Building a Mars Inhabited Exploration Vehicle on the lunar surface is feasible with current technology.
By George N. Bullen
President and CEO
Smart Blades Inc.
Moon or Orbit
A number of years ago I was asked to participate in a study at NASA’s Jet Propulsion Laboratories (JPL) in Pasadena, CA, to determine the best approach to build an inhabited vehicle for Mars exploration. At the time, President George W. Bush had approved a plan to return to the moon and proceed onto Mars as an extension of Project Constellation. The initial decision was made to either assemble the vehicle in Earth orbit or on the Moon. These two choices were established as an outcome of the huge amount of energy it would take to lift a heavy vehicle and its human cargo through Earth departure and onto Mars. The vehicle mass would be primarily composed of fuel and provisions for the long six-month journey to the red planet, dwell-time on the surface, liftoff, and safe return to Earth.
NASA’s Project Constellation at the time was composed of two lift vehicles, one for humans and one for cargo. The idea was to launch the inhabited vehicle’s segments into space or to the moon using the uninhabited heavy-lift cargo-carrier named ARES V. Once in orbit or in position on the Moon, humans would be sent via the human lift vehicle called ARES I to assemble the Mars inhabited exploration vehicle.
Many of the study team had never been to space so the first order of business was to interview astronauts to build a detailed understanding of what the challenges were to operate, survive, and work in a zero-gravity environment. Astronaut experience would be the critical building block to construct a decision matrix for a comparative analysis between the Moon or Earth-orbit vehicle assembly choices.
The decision to build an automated assembly plant on the Moon (rather than assemble a vehicle in earth orbit) for construction and launch of a Mars inhabited exploration vehicle included two primary considerations. They were gravity and readily available resources such as water on the Moon.
It’s a Matter of Gravity
After our interviews with astronauts it became apparent that the labor and difficulty for humans to work in zero gravity to assemble the vehicle would be an exhaustive level of effort. While it is true the Space Station was assembled in space, an inhabited Mars exploration vehicle is considerably more complex and would require fueling and provisioning for the long round-trip journey to Mars.
The small amount of gravity on the Moon would be helpful to provide a foundation to anchor and operate machinery, facilitate an assembly plant, and provide a base for minimal energy utilized for liftoff to Mars.
If water was present, it would also provide resources for fuel and hydration for the crew when they arrived in preparation for their journey.
In either approach, orbiting fuel stations would have to be built. For the Moon assembly plant the heavy-lift ARES V would sacrifice fuel for payload and stop in low Earth orbit to top off its fuel tanks before continuing the journey to deliver its payload to the Moon. This concept was originally presented by Werner Von Braun in the 1960s. The fuel stations would have to be aligned and in stationary position to prevent extreme variations in heat and cold to keep the hydrogen/oxygen fuel stable. These “cryogenic fuel tanks” would be constructed of lightweight composite materials and lifted into low Earth orbit and chained together. NASA has constructed, tested, and validated low-cost manufacturing processes for lightweight composite cryo-tanks to use in space and on space vehicles.
The Lunar Crater Observation and Sensing Satellite (LCROSS) was launched on June 18, 2009, and traveled to the Moon moving at a speed of more than 1.5 miles per second. On October 9, 2009, the Centaur upper stage intentionally hit the lunar surface, creating an impact that instruments aboard LCROSS observed for approximately four minutes. The signature of water was seen in both infrared and ultraviolet spectroscopic measurements: There’s water ice on the moon, and lots of it. When melted, the water could be used to drink and extract hydrogen and oxygen for rocket fuel. Rocket fuel is composed of liquid oxygen and liquid hydrogen, which are both cryogenic. Liquid hydrogen when combined with an oxidizer such as liquid oxygen yields the highest specific impulse, or efficiency in relation to the amount of propellant consumed of any known rocket propellant. They are gases that can be liquefied only at extremely low temperatures and are highly volatile. Liquid hydrogen must be stored at -423°F (-269.4°C) and handled with extreme care.
The DIVINER instrument on the Lunar Reconnaissance Orbiter (LRO) has measured the surface temperatures of the polar regions and found these dark areas to be extremely cold, never reaching surface temperatures greater than about 25–30° above absolute zero (–272° C/-457.6° F). Consequently, the extremely cold temperatures in these areas permit any volatile substance like water to accumulate and if processed to be stored safely once converted to rocket fuels like liquid hydrogen.
Water is a crucial resource on the Moon. Transporting to space the amount of water needed for human and exploration needs is not practical. Finding natural resources such as water on the Moon is a critical component for success.
The significance of water means that fuel can be produced in an automated mining and refinement factory for filling up a Mars exploration vehicle. It also means that humans who have arrived and are preparing the vehicle for final integration and launch, and the crew, have a critical resource for survival: water.
The ability to mine and refine fuel and water is a major benefit to Moon vehicle assembly, and Moon worker’s and Mars exploration astronaut’s survival.
