ESA Document - Emits - ESA

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HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 206 of 422
• The maximum range that should be supported is 2.7 A.U. (max. distance Earth / Mars).
• The telecommand (TC) and telemetry (TM) data rates shall be selectable to improve the
data rate depending on the distance.
• Data rates shall be optimised by giving realistic assumption of on-board equipment and
ground segment availability.
• During all mission phases, data consists of housekeeping, high-quality audio and video
channels, and any additional data (for example internet access).
• In August 2034 there is a solar superior conjunction, communications shall be provided
during it.
• Minimum and average data rates requirements are shown in Table 3-40. The maximum
data rate will be traded off with respect to complexity and cost, taking into account the
expected technology development in the future.
Uplink Downlink
Maximum Data Rate (overall, kbps) 11280 9232
Average Data Rate (overall, kbps) 3484 1436
Minimum Data Rate (overall, kbps) 160 160
3.3.7.2 Assumptions and trade-offs
Table 3-40: Data rate requirements for TV
3.3.7.2.1 S-, X-, Ka-band and laser communications
The present situation of S-band (which is shared by Space Research (SR) Cat. A, Space
Operation (SO) and Earth observation Services, plus high density mobile systems) is that high
congestion and sharing difficulties with fixed systems have already appeared. Therefore S-band
will be noisy. For this reasons, it is expected that ESA will reduce support to that band in long
term.
Considering X-band versus S-band, the most favourable frequency of operation depends on the
types of antenna used at both ends of the link (ground and space):
• Assuming constant apertures at both ends, the communication performance can be
improved by a factor of 13.5 dB (theoretical) if the frequency of operations is increased
from S- to X-band.
• Assuming constant aperture at the ground station and fixed antenna coverage on-board
(e.g. communications via LGA), the communications performances of S- and X-bands
are similar in clear sky conditions (atmospheric absorption and rain losses are higher in
X-Band).
Considering Ka-band versus X-band, the following factors are important:
• Assuming constant apertures at both ends, the communication performance can be
improved by a factor of 13 dB (theoretical) if the frequency of operations is increased
from X- to Ka-band.
• The weather dependence of Ka-band is high, so the availability of the link is lower than
in S- and X-bands.