NASA’s Pulsed Plasma Rocket (PPR) could shorten mission times to Mars and open the door to interstellar travel by using the Sun as a giant telescope.
NASA, as usual, is exploring the next generation of thrusters to support increasingly ambitious space missions. One idea currently in Phase II of the NASA Innovative Advanced Concept (NIAC) program is the Pulsed Plasma Rocket (PPR). This innovative system uses nuclear energy from fission to rapidly cause the fuel to transform from solid to plasma during a pulsed cycle, as described in an article dedicated to the system.
The PPR uses a highly moderated Low Enriched Uranium (LEU) projectile along with an unmoderated LEU barrel to generate thrust-generating plasma explosions. A short section of Highly Enriched Uranium (HEU) at the base of the barrel, combined with an innovative drum control mechanism, allows for rapid and controlled growth of the neutron population to transition to the plasma state in a fraction of a second. It is estimated that the system can generate up to 100,000 N of thrust.
The exceptional performance of the PPR, which combines high Isp (Specific Impulse) with high thrust, could revolutionize space exploration. According to NASA, the Howe Industries thruster could enable crewed missions to Mars to be completed in just two months. Furthermore, the PPR could support the transportation of heavier spacecraft equipped with shielding against Galactic Cosmic Rays, reducing crew exposure to negligible levels.
NASA points out that PPR could be employed for even more distant missions, taking spacecraft into the asteroid belt and beyond, up to 550 astronomical units (AU), with one AU representing the distance between the Earth and the Sun. Although l While the immediate focus is on its use to accelerate heavier, crewed missions to Mars in significantly shorter times than current propulsion systems, NASA also mentions the thruster’s potential for interstellar travel.
In practice, if we could bring equipment to 550 AU from the Sun, we could use our star as a giant telescope. According to Einstein’s theory of general relativity, massive objects in the universe bend space-time, altering the path of light. By using such objects as lenses, we could observe light coming from regions beyond them.
The Sun’s gravitational field acts like a spherical lens, amplifying the intensity of radiation coming from a distant source along a semi-infinite focal line, as described by Von Russel Eshleman, the first to propose this concept. A spacecraft positioned on such a line could potentially observe, listen and communicate over interstellar distances, using instruments similar to those currently used for interplanetary distances.
While there are still astronomical challenges ahead for such a mission, such as the significant distortion introduced by gravitational lensing and moving spacecraft across vast distances to observe objects of interest, in theory it would be possible to image the actual surfaces of other worlds.
The region where we could exploit this gravitational lens to image remote distances begins at around 550 AU, far beyond what has been achieved so far. For example, Voyager I has achieved just over 160 AU since its launch in 1977. However, with the next generation of thrusters, this mission could become more achievable, allowing us to use the Sun as a telescope to observe other planets.
How gravitational lensing works.
NASA, ESA and Goddard Space Flight Center/K. Jackson
Links:
