NASA plans to return to the Moon by 2020. For a sustained lunar presence, however, astronauts need habitats that can support them and their experments. To this end, researchers at NASA Langley, working with NASA contractor ILC Dover (Frederica, DE), are developing the "planetary surface habitat and airlock unit," a prototype inflatable structure that could be deployed on the lunar surface. Karen Whitley is the project lead.
NASA Tech Briefs:
What is the planetary surface habitat and airlock unit?
Karen Whitley: The lunar habitat and airlock unit is an expandable structure that was built by ILC Dover as a technology demonstrator. It is a full-scale, working airlock that is attached to a larger, inflated habitat unit. The INFLEX, which stands for "intelligent flexible materials," was awarded to ILC Dover upon NASA issuing a broad agency announcement in 2004 under the Exploration Systems Research and Technology directorate.
NTB: Why is the habitat being developed?
Whitley: First, let me say that I think inflatable or expandable structures will play a major role in future exploration missions. Expandable structures are being investigated as options for several different applications, including airlocks, lander alcoves, habitats, connecting tunnels, maybe safe havens or shelters, or pressurized rover compartments. The primary advantage of expandable structures is the extra volume that can be achieved for the size of the launch package.
Our technology demonstrator was to demonstrate the feasibility of an expandable structure that would represent a habitat-like compartment and accompanying airlock. Our future work may include damage tolerance. One of the questions we need to ask ourselves still is, how durable is this material in a lunar environment? We want to do some materials testing. Packaging and deployment are also future concerns. We are hoping to build another unit with the help of ILC Dover and demonstrate packing. In the future, we do plan on outfitting the demonstrator with some interior mock-ups in order to investigate different outfitting and packaging scenarios, and we would do volume-utilization studies, because packing everything on a launch vehicle for the Moon is pretty critical.
NTB: Describe the habitat.
Whitley: The habitat has been described as a giant Tylenol capsule with legs, standing on end. The main habitat has a 12-foot diameter, and it is 17 feet high. The habitat is 53 cubic meters of space, total. And attached to that structure is a smaller, inflatable structure that serves as the demonstration airlock. The airlock is a five-foot-diameter structure. Both are essentially pressurized cylinders connected by an airtight door. Both are made of a multilayer nylon fabric and webbing - but I want to note that nylon is not rated for a lunar environment. It was used for the demonstration model only. Johnson Space Center has a contract with ILC Dover, who will be building a test article for Johnson. It's going to be an inflatable habitat-type unit that they are going to take to the Antarctic for temperature materials studies. Being made of nylon, ours would freeze.
An actual lunar habitat would be made of materials that could include Dextran or Kevlar or other things besides nylon. There are three blowers located under the floor of the main habitat that are used to inflate the structure. At the moment, it could fit about four people, but we have other teams of people, including the Lunar Architecture Team, that are feeding us requirements, and they are constantly updating those requirements. I believe the latest requirement that they have for the habitat unit is for about 100 cubic meters of space.
You are in ambient atmosphere, in the lab or on the Moon, and you go with your astronaut suit to the airlock. Then, you close the exterior door to the airlock, and then there is an inner door between the airlock chamber and the main habitat. There is a vent you can open that will equalize the pressure between the habitat and the airlock. When you open the inner door to let yourself into the main habitat, it would then be closed. You would then be under pressure in the main habitat. Our demonstrator is only about a tenth of a psi, but you could tell a little bit of a pressure difference, just enough to make your ears pop and no worse than being on an airplane. The concept is that you are in the main habitat, under pressure, you close the door between the main habitat and the airlock so that then another astronaut could enter from outside.
If you open the wrong door at the wrong time, the structure could deflate. There are structures in place to retain the habitat's shape; on this demonstrator, we have support arches on the inside that are used to hold up the fabric material when it is deflated so that the habitat doesn't totally loose its shape and collapse. The doors, which are much heavier than the material of the walls, would remain standing.
NTB: How would the structure be deployed?
Whitley: When the habitat is packed up, the legs are first removed and the center sections of the floors are removed so the diameter of the main habitat is reduced. Also, the airlock section is detached. The deployment basically consists of turning on the blowers that are located under the floor of the habitat, inflated the structure. But I might point out that because as an Earth-rated demonstrator, the deployment of the habitat is somewhat labor intensive, and requires the use of forklifts. IBA time for astronauts is an important issue to consider, and we want to make an expandable structure "astronaut-friendly." The purpose for this demonstrator wasn't necessarily packaging or lunar deployment. It was more of an airlock, inflatable-technology demonstrator. So in the next stage of technology development, packaging and deployment issues will be studied. Deployment on the lunar surface is pretty critical.
One of the lessons learned from this particular concept is that it is not extremely packable. If you think about going camping with your family of four, and all the stuff you want to take, and you can take only one vehicle - how do you package it all? And so, this is only one particular concept out of several that are continuing to be considered and developed. One of the next concepts developed looks more like a Slinky, rather than an upended Tylenol. It's a horizontal unit that collapses just as a Slinky would, with maybe an expandable or inflatable center, with hard end-shells. The habitat unit came to us from ILC Dover in a crate on a flatbed truck. It took forklifts and overhead cranes about four people to take this thing out of the crate. We had to attach the legs, put the floor in, put the doors on - which were pretty heavy because it was Earth-rated - and then, after all the units were appropriately connected, then we pushed a button and it inflates.
NTB: What are its advantages over a rigid structure?
Whitley: Packability. With a rigid structure, you would have to take full-sized components to the site. With an expandable structure, thinking again about a Slinky, it can be packed into a very small volume. When you get in on the Moon, you can end up with a very large volume. I think packing on the launch vehicle will be the biggest advantage for expandable structures.
NTB: How would the habitat sustain a suitable environment on the Moon?
Whitley: Power will have to be generated on the Moon. There are different concepts for power generation. Fuel cells could be one of them; solar power will be one of them. Several of the layers that will be in the habitat wall will compose a thermal protection layer. The habitat would be heated and fully insulated. I think NASA's timeline is to be on the Moon by 2020. I believe that when they go to the Moon, expandable structures will definitely be a part of their lunar base or lander vehicle, even if it is in the way of just an alcove, or maybe a leveling tool or support structure. Inflatables can be very hard. You could punch the side and it would flex some, but on the Moon, the pressure of the habitat will be eight or nine psi, and that will be a very hard structure. We used a basketball as a demonstrator at the National Space Symposium.
NTB: Could the habitat be used for Earth-bound applications?
Whitley: The habitat demonstrator currently is not outfitted with equipment on the inside. It was for the demonstration of the airlock. It has a floor and walls, but other than that, it is empty on the inside. It currently has nothing like a toilet or running water. However, they could be used for emergency housing, I think. If we had them outfitted for livable conditions and radiation protection, they could be used for housing after a hurricane or other disaster.