Value chain · CLM-1438
In plain terms
The ring of geostationary orbit lies over the Earth's equator. That ring is tilted by about 23.4 degrees to the flat plane in which the Earth travels round the Sun. So for most of the year the Sun is above or below the ring, and it lines up with the ring only around the two equinoxes.
The claim as recorded
The 1978 DOE/NASA reference report considers three inclinations for a geosynchronous orbit. It says that "Zero inclination gives a stationary satellite" and that "A 23.4[deg] inclination places the orbit in the ecliptic plane". Rockwell's 1980 orbit selection trade lists the "EQUATORIAL" orbit at 0 deg and the "ECLIPTIC" orbit at 23.4 deg. Taken together, the plane of the zero-inclination (geostationary) orbit is tilted about 23.4 deg to the ecliptic, the plane of the Earth's yearly path round the Sun. The 1978 report adds that, for this orbit, the Sun is outside the orbit plane at all times except at the equinoxes, and that "the maximum sun angle is 23.4[deg]".
Evidence behind this: T3: the 1978 DOE/NASA reference system report and a Rockwell paper in the April 1980 DOE/NASA programme review. Both are government programme documents, read at the rendered page. SRC-416, a 2007 interim US government study, adds the link to time in shadow.
Scope and limits
Both documents give 23.4 deg to one decimal place as a design input, with no date and no source for the value. SRC-085 and SRC-449 come from the same DOE/NASA programme of 1977 to 1980, so they are not independent of each other. SRC-416 links the small time in shadow to the Earth's axial tilt, but it gives no angle, and it is an interim release. None of these pages sizes the eclipse season or its length.
What it assumes
That the inclinations are measured from the Earth's equatorial plane. SRC-449 Figure 1 shows this by labelling the 0 deg orbit "EQUATORIAL". So an orbit at 23.4 deg lies in the ecliptic, and the 0 deg geostationary orbit lies 23.4 deg from it. The 1978 report's "sun angle" is read as the angle between the direction of the Sun and the orbit plane, which its sentence on the equinoxes implies.
Where it comes from
PDF p.101 (printed A-2), section A "Design Considerations", "Orbit Selection", read at the rendered page: "Three inclinations have been considered (figure A-1). Zero inclination gives a stationary satellite, simplifying the rectenna design."; "A 23.4[deg] inclination places the orbit in the ecliptic plane, permitting the satellite to be oriented simultaneously toward the sun for maximum output and perpendicular to the orbit plane (POP) for minimum gravity gradient torque."; and "All studies have concluded that zero inclination is preferred." PDF p.102 (printed A-3), Figure A-1 "SPS Orbit Inclinations", labels three orbits 0, 7.3 and 23.4 degrees. PDF p.103 (printed A-4): "In summary, the preferred orbit for the SPS is geosynchronous with zero inclination and eccentricity; i.e., geostationary."; and, under "Orientation and Attitude Control": "the sun is not in the orbit plane (that is, at all times except at the equinoxes)" and "Since the maximum sun angle is 23.4[deg], however, the SECS can be held in a POP attitude at all times." SRC-449 PDF p.190 (printed 168), Figure 1 "Orbit Selection Trade", under "INCLINATION (DEG)": "ECLIPTIC" 23.4, "EQUATORIAL" 0, "MIN. N-S STATION-KEEPING" 7.3. The text on the same page: "The geosynchronous equatorial orbit is preferred because of the large cost of the increased rectenna size associated with the two other orbits." SRC-416 PDF p.47 (printed A-2), of GEO: "due to the axial tilt of the Earth with respect to the Sun, spends less than 1% of the total time in shadow."
Basis: degrees of orbit inclination, measured from the Earth's equatorial plane
Cite this
energyaperture.com/c/clm-1438
CLM-1438, Energy Aperture, as of 1980-04.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-085
- CLM-0013The paper that modern UK studies rely on for the beam figure calls anything below 1 kilowatt per square metre safe, with 230 watts per...CLM-0020The original 1978 design set the beam at 230 watts per square metre in the middle of the receiving site, about one twenty-third of that at...CLM-0023In the 1978 reference design, two limits set the size of the transmitter and the receiving site: how much heat the transmitter can shed...CLM-0039The 1978 report set the figure to protect radio and navigation systems from a disturbed ionosphere, called the number theoretical and...CLM-0045The apparent conflict between 12 and 23 was not an error. The underlying study gave a range, and the figure adopted sits near the top of it.CLM-0101The 1978 contract required the researchers to report fixes if ionospheric disturbance pushed the pilot-beam phase error past 2 to 3...CLM-0137In four major space solar power studies from 1978 to 2007, none put a number on how much of the beam's energy would be lost if the beam...CLM-0138The original 1978 government design for beaming power down from space adds up all the expected energy losses to get 63% overall efficiency...More on the source page.
- Also from SRC-416
- CLM-1437A satellite in geostationary orbit, about 36,000 km up, goes round the Earth once in the time the Earth takes to turn once, which is just...
- Also from SRC-449
- CLM-0964To build two of these satellites a year, about 300 tonnes of material had to arrive at the orbital construction site every day. Getting it...CLM-0974The 1978 reference design shows every loss between sunlight and the power grid as a chain of numbered boxes, and the boxes multiply out...CLM-0975Depending on which published assumptions you take, a satellite needs between about 2 and 6 square kilometres of solar blanket for every...CLM-1058The often-repeated claim that the magnetron is 188 decibels quieter than its carrier traces to a conference abstract in which the tube...CLM-1059By spring 1980 the engineers, the reviewing panel and the ionosphere experimenters were all saying the beam-intensity ceiling the whole...CLM-1060The 1980 review did not agree with itself on how much of a satellite's cost was rockets: one paper said over a third, the programme's own...CLM-1061In one 1980 volume the satellite cost anywhere from about 2,300 to 3,800 dollars a kilowatt depending on who added what - and the programme...CLM-1062In 1980 the launch vehicle that everything was costed on was said by its own designers to be arbitrarily big, and they proposed a rocket a...More on the source page.