If you make a selection of the most important inventions of mankind since the 20th century, I believe that lasers, which are known as "the brightest light" and "the fastest knife", will surely be able to occupy a place in it.
On May 15, 1960, the first laser in human history was introduced, and since then the laser has entered the practical stage and has rapidly shined in industry, agriculture, medical treatment, military and other fields. As people's understanding of lasers deepens, scientists have also begun to try to explore the possibility of more applications of lasers.
Figure | Laser show (Source: Pixabay)
For example, can a laser propel a spacecraft into Mars?
Recently, a research team from McGill University in Canada responded to this bold idea, believing that it is completely achievable.
The team proposed a laser thermal propulsion system that, with the help of a large laser matrix located on the Earth's surface, would heat up the hydrogen plasma stored at the end of the space vehicle, creating a powerful thrust to quickly send the vehicle to Mars, a process that is expected to take only 45 days [1].
Previously, SpaceX also proposed a solution for Mars exploration, but they used chemical fuels to propel the rocket, which is expected to take up to 6 months. This also means that efficient laser thermal propulsion enables rapid interplanetary missions, which in turn can have a positive impact on the entire space exploration and transportation program.
The study, published in the journal Acta Astronautica, was titled "Design of a Rapid Transit to Mars Mission Using Laser-thermal propulsion," by Emmanuelle Duplay, an engineering b.A. from McGill University.
Figure | Related paper (Source: Acta Astronautica)
In fact, as a new type of propulsion technology, laser thermal propulsion has significant advantages in cost and payload ratio compared with traditional rocket propulsion methods, and has long been valued by various countries around the world and widely used in satellite launch and orbit control. Therefore, the team's vision is not imaginary.
It is understood that the reason why DuPelli's team came up with the idea of entering Mars with the help of laser matrix is actually to complete a challenge launched by NASA in 2018.
At the time, NASA asked scientists to devise a program to "provide at least 1,000 kilograms of payload in no more than 45 days, and to move in and out of the solar system for longer periods of time." "If successfully completed, this mission will greatly reduce the physical damage that future astronauts will encounter during space flight, such as radiation from cosmic rays."
The conundrum, however, is that scientists have realized that the thrust of rocket fuel is not enough to allow humans to reach farther afields such as Mars, and new dynamics are urgently needed.
In this case, the mcGill university research team naturally locked their eyes on the much-talked about laser propulsion technology.
In the team's vision, the laser thermal propulsion system will abandon the large amount of fuel that the spacecraft must carry and replace it with lasers, thus making the spacecraft lighter and faster.
The specific principle is to use a large laser array located on The Earth to emit many high-energy laser beams at a long distance. When the spacecraft is flying in Earth-Moon space according to a given orbit, it will pass through an inflatable device and gather these invisible laser beams into a hydrogen heating chamber, which resembles a combustion chamber on a rocket, except that it contains hydrogen plasma.
Then, when the lasers gathered together reach a certain critical point in energy density, the hydrogen flowing in the heating chamber will be discharged through the nozzle, forming a powerful thrust, thereby pushing the spacecraft to fly rapidly.
Figure | Laser thermal propulsion system concept (Source: Acta Astronautica)
It is reported that through this method of propulsion, the speed of the spacecraft will exceed 17 km / s. This means that it can cross the orbital distance of the moon in no more than half a day. On top of that, even after 45 days, the spacecraft was able to continue flying at an approximate speed.
However, new questions arise, how can fast-flying payloads be successfully placed in their intended positions after the spacecraft arrives in the Martian atmosphere?
Previously, spacecraft carrying payloads typically used reaction forces from chemical fuels to slow down, but laser propulsion systems clearly lacked this necessary condition.
The team said that before building the Mars laser matrix, perhaps "aerial capture will become the only way to slow down payloads on Mars." "However, this type of deceleration is quite risky. Due to the high speed generated by laser propulsion, aerial capture will easily lead to strong atmospheric friction, which is a big test for the thermal system protection materials on the spacecraft.
But in any case, the laser thermal propulsion system concept represents an advanced power technology. In addition, the system can achieve an unprecedented mass-to-power ratio of 0.01kg/kW or less.
"One of the great advantages of laser thermal propulsion is the ability to achieve a 1-ton rapid transport mission using a laser array the size of a volleyball court," Dupelle said. He further explains, "Its mass-to-power ratio is even much lower than nuclear propulsion technology because its power source comes from Earth and can be processed by low-mass inflatable reflectors." ”
However, in DuPelli's view, laser thermal propulsion technology is not mature at present, and it may still take nearly 20 years to continue to develop if it wants to become a reality.
-End-
reference:
1.Duplay, Emmanuel, et al. "Design of a rapid transit to Mars mission using laser-thermal propulsion." Acta Astronautica（2021）.
https://phys.org/news/2022-02-laser-mars.html