Interaction between a body and its environment during a cometary fly-by

The surface of a spacecraft is submitted to the bombardment of dust grains and neutral molecules during an atmospheric re-entry or a cometary fly-by. These particles create secondary ions and electrons which form a plasma cloud around the body and control the electric potential of its surface. Computer simulation models are used to predict the structure and dynamic behaviour of the charged particle density distribution for the cases of planar and cylindrical bodies. It is found that an ion and an electron layer form in the vicinity of the surface at distances of the order of the ion and electron Debye lengths, respectively. The potential of the surface is positive on the average and is a function of the electron mean kinetic energy. A positive potential barrier develops at the location of the ion layer and its height is governed by the sum of the electron and ion mean kinetic energies. The threat caused by this interaction to the spacecraft and its instrumentation is discussed and an in-situ observation of this phenomenon is proposed as a possible diagnostic technique of the environment.     

A passive millimeter wave camera for aircraft landing in lowvisibility conditions

Fog and low visibility conditions have hampered aviation since its inception. Fog-related accidents are numerous, and canceled take-offs and landings due to fog and low visibility conditions (Cat III) have significant economic impact on airlines, parcel carriers and general aviation. Millimeter waves have good propagation properties in weather and give adequate spatial resolution when used to image the forward scene. Passive millimeter wave focal plane array cameras are new sensors which, integrated into future guidance and landing systems, promise to be an effective aid, or alternative, to existing technology for aircraft landings and take-offs under Cat III conditions. They can produce visual-like radiometric images at real time frame rates (up to 30 Hz), and are directly amenable to image fusion with infrared and visible images. TRW has been actively involved in developing and productizing this technology both at the hardware and the system levels     

Star wars brought to earth

This article considers the thinking behind, and the ramifications of, President Reagan's Star Wars ‘vision’. The author argues that the Strategic Defense Initiative (SDI) is incompatible with other aspects of the Reagan administration's own defence policies and that the ‘security shield’ version of it would make future US-Soviet arms agreements impossible. Only the so-called ‘prudent hedge’ research looks viable in the longer term. The SDI's main value will have been in bringing the USSR back to the negotiating table.     

Euler angle dilution of precision in GPS attitude determination

The geometric dilution of precision (GDOP) is a useful parameter that indicates the effectiveness of the GPS satellite geometry on the positional navigation performance. In this work, the concept of the dilution of precision is extended to the attitude navigation solution. A new set of parameters, referred to as the Euler angle dilution of precision (EADOP), is defined. The validity and the usefulness of the new parameters are verified through simulations. Two scenarios involving a stationary platform and a moving platform are investigated. The results show that the EADOP is a good indication of the expected accuracy of the Euler angle estimates     

Modified input estimation technique using pseudoresiduals

An adaptive tracking filter for maneuvering targets is proposed using modified input estimation technique. Pseudoresiduals are defined using measurements and the velocity estimate at the hypothesized maneuver onset time. With the pseudoresiduals and a new target model representing transitions of nominal accelerations, a new input estimation method for tracking a maneuvering target is derived. Since the proposed detection technique is more sensitive to maneuvers than previous work, the shorter window length can be employed to detect and compensate target maneuvers. Also shown is that the tracking performance of the proposed filter is similar to that of interacting multiple model method (IMM) with 3 models, while computational loads of our method are drastically reduced     

Generation of satellite tracking profile: Problems and validation algorithms

Recently, as a satellite mission becomes complicated, it has been required to generate the schedule of satellite antenna movements automatically without relying upon operator’s ad hoc knowledge. To generate the satellite antenna schedule autonomously, this paper first addresses geometrical problems associated with the antenna scheduling and mission planning problems that can be formulated from satellite navigation and antenna orientation information. Then, based on the solutions of the geometrical problems, a set of antenna azimuth and elevation angles that enables the antenna to point towards the desired ground station is obtained systematically. Using the computed azimuth and elevation angles, the satellite tracking profile (TP) is generated, and to validate it, TP validation algorithms are developed.     

A new approach to the telescope operation method for satellite tracking using a time synchronization technique

For the development of a telescope that is capable of precisely tracking satellites and high-speed operation such as satellite laser ranging, a special method of telescope operation is required. This study aims to propose a new telescope operation method and system configuration for the independent development of a mount and an operation system which includes the host computer. Considering that the tracking of a satellite is performed in real time, communication and synchronization between the two independent subsystems are important. Therefore, this study applied the concept of time synchronization, which is used in various fields of industry, to the communication between the command computer and the mount. In this case, communication delays do not need to be considered in general, and it is possible to cope with data loss. Above all, when the mount is replaced in the future, only the general communication interface needs to be modified, and thus, it is not limited by replacement in terms of the overall system management. The performance of the telescope operation method developed in this study was verified by applying the method to the first mobile SLR system in Korea. This study is significant in that it proposed a new operation method and system configuration, to which the concept of time synchronization was applied, for the observation system that requires an optical telescope.     

DGPS/IMU integration-based geolocation system: Airborne experimental test results

This paper addresses differential global positioning system (DGPS)/inertial measurement unit (IMU) integration-based geolocation system developed for airborne remote sensing cameras. First, we provide a brief review on sensor calibration, alignment and sensor fusion as background material of this research. After presenting those background material, as a main part of this paper we present a geolocation algorithm designed for an airborne imaging system. The geolocation system developed is tested through actual airborne experiments. For the verification of the geolocation system developed, we compare initial stationary states of the airplane before-taking off with states after-landing. From the actual test results, we find that it is critical to do an accurate time synchronization between IMU, DGPS, and airborne images, and to compensate for the data delay occurred during the network transfer.     

Three-axis attitude determination using incomplete vector observations

Attitude determination refers to determining the orientation of a vehicle relative to its reference coordinate system. This paper presents a new algorithm for three-axis attitude determination using measurement vectors composed of incomplete vector components. The attitude determination performance of the proposed algorithm is compared with those of the TRIAD and QUEST algorithms in a simulation.