Options for Fabrication of a Full Scale Arusha Cabin Mockup

Marie Jeanne Steady Ndiaye
NSBE Space SIG
Charleston, SC, USA
/ Gidley Dorley
NSBE Space SIG
Meriden, CT
/ Alexandria Langford
NSBE Space SIG
Moffet Field, CA, USA
/

Abstract - Mockups are an important part of the process of developing human centered spacecraft designs. Lessons learned from NASA mockup activity inspired the NSBE Arusha team to first develop a low fidelity cabin mockup in 2009. NSBE currently desires to build a medium fidelity cabin mockup based on design updates and corrections made in the wake of the initial mockup study. This paper investigates various material solutions to the challenge of providing a cabin structural shell for the mockup. Initial investigations focused on pre-integrated structures, such as an Airstream trailer or the shell of a retired aircraft. Additionally, the paper investigates materials used to fabricate a shell from scratch, including wood, aluminum, custom formed polyethylene, and fiberglass. Finally, the paper discusses implications for the mockup’s physical location and storage.

Keywords: Arusha, NSBE, mockup, fidelity, evaluation, lunar, rover.

1  Introduction

The current Arusha rover mockup assessment builds on the findings of the 2009 Arusha rover low fidelity mockup evaluation. This earlier evaluation used a low fidelity mockup that enabled team members to evaluate the proposed cabin layout. The exercise helped identify deficiencies in both the architecture and layout that were be mitigated by subsequent design modifications such as the suit port concept and inclusion of deployable medical and maintenance workstations. It further helped refine design details such as the deployable table used for crew meetings and dining. Beyond the inherent practicality of mockup use - driving design and operational details - having a mature mockup also provides the tangible visibility needed to facilitate community engagement/ outreach activities, garner the media's interest, and generate excitement/ interest from sponsor sources.

1.1  Value of Mockups

Mockups have always played a critical role in the design of habitable spacecraft. Mockups were commonplace throughout the development of the Apollo lunar program and have continued in use with NASA to the present day.

1.2  NASA

During NASA’s Constellation program, NASA routinely sent teams to the Arizona desert to evaluate lunar rover and habitat mockups through the Desert Research and Technology Studies (DRATS). Lessons learned during DRATS refined the interior configuration of the Deep Space Habitat and developed operations concepts for the Lunar Electric Rover.

1.3  Arusha

Similarly, the NSBE Arusha project has benefitted from the use of mockups. In 2009, NSBE borrowed the NASA Constellation Core Habitat mockup, shown in Figure 1, and outfitted the interior as a low fidelity Arusha mockup.

Figure 1. NASA Core Habitat Mockup

This low fidelity mockup uncovered serious flaws with the initial concepts for extravehicular activity (EVA) and crew sleep. These problems did not show up on paper but were immediately obvious when the team entered the full scale cabin mockup. Prior to use of the mockup, all team visualizations had been two dimensional drawings, which simply cannot capture the implications of a cylindrical spacecraft. Figure 2 shows the interior of the Core Habitat Mockup prior to its conversion to an Arusha cabin interior.

As the concepts for the Arusha long range rover have matured, there is value in developing a second vehicle mockup, this one a medium fidelity representation of the rover with functional internal workstations. This study will investigate different options for the fabrication of the shell of this cabin mockup. In particular, different material options will be considered with recommendations made.

Figure 2. Core Habitat Mockup Interior

2  Airstream Trailer

In the space program, the Airstream trailer is best known for its use as the mobile quarantine facility (MQF) during the Apollo mission era, shown in Figure 3. The MQF was used to temporarily quarantine astronauts returning from the moon in order to prevent the potential spread of lunar contagions with other people. [1] It was first used when the Apollo 11 astronauts returned from the moon and contained the astronauts for 88 hours until doctors and scientist determined it was safe. The MQF was continuously used for the next 3 Apollo missions following Apollo 11 but after Apollo 14 it was concluded that the moon environment did not have any signs of life that would be hazardous if they were spread to Earth’s environment. [2]

