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Biprop engine for Surveyor, the first American spacecraft to achieve a soft landing on the moon (or anywhere off-world for that matter). Part of the FV Space Collection.

It is resting on its transfer case as JPL would have received it, with the desiccant plugs installed (upper right corner) for shipping.

This Vernier engine was of critical importance to provide propulsion for trajectory correction maneuvers, attitude & velocity control before & during landing. Surveyor-2 crashed hard into the moon after an improper mid-course correction burn of a vernier engine put it into a tumble.

Each craft was planned to slow to about 110 m/s (4% of speed before retrofire) by a main solid fuel retrorocket, which fired for 40 seconds starting at an altitude of 75 km above the Moon, and then was jettisoned along with the radar unit at 11 km from the surface. The remainder of the trip to the surface, lasting about 2.5 minutes, was handled by smaller doppler radar units and three vernier engines running on liquid fuels fed to them using pressurized helium. Each engine’s thrust could be throttled over a range of 30 to 104 lb. Two of the engines were fixed, while the third could gimbal. Heroicrelics has a detailed description of this TD-339 rocket engine.

Developed by Reaction Motors Division of the Thiokol Chemical Corporation and first used operationally on Surveyor 1, which soft landed on the Moon June 1, 1966. Roughly 9″x6″x7″ Serial #1. You can see the bright gold of it on the extra Surveyor spacecraft at the Smithsonian NASM, bottom right. They also have a spare TD-339 vernier engine in their collection.

It used a regeneratively-cooled combustion chamber with a silicon carbide throat insert. The engine employed a somewhat unusual vortex injector. Each engine had a dedicated pair of propellant tanks, using mixed oxides of nitrogen (90% nitrogen tetroxide with 10% nitric oxide) as an oxidizer and monomethyl hydrazine monohydrate (MMH with water) as fuel; this combination ignites hypergolically when mixed in the thrust chamber.

One response to “Lunar Surveyor Rocket Engine TD-339”

  1. jurvetson Avatar
    jurvetson

    More from rocket relics: A Thiokol Chemical Corporation – Reaction Motors Division (RMD) TD-339 regenerative fuel-cooled Vernier thrust chamber developed for the Surveyor Lunar Lander program. Three of these gold-plated, engines were attached to the “knee” of each of the Surveyor’s three legs; 2 in a “fixed” configuration and the third (on Leg 1) gimbalable ± 6 degrees about an axis allowing its use for roll control of the spacecraft. The purpose of the Vernier was to provide propulsive power for mid-course correction maneuvers, attitude control before and during the main terminal descent phase from 66 nautical miles altitude above the lunar surface to touchdown, and prime retro power after the main solid-fuel Thiokol retro was jettisoned from the Surveyor spacecraft.

    The 100 pound engine utilized hypergolic Monomethyl Hydrazine Hydrate (MMH-H2O) as the fuel and mixed oxides of nitrogen – Nitrogen Tetroxide with 10 percent Nitric Oxide (MON-10) as the oxidizer at a maximum chamber pressure of 250 psia. NO was added to the oxidizer to reduce the freezing point.

    Assembly consists of a linked upstream throttle valve (each engine was individually throttleable between 30 and 104 pounds), a regeneratively fuel-cooled cylindrical thrust chamber of concentric stainless steel with vortex injector and ceramic liner of Zirconium Oxide (Rokide-Z), Silicon Carbide insert throat block and a molybdenum nozzle extension; collectively these engines subassemblies implemented a “Voramic Chamber” concept which was introduced by RMD to mitigate heat transfer issues associated with potential boiling and decomposition of the propellant applied to regeneratively cool the Vernier. A fuel regulator also maintained constant high pressure to inhibit fuel boiling within the chamber cooling jacket. The fuel itself was chosen for its thermal stability so it could operate through the full range of Surveyor’s throttling modes. The gold plating seen on the exterior of the engine is 0.0001 inch (.00025 cm) thick and was applied for rejection of thermal/cosmic radiation from the sun.

    This artifact is displayed in its transport case mounting, exactly as it would have been received by the Jet Propulsion Laboratory (JPL) from the manufacture (RMD) with installed desiccant plugs for shipment.

    The Surveyor project was conceived by JPL scientists primarily as a series of robotic precursor missions to prepare the way for human landings and exploration on the lunar surfaces during the Apollo project. The Vernier Propulsion System (VPS) was one of the most difficult developments undertaken by the Surveyor project. Seven Surveyor missions were conducted between May 1966 and January 1968, two of which (Surveyors 2 and 4) were not successful. A significant achievement occurred in 1967 with the TD-339 enabling the first flight from the Lunar Surface with the lift off of Surveyor 6 as it performed a 2.5 meter “hop” maneuver (the maneuver was executed to observe surface disturbances produced by the initial landing and the effects of firing rocket engines close to the lunar surface – important information required to properly engineer the Apollo Lunar Module Descent Engine).

    Ultimately RMD’s (Thiokol) demise in the small thruster market has been attributed to the complexity of a combination regenerative/radiation cooled motor. Other manufacturers developed 100% radiation cooled motors utilizing Niobium (Columbium) as the chamber material.TD-339 Vernier Engine installed on Surveyor S-10 Engineering Model in the National Air & Space Museum:Surveyor 3 at Oceanus Procellarum (Ocean of Storms) – Apollo 12 LM Intrepid in the Background):

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