“The Statite—A Non-Orbiting Spacecraft”, 1989-07-10 ():
In this paper I describe a completely new type of space vehicle, called a statite [static satellite]–a spacecraft that does not orbit.
The statite can be used for placing and maintaining a space services system so it is continuously viewable from either the north or south hemisphere of Earth, yet it does not take up space on the crowded equatorial geosynchronous orbit.
To properly appreciate the statite concept, it is important to realize that all the thousands of space objects presently in orbit around the Earth use the centrifugal force generated by their orbital motion to balance the Earth’s gravitational force. In contrast, the statite is a space object that does not use centrifugal force from orbital motion about the Earth to counteract any substantial portion of the Earth’s gravitational force.
Instead, the statite uses a solar sail propulsion system to maintain the statite and its payload in a desired non-orbiting static position adjacent to the Earth by balancing light pressure force against the Earth’s gravitational force. In most versions of the system, the statite is offset from the polar axis toward the dark side of the Earth. The statite stays fixed at a point above the dark side, while the Earth spins beneath it. The statite can be placed anywhere over a large area on the dark side of the Earth. This is in contrast to the single linear arc of the equatorial geostationary arc.
From the viewpoint of an observer on the rotating Earth, this version of the statite rotates around the pole once every 24 hours (a solar day). Thus, ground stations for communication with these statites must have their antennas on a polar mount with a 24-hour clock drive. Since the distance between the ground station and the statite does not change substantially in magnitude, and the Doppler shifts are very low, the electronics needed for these versions of the system are nearly as simple as those at the fixed position ground stations. A typical distance of a statite from the center of the Earth is 30–300 Earth radii. The better the performance of the sail, the closer the balance point. (For reference, geostationary orbit is at 6.6 Earth radii and the Moon is at 63 Earth radii.) The round-trip delay time for 100 Earth radii is 4.2 seconds.
The advantages of the statite concept are: it provides continuous service to a region using a single spacecraft without requiring a slot on the crowded equatorial geostationary orbit, and it provides continuous coverage to regions of the Earth that are too close to the poles to use the existing equatorial geostationary orbit satellites.
The disadvantages of the statite concept are: constant control is required to maintain station, larger antennas will be needed because of the greater communication distance, the round-trip communication time is in seconds, and in most versions the ground station antenna must rotate once a day.
View PDF: