The image quality of high-definition television (HDTV) cameras and camcorders for space activity is degraded by the presence of permanent bright pixels (so-called “white defects”) due to space radiation. We studied the space radiation damage to HDTV charge-coupled devices (CCDs; 2 × 106 pixels per chip) loaded in the Russian service module (SM) of the International Space Station (ISS) for 71 days, 256 days and 446 days. We used the “Passive Dosimeter for Lifescience Experiments in Space” (PADLES), which consists of CR-39 plastic nuclear track detectors (PNTDs) and thermoluminescent dosimeters, to measure space radiation doses received by the HDTV CCDs in the SM during loading periods. The average production rates of white defects for output voltage greater than 0.5 mV were 2.366 ± 0.055 pixels/day in Si and 5.213 ± 0.071 pixels/mGy in Si. We also investigated the correlation between the position of the white defects and tracks of high-energy particles with LET∞,Si of approximately 300 keV/μm or more using stacks of CR-39 PNTDs and the HDTV CCD chips. We found that approximately 30% of these high-energy high-LET particles coincided with the position of white defects on the HDTV CCDs in the SM.
This paper presents the results for the first ever flight demonstration of the Zero Propellant Maneuver (ZPM) TM attitude control concept. On November 5, 2006, the ZPMTM was used to reorient the International Space Station by 90 degrees without using any propellant. By maneuvering along a pre-planned trajectory which was optimized to take advantage of naturally occurring environmental torques, the Space Station CMGs were maintained within operational limits. The trajectory was obtained from a PseudoSpectral solution to a new optima attitude control problem. With the flight test, the breakthrough capability to simultaneously perform large angle attitude maneuver and momentum desaturation without the need to use thruster was established. The flight implementation did not require any modification to flight software. The approach is applicable to any spacecraft that are controlled by momentum storage devices.
The MIT Space Systems Laboratory (SSL) has developed a testbed for the testing of formation flight and autonomous docking algorithms in both 1-g and microgravity environments. The SPHERES testbed consists of multiple micro-satellites, or Spheres, which can autonomously control their position and attitude. The testbed can be operated on an air table in a 1-g laboratory environment, in NASA"s KC-135 reduced gravity research aircraft and inside the International Space Station (ISS). SPHERES launch to the ISS is currently manifested for May 19 2004 on Progress 14P. Various types of docking maneuvers, ranging from docking with a cooperative target to docking with a tumbling target, have been developed. The ultimate objective of this research is to integrate the different algorithms into one program that can assess the health status of the target vehicle, plan an optimal docking maneuver while accounting for the existing constraints and finally, execute that maneuver even in the presence of simulated failures. In this paper, results obtained to date on the ground based air table using the initial version of the program will be presented, as well as results obtained from microgravity experiments onboard the KC-135.
The Resonant Inductive Near-Field Generation System uses a single set of hardware to perform both electromagnetic formation flight and wireless power transfer operations in a six-degree-of-freedom microgravity environment. The system serves primarily as a test bed for control algorithms, and operation onboard the International Space Station allows for more complicated and realistic algorithms to be tested. This offers an advantage compared with the restrictive, dynamic environment of flat floor facilities on the ground or the limited duration of reduced-gravity flights. The hardware attaches to the formation flight-test facility inside the International Space Station referred to as the Synchronized Position Hold, Engage, Reorient, Experimental Satellites. Design and development of the support hardware and electronics, as well as some test results from ground testing, a parabolic flight campaign, and preliminary test sessions on the International Space Station are presented. Ground tests and the parabolic flight campaign results include preliminary inertia and thruster characterization of the combined Resonant Inductive Near-field Generation System/Synchronized Position Hold, Engage, Reorient, Experimental Satellites assembly. Preliminary on-orbit test results include data demonstrating wireless power transfer of approximately 30% and qualitative observations of electromagnetic formation flight with one Resonant Inductive Near-Field Generation System unit restrained and the other unit free floating.
This paper describes a novel miniature microcontroller based curve tracing circuit, which was designed to monitor the environmental effects on Silicon Carbide Junction Field Effect Transistor (SiC JFET) device performance, while exposed to the low earth orbit environment onboard the International Space Station (ISS) as a resident experiment on the 7th Materials on the International Space Station Experiment (MISSE7). Specifically, the microcontroller circuit was designed to operate autonomously and was flown on the external structure of the ISS for over a year. This curve tracing circuit is capable of measuring current vs. voltage (I-V) characteristics of transistors and diodes. The circuit is current limited for low current devices and is specifically designed to test high temperature, high drain-to-source resistance SiC JFETs. The results of each I-V data set are transmitted serially to an external telemetered communication interface. This paper discusses the circuit architecture, its design, and presents example results.
