NASA says Voyager 2 is nearing the interstellar space. They know it ‘because it is detecting an increase in cosmic rays that originate outside our solar system’. This space craft has traveled 17.7 billion kilometers since it was launched more than 41 years ago on August 20, 1977. This distance is really only 118 times the distance between earth and sun. But how does Voyager convey to us that it is detecting increase in cosmic rays. Back of the envelope calculation, or more contemporarily, your smart phone calculator, will tell you that a message from Voyager will take more that 18 hours to reach earth. In a World where cell phones keep on dropping local calls, how do we get messages from this tiny speck in the deep space! This is where faith comes in. Get this: The power of signals that earth based antennas receive from the Voyager is 20 billion times weaker than what is needed to run a digital watch. On Voyager they use a 22.4 Watt Transmitter (for Voyager 1); something equivalent to a refrigerator light bulb, but by the time its beacon reaches us, the power has been reduced to roughly 0.1 billion-billionth of a Watt. To detect this signal NASA has built a Deep Space Network (DSN) on earth with antennas at locations near Canberra, Australia; Madrid, Spain; and Goldstone, California. The largest of the four antennas at each site is 70 meters in diameter. The Voyager has an antenna that is 3.7 meters in diameter. Voyagers technology is 41 years old, with computers each having 69.63 kilobytes of memory. Absolutely non-upgradable. Although DSN technology is being continuously upgraded. The DSN antennas can locate a spacecraft extremely accurately in the celestial sphere with angular measurement error measured in nano-radians (one nano-radian of error at 1 million kilometers is 100 cm). This means a certainty of knowing that Voyager is within a given sphere of diameter as small as 1800 km. That is equivalent of distance between Delhi and Chennai, looking from a distance of 17.7 billion kilometers. The Voyager is transmitting in the 8 GHz range. Since there is not a lot of interference from man-made electromagnetic noise at this frequency, the antenna on Earth can use an extremely sensitive amplifier and still make sense of the faint signals it receives. But when the earth antenna transmits back to the spacecraft, it uses extremely high power (tens of thousands of watts) to make sure the spacecraft gets the message. So yes! NASA says Voyager 2 is nearing the interstellar space. They know it ‘because it is detecting an increase in cosmic rays that originate outside our solar system’. Faith! Actually not!! https://www.nasa.gov/feature/jpl/nasa-voyager-2-could-be-nearing-interstellar-space https://spaceplace.nasa.gov/dsn-antennas/en/ https://www.wired.com/2013/09/vintage-voyager-probes/ https://www.allaboutcircuits.com/news/voyager-mission-anniversary-celebration-long-distance-communications/ |
This is our irregular blog. We will post about space, cartoons, science, happenings or whatever takes our fancy. Any comments can be e.mailed to neeraj[dot]jain4e4a[at]gmail[dot]com
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