4 Precursor Mission Design 4.6 Mission Architecture

4.6.4 Ground Support

Introduction

It may become necessary to build a new tracking, telemetry and control system (TTCS) for the Lunar Rover Race Mission. NASA's Space Tracking and Data Network (STDN) is being shut down and the Tracking and Data Relay Satellite System (TDRSS) can only communicate with spacecraft below GEO. The NASA/JPL Deep Space Network (DSN) is a possibility, but time on DSN is extremely difficult and expensive to obtain due to both the great number of missions already supported by DSN and the bandwidth requirements of the LRR.

Overall Telecommunications Requirements

Telecommunications between the Earth and the Moon shall be carried out directly from each rover, the media vehicle, and the lander back. The telecommunication equipment on the rovers, the media vehicle and the lander should be small in size and require little power. The overall telecommunication network is shown in Figure 4-33.

Figure 4-33: Overall Telecommunications Network

The telecommunication data rate requirements are listed in Table 4-5

Table 4-5: Telecommunication Data Rate Requirements

 Traffic Type

 Data Rate

 Number of Links
 Digital TV  Lander/Media Vehicle to Earth  34 Mbps  2
  Rovers to Earth  2 Mbps  10
 TT&C Lander And Media Vehicle to Earth  100 kbps  12
Earth to Rovers, Lander And Media Vehicle  2 Mbps  12
 ISDN (Between Mission Center and Data Users)  144 kbps  Many


Design of Telecommunication Links between Earth and Moon

If possible, telecommunications between the Earth and the Moon could be carried out via the NASA/JPL Deep Space Network (DSN). However, as stated earlier time on DSN is extremely difficult and expensive to obtain due to the great number of missions already supported by the network and the bandwidth requirements of the LRR.

The DSN system includes three communications complexes located approximately 120° of longitude apart around the world: near Madrid (355°45', 40°14'), Spain; near Canberra (148°58', -35°13'), Australia; and at Goldstone (243°06', 35°14'), USA. The DSN permits continuous communications with spacecraft as the Earth rotates. The 70-meter stations of the DSN will be used for telecommunications between the Earth and the Moon, each of them includes L-band, S-band, X-band and K-band channels. The 70-meter antenna is shown in Figure 4-34. X-band uplink, X-band downlink and K-band downlink are used for the lunar rover race mission. Link budget and feasibility analysis of the Earth-Moon telecommunication system is given in Appendix A.

Figure 4-34: 70-meter Antenna of DSN (Courtesy of NASA)

Table 4-6: Earth-Moon Links Design

 Design
Param-rs

 Each Rover

Lander& Media Vechicle 

   DSN Stations

  Tx Power
  5 w  5 w  35 w  35 w  0  00

3000

w x12

 Tx Antenna Diameter
  0.15 m  0.15 m  0.35 m  0.35 m  -  -  70 m

 Tx Frequency

 K-

band

 K-

band

 X-

band

 X-

band

  - - 

 K-

band

Tx Data Rate
  2 Mbps  100 kbps  34 Mbps  100 kbps -   -  2 Mbps

 LNA Noise Temp.
  -  60 K  -  60 K  60 K  40 K  60 K

 Rx Antenna Diameter
 -   0.15 m -  0.35 m   70 m  70 m  70 m

 Rx Frequency Band
 - 

 K-

band

  -

 K-

band

 K-

band

 X-

band

 X-

band
 Rx Data Rate  -  2 Mbps -   2 Mbps  2 MHz x 10

 34

Mbps

x2+10

 100 kbps

x 10

Signal Flow Diagram

The signal flow diagram of telecommunications between the Earth and the Moon is shown in Figure 4-35.

Figure 4-35: Signal Flow Diagram of Communications


Data Distribution Links

ISDN (2B+D) links on the Earth are used for data distribution from the Mission Operation and Control Center to data application departments all over the world, including universities, research centers and high schools. The mission data flow overview is shown in Figure 4-36.

Figure 4-36: Data Handling and Distribution


Conclusions

  • It is possible and feasible to carry out the direct telecommunications between the Earth and the Moon.
     
  • If they could be made available, the 70-meter antenna systems of the DSN should be used for telecommunications with the lander, the media vehicle, and the rovers. K-band equipment is used for low data rate video information (2 Mbps) acquisition and TT&C of the rovers and X-band equipment is used for high data rate video images (34 Mbps) acquisition and telemetry of the Media Vehicle and the lander.

It is very important to improve the performance of robots, especially the solar power aspect, in order to guarantee the link margin.

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