Figure 3. Airstream Trailer

The MQF is simply a converted Airstream trailer composed of aluminum and glass. It is approximately 8.58’ (2.62 meters) tall x 9’ (2.74 meters) wide x 35’ (10.67 meters) deep. In comparison to the projected size of the Arusha cabin (32’ 10” long x 9’ 10” wide) the two are somewhat similar. The similarity on the surface makes the idea of using an Airstream trailer similar to the MQF as a mockup a thought worth initial consideration and its on the surface similarity caused the Cabin Structures team to initial consider the Airstream as a likely option.

An appealing benefit to using an Airstream trailer as a mockup for the Arusha cabin is the opportunity to be mobile. Since the Airstream is a trailer it can easily be transported from one location to another without having to incorporate an additional towing system. This allows the Arusha team to more easily move the mockup to various locations than if it did not incorporate a trailer. This is especially helpful since a lot of the Arusha project teams and collaboration partners are located across the country. Having a mockup that is inherently mobile reduces the cost of shipping significantly. Being mobile also allows more exposure to the public so that people can see the space projects that NSBE is working on.

A potential showstopper to using an Airstream trailer as the baseline for the Arusha cabin mockup is cost. NASA created four MFQs, all of which are on display at various museums across the country. The likelihood of turning a museum artifact into a mockup is practically zero, especially when said conversion would destroy all historical value of the artifact. The only reasonable option is to purchase an Airstream trailer. Prices for Airstream trailers vary wildly on the internet, with eBay options ranging from as low as $1,500 to as great as $35,000. [3]

However, cost is not the greatest problem. The more closely one looks at the dimensions of the Airstream trailer, the more the supposed advantages break down. The shape of the trailer seems comparable at a high level. Both are slightly rounded with the longest dimension in the longitudinal direction giving a shape similar to that of a cylinder. But in actuality, the moldline is not the same at all. Literally, every surface is in the wrong place. Even the interior layout is problematic. Most Airstream trailers come equipped with a kitchen, restroom, and sleeping quarters, but these are not be in the same locations as the Arusha model and would have to be removed. In addition, specific accommodations needed for the Arusha cabin that would otherwise not be in the Airstream trailer would have to be added, such as suit ports and cockpit windows. Even the floor in the Airstream is not correct and cannot be used. Effectively, the entire Airstream trailer above the axles would have to be gutted and replaced. None of it is usable except as scrap material. The Airstream trailer literally could not be used except as a trailer mounting upon which to attach a cabin shell made through some other means.

3  Aircraft Shell

A somewhat unconventional idea brainstormed by the Cabin Structures is to use an aircraft shell as the rover cabin shell. At least in the case of an aircraft shell the fuselage is in some cases circular. There are numerous bone yards in the American southwest where fleets of aircraft have been abandoned. One of these forgotten aircraft, such as the one shown in Figure 4, could potentially be turned into the cabin of the Arusha rover.

Figure 4. Abandoned Aircraft Shell

An advantage of an aircraft shell is that it is already weather treated and could be stored outside or moved during a rainstorm without fear of damaging it.

Obviously a challenge in use of an aircraft structure is obtaining one. It is possible that such an airframe could be donated by an airline or a manufacturer, but outside of such a solution one would have to be purchased from a curator of such a bone yard.

A second challenge in the use of an aircraft structure is finding one of the proper diameter. The entire Boeing aircraft family is too large and the CR-J family is too small. The Embraer E-Jet family is close, but still not an exact 3 meter diameter inner dimension. [4]

Additionally, even if the fuselage is the proper 3 meter inner diameter, the Arusha rover cabin has unusual protrusions for the suit ports that would not exist on any aircraft and would have to be cut into the metal. Similarly, the forward and aft domes would not exist and would also have to be manufactured. If any of the cabin interior remains, it would have to be gutted completely until nothing but the outer shell remains. Even the flooring may be in an incorrect position and may need to be cut away. Also, airframes are often only circular between the nose and the point where they intersect with the wings, as shown in Figure 5, so it might be necessary to take the forward section of more than one Embraer in order to obtain the proper length for the Arusha rover.

