NASA researchers talk about progress in the development of a solar-powered interstellar probe
Engineers at Johns Hopkins University's Applied Physics Laboratory, led by scientist John Benkoski, have assembled a prototype solar-thermal engine for an interstellar probe. The installation will not be able to be used on a real probe for a long time, but this was not the purpose of the experiment - the scientists wanted to confirm that such a principle of operation makes sense and its efficiency will be high, writes Wired.
The installation is located in the backyard of the university campus and consists of two parts: an array of LEDs, which researchers call a "solar simulator", and the engine itself. It looks like a black and white tile through which liquefied helium flows - the gas passes through the coil. When the light is turned on, the "simulator", according to scientists, shines with an intensity 20 times higher than the solar one (at what distance from the star is not specified), helium absorbs heat and escapes from the nozzle, thus creating a jet thrust.
This is the first time this solar-powered engine setup is being tested. The scientists explained that it was theoretical verification that was the main goal of the experiment: “This shows that solar heat engines are not fiction. They can really work, ”Benkoski says. So far, the researchers have not named any specific numbers, only noting that the system worked. Scientists promise to publish a more detailed report in 2021.
At the moment, only two spacecraft (allegedly) have been able to leave the solar system - Voyager 1 and Voyager 2. However, they were built for the study of Jupiter, Saturn, Uranus, and Neptune, while they are not suitable for travel outside the system - the devices are not equipped with a sufficient number of instruments that would help to study the border of the Solar system and interstellar space - the heliopause. In addition, the Voyagers move too slowly - only 60 thousand kilometers per hour, which allowed them to approach the heliopause in only 50 years.
In late 2019, NASA turned to the Applied Physics Lab to study interstellar mission concepts. The agency and laboratory are now working together on this task. Scientists have to figure out how to get into interstellar space in a relatively reasonable amount of time - and using solar-powered engines could be the solution to this problem.
A team of researchers is working to create a probe that, in the same 25 years, could travel four times the distance from the Sun to the edge of the Solar System. Benkoski said this will require building a probe that is unlike any previously used. So, scientists propose to conduct a gravitational maneuver near the star - this will allow the apparatus to accelerate to 320 thousand kilometers per hour by obtaining the necessary heat from the Sun and acquiring additional momentum due to the Obert effect.
In this case, the gravity assist itself will last a few hours. This means that the probe will have to pass very close to the Sun, and this is one of the main problems. "Adapting to a thermonuclear explosion the size of the sun is a tough challenge in terms of material selection," says Dean Sheikh, materials scientist at NASA's Jet Propulsion Laboratory. During the mission, the probe will have to spend about two and a half hours at temperatures of the order of 2500 ° C, which can lead to melting. Therefore, Sheikh's team has selected new materials that can be applied as an outer coating to the probe body, which will reflect heat energy.
In addition, the researchers suggest using hydrogen instead of helium in a jet engine as one of the possible options. In theory, this can significantly increase the efficiency of the engine. However, hydrogen will heat up to extremely high temperatures. Therefore, scientists will also have to select materials for the coating for the probe's heat shield.
According to Benkoski, the scientists still have a lot of work to do - the experiments they have conducted are too limited so far. The experiments were carried out at relatively low temperatures, and also did not use the same materials and fuels that would be used in a real mission. However, the results of the experiments are consistent with models that predicted the operation of the interstellar probe on solar power, and this is the main thing, the engineers say.
“We launched a system that can never fly. And now the next step - we start replacing each of its components with the material that we would put on a real spacecraft for a successful gravity assist, ”says Benkoski.