Design and Operational Elements of the Robotic Subsystem for the e.deorbit Debris Removal Mission

This paper presents a robotic capture concept that was developed as part of the e.deorbit study by ESA. The defective and tumbling satellite ENVISAT was chosen as a potential target to be captured, stabilized, and subsequently de-orbited in a controlled manner. A robotic capture concept was developed that is based on a chaser satellite equipped with a seven degrees-of-freedom dexterous robotic manipulator, holding a dedicated linear two-bracket gripper. The satellite is also equipped with a clamping mechanism for achieving a stiff fixation with the grasped target, following their combined satellite-stack de-tumbling and prior to the execution of the de-orbit maneuver. Driving elements of the robotic design, operations and control are described and analyzed. These include pre and post-capture operations, the task-specific kinematics of the manipulator, the intrinsic mechanical arm flexibility and its effect on the arm's positioning accuracy, visual tracking, as well as the interaction between the manipulator controller and that of the chaser satellite. The kinematics analysis yielded robust reachability of the grasp point. The effects of intrinsic arm flexibility turned out to be noticeable but also effectively scalable through robot joint speed adaption throughout the maneuvers. During most of the critical robot arm operations, the internal robot joint torques are shown to be within the design limits. These limits are only reached for a limiting scenario of tumbling motion of ENVISAT, consisting of an initial pure spin of 5 deg/s about its unstable intermediate axis of inertia. The computer vision performance was found to be satisfactory with respect to positioning accuracy requirements. Further developments are necessary and are being pursued to meet the stringent mission-related robustness requirements. Overall, the analyses conducted in this study showed that the capture and de-orbiting of ENVISAT using the proposed robotic concept is feasible with respect to relevant mission requirements and for most of the operational scenarios considered. Future work aims at developing a combined chaser-robot system controller. This will include a visual servo to minimize the positioning errors during the contact phases of the mission (grasping and clamping). Further validation of the visual tracking in orbital lighting conditions will be pursued

Coupled Control of Chaser Platform and Robot Arm for the e.Deorbit Mission

The e.Deorbit mission is devoted to safely remove Envisat from its orbit by robotic capture means. The major challenges in the close range are the motion synchronisation between the Chaser and the Target satellite Envisat and the coupled control during capture employing the robot arm. This paper is devoted to the coupled control phase, during which the Chaser performs station keeping at the Capture Point, which is a point relative to the Target in the Target body frame, while the robot is grasping the Target. The robot arm has to place the end-effector at the Grasping Point, a well-defined position at the Target's launch adapter ring, while compensating the station keeping errors of the Chaser platform. The impedance controlled robot operates in operational space coordinates defining the pose of the robot end-effector with respect to the Grasping Point and also directly controls the robot joint configuration. The bandwidths of the two controllers considered in this study differ by more than two orders of magnitude, allowing independent control design of the two. The overall performance of the coupled control in terms of station keeping performance for the Chaser and positioning performance of the end-effector is demonstrated in Monte Carlo simulations

GNC Architecture for the e.Deorbit Mission

The GNC architecture presented in this paper has been developed in the frame of e.Deorbit phase B1. The architecture is dedicated to approach and capture the uncooperative target satellite Envisat, comprising ascent from launch orbit to the target orbit, rendezvous with the target satellite, capture and stabilization of the coupled system and de-orbiting. The homing and closing trajectories are based on e/i separation allowing a passively safe approach until the proximity operations begin. The chaser has to synchronize its motion with the target due to its large dimensions. The safety monitoring concept is briefly discussed. The propellant budget and the GNC performance requirements are consolidated by Monte Carlo simulations

High Risk of Anal and Rectal Cancer in Patients With Anal and/or Perianal Crohn’s Disease

International audienceBackground & AimsLittle is known about the magnitude of the risk of anal and rectal cancer in patients with anal and/or perineal Crohn’s disease. We aimed to assess the risk of anal and rectal cancer in patients with Crohn’s perianal disease followed up in the Cancers Et Surrisque Associé aux Maladies Inflammatoires Intestinales En France (CESAME) cohort.MethodsWe collected data from 19,486 patients with inflammatory bowel disease (IBD) enrolled in the observational CESAME study in France, from May 2004 through June 2005; 14.9% of participants had past or current anal and/or perianal Crohn’s disease. Subjects were followed up for a median time of 35 months (interquartile range, 29–40 mo). To identify risk factors for anal cancer in the total CESAME population, we performed a case-control study in which participants were matched for age and sex.ResultsAmong the total IBD population, 8 patients developed anal cancer and 14 patients developed rectal cancer. In the subgroup of 2911 patients with past or current anal and/or perianal Crohn’s lesions at cohort entry, 2 developed anal squamous-cell carcinoma, 3 developed perianal fistula–related adenocarcinoma, and 6 developed rectal cancer. The corresponding incidence rates were 0.26 per 1000 patient-years for anal squamous-cell carcinoma, 0.38 per 1000 patient-years for perianal fistula–related adenocarcinoma, and 0.77 per 1000 patient-years for rectal cancer. Among the 16,575 patients with ulcerative colitis or Crohn’s disease without anal or perianal lesions, the incidence rate of anal cancer was 0.08 per 1000 patient-years and of rectal cancer was 0.21 per 1000 patient-years. Among factors tested by univariate conditional regression (IBD subtype, disease duration, exposure to immune-suppressive therapy, presence of past or current anal and/or perianal lesions), the presence of past or current anal and/or perianal lesions at cohort entry was the only factor significantly associated with development of anal cancer (odds ratio, 11.2; 95% CI, 1.18-551.51; P = .03).ConclusionsIn an analysis of data from the CESAME cohort in France, patients with anal and/or perianal Crohn’s disease have a high risk of anal cancer, including perianal fistula–related cancer, and a high risk of rectal cancer