Figure 5. Irregular Shape of Aircraft Fuselage

4  Wood

The previous ideas required finding an already existing element that can be used as the cabin. By comparison, wood is a building material that can be used to fashion the unique shape of the Arusha. It is a readily available, relatively low cost material and is sufficiently study to provide structural rigidity. Simple 4’ x 8’ x ½” maple plywood sheets would be appropriate for flooring, while thinner sheets might be used for the cylindrical barrel sections. The low cost of this option is very appealing and might be good to pursue as a first version of the mockup. Assembly and disassembly can be simplified by designing the mockup in separate sections which can be fabricated and joined together. This may also allow for reconfigurations in various segments of the pressure vessel without having to replace the entire shell.

As a wood mockup, the Arusha cabin would be relatively lightweight and easy to move around if placed in a lab but could be difficult to move if it needed to travel on the road to another location. It is worth noting that the NASA Constellation mockup used by Arusha in 2009 was a fixed, wooden mockup. Unlike NASA’s MMSEV and Habitat Demonstration Unit prototypes, the Core Habitat Mockup was never intended for transportation to other states or for the conduct of multi-day analog mission tests. It was on occasion moved to different sides of the same high bay where it was built, but was never moved to other buildings.

Building a sufficiently rigid wooden mockup for highway travel could offset the cost and simplicity of using wood. The limited mobility would also prevent the amount of Arusha team members that could physically work on the construction of the cabin if travel to another location were difficult. In the case of a wooden mockup it is best to assume a fixed location with the knowledge that it will not move from that location. While the focus of this investigation is a full cabin mockup, it is worth noting that wood may be ideal for construction of mockup sections, such as individual workstations. This may be well suited for subsystem or workstation development.

5  Aluminum

Another option for a custom fabrication is aluminum. Aluminum sheet metal can be formed and welded to create the exact shape of the Arusha cabin pressure vessel. Clearly, this is not a fabrication that can be performed by project team members, but would instead be ordered from a metalworking vendor.

Figure 6. Aluminum NASA Orion Mockup

The high strength to weight ratio of aluminum serves as an advantage for such a construction and would support eventually attaching the mockup to a motorized chassis. The NASA Orion mockup shown in Figure 6 is constructed from aluminum, which gives it the strength to be used to refine the ground support systems needed to prepare the spacecraft for launch. [5] Further, selecting a corrosion resistant aluminum alloy will allow the mockup to be stored outside, or not require special protection when being transported. Cost would be greater for an aluminum construction than wood, of course.

6  Polytank or Fiberglass

Much like custom aluminum can be ordered, so can custom polyethylene tanks (polytanks) or fiberglass. Supplied with a CAD model, a vendor can prepare a mold to produce the exact dimensions of the Arusha rover cabin.

However, depending on thickness, polyethylene and fiberglass may not, have the structural strength needed to hold the cabin shape as well as provide strength for all of the load bearing equipment that must be mounted inside the vehicle. (And if the structure is too thick it will interfere with features of the mockup design, such as the suit port and hatch interfaces.) The construction may need to be supplemented with metal frames and stringers.

As an advantage, polytanks and fiberglass are waterproof. Thus, only insulation and air conditioning would be needed to enable outdoor use and storage of the mockup. And transportation can be conducted without regard to weather conditions. Figure 7 shows a polytank approximately the same diameter (but shorter in length) of the Arusha rover. [6]

Figure 7. Polytank on a Tilting Trailer

7  Mockup Storage

Regardless of the construction material used to build the mockup, the issue of storage remains a thorny one. The rover cabin is far too large for a traditional garage. It can only be stored indoor if a significant high bay facility is made available. And even if the shell can withstand the elements, there are few locations in the country that are so benign that the interior contents would be able to survive the vehicle being stored outside without significant environmental conditioning.