JAXA+: What if Japan had an unlimited space budget? (KSP Real Solar System)

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My most recent project in Kerbal Space Program with the Real Solar System and Realism Overhaul mods is to imagine what it would be like if the Japan Aerospace Exploration Agency was in a world where stagnant economies and small budgets don't matter.

The H-IIA uses large single-segment SRBs (similar to the Castor 120). So I made the H-Z, which uses the largest monolithic SRB ever tested, the AJ-260. It is larger than SLS or Starship, capable of lifting 485 (4 SRBs) to 900 tonnes (2 LRBs, 2 SRBs) to low Earth orbit.

More info here.

"Tsukuyomi" Moon base (2026)



"Kagutsuchi" Mars mission (2030-2035)

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With a mass of 175 tonnes and launching in 2026, Tsukuyomi combines a two-stage direct ascent lunar lander with a lunar base (3 astronauts for 1 year). It is powered by two Kilopower reactors for lunar nights, requiring six large radiators to dissipate heat. Propulsion consists of five LE-5B-3 engines on the descent stage, and five Lunar Module Ascent Engines for return to Earth. It is shorter than Starship HLS but only requires one H-Z 204L launch with a third stage.

Kagutsuchi is a conjunction-class (long stay) Mars mission which first launches the Mars Habitat Module in 2030. Arriving in the next year, a Hypersonic Inflatable Aerodynamic Decelerator is used for entry, descent, and landing (after propulsive capture). In 2033, the 1700-tonne chemical Mars Transfer Vehicle is assembled over four launches. Modified LE-7 engines are used for main burns, with LE-5 engines used for course corrections. Docked to it is the Mars Ascent Vehicle, capable of launching as a single stage to Mars orbit, refueling at the MTV, and landing on the moons of Mars. The MHM and MAV both use the methalox CECE configuration of the RL10 engine. Return to Earth occurs in 2035.

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The Ame-no-Uzume Venus mission started in 2037 with the launch of an uncrewed atmospheric balloon habitat and ascent vehicle (1200 t IMLEO with transfer stages), arriving in low Venus orbit the next year. In 2039, the crewed interplanetary transport (2400 t IMLEO) was sent to make an orbital rendezvous with the balloon habitat. Two out of three crew transferred into the habitat, which entered the Venusian atmosphere and floated 53 km above the surface. After a 30-day stay (opposition-class), the ascent vehicle used a Raptor and RL10 engines (CECE methalox) to launch back into orbit. The crew returned to Earth in 2040.

(inspired by HAVOC)

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The Koujin and Inari missions to Vesta and Ceres occurred simultaneously during the mid-2040s. In 2043, two pairs of habitat and lander modules (the transfer stages massing over 700 t) were launched to the asteroid belt using several "LE-N2" nuclear thermal engines (based on the NERVA II proposal). The crew transports each massed over 3600 t, departing to Vesta and Ceres in 2044 and 2045. As they arrived, the transports rendezvoused with the small landers waiting in orbit before they descended to the surface. Explorations were conducted at Marcia Crater on Vesta (in 2045) and Occator Crater on Ceres (in 2047), returning to Earth in 2047 and 2048, respectively.