High-precision, temperature control technology is currently an important research field in spacecraft thermal control. High-precision temperature control based on grading-structure and PID-feedback strategies determine by theoretical analysis and grading a thermal control experiment is proposed in this paper. A sensitivity analysis of the key parameters influencing temperature control precision is investigated. The key parameters mainly include the inner emissivity of the transition section εt, outer emissivity of the central section εc, effective emissivity from the transition section to the central section εi/o, inner emissivity of the central section εi, outer emissivity of the equipment εeq, outer emissivity of the mounting plate εd, electronic equipment power Pe, and the conductivity coefficient of the equipment mounting insulation pad λ. Both the theoretical and experimental results show that the strategies developed during this research can achieve temperature control precision better than 0.05°C (or ±0.025°C). Parameters εt, εeq, and εd not only influence the temperature level, but also influence steady time. Pe, εc, and εi only influence the temperature level. εi/o not only influences the temperature level, but also influences temperature control precision. Thermal conductivity λ influences temperature level rather than temperature control precision because of the active temperature control of the mounting plate. This study provides a new method for the high-precision thermal control of equipment in spacecraft and specifies new directions for future research work.
A new subsurface sampling device is proposed for use in small-body exploration. The device proposed has a multi-stage telescopic structure that is extended into regolith using high-pressure gas. High-pressure gas is also used to collect the sample. Since the device proposed has no actuator, it is expected to be highly reliable. We experimentally demonstrated that this device can excavate a dummy regolith layer up to a depth of 1 m and collect sufficient samples located deeper than 1 m for in-situ analysis. These results indicate that the device proposed is a viable candidate for actual exploration missions.
Due to the lack of matched dedicated small satellite launch vehicles, launch opportunities as a rideshare or piggyback using a highly reliable launch system has become increasingly important for small satellite developers. The objective of this paper is to provide an aggregated value method as a strategy for developers to evaluate launch opportunities, as well as an approach for the launchers to capture the market dynamics. Based on an up-to-date launch record, a reliable launch database for multi-attribute evaluation is established. Efforts are made to quantify the abstract and concrete attributes of launch systems. An aggregated preference value model is developed, translating different inherited capabilities of launch systems into integrated preference value as a reference for decision-making. The preference values of the launch opportunities of different launch vehicles are explored in a case study by the method proposed, and its feasibility and applicability for small satellite launch system evaluation tasks is validated.
The satellite platform BIROS is the second technology demonstrator of DLR’s ‘FireBIRD’ space mission aiming to provide infrared remote sensing for early fire detection. Among several mission goals and scientific experiments, to demonstrate a high-agility attitude control system, the platform is actuated with an extra array of three orthogonal ‘High-Torque-Wheels.’ However, to enable agile reorientation, a challenge arises from the fact that time-optimal slew maneuvers are, in general, not of the Euler-axis rotation type; especially whenever the actuators are constrained independently. Moreover, BIROS’ on-board computer can only accommodate rotational acceleration commands twice per second. The objective is therefore to find a methodology to design fast slew maneuvers while considering a highly dynamic plant commanded by piecewise-constant sampled-time control inputs. This is achieved by considering a comprehensive analytical nonlinear model for spacecraft equipped with reaction wheels and transcribing a time-optimal control problem formulation into a multi-criteria optimization problem. Solutions are found with a direct approach using the trajectory optimization package ‘trajOpt’ of DLR-SR’s optimization tool, Multi-Objective Parameter Synthesis (MOPS). Results based on numerical simulations are presented to illustrate this method.
Multi-rotor unmanned aerial vehicles (UAVs) are used in various applications because they can hover and take off and land vertically. Although they are useful for civilian applications, their cruise flight speeds are limited owing to the generation of a pitching moment in a uniform flow. However, aerodynamic forces acting on multi-rotor UAVs have not been precisely examined. The effects of the body-yaw angle, body-pitch angle, and distance between rotors on the pitching moment and thrust in a uniform flow are important considerations when designing UAVs. Furthermore, rotor flow interaction can affect the rotor performance in horizontal flight. The objective of the present study is to examine the thrust and pitching moment of a quad-rotor UAV in a uniform flow using different configurations. First, the rotor thrust and pitching moment on two rotors were measured while changing the relative rotor positions in a wind tunnel. Second, the thrust and moment of a quad-rotor UAV were measured at different yaw directions, pitch angles, and rotors distances. Experiment results clarify that maintaining the yaw direction in a plus configuration, rather than an X configuration, with regard to the flow direction can reduce the pitching moment.