CubeSats are excellent platforms to rapidly perform simple space experiments. Several hundreds of CubeSats have already been successfully launched in the past few years and the number of announced launches grows every year. These platforms provide an easy access to space for universities and organizations which otherwise could not afford it. However, these spacecraft still rely on RF communications, where the spectrum is already crowded and cannot support the growing demand for data transmission to the ground. Lasercom holds the promise to be the solution to this problem, with a potential improvement of several orders of magnitude in the transmission capacity, while keeping a low size, weight and power. Between 2016 and 2017, The Keck Institute for Space Studies (KISS), a joint institute of the California Institute of Technology and the Jet Propulsion Laboratory, brought together a group of space scientists and lasercom engineers to address the current challenges that this technology faces, in order to enable it to compete with RF and eventually replace it when high-data rate is needed. After two one-week workshops, the working group started developing a report addressing three study cases: low Earth orbit, crosslinks and deep space. This paper presents the main points and conclusions of these KISS workshops.

Growing large defect-free semiconductor nanowires (NW) on lattice-mismatched substrates is important for solar cell applications. Here, we evaluate the critical dimensions of NWs in several strain-releasing growth configurations of interest to experimentalists. We quantify the expected increase in NW volume that may be grown coherently for NWs stacked on lattice mismatched pillars and embedded quantum dot (QD) layers, compared to NWs grown on simple substrates. We also calculate the variations in strain energy for NWs positioned off-axis from embedded QDs, as may occur during fabrication. We predict significant increases in coherent NW volume allowing greater absorption efficiency in solar cells.

Abstract-The laser beacon power required by a communication terminal for acquisition and tracking in deep space optical link scenarios can be reduced by a factor of 10 to 100 by replacing an integrating array, such as a CCD, with an array of single photon detectors. An additional benefit of the single photon detector array is that each pixel can have MHz bandwidths, allowing simultaneous recovery of photon time-ofarrival information that can be used for uplink data recovery or range measurements.

A hardware prototype of a flight receiver for deep space optical communications has been developed where a single detector array is used for acquisition, tracking, and high-speed data recovery. A counting algorithm accumulates pulses on every pixel in a photon-counting array and extracts signal information encoded with a nested modulation scheme.

Free-standing semiconductor nanorods grown on lattice-mismatched substrates have become of interest as novel devices, including solar cells. Here, we study the effect of substrate strain on the critical diameter for defect-free growth of free-standing nanorods using continuum elasticity theory. Unlike a thin film, nanorods release strain by relaxing in the lateral direction. We find that substrate relaxation is crucial for defect-free growth of InAs nanorods fabricated on GaAs. The calculation results show that below a critical diameter, the nanorods can grow to infinite length without emitting dislocations. Our findings lend support to the recent experimental efforts to grow defect-free arrays of nanorods providing improved absorption efficiency for next-generation solar cell technology.