Trajectory correction maneuver design based on B-plane targeting for low-thruster
For the interplanetary mission, the spacecraft must require the trajectory correction maneuver (TCM) to reduce the trajectory error due to the influence of unexpected external perturbation forces. There are many kinds of researches focused on these TCM techniques for the impulsive thrust. Among them, the B-plane targeting method is mainly applied to the interplanetary mission as TCM method. However, there are brilliant developments in the propulsion systems; especially the electrical propulsion system is adopted in some spacecraft. Thus, it is necessary to design the TCM algorithm for such low-thruster for future interplanetary missions. Therefore, in this paper, the TCM algorithm for the low thrust such like electrical propulsion system is suggested to correct the target B-vector and target time to closest approach (TCA). To design the low thrust guidance scheme, the Lyapunov feedback control is used in this paper.
LYAPUNOV-BASED TRANSFER BETWEEN ELLIPTIC KEPLERIAN ORBITS
We present a study of the transfer of satellites between elliptic Keplerian orbits using Lyapunov stability theory specific to this problem. The construction of Lyapunov functions is based on the fact that a non-degenerate Keplerian orbit is uniquely described by its angular momentum and Laplace (- Runge-Lenz) vectors. We suggest a Lyapunov function, which gives a feedback controller such that the target elliptic orbit becomes a locally asymptotically stable periodic orbit in the closed-loop dynamics. We show how to perform a global transfer between two arbitrary elliptic orbits based on the local transfer result. Finally, a second Lyapunov function is presented that works only for circular target orbits.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.