Integrated Network Architecture for Sustained Human and Robotic Exploration

1. Integrated Network Architecture forSustained Human and Robotic Exploration Gary Noreen Telecommunications Architect Communications Architecture and Research Section Jet Propulsion Laboratory (818) 354-6048 gary.k.noreen@jpl.nasa.gov

2. Lunar Telecommunications Network Presumed Requirements Strawman Architecture Ground Segment Space Segment Orbit Design RF Payload Frequency Plan Mars Telecommunications Network Presumed Requirements Strawman Architecture Ground Segment Space Segment Orbit Design RF Payload Frequency Plan Emergency Communications Agenda

3. Strawman Return Link Requirements

4. Strawman Lunar Network Architecture • Terrestrial ground network to support lunar exploration • Spacecraft en route to and near the moon • Earth connection to lunar relay orbiters, lunar stations • Lunar relay constellation • 3 Lunar Telecom Orbiters • South Pole base • Limited far side coverage • Malapert Station • Repeater on summit of Malapert Mountain near lunar South Pole

5. 3 Earth complexes ~120° apart (DSN) Eight 12 m antennas at each complex 1 for each LTO – 3 total 1 for Malapert Station 2 for spacecraft en route & on near side of moon 2 backup Terrestrial Ground Network Potential Terrestrial Ground Network Data Rates *Assumes the moon is within the beamwidth of the ground antenna.

6. Strawman Lunar Relay Constellation • 3 Lunar Telecom Orbiters (LTO) • Communications payload • 15 dB UHF relay MGA • 1 m diameter relay HGA • 1 m diameter Earth HGA • Inclined elliptical orbits • Quasi-stable • Apoapses stay in southern hemisphere • Presumed requirements: at least 2 orbiters in view of base near lunar pole all the time

7. Quasi-Stable Lunar Relay Orbits • Perilune altitude 125 km to 1150 km; maximum range to pole is 11,600 km • Mean pass length over pole is 10.6 hours; mean gap time 3.5 hours. • Inclination between 46º and 63º • Eccentricity between 0.56 and 0.72 • At least two orbiters 10° or higher elevation all the time from polar base

8. Relay Data Rates • 1 m relay antenna used in calculations • 1.5 m relay antenna would provide performance comparable to TDRS • TDRS 4.5 m Single Access antenna • Geostationary altitude (earth): 35,000 km • Maximum LTO altitude: 11,600 km

9. Mars Network Strawman Requirements • One sustained human base • Mid-latitude location • Other requirements assumed similar to lunar case, including customer set • Big differences • Two-way light time 6.3 to 44.5 minutes • Mars-Earth range extremely high (up to 2.67 AU) – must cope with incredibly low signal levels

10. Strawman Mars Network Architecture • Terrestrial ground network to support Mars exploration • Spacecraft en route to and near Mars • Earth connection to Mars relay orbiters, Mars stations • Mars relay constellation • 2 Mars Communication Satellites (Comsats) • Areostationary orbits • Partially overlapping footprints • Human base in view of both

11. Terrestrial Ground Network for Mars Exploration • 3 Earth complexes ~120° apart (DSN) • Arrays of 12 m antennas at each complex • The DSN is planning arrays of 400 12 m antennas at each complex • Array of 10 12 m antennas = one 34 m • Array of 40 12 m antennas = one 70 m • A spacecraft with a 6 m HGA and a 1 kW transmitter at maximum Mars range can send 500 Mbps to an array of 180 12 m antennas • Optical may be deployed if proven viable by Mars Telecommunications Orbiter

12. Strawman Mars Comsat Constellation • Sacagawea & Pocahontas Mars communication satellites • Areostationary orbits (akin to geostationary) • 17,033 km altitude • Overlapping footprints at human base • Extended coverage for robotic exploration • Communications payload • 6 m High Gain Antenna for deep space link (Earth) – optical optional • 2.2 m High Gain Antenna for proximity link (Mars) Mars Base

13. THURAYA SATELLITE PHONE Relay Data Rates • Areostationary altitude: 17,033 km • Geostationary altitude: 35,000 km • Proximity link performance • 2.2 m antenna → comparable to TDRS • 7 m antenna → comparable to Thuraya

14. Emergency Deep Space Communications • Robotic deep space experience • Sun-point mode in the event of an anomaly • Accept very low data rates (10 bps) • More robust communications may be necessary for humans • Gemini 8: spacecraft may spin uncontrollably • Humans are likely to demand voice communications • At least 1 kbps • Additional engineering data to monitor humans as well as CEV • Sending back 1 kbps from a spinning spacecraft near maximum Mars range is very challenging • Inadequate margin even assuming array of 400 12 m antennas on the ground and 1 kW transmitter on the spacecraft

15. Conclusions • A modest network of 3 LTOs and 24 12 m ground antennas could provide continuous redundant links to human and robotic missions to the near side of the moon and to one of the poles. JPL has identified a stable orbit for the LTOs that maintains near-ideal phasing. • A network of two areostationary Mars communications satellites in conjunction with large arrays of small ground antennas at Earth could provide continuous redundant links to human and robotic missions in the vicinity of a mid-latitude Martian base and receive high rate data (500 Mbps). • The greatest challenge may be the provision of emergency communications services to human missions en route to Mars.