VOYAGERS INTO INTERSTELLAR SPACE

Sure, Armstrong's walk on the Moon was remarkable.  Our space exploits helped bankrupt the Soviet Union, leading to the end of the Cold War.  Yes, the James Webb Space Telescope is doing wonders.  

However, maybe the most impressive NASA space project has to be those two Voyagers hurtling into interstellar space.  You can keep track of their status here.  Voyager 1 is 14.8 billion miles and Voyager II is 12.4 billion miles away from Planet Earth.  They are moving along at 38,027 miles/hour (I) and 34,391 MPH (II).  It has been more than 45 years since they were launched.  Light would take more than 22 hours to reach Voyager I.  Every day they move away by another three to four light-seconds.  See Voyager I's path.

Tim Folger has an excellent article in the July 2022 issue of Scientific American, entitled Record-Breaking Voyager Spacecraft Begin to Power Down.  I'd recommend you read it, but the story is so extraordinary that I feel compelled to summarize the essence.

• First of all, there never would have been any Voyagers if not for two freaky circumstances.
• 60 years ago no one was really aware of a rare planetary arched syzygy that had occurred in the time of the presidency of Thomas Jefferson,
• In 1965, a few years before the first walk on the Moon, Gary Flandro (above), a PhD student at CalTech, had been tasked with finding the most efficient way to send a space probe to Jupiter, and maybe even Saturn, Uranus or Neptune.

• 
  Using a man-made technology called a pencil, he charted planetary orbital paths and discovered in the late 1970's and early 1980's, all four planets would be strung along a long arc with Earth.
• This coincidence meant that a space vehicle could get a speed boost from the gravitational pull of each giant planet to the next, cutting the flight time between Earth and Neptune from 30 years to 12.

• 
  This happened only every 176 years, so timing was crucial, and any spacecraft to take this journey would have to be launched by the mid-1970's.  Remember, this was 1965.
• NASA drew up plans for a Grand Tour, to send five probes to the four giant planets...and Pluto, also in line.  Congress initially turned it down, but eventually allowed for two at minimal cost.

• 
  With funds, NASA planned for a four-year mission of limited scale.  However, without telling even the management, insiders of the project added equipment for a more ambitious effort.
• Mind you, in the early 1960's NASA had attempted 12 failed missions to find a future Moon landing site, and finally succeeded on the 13th.  Failure was expected.
• 
  For the Voyagers, there was a worse hurdle, as they had to fly through the asteroid belt and could be torn to pieces.  Fortunately, Pioneer 10 and 11 in 1972 passed through, improving confidence.  For the Voyagers, launch was not yet to be until 1977,

• 
  Remember, these Voyagers were not tiny.  Each was as large as an old Volkswagen Beetle.
• Each had a computer with 69 kilobytes of memory.
• This was 1/100,000 the capacity of a typical smartphone today.
• Actually, that does not do the comparison justice.  These Voyager computers had less memory than the key fob that opens your car door.
• 
  All data collected would be stored on 8-track tape recorders and then sent back to Earth by a 23-watt transmitter, which is about the power level of your refrigerator light bulb.
• They hoped that this weak signal could be adequately transmitted using a 12-foot wide dish antenna.
• That was the top of the technology in those days.

If you can't read that graphic, go to the article.  Note that Voyager II was launched before I, because it had a longer path, and the Voyagers are today headed in different directions.  Also appreciate that a four-year project is now in its 46th year.

• 
  Voyager I reached Jupiter in March of 1979, 546 days after launch, with II getting there in July of 1980.
• Pictures began to be sent a few months before the encounter.
• The data came in line by line.  I had a similar experience in 1976 when Viking I sent the first photo of Mars to the NASA Ames Research Center, where a group of us, including Carl Sagan, sat in impatient awe.  We were the first to see Mars before the photo was sent out to the media.
• One image was of Jupiter's moon Io, which came in an unexpected bright orange (below right).  
• Instruments also detected oxygen and sulphur a thousand times higher than anticipated.  
• 
  Io, about the size of our Moon, had volcanoes, which was a shock, for scientists then thought it was only Earth that had any in our solar system.  And Io's volcanoes had 10 times the activity of our planet.  Debris from just one, Pele, covered an area the size of France.
• The Voyagers took more than 33,000 photographs just of Jupiter and its moons.

• 
  Plus, Jupiter, it turned out, had rings, and 53 moons.
• One, Europa was covered with ice, estimated to be 60 miles thick.
• It is here that both Voyagers got that farewell gravitational kick to allow them to reach interstellar space.  
• They parted company at Saturn, with II heading to Uranus and Neptune.   
• II found 10 new moons around Uranus and saw it too was ringed.  
• Much of this new information was overshadowed, however, by the 20January1986 explosion of the space shuttle Challenger shortly after launch, killing all seven on board.

• 
  Voyager II went on to pass Neptune's azure methane atmosphere, and measured the highest wind speeds in our solar system...up to 1000 MPH.  Neptune's largest moon Triton was found to have a surface temperature of -391 F, maybe the coldest in our solar system.  Ice volcanoes on Triton spewed nitrogen gas and powdery particles five miles into its atmosphere.
• 
  At this point NASA had planned to turn off the cameras on both probes, but Carl Sagan got them to have Voyager I transmit one last series of images on Valentine's Day in 1990, aiming back to us with 60 shots, including that Pale Blue Dot, with Earth 3.7 billion miles away.  That key photo had 640,000 pixels.  Earth represented only one pixel.  Sagan penned a book using that title in 1994.  He passed away two years later.

Finally:

• Voyager I crossed the heliopause on 25August2012, and Voyager II reached the interstellar shoreline in November of 2018.  Then again, maybe not.  
• The Voyagers will reach the Oort cloud of comet-like bodies in about 300 years.  
• In the meantime I has four functioning instruments and II has five, all still powered by converting heat from the radioactive decay of Plutonium into electricity.  
• 
  To conserve energy, NASA two years ago turned off the heater for the cosmic-ray detector.  The temperature dropped 60-70F, but the instrument kept working.
• In another 16,700 years, Voyager 1 will pass our nearest neighboring star, Proxima Centauri, with II similarly doing so in another 3,600 years.  That was from the Scientific American article.  Readers have interjected that Voyager I will take 40,000 years to get halfway there, and that Voyager II will take over 73,000 years to reach Proxima Centauri. 
• But:

FOLGER REPLIES: To answer Cary: In 40,000 years the Voyagers will reach the outer edge of the Oort cloud, which is indeed about halfway to Proxima Centauri. But tens of thousands of years before that time, Voyager 1 and 2 will make their closest encounter with that star, coming within about 3.5 and 2.9 light-years of it, respectively. That’s not very close: the sun is currently about 4.2 light-years away from Proxima Centauri. On a cosmic scale, the sun and the Voyager spacecraft are essentially the same distance from our nearest stellar neighbor. But because the spacecraft are moving away from the sun, and Proxima Centauri is moving toward it, the Voyagers’ closest approach to our neighboring star will occur in 16,700 and 20,300 years.

•  Thus, they are not heading towards Proxima Centauri, for they are going in different directions anyway.  In any case, that is a long time from today.

• 
  Will any alien civilization find them?
• The Voyagers are the most distant man-made objects.
• But we won't know anything after 2025 because the spaceship power will runout...unless it is found.  Then, who knows?  Will there then be a call from another civilization?
• Each has a record made of copper and coated with gold and sealed in an aluminum cover.
• The executive producer of these Golden Records was Carl Sagan.

• 

  There are pictures of children, sunsets, