In spaceflight, a path-constrained rendezvous is the process of moving an orbiting object from its current position to a desired position and velocity, in such a way that no obstacles are contacted along the way. It is a more constrained instance of the general problem of orbital rendezvous.
When no obstacles need consideration, the problem of rendezvous is straightforward, and many efficient algorithms are available to plan the necessary maneuvers. Depending on the desired time taken to accomplish the rendezvous, there are an infinite number of possible rendezvous paths.
The presence of obstacles posing a collision risk complicates the problem. The shortest-time or lowest-energy rendezvous might be made infeasible by obstacles, so a path requiring more time or more energy would have to be employed. For instance, if the purpose is to rescue an astronaut in distress on the far side of a large space station, speed is important. One may have to find quickly the rescue path requiring minimal time to execute, yet avoiding contact with the space station structure.
A natural object of study is the problem of maneuvering in the vicinity of a large orbiting sphere, since a collision with a more complex structure can be avoided by selecting rendezvous paths that avoid contact with a virtual sphere enclosing the structure. Early research considered the problem of departure and arrival points lying on the surface of an orbiting sphere. This led to a pair of necessary conditions called the tangential departure and tangential arrival conditions.
A.J. Grunwald, A. Abramovitz, S.R. Ellis. Interactive method for planning fuel-efficient proximity operations using visual optimization aids. 1995 IEEE International Conference on Systems, Man and Cybernetics. Intelligent Systems for the 21st Century, 2318–2323.
Der-Ren Taur, Victoria Coverstone-Carroll, John E. Prussing. (1995) Optimal Impulsive Time-Fixed Orbital Rendezvous and Interception with Path Constraints. Journal of Guidance, Control, and Dynamics 18:1, 54-60
Ismael Lopez, Colin R. McInnes. (1995) Autonomous rendezvous using artificial potential function guidance. Journal of Guidance, Control, and Dynamics 18:2, 237-241
Russel S. Wenzel, John E. Prussing. (1996) Preliminary study of optimal thrust-limited path-constrained maneuvers. Journal of Guidance, Control, and Dynamics 19:6, 1303-1309
In the context of spaceflight, launch period is the collection of days and launch window is the time period on a given day during which a particular rocket must be launched in order to reach its intended target. If the rocket is not launched within a given window, it has to wait for the window on the next day of the period. Launch periods and launch windows are very dependent on both the rocket's capability and the orbit to which it is going.
The Interplanetary Transport Network (ITN) is a collection of gravitationally determined pathways through the Solar System that require very little energy for an object to follow. The ITN makes particular use of Lagrange points as locations where trajectories through space can be redirected using little or no energy. These points have the peculiar property of allowing objects to orbit around them, despite lacking an object to orbit. While it would use little energy, transport along the network would take a long time.
Soyuz T-8 was a crewed mission to the Salyut 7 space station in 1983. Shortly into the mission, the spacecraft failed to dock with the space station due to an incident involving an antenna being torn off the craft by the protective launch shroud. After a fuel-consuming attempt made in darkness for an optical rendezvous with Salyut 7 resulted in an abort in order to avoid collision, it was decided to de-orbit T-8 two days into the mission in order to ensure that the spacecraft had a sufficient amount of propellant for the de-orbit maneuver. After de-orbiting, landing of the craft occurred normally.
In spaceflight, an orbital maneuver is the use of propulsion systems to change the orbit of a spacecraft. For spacecraft far from Earth an orbital maneuver is called a deep-space maneuver (DSM).
In astrodynamics, orbital station-keeping is keeping a spacecraft at a fixed distance from another spacecraft or celestial body. It requires a series of orbital maneuvers made with thruster burns to keep the active craft in the same orbit as its target. For many low Earth orbit satellites, the effects of non-Keplerian forces, i.e. the deviations of the gravitational force of the Earth from that of a homogeneous sphere, gravitational forces from Sun/Moon, solar radiation pressure and air drag, must be counteracted.
A space rendezvous is a set of orbital maneuvers during which two spacecraft, one of which is often a space station, arrive at the same orbit and approach to a very close distance. Rendezvous requires a precise match of the orbital velocities and position vectors of the two spacecraft, allowing them to remain at a constant distance through orbital station-keeping. Rendezvous may or may not be followed by docking or berthing, procedures which bring the spacecraft into physical contact and create a link between them.
DART, or Demonstration for Autonomous Rendezvous Technology, was a NASA spacecraft with the goal to develop and demonstrate an automated navigation and rendezvous capability. At the time of the DART mission, only the Roscosmos and JAXA had autonomous spacecraft navigation. Orbital Sciences Corporation (OSC) was the prime contractor for construction, launch and operation of the DART spacecraft with a project cost of US$110 million (2005). The contract was awarded in June 2001 and the spacecraft was launched on 15 April 2005. The mission ended prematurely, very shortly after an anomalous slow-velocity collision with its target spacecraft, having completed less than half of the original mission autonomous rendezvous objectives.
