Paihau—Robinson Space Blog

One the primary requirements for Hēki’s design was to figure out how to use a relatively small amount of power (<100 Watts) to accomplish our mission goals. The largest part of the power budget was for cooling the magnet to superconducting temperatures (about -200C). As anyone who owns a refrigerator knows, making things cool takes a lot of energy!  On the other hand: in order to maintain Hēki’s components at a constant temperature, the heat generated by Hēki’s energy use needs to be efficiently conducted or radiated away. Designing and testing Hēki to ensure thermal stability in space was a significant challenge. As noted in this post, confirming that we’d gotten the the thermal design right has been a crucial part of early on-orbit operations.

Hēki uses a mechanical device called a “cryocooler” to chill the magnet into its superconducting temperature range (see header photo, and below). Hēki’s cryocooler is a commercial off-the-shelf product about the size of a soda can. The cryocooler uses energy to move the heat from the magnet to Hēki’s radiator, where it can radiated away, keeping Hēki’s components at a stable temperature.

Today we are able to confirm that Hēki has achieved thermal stability with the magnet at superconducting temperatures – checking off #7 of of Hēki’s 12 crucial mission success criteria (below). Tomorrow, it will be time for Hēki’s flux pump to start energising the magnet!

Left: Hēki’s cryocooler; Centre: Hēki’s cryocooler embedded in support structure; Right: interior of Hēki’s “active” (Earth-facing) side, showing cryocooler location during assembly. The cover with a reflective & emissive radiator surface was installed later in the assembly process.

Hēki Success Criteria Tracking

Before Launch
✅	1	Build low-power, superconducting magnet system
✅	2	Verify Hēki can survive journey to – and operations in – space
✅	3	Comply with NASA safety requirements
✅	4	Demonstrate successful communication between Hēki and space station computer simulator
✅	5	Verify Hēki team’s readiness for operations in space
In space
✅	6	Successfully power on after installation on space station
✅	7	Verify magnet is cooled to superconducting temperature (-200C)
	8	Meet or exceed required magnetic field (300mT)
	9	Measure effectiveness of magnetic field as a shield for space radiation
	10	Demonstrate successful operation throughout the mission, including at least three magnetic field cycles
After return to Earth
	11	Characterize Hēki to determine if there has been any degradation in performance
	12	Repeat characterization after forcing a magnetic “quench” to show that Hēki can safely dissipate stored energy if superconductivity is lost.