Space science/space station attached payload pointing accommodation study: Technology assessment white paper

Technology assessment is performed for pointing systems that accommodate payloads of large mass and large dimensions. Related technology areas are also examined. These related areas include active thermal lines or power cables across gimbals, new materials for increased passive damping, tethered pointing, and inertially reacting pointing systems. Conclusions, issues and concerns, and recommendations regarding the status and development of large pointing systems for space applications are made based on the performed assessments

Steering Mirror System with Closed-Loop Feedback for Free-Space Optical Communication Terminals

Precision beam pointing plays a critical role in free-space optical communications terminals in uplink, downlink and inter-satellite link scenarios. Among the various methods of beam steering, the use of fast steering mirrors (FSM) is widely adopted, with many commercial solutions employing diverse technologies, particularly focusing on small, high-bandwidth mirrors. This paper introduces a method using lightweight, commercial off-the-shelf components to construct a custom closed-loop steering mirror platform, suitable for mirror apertures exceeding 100 mm. The approach involves integrating optical encoders into two off-the-shelf open-loop actuators. These encoders read the signal reflected on purposefully diamond-machined knurled screw knobs, providing maximum contrast between light and dark lines. The resulting steering mirror has the potential to complement or replace FSM in applications requiring a larger stroke, at the expense of motion speed. In the presented setup, the mirror tilt resolution achieved based on the encoder closed-loop signal feedback is 45 μrad, with a mean slew rate of 1.5 mrad/s. Importantly, the steering assembly is self-locking, requiring no power to maintain a steady pointing angle. Using the mirror to actively correct for a constantly moving incoming beam, a 5-fold increase in concentration of the beam spot on the center of the detector was obtained compared to a fixed position mirror, demonstrating the mirrors ability to correct for satellite platform jitter and drift

An advanced 10.6-micro laser communication experiment

Carbon dioxide laser capability of high data rate intersatellite communicatio

Practical strategies to stabilize a nanosatellite platform with a space camera and integrated mechanical parts

The growth and speed of nanosatellite capabilities has led to an increasing demand on the respective attitude control systems. Typically, nanosatellites utilise minaturised reaction wheels for 3-axis stabilisation/manoeuvres, which are desaturated using magnetorquers. Small space telescopes have been deployed from nanosatellites in the past with capability ever increasing to push the limit of detectors. Previous work has established the feasibility of achieving GSD of 0.7 m in low Earth orbit for a 2.5 U CubeSat using deployable mirrors from a 400 km orbit. The dynamic model of nanosatellite with the telescope + the deployed mirror systems will be built in this research work. The deployed mirror system will use a diamond turned mirror - it's an off axis paraboloid. The mirror would be light-weighted as much as possible, i.e. the back surface would be carved away with good thermal stability. The mechanisms for mirror systems may use methods like minature geared motors, stiction motors and shape memory alloy hinges. The sensoring and directing of the mirror surface will use an image based detection methods. A closed loop control of the mirror position will be used to iterate to a fully aligned system. This work also considers control strategies to stabilise such a platform against the effects of firstly, the external aerodynamics and secondly, any internal disturbances induced by and the movement of focussing elements. A pointing accuracy of 5-10 arcsec for a 20 min observation over the UK is targeted at a baseline orbit of 350 km sun-synchronous. Following an initial baseline to establish current state-of-art both based on in-orbit performance and off-the-shelf subsystems available to the market within the constraints of a 3U nanosatellite system, a number of feed-forward/feedback control loops and sensor systems are studied to determine a simple process for compensating for the motion

Control of piezoelectric scanner dynamics using magnetorheological fluid

The developed one-dimensional laser beam scanner, driven by a piezoelectric disctype unimorph actuator is presented in this paper. The dynamics of a piezoelectric actuator is analyzed. A magnetorheological fluid (MRF) damper is used to eliminate transient vibrations of the scanner eigen frequencies induced by the stepped driving voltage. Experimental results demonstrate the effectiveness of the MRF damper in residual-vibration reduction in the laser beam scanner

A spaceborne optical interferometer: The JPL CSI mission focus

The JPL Control Structure Interaction (CSI) program is part of the larger NASA-wide CSI program. Within this larger context, the JPL CSI program will emphasize technology for systems that demand micron or sub-micron level control, so-called Micro-Precision Controlled Structures (u-PCS). The development of such technology will make it practical to fly missions with large optical or large precision antenna systems. In keeping with the focused nature of the desired technology, the JPL approach is to identify a focus mission, develop the focus mission CSI system design to a preliminary level, and then use this design to drive out requirements for CSI technology development in the design and analysis, ground test bed, and flight experiment areas

Design of a scanning laser radar for spaceborne applications, phase 3

Design of scanning laser radar for spaceborne application

Setup of a Beam Control System for High Power Laser Systems at DLR

Different types of high power or high energy lasers in the multi kW class are currently available or are under development with promising progress reports. A major challenge is to deliver as much as possible of the available power onto a small and fast moving target over a long distance through a disturbing atmosphere. High resolution imaging is a common way to identify the category of targets dedication and to determine the spatial position relative to the observer. By illuminating the target with a laser the imaging system becomes more resilient towards ambient light and the exposure time can be reduced drastically. Fast and deterministic control loops are demanding for the moving parts in order to maintain a high accuracy for the pointing of the turret and aiming of the laser countermeasure system. Here, we report on the progress of such a beam control system developed at the Institute of Technical Physics of DLR. In an overview we present the beam control system and explain different sub-systems. Performance tests were taken at our outdoor test range. We investigated various scenarios for probing the limits of the tracking and pointing accuracy with a target sample mounted on a fast moving linear stage. We present first results of the beam control system performance

High Precision Dual-Stage Pointing Mechanism for Miniature Satellite Laser Communication Terminals

This paper presents an innovative mechatronic design of a high-accuracy pointing mechanism for orbital laser communication terminals. The system is based on a dual-stage architecture and is miniaturized to fit nanosatellite-class spacecraft, aiming to enable optical communication on small-size space platforms. The focus is on control design aspects and on the performance assessment of an experimental prototype under emulated external environmental disturbances

The Fourier-Kelvin Stellar Interferometer a Low Complexity, Low Cost Space Mission for High-Resolution Astronomy and Direct Exoplanet Detection

The Fourier-Kelvin Stellar Interferometer (FKSI) is a mission concept for a spacecraft-borne nulling interferometer for high-resolution astronomy and the direct detection of exoplanets and assay of their environments and atmospheres. FKSI is a high angular resolution system operating in the near to midinfrared spectral region and is a scientific and technological pathfinder to the Darwin and Terrestrial Planet Finder (TPF) missions. The instrument is configured with an optical system consisting, depending on configuration, of two 0.5 - 1.0 m telescopes on a 12.5 - 20 m boom feeding a symmetric, dual Mach- Zehnder beam combiner. We report on progress on our nulling testbed including the design of an optical pathlength null-tracking control system and development of a testing regime for hollow-core fiber waveguides proposed for use in wavefront cleanup. We also report results of integrated simulation studies of the planet detection performance of FKSI and results from an in-depth control system and residual optical pathlength jitter analysis