universe Today via email, the problem with spaceflight is that it’s still part of the Rocket Equation:
“Spaceships and all modern rockets fly by adding fuel. The faster the fuel is dumped, the more efficient the rocket is. However, there is less fuel that we can carry. Therefore, the speed of the spaceship is faster. This is governed by the Rocket Equation .The limits of the Rocket Equation mean space exploration is slow and expensive.
The Solar Gravitational Lens (SGL) is a revolutionary concept that could be the most powerful telescope ever built. Examples include the Solar Gravity Lens, which was selected in 2020 for NIAC Phase III.
This theory relies on a phenomenon predicted by Einstein’s Theory of General Relativity called Gravitational Lensing, when massive objects change the curvature of space-time, amplifying light from background objects. This method enables astronomers to study distant objects with greater accuracy and precision.
By placing the spacecraft at the heliopause (~500 AU from the Sun), astronomers can study exoplanets and distant objects with a mirror image starting at 100 km (62 miles) in diameter. The challenge is to design a flight path that can get the spacecraft to reach this distance in a reasonable amount of time.
To date, the only spacecraft to reach space are the Voyager 1 and 2 probes, which were launched in 1977 and are currently approximately 159 and 132 AUs from the Sun (respectively).
When it left the Solar System, the Voyager 1 probe was traveling at a maximum speed of about 17 km/s (38,028 mph), or 3.6 AU per year. However, this search still took 35 years to reach the boundary between the Sun’s solar wind and the interstellar medium (heliopause).
At its current speed, it will take Voyager 1 40,000 years to fly past another star – AC+79 3888, an obscure star in the constellation Ursa Minor. For this reason, scientists are looking for a method of electric propulsion (DE) to speed up light sails, which can reach another star after many years.
As Prof. Davoyan explained, this approach has its advantages but also its disadvantages:
“Laser sailing, unlike conventional airplanes and rockets, does not require fuel to accelerate. Here the acceleration comes from the laser pushing the ship with radiation energy. In fact, speeds close to light can be reached with this method. However, laser beams they are separated by a long distance, meaning that there is only a small distance for a ship to accelerate. , or to limit the number of aircraft in space.”
Examples of the laser-beam concept are Project Dragonfly, a feasibility study by the Institute for Interstellar Studies (i4is) on a mission that could reach nearby stars within a century.
Then there’s Breakthrough Starshot, which requires a 100-gigawatt (Gw) laser array that can accelerate gram-scale nanocraft (Starchip).
At a maximum speed of 161 million km (100 million miles) or 20 percent of the speed of light, Starshot will be able to reach Alpha Centauri in about 20 years. Encouraged by these facts, Prof. Davoyan and his colleagues propose a new idea to change the concept: the concept of the pellet tree.
The concept of this mission could work like a fast interstellar shuttle, like Starshot and Dragonfly.
But for their own purposes, Davoyan and his team evaluated a pellet machine that could carry ~900 kg (1 US ton) a distance of 500 AU in less than 20 years. Davoyan said:
“For us, the beam that propels the ship is made of small pieces of wood, that’s why [we call it] pellet price. Each pellet is accelerated to a high velocity by laser ablation, and then the pellets carry their energy to propel the ship.
Unlike the laser beam, the pellets do not disperse quickly, which allows us to fire a very heavy ship. Pellets, being heavier than photons, travel faster and can transfer more energy to the spacecraft.”
In addition, the small size and low density of the pellets means that they can be driven by very low laser beams. Overall, Davoyan and colleagues estimate that a 1-ton spacecraft could be accelerated to ~30 AU per year using a 10-megawatt (Mw) laser beam.
In Phase I testing, they will demonstrate the feasibility of the pellet cost concept through detailed modeling of various subsystems and proof-of-concept testing. They will also see how pellet-beams can help interstellar missions that could explore nearby stars in our lifetime.
“The pellet bridge aims to change the way deep space is illuminated by supporting expeditions to remote areas,” said Davoyan. “With the pellet beam, the outer planets can be reached in less than a year, 100 AU in about three years, and the solar gravitational lens at 500 AU in about 15 years. Most importantly, contrary to some ideas, the pellet beam can drive the heaviest ship. (~ 1 ton), which increases the number of possible missions.”
If detected, the SGL spacecraft would allow astronomers to directly image nearby exoplanets (such as Proxima b) with multiple pixels and obtain views from space. This can provide direct atmospheric evidence, biosignatures, and perhaps even technosignatures.
In this way, the same technology that allows astronomers to directly image exoplanets and examine them in detail also enables interstellar missions to directly explore them.
This article was originally published by Universe Today. Read the first article.