Nothing in, nothing out
Here’s how our Lab2Moon interns designed a hermetic chamber to keep things safe and secure
A hermetic seal is one through which nothing gets in or out. On Earth, a hermetic seal is often about keeping things out — like oxygen to prevent food from spoiling — but in space, it tends to be about keeping things in.
The Lab2Moon experiments traveling to the lunar surface aboard the TeamIndus lander were originally designed to soda can specs. As the teams have been working with Moon mission engineers to shape their ideas into something suitable for space, dimensions have changed or shrunk. The outer casings — the hermetic chambers — have been redesigned as well. And it wasn’t a one-size-fits-all situation: all the six experiments have different operational requirements to be considered.
The process is simple — if the pressure inside the chamber is more than the pressure outside, things will try to move from inside to outside. Not only could this cause the structure to warp and bend; unless the material for the chamber is chosen carefully, it can evaporate over time into the vacuum (known as out-gassing), and if it condenses onto nearby cold surfaces, it could potentially affect the experiments as well as components of the TeamIndus lander.
With the goal to maintain Earth-like pressure conditions, the teams got to work. How you seal the joints of these containers is what ultimately makes the chamber airtight. ‘Gases are most elusive. If you keep gas in, everything stays in,’ explains Siddharth Bharteeya, one of the young engineers who has been working to solve this problem for the past 3 months.
Build right
The conversation on the hermetic chambers started with aluminum, which is also the main material in the structure of the TeamIndus spacecraft. The team was working towards this when they realized that aluminium would not be suitable due to mass restrictions.
Also, a few of the teams had included windows to allow the passage of light, and this would potentially create weakness. So they started the search for a polycarbonate that was transparent, as well as biocompatible. Team ZΩI, which is testing if photosynthesis is possible on the moon, was concerned that in materials without space heritage, the impact of radiation would be impossible to predict, and might inadvertently affect the experiment. So during a brainstorming session with TeamIndus experts, the conversation turned to spacesuits, and the material used for astronaut’s visors. Which brought them to a polycarbonate by the name of Lexan.
In talks with the manufacturer of the material, they learned about Ultem which is completely transparent, and began to toy with that. But it was eventually rejected as it is difficult to procure in a short time, and in the relatively small amounts needed for Lab2Moon.
For Team EARS, testing whether electrostatics can be used to create an active radiation shield in space using a Van de Graaf generator, the original design had no chamber at all. But they then realized that for the charge transfer mechanism to take place, air needed to be present, making a hermetic chamber necessary.
‘We were considering other materials, but due to its space heritage, we went for PEEK. It is a non-conductive material, with good mechanical strength and is one of the strongest polycarbonates being used in the aerospace industry. Also, it is easy to machine,’ explains Saumil Vaidya of Team EARS.
The Team ran simulations on OLTARIS — or the On-line Tool for Assessment of Radiation in Space, NASA’s open source software. This was critical because the team needs radiation to penetrate through the chamber walls in order to measure the effectiveness of its shield.
Seal it tight
But what essentially makes the container ‘hermetic’ is the seal. Any module with joints and moving parts, no matter what it is made of, can leak. The solution is an O-ring — a gasket that will not let the air in or out despite the thermal impact of space. These are made from Neoprene, a synthetic rubber. The chambers have also been designed so they have the smallest number of seals, creating the fewest possible points of vulnerability.
“The chambers will be able to withstand 3x atmospheric pressure, as well as vibrations up to 25g, leaving us very wide margins,’ explains Nirmal Suraj Gadde, TeamIndus systems engineer and Lab2Moon mentor.
The other point of contact for the experiment is with the deck of the spacecraft, to which the experiments will be bolted. As the deck is made of aluminium, it will be much hotter than the polycarbonate canisters of the experiments. This is being address by adding a thermal spacer — insulation material — between the payloads and the deck.
This is still work-in-progress. Till the materials come in and tests are done, there are grey areas. But by using materials with space heritage, and taking the safe approach, these hermetic chambers should create a secure environment for the first student-made scientific payloads heading for the moon.