Tests of shielding effectiveness of Kevlar and Nextel onboard the International Space Station and the Foton-M3 capsule
Radiation assessment and protection in space is the first step in planning future missions to the Moon and Mars, where mission and number of space travelers will increase and the protection of the geomagnetic shielding against the cosmic radiation will be absent. In this framework, the shielding effectiveness of two flexible materials, Kevlar and Nextel, were tested, which are largely used in the construction of spacecrafts. Accelerator-based tests clearly demonstrated that Kevlar is an excellent shield for heavy ions, close to polyethylene, whereas Nextel shows poor shielding characteristics. Measurements on flight performed onboard of the International Space Station and of the Foton-M3 capsule have been carried out with special attention to the neutron component; shielded and unshielded detectors (thermoluminescence dosemeters, bubble detectors) were exposed to a real radiation environment to test the shielding properties of the materials under study. The results indicate no significant effects of shielding, suggesting that thin shields in low-Earth Orbit have little effect on absorbed dose.
Contraction theory approach to generalized decentralized cyclic algorithms for global formation acquisition and control
This paper presents a new approach to distributed nonlinear formation control, inspired by recent results on properties of cyclic topologies. Tools from contraction theory are used in the analysis of nonlinear control laws that only employ local information to globally converge to a formation. Specifically, a generalization of the cyclic pursuit extended to develop properties not addressed before such as non-rotating arrays, global convergence to a specific size, and time/state varying gains. Experiments on the International Space Station using the SPHERES testbed validate their properties and effectiveness for formation flight missions where specific array geometry is a metric of interest.
PCsat was designed and built as a student project at the US Naval Academy and launched on 29 Sept 2001 on the Kodiak Star mission as an experimental communications payload to not only introduce students to space systems engineering, but also to begin a series of experiments in low cost spacecraft telemetry system and data communications for mobile satellite users. An additional unique feature of PCsat was the integration of multiple worldwide Internet linked ground stations allowing around the world access to satellite telemetry and communications live from anywhere. PCsat was a complete success and it has been used by thousands of users in its first 9 months of flight. It has validated the viability of our using off-the-shelf AX.25 for all Telemetry Command and Control as well as supporting a bent-pipe mission. As our first satellite, we have a lot of lessons learned and experiences with spacecraft operations and many ideas for the future. This paper sumarizes the design details for PCsat and highlights of the first year in space including what we have learned and what new experiments we want to do on our nextcommunications mission.
Flight controllers manage the orientation and modes of eight large solar arrays that power the International Space Station (ISS). The task requires generating plans that balance complex constraints and preferences. These considerations include context-dependent constraints on viable solar array configurations, temporal limits on transitions between configurations, and preferences on which considerations have priority. The Solar Array Constraint Engine (SACE) treats this operations planning problem as a sequence of tractable constrained optimization problems. SACE uses constraint management and automated planning capabilities to reason about the constraints, to find optimal array configurations subject to these constraints and solution preferences, and to automatically generate solar array operations plans. SACE further provides flight controllers with real-time situational awareness and what-if analysis capabilities. SACE is built on the Extensible Universal Remote Operations Planning Architecture (EUROPA) model-based planning system. EUROPA facilitated SACE development by providing model-based planning, built-in constraint reasoning capability, and extensibility. This article formulates the planning problem, explains how EUROPA solves the problem, and provides performance statistics from several planning scenarios. SACE reduces a highly manual process that takes weeks to an automated process that takes tens of minutes.
The Middeck Active Control Experiment Reflight (MACE II) Program was the first on-orbit demonstration of adaptive structural control technology and the first active science experiment flown aboard the International Space Station. Our program objectives were to (1) greatly decease the need to modeling and ground testing to develop controllers and (2) allow for autonomous configuration of the control system to changing dynamic characteristics and sensor/actuator failures. This paper discusses the development of the MACE II program, an overview of the technical success of the MACE II mission, and lessons learned from both a technical and programmatic standpoint dealing with the Space Test Program and NASA.