Lunar Lander

Overview

A lunar lander solves one problem: the Moon has no atmosphere, so every metre per second of orbital velocity, about 1,700 of them, must be removed by rocket thrust, finishing at zero exactly at the surface. The vehicle is therefore mostly propellant. Of a typical 1,900 kg separated mass, more than 1,100 kg is the MMH and MON-3 stored in the four spheres of the Propellant Tanks & Pressurization, leaving a dry structure, avionics, and up to a tonne of payload on the Payload Deck.

The propulsion is deliberately simple. There are no turbopumps: helium from the Helium Pressurant Bottle bottles, stepped down by the Helium Pressure Regulator, squeezes propellant out of the tanks at about 16 bar. Hypergolic propellants ignite on contact, so there is no igniter to fail, and the engines restart as many times as guidance asks.

The descent engine

The defining component is the throttleable Throttleable Main Engine. A fixed-thrust rocket cannot land: as propellant burns off the vehicle gets lighter, and the final approach needs thrust barely above lunar weight. The engine throttles 10:1 using a Pintle Injector, a single coaxial element whose central sleeve slides to vary the injection area, keeping injection velocity (and therefore mixing and combustion stability) roughly constant from 3.5 kN down to 350 N. The Throttle Valve pair meters flow upstream, and the Engine Control Unit closes the thrust loop on chamber pressure at 100 Hz.

Cooling is passive: the Combustion Chamber is silica-phenolic ablative, charring at a known rate over the 12-minute burn, and the Engine Nozzle Extension is a columbium extension that simply glows. Each engine swings ±6° on Gimbal Actuator pairs for steering, fed through bellows-jointed Flex Feedline runs.

Navigation to a safe spot

Powered descent starts about 15 km up. The Inertial Measurement Unit propagates the state, but inertial navigation alone drifts kilometres over a descent, so the Terrain Navigation Camera matches surface images against stored orbital maps, pinning position to tens of metres, terrain-relative navigation. From 20 km down, the Doppler Landing Radar measures altitude and three-axis velocity directly off the surface by Doppler.

At about 500 m the vehicle pitches vertical and the Hazard Detection Lidar scans the landing ellipse, building a 5 cm elevation map. The Flight Computer pair grades it for slopes and boulders, selects the safest reachable point, and flies the divert. Sixteen RCS Thruster units in four RCS Thruster Pod clusters null residual horizontal velocity. When a Surface Contact Probe touches regolith, guidance cuts the engines roughly a metre up, landing under thrust would blast a crater under the vehicle and cook the deck with reflected plume, which is also why the Plume Shield foils protect the tank bottoms.

Touchdown and surface operations

Each Landing Leg Assembly absorbs its share of the impact not with a hydraulic damper but a Crushable Honeycomb Cartridge: an aluminium honeycomb column inside the Primary Strut that crushes once at a controlled force. It is single-use, light, and works at any temperature. The Secondary Strut pairs triangulate the leg, the Leg Downlock Latch rigidizes it after the Leg Deployment Mechanism swings it down, and the broad Footpad keeps bearing pressure low enough that the pads sink only centimetres into regolith. The geometry tolerates a 10° slope with one pad on a 30 cm rock.

On the surface, the three body-fixed Solar Panel faces deliver about 450 W, recharging the Descent Battery drawn down during descent. The Steerable Medium-Gain Antenna tracks Earth for a ~2 Mbit/s X-band payload downlink through the Solid-State Power Amplifier, while the Low-Gain Omni Antenna pair guarantees commandability regardless of attitude. Payloads bolt to the deck's insert grid; a rover drives off on the Rover Egress Ramp rails.

The baseline mission ends with the lunar night: 14 days at down to −180 °C exceeds what the Thermal Control Subsystem heaters can hold off on battery energy alone, so most landers of this class are designed for one daylight period, with night survival an extended-mission goal rather than a requirement.