Alloy solidification

Who it is for

• Aluminium casting and alloy producers (automotive, aerospace) who use solidification models to set process windows
• Suppliers of grain refiners who need clean data on how equiaxed grains start and grow
• University and institute solidification groups that test phase-field, front-tracking and CAFE models
• Software vendors who validate casting and welding simulation codes
• Space agency materials science programmes that want more flight opportunities between ISS increments

What earlier flights found

How LELP-1 runs it

Sample. Transparent model alloy: succinonitrile (SCN) with a small camphor addition (for example 0.24 wt% camphor, the DECLIC-DSI composition), degassed, filled under vacuum and sealed on the ground. Option: a second crucible with a different solute content. Container. Sealed glass or quartz cylindrical crucible, about 10 mm inner diameter and about 100 mm long, with thermocouples along the wall. It sits in a miniature Bridgman stage (hot zone plus cold zone with a translation stage) inside a large-bay containment shell. Launch. Solid alloy sample at bay temperature (SCN melts near 57 C, so it stays solid at a 20 C launch setpoint). Light and gas. No gas exchange: the crucible is sealed. Transmitted LED light is on only while images are taken. The hot zone runs at about 70 C and the cold zone at about 30 C, giving roughly 19 K/cm across the interface (our estimate, sized to match DECLIC-DSI). The 70 C hot zone is above the 45 C limit of the standard bay block, so the module needs its own insulated heater (see needs).

1. day 0

   Launch with the sample solid. Bay block holds 20 C. Module unpowered except housekeeping sensors.

2. day 1

   After satellite commissioning, ground confirms an arm-quiet window. Bay block set to 30 C (cold-zone sink). Hot-zone heater ramps to 70 C. Part of the sample melts and the interface settles in the gradient. Hold 24 h so solute spreads out by diffusion. Reference images every 10 min.

3. day 2

   Run 1: pull at 1.5 um/s for about 6 h (about 30 mm). Images every 1 to 2 min, thermocouple and accelerometer logs at 1 Hz. The arm stays parked.

4. day 3

   Move the crucible back to remelt the grown part. Hold 24 h to homogenise again. Downlink a reduced image set for the ground team to check.

5. day 4

   Run 2: pull at 2.0 um/s for about 5 h. Same imaging.

6. day 5

   Remelt and hold 24 h.

7. day 6

   Run 3: step change in velocity during the run (for example 1.5 to 2.0 um/s) to watch the cell pattern change and grain competition. Ground may change the velocities for runs 3 and 4 based on runs 1 and 2 (signed command checked by the mission guardian).

8. day 7

   Remelt and hold 24 h.

9. day 8

   Run 4: repeat run 1 to check reproducibility, or a slower velocity chosen by the science team.

10. day 9

    Final directional solidification of the whole sample at a low velocity so all of it is solid. Turn off the hot zone. Bay block brings the sample to 15 C.

11. day 10

    Hold at 15 C through de-orbit, re-entry and splashdown. Full image archive kept on board as a backup to the downlinked set.

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.

• The crucible moves, the blocks stay: the pull stage draws the sample from the hot block through the 10 mm gap into the cold block, and the camera watches the solidification front in the gap. The cold block dumps its heat into the cold wall through a copper strap.
• The catalog gives 1.52 kg for structure and containment; as an aluminium box that is a 0.49 mm skin on 0.80 kg of posts and shelves. Thin: the bay rails have to carry the launch loads, or the module needs more structure mass.
• 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-spare module with crucibles filled from the same alloy batch runs the same timeline (same gradients, velocities and hold times) in the customer's lab or ours. It runs once with gravity along the growth direction and once against it, so convection effects can be separated from the microgravity result. Thermal and imaging settings are copied from the flight log. Published ISS DECLIC-DSI results on SCN-camphor serve as an outside benchmark.

Coming home

Most of the science is in the downlinked images, so return is not urgent. Keep the transparent alloy well below its melting range (pure SCN melts near 57 C) so the final pattern stays frozen. 4 to 25 C is fine. Avoid mechanical shock to the glass crucible. Solid metallic samples from the furnace option have no temperature limit once they cool.

Limits of this flight

• A standard bay cannot melt metal. Al-based alloys need furnace temperatures of several hundred C and power far above 30 W. The standard offer is limited to transparent organic model alloys, which melt near 57 C and still need a module heater above the 45 C bay limit.
• No in situ X-ray radiography of metals. XRMON-type X-ray imaging needs a source, detector and power well beyond a bay. Metal samples in the furnace option would be studied only after return.
• Sample size is small (about 10 mm by 100 mm, our estimate). Long rods and multi-sample cartridges like those processed in ISS rack furnaces are not possible.
• No crew. Crucibles cannot be swapped, refilled or re-aligned. A bubble or a stuck stage cannot be fixed, and the number of runs is limited to what one sealed crucible allows (about 4 to 5 remelt-and-grow cycles in 10 days).
• Lab operations last at most 14 days. Very slow growth or diffusion-limited holds that take weeks cannot be done.
• Arm motion raises acceleration to 1e-4 to 1e-3 g, so runs must be scheduled around robotic operations. Customers with other bays may need to accept arm-free windows.
• Downlink bandwidth limits image rate and resolution. The full high-rate data is only available after recovery.
• The metallic furnace bay is a proposal, not a current LELP-1 service. It would take two large-bay slots and a share of satellite power during each run, which affects the rest of the mission plan.