By Greg Rienzi
NASA’s New Horizons wowed the world last summer when it snapped and sent home stunning high-resolution images of Pluto’s icy surface, captured by the craft’s Long-Range Reconnaissance Imager, nicknamed LORRI.
LORRI collected a treasure trove of data during the six-month-long reconnaissance flyby that ultimately brought the craft within 7,800 miles of the dwarf planet. These surface images were just an appetizer for a full course of scientific data heading our way.
How does all the information get back to us, from billions of miles away?
Chris DeBoy, MS ’93, who joined the Johns Hopkins University Applied Physics Laboratory while earning his master’s degree in electrical engineering at the Whiting School, helps oversee the data “downlink” from New Horizons to Earth as the lead RF—wireless and high-frequency signals—communications engineer for the mission.
As the data come in, DeBoy notes, the New Horizons mission will tell us more about:
- The composition and structure of Pluto’s dynamic atmosphere
- The geology of the planet’s surface
- Interactions between Pluto and the solar winds
- The materials that escape the planet’s atmosphere
- Dust grains produced by collisions of asteroids and other Kuiper belt objects
New Horizons collected so much data—stored on a pair of 32-gigabit solid-state drives—that it will take over a year to transmit, he says. The information will travel more than 3 billion miles. Even moving at the speed of light, that’s a 4.5-hour trip for a single image.
As instruments made observations, data was transferred to a solid-state recorder where it will be compressed, reformatted, and transmitted to Earth through the spacecraft’s radio telecommunications system and its 2.1-meter high-gain antenna.
Just like Earth-bound computers, New Horizons speaks in a stream of ones and zeros that traverses space via high-frequency radio waves. “That signal spreads out so much across billions of miles, it’s a radio equivalent of a whisper by the time it gets to Earth,” DeBoy says.
Data received on Earth is sent to the New Horizons Mission Operations Center at APL, where it is “unpacked” and stored. The packets of bits need to be decoded and pieced together to make each image. That’s the job of the Science Operations Center at the Southwest Research Institute in Boulder, Colorado.
How It Works
It took nine years and nearly 3 billion miles for NASA’s New Horizons spacecraft to reach the Pluto system. On July 14, 2015, the probe—about the size of a baby grand piano and carrying seven scientific instruments—gathered a wealth of data about the dwarf planet and its moons as it streaked past at 31,000 miles per hour.
- The data includes high-resolution images taken by the Long-Range Reconnaissance Imager (LORRI). Dubbed the “eagle eyes” of New Horizons, LORRI is essentially a digital camera with a large telephoto telescope, fortified to operate in cold, hostile environs.
- During encounter, the data was transferred and saved to a solid-state recorder—similar in function to a flash memory card for a digital camera, except built for space and highly reliable.
- Bits of data are coded for transmission using modern error- correcting codes (turbo codes). Encoded bits are modulated onto a high-frequency radio signal, amplified to 12 watts, and routed to the large, 2.1-meter-diameter, high-gain dish antenna to be sent home. The spacecraft spins slowly to keep this antenna’s beam pointed toward Earth.
- About twice each day, these radio signals are detected by NASA’s Deep Space Network, a network of large—up to 70-meter-diameter—antennas in the U.S., Spain, and Australia. Chris DeBoy compares it to “pointing a high-powered telescope directly at the spacecraft to pick up a dim, 12-watt searchlight 3 billion miles away. It’s very faint by the time it gets to Earth, but we are able to lock onto the carrier frequency and decode the data on the signal,” he says.
- Even with the DSN, the long distance to Pluto limits the downlink rate to between 2,000 and 4,000 bits per second. Thus, it will require up to 16 months to send the full set of Pluto encounter science back to Earth.
- The data received through the DSN is sent to the Mission Operations Center at Johns Hopkins’ Applied Physics Laboratory, where it is unpacked and forwarded to science teams for reassembly into pictures and measurements.
SOURCE: Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland