Richard P. Welle

LEO to ground optical communications from a small satellite platform

A pair of 2.2 kg CubeSats using COTS hardware is being developed for a proof-of-principle optical communications demo from a 450-600 km LEO orbit to ground. The 10x10x15 cm platform incorporates a 25% wall-plug efficient 10-W Yb fiber transmitter emitting at 1.06 μm. Since there are no gimbals on board, the entire spacecraft is body-steered toward the ground station. The pointing accuracy of the LEO craft, which governs the data rate capability, is expected to be ~ 0.1-0.2 deg. Two optical ground stations, located at the Mt. Wilson observatory, have receiver apertures of 30 and 80 cm. Launch of the CubeSat pair is anticipated to be mid to late 2015.

Peltier-actuated microvalve performance optimization

Valves for microfluidic systems have, for various reasons, proven to be difficult to fabricate, cumbersome to operate, and/or unreliable. We have explored the performance of a novel microfluidic valve formed by creating a flow channel past a Peltier junction. When the Peltier junction is used as a thermoelectric cooler it is possible to freeze the fluid in the valve, forming an ice plug that blocks flow through the valve. This type of valve is fundamentally leak-free, has no moving parts, and is electrically actuated. We have fabricated several experimental prototypes and evaluated their performance. We find that they are reliably capable of closing in less than 100 ms, and of opening substantially faster.

Standoff Pressures and Thermal Characterization of the Peltier-Actuated Microvalve

Experiments were conducted with Peltier-actuated microvalves to determine the maximum stand-off pressures possible with such valves, and to investigate the effect of supercooling on valve operation. Stand-off pressures were found to exceed the limits of measurability at 10 MPa. The experimental data, supported by thermal modeling, indicated that supercooling in linear-junction microvalves was typically about -15 C, while supercooling in tube-type Peltier valves ranged from -8 to -20 C

Aerodynamically Induced Fracture of Ice Shed from the Space Shuttle External Tank

After the STS-107 (Columbia) failure, a major part of the Space Shuttle return-to-flight effort involved risk assessments of Orbiter impact damage due to debris that might be shed by the External Tank (ET) during ascent. One potential source of debris that attracted attention was ice that forms, due to condensation of moisture, on bellows in the liquid oxygen feedline and on brackets holding the line in place. In an effort to gain insight into the fracture characteristics of ice during Space Shuttle ascent, an experiment was designed to investigate the behavior of ice as it accelerates in a supersonic crossflow as well as to study the behavior of ice upon impact with ET insulating foam. These tests demonstrated that ice has good structural resilience to loads associated with aerodynamic acceleration and recontact foam impacts.

Peltier-actuated microvalves: performance characterization

Valves for microfluidic systems have, for various reasons, proven to be difficult to fabricate, cumbersome to operate, and/or unreliable. We have explored the performance of a novel microfluidic valve formed by creating a flow channel past a Peltier junction. Using the Peltier junction as a thermoelectric cooler causes the fluid in the valve to freeze, forming a plug that blocks flow through the valve. Reversing the current in the Peltier junction causes the fluid to melt, reopening the valve. This type of valve is fundamentally leak-free, has no moving parts, and is electrically actuated. We have fabricated an experimental prototype capable of closing in less than one second, and of opening substantially faster. We have also developed a finite-element thermal model of the valve, and exercised it to optimize valve design. An optimized valve is predicted to have a cycle time on the order of 10 ms.

CubeSat-Scale High-Speed Laser Downlinks

The recent surge in the development of new commercial services hosted by satellites in low Earth orbit will lead to rapid increases in the demand for data downlinking, presenting a challenge for conventional radio-frequency communication systems. Optical communication systems offer a significant but so far unrealized potential for ultrahigh- volume downlinking. A number of demonstration laser communication missions have flown in space, but no optical systems are in routine operational use. Existing optical communication systems are typically too large for use in next-generation small commercial satellite systems.

On-orbit characterization of space solar cells on nano-satellites

The Aerospace Corporation has been building, testing, and flying miniature satellites in the pico-and nano-satellite class for over a decade. Significant advances have been made to the bus avionics unit and other satellite subsystems during this time. The advances have enabled various on-orbit tests and experiments, one of which has been to host space solar cell experiment payloads. Recent solar cell flight experiments on Aerospaces CubeSats (AeroCubes) demonstrated several subsystems can simultaneously operate to obtain precise measurements of space solar cell performance. Low cost, rapid return CubeSat missions can be valuable development tools for advancing the readiness level of space technologies.