Ground-based lasers could accelerate spacecraft to other stars

The future of space exploration includes some ambitious plans to send missions farther from Earth than ever before. In addition to existing proposals to build infrastructure in cis-lunar space and send 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. Nearest stars to discover exoplanets. Achieving these goals requires next-generation propulsion that enables greater thrust and sustained acceleration.

Focused arrays of lasers—or directed energy (DE)—and light cells are a source of mass research—such as the breakthrough Starshot and the swarming Proxima Centauri. Beyond these proposals, a team at McGill University in Montreal has proposed a new type of directed energy propulsion system for solar system exploration. In a recent paper, the team shared preliminary results from their Laser Thermal Propulsion (LTP) thruster facility, showing that the technology is capable of providing both high thrust and specific impulse for interstellar missions.

The research team was led by Gabriel R. Dube, an undergraduate research trainee with the McGill Interstellar Flight Experimental Research Group (IFERG), and Associate Professor Andrew Higgins, IFERG’s principal investigator. He was joined by Emmanuel Duple, graduate researcher at Technische Universiteit Delft (TU Delft); Joined Summer Research Assistant with Sierra Rail, IFERG; and Jason Louisau, an associate professor at the Royal Military College of Canada.

The team presented their findings at the 2024 AIAA Science and Technology Forum and Exposition A paper Published in AIAA SCITECH 2024 Forum.

Higgins and his colleagues originally proposed the concept a 2022 paper which appeared in Acta Astronautica Titled “Design of Rapid Transit to Mars Mission Using laser thermal propulsion.”

As Universe Today reported at the time, LTP was inspired by interstellar concepts like Starshot and Project Dragonfly. However, Higgins and his colleagues from McGill were interested in how this technology could enable a high-speed mission to Mars in just 45 days and across the entire solar system. It could also validate the technologies involved in the procedure and serve as a stepping stone toward interstellar missions, he said.

As Higgins told Universe Today via email, the concept came to him during the pandemic when he was unable to get to his lab:

“[M]y Students conducted a detailed concept study of how we could use the large laser arrays envisioned for a breakthrough starshot for a more near-term mission to the solar system. Instead of a 10-km-diameter, 100-GW laser for the breakthrough Starshot, we limited ourselves to a 10-m-diameter, 100-MW laser and showed that it was capable of powering a spacecraft at distances of approx. will be done. By heating the moon’s hydrogen propellant to 10,000 K, the laser enables the ‘holy grail’ of high thrust and high specific motion.”

The concept is similar to nuclear thermal propulsion (NTP), which NASA and DARPA are currently developing for rapid transit missions to Mars. In an NTP system, a nuclear reactor generates heat that causes hydrogen or deuterium propellant to expand, which is then concentrated through nozzles to create thrust.

In this case, phased array lasers are focused into a hydrogen heating chamber, which is then fired through a nozzle to realize a specific pulse of 3,000 seconds. Since Higgins and his students returned to the lab, he said, they’ve been trying to confirm their idea experimentally:

“Obviously, we don’t have a 100 MW laser at McGill, but we now have a 3 kW laser setup in the lab (which is pretty awesome) and are studying how lasers use their energy as propellants. How will it combine with. Eventually hydrogen, but for now argon only because it’s easier to ionize. The AIAA paper reports on the design, construction, and ‘shakedown’ of our 3-kW laser facility.”

Higgins and his team used their tests to create an apparatus containing 5 to 20 bars of static argon gas. While the final concept would use hydrogen gas as a propellant, they used argon gas for the test because it is easier to ionize. They then fired a 3-kW laser in pulses at 1,070 nanometers (equivalent to near-infrared wavelengths) to determine the threshold power necessary for laser-sustained plasma (LSP). Their results indicated that about 80% of the laser energy was deposited in the plasma, which is consistent with previous studies.

The pressure and spectral data they obtained also showed a peak LSP temperature with the working gas, although they stress that more research is needed for definitive conclusions. He also emphasized that a dedicated equipment is needed to perform forced flow and other LSP tests. Finally, the team plans to measure the thrust later this year to estimate how much acceleration (delta-v) and specific thrust the laser thermal propulsion system can produce for future missions to Mars and other planets in the Solar System. Impulse (ISP) can provide

If the technology is up to the task, we could see a system capable of delivering astronauts to Mars in weeks instead of months. Other concepts selected for NIAC this year include tests to evaluate hibernation systems for long-duration missions in microgravity. Alone or in combination, these technologies can enable high-speed transit missions that require less equipment and supplies and minimize astronaut exposure to microgravity and radiation.