Designing A Pressure Vessel For A Lunar Greenhouse

Dominik Adriany, Krish Arora, JP Kahlert, Dylan Kipp, Peter Landine, Veer Sambaragi and Usama Seifeddine

Community Partner: Canadian Space Agency
Degree: Bachelor of Applied Science
Program:
- Materials Engineering
Campus: Vancouver

Our project

A lunar greenhouse that can grow plant life in extraterrestrial conditions is an important step in supporting longer-term human missions to the moon. We designed and manufactured a pressure vessel in collaboration with the Canadian Space Agency to house components of the OASYS Lunar Greenhouse.

In addition to designing and manufacturing a pressure vessel capable of withstanding the harsh conditions of the moon (including its lack of atmosphere and extreme temperature fluctuations), we were also in charge of integrating system components developed by six other capstone teams from other universities across Canada.

Canadian Space Agency

Our design solution and process

Our vessel design needed to meet a wide range of design criteria, including maintaining an internal pressure suitable for plant growth, being able to support specific structural loads, using materials that do not off-gas and that are food safe, and being able to withstand significant changes in temperature.

There are four main components to our pressure vessel design: a removable end-cap plate, L-beams made from a glass fibre reinforced polymer, hand laid-up carbon fibre reinforced polymer plates with an epoxy matrix, and an internal mounting frame.

The inside of the vessel will ultimately include a plant growth chamber, a collection chamber, an artificial light system, power supply, solar panels, gantry system and irrigation system. These components were all developed by other design teams from across the country, and it was our job to make sure that they could be mounted in our vessel.

Our process started with research on pressure vessels to see how different designs impacted the performance and stress concentrations.

Then we went on to exploring current operating lunar technology to see how they addressed challenges associated with harsh conditions on the lunar surface. We also reviewed existing greenhouse designs and explored different vessel shapes and orientations.

In the second semester, we focused on the manufacturing and assembly, including purchasing materials for the internal frame and vessel skin and solidifying the manufacturing methods to build the model.

CSA asked us to design two models: a ground model (which we actually built) and a lunar model (what we would recommend building if we had the equipment, resources and expertise to produce our ideal solution).

Our lunar model is a similar size and shape, but incorporates a material that would be too costly for us to use in our ground model and uses manufacturing techniques not available to us as students.

We had to collaborate with other teams based on the size, shape and weight requirements of their systems, which sometimes required making adjustments to our design. Throughout the process we ran software simulations to identify the effects of different geometries and skin thickness on stress distribution.

The challenges we faced

We were integrating the work of six other capstone teams from across Canada, which led to logistical issues and delays when teams didn’t deliver designs according to schedule or altered their initial design dimensions. However, being responsible for integrating the work of the subteams was a great learning experience of what it is like to be part of a complex engineering project.

There were some challenges with selecting materials that met the design criteria of being moisture resistant, able to support mechanical and structural loads, able to be pressurized and able to operate within a defined vacuum environment.

We also needed to choose materials that were food safe and that had minimal off-gassing, which limited our choices.

There were also challenges manufacturing the assembly due to some warpage of the plates, which has required additional machining so the components all fit together.

What we’re most proud of

One of the most rewarding aspects of this project was getting to work with the Canadian Space Agency and understanding the level of detail and rigour expected in real aerospace applications.

It was exciting to lead the development of the manufacturing assembly procedure by focusing on everything from machining and bonding to post-processing as well as the fastener integration for our composite pressure vessel.

We’re proud of the hands-on composite manufacturing work we did using hand lay-up techniques, and how we paired that with non-destructive testing such as thermal imaging and ultrasonic tests to validate our design. These tests were conducted under the supervision of Marco Didonè, a PhD candidate under our UBC supervisor, Dr. Sergey Kravchenko. The results showed that the 3 mm laminate was laid up perfectly, with no voids or delaminations. The 4.5 mm laminate had a few micro-voids uniformly spread in the centre, but the edges were flawless. These micro-voids were expected due to our use of an oven instead of an autoclave, and not because of any error in lay-up technique. Bridging the gap between classroom learning and real-world composite design, testing and validation was a truly meaningful experience.

Working within tight budget and sourcing constraints also taught us to problem-solve creatively, especially while coordinating with suppliers across Canada to meet CSA timelines. Overall, this project really helped us grow technically and professionally.

Our project’s future

We will be shipping our prototype to the Canadian Space Agency in Montreal. The agency will integrate the work from the other design teams, mounting their systems into our vessel and then pressurizing it and running tests to simulate several cycles of the moon’s nights and days. Our understanding is that there will be further iterations of the project and other elements will be incorporated, such as the airlock design.