This past summer, the Gilroy Lab team traveled to Kennedy Space Center (KSC) at the Space Life Science (SLS) lab in Florida for our Science Verification Test (SVT). I returned to KSC two weeks later to process and ship our samples.
The results from our SVT were nothing like we expected! I’ll explain more about this in a moment.
The SVT is the first run for our experiment inside the actual space hardware called a Petri Dish Fixation Unit (PDFU). This hardware with our experiment inside is “integrated” by NASA engineers and staff during the SVT (i.e. the whole equipment is put together as if it was ready for being sent to the International Space Station). This is so that everyone knows what will happen when the time comes to do it for real a few days before launch. Then, during the SVT the experiment is run in the SLS lab inside a special growth chamber called an Orbital Environmental Stimulator (OES) that mimics conditions on the space station. At the end of the experiment, our samples are then “deintegrated,” that is, the PDFU is taken apart and the petri dish containing our plants is removed. Finally, our samples are processed and shipped to the Gilroy Lab at UW-Madison for analysis.
It is a requirement that the SVT practice run be completed so all of us can be confident that the experiment as planned has the highest probability of success.
Assembling the PDFU’s is no small task. NASA’s Susan is the integration team leader, and has an amazing ability to stay focused for hours doing the detailed work required to assemble PDFU after PDFU. During assembly, Susan calls out each component that she puts in place and Jennifer, the NASA quality control expert, takes note to confirm all is done correctly. Everything needs to be sterile, so all PDFU parts have been autoclaved and the assembly work is done in a sterile hood. This video shows Susan assembling a PDFU for a different NASA experiment from John Kiss’ lab; the process for our experiment is similar.
Once the PDFUs are put together with our science inside, a stack of 5 PDFU are placed in the aluminum BRIC canister. The sixth space in the BRIC is for a temperature data logger called a HOBO. Next, another team of NASA specialists conducts a leak test by placing the assembled BRIC in a pressure chamber. All of our PDFUs passed the leak test!
For the actual launch, our two freshly assembled BRICs will be placed in the fridge until transfer in cold storage to the SpaceX launch vehicle. Once the BRICs are on the space station, they will be brought to room temperature (22 deg C) and then a day later an astronaut will actuate the injection of growth media to start our experiment. For our SVT, this temperature regime and injection timing is replicated on the ground at the lab.
Then, after 8 days of growth, a fixative is added to our petri plates via another injection. After sitting in fixative at room temperature for a day, the BRICs are frozen until they can be returned to Earth, taken apart, and the samples shipped to the Gilroy Lab for analysis.
So, why then were our SVT results nothing like we had expected? We were disappointed to observe that when we got our SVT petri plates back from KSC that very few of the seeds had germinated.
In the weeks that followed, we did as much testing as we could in the Gilroy Lab to troubleshoot this germination problem. Was the PDFU plastic releasing a volatile chemical inhibiting germination? We tried activated charcoal cloth with the idea that it would absorb volatiles, however, the addition of charcoal cloth did not help. Was it the glue used to attach the filter paper to the dish? We confirmed that with enough drying time, the presence of glue had no impact on germination rate.
Was the germination problem due to the filter paper that the seeds were attached to? We tried different batches of filter paper to see if we could improve germination. It turned out that the old batch of paper we initially used was much better than the new. What could be different? We washed the filter paper before autoclaving, and that seemed to help somewhat. Then, we treated the paper with an ion solution before autoclaving; this treatment also improved our seed germination rate.
Our backup plan is to use petri plates containing a layer of nutrient solution in a gel called Phytagel, and place our seeds on top of that. This experimental design with wet gel is not as good as dry filter paper because the seeds will imbibe prior to launch. Thus, our dry seeds will start taking up moisture when they are placed on the gel during integration and not at the point when the astronauts inject growth media. However, the canisters holding our petri plates will be in cold storage in the fridge, therefore seeding growth will not be significant until the experiment starts at room temperature on the space station. This is a good alternate plan, and in fact the nutrient gel method has been used in past plant biology BRIC experiments with success.
We’ve got another test run before actual launch, called the Payload Verification Test (PVT) in October. We’re hoping that we’ve sorted out any possible problems and that our PVT will be a success!