Marcelo de Oliveira Souza, an astrophysicist at the State University of Northern Fluminense in Brazil, did not design a new engine or invoke exotic physics. He took the preliminary 2015 orbit of asteroid 2001 CA21 and used it as a geometric template. The asteroid\u2019s early data sketched a stretched, low-inclination ellipse that crossed the paths of both Earth and Mars. Later observations refined that orbit into a different shape, but the raw early numbers offered something rare: a clean reference plane for testing extreme transfer angles.<\/p>\n
![\"Complete](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/04\/Complete-2031-Earth\u2013Mars\u2013Earth-round-trip-configuration-for-the-feasible-rapid-case-1200x543.jpg.web.webp\")
Complete 2031 Earth\u2013Mars\u2013Earth round-trip configuration for the feasible rapid case (56-day outbound and 135-day return). Credit:\u00a0Acta Astronautica\u00a0(2026)<\/p>\n
De Oliveira Souza imposed a strict rule. Any candidate trajectory had to stay within five degrees of the asteroid\u2019s orbital plane. He then ran three future Mars opposition windows through a Lambert solver, a standard astrodynamics tool that computes possible paths between two points in space. The years 2027 and 2029 failed the test. Either the energy demand spiked too high or the geometry refused to close the loop for a return flight.<\/p>\n
The 2031 window behaved differently. It produced two complete round-trip architectures, both departing Earth on the same April day. The first, labeled extreme, combines a 33-day outbound sprint, a 30-day surface stay, and a 90-day return, totaling 153 days. The second pairs a 56-day outbound flight with a 35-day stay and a 135-day return, totaling 226 days. <\/p>\n
The Speed That Breaks Chemical Propulsion<\/p>\n
Speed in interplanetary travel is measured by hyperbolic excess velocity, the leftover velocity a spacecraft carries after escaping Earth\u2019s gravity well. For the 56-day trajectory, that figure hits roughly 16.9 kilometers per second.<\/p>\n
The practical meaning is stark. The launch requires about 15 times more energy than a conventional Mars mission and roughly 1.5 times the departure energy NASA gave the New Horizons probe on its way to Pluto<\/a>. New Horizons was a half-ton robot. A crewed Mars stack, with life support, habitat, and ascent vehicle, would mass many times more.<\/p>\n The 33-day option demands about 40 times standard mission energy. Its departure velocity of 27.5 kilometers per second sits beyond the theoretical ceiling of any chemical stage ever flown.<\/p>\n Arrival does not let up. The 56-day trajectory slams into Mars at 16.6 kilometers per second and re-enters Earth\u2019s atmosphere at 15.1 kilometers per second. Both numbers test the upper envelope of thermal protection materials still in development, shields that must survive heating rates far beyond those of a lunar return.<\/p>\n Why Nuclear Engines Are the Only Lever<\/p>\n The paper draws a hard line: chemical rockets cannot close this gap. The alternative it names is nuclear thermal propulsion, or NTP, which heats liquid hydrogen through a reactor core and expels the gas at roughly twice the efficiency of chemical combustion.<\/p>\n![\"Rocket,lunch,a,spacex,falcon,heavy,rocket,carrying,nasas,europa\"](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/04\/The-56-day-outbound-demands-15-times-the-energy-of-a-standard-Mars-mission.jpg.webp.webp\")
The 56-day outbound demands 15 times the energy of a standard Mars mission, far beyond chemical rockets. Image credit: Shutterstock<\/p>\n
![\"Only](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/04\/Only-nuclear-thermal-propulsion-can-close-the-energy-gap.jpg.webp.webp\")
Only nuclear thermal propulsion can close the energy gap, and Europe is already testing the concept. Image credit: NASA<\/p>\n