Put power where it helps

Hermes, the Communications Technology Satellite or CTS, launched on January 17, 1976. It was a Canadian–United States experiment in communications technology and its uses. Canada’s Department of Communications and NASA led the partnership; the European Space Research Organization also supplied hardware. This Hermes is the communications satellite, distinct from the European spaceplane project and the earlier American rocket program.

The central question was practical: could more capable equipment in orbit make satellite communication useful to people with smaller, less expensive ground terminals? The program tested both spacecraft technology and ways to use it. A successful transmitter and a useful remote classroom were related achievements, but they required different evidence.

The preserved NASA spacecraft photograph shows antennas and an extended solar array before launch. The array supplies electrical energy; the antennas direct radio signals. Their different jobs make the photograph a useful map of a system, even though the image alone cannot measure either power output or communication quality.

NASA’s project summary lists a 200-watt radio amplifier and a lightweight solar-array objective exceeding one kilowatt. The figures describe different parts of the energy chain. Electrical energy feeds equipment; some becomes transmitted radio energy, while some becomes heat. Other spacecraft systems also consume electricity.

Use an original simplified amplifier example: 400 watts of electrical input produces 200 watts of radio output. Efficiency is useful output divided by input, so 200 / 400 = 0.50, or 50 percent. The remaining 200 watts must be accounted for as other energy, principally heat in this model. These are invented operating conditions, not a measurement of Hermes.

A more efficient amplifier can reduce input power for the same output. At a fictional 80 percent efficiency, a 200-watt output would require 200 / 0.80 = 250 watts of input. That does not mean the spacecraft’s entire electrical system draws only 250 watts: pointing, control and other loads remain outside this amplifier calculation.

Account for power before claiming efficiency

For a deliberately simplified comparison, hold distance, frequency, pointing, transmitter antenna pattern and receiver performance fixed. Then received signal power scales with transmitted power and the receiving antenna’s effective collecting area. This proportional model is useful for a trade study; it is not a complete radio-link budget.

Imagine increasing transmitted power by a factor of four. The same modeled received power can then be obtained with one quarter of the collecting area. For geometrically similar circular dishes with the same efficiency, area scales with diameter squared: halving the diameter quarters the area. A two-metre dish becoming a one-metre dish illustrates that geometry; these are not Hermes terminal specifications.

The assumptions matter. Rain losses, interference, poor pointing or changed equipment can alter the result. More power does not eliminate the need to test the actual connection. The model explains one reason powerful spacecraft and smaller terminals can complement each other, without promising a particular service everywhere.