As always, NASA is testing the next generation of engines to enable ever more ambitious space missions. One idea currently in 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 solid-to-plasma phase change in a propellant projectile during a pulsed cycle,” according to a paper about the system. “To generate the plasma bursts that provide thrust, a heavily moderated 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 barrel base, together with a novel control drum mechanism, enables controlled and rapid neutron population growth, transitioning to a plasma state in a fraction of a second.” The system could potentially generate thrust of up to 100,000 N.
“The PPR’s exceptional performance, combining high ISP and high thrust, has the potential to revolutionize space exploration. The high efficiency of the system enables manned missions to Mars to be carried out in just two months,” NASA explains about the engine from Howe Industries in a press release. “Alternatively, the PPR enables the transport of much heavier spacecraft equipped with shielding against galactic cosmic rays, reducing crew exposure to negligible levels.”
NASA further explains that the PPR could be used for many more missions, carrying spacecraft to the asteroid belt and beyond, perhaps even 550 Astronomical Units (AU), where an AU is the distance between the Earth and the Sun.
While the immediate focus is on how it could power heavier, manned missions to Mars on much shorter timescales than are possible with current propulsion systems, NASA mentions a mission that could enable the engine’s potential for long-distance flights. In short, if we get equipment with a range of 550 AU from the Sun, we could use our star as a giant telescope.
As Einstein’s general theory of relativity suggests, giant objects in the universe bend space-time, changing the path of light.
How gravitational lenses work.
Photo credit: NASA, ESA and Goddard Space Flight Center/K. Jackson
When we use solid objects as a lens, we can see light from outside the object in question. This is not an abstract idea, but something we can do fairly regularly with telescopes like the JWST. Although it’s cool, we are limited by the location of these objects and the objects that happen to be behind them.
But we already have a massive object near us that is causing gravitational lensing.
“The Sun’s gravitational field acts as a spherical lens to amplify the intensity of radiation from a distant source along a semi-infinite focal line,” wrote Von Russel Eshleman, who first proposed the concept, in a paper. “A spacecraft anywhere along this line could in principle observe, listen, and communicate at interstellar distances using equipment comparable in size and power to that used today for interplanetary distances. Neglecting coronal effects, the maximum magnification factor for coherent radiation is inversely proportional to wavelength, i.e. 100 million at 1 millimeter.”
Although there are still astronomical challenges ahead for such a mission (including significant distortions from gravitational lensing and moving spacecraft over long distances to observe the object behind you that you are interested in), in theory it could be used to create images of the actual surfaces of other worlds.
The range at which we can use this gravitational lens to look at more distant distances starts at about 550 AU, which is far beyond what we have achieved so far. Voyager I has reached just over 160 AU since its launch in 1977. But with the next generation of engines, this mission may soon be easier to achieve and we can use our own star as a telescope to observe other planets.