The New Horizons spacecraft continues to deliver.
After swinging within one Earth diameter of Pluto and gathering hundreds of images of the remote icy world, NASA’s New Horizons spacecraft is heading another billion kilometres outward toward a 45-kilometre-diameter Kuiper belt object known as MU69. It will reach its destination for an image-gathering flyby on January 1, 2019.
In the meantime, for the next six to eight months at least, the 80 percent of the New Horizons’ library of images and data still in the spacecraft’s memory storage will be transmitted back to NASA’s Deep Space Network antennas.
Why is it taking so long?
New Horizons is outfitted with cameras, spectrographs and particle detectors and has the latest (at the time of its launch) data storage and transmission equipment. You might expect that all we would have to do is transmit the data back to Earth at the speed of light. It takes sunlight more than eight minutes to reach Earth, and data from Mars can take as much as 20 minutes, but New Horizons is so distant that it takes more than five hours for data to be transmitted to Earth.
While it’s true that data are sent to us from the spacecraft at light-speed, the signal spreads out over distance, and it requires a Deep Space Network 70-metre-diameter antenna to capture the faint, diffuse signal arriving on Earth from New Horizons, which is five billion kilometres away. And even an antenna that large can collect only 125 bytes of data per second from such a remote source of relatively low power.
For a single image from the onboard camera instrument — roughly a 2.5-megabit image when compressed — it takes 20 to 40 minutes for the 70-metre dish to collect the data. Some high-resolution images take much longer than that. For this reason and because the Deep Space Network antennas have other tasks to handle, the entire library of images stored on New Horizons will not be safely on Earth until late this year.
Editor Terence Dickinson invites your comments and astronomy-related observations and photos, which can be directed to him at dickinsonSkyNews@gmail.com.
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