The temperature of the orbiting space station’s Sun-facing side could be up to 250 °F (≈120 °C) and will be a significant antenna noise temperature contributor for visiting spacecraft communication and tracking systems during rendezvous. The conventional antenna noise temperature calculation does not take into account the space station reflection effects, and results in an underestimated antenna and system noise temperature. Thus, the visiting spacecraft communication and tracking system performance could be overestimated during rendezvous.
A rigorous computation method was developed for the visiting spacecraft antenna noise temperature calculation. The antenna noise temperature could be theoretically determined by integration of the black body brightness temperature distribution over antenna gain pattern. The most significant noise contributors come from the Earth ground and the Sun, Moon, and other hot bodies of the sky. However, for the space station visiting spacecraft, the sunlight reflections off the space station could be a significant antenna noise contributor. This calculation method could greatly increase the accuracy of the calculated antenna noise temperature by including the sunlight reflections off the space station noise contributions.
The calculation procedure is as follows: (1) Compute the antenna gain pattern including the electromagnetic wave interactions (reflections and diffractions) from the visiting spacecraft using the rigorous computational electromagnetic techniques such as the hybrid geometrical theory of diffraction (GTD) and the method of moment (MOM) approach. (2) Calculate the antenna noise temperature contribution from the black bodies such as the Earth, the Sun, the Moon, and the galaxy by integrating the black body temperature over the visiting spacecraft antenna gain pattern. (3) If the space station is illuminated by the Sun, calculate the antenna noise temperature contribution from the sunlight-illuminated space station by integrating the space station temperatures over the visiting spacecraft antenna gain pattern. The visiting spacecraft antenna noise temperature is the sum of the results from (2) and (3).
This work was done by Shian-uei Hwu, Buveneka Kanishka DeSilva, Cindy Jih, Mark Chavez, Timothy Early, and Catherine Sham of Johnson Space Center. MSC-25453-1