Small, fast-moving bullets fired at a spacecraft might hasten the journey to the stars

 

By Matt Williams 

January 26, 2023

                                     Numerous space agencies are now looking into cutting-edge propulsion concepts that will enable quick trips to other solar system worlds.

These include Chinese nuclear-powered spacecraft that might investigate Neptune and its biggest moon, Triton, and NASA's Nuclear-Thermal or Nuclear-Electric Propulsion (NTP/NEP) designs that could permit transit times to Mars in 100 days (or even 45).

Getting outside the Solar System offers several significant hurdles, despite the fact that these and other concepts could enable interplanetary exploration.

It would take a spaceship utilising conventional propulsion anywhere between 19,000 and 81,000 years to go to even the closest star, Proxima Centauri, as we discussed in a recent post (4.25 light-years from Earth). To do this, experts are looking at ideas for unmanned spacecraft that use lasers to accelerate light sails to a fraction of the speed of light.

An alternative to the beam-sail concept has been proposed by UCLA researchers. The pellet-beam idea would accelerate a 1-ton spacecraft to the edge of the Solar System in less than 20 years.

The idea was first out by Artur Davoyan, an assistant professor of mechanical and aerospace engineering at the University of California, Los Angeles, under the title "Pellet-Beam Propulsion for Breakthrough Space Exploration" (UCLA).

The proposal was chosen by the NASA Innovative Advanced Concepts (NIAC) programme as one of fourteen that were considered for their 2023 selections. A total of US$175,000 in grants were given to further develop the technologies. In order to construct a Solar Gravitational Lens, Davoyan's idea expands on recent work with directed-energy propulsion (DEP) and light sail technologies.

The issue with spacecraft is that they are still dependent on the Rocket Equation, as Prof. Davoyan explained to Universe Today via email:

                        "At the moment, expanding fuel powers all rockets and spacecraft. The rocket is more effective the faster the fuel is burned off. We can only bring a certain quantity of gasoline on board, though. The maximum velocity to which a spacecraft may be propelled is therefore constrained. The Rocket Equation establishes this basic restriction. Due to Rocket Equation's constraints, space exploration is relatively expensive and sluggish. With present spacecraft, missions like the Solar Gravitational Lens are not possible."

A ground-breaking idea called the Solar Gravitational Lens (SGL) calls for building the most powerful telescope ever imagined. One such is the Solar Gravity Lens, which was chosen for NIAC Phase III development in 2020.

The idea is based on a phenomenon known as gravitational lensing, which occurs when huge objects change the curvature of spacetime, enhancing the light from objects in the background. Astronomers may investigate far-off objects with better clarity and accuracy using this method.

Astronomers might examine exoplanets and distant objects with the precision of a main mirror of about 100 km (62 miles) in diameter by placing a spacecraft near the heliopause (about 500 AU from the Sun). The difficulty is in creating a propulsion system that might propel the spaceship to this distance in a timely manner.

The Voyager 1 and 2 probes, which were launched in 1977 and are now situated 159 and 132 AUs from the Sun, are the only spacecraft to have reached interstellar space to yet (respectively).

The Voyager 1 probe was flying at a record-breaking speed of around 17 km/s (38,028 mph) or 3.6 AU per year when it exited the Solar System. Even so, it took this probe 35 years to get to the point where the solar wind from the Sun meets the interstellar medium (the heliopause).

Voyager 1 won't pass another star system until it has travelled almost 40,000 years at its current pace, the inconspicuous star system AC+79 3888 in the constellation Ursa Minor. Due to this, researchers are looking at directed energy (DE) propulsion, which might speed up light sails and allow them to travel to another star system in a couple of decades.

According to Prof. Davoyan, this approach has a number of clear benefits but also some disadvantages:

                            "Unlike traditional spaceships and rockets, laser sailing doesn't need fuel to speed. Here, the spaceship is propelled forward by a laser using radiation pressure. Theoretically, with this technique, speeds close to the speed of light might be attained. However, a spacecraft can only be accelerated across a certain range of distances because laser beams diverge at great distances. This restriction on laser sailing necessitates the use of gigawatt- and, in some ideas, terawatt-level laser powers, or it places a limit on the mass of spacecraft."

Project Dragonfly, a feasibility assessment by the Institute for Interstellar Studies (i4is) for a mission that may reach a neighbouring star system within a century, is an example of the laser-beam idea.

Additionally, Breakthrough Starshot suggests using a 100-gigawatt (Gw) laser array to accelerate gram-scale nanocraft (Starchip).

Starshot will be able to travel to Alpha Centauri in around 20 years at a maximum speed of 161 million kilometres (100 million miles), or 20 percent of the speed of light. Prof. Davoyan and his coworkers provide a fresh spin on the idea—the pellet-beam concept—that is motivated by these ideas.

Similar to Starshot and Dragonfly, this mission design might be used as a fast-transit interplanetary precursor mission.

But for their needs, Davoyan and his colleagues looked at a pellet-beam system that could send a payload of 900 kg (about a U.S. tonne) to 500 AU away in less than 20 years. Davyanov said:

                                "We refer to the beam pushing the spacecraft in our instance as the pellet beam since it is formed of small pellets. Each pellet is laser-accelerated to extremely high speeds before being propelled into the spaceship with their momentum.

We can accelerate a heavier spacecraft because pellets do not diverge as fast as a laser beam does. The pellets may exert a greater pull on a spaceship since they are heavier than photons and carry more momentum."

The pellets can also be driven by relatively weak laser beams due to their tiny size and low mass. Overall, according to Davoyan and his coworkers, a 10-megawatt (Mw) laser beam could propel a 1-ton spacecraft to speeds of up to 30 AU per year.

Through thorough modelling of the various subsystems and proof-of-concept tests, they will show in the Phase I effort that the pellet-beam idea is feasible. They will also look at how the pellet-beam technology may be used in future interstellar expeditions that could visit nearby stars.

By permitting quick transit missions to far locations, the pellet beam "aims to alter how deep space is studied," according to Davoyan. "With the pellet beam, it takes less than a year to reach the outer planets, three years to travel 100 AU, and fifteen years to travel 500 AU to the solar gravity lens. Importantly, the pellet-beam can drive hefty spacecraft (up to one tonne), unlike earlier proposals, thus expanding the range of potential missions."

Astronomers would be able to directly scan nearby exoplanets (like Proxima b) with multi-pixel resolution and collect spectra from their atmospheres if an SGL spacecraft were to be built. These findings would provide conclusive proof of atmospheres, biological signatures, and potentially technological signals as well.

In this approach, interstellar expeditions would be able to directly investigate exoplanets using the same technology that allows scientists to directly see them and study them in great detail.

Under the terms of a Creative Commons licence, this article has been taken from Science Alert. Go here to read the original article.