Lockheed Martin Lunar Landers revealed

by David Harris, Chris Bergin

After recently winning the Orion CEV contract, Lockheed Martin is looking to the future, with a new study exploring a variety of possible Lunar Surface Access Module (LSAM) strategies and configurations.The study explores three unique ideas for using a LH2/LOX fueled LSAM to facilitate VSE (Vision For Space Exploration) lunar landings.

The superb Lockheed Martin Lunar Landers Presentation is available to download on L2.
**Click here for larger, selected images, showing the three concepts**

The thrust of the new report is a focus on adapting LOX/LH2 landers for simple use as a lunar transportation system. LOX/LH2 is extremely efficient and can be used both for providing electricity and water in fuel cells – and in conjunction with a lunar ISRU system. However, because LH2 is so bulky and the high area ratio LOX/LH2 engines are so long, it has been difficult to design effective landers that use LOX/LH2 in their propulsion system.

The new Lockheed Martin report draws on experience with the Centaur upper stage rocket and gives high priority to easy surface access for crew and cargo. The study notes that the designs presented are not ‘promoted as final designs, nor intended as comparative trades,’ but are instead meant to provide innovative approaches to implementing high-efficiency LOX/LH2 fuel without letting the bulky LH2 tanks impede surface access.
The study begins by pointing out that typical lander designs such as that presented in the ESAS are problematic because they include multiple fuel tanks clustered around an engine. This is problematic from the point of view of cryogenic storage because the surface area is much larger per unit volume on these tanks, and the required large number of heat conducting struts and plumbing increasing boiloff losses dramatically.  Numerous tanks also vastly increase the complexity and cost of the propulsion system overall. Instead, the new lander designs presented in the study use large single thin-walled monocoque tanks for propellant storage.
The first concept is called the Dual-Thrust Axis Lander. This lander ‘uses an axial main engine to perform LOI and most of the descent burn’; a set of smaller, lateral engines perform the final landing maneuvers allowing the lander to set down on its side. This horizontal landing puts the crew and cargo very close to the surface because the bulky propellant tanks and large cryo engine are to the side of the lander rather than beneath the crew compartment.

The lander uses an existing single LOX/LH2 pump-fed RL-10 engine for most of the descent and uses low thrust, highly throttleable, pressure fed hypergolic engines to perform the final landing. Once on the surface, the crew performs EVAs via an inflatable airlock, eliminating the need for extremely long ladders. The crew can access cargo once on the surface via 10 200-kg side rack cargo pallets. The Dual-Thrust Axis Lander offers large gimbaling solar panels and 28 m^3 of habitable volume on two decks.  The vast residual LOX/LH2 from the Descender stage are sufficient to power lunar operations through the lunar night.

The majority of vehicle systems, including power, heat rejection and life support as well as commodities (H2, O2, N2O4, water) are stored on the Descender stage ‘service module.’  This keeps the crew habitat/hypergolic ascent stage as light as possible.  Following ascent stage departure, the remaining Descender stage / service module has utility to support continued growth of a lunar base.  The large cryo tanks, pressure vessels, heat rejection system, and 10 kw of solar and 8 kw of fuel cell power will prove invaluable to the fledgling lunar base.
The second vehicle is called the Retro-Propulsion Lander. In this configuration, an RL-10 also performs the LOI and most of the descent maneuvers, but is jettisoned shortly before landing. Landing is performed with a set of small NTO/MMH thrusters. Like the Dual-Thrust Axis Lander, the Retro-Propulsion Lander puts the crew and cargo very close to the lunar surface.  This concept results in a small, compact landed module that is potentially more maneuverable than concept 1.

The vehicle has some mass penalties compared with the Dual-Thrust Axis Lander, because it cannot use the LOX/LH2 for power generation and must incorporate all of the electricity and life support systems onto the ascent stage. Therefore, the Retro-Propulsion Lander is only appropriate for missions that do not exceed seven days in duration, or for longer missions to an emplaced lunar base.

Both the Dual-Thrust Axis Lander and Retro-Propulsion Lander offer the innovative idea of wheels on the landers. The study reports several advantages to wheeled landers. First, they allow greatly enhanced mobility beyond the landing zone for short exploration missions; during a 7-14 day mission, over 100 km could be covered if the lander itself moves as slowly as 1 km/hr. This enables the astronauts to visit distant targets without spending their entire time commuting.

Also, when accessing a lunar base, wheels offer a number of advantages. Cargo and crew landers will have to land several hundred meters from the base to avoid damage deployed elements. A wheeled lander offers significantly easier transport of large cargo elements rather than having to haul them up to a kilometer to the base. This also prevents a ring of spent landers building up around the base; instead, each lander could be towed or driven to what the study calls a ‘boneyard’ of spent descent stages. The Dual-Thrust and Retro landers only are meant to be towed, but motors could be easily added.

The third design is a single-stage lander that performs LOI, descent, landing, and lunar orbit ascent all with the same propulsion system. The study states that because it is much easier to reach lunar orbit than Earth orbit, that depending on requirements of the lander, a single-stage lander can actually be lighter than a two-stage system.  This is due to the reduction in subsystem mass and the use of high-performance LOX/LH2 for both descent and ascent.  The other 2 concepts used lower-Isp, storable propellant ascent stages.

The single-stage lander could be completely reusable if it were refueled in lunar orbit with propellant from Earth, or on the lunar surface from locally derived LOX and LH2. Reusability also prevents dozens of discarded descent stages from building up around a lunar base.

The single-stage lander has some disadvantages as well. The crew cabin is very small and quite far from the surface; therefore, the study recommends this design for ‘outpost support missions’ so that the crew would not have to live in the lander cabin. The single-stage lander has a cargo bay on bottom, but is not as well-suited to delivering large monolithic cargo elements as are the first two designs.

While the contract award and detailed design of the LSAM are still several years away, these studies from Lockheed Martin show that innovative designs for the future lander are being constantly generated and refined.

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