ESA Document - Emits - ESA
ESA Document - Emits - ESA ESA Document - Emits - ESA
s HMM Assessment Study Report: CDF-20(A) February 2004 page 344 of 422 • The telecommand (TC) and telemetry (TM) data rates shall be selectable to improve the data rate depending on the distance to the receiving unit. • During descent phases, data consist of housekeeping audio and any additional data. 4.4.4.2 Baseline Communications during undocking, entry, descent and landing will be done using an UHF and a X-band link. An UHF slot antenna will be located in the docking port of MAV and will be used to communicate with the TV. Three switched X-band patches antennas will be located in the DM back shell (thermal protection) and will use the transponders and amplifiers located in the MAV (see MAV communications section 4.5.10 for further details). Therefore, the DM will not have active elements, since they will be present in SHM and MAV. After the DM shell is released, MAV antennas and transponders will be used for communications with the relay satellite. The achieved data rates are shown in Figure 4-85. See section 4.3.8 TV report for details about the UHF link, MEV-TV link in it. DM patch antenna Relay antenna: 1 m with steering mechanism Uplink Downlink Frequency 7.23 GHz 8.5 GHz Tx power 65 W 65 W Modulation QPSK QPSK Coding Concatenated, Interleaving=5 FER 10 -5 Bit rate: Max distance 18 600 km Min distance: 16 530 km 4.4.4.3 Contingency communications 172 kbps 97 kbps Table 4-42: X-band link DM-Relay satellite Direct communications with the Earth could be possible using the X-band patches antennas, but at a very low data rate.
s Figure 4-85: Communications MEV/MAV-TV during take off – rendezvous and undocking-landing 4.4.4.4 Budgets 4.4.5 GNC Unit Number Unit massTotal massPower of units (Kg) (Kg) (W) UHF slot omnidirectional antenna 1 1.5 1.5 X-band patch antenna 3 0.1 0.3 Harness 3 Total : 4.8 0 Table 4-43: DM communications budget HMM Assessment Study Report: CDF-20(A) February 2004 page 345 of 422 4.4.5.1 Requirements and design drivers The MEV entry, descent and landing is a 6-degree of freedom (6DoF) closed loop control entry with automatic steering law that will allow the safe landing of the astronauts to the Martian surface. The GNC requirements can be listed as follows: • Starting from a 3DoF optimal trajectory that satisfies certain boundary and path constraints • To find a flyable 6DoF trajectory within allowable margins that follows the optimal 3DoF trajectory previously calculated off-line • To define a GNC equipment that controls and steers the MEV in terms of sensors and actuators The initial and final boundary constraints as well as the path constraints are as follows: • Safety of the astronauts with a possible manual control during entry, descent and landing • Minimise the heat flux • Maintain a given load factor for the health of the crew • Minimise the descent time to be able to cope with the limited life support system available on-board the MEV • Touch down in a specified point on the Martian surface The output of the optimal trajectory establishes the corresponding roll, pitch and yaw profiles to be followed by the control law of the MEV. The Figure 4-86 shows the MEV model during this study:
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s<br />
HMM<br />
Assessment Study<br />
Report: CDF-20(A)<br />
February 2004<br />
page 344 of 422<br />
• The telecommand (TC) and telemetry (TM) data rates shall be selectable to improve the<br />
data rate depending on the distance to the receiving unit.<br />
• During descent phases, data consist of housekeeping audio and any additional data.<br />
4.4.4.2 Baseline<br />
Communications during undocking, entry, descent and landing will be done using an UHF and a<br />
X-band link. An UHF slot antenna will be located in the docking port of MAV and will be used<br />
to communicate with the TV. Three switched X-band patches antennas will be located in the DM<br />
back shell (thermal protection) and will use the transponders and amplifiers located in the MAV<br />
(see MAV communications section 4.5.10 for further details). Therefore, the DM will not have<br />
active elements, since they will be present in SHM and MAV. After the DM shell is released,<br />
MAV antennas and transponders will be used for communications with the relay satellite.<br />
The achieved data rates are shown in Figure 4-85. See section 4.3.8 TV report for details about<br />
the UHF link, MEV-TV link in it.<br />
DM patch antenna<br />
Relay antenna: 1 m with steering mechanism<br />
Uplink Downlink<br />
Frequency 7.23 GHz 8.5 GHz<br />
Tx power 65 W 65 W<br />
Modulation QPSK QPSK<br />
Coding Concatenated, Interleaving=5<br />
FER 10 -5<br />
Bit rate:<br />
Max distance 18 600 km<br />
Min distance: 16 530 km<br />
4.4.4.3 Contingency communications<br />
172 kbps<br />
97 kbps<br />
Table 4-42: X-band link DM-Relay satellite<br />
Direct communications with the Earth could be possible using the X-band patches antennas, but<br />
at a very low data rate.
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