Sailcraft
Encyclopedia
For sailcraft referring to a boat etc., see
Sailcraft can also refer to sailing
skills
- sailboatSailboatA sailboat or sailing boat is a boat propelled partly or entirely by sails. The term covers a variety of boats, larger than small vessels such as sailboards and smaller than sailing ships, but distinctions in the size are not strictly defined and what constitutes a sailing ship, sailboat, or a...
- yachtYachtA yacht is a recreational boat or ship. The term originated from the Dutch Jacht meaning "hunt". It was originally defined as a light fast sailing vessel used by the Dutch navy to pursue pirates and other transgressors around and into the shallow waters of the Low Countries...
- dinghyDinghyA dinghy is a type of small boat, often carried or towed for use as a ship's boat by a larger vessel. It is a loanword from either Bengali or Urdu. The term can also refer to small racing yachts or recreational open sailing boats. Utility dinghies are usually rowboats or have an outboard motor,...
- ice boatIce boatAn ice boat is a boat or purpose-built framework similar in functional design to a sail boat but fitted with skis or runners and designed to run over ice instead of through water. Ice yachting is the sport of sailing and racing iceboats. Sailable ice is known in the sport as "hard water" versus...
- land yacht
Sailcraft can also refer to sailing
Sailing
Sailing is the propulsion of a vehicle and the control of its movement with large foils called sails. By changing the rigging, rudder, and sometimes the keel or centre board, a sailor manages the force of the wind on the sails in order to move the boat relative to its surrounding medium and...
skills
- In the context of spaceflight, Sailcraft is a short name for spacecraft endowed with sail for propulsion purposes. In principle, the sail and its supporting structures, or the sail system, are not restricted to be for solar-sail propulsion, but they could be designed for either laser or microwave propulsion (i.e. beam-driven propulsion) or, as recently proposed, for solar and beam-driven purposes. The key point – from the spacecraft design viewpoint – is the presence of a system with a surface overwhelming those of any other systems the spacecraft is composed of. This affects the geometrical and physical configurations of the spacecraft systems considerably. Nevertheless, the benefits from using a solar sailSolar sailSolar sails are a form of spacecraft propulsion using the radiation pressure of light from a star or laser to push enormous ultra-thin mirrors to high speeds....
would be enormous.
- The sail orientation is specified by its axis, or the unit vector, say, n orthogonal to the mean plane of the sail, usually put in the back sail semispace; the fronside of a sail is the side of its reflective layer (e.g. a very thin layer of AluminiumAluminiumAluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
), whereas the backside is the side of either its plastic support layer (e.g. KaptonKaptonKapton is a polyimide film developed by DuPont which can remain stable in a wide range of temperatures, from -273 to +400 °C...
) or the emissive layer (e.g. an ultra-thin film of ChromiumChromiumChromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
), if any. If the sail is perfectly flat (as often it is assumed to be), n is automatically determined. This axis definition is appropriate for orienting the sail naturally with respect to the direction of the local incident solar light. Thus, a sail orthogonal to the Sun-light and receiving the maximum fluxFluxIn the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as flow per unit area, where flow is the movement of some quantity per time...
of light has its axis at zero angle with the direction of the incident solar photons. In general, the sail axis is expressed as a function of some pair of angles, say, n(α, δ) that are defined in a suitable frame of referenceFrame of referenceA frame of reference in physics, may refer to a coordinate system or set of axes within which to measure the position, orientation, and other properties of objects in it, or it may refer to an observational reference frame tied to the state of motion of an observer.It may also refer to both an...
. These angles generally act as the control angles for orienting the sail.
- Some Design Parameters
- a key parameter in designing a sailcraft is the total spacecraft mass on the effective sail area ratio, named the sailcraft sail loading, often expressed in grams per square meter.
- together with the thermo-optical properties of the sail material (reflection, diffusion, absorption and emission of light), the sail loading determines the maximum solar-pressure acceleration the spacecraft undergoes at a certain distance from the Sun. This is the value of the thrust acceleration one could get if the sail were orthogonal to its Sun-line and at rest. In this case, the sailcraft acceleration would be totally radial, namely, parallel to the Sun-to-vehicle straight line.
- in general, the sailcraft motion should happen by the sail tilted for achieving the mission goals. Thus, the actual vector thrust acceleration can be resolved into three orthogonal components, named the radial, the transversal and the normal ones. The normal component is directed orthogonally to the instantaneous sailcraft trajectory plane.
- what matters for the sailcraft trajectory computation is the ratio of such accelerations to the local solar gravitational acceleration. These numbers can change with time mainly because the sail orientation generally varies with respect to the local frame of referenceFrame of referenceA frame of reference in physics, may refer to a coordinate system or set of axes within which to measure the position, orientation, and other properties of objects in it, or it may refer to an observational reference frame tied to the state of motion of an observer.It may also refer to both an...
consisting of the Sun-line and its orthogonal plane (where two other orthogonal axes can be defined). The three mentioned scalars altogether constitute a vector function of time, named the lightness vector, say L(t). The magnitude of this vector is the sailcraft's lightness number. The lightness vector is particularly important since the sailcraft orbital energy and angular momentum, and their time rates, are linearly dependent on the L components. These ones, in turn, chiefly depend on α and δ (non-linearly) and the thermo-optical parameters (linearly) of the sail materials. (There are other thrust contributions due to the aberrationAberrationAn aberration is something that deviates from the normal way.Aberration may refer to:In optics and physics:*Optical aberration, an imperfection in image formation by an optical system...
of light and the physical Sun, which is not a point-like source; however, such effects can be neglected except for some special class of solar-sail missions). - another useful parameter is the (scalar) characteristic acceleration, which is defined as the magnitude of the solar-pressure acceleration vector that a sailcraft would experience at one astronomical unitAstronomical unitAn astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
with the sail orthogonal to the local Sun-line and at rest. Different solar-sail missions could be compared by using the related values of the characteristic acceleration; equivalently, one could use either the maximum lightness number or the sailcraft sail loading and the thrust efficiency at 1 AU. Thrust efficiency accounts mainly for the non-ideal optical parameters and the non-flat geometry of the sail.
- The main goal of the sailcraft mission analyst is to compute the best time history of the sail n, or the vector function n(α(t), δ(t)), for the specific space mission under consideration. The ensuing admissible trajectories have to be connected to the sailcraft technology via an iterative optimization process which shall result in the final optimized design of both the whole mission and sailcraft (quite similarly to the past/current space mission designs).
- Of special importance for many envisaged very deep space solar-sail missions is the design of sailcraft capable to accomplish the fast solar sailing mode.
- References
- J. L. Wright, Space Sailing, Gordon and Breach Science Publishers, Amsterdam, 1993
- G. Vulpetti, 3D High-Speed Escape Heliocentric Trajectories by All-Metallic-Sail Low-Mass Sailcraft, Acta Astronautica, Vol. 39, pp 161–170, July-August 1996
- G. Vulpetti, Sailcraft at High Speed by Orbital Angular Momentum Reversal, Acta Astronautica, Vol. 40, No. 10 pp. 733-758, May 1997
- C. R. McInnes, Solar Sailing: Technology, Dynamics, and Mission Applications, Springer-Praxis Publishing Ltd, Chichester, UK, 1999
- G. L. Matloff, Deep-Space Probes: to the Outer Solar System and Beyond, 2nd ed., Springer-Praxis Chichester, UK, 2005