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.
Lunar capture guidance scheme using Lyapunov feedback control
A lunar orbital capture guidance law is presented for a spacecraft with electrical propulsion system using Lyapunov feedback control approach. Construction of the Lyapunov function candidate is based on orbital elements which consist of angular momentum and eccentricity vectors. Unlike the orbit transfer problem between closed orbits, the lunar capture problem has two constraints. One thing is that the spacecraft coming to the planet with hyperbola orbit conditions must be accomplished the closed orbit conditions before passing the first perilune. And the other one is that the perilune altitude of the spacecraft does not smaller than zero to prevent the crashing problem. For this reason, the variable gain approach is used to accomplish the closed orbit conditions rapidly.
The benefits of automated suturing devices in gynecologic endoscopic surgeries: the Endo Stitch and SILS Stitch.
Traditional laparoscopic suturing and knot tying requires a steep learning curve and is often the rate-limiting step in performing advanced laparoscopic gynecologic surgical procedures. It is particularly challenging due to difficulties with tissue handling and needle control while performing the procedure on a two-dimensional screen, oftentimes at unfavorable suturing angles. Automated suturing devices have greatly simplified the process and allow less-experienced surgeons to safely and efficiently perform laparoscopic suturing and knot tying. The Endo Stitch (Covidien, Mansfield, MA) is a 10-mm single-use suturing device that allows placement of multiple suture types during laparoscopic surgery, and simplifies the process of laparoscopic knot tying. The SILS Stitch (Covidien, Mansfield, MA) is based on the same technology as the Endo Stitch with the added advantage of articulation up to 75 degrees and rotation up to 360 degrees. This enables surgeons to operate in tight spaces during advanced laparoscopic procedures, and to reach tissues in their natural anatomical position rather than pulling or manipulating tissue into the suturing device. Newer technologies in laparoscopic surgery, such as the Endo Stitch and SILS Stitch, may allow gynecologic surgeons to expand their surgical repertoire of advanced laparoscopic procedures.