Almost everyone has heard of the NASA’s Curiosity Mars Rover. This robotic vehicle weighs in at approximately 1 ton (0.9072 t). On Mars, it weighs about half that amount. Commands are sent from earth and travel across a mean distance of approximately140 million miles (225,308,160 km), taking approximately11 minutes to arrive. Little known is the Rover’s ability to operate and travel autonomously using its sensors and logic to avoid objects.
If the Rover were on the Moon, commands would travel across approximately 240,000 miles (386,242 km) and take a little over a second. The 1-ton Rover would weigh in there at about 332 lb (149 kg). The advantage of robots on the Moon is their ability to lift greater loads. On the Moon a robot with a 200-lb (90-kg) lift capacity can lift and position an object that would weigh 1200 lb (540 kg) on earth but which on the Moon weighs only 200 lb. This means lighter weight robots could be dispatched to perform assembly operations while minimizing the number of trips to meet the vehicle assembly, mining, and construction requirements.
The advancement of autonomous vehicle software and the short earth-to-moon communication time enable a robot that could be positioned, set up, and operating upon arrival on the lunar surface. Lightweight, rapidly deployable enclosures could be sent with the lunar-robots to provide thermal, environmental (dust), and radiation protection for the vehicle components and subassemblies as they arrive on-station. The robots would anchor, seal, and validate the enclosures while adding the facility requirements necessary for a fully functioning automated assembly plant. Rapidly deployable structures would be sent later as the time approached for human arrival and the mining and conversion operations met water and fuel needs for sustaining life.
Lightweight composite fuel and water storage tanks could be sent after or ahead of the lunar robots for positioning and assembly into a fuel/water processing and storage facility. The mining, processing, and storage operation would be the responsibility of limited-task robots controlled by a hierarchy of robots coordinated through a central command center where the human population would eventually arrive. Stationary or semi-stationary limited purpose robots would populate an enclosed lunar factory and a bio-center where plants would be grown for food. Higher-order autonomous and semi-autonomous robots would travel between operating environments for maintenance, observation, and communication to facilitate a broad-based architecture of functioning robots to manage the master build schedule of the Lunar Based Mars Vehicle Assembly and Exploration Center.
Within the assembly center, transport robots (AGVs) would retrieve arriving Mars vehicle components and deliver them to the assembly floor where quality validation robots would inspect the arriving subassemblies and components for shipping damage while simultaneously sending images to earth for further subassembly evaluation. Damaged parts could be evaluated and corrective action and repair performed by robots directed by human specialists on earth.
Once each subassembly had been joined with its mating structure, test and evaluation robots validate form, fit, function, and continuity of the systems before next assembly. When the engines are delivered for the Mars vehicle, robots would transport them to a test facility to run a trial “burn” to validate their conformance to specified performance before vehicle integration.
Humans could be transported to the lunar surface upon completion of the vehicle assembly, integration, and testing and habitation enclosures, water, and fuel processing and storage. Once they arrive they would begin acclimation and final preparation for their long journey to Mars.
Any anomalies found during on-site human inspection could be corrected by robotic assistance. Robotic design would incorporate structural components that would transform former task-driven roving robots into Segway human transport vehicles to speed movement through tunnels connecting buildings.
Building an automated assembly plant on the Moon and mining the necessary resources to fuel the vehicle and hydrate astronauts traveling to the Moon and then onto Mars is an enormously complex subject. When presenting the depth and breadth of its concepts and execution they exceed the framework of this medium. The general concept described in this article was to provide select options to build and assemble an inhabited Mars exploration vehicle on the Moon with automation. The far-reaching potential of automated lunar assembly to enhance the success for human Mars exploration is apparent when considering the enormity of the mission.
Autonomous vehicles and robots are operating all around us. A US Navy Uninhabited Aerial Vehicle (UAV) called NUCAS took off and landed on a carrier deck and a Global Hawk UAV refueled another Global Hawk. While singular examples exist of autonomous vehicles operating singularly or occasionally in pairs, the challenge is to get batches of UAVs and other autonomous type vehicles to operate harmoniously as integrated collectives. This challenge is the focus of vigorous research activity and is referred to in air vehicles as flocking. The term flocking refers to birds and their ability to act severally and yet harmoniously for the greater good of the flock.
Preprogrammed robots operate in factories worldwide and are most visible and recognized in the auto and electronics industries. Clusters of rapidly moving robots position and fasten parts together by various means. The motion of the collections of robots within the workcells are so closely synchronized that it appears that they are in communication with one another.
At a recent automation conference there was much discussion regarding the need to integrate robots so they could communicate and vary their preprogrammed routines to operate based on feedback from their fellow robots. This optimality process through autonomous interactive robotic action has taken on “legs” and is known as advanced analytics for actionable machine intelligence. The movement towards actionable machine intelligence when combined with flocking capability for autonomous vehicles provides the critical keystone for a foundation to support a lunar automated assembly factory.✈
This article was first published in the 2014 edition of the Aerospace & Defense Manufacturing Yearbook.