We wish to express a warm happy birthday to….
… to “Curiosity”, NASA’s Mars rover, who was named by a sixth grader, Clara Ma. Curiosity landed on Mars on August 5, 2012 (launched Nov 26, 2011) and is still continuing to send data in spite of it’s intended lifetime of 1 Martian year (686 Earth days).
Huge congrats to all or the contributing NASA centers, and especially, JPL, for an incredible project and more than a breathtaking deployment using a “sky crane” on the Red Planet. From a conventional engineering point of view, I honestly thought this was insanity when I heard about it, but with madness comes brilliance. A buddy of mine was on an executive rotation on this mission. What astounding team work and brilliant people involved.
Note the rover’s use of UHF (~400MHz) for near relay link communications with orbiting Mars satellites (e.g. MRO, Odyssey) and X-band (~8 GHz) links using steerable dish for weak signal comm via the Deep Space Networks.
Curiosity has three antennas:
- High Gain Antenna (HGA). A 25×29cm patch antenna with transmit gain of 25.5 dBi and receive gain of 20.2 dBi. Used for direct-to-Earth (DTE) communcations for telemetry and direct-from-Earth (DFE) for commanding.
- Low Gain Antenna (LGA). Gain of 5dBi. Used for low rate DFE commands. Not intended for use for DTE as the data rate is very low.
- UHF antenna. Used for communicating to/from Earth via the Mars relays: MRO and as a backup, Odyssey.
The HGA and LGA are used for X-band communications. The DTE transmit power is 15 W. The minimum requirement for downlink data rate using the HGA is 160 b/s to a 34-m antenna and 800 b/s to a 70-m antenna. The uplink data rate requirement is 1 kb/s using the HGA, allowing for commands to be sent to Curiosity. As a backup the LGA can be used (it has a much wider beamwidth and therefore doesn’t need as accurate positioning as the HGA), but because of the weaker signal a data rate of about 15 b/s is expected.
The downlink (relay to Curiosity) data rates range from 2 kb/s to 2048 kb/s. Odyssey only supports up to 256 kb/s. The uplink data rates range from 2kb/s to 256 kb/s (Odyssey: 8 and 32 kb/s only). The big dish in the photos below is one of several portable antennas at the W5RRR shack. We typically keep it stored in the backroom to avoid getting it wet…