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Put the laser on Mars

Laser heat-propelled spacecraft in Earth orbit are waiting for their departure. Credit: Creative Commons Attribution 4.0 International License

Can lasers send spacecraft to Mars? This is a mission proposed by a group at McGill University designed to meet the demands of NASA. A 10-meter-wide array of lasers on Earth heats the hydrogen plasma in the chamber behind the spacecraft, producing thrust from the hydrogen gas and sending it to Mars in just 45 days. There, it applies aerobraking in the atmosphere of Mars and transports supplies to human settlers, or eventually to humans themselves.


In 2018, NASA asked engineers to design a mission to Mars. This mission will provide a payload of at least 1,000 kilograms within 45 days, enabling longer travel into and out of the solar system. Fast delivery is motivated by the desire to ferry cargo and astronauts to Mars while minimizing exposure to the adverse effects of galactic cosmic rays and solar storms. Elon Musk SpaceX Concept A human journey to Mars will take six months on a chemical-based rocket.

Magill’s concept called laser-Thermal propulsion relies on an array of Earth-based infrared lasers 10 meters in diameter, combined with many invisible infrared beams, each with a wavelength of about 1 micron, for a total of 100 megawatts of power. Will be. Electric power Needed for about 80,000 US households. The payload, which orbits the medium earth orbit of an elliptical orbit, has a reflector that directs a laser beam from the earth to a heating chamber containing hydrogen plasma. When the core is heated to 40,000 Kelvin (72,000 degrees Fahrenheit), the hydrogen gas flowing around the core reaches 10,000 K (18,000 degrees Fahrenheit) and is ejected from the nozzle, generating thrust and moving the ship away from the earth. 58 minute intervals. (The side thrusters keep the aircraft aligned with the laser beam as the Earth rotates.)

When the beam stops, the payload is compressed against the Earth at a speed of about 17 kilometers per second. This is fast enough to traverse the lunar orbital distance in just eight hours. Even if it reaches the atmosphere of Mars in a month and a half, it will move at 16 km / s. But once you get there, placing the payload in an orbit of 150 km around Mars is a difficult problem for engineering teams to solve.

The payload is difficult because it cannot carry the chemical propellant to launch and slow down the rocket. The required fuel reduces the payload mass to less than 6% of the original 1,000 kilograms. Aerocapture then slows down the payload on Mars until humans on the Red Planet can build an equivalent laser array for the incoming aircraft to use its reflectors and plasma chambers to provide thrust. The only way to do it.

Still, aerocapture or aerobrake in the atmosphere of Mars can be a dangerous operation, as spacecraft experience decelerations of up to 8 g (g is gravitational acceleration on the surface of the Earth, 9.8 m / s2). there is. Human limits of just a few minutes, as they are captured within a single path around Mars. The large heat flux of the aircraft due to atmospheric friction exceeds the materials of traditional thermal protection systems, but it is not actively developed.

Laser thermal propulsion of spacecraft into deep space such as Mars is in contrast to other previously proposed transportation methods, such as laser electric propulsion. Laser beam It collides with a photovoltaic (PV) cell behind the payload. Solar electric propulsion where the sunlight of the solar cell produces propulsion. Nuclear electric propulsion where a nuclear reactor produces electricity and produces ions emitted from a thruster. Nuclear heat promotion, ReactorThe heat converts a liquid into a gas, which is propelled by a nozzle to produce thrust.

“Laser thermal propulsion enables high-speed transport missions of 1 ton on volleyball court-sized laser arrays. Laser electric propulsion can only be performed on kilometer-class arrays,” said the lead author of the study. Emmanuel Duprey states. A two-year project while part of the McGill University Faculty of Engineering Summer Undergraduate Research Program. Duplay is currently a member of the Delft University of Technology’s Master of Science Program in Aerospace Engineering, specializing in space flight.

A great advantage of the concept of laser heat propulsion missions presented by Duplay et al. Is a very low mass-to-power ratio in the range of 0.001 to 0.010 kg / kW, they write, “unmatched.” The Earth and the flux supplied can be processed with a low mass inflatable reflector. “

Laser thermal propulsion was first studied in the 1970s using 10.6 micron CO.2 The most powerful laser of the time. Today’s fiber optic lasers are 1 micron and can be combined with massively parallel phased arrays with large and effective diameters. This means a focal length power supply that is more than two orders of magnitude higher. The Duplay laser is 50,000 km. The concept of heat promotion.

Duplay explains it Phased array laser architecture Developed by a group led by Philip Lubin, a physicist at the University of California, Santa Barbara. Rubin’s group of arrays each uses a separate laser amplifier of approximately 100 watts. Each amplifier is a simple loop of fiber optics and LED lights as a pump and can be mass-produced inexpensively. Therefore, the Mars mission envisioned here would require an order of one million. Individual amplifier.

The first humans to Mars may not reach there using laser heat propulsion technology. “But more humans will travel to maintain long-term colonies, so we will need Promotion A system that gets us there faster just to avoid the danger of radiation, “says Duprey.


NASA’s Saiki spacecraft will be powered by solar electric propulsion


For more information:
Emmanuel Duprey and others, designing high-speed transportation to Mars missions using laser thermal propulsion, Acta Astronautica (2021). DOI: 10.1016 / j.actaastro.2021.11.032

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Quote: Place the laser on Mars (February 8, 2022) February 8, 2022 Obtained from https://phys.org/news/2022-02-laser-mars.html

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