Heliogyros generate attitude control moments by pitching their sail membrane blades collectively or cyclically, similar to a helicopter. Past work has focused on simple blade pitch profiles with the heliogyro normal to the sun; however, most solar sail missions will require sun angles of at least 35 deg. Furthermore, combination pitch profiles (e.g., cyclic plus collective) are needed for attitude control during all mission segments. The control moments for such situations vary in an unintuitive, nonlinear fashion. This paper explores heliogyro control moment authority with varying sun angles and combinations of pitch profiles, providing critical insight for future development of heliogyro attitude control schemes. Three tactics for generating control moments using various profile combinations are introduced for three-axis attitude control during a variety of practical mission scenarios. These tactics indicate that the heliogyro can generate control moments from any orientation, including edge-on to the sun. A restricted, nonlinear, constrained optimization is used to determine the blade pitch profile combination required to generate the desired attitude control torques. This approach could be employed for analyzing mission performance and for designing closed-loop attitude control. Nomenclature A = total sail area, m 2 a xx = collective (where xx equals co), half-p (where xx equals hp), or cyclic (where xx equals cy) profile amplitude, rad, deg D, d x = despun frame F = solar radiation pressure thrust vector, N h = sail membrane thickness, m h = orbit momentum unit vector J n = nth element mass moment of inertia, kg · m 2 M = solar radiation pressure moment vector, N · m, subscript d indicates desired moments N = number of bladeŝ l = local horizontal with respect to sun in orbit plane P = solar radiation pressurê p = reference axis for clock angle δ R = heliogyro blade radius, m S = sun framê s = sun-spacecraft unit vector t = time, s β = blade flap bending angle, rad, deg γ = sail cone angle/Sun angle, angle betweenŝ andd 1 , rad, deg δ = clock angle betweenp andd 3 , rad, deg θ = blade pitch, follows right-hand rule about blade span (radius) axis, rad, deg ϕ xx = half-p (where xx equals hp) or cyclic (where xx equals cy) phase angle, rad, deg χ i = ith blade angle relative to blade 1 in the rotation plane, where χ 1 equals zero, rad, deg Ψ = in-plane moment M 23 azimuth angle, rad, deg ψ i = ith blade azimuth angle in the spin plane, rad, deg Ω = heliogyro inertial spin rate about primary spin axis, rad∕s
Solar sailing is an elegant form of space propulsion that reflects solar photons off a large membrane to produce thrust. Different sail configurations exist, including a traditional fixed polygonal flat (FPF) sail and a heliogyro, which divides the membrane into a number of long, slender blades. The magnitude and direction of the resulting thrust depends on the sail's attitude with respect to the Sun (cone angle). At each cone angle, an FPF sail can only generate force constrained to a particular magnitude and direction, while the heliogyro can arbitrarily reduce the thrust magnitude through the additional control of pitching the blades. This gives the heliogyro more force control authority, which is exploited in this paper for orbital control of solar sail, Sun-Earth, sub-L1 halo orbits through a linear-quadratic regulator feedback controller. Two test cases are considered, quantifying either the maximum error in the injection state or the maximum delay in solar sail deployment due to
The recent successful flight of the JAXA IKAROS solar sail has renewed interest within NASA in spinning solar sail concepts for high-performance solar sailing. The heliogyro solar sail, in particular, is being reexamined as a potential game-changing architecture for future solar sailing missions. In this paper, we present an overview of ongoing heliogyro technology development and feasibility assessment activities within NASA. In particular, a small-scale heliogyro solar sail technology demonstration concept will be described. We will also discuss ongoing analytical and experimental heliogyro structural dynamics and controls investigations and provide an outline of future heliogyro development work directed toward enabling a lowcost heliogyro technology demonstration mission ca. 2020.
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