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Mars Science Laboratory

X-band Radio Waves

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Phoning Home: Communicating from Mars
How will we know if Curiosity has landed safely on the surface of Mars?

X-band radio waves used by the rover to communicate

The rover communicates with the orbiters and the DSN through radio waves. They communicate with each other through X-band, which are radio waves at a much higher frequency than radio waves used for FM stations.

Curiosity Spotted on Parachute by Orbiter
Curiosity Spotted on Parachute by Orbiter

The radio waves to and from the rover are sent through the orbiters using UHF antennas, which are close-range antennas that are like walkie-talkies compared to the long range of low-gain and high-gain antennas. All three orbiters active at Mars — NASA’s Mars Odyssey and Mars Reconnaissance Orbiter and the European Space Agency’s Mars Express — were at positions where they could receive transmissions from the Mars Science Laboratory spacecraft during its entry, descent and landing. Only Odyssey relayed the information immediately, however. The other two orbiters recorded Mars Science Laboratory data from the Mars Science Laboratory spacecraft, holding it onboard, and sending it to Earth hours later. Mars Reconnaisance Orbiter even captured images of the spacecraft on its parachute during entry, descent and landing.

The cruise stage had two antennas that were used to communicate with the Earth. The low-gain antenna was omni-directional and was used when the spacecraft was near the Earth. Because it radiated in all directions, the low-gain antenna did not need to be pointed at the Earth to enable a communications link. The medium-gain antenna was a directional antenna that had to be pointed toward the Earth for communications, but had more power to communicate when the spacecraft was farther away from the Earth. The medium-gain antenna acted like a floodlight and could direct the energy into a tighter beam to reach Earth. Just like a floodlight directs more light into a focused area than a normal light bulb does out of a lamp, the medium-gain antenna could direct the data from the spacecraft into a tighter beam than the low-gain antenna.

When the rover speaks directly to Earth (from the surface of Mars), it sends messages via its high-gain antenna (HGA). 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.