As always, NASA is looking to the next generation of thrusters to enable ever more ambitious space missions. One idea currently moving into Phase II of NASA’s Innovative Advanced Concept (NIAC) program is the Pulsed Plasma Rocket (PPR).
The PPR “uses a fission-based nuclear power system to rapidly cause a phase change in the propellant projectile from solid to plasma during the pulse cycle,” a paper on the system explains. “A highly moderated low-enriched uranium (LEU) projectile can be used in combination with an unmoderated LEU barrel to preferentially heat the projectile to create the plasma discharges that provide thrust. A short section of high-enriched uranium (HEU) at the base of the barrel, along with a new by the control drum mechanism, allows the controlled and rapid growth of the neutron population to transition to the plasma state in a fraction of a second.” The system could potentially generate up to 100,000 N of thrust.
“The exceptional performance of PPR, which combines high ISP and high thrust, has the potential to revolutionize space exploration. The system’s high efficiency allows manned missions to Mars to be completed in just two months,” NASA explains about the Howe Industries thruster. in a press release. “Alternatively, PPR allows for the transport of much heavier spacecraft that are equipped with galactic cosmic ray shielding, reducing crew exposure to negligible levels.”
NASA goes on to explain that the PPR could be used for many more missions that would take spacecraft to the asteroid belt and beyond, perhaps as much as 550 astronomical units (AU), where one AU is the distance between Earth and the Sun.
While the immediate focus is on how it could be used to propel heavier manned missions to Mars in much shorter time frames than current propulsion systems allow, NASA mentions one mission that the thruster’s potential for long-distance travel could enable . In short, if we can get a device 550 AU from the Sun, we could use our star as a giant telescope.
According to Einstein’s general theory of relativity, giant objects in space bend space-time and change the path of light.
How gravitational lensing works.
Image credit: NASA, ESA and Goddard Space Flight Center/K. Jackson
Using massive objects as a lens, we can see light from behind the object. This is not some abstract idea, but something we can do fairly regularly with telescopes like JWST. While this is cool, we are limited by the placement of these objects and the objects behind them.
But we already have a massive object nearby that causes gravitational lensing.
“The Sun’s gravitational field acts as a spherical lens that magnifies the intensity of radiation from a distant source along a semi-infinite focal line,” wrote Von Russel Eshleman, who first proposed the concept. “A spacecraft anywhere along this line could in principle observe, eavesdrop, and communicate at interstellar distances using equipment of comparable size and power to what is now used for interplanetary distances. If we neglect coronal effects, the maximum magnification factor for coherent radiation is inversely wavelength, which is 100 million per 1 millimeter.”
While there are still astronomical challenges ahead of such a mission (including significant distortion caused by gravitational lensing and moving the spacecraft vast distances to observe the object behind it of interest), in theory it could be used to create images of the actual surfaces of other worlds.
The region where we can use this gravitational lens to image 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 thrusters, perhaps this mission will soon become more achievable, and we can use our own star as a telescope to observe other planets.