Mars in the next decade. While this represents a tremendous leap in terms of space exploration, it also presents significant logistical and technological challenges. For starters, missions can only launch for Mars every 26 months when our two planets are at the closest points in their orbit to each other (during an “Opposition“). Using current technology, it would take six to nine months to transit from Earth to Mars.
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:
“The ultimate application of directed-energy propulsion would be to propel a lightsail to the stars for true interstellar travel, a possibility that motivated our team that did this study. We were interested in how the same laser technology could be used for rapid transit in the solar system, which will hopefully be a nearer-term steppingstone that can demonstrate the technology.”
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:
“Our approach is complimentary to these concepts, in that it uses the same phased-array laser concept, but would use a much more intense laser flux on the spacecraft to directly heat propellant, similar to a giant steam kettle. This permits the spacecraft to accelerate rapidly while it is still near earth, so the laser does not need to focus as far into space.
“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.”
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:
“[A]fiber optic laser arrays that act as a single optical element, inflatable space structures that can be used to focus the laser beam as it arrives at the spacecraft in the heating chamber, and the development of high temperature materials that allow the spacecraft to break away from the Martian atmosphere upon arrival.
This last element is essential given that there is no laser array on Mars to slow down the spacecraft once it reaches Mars. “The inflatable reflector is a key to other directed-energy architectures: designed to be highly reflective, it can support greater laser power per unit area than a photovoltaic panel, making this mission feasible with a laser array size modest 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 previously thought to be possible only with nuclear-powered rocket engines. The most immediate benefit is that it presents a solution to the dangers of deep space transits, such as prolonged exposure to radiation and microgravity.
At the same time, says Duplay, the mission presents some hurdles because many of the technologies involved are state-of-the-art and have yet to be tested:
“The laser heating chamber is probably the biggest challenge: can we contain hydrogen gas, our propellant, as it is heated by the laser beam to temperatures above 10,000 K while keeping the walls Our models indicate that this is feasible, but full-scale experimental testing is not possible at this time as we have not yet built the necessary 100 MW lasers.
While much of the technology in this proposed mission architecture – and other similar proposals – is still in the theory and development phase, there is no doubting their potential. Reducing the time needed to travel to Mars to weeks from months will address two of the biggest challenges of Mars missions: logistical and health considerations.
In addition, the establishment of a rapid transit system between Earth and Mars will accelerate the creation of infrastructure between Earth and Mars. This could include a gateway-type space station orbiting Mars, such as Lockheed Martin’s proposed Mars Base Camp, as well as a laser array to slow down incoming spacecraft. The presence of these facilities would also accelerate plans to create a permanent human presence on the surface. As Professor Higgins concluded:
“The Mars-in-45-days design study that Emmanuel led was motivated by exploring other near-term applications of phased array laser technology that Philip Lubin’s group is developing. The ability to deliver power deep into space via laser would be a disruptive technology for propulsion and power. Our study looked at the thermal laser approach, which sounds encouraging, but the laser technology itself is a real game-changer. »
Originally published on Universe Today.