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! The research was led by Emmanuel Duplay, a McGill graduate and current MSc Aerospace Engineering student at TU Delft. He was joined by Associate Professor Andrew Higgins and multiple researchers with the Department of Mechanical Engineering at McGill University. Their study, titled “Design of a rapid transit to Mars mission using laser-thermal propulsion,” was recently submitted to the journal Astronomy & Astronomy. In recent years, directed-energy (DE) propulsion has been the subject of considerable research and interest. Examples include the Starlight program – also known as the Directed Energy Propulsion for Interstellar Exploration (DEEP-IN) and Directed Energy Interstellar Studies (DEIS) programs – developed by Prof. Phillip Lubin and the UCSB Experimental Cosmology Group (ECG). As part of NASA-funded research that began in 2009, these programs aim to adapt large-scale DE applications for interstellar missions. There’s also Breakthrough Starshot and Project Dragonfly, both of which emerged from a design study hosted by the Initiative for Interstellar Studies (i4iS) in 2013. These concepts call for a gigawatt-power laser array to accelerate a lightsail and a small spacecraft to a fraction of the speed of light (aka. relativistic speeds) to reach nearby star systems in decades, rather than centuries or millennia. But whereas these concepts are interstellar in focus, Duplay and his colleagues explored the possibility of an interplanetary concept. As Duplay explained to Universe Today via email: Aside from laser sail propulsion, DE is being explored for several other space exploration applications. This includes power beaming to and from spacecraft and permanently-shadowed habitats (e.g., the Artemis Program), communications, asteroid defense, and the search for possible technosignatures. There’s also a concept for a laser-electric spacecraft being investigated by NASA and as part of a collaborative study between the UCSB ECG and MIT. For this application, lasers are used to deliver power to photovoltaic arrays on a spacecraft, which is converted to electricity to power a Hall-Effect Thruster (ion engine). This idea is similar to a nuclear-electric propulsion (NEP) system, where a laser array takes the place of a nuclear reactor. As Duplay explained, their concept is related but different: In this respect, the concept proposed by Duplay and his colleagues is akin to a nuclear-thermal propulsion (NTP) system, where the laser has taken the place of a nuclear reactor. In addition to DE and hydrogen propellant, the mission architecture for a laser-thermal spacecraft includes several technologies from other architectures. As Duplay indicated, they include: “Our spacecraft is like a dragster that accelerates very quickly while still near earth. We believe we can even use the same laser-powered rocket engine to bring the booster back into earth orbit, after it has thrown the main vehicle to Mars, enabling it to be quickly recycled for the next launch.” This last element is essential given that there’s no laser array at Mars to decelerate the spacecraft once it reaches Mars. “The inflatable reflector is a key from other directed-energy architectures: designed to be highly reflective, it can sustain a greater laser power per unit area than a photovoltaic panel, making this mission feasible with a modest laser array size compared to laser-electric propulsion,” added Duplay. By combining these elements, a laser-thermal rocket could enable very fast transits to Mars that would be as short as six weeks – something that was considered possible only with nuclear-powered rocket engines before. The most immediate benefit is that it presents a solution to the hazards of deep-space transits, like prolonged exposure to radiation and microgravity. At the same time, says Duplay, the mission presents some hurdles since many of the technologies involved are bleeding-edge and have not been tested just yet: While most of the technology in this proposed mission architecture – and other comparable proposals – is still in the theoretical and research stages, there is little question about its potential. Reduced travel time to Mars from months to weeks will solve two of the most difficult obstacles for Mars missions: logistical and health considerations. Furthermore, developing a rapid-transit system between Earth and Mars will hasten the development of infrastructure between the two planets. This might comprise a Gateway-like space station in Mars orbit, similar to Lockheed Martin’s Mars Base Camp, as well as a laser array to slow arriving spacecraft. The existence of these facilities would also hasten attempts to establish a permanent human presence on the planet’s surface. As Professor Higgins concluded: Adapted from an article originally published on Universe Today.
