Investigation of a network of advanced microcomputers into research & instructional programs of the School of Mathematics

Issued as Final report, Project no. G-37-60

The Relationship between Cost Analysis and Program Management

Cost analysis if often viewed as applying basic principles and cost methodologies to determine total system cost. These finished estimates then flow into a decision making process and the cost estimator leaves the stage. Reality shows that the cost estimator is actually one of the main contributors to the decision making process. Our introduction to this special issue explores the areas where cost estimating plays a major role in program management in areas beyond the normal program estimate. We have included articles that show the key role estimators can play in source selection strategies and evaluation; cost of delay analysis for management decisions, earned value management methods to predict program costs; decision criteria to rank competing projects that complement traditional cost-based methods; and a new methodology for determining research and development budget profiles

Optomechanical Design and Analysis for Nanosatellite Laser Communications

The CubeSat Laser Infrared CrosslinK (CLICK) mission is a technology demonstration of a 1.5U laser communications terminal for an intersatellite link. The terminal is deployed on a pair of 3U CubeSats in Low Earth Orbit (LEO). The pointing, acquisition, and tracking (PAT) approach includes both coarse and fine systems. The coarse tracking system uses a beacon laser transmitter and receiver camera. The fine tracking system uses a fast steering mirror and quadrant photodiode. The communications transmit and receive paths include a refractive telescope, transmit laser collimator, and avalanche photodetector (APD) receiver. The communications laser full-width, half maximum (FWHM) beam divergence angle is 14.6 arcseconds, and the beacon laser FWHM divergence is 0:75° (2700 arcseconds). The opto-mechanical design process includes prediction & verification of assembly alignment & calibration, thermoelastic effects, structural modes & static loading, and fastener analysis. The opto-mechanical assembly has the sensors and laser transmitters kinematically mounted to enable on-ground calibration to less than 25.4 mm decenter, or 0.1° tip/tilt. The thermoelastic alignment error between the payload and bus star tracker is estimated via finite element analysis to be less than 9 arcseconds. The payload optical bench is designed with custom thermal isolation and control to maintain 20 ± 10 ° C. The thermal modeling of the payload is described in detail. Structural static loading and fastener analyses of the CLICK payload under launch loads of 30 G verify margins of safety are greater than 10 and above the recommended values. Modal analyses predict the first resonant frequency to be 888 Hz, above typical vehicle structural vibration ranges with a factor of safety greater than 3.5

CLICK-A: Optical Communication Experiments From a CubeSat Downlink Terminal

The CubeSat Laser Infrared CrosslinK (CLICK) mission is a technology demonstration of low size, weight, and power (SWaP) CubeSat optical communication terminals for downlink and crosslinks. The mission is broken into two phases: CLICK-A, which consists of a downlink terminal hosted in a 3U CubeSat, and CLICK-B/C, which consists of a pair of crosslink terminals each hosted in their own 3U CubeSat. This work focuses on the CLICK-A 1.2U downlink terminal, whose goal was to establish a 10 Mbps link to a low-cost portable 28 cm optical ground station called PorTeL. The terminal communicates with M-ary pulse position modulation (PPM) at 1550 nm using a 200 mW Erbium-doped fiber amplifier (EDFA) with a 1.3 mrad FWHM beam divergence. CLICK-A ultimately serves as a risk reduction phase for the CLICK-B/C terminals, with many components first being demonstrated on CLICK-A. CLICK-A was launched to the International Space Station on July 15th, 2022 and was deployed by Nanoracks on September 6th, 2022 into a 51.6° 414 km orbit. We present the results of experiments performed by the mission with the optical ground station located at MIT Wallace Astrophysical Observatory in Westford, MA. Successful acquisition of an Earth to space 5 mrad FWHM (5 Watts at 976 nm) pointing beacon was demonstrated by the terminal on the second experiment on November 2nd, 2022. First light on the optical ground station tracking camera was established on the third experiment on November 10th, 2022. The optical ground station showed sufficient open, coarse, and fine tracking performance to support links with the terminal with a closed-loop RMS tracking error of 0.053 mrad. Results of three optical downlink experiments that produced beacon tracking results are discussed. These experiments demonstrated that the internal microelectromechanical system (MEMS) fine steering mirror (FSM) corrected for an average blind spacecraft pointing error of 8.494 mrad and maintained an average RMS pointing error of 0.175 mrad after initial blind pointing error correction. With these results, the terminal demonstrated the ability to achieve sufficient fine pointing of the 1.3 mrad FWHM optical communication beam without pointing feedback from the terminal to improve the nominal spacecraft pointing. Spacecraft drag reduction maneuvers were used to extend mission life and inform the mission operations of the CLICK-B/C phase of the mission. Results from the spacecraft drag maneuvers are also presented

