Pulsed plasma thruster, funded by NASA, could make one of the coolest space missions possible

NASA, as always, is exploring the next generation of thrusters to enable increasingly ambitious space missions. One idea currently moving to Phase II of the NASA Innovative Advanced Concept (NIAC) program is a Pulsed Plasma Rocket (PPR).

The PPR “uses a fission-based nuclear power system to rapidly induce a phase change in a fuel projectile from solid to plasma during a pulsed cycle,” an article about the system explains. “To create the plasma bursts that provide thrust, a strong moderate low enriched uranium (LEU) projectile can be used in combination with an unmoderated LEU barrel to preferentially heat the projectile. A short section of highly enriched uranium (HEU) at the base of the barrel, together with a new control drum mechanism, allows a controlled and rapid growth of the neutron population to transition to a plasma state in a fraction of a second. The system could potentially generate up to 100,000 N of thrust.

“The PPR’s exceptional performance, combining high Isp and high thrust, has the potential to revolutionize space exploration. The system’s high efficiency will allow crewed missions to Mars to be completed in just two months” , NASA explains about the Howe Industries thruster in a press release. “Alternatively, the PPR allows the transport of much heavier spacecraft equipped with galactic cosmic ray protection, limiting crew exposure to negligible levels.”

NASA goes on to explain that the PPR could be used for many more missions, taking spacecraft to the asteroid belt and beyond, perhaps even 550 astronomical units (AU), where one AU is the distance between Earth and the Sun.

While the immediate focus is on how this could be used to perform heavier, crewed missions to Mars on much smaller timescales than current propulsion systems allow, NASA mentions one mission that will enable the thruster’s potential for long-distance travel could make. Basically, if we can get equipment from 550 AU from the Sun, we can use our star as a giant telescope.

As implied by Einstein’s theory of general relativity, giant objects in the universe bend space-time, changing the path of light.

A diagram showing how light can bend around massive objects.

How Gravitational Lenses Work.

Image credit: NASA, ESA and Goddard Space Flight Center/K. Jackson

By using solid objects as lenses, we can see light from outside the object in question. This is not an abstract idea, but something we can do quite regularly using telescopes like the JWST. While we are cool, we are limited by the location of these objects and the objects behind them.

But we already have a huge object nearby that is causing gravitational lensing.

“The Sun’s gravitational field acts as a spherical lens to magnify the intensity of radiation from a distant source along a semi-infinite focal line,” wrote Von Russel Eshleman, who first proposed the concept, in an article. ‘A spacecraft anywhere along that line could, in principle, observe, eavesdrop and communicate across interstellar distances, using equipment comparable in size and power to what is now used for interplanetary distances. If one neglects coronal effects, the maximum magnification factor for coherent radiation is inversely proportional to the wavelength, being 100 million to 1 millimeter.”

While there are still astronomical challenges ahead for such a mission (including significant distortion caused by gravitational lensing, and moving spacecraft over great distances to observe the object you’re interested in behind), this could in theory be used to build up images of the actual surfaces of other worlds.

The region where we can use this gravitational lens to view far distances starts around 550 AU, which is much further than what we have reached so far. Voyager I has reached just over 160 AU since its launch in 1977. But with the next generation of thrusters, this mission may soon be more feasible and we can use our own star as a telescope to view other planets.

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