Microalgae and cyanobacteria for oxygen and food

Who it is for

• Space-agency life support programmes that study bioregenerative systems, such as ESA's MELiSSA project
• University and institute groups that study algal and cyanobacterial physiology in space (for example the ICGEB New Delhi groups that flew experiments on Axiom-4)
• Companies building photobioreactors or algal food and feed products that want flight data on their hardware or strain
• Groups testing nutrient recycling from waste streams, such as urea as a nitrogen source

What earlier flights found

How LELP-1 runs it

Sample. Limnospira indica PCC 8005 (axenic culture, the MELiSSA strain). A Chlorella strain can be flown instead in the same hardware. Container. Four flat-panel membrane photobioreactors (about 40 ml liquid each, 15 mm deep). Each has a liquid chamber and a gas headspace separated by a hydrophobic PTFE membrane. They sit in a large-bay cassette with an LED panel, a recirculation pump, and optical-density and oxygen sensors. Launch. Live culture at low density in bicarbonate-rich medium, kept dark at 10 C to slow growth until activation (our design choice; ground tests must confirm the culture survives the hold). Light and gas. Red/white LED light at about 35 to 80 umol photons m-2 s-1, set per reactor (our choice). Carbon comes from bicarbonate in the medium because the sealed bay has no CO2 supply. Oxygen collects in each reactor's headspace and is measured by pressure and an optical O2 sensor. Each headspace has a pressure relief; Arthrospira-B used 1.15 bar.

1. day 0

   Launch with reactors filled, lights off, bay held at 10 C. Log temperature, acceleration and dose.

2. day 1

   After orbit checkout, warm to 33 C, start recirculation mixing and switch on the LEDs. Reactors 1-2 at 35 umol photons m-2 s-1, reactors 3-4 at 70 umol photons m-2 s-1.

3. day 1

   Start logging optical density every 30 min, and headspace pressure and O2 every 5 min. Take a baseline microscope image of each reactor's sampling window.

4. day 4

   Pump 2 ml from each reactor into fixative wells (for RNA/protein) and image trichome shape and chlorophyll autofluorescence.

5. day 7

   Repeat sampling and imaging. If a headspace nears its pressure limit, vent it through the bay's relief path and log the vented volume.

6. day 7

   Replace 20 ml of culture in reactors 3-4 with fresh medium from the reservoir (semi-continuous mode) to test growth after dilution and bicarbonate top-up.

7. day 10

   Final sampling into fixative wells and final imaging.

8. day 11

   Switch off the LEDs, stop mixing, cool the bay to 4 C. Live culture stays in the reactors for viability and purity tests on the ground.

9. day 12

   Hold at 4 C through deorbit, splashdown and handover to the customer's courier.

The payload module, in CAD

Every item in the module sheet, drawn and packed into the large bay deck by deck. The back face mates with the bay: blind-mate connector, and a cold wall against the bay's thermoelectric block. The front face carries Dexter-L's grapple fixture, and the fluid lines run down a channel just behind it. What you load before launch is marked blue in the configurator's payload guide.

CAD generated by cad/build_modules.py (CadQuery, OpenCascade kernel) from the catalog's module items: concept geometry, not a released design. Standard parts keep their real formats; the rest are sized from their catalog mass. The front panel and grapple fixture are left off in the 3-D view and are in the STEP.

• Each photobioreactor has its own LED panel on one face and an optical-density pair across it; the four are plumbed in series.
• Reagent volumes the catalog does not state are split evenly from 75 % of the reservoir item's mass.
• Fluid pack: 3 reagent bags in 1 layer (285 x 138 x 23 mm), every port on a front edge.
• The catalog gives 1.20 kg for structure and containment; as an aluminium box that is a 0.60 mm skin on 0.36 kg of posts and shelves.
• The grapple fixture stands 26 mm proud of the front panel, into the bay opening; everything else is inside the bay envelope.

Ground control

An identical flight-model module runs on the ground at the same time. It uses the same culture lot, medium batch, light settings, temperature profile (replayed from flight telemetry, including the 10 C launch hold and 4 C return) and sampling times. Optional: a second set of reactors on a 1 g centrifuge in flight would separate microgravity effects from launch and radiation effects.

Coming home

Fixed samples and live culture both stay at 4 C and in the dark. Cool-down is on day 11, splashdown about a day later, and the courier needs 1-2 days, so plan for up to about 96 h from cool-down to the lab. The live culture is only for viability and purity; fixed samples tolerate longer. This is our estimate and must be confirmed by the customer's ground tests.

Limits of this flight

• The sealed bay has no CO2 supply, so growth is batch or semi-continuous on bicarbonate in the medium. It cannot copy a reactor fed by cabin CO2 the way PBR@LSR was. Arthrospira-B saw oxygen output drop late in each batch, which its authors linked to bicarbonate limitation.
• 12 days and about 160 ml of culture cannot test the months-long stability a real life support reactor needs. PBR@LSR was designed for up to 180 days.
• No crew: bubbles, membrane fouling or a stuck pump cannot be fixed by hand. Running four reactors in parallel is the only backup.
• No pH probe or pH control in this design (Arthrospira-B had none either), so pH drift is only measured after return.
• There is too little biomass to test taste, food safety or feeding. Only composition and purity can be checked.
• The live culture must survive a dark hold at launch and several days of cold return. This may bias viability and gene expression results.
• Radiation in a 550 km sun-synchronous orbit differs from the ISS, so dose results do not compare directly with ISS data.
• Robotic-arm moves raise acceleration to about 1e-4 to 1e-3 g. Arm activity should pause during key measurements.