TELECOMMUNICATIONS INTRODUCTION There are enormous antennas that enable

TELECOMMUNICATIONS

INTRODUCTION • There are enormous antennas that enable humans to reach out to spacecraft millions of miles away. • Each Mars Exploration Rover spacecraft carries multiple antennas used for different phases of the mission and allows it to communicate to multiple places and with other spacecraft at different speeds. • Telecommunications to the Earth may be accomplished using directto-Earth links via the Deep Space Network (DSN) or by means of relay links provided by orbital missions at Mars.

INTRODUCTION • The Mars Science Laboratory rover, Curiosity, is able to "talk" to Earth using any one of three antennas. o Low gain antenna. o High gain antenna. o UHF ( Ultra High Frequency) antenna.

WHY TELECOMMUNICATIONS • No data transmitted to earth • No scientific data • We have a problem

ANTENNA • Antennas are used to communicate directly with Earth. • Rover has three antennas that serve as both its "voice" and its "ears. " They are located on the rover equipment deck (its "back"). • This capability gives the mission team several different ways to send commands and return data back to Earth.

ANTENNA v. Low gain antenna • Omni Directional. • Transmit Radio waves at low rate to Deep Space Network(DSN) on Earth. • Serves as the rover's primary link to Earth. • These signals spread out as they leave the antenna. • The disadvantage is that they have lower gain and therefore the signals received will be much weaker, leading to lower data rates.

ANTENNA v. High gain antenna • HGA is a 3 metre diameter parabolic dish antenna. • Unidirectional. • Once mission controllers have determined the rover's location of the signals, they will switch communications to the High-Gain Antenna. • The High-Gain Antenna sends a more efficient signal focused directly at Earth.

ANTENNA v. High gain antenna • The high-gain antenna can send a "beam" of information in a specific direction, and it is steerable, so the antenna can move to point itself directly to any antenna on Earth. • The benefit of having a steerable antenna is that the entire rover doesn't necessarily have to change positions to talk to Earth. Like turning your neck to talk to someone beside you rather than turning your entire body, the rover can save energy by moving only the antenna. • HGA at 264 bytes/sec (1. 85 kilobits/sec) while the uplink data rate is 125 bytes/sec (0. 875 kilobits/sec)

ANTENNA v. Ultra high frequency antenna • Rover will likely send radio waves through its ultra-high frequency (UHF) antenna (about 400 Megahertz) to communicate with earth through Mars Odyssey and Mars Reconnaissance Orbiters. • This are close-range antennas used at low power. These are like walkie-talkies compared to the long range of the low-gain and highgain antennas.

COMMUNICATION TIME • Mars is at 56 millions km from the Earth, a distance as short as 0. 37 AU (1 A. U. = 149. 56 million km), it takes 3 minutes and 7 seconds for a signal emitted by the DSN to reach Mars. But when Earth and Mars are the farthest apart at 2. 52 A. U. , it takes 20 minutes and 57 seconds to transmit the same radio signal. • Due to these time delays it is impossible to communicate with and control the rover in real time. • This distance is not as much of a problem as having the Sun in the way, for it produces a lot of radio interference making communication almost impossible.

DATA TRANSMISSION • Two way to transmit data from mars to Earth. 1)Direct To Earth 2)Via Orbiters

Direct To Earth Direct communication from mars surface to earth. Limited transmitter. Communication is weak Limited data reliability. Limited data rates The data rates Direct-to-earth varies from 500 bits per second to 32, 000 bits per second. • 250 megabits would take up to 20 hours to transmit direct to earth. • The rover can transmit direct-to-earth for a 3 hours a day due to power limitations. • • •

Via Orbiters • Orbiters can use MRO(Mars Reconnaissance Orbiter) and Odyssey to transmit data. • An orbiter passes over the rover and is in the vicinity of the sky to communicate with the rover for about 20 -25 minutes at a time, per sol. • There are 2 such contacts {every morning i. e. AM and evening i. e. PM} with both orbiters per sol. • In that time, between 100 and 250 megabits of data can be transmitted to an orbiter. • The orbiters can see Earth for about 2/3 of each orbit or about 16 hours a day. • They can send much more data direct-to-Earth than the rover because they have lot of power and bigger antennas than the rover.

Telecommunications Sub Systems • MRO • Odyssey • X-Band • UHF • Ka-Band

Communication Via Orbiters

Orbiter - MRO • The Mars Reconnaissance Orbiter (MRO) is a 1000 kg spacecraft Launched in 2006. • It has two goals: conduct science experiments to better understand the climate and surface of Mars, especially with regard to finding water sources; act as a communications relay back to Earth for other missions that have spacecraft or rovers near or on Mars. • MRO orbits around Mars every 1 hour and 52 minutes, with the closest point to the surface being 250 km and the furthest 316 km. • MRO is used as data relay.

Orbiter - MRO • It is used for sending the data back to earth at more higher rate. • Data rates: 0. 5 Mbps to 4 Mbps • MRO is able to send the data back to earth 10 times faster than previous mission • A 3 m long high gain antenna and 100 watts. • Data rate - maximum around 6 Mbps when distance between earth and mars is minimum (approx. 55. 7 million km ) • Data rate - minimum around 0. 6 Mbps when distance between earth and mars is maximum (approx. 401. 3 million km)

Orbiter - Odyssey • The Mars Odyssey Orbiter is a 380 kg spacecraft Launched in 2001. • The data rate to the odyssey orbiter is selectable 1, 28, 000 or 2, 56, 000 bits per second(4 -8 times faster than a home modem). • Odyssey orbits around Mars every 1 hour and 58 minutes, with the closest point to the surface being 370 km and the furthest 444 km. • 120 Mega bits allocated on board memory of Mars Odyssey.

