Solar Charging Testbed

Solar Charging Testbed

Photo credit: Tori Repp/Fotobuddy

For proving out our CubeSat power budgets as reliably power-positive (by test rather than error-prone analysis), Shannen Prindle ('23), Will Huang ('25) and Anuja Magdum ('26) designed, built and tested one of the first-of-its-kind CubeSat solar charging testbeds. The testbed's "sun" is a ThorLabs SLS302 high-power (~10W) Quartz Tungsten-Halogen (QTH) lamp, which admittedly cannot produce a truly sunlike AM0 broadband spectrum, but was specified (and successfully tested) to be realistically (conservatively) well-matched to the EQE of our DIY monocrystalline silicon solar panels.  Upgrade of the testbed for use with space-grade (GaAs triple- or quad-junction) solar panels would likely demand upgrade to a more sunlike lamp (such as a Xenon arc lamp). 

The testbed includes custom motorized (belt-driven) actuation of the lamp's shutter, to enable programmed simulation of alternating sunlit and eclipse orbit phases (such as a familiar ISS-like orbit).   Also included is a custom motorized turntable, to slowly tumble the CubeSat (in a variety of selectable best- and worst-case orientations) at a range of flightlike RPMs.  

Helmholtz Cage

Helmholtz cage

For simulating the ambient magnetic field surrounding a CubeSat in a LEO orbit, Dave Singh ('24) designed, built and tested our Helmholtz Cage.  We believe his design to be the first-of-its-kind to be rigorously, simultaneously optimized for not only compactness (in a small lab) but also spatial homogeneity (of the generated magnetic field).  We believe spatial homogeneity to be important for the cage's use case, since the in-orbit ambient field should in reality be very homogenous, whereas a heterogenous simulated field could "confuse" a lot of our (tumbling) testbed experiments (such as those experiments characterizing or proving out our magnetometers, magnetorquers, or hysteresis rods).  

We are particularly interested in how a passive magnetic attitude stabilization system may (or may not) perform in transient orbital conditions (for example, when overflying the poles in a sun-synchronous orbit), so a large part of Dave's project was the design and test of a custom transient current controller for energizing the Helmholtz coils.  One of his important findings was that the rapid pulses of a typical simple PWM current controller can yield overly-optimistic predicted detumbling capability of magnetic hysteresis rods, so he thus had to implement some important custom current-smoothing features atop his basic current controller. 

To simulate near-frictionless tumbling of our CubeSats within the cage, we have PI's "PIglide" Rotary Air Bearing installed into the center of the cage.  At the moment, we have only the single-axis (rotary) bearing (for single-axis simulated tumbling), but we hope to implement a triaxial hemispherical variant soon.  To Princeton MAE students: come build this for us!

PI rotary air bearing
PI spherical air bearing


Helmholtz cage group

Photo credit: Tori Repp/Fotobuddy