Introduction to Design and Optimization of HVAC System of Spacecraft
From Manned spacecraft and space shuttle to the scale of space station, the technology of manned spacecraft has been developing. The astronauts have to work and live in the cabin for much longer time. Therefore, the spacecraft environmental control and life support systems is not only asked to control the cabin environment parameters within a certain range, but also to ensure the cabin environment with high thermal comfort which can meet the physical and psychological needs of astronauts, also improve the efficiency of equipments, structural components in the manned space System. The ventilation, air conditioning problems and the air flow arrangement of the cabin directly affect the environmental parameters controlling and the thermal comfort of the cabin environment. So, it has an important significance to research the ventilation, air quality, thermal environment and comfort of the astronauts in the cabin under the microgravity condition. There is 10 -3 ~ 10 -6 -g0 level of micro-gravity (g0=9.8 m2 /s) inside the cabin of spacecraft or the space station. At this point, the phenomena which are common with ground gravity such as natural convection, static pressure differential …
Introduction to Modularity and Reliability in Low Cost AOCSs
The use of off the shelf electronic components is now common in university and low cost satellites. The advantage against space qualified parts consists in a significant cost reduction, a wider range of components selection, better second sourcing capabilities and an effective reuse of existing technologies, devices, circuits and systems from other engineering domains. Commercial Off The Shelf Components (COTS) are sometimes subject to reliability requirements which are often tougher than those applied to space devices, as they have to be used in markets (e.g., automotive) where safety concerns and the huge number of systems manufactured set demanding constraints on the components. Yet, the drawbacks of COTS components and other low cost design methods, mostly in space missions, remain the higher sensitivity to radiation-induced effects and the reduced system level tolerance to faults. Compensation of these weak points is possible with the development of appropriate design techniques and their proper application throughout the lifecycle of the system, from system level design down to manufacturing. The use of COTS components has thus enormous capabilities and benefits in, but not limited to, small satellite missions. Low cost spacecraft design not only refers to COTS devices but to several other aspect of the design of a spacecraft. A low-cost approach to spacecraft design will have a huge impact on the development of space technology in the future, provided that system-level approaches are applied to the design in order to contemporarily reduce cost and increase reliability. This chapter will analyze several aspects in the low cost and high reliability design of a specific spacecraft subsystem, namely an Attitude and Orbit Control System (AOCS), developed at Politecnico di Torino as part of the AraMiS modular architecture for small satellites. We will show how an appropriate mixture of innovative techniques can produce a high reliability and high performance, low cost AOCS. The topics will be covered at both system and subsystem level, with references to commercially available devices (sensors, actuators, drivers and microcontrollers) and following the object-oriented modeling used for both system management, subsystem development and programming. This chapter will therefore present several technical solutions (at different design levels) which the authors have developed and applied to the development of the AraMiS built-in AOCS…
Introduction to Spacecraft Relative Orbital Motion
The relative orbital motion problem may now be considered classic, because of so many scientific papers written on this subject in the last few decades. This problem is also quite important, due to its numerous applications: spacecraft formation flying, rendezvous operations, distributed spacecraft missions. The model of the relative motion consists in two spacecraft flying in Keplerian orbits due to the influence of the same gravitational attraction center (see Fig. 1). The main problem is to determine the position and velocity vectors of the Deputy satellite with respect to a reference frame originated in the Leader satellite center of mass. This non-inertial reference frame, traditionally named LVLH (Local-Vertical-Local-Horizontal) is chosen as follows: the Cx axis has the same orientation as the position vector of the Leader with respect to an inertial reference frame originated in the attraction center; the Cz axis has the same orientation as the Leader orbit angular momentum; the Cy axis completes a right-handed frame. Consider ω = ω(t) the angular velocity of the LVLH reference frame with respect to an inertial frame originated in the attraction center. By denoting rc the Leader position vector with respect to an inertial frame originated in O (the attraction center), fc = fc (t) the true anomaly, ec the eccentricity and pc the semilatus rectum of the Leader orbit, it follows that vector ω has the expression: where μ > 0 is the gravitational parameter of the attraction center and Δr; Δv represent the relative position and relative velocity vectors of the Deputy spacecraft with respect to LVLH at the initial moment of time t0 ≥ 0. The analysis of relative motion began in the early 1960s with the paper of Clohessy and Wiltshire (Clohessy & Wiltshire (1960)), who obtained the equations that model the relative motion in the situation in which the chief spacecraft has a circular orbit and the attraction force is not affected by the Earth oblateness. They linearized the nonlinear initial value problem that models the relative motion by assuming that the relative distance between the two…