RADIO FREQUENCIES X BAND • X-Band can transmit more data in the same amount of time using smaller, shorter wavelengths, but the transmissions must be more narrowly focused to be received at the other end. • Microwave frequency Transmit: 7145 Mhz-7190 Mhz Receive: 8400 Mhz-8450 Mhz • Used between rovers and earth

X-Band Functions • Receive an X-band uplink carrier from the DSN. unmodulated or modulated by command data or by a ranging signal or both. • Demodulate the command data and the ranging signal. • Generate an X-band downlink carrier either by coherently multiplying the frequency of the uplink carrier.

X-Band Components • X-Band Cruise: • Communication on rover provided by x-band transponder, solid state power amplifier and UHF transceiver. • During cruise the x-band transponder receive and transmit via cruise LGA or medium gain antenna. • EDL Surface: • UHF is also used for the portion of EDL where the lander was suspended. • This radio is capable of rates of 8, 32, 128, or 256 kbps for either transmission or reception.

UHF BAND • similar to those used for television broadcasts. • Each conversation will last about 15 minutes, the length of time it takes for the orbiter to pass from horizon to horizon. • Ultra High Frequency(300 to 3000 Mhz) from 390 to 450 MHz on mars missions. • Used between landers, rovers and orbiting spacecraft • UHF Components • Transceiver, which performs transmission and reception of UHF communications. It is also the interface with the Avionics subsystem. • Two UHF antennas: • DUHF - used to transmit to MGS during EDL • RUHF - used to transmit and receive with orbiters during surface operations • Diplexer and coaxial switch to connect the transceiver to one of the two antennas.

UHF Operations • Power consumption 6 W (receiving only), 43 W (transmitting/receiving) • RF output 12 W (typical, transmitting) • Frequency • One forward frequency (orbiter to rover) of 437. 1 MHz • Two return frequencies (rover to orbiter): • 401. 585625 MHz (Odyssey and MEX) • 401. 528711 MHz (MGS) • Data Rates • Forward link: 8, 32, 128, 256 kbps 11 • Return link: 8, 32, 128, 256 kbps 12

KA-BAND • microwave frequency Transmit: 34200 Mhz - 34700 Mhz Receive: 38100 - 32300 Mhz • Used as secondary link between landers and orbiters • previously untested radio frequency • Frequency X 4 allow an higher data rate than using X-band. • Ka-band provides more power at the receiver then X-band

Mars relay system Links

DEEP SPACE NETWORK • The NASA Deep Space Network (DSN) is an international network of antennas that provide the communication links between the scientists and engineers on Earth to the Mars Exploration. • Communication between the MER spacecraft and the DSN has been at X-band Rovers in space and on Mars. • The DSN consists of three deep-space communications facilities placed approximately 120 degrees apart around the world

Size of Deep Space Network • 70 meter diameter parabolic dish antenna. • 34 meter diameter HEF parabolic dish antenna. • 34 meter diameter BWG parabolic dish antenna.

Rover transmits to Earth directly or via three relay satellites in Mars orbit

SPECIFICATIONS Rover has 3 Antennas for communications. Diameter of HGA is 3 meters. It uses X-Band UHF for data transmission. The signals from Mars requires on an average, 14 minutes, 6 seconds to travel to Earth. • The DTE speed for data transmission is only up to 32 kbit/s, so MRO and ODYESSY is used for relay. • Data transfer speeds between Rover and orbiter is between 256 kbit/s and 2 Mbit/s. • •

REQUIREMENTS • Power is needed to operate the Antenna. So the Power should be turned on. Up to 300 Watts of power is required. • MRO and ODYSSEY orbiters are required for transmission, as Rover cannot communicate to Earth directly all the time.

CONSTRAINTS • Uplink frequency cannot be more than 256 kbps • Downlink frequency cannot be more than 2048 kbps • Power consumption of the antenna cannot be more than 300 Watts. • The Rover will be available in position to send the signals only for about 15 mins. So this time needs to be considered.

CHALLENGES • Large transmission delays RTT between earth and mars varies between 7 min and 46 min • Great distance between 55. 7 and 401. 3 million km • Limited bandwidth available • Disrupted links (orbital visibility)

COMMANDS • TEL_POWER_ON This command switches ON the power to the antenna. If no power is available, it will give an error message indicating that the power is not available. • TEL_POWER_OFF This command switches OFF the power to the antenna. • TEL_RELAY_TO_ROVER This command helps the Earth ground systems to send the data to the rover. Once this command is called by the Earth module, the server waits for an order from the Earth, which it forwards to the Central Control and Data Systems. • TEL_RELAY_TO_EARTH This command tells the rover to send the data to the Earth. Once the command is received, the rover starts to transmit the data which is locally stored in the buffer.

COMMANDS • TEL_FREQUENCY This command is used by the Earth Ground Systems to determine the frequency being used for the communication. It is measured in Hertz or bits per second. • TEL_BANDWIDTH This command helps the Earth Ground Systems to determine the bandwidth of the frequency. • TEL_PRINT_INFO This command helps to print the current state of the Antenna.

COMMANDS • TEL_CHANNEL This command is used to determine the channel being used for communications, i. e. the Uplink or the Downlink channel. • TEL_NOISE This command helps the Earth Ground Systems to determine the Noise factor in the received signal. • TEL_SIGNAL_MAXPOWER This command prints the maximum power of the signal received.

EARTH ORDERS AND DATA TELECOMUNICATION DATA AND COMMANDS CCD OTHER MODULES