Thermally controlled buoyancy device

A thermally controlled buoyancy device comprising:

• a first shell having a concave inner surface and a convex outer surface and with a first coefficient of thermal expansion and said first shell having a thickness, a cross sectional shape of a portion of a symmetric bell curve, a longitudinal extent, a first flattened end, a second flattened end and a peripheral edge in a plane;
• a second shell having an inner concave surface and an outer convex surface and with a second coefficient of thermal expansion, said second shell having thickness, a cross sectional shape of a circular arc with a center of symmetry and a longitudinal extent, the inner surface of said second shell bonded to the outer surface of said first shell, said second shell aligned longitudinally with said first shell and said center of symmetry of said first shell aligned with the center of symmetry of said second shell;
• a third shell having a concave inner surface and a convex outer surface and with the first coefficient of thermal expansion, said third shell having thickness, a cross sectional shape of a portion of a symmetric bell curve with a center of symmetry, a longitudinal extent, a first flattened end, a second flattened end, and a peripheral edge lying in a plane, said third shell positioned with said concave inner surface of said third shell facing said concave inner surface of said first shell with said peripheral edge of said third shell bonded to said peripheral edge of said first shell enclosing a volume between said first shell and said third shell;
• a fourth shell having an inner surface and an outer surface and with the second coefficient of thermal expansion, said second shell having thickness, a cross sectional shape of a circular arc with a center of symmetry, and a longitudinal extent, the inner surface of said second shell being bonded to the outer surface of said third shell, said fourth shell aligned longitudinally with said third shell and said center of symmetry of said third shell aligned with said center of symmetry of said fourth shell;
• and
• a heating element bonded to said inner concave surface of said first shell and said inner concave surface of said third shell, said heating element electrically connected to an electrical source;
• wherein said first and second shells and said third and fourth shells have a first position responsive to the temperature of said shells in which a space defined between said first and third shells is minimized and a second position responsive to the temperature of said shells in which the space defined between said second and third shells is maximized by expansion and contraction of said first shell, of said second shell, of said third shell, and of said fourth shell in response to temperature in degrees reactive to differences in coefficients of thermal expansion.