Introduction to Physics-Based Control Methods
Spacecraft control suffers from inter-axis coupling regardless of control methodology due to the physics that dominate their motion. Feedback control is used to robustly reject disturbances, but is complicated by this coupling. Other sources of disturbances include zero-virtual references associated with cascaded control loop topology, back-emf associate with inner loop electronics, poorly modeled or un-modeled dynamics, and external disturbances (e.g. magnetic, aerodynamic, etc.). As pointing requirements have become more stringent to accomplish missions in space, decoupling dynamic disturbance torques is an attractive solution provided by the physics-based control design methodology. Promising approaches include elimination of virtual-zero references, manipulated input decoupling, which can be augmented with disturbance input decoupling supported by sensor replacement. This chapter introduces these methods of physics-based control. Physics based control is a method that seeks to significantly incorporate the dominant physics of the problem to be controlled into the control design. Some components of the methods include elimination of zero-virtual reference, observers for sensor replacements, manipulated input decoupling, and disturbance-input estimation and decoupling. In addition, it will be shown that cross-axis coupling inherent in the governing dynamics can be eliminated by decoupling a normal part of the physics-based control. Physics-based controls methods produce a idealized feedforward …
Introduction to Middle Atmosphere: Discharge Phenomena
The layer between 10 and 100 km altitude in the Earth atmosphere is generally categorized as the middle atmosphere (Brasseur & Solomon, 1986). The boosting development of rocket and satellite technologies during the past 50 years has made it possible to directly probe the middle atmosphere (Brasseur & Solomon, 1986). Recently, transient luminous events (TLEs) open up another window; through observing the discharge phenomena in the middle atmosphere from both the ground and the space, the physical processes in this region can be inferred. Besides the present satellite missions (ISUAL, Tatiana-2, SPRITE-SAT, Chibis-M mission), future orbit missions include JEM-GLIMS, ASIM, TARANIS will soon join the efforts. These space missions provide the unique platforms to explore the plasma chemistry and atmospheric electricity in the middle atmosphere, and also investigate the possible TLE impact on spacecrafts. Discharge phenomena in the middle atmosphere The discharge phenomena in the middle atmosphere collectively carry the name of the transient luminous events (TLEs), owing to their fleeting nature (sub-milliseconds to tens of milliseconds) and high luminosity over the thunderstorms; see Fig. 1. The transient luminous events were accidentally observed in the ground observation (Franz et al., 1990) and Earth orbit observation (Boeck et al., 1992), and were soon recognized as the manifestations of the electric coupling between atmospheric lightning and the middle atmosphere/ionosphere. The thunderstorm plays the role of an electric battery in the atmosphere-ionosphere system. The thunderstorms, ~3000 of them at any time on Earth, generate a total electric current of 1.5 kA flowing into the ionosphere, and sustain the electric potential ~200 MV of the ionosphere (Volland, 1987). With the thunderstorms, the electric energy gradually accumulates in the middle atmosphere and a part of the deposited energy later is released as the luminous TLEs, in a way similar to the capacitor discharge. However, how the light emission and electric…
Surface Reflectance Characteristics and Snow Surface Variations from GNSS Reflected Signals
Nasser Najibi1, 2, 3 and Shuanggen Jin1 Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai, China University of Chinese Academy of Sciences, Beijing, China The City University of New York, The City College…
Sea Level Changes Along Global Coasts from Satellite Altimetry, GPS and Tide Gauge
Guiping Feng1, 2 and Shuanggen Jin1 Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai, China College of Marine Sciences, Shanghai Ocean University, Shanghai, China Introduction The average global sea level was rising…
High-order Ionospheric Effects on GPS Coordinate Time Series
Weiping Jiang1, Liansheng Deng2 and Zhao Li3 Research Centre of GNSS, Wuhan University, Wuhan, China School of Geodesy and Geomatics, Wuhan University, Wuhan, China Faculté des Sciences, de la Technologie et…
GPS-based Non-Gravitational Accelerations and Accelerometer Calibration
Andres Calabia1, 2 and Shuanggen Jin1 Shanghai Astronomcial Observatory, Chinese Academy of Sciences, Shanghai, China University of Chinese Academy of Sciences, Beijing, China Introduction Within the process of deriving satellite accelerations from…