Design and Prototyping of a Nanosatellite Laser Communications Terminal for the Cubesat Laser Infrared CrosslinK (CLICK) B/C Mission

The CubeSat Laser Infrared CrossLink (CLICK) mission goal is to demonstrate a low cost, high data rate optical transceiver terminal with fine pointing and precision time transfer in aleq1.5U form factor. There are two phases to the technology demonstration for the CLICK mission: CLICK-A downlink, and then CLICK-B/C crosslink and downlink. The topic of this paper is the design and prototyping of the laser communications (lasercom) terminal for the CLICK-B/C phase. CLICK B/C consists of two identical 3U CubeSats from Blue Canyon Technologies that will be launched together in Low Earth Orbit to demonstrate crosslinks at ranges between 25 km and 580 km with a data rate of ≥20 Mbps and a ranging capability better than 0.5 m. Downlinks with data rates of ≥10 Mbps will also be demonstrated to the Portable Telescope for Lasercom (PorTeL) ground station. Link analysis using current parameters & experimental results predicts successful crosslink & downlink communications and ranging. Moreover, closed-loop 3σ fine pointing error is predicted to be less than 39.66 μrad of the 121.0 μrad 1/e² transmit laser divergence. The status of the payload EDU and recent developments of the optomechanical and thermal designs are discussed

Testing of the CubeSat Laser Infrared CrosslinK (CLICK-A) Payload

The CubeSat Laser Infrared CrosslinK (CLICK-A) is a risk-reduction mission that will demonstrate a miniaturized optical transmitter capable of ≥10 Mbps optical downlinks from a 3U CubeSat to aportable 30 cm optical ground telescope. The payload is jointly developed by MIT and NASA ARC, and is on schedule for a 2020 bus integration and 2021 launch. The mission purpose is to reduce risk to its follow-up in 2022, called CLICK-B/C, that plans to demonstrate ≥20 Mbps intersatellite optical crosslinks and precision ranging between two 3U CubeSats. The 1.4U CLICK-A payload will fly on a Blue Canyon Technologies 3U bus inserted into a 400 km orbit. The payload will demonstrate both the transmitter optoelectronics and the fine-pointing system based on a MEMS fast steering mirror, which enables precision pointing of its 1300 μrad full-width half-maximum (FWHM) downlink beam with anestimated error of 136.9 μrad (3-σ) for a pointing loss of -0.134 dB (3-σ) at the time of link closure. We present recent test results of the CLICK-A payload, including results from thermal-vacuum testing, beam characterization, functional testing of the transmitter, and thermal analyses including measurement of deformation due to the thermal loading of the MEMS FSM

Thermomechanical design and testing of the Deformable Mirror Demonstration Mission (DeMi) CubeSat

The Deformable Mirror Demonstration Mission (DeMi) is a 6U CubeSat that will operate and characterize the on-orbit performance of a Microelectromechanical Systems (MEMS) deformable mirror (DM) with both an image plane and a Shack-Hartmann wavefront sensor (SHWFS). Coronagraphs on future space telescopes will require precise wavefront control to detect and characterize Earth-like exoplanets. High-actuator count MEMS deformable mirrors can provide wavefront control with low size, weight, and power. The DeMi payload will characterize the on-orbit performance of a 140 actuator MEMS DM with 5.5 μm maximum stroke, with a goal of measuring individual actuator wavefront displacement contributions to a precision of 12 nm. The payload is designed to measure low order aberrations to λ/10 accuracy and λ/50 precision, and correct static and dynamic wavefront phase errors to less than 100 nm RMS. The thermal stability of the payload is key to maintaining the errors below that threshold. To decrease mismatches between coefficients of thermal expansion, the payload structure is made out of a single material, aluminum 7075. The gap between the structural components of the payload was filled with a thermal gap filler to increase the temperature homogeneity of the payload. The fixture that holds the payload into the bus is a set of three titanium flexures, which decrease the thermal conductivity between the bus and the payload while providing flexibility for the payload to expand without being deformed. The mounts for the optical components are attached to the main optical bench through kinematic coupling to allow precision assembly and location repeatability. The MEMS DM is controlled by miniaturized high-voltage driver electronics. Two cross-strapped Raspberry Pi 3 payload computers interface with the DM drive electronics. Each Raspberry Pi is paired to read out one of the wavefront sensor cameras. The DeMi payload is ~4.5U in volume, 2.5 kg in mass, and is flying on a 6U spacecraft built by Blue Canyon Technologies. The satellite launch was on February15,2020 onboard a Northrop Grumman Antares rocket, lifting off from the NASA Wallops Flight Facility. We present the mechanical design of the payload, the thermal considerations and decisions taken into the design, the manufacturing process of the flight hardware, and the environmental testing results

