The performance of an elecrodynamic tether orbit transfer system was analyzed in consideration of the tether lifetime in relation to the possible impact of debris to examine the possibility of its application to round-trip transportation missions between near-earth orbits. The mass, the electric power, and the mission duration of a tether orbit transfer system were determined by using the operating principles of an electrodynamic tether, with the mission analysis based on a simplified orbit transfer analysis model of a low-thrust thruster for representative parameters. The results were compared with those of an ion thruster orbit transfer system. A tether lifetime was determined by using a “ORDEM96” space debris model produced by NASA and the relation of impact cross-section between tether wire and debris. The results showed the existence of a lower limit of mission duration for each altitude of arrival orbit and a higher limit of arrival orbit altitude for each mission duration, and the increase of tether length or the number of tethers was not necessarily effective in regard to tether lifetime and the possibility of debris impact. The results also showed that the tether orbit transfer system had a mass advantage when compared to the ion thruster orbit transfer system for the same missions up to an altitude of 6,000 km.
In this paper we propose a new method known as “the stacking method” to detect small pieces of unknown GEO debris, in which several images taken with a CCD camera are used to detect this debris. With this method, the streaks of stars are completely eliminated, and the sky background fluctuation decreases significantly. This allows the detection of very dark debris that is not visible on a single image. We tested this method by using the 45 cm telescope at the Yatsugatake Observatory and a small CCD camera manufactured by Nakanishi Image Laboratory (N.I.L). The globular cluster M13 was observed to evaluate the method and to calculate the limiting magnitude. The three regions of the geostationary orbit were also observed to search for unknown GEO debris. One possible piece of GEO debris about 1 m big was detected as a result of analysis that used the stacking method. The limiting magnitude shows that we can detect GEO debris of about 50 cm in size. With this method, by means of observation using the facilities at the Bisei Spaceguard Center (BSGC), a 1 m telescope, and an SITe CCD camera, we may be expected to detect GEO debris of about 10 cm in size.
Based on Hill guidance, the optimization of trajectories for the manned maneuvering unit rescuing an astronaut or equipment that becomes separated from a space station is studied because of minimum fuel, rendezvous accuracy, and time constraint requirements. The Hill guidance targeting errors induced by navigation error, target measurement error, and actuation error are analyzed. The minimum fuel solutions for 17 typical cases are found, and designing rules for the rescue trajectories are developed. A multi-impulse Hill guidance scheme is presented for simultaneously realizing accurate rendezvous and saving energy. Simulation results reveal that the multi-impulse scheme is much more superior to the conventional double-impulse Hill guidance scheme in rendezvous accuracy and consumes nearly the same amount of fuel as the later does.
A numerical method has been developed for the analysis of interactional aerodynamics between helicopter rotor and fuselage in forward flight. A 3-D steady compressible Euler solver is used to compute time-averaged interactional effects between the rotor and the fuselage. The rotor is modeled as an actuator disk with zero thickness carrying pressure jump across it. Collective and cyclic pitch angles are calculated to satisfy the rotor trim condition. Unstructured meshes are used to model complex rotor-fuselage configurations. Calculations are performed for two generic helicopter fuselage geometries. The results are compared with available experimental data for validation.
The performance of pulse detonation engines was analytically estimated by using a simple model. A pulse detonation engine was modeled as a straight tube. One end of the tube was closed and the other was open, and a detonation wave was ignited at the closed end. One cycle of the pulse-detonation-engine operation was divided into three phases: combustion, exhaust, and filling phases. The combustion and exhaust phases were theoretically analyzed with some simplifications, using the Hugoniot relation for the Chapman-Jouguet detonation wave and flow relations for self-similar rarefaction waves. Based on the simplified theoretical analysis, useful formulas for impulse density per one-cycle operation and time-averaged thrust density were derived.
Self-filed magneto-plasma dynamic (MPD) viscous flows are numerically investigated. The axisymmetric compressible Navier-Stokes equations with the Lorentz force and Joule heating, the equation of magnetic induction derived from Maxwell’s equations with Ohm’s law, and the continuity equation of electrons are simultaneously solved with the use of an implicit time-marching method based on the LU-SGS scheme. Partially ionized flows in the experimental MPD thruster are simulated and compared with the experimental results. The calculated current stream lines and the pressure of the cathode tip are found to agree well with the experiments. The values of the pressure of the cathode tip and the thrust are also numerically predicted by changing the distance from the cathode tip to the anode.
The present paper proposes a new approach to control flow separation around a body. Flow separation is controlled by inserting simple tabs inside the separated region to suppress the reverse flow action. This is expected to increase the pressure in the base region of the body, thus reducing drag. Moreover, flow instability is also expected to decrease because of change in the wake profile. The cases considered in the present investigation are flows around a circular cylinder at M=0.6 and 0.73. Tabs having lengths of 10% and 20% of the cylinder diameter were used. The results show that the base pressure of the cylinder can be increased when these tabs are inserted inside the separated region. The smallest drag on the cylinder/tab body was achieved when the two pairs of tabs were installed on both sides of the cylinder at angles of ±120° and ±140°, measured from the front stagnation point of the cylinder. Compared to the plain cylinder, drag was reduced by 32% at M=0.6 and by 18% at M=0.73. Schlieren photography reveals that the vortex formation length is increased when the tabs are installed. Moreover, the tabs greatly suppress the level of pressure fluctuations on the cylinder surface. This can be attributed to change in the wake profile that is associated with drag reduction. Furthermore, the frequency of the Karman vortex street is also increased. The analysis of the results was assisted by numerical calculations based on Large Eddy Simulation (LES). From these results, five significant effects of the tabs were identified: restriction of the reverse flow action, trapping of vorticity in the region upstream of the tabs, suppression of the shear layers’ movement, more rapid vortex roll-up downstream of the body, and reduced strength of the downstream vortices.