IEEE - Aerospace and Electronic Systems - August 2022 - 11

Avram et al.
This has a significant effect on which TUT is seen by the
S/C at a given time and on the visibility duration.
Although small variations of RAAN and AOP could be
desirable for an extremely accurate analysis, an angular
step of 12.5
was selected for both angle variations to
achieve an acceptable discretization and in parallel limit
the computational cost. As shown in Figure 8, each radio
telescope discerns a conical portion of the sky in which
the satellite could be visible; the radius R ofthe cone's circular
base can be estimated using
R ¼½ðrS/CREÞ hGS tan ð90EminÞ
Figure 7.
SNR of the calibration signal as a function of the pointing offset
angle between the TUT main lobe axis and the MAC direction.
Results for five telescope apertures are shown, orbit SET 3 with
an altitude equal to 610 km and an elevation angle of 20 has
been considered. The noise rms is equal to 6 105 pW, a 1 s of
integration with telescope bolometer NEP) equal to 6 1017 W/
Hz0:5 has been assumed. The signal is identifiable as the SNR is
greater than 30 dB. 10-m class telescopes require a pointing accuracy
better than 4 arcmin if a maximum signal attenuation of50%
is required.
supposed to emit a 150-GHz polarized microwave signal
adjustable both in frequency and amplitude by means of a
Gunn oscillator. CMB telescopes with an aperture ranging
from 0.5 up to 10 m have been considered in the simulation.
Atmospheric loss has been computed according to the ITUR
P.676-12 model using the International Standard Atmosphere
model for pressure and temperature profiles, and
standard vapor profile by ITU-R P.835-2 model [33]. Noise
power has been calculated assuming 1 s ofintegration and a
telescope bolometer noise equivalent power (NEP) equal to
6 1017 W/Hz0:5, which is a typical value for the considered
telescopes, see as example [34].
Figure 6 shows the expected SNR as a function of the
radio telescope aperture, tested orbits, and CubeSat elevation
as seen by the TUT. It is possible to observe that to
obtain an SNR grater that 30 dB, a CubeSat elevation
greater than 20 is requested. To ensure that the signal is
received with sufficient strength, the MAC and the telescope
to calibrate must point toward each other. Figure 7
shows SNR as a function of MAC to TUT pointing error
for the worst case, orbit altitude 610 km and CubeSat elevation
20. With the aim of limiting the signal reduction
to 50%, in the case of a telescope with an aperture of
10 m, the pointing error must not exceed 4 arcmin.
RESULTS OF SATELLITE VISIBILITY SENSITIVITY TO
RAAN AND AOP
The combination ofRAAN and AOP defines the satellite's
initial orbital position and, therefore, its evolution in time.
AUGUST 2022
(10)
Figure 8.
Visibility cone for the active pointing telescope considering a
minimum elevation detectability of 20. TUTs are represented as
black dots, S/C as a red dot evolving on the yellow orbit.
Figure 9.
Visibility cone for the active pointing telescope considering a
minimum elevation detectability of 20 (green cone), FWHM
main lobe (red cone) of a TUT pointing toward the S/C (blue
dot), and S/C payload FOE (yellow cone).
IEEE A&E SYSTEMS MAGAZINE
11
IEEE - Aerospace and Electronic Systems - August 2022

Table of Contents for the Digital Edition of IEEE - Aerospace and Electronic Systems - August 2022
