Non-fiction: Interplanetary Transport System (concept)

Overview
Elon Musk’s 2016 Interplanetary Transport System (ITS) laid out a technically grounded vision for making human life multiplanetary by driving down the cost and risk of travel to Mars. Presented at the International Astronautical Congress in Guadalajara, the concept proposed a fully reusable, methane-oxygen launch and spacecraft architecture built for high payload capacity, rapid reusability, in-orbit refueling, and production of return propellant on Mars. The goal was to transform one-off exploratory missions into a scalable transport system capable of moving large numbers of people and cargo to build a self-sustaining city.

Architecture
ITS consisted of three primary elements sharing a common 12-meter-diameter design language: a gigantic first-stage booster, an interplanetary spaceship, and a tanker version of the ship for orbital refueling. The booster was to loft the ship to low Earth orbit; the tanker would then launch multiple times to fill the ship’s tanks. The interplanetary ship, designed for up to 100 passengers and significant cargo, included pressurized habitation space, life support systems for months-long voyages, thermal protection for atmospheric entries, and large solar arrays for power in deep space.

Propulsion and Propellants
The entire system used liquid methane and liquid oxygen (methalox), chosen for high performance, clean-burning reusability, deep cryogenic densification, and the ability to synthesize both propellants on Mars using in-situ resource utilization. Propulsion centered on SpaceX’s full-flow staged-combustion Raptor engines. The booster was to fly with a very high engine count and liftoff thrust exceeding 120 meganewtons, enabling both massive payloads and engine-out robustness. The ship combined sea-level Raptors for landing and high-expansion vacuum Raptors for efficient interplanetary burns.

Mission Profile
A typical mission would launch the ship to orbit with minimal propellant, then conduct a series of tanker flights to refuel it on-orbit. Once topped off, the ship would depart during a favorable Earth–Mars window, using a heliocentric transfer trajectory. In Mars orbit and entry, the vehicle would rely on heatshielding and aerodynamic braking before executing supersonic retropropulsion for a precise propulsive landing. After unloading, a surface propellant plant powered by solar arrays would manufacture methane and oxygen from atmospheric CO2 and water ice, enabling refueling for the return trip to Earth and fully closing the reusability loop.

Economics and Reusability
Musk argued that cost per person must approach contemporary house prices to make a Mars city feasible. The cost model hinges on four multipliers: full reusability of all major elements, refueling in Earth orbit to maximize payload fraction, production of propellant on Mars to avoid shipping return fuel, and using optimal propellants and engines to raise efficiency. The booster would land back near the launch site minutes after liftoff for rapid turnaround, while the tanker and ship were designed for repeated flights across multiple synodic windows.

Safety and Systems
Redundancy was built into propulsion with many engines and independent bays. The ship’s structure and shielding, coupled with mission planning, were intended to keep radiation exposure within acceptable limits. Large deployable solar arrays on the ship provided roughly hundreds of kilowatts for habitation, life support, and cryogenic propellant management. Thermal protection and stainless or advanced composite structures were studied to balance mass and durability.

Timeline and Challenges
The 2016 roadmap targeted aggressive early cargo and crewed missions in the 2020s, acknowledging substantial challenges: engine maturation, orbital refueling operations, high-cadence reusability, Mars ISRU at scale, long-duration life support, and financing. The concept served as a north star rather than a fixed design.

Legacy
ITS evolved into the smaller-diameter BFR and ultimately the 9-meter Starship/Super Heavy architecture, but its pillars remained intact: methalox propulsion, full reuse, on-orbit refueling, and Mars propellant production. The 2016 concept reshaped industry expectations by treating interplanetary transport as a solvable engineering and economic problem, not a one-off mission plan.