358
10 TT&C and Telecommunication Technology …
Fig. 10.14 Reflection of
radio wave on lunar surface
2
h
1
h
1
d
2
d
1
r
r
2
r
To be strict, the mirror reflection principle was only applicable to the case when
the reflecting surface was a plane. The lunar surface is actually spherical. The obvious
difference between the plane reflection and the spherical reflection is that the diffusion
of the two beams is different. The spherical emission signal can be equivalent to a
plane reflection by the spherical emission diffusion factor.
The loss formula caused by lunar surface reflection and scattering is:
L mp =
1 − D|R|
r
r 1 + r 2
2
+ 4D|R|
r
r 1 + r 2
cos
2
1
2
ϕ
(10.1)
where: D is the spherical reflection diffusion factor; |R| is the lunar surface reflection
coefficient, or the equivalent reflection coefficient in case of scattering; r is the
distance of the effective radiation source of the receiving and transmitting antenna;
r 1 + r 2 is the distance between the transmitting and receiving antennas (shown in
Fig. 10.14); ϕ’ is the phase difference between the reflected wave and the direct
wave.
2. Propagation model in free space
When there is no obstacle between the transmitting end and the receiving end, i.e.,
when there is a direct path, the free space model can be used to predict the strength
of the received signal.
When radio wave propagates in free space, the energy is attenuated by diffusion.
This attenuation is called the transmission loss of free space [11]. In order to calculate
in practice, the telecommunication distance d is taken as km, and the wave-length
is replaced with the corresponding frequency f in MHz. Then the expression of the
transmission attenuation in free space is:
L 0 = 32.45 + 20 lg d + 20 lg f
(10.2)
The total link attenuation can be calculated by plus of Eqs. (10.1) and (10.2).
10.5 Testing and Verification
A series of test and verification should be conducted for the onboard TT&C and
telecommunication subsystem of the lunar lander before launch to ensure that it could
meet mission requirements. Besides general tests such as environmental adaptability
10 TT&C and Telecommunication Technology …
Fig. 10.14 Reflection of
radio wave on lunar surface
2
h
1
h
1
d
2
d
1
r
r
2
r
To be strict, the mirror reflection principle was only applicable to the case when
the reflecting surface was a plane. The lunar surface is actually spherical. The obvious
difference between the plane reflection and the spherical reflection is that the diffusion
of the two beams is different. The spherical emission signal can be equivalent to a
plane reflection by the spherical emission diffusion factor.
The loss formula caused by lunar surface reflection and scattering is:
L mp =
1 − D|R|
r
r 1 + r 2
2
+ 4D|R|
r
r 1 + r 2
cos
2
1
2
ϕ
(10.1)
where: D is the spherical reflection diffusion factor; |R| is the lunar surface reflection
coefficient, or the equivalent reflection coefficient in case of scattering; r is the
distance of the effective radiation source of the receiving and transmitting antenna;
r 1 + r 2 is the distance between the transmitting and receiving antennas (shown in
Fig. 10.14); ϕ’ is the phase difference between the reflected wave and the direct
wave.
2. Propagation model in free space
When there is no obstacle between the transmitting end and the receiving end, i.e.,
when there is a direct path, the free space model can be used to predict the strength
of the received signal.
When radio wave propagates in free space, the energy is attenuated by diffusion.
This attenuation is called the transmission loss of free space [11]. In order to calculate
in practice, the telecommunication distance d is taken as km, and the wave-length
is replaced with the corresponding frequency f in MHz. Then the expression of the
transmission attenuation in free space is:
L 0 = 32.45 + 20 lg d + 20 lg f
(10.2)
The total link attenuation can be calculated by plus of Eqs. (10.1) and (10.2).
10.5 Testing and Verification
A series of test and verification should be conducted for the onboard TT&C and
telecommunication subsystem of the lunar lander before launch to ensure that it could
meet mission requirements. Besides general tests such as environmental adaptability