altitude above the Earth's surface of 500 to 39,900 km has what orbital period?
CREATE TABLE "escape_velocities_at_altitude" (
  "orbit" text,
  "center_to_center_distance" text,
  "altitude_above_the_earth_s_surface" text,
  "orbital_period" text,
  "specific_orbital_energy" text
);
SELECT "orbital_period" FROM "escape_velocities_at_altitude" WHERE "altitude_above_the_earth_s_surface"='500 to 39,900 km';