Eine Naturforscherfahrt durch Aegypten und den Sudan : mit 27 photographischen Aufnahmen von Leopold Ritter v. Portheim und 21 Zeichnungen von Carola N.....

Die Biologische Versuchsanstalt in Wien organisierte während der Monate Dezember 1903 und Jänner 1904 eine Reise durch Aegypten und den englisch-ägyptischen Sudan, und zwar zu dem Zwecke, lebendes Untersuchungsmaterial aus der Pflanzen- und Tierwelt jener Länder mit nach Europa zu bringen. Insbesondere galt es. solche Arten kleinerer Lebewesen aufzufinden, welche sich in irgend einer Beziehung zu Versuchen auf dem Gebiete der experimentellen Morphologie (der Lehre yon den die Formbildung der Organismen verursachenden und beeinflussenden Faktoren) eignen. In dem Bestreben, das gesammelte Material lebend heimzubringen, bestand das Neue dieser Expedition im Vergleiche zu anderen wissenschaftlichen Sammelreisen, welche ihr Hauptaugenmerk auf konserviertes Material zu richten pflegen. Sollten nun die Transporte und später die Versuche an den mitgebrachten Pflanzen und Tieren gelingen, so stellte sich als erstes Erfordernis die Wahl solcher Pflanzen und Tiere heraus welche bei Veränderungen der äusseren Lebensbedingungen über eine gewisse Widerstandskraft verfügen und daher vor allem auch.die Gefangenhaltung gut ertragen. Die Teilnehmer der Reise waren: LEOPOLD RITTER v. PORTHEIM als Botaniker, Dr. HANS PRZIBRAM und der Verfasser vorliegender Reiseschilderung als Zoologen, sowie Dr. GUlDO BUNZEL als Jagdfreund und Amateurphotograph

Wigner Measure Propagation and Conical Singularity for General Initial Data

We study the evolution of Wigner measures of a family of solutions of a Schr\"odinger equation with a scalar potential displaying a conical singularity. Under a genericity assumption, classical trajectories exist and are unique, thus the question of the propagation of Wigner measures along these trajectories becomes relevant. We prove the propagation for general initial data.Comment: 24 pages, 1 figur

Experimental Design for the Evaluation of Detection Techniques of Hidden Corrosion Beneath the Thermal Protective System of the Space Shuttle Orbiter

The United States Space Operational Space Shuttle Fleet Consists of three shuttles with an average age of 19.7 years. Shuttles are exposed to corrosive conditions while undergoing final closeout for missions at the launch pad and extreme conditions during ascent, orbit, and descent that may accelerate the corrosion process. Structural corrosion under TPS could progress undetected (without tile removal) and eventually result in reduction in structural capability sufficient to create negative margins of . safety and ultimate loss of local structural capability

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

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