Can a laser send a spacecraft to Mars? This is the intended mission of the group from McGill University, designed to meet the NASA request. A 10-meter-wide laser on Earth would heat hydrogen plasma in a chamber behind the spacecraft, creating hydrogen gas thrust for the spacecraft, and sending it to Mars in just 45 days. There it would slow down in the Martian atmosphere, delivering supplies to the human colonists, or perhaps someday even delivering the humans themselves.
In 2018, NASA challenged engineers to develop a mission to Mars that would deliver a payload of at least 1,000 kg in no more than 45 days, as well as make longer journeys deep into the solar system and beyond. The short delivery times are motivated by the desire to get payloads and, someday, astronauts to Mars while minimizing their damaging effects from galactic cosmic rays and solar storms. Elon Musk's SpaceX suggests a human mission to Mars will take six months with its chemical-based rockets.
McGill's concept, called a laser-thermal engine, is based on an array of infrared lasers located on Earth, 10 meters in diameter, combining many invisible infrared beams, each with a wavelength of about one micron, for a total power of 100 megawatts. Power needed for approximately 80,000 US households. The payload, orbiting in an elliptical medium Earth orbit, will have a reflector that directs a laser beam coming from Earth into a heating chamber containing hydrogen plasma. After its core is heated to 40,000 degrees Kelvin (72,000 degrees Fahrenheit), the hydrogen gas flowing around the core will reach 10,000 K (18,000 degrees Fahrenheit) and will be expelled through a nozzle, creating thrust to push the the ship from the Earth with an interval of 58 minutes. (The side thrusters will keep the ship in line with the laser beam as the Earth rotates.)
When the radiation stops, the payload is blown away at nearly 17 kilometers per second relative to Earth — fast enough to cover the Moon's orbital distance in just eight hours. When it reaches the Martian atmosphere in a month and a half, it will still be traveling at 16 km/s; however, once there, placing the payload in a 150 km orbit around Mars will be a challenge for the engineering team.
It's tricky because the payload can't carry the chemical propellant to launch the rocket to slow itself down - the propellant needed would reduce the mass of the payload to less than 6 percent of the original 1,000kg. And until people on the red planet can build an equivalent laser array for an approaching ship to use its reflector and plasma chamber to provide reverse thrust, aerocapture will be the only way to slow the payload on Mars.
Even so, aerocapture or aerobraking in the Martian atmosphere can be a risky maneuver, as the spacecraft experiences deceleration of up to 8 g (where g is the acceleration due to gravity at the Earth's surface, 9.8 m/s2), roughly the human limit, by only a few minutes, since it was filmed in one pass around Mars. Large heat fluxes on the ship due to friction with the atmosphere will be higher than the traditional materials of the thermal protection system, but not those that are in active development.
Spacecraft laser-thermal propulsion into deep space—Mars and beyond—contrasts with other previously proposed transportation methods, such as laser-electric propulsion, in which a laser beam hit photovoltaic (PV) elements behind the payload; a solar-electric motor in which sunlight on photovoltaic cells creates traction; a nuclear electric engine, in which the nuclear reactor generates electricity that produces ions emitted by the engine; and a nuclear thermal propulsion system, in which heat from a nuclear reactor converts liquid into gas, which is expelled from a nozzle to generate thrust.
“Laser-thermal propulsion allows for the rapid transport of 1 ton with volleyball-sized laser arrays — something that laser-electric propulsion can only do with kilometer-class arrays,” says Emmanuel Duplay, lead author of the study, who worked on the project for two years. years as part of the bachelor's summer program in engineering studies at McGill University. Duplay is currently studying at the Delft University of Technology on a Master of Science program in Aerospace Engineering with a specialization in Space Flight.The great advantage of the laser-thermal propulsion concept presented by Duplay et al. is its extremely low mass-to-power ratio, in the range of 0.001-0.010 kg/kW - "unprecedented", they write, "far below even those given for advanced nuclear propulsion technology, due to the fact that the power source remains on at The ground and the delivered stream can be treated with a low-mass inflatable reflector.”
Laser-thermal motion was first studied in the 1970s using 10.6-micron CO2 lasers, the most powerful at the time. Modern one-micron fiber optic lasers, which can be combined into massively parallel phased arrays with large effective diameters, mean that the focal length of energy transfer is two orders of magnitude higher - 50,000 km in a Duplay laser.
Duplay explains that the phased array laser architecture is being developed by a group led by physicist Philip Lubin at the University of California, Santa Barbara. The Lubin group's array uses individual laser amplifiers of about 100 watts each - each amplifier is a simple loop of fiber and LED as a pump, and can be mass-produced inexpensively - so the Mars mission envisioned here would require on the order of 1 million individual amplifiers.
The first humans on Mars likely won't get there with laser-thermal technology. “However, as more people make the journey to support a long-term colony, we will need propulsion systems that get us there faster, if only to avoid the radiation hazard,” says Duplay. He believes that a laser-thermal mission to Mars could begin 10 years after the first human flights, that is, around 2040.
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