ESA Document - Emits - ESA

s
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 313 of 422
Improvement in video compression techniques is assumed by the mission date, so with 1.8 Mbps
medium-high quality video can be transmitted.
The communication should be possible even if there is no direct visibility between the astronaut
and the SHM. For this situation, a repeater should be used.
In the study’s, attenuation because multipath effect on the Martian surface is considered, and its
value is 20 dB (a more optimistic value of 15 dB was taken for NASA Mars Pathfinder).
4.3.7.3 Baseline design
Data estimation for return link (EVA subject –> base):
Biomedical/Space
Vehicle
suit or
32 kbps
High Quality Voice 160 kbps
Medium quality video 1848 kbps
Other data 8 kbps
Total 2048 Kbps
Data estimation for forward link (base -> EVA subject)
High Quality Voice 160 kbps
Other data 96 kbps
Total 256 Kbps
Table 4-17: Data requirements calculation for EVA operations.
4.3.7.3.1 SHM communications
SHM will have three main communication links:
� X-band: with the relay satellite. In case of contingency with the relay, a link to Earth G/S
could be established using the same antenna
� UHF: for communications with the TV in case of contingency. The UHF antenna and
transmitter of MAV would be used
� UHF: for EVAs. See section 4.3.7.3.3.
The SHM communications direct link availability, considering just the direct visibility in the
worst case, with the different mission elements is:
� G/S: 50% of the time
� TV: UHF or X-band in contingencies, 12 %
� Relay sat: continuous communications, 100% availability
The X-band transponder characteristics are shown in Table 4-18. Two 1 m dish antennas with
steering mechanism are included in the SHM, but only one will work at once depending on the
aerostationary satellite or Earth position. The steering mechanism features are a coverage of 180°
hemispherical, and a minimum pointing accuracy of 2º. See section 4.3.7.4 for details about the
communications units.