ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test general relativity with an improvement in sensitivity of over three orders of magnitude, improving our understanding of gravity and aiding the development of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and our knowledge of the solar system; and to measure the time rate of change of the gravitational constant with an order of magnitude improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is an international project, with major contributions from Europe and China and is envisaged as the first in a series of ASTROD missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way, twowavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth, to achieve the ASTROD I goals. A second mission, ASTROD (ASTROD II) is envisaged as a three-spacecraft mission which would test General Relativity to 1 ppb, enable detection of solar g-modes, measure the solar Lense-Thirring effect to 10 ppm, and probe gravitational waves at frequencies below the LISA bandwidth. In the third phase (ASTROD III or Super-ASTROD), larger orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below the ASTROD II bandwidth.
Interest in autonomous planetary precision landing missions has been increasing in the scientific and engineering community, and is likely to continue to do so for the foreseeable future. As an enabling technology in the context of lunar landing, DLR, German Aerospace Center has been developing a terrain absolute navigation system that matches craters detected in image data to globally available lunar crater maps. The proposed Crater Navigation (CNav) system is adaptive, comprising three different crater matching methods that are specifically tailored to different navigation conditions encountered during the vehicle descent, so that it may be used as a stand-alone navigation sensor that can be closely integrated with a lander guidance, navigation, and control system to enable reliable absolute navigation throughout the entire descent phase of a mission. As robustness is a vital aspect to mission success, the CNav system includes verification mechanisms that ensure high dependability of the resulting navigation solution. This robustness is verified separately for all of the three different matching techniques presented in this paper. Closed-loop performance of the matchers is demonstrated as well, both for simulated image data sets, as for navigation camera images acquired during the Chinese Chang'e-3 landing mission. Successful uninterrupted estimation of the entire Chang'e-3 kinematic vehicle state during the powered descent until a final altitude of 350 m above ground, with neither known camera calibration nor inertial measurement unit data available, showcases the potential of the CNav system.
Since 2010 the German Aerospace Center (DLR) is working on the project ATON (Autonomous Terrain-based Optical Navigation). Its objective is the development of technologies which allow autonomous navigation of spacecraft in orbit around and during landing on celestial bodies like the Moon, planets, asteroids and comets. The project developed different image processing techniques and optical navigation methods as well as sensor data fusion. The setup-which is applicable to many exploration missions-consists of an inertial measurement unit (IMU), a laser altimeter, a star tracker and one or multiple navigation cameras. In the past years, several milestones have been achieved. It started with the setup of a simulation environment including the detailed simulation of camera images. This was continued by hardware-in-the-loop tests in the Testbed for Robotic Optical Navigation where images were generated by real cameras in a simulated downscaled lunar landing scene. Data was recorded
Future exploration missions require advanced optical sensors for precise navigation and landing site evaluation. The Testbed for Robotic Optical Navigation (TRON) is a Hardwarein-the-Loop test environment, with the purpose to support the development of optical navigation technology, and to qualify breadboards to TRL 4, and to qualify flight models to TRL 5-6. In this paper the design and ongoing realization of TRON is discussed. The first application of TRON is to simulate relevant parts of the lunar landing. After illustrating the concept, the building blocks of the laboratory are explained in detail. These are the simulation of the scaled dynamics via a 7-DOF robot, the simulation of the optical environment via a black out system and a lighting system, and the simulation of the terrain geometry via scaled 3D terrain models. With modifications TRON can also provide relevant environments for Mars, asteroids and moons.
International audienceAutonomous soft, safe and precise landing on celestial bodies like the Moon, planets and asteroids is still a challenging task for future exploration missions. To achieve a maximum of payload mass landed on the target body the trajectories of landing vehicles need to be (fuel) optimized. In order to allow an adjustability of the trajectory and a compensation of disturbances for all vehicles so far a thrust modulation is required. The drawback is that currently no main engine is available which allows the needed thrust modulation for an efficient, robust and safe landing on a celestial body like the Moon. The technology of the Apollo missions is not available anymore.Most planned lunar missions rely on the modulation capability of multiple engines where in some cases the thrust of the auxiliary engines for modulation is in the order of main engine thrust. This approach requires a large number of smaller engines to achieve the needed thrust modulation adding complexity and increasing the probability of failure. This paper shows a different approach to compute and control optimal trajectories for landing vehicles. It provides a new method for computing fuel efficient optimal trajectories which require minimal thrust modulation. A corresponding tracking control scheme is presented which allows the pre-computed optimal trajectory to be followed. The robustness of the method is discussed with results of a simulation
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