A position control method for precise formation flying is proposed and evaluated in this paper. We focus on a simple case where the distance between two spacecraft in the along-track direction must be kept constant. Major perturbations such as the J₂ gravitational perturbation and atmospheric drag are taken into account, and the control effort necessary to maintain the distance constant is estimated. Numerical simulations validate the analytical results.

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A simplified calculation method for estimating a flight limit load of the V-band clamp separation shock was established. With this method, the flight limit load is estimated through addition of an appropriate envelope margin to the results acquired with the simplified analysis method proposed in our previous paper. The envelope margin used in the method was calculated based on the reviews on the differences observed between the results of a pyroshock test and the analysis. Using the derived envelope margin, a calculating formula of the flight limit load, which envelopes the actual pyroshock responses with a certain probability, was developed. Based on the formula, flight limit loads for several actual satellites were estimated and compared to the test results. The comparative results showed that the estimated flight limit loads appropriately envelope the test results, which confirmed the effectiveness of the proposed method.

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We propose a water/liquid nitrogen rocket engine as a new non-combustion type rocket engine. Liquid nitrogen is mixed with heated water and specific volume of nitrogen is increased by evaporation. Thrust force is obtained by exhaust of nitrogen gas through a nozzle with water particles. Results of previous experiments indicated a specific impulse is 60 % of the theoretically estimated value. By evaluating the characteristic exhaust velocity and other thrust characteristics, we found that the lower-than-expected specific impulse is due to insufficient propellant mixing and heat transfer between heated water and liquid nitrogen in the mixing chamber. We also performed high-speed imaging experiments to visualize impinging and mixing of propellants. Results indicate that in the original injection setup, heat conveyed by heated water is not adequately transferred to the liquid nitrogen. An alternative injection pattern was tested, which resulted in a 10% increase in the characteristic exhaust velocity. In addition, we tested a new type of injector designed for more efficient mixing and heat transfer that exhibited 30 % increase in characteristic exhaust velocity. Furthermore, we modified the theoretical expression for the characteristic exhaust velocity based on multi-phased flow theory so that it agrees well with the experimental results.

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Recent research has been extending the applications of small satellites called microsatellites, nanosatellites, or picosatellites. To further improve capability of those satellites, a lightweight, active attitude-control mechanism is needed. This paper proposes a concept of inertial orientation control, an attitude control method using movable solar arrays. This method is made suitable for nanosatellites by the use of shape memory alloy (SMA)-actuated elastic hinges and a simple maneuver generation algorithm. The combination of SMA and an elastic hinge allows the hinge to remain lightweight and free of frictional or rolling contacts. Changes in the shrinking and stretching speeds of the SMA were measured in a vacuum chamber. The proposed algorithm constructs a maneuver to achieve arbitrary attitude change by repeating simple maneuvers called unit maneuvers. Provided with three types of unit maneuvers, each degree of freedom of the satellite can be controlled independently. Such construction requires only simple calculations, making it a practical algorithm for a nanosatellite with limited computational capability. In addition, power generation variation caused by maneuvers was analyzed to confirm that a maneuver from any initial attitude to an attitude facing the sun was justifiable in terms of the power budget.

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In order to clarify the temporal variations of internal ballistics during firing in a cascaded multistage impinging-jet (CAMUI)-type fuel grain, observations of instantaneous flow fields by numerical analysis along with instantaneous grain geometries were conducted. Two static firing tests were conducted under the same conditions, with the exception of firing duration, to obtain the temporal shapes of fuel grains and the characteristics of the regression progress. Two numerical analyses were conducted using the initial and instantaneous geometries to observe internal flow fields. A pair of vortices that is formed near the circumference of the grain due to the change in direction of the flow from the wall jet to the port flow induces a fan-like regression distribution. Two wall jets collide with each other at the center of the grain, roll up and form a fountain-like flow and a pair of gap-scale vortices. These vortices cause an unequal regression distribution on the end faces. On the downstream-end face, the vortices enhance the local regression rate near the axis of the grain. On the forward-end face, in addition to the region near the axis of the grain, the local regression rate at the reattachment points of the vortices increases. These gap-scale vortices disappear as regression progresses because of the dilation of the clearance between the fuel blocks. As a result, the regression rate distributions on both end faces become nearly flat with the progress of fuel regression.

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