Integrated Power, Propulsion, and Attitude Control for CubeSats

TUI is currently developing a module for CubeSats that integrates power generation, green-propellant propulsion, and attitude control. This module, called PowerCube™, enables the low-cost CubeSat platform to perform missions requiring large ∆Vs, orbit agility, precision pointing, and high-power capabilities. The 1U PowerCube module provides:

These capabilities support a 2U payload, enabling high-performance, agile CubeSat missions in Earth orbit and beyond. In order to provide these capabilities the PowerCube system combines a high-power deployable solar array, electrolysis fuel cell, thruster, and ‘carpal joint’ gimbal shown below.

The sun-tracking deployable solar array, coupled with energy storage, provides 50 W of orbit-averaged power, to supply both the payload and the electrolysis thruster subsystem. This array stows within the 6.5 mm thick ‘extra volume’ allowed by the P-POD payload spec beyond the nominal 10 cm x 10 cm CubeSat footprint. Three composite 7-cell panels fold up along each of the four long sides of the CubeSat. The array is available in different panel configurations to meet varying mission needs, and deployment testing in zero-g has been accomplished.

The power system supplies energy to a PEM electrolysis fuel cell that evolves gaseous hydrogen and oxygen to feed a pulsed thruster, capable of providing up to 6 m/s of ΔV per 90-minute orbit, and 300 Ns of total impulse for every 100 g of water. By creating fuel on-orbit from water, the Water Electrolysis Thruster (WET) Propulsion subsystem enables missions requiring large delta-Vs while complying with P-POD restrictions that preclude the launch of useful quantities of energetic propellant.

The 3DOF carpal joint enables pointing of the solar array over a full hemisphere without cable windup, providing robust solar tracking. Furthermore, the gimbal joint permits the thrust vector to be controlled relative to the center of mass of the CubeSat, and this allows the CubeSat to be capable of both orbit adjustment and thrust-driven attitude control. During periods when thrust events and solar collection are not taking place, the joint allows the attitude of the payload section to be controlled relative to the PowerCube section, by using the inertia of the PowerCube module. Bringing together the components of the overall system, the PowerCube has an estimated mass of 1.9 kg. These masses are a conservative estimate, and are primarily based off of existing prototype hardware. Through further development it is expected that the fuel cell and thruster weight can be reduced with further engineering effort and through the use of improved materials as compared to those employed in the prototype.

These capabilities provide unprecedented mission options for CubeSats. The PowerCube system can serve as a complete bus for small satellites, for applications ranging from rapid-response Earth-sensing to orbital debris remediation. This highly integrated system will enable the CubeSat platform to be used to perform missions previously possible only on much larger platforms, including formation flight for long-baseline sensing; orbit-agile systems for Space Situational Awareness (SSA), Active Debris Removal (ADR), and multipoint science; as well as lunar and asteroid science missions. Allocating a larger portion of the CubeSat mass to fuel (~700 g, at 300 Ns of impulse per 100 mL of water) would enable PowerCube to be used for CubeSat missions to the moon. Cost-effective inspection of in-orbit resources is also possible, from the space station to orbiting satellites. Lastly, the PowerCube could serve as a low-cost technology test platform, providing a testbed that can deliver propulsion, attitude control, and power to experiments or technical demonstrations.

Download a PowerCube Product Brochure.

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