With a bunch of master student from a french engineering school, <e have limited knowledge of biological sciences, we are looking to participate in the ESA rexus program (a program to fly experiences onboard a sounding rocket up to 90km of altitude)
We are working on our proposal for october 2025, one of them would be to see the chemotaxi of e coli bacterias in zero G (the rocket flight path provide arround 120s of micro g).
We would like to observe this in flight by developping an adapted version of the open flexure microscope to follow those bacteria during flight.
I have some question about the openflexure Microscope, in its curent design how sensitive is it to vibration ? Is there any āknownā way in the industry to reduce the sensibility of a microscop to vibration ? Apart from the PLA used, is there something in the design that would be sensitive to low pressure (almost void) and micro g exposition ?
My last question is about how to select the best magnifying lens for the experiment, is there any āprocessā to find the best lens for an experiment ? From my research i found a x100 lens would be needed, Iāve read the recommandation on openflexure to use x40 lens. What would be the consequences of using a x100 lens ? Same question with a dry vs oil lens ?
Thank you very much for any information or answer for this project, it would be greatly appreciated !
Iām new here and i apology in advance if I chose the wrong category to post.
This seems like a very exciting project! Couple of points to consider about openflexure on a rocket (just from having worked with OFM for a long time, I never strapped it to rocket):
Especially with the high resolution objective (which is heavy), the z-flexure is fairy fragile, I would be worried about how it survives the high g (what is the max?) and vibrations. You might need to include some form of locking system to prevent excess forces on the flexures during launch. A mechanical backstop slightly below the correct focal position might work, after the engine cuts out you would move back to focus and can move freely. (You can probably put the microscope in a box on a string a spin it around to test).
Make sure to secure the SD card to the pi, and probably other connectors to just in case (maybe hot glue?). I think for thermals the electronics should be fine with just radiative cooling for the short period in vacuum (people have used RPis on weather balloons). Basically nothing there will be airtight but consider vent holes on some parts due to the rate of pressure change (this might not be a problem, I donāt have much intuition for how quickly air can escape e.g. the illumination module or the optics module, but in both excess pressure could push the lens out). Also beware of potential moisture issues with it condensing and freezing on the optical components.
What is your plan with the imaging during the 120s? Do you want to record multiple fields of view or will you just record a video of a single position?
The max acceleration will be arround 20G. The points on the internal pressure and temperature of the optic is a very interesting, I guess we will have to check with the supplier.
Itās still evolving, right now we would like to observe the effect of microgravity on the Dictyostelium discoideum phagocytosis ! We only want to record a video of a single position, would recording with multiples fields of view be useful here ?
If you only need a single position you might want to consider something similar to the flat top OFM ( Richard Bowman / openflexure-flat-top-microscope Ā· GitLab , see also this thread Flat Top Microscope | IIBM UC | Chile ). You will need to motorise the z axis as you might need to refocus in flight. Having no xy stage allows you to secure the sample in position fully so that it doesnāt shift during flight and it removes additional failure points. But whether this is feasible will also depend on the payload integration timeline. You might also need to consider that the rocket is spin-stabilised, I donāt know how that will affect your sample, you want to make sure that you donāt end up with everything moved to the edge of whatever chamber you are using. For illumination you might want remove the dovetail and print a single part illumination setup (tightening and threadlocking the thumbscrew might be ok too, the illumination sliding into the sample would be an embarrassing failure).
The OpenFlexure Microscope will work with 100x, oil immersion or dry, as well as 40x. Which objective you need will depend on what you are trying to see. A 100x oil immersion lens will be more difficult to use. You will need to deal with the immersion oil, I donāt know how that behaves in vacuum, and it will make it harder to move the lens away to a safe position for launch and then back to the sample as the oil may move off the lens. The lens that you want will depend on the field of view that you need, as well as the required resolution. A 100x lens will see detail of the bacteria, but will only have a small field of view in which to see the chemotaxis. You can tell that bacteria are present at much lower magnification - just not in enough detail to identify the type etc. In your case you will know that there are either e.coli or nothing. A much lower magnification would give a bigger field of view to see some blobs moving. Lower magnification also give a larger depth of focus - so the bacteria do not need to remain at precisely the same height when moving.
If 20x is acceptable then the ālow-costā version of the OpenFlexure Microscope optics removes the need for a heavy microscope objective lens, which will greatly reduce the problems of the weight moving and breaking the flexures during high-G phases of the flight.
The flat top version is indeed quite more adapted ! The rocket is indeed spin stabilised up to 0.08Hz, we would have a āfloorā of the rocket meaning we will be able to place the sample in the middle. I think we will modify the flat top design with stiffer part to avoid any damage during the acceleration, we will also check with the optic supplier if it can even survive 20G
Hi William, thank you so much for you comment. Indeed we rework our objectives to use a smaller magnification, we will probably use a 40x lens, keeping the design for the lens and camera support but producing it in a stronger material !
Weāve made quite a bit of progress on different parts of our experiment proposal, Iāve attached the first CAD draft ! I have two quick questions regarding the flexure system on the OFM:
Are STEP files of the microscope available on request, specifically for the flexure part?
I havenāt 3D-printed one yet, so Iām wondering: how strong are the flexures? Do they move easily? Are they elastic?
The OpenFlexure Microscope is designed in OpenSCAD. This is mainly because we need to be able to have multiple developers in different places and we need version control. OpenSCAD has many quirks, but it is text based which means that we can use Git for version control and releases.
This means that STEP files cannot exist. OpenSCAD uses a constructive solid geometry representation to define a 3D shape, and this type of representation can only be made into a solid as an STL.
All of the source files are available on our Gitlab repository, and some notes on how to compile locally.
It would be very helpful for you to print and assemble a microscope. Then you will see how it goes together and how the flexures work. I see in your CAD image that you have chopped out the optics z-flexure from the main body. If you look at the Upright version of the Microscope you will see a part separate_z_actuator.stl. Building that would show you exactly how it works, and also what extra space you need around the part for the foot and to allow it to move.