Development of CubeSat Spacecraft-to-Spacecraft Optical Link Detection Chain for the CLICK B/C Mission

The growing interest in and expanding applications of small satellite constellation networks necessitates effective and reliable high-bandwidth communication between spacecraft. The applications of these constellations (such as navigation or imaging) rely on the precise measurement of timing offset between the spacecraft in the constellation. The CubeSat Laser Infrared CrosslinK (CLICK) mission is being developed by the Massachusetts Institute of Technology (MIT), the University of Florida (UF), and NASA Ames Research Center. The second phase of the mission (CLICK-B/C) will demonstrate a crosslink between two CubeSats (B and C) that each host a \u3c 2U laser communication payload. The terminals will demonstrate full-duplex spacecraft-to-spacecraft communications and ranging capability using commercial components. As part of the mission, CLICK will demonstrate two-way time-transfer for clock synchronization and data transfer at a minimum rate of 20 Mbps over separation distances ranging from 25 km to 580 km. The payloads of CLICK B and C include a receiver chain with a custom photodetector board, a Time-to-Digital Converter (TDC), a Microchip Chip-Scale Atomic Clock (CSAC), and a field-programmable gate array (FPGA). The payloads can measure internal propagation delays of the transmitter and the receiver, and cancel environmental effects impacting timing accuracy. The photodetector board is 2.5 cm x 2.5 cm and includes an avalanche photodiode (APD) and variable-gain amplifiers through which the detected signal is conditioned for the TDC to be time-stamped. This design has been developed from the UF and NASA Ames CubeSat Handling Of Multisystem Precision Time Transfer (CHOMPTT) project and associated MOCT (Miniature Optical Communication Transceiver) demonstration. The TDC samples the signal at four points: twice on the rising edge at set thresholds, and twice at the falling edge at those same thresholds. These four time-offset samples are sent to the FPGA, which combines the measurements for a reported timestamp of the detected laser pulse. These timestamps can then be used in a pulse-position modulation (PPM) demodulation scheme to receive data at up to 50 Mbps, to calculate range down to 10 cm, and for precision time-transfer with \u3c 200 ps resolution. In this paper, we will discuss the designed capabilities and noise performance of the CLICK TDC-based optical receiver chain

A Flagellar A-Kinase Anchoring Protein with Two Amphipathic Helices Forms a Structural Scaffold in the Radial Spoke Complex

A-kinase anchoring proteins (AKAPs) contain an amphipathic helix (AH) that binds the dimerization and docking (D/D) domain, RIIa, in cAMP-dependent protein kinase A (PKA). Many AKAPs were discovered solely based on the AH–RIIa interaction in vitro. An RIIa or a similar Dpy-30 domain is also present in numerous diverged molecules that are implicated in critical processes as diverse as flagellar beating, membrane trafficking, histone methylation, and stem cell differentiation, yet these molecules remain poorly characterized. Here we demonstrate that an AKAP, RSP3, forms a dimeric structural scaffold in the flagellar radial spoke complex, anchoring through two distinct AHs, the RIIa and Dpy-30 domains, in four non-PKA spoke proteins involved in the assembly and modulation of the complex. Interestingly, one AH can bind both RIIa and Dpy-30 domains in vitro. Thus, AHs and D/D domains constitute a versatile yet potentially promiscuous system for localizing various effector mechanisms. These results greatly expand the current concept about anchoring mechanisms and AKAPs

Application of Terahertz Radiation to the Detection of Corrosion under the Shuttle's Thermal Protection System

There is currently no method for detecting corrosion under Shuttle tiles except for the expensive process of tile removal and replacement; hence NASA is investigating new NDE methods for detecting hidden corrosion. Time domain terahertz radiation has been applied to corrosion detection under tiles in samples ranging from small lab samples to a Shuttle with positive results. Terahertz imaging methods have been able to detect corrosion at thicknesses of 5 mils or greater under 1" thick Shuttle tiles and 7-12 mils or greater under 2" thick Shuttle tiles