Spacecraft flight dynamics is the application of mechanical dynamics to model how the external forces acting on a space vehicle or spacecraft determine its flight path. These forces are primarily of three types: propulsive force provided by the vehicle's engines; gravitational force exerted by the Earth and other celestial bodies; and aerodynamic lift and drag.
Trajectory optimization is the process of designing a trajectory that minimizes some measure of performance while satisfying a set of constraints. Generally speaking, trajectory optimization is a technique for computing an open-loop solution to an optimal control problem. It is often used for systems where computing the full closed-loop solution is not required, impractical or impossible. If a trajectory optimization problem can be solved at a rate given by the inverse of the Lipschitz constant, then it can be used iteratively to generate a closed-loop solution in the sense of Caratheodory. If only the first step of the trajectory is executed for an infinite-horizon problem, then this is known as Model Predictive Control (MPC).
A gravity turn or zero-lift turn is a maneuver used in launching a spacecraft into, or descending from, an orbit around a celestial body such as a planet or a moon. It is a trajectory optimization that uses gravity to steer the vehicle onto its desired trajectory. It offers two main advantages over a trajectory controlled solely through the vehicle's own thrust. First, the thrust is not used to change the spacecraft's direction, so more of it is used to accelerate the vehicle into orbit. Second, and more importantly, during the initial ascent phase the vehicle can maintain low or even zero angle of attack. This minimizes transverse aerodynamic stress on the launch vehicle, allowing for a lighter launch vehicle.
Spacecraft collision avoidance is the implementation and study of processes minimizing the chance of orbiting spacecraft inadvertently colliding with other orbiting objects. The most common subject of spacecraft collision avoidance research and development is for human-made satellites in geocentric orbits. The subject includes procedures designed to prevent the accumulation of space debris in orbit, analytical methods for predicting likely collisions, and avoidance procedures to maneuver offending spacecraft away from danger.
DIDO is a MATLAB optimal control toolbox for solving general-purpose optimal control problems. It is widely used in academia, industry, and NASA. Hailed as a breakthrough software, DIDO is based on the pseudospectral optimal control theory of Ross and Fahroo. The latest enhancements to DIDO are described in Ross.
Spacecraft attitude control is the process of controlling the orientation of a spacecraft with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, etc.
A zero-propellant maneuver (ZPM) is an optimal attitude trajectory used to perform spacecraft rotational control without the need to use thrusters. ZPMs are designed for spacecraft that use momentum storage actuators. Spacecraft ZPMs are used to perform large angle rotations or rate damping (detumbling) without saturating momentum actuators, and momentum dumping without thrusters.
Named after I. Michael Ross and F. Fahroo, the Ross–Fahroo lemma is a fundamental result in optimal control theory.
Isaac Michael Ross is a Distinguished Professor and Program Director of Control and Optimization at the Naval Postgraduate School in Monterey, CA. He has published a highly-regarded textbook on optimal control theory and seminal papers in pseudospectral optimal control theory, energy-sink theory, the optimization and deflection of near-Earth asteroids and comets, robotics, attitude dynamics and control, orbital mechanics, real-time optimal control and unscented optimal control. The Kang–Ross–Gong theorem, Ross' π lemma, Ross' time constant, the Ross–Fahroo lemma, and the Ross–Fahroo pseudospectral method are all named after him.
The Clohessy–Wiltshire equations describe a simplified model of orbital relative motion, in which the target is in a circular orbit, and the chaser spacecraft is in an elliptical or circular orbit. This model gives a first-order approximation of the chaser's motion in a target-centered coordinate system. It is used to plan the rendezvous of the chaser with the target.
Orbital Mechanics for Engineering Students is an aerospace engineering textbook by Howard D. Curtis, in its fourth edition as of 2019. The book provides an introduction to orbital mechanics, while assuming an undergraduate-level background in physics, rigid body dynamics, differential equations, and linear algebra.
The Gemini Guidance Computer was a digital, serial computer designed for Project Gemini, America's second human spaceflight project. The computer, which facilitated the control of mission maneuvers, was designed by the IBM Federal Systems Division.
In orbital mechanics, low-thrust relative transfer is an orbital maneuver in which a chaser spacecraft covers a specific relative distance relative to the target spacecraft using continuous low-thrust system with specific impulse of the order of 4000-8000s. This is in contrast to conventional impulsive transfers in the orbit which uses thermal rocket engines to develop impulse of the order of 300-400s. Such type of transfer uses low-thrust propulsion systems such as electrically powered spacecraft propulsion and solar sail.
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