Compare India's two-module Gaganyaan orbital module architecture with the three-module configurations used by Russia and China. What are the trade-offs?

Gaganyaan's Orbital Module (OM), injected by the HLVM3, consists of just two elements — a Crew Module (CM) and a Service Module (SM) [1] — whereas Russia's Soyuz and China's Shenzhou fly a three-module stack [2][6]. The divergence reflects mission design intent, not a capability gap.

Architecture compared

• India (two-module): the CM is a double-walled habitable capsule with a pressurised inner structure, unpressurised outer shell and Thermal Protection System, carrying crew interfaces, life support, avionics and deceleration systems; the unpressurised SM houses propulsion, power and thermal management [1].
• Russia/China (three-module): Soyuz adds a separate orbital module — living space with a docking hatch — alongside the descent module (crew station for launch and landing) and the instrumentation-propulsion module (life support, batteries, solar panels, engines) [2]; Shenzhou follows the same layout [6].
• Common principle: only the descent/crew module survives re-entry; the remaining modules are ejected and burn up [1][2]. Gaganyaan's CM carries its own bi-propellant RCS of 12 × 100N thrusters for three-axis control after SM separation until parachutes deploy [3].

Trade-offs

• Volume vs mass: the third module buys habitable volume, docking capability and stowage; India compresses these functions into one CM — sufficient for a short low-Earth-orbit demonstration flight, but limiting for docking-dependent missions [1][6].
• Simplicity vs endurance: fewer modules mean fewer separation events and fewer single-point failures, though the three-module design better suits long-duration station-ferry roles.
• Safety assurance: India offsets compactness with redundant avionics [1] and qualification of the up-righting, umbilical-separation and apex-cover systems [4].
• Cost discipline: a lighter OM lowers launch mass and programme cost for a maiden effort.

India's choice is therefore an appropriate first-generation configuration — safety-optimised and affordable. As the programme enters its final phase ahead of the 2027-28 crewed flight [5], scaling toward docking-capable variants for the Bharatiya Antariksh Station will be the natural next step in self-reliant human spaceflight.