Dextre

Abstract: Free-flying robotic spacecraft play a significant role in the space industry today. Unlike ground-based robots, the manipulator motion in a space robot can cause undesirable disturbances to the spacecraft platform, causing its attitude to change, potentially disrupting communication and solar energy collection processes as a result. Thus, coordinated control of both the spacecraft attitude and the manipulator motion become essential for successful space operations. Though past research has developed dynamic models for spacecraft manipulators, the contribution of reaction wheels to the angular momentum of the entire system needs further consideration. This paper reformulates the dynamic equations of a free-flying space robot by taking the aspect of reaction wheels into account. A diagonalization method is introduced to decouple the highly nonlinear multi-input/multi-output system model. A novel adaptive variable structure control method is then applied to implement a robust coordination controller for the ...

Abstract: Canada has already delivered two of the main elements of its Mobile Servicing System (MSS) for the International Space Station (ISS) to NASA: the Mobile Base System (MBS) and the Space Station Remote Manipulator System (SSRMS) which was launched April 19 th , 2001. Currently under development is the MSS's most sophisticated robotic component, the Special Purpose Dexterous Manipulator (SPDM). This paper presents a brief overview of the SPDM system before describing in more detail several of the advanced control features of the SPDM. In particular this paper focuses on the implementation of automatic singularity avoidance and force-moment accommodation. Developmental test results are presented and key findings are summarized.

Abstract: NASA’s experience servicing the Hubble Space Telescope, including the installation of optical elements to compensate for a mirror man ufacturing error; replacement of failed avionics and worn -out batteries, gyros, thermal insulation and solar arrays; upgrades to the data handling subsystem; installation of far more capable instruments; and retrofitting the NICMOS experiment with a mechan ical cryocooler has clearly demonstrated the advantages of on -orbit servicing. This effort produced a unique astronomical observatory that has been operated successfully for several times its design life, and is orders of magnitude more capable than when it was launched. This paper discusses application the lessons learned from HST and our plans for servicing the Advanced X -ray Astrophysical Observatory, Orbital Maneuvering Vehicle, and the Space Station Freedom Customer Servicing Facility to future space observatories designed to operate in heliocentric orbits. It postulates the use of human and robotic in -space capabilities developed to support NASA’s exploration initiative; describes possible operational scenarios; and identifies the capabilities requi red to support future space observatories . I. In The Beginning CIENTISTS and engineers h ave been developing practical approaches to spaceflight and in -space operations since the w ritings of Tsiol kovsky, Oberth and the experiments of Robert Goddard in the early 20th century. In addition to discussing liquid -rocket propulsion using hydrogen and oxygen, multistage rockets, engine thrust, and escape velocities great detail, these visionaries also considered concepts such as space suits, space stations, and sp ace colonies based on solar power 1 . In the late 1940’s and early 1950’s, space enthusiasts such as Willy Ley and Wernher von Braun popularized the idea of spaceflight with books and a series of articles in Collier’s Magazine describing a detailed technical blueprint for space exploration. The series described everything from space taxis and space suits, to Moon shuttles and lunar bases, to the details of a massive manned Mars expedition. World War II and the Cold War provided the impetus to develop the laun ch vehicle technologies that provided access to space, and the early space program developed life support, communication, navigation, rendezvous and docking and EVA required for the manned lunar program of the 1960’s and early 1970’s . NASA’s attention was then turned to developing the infrastructure for a permanent presence in space and eventual manned missions to Mars. The original architecture called for space stations in orbit around the Earth and the Moon, and eventually Mars, with a shuttle to carry passengers to the LEO (Low Earth Orbit) st ation, where they could board lunar or Mars transfer vehicles. When funding for this program failed to materialize, plans were scaled back to building the LEO shuttle and space station. This LEO space station was originally conceived by JSC as a space operations center with a customer servicing facility where space vehicles could be assembled and fueled before beginning their mission, and later returned to the station (with the aid of a space tug) for servicing 2,3. Its role was later expanded to include scientific research in wide variety of areas, including astronomy, biology, fluid physics, life sciences, materials science, micro -gravity effects, pharmaceutical manufacturing, particle physics and the space environ ment. Ultimately, budget realities and cost growth caused the cancellation of plans for these on -orbit assembly and servicing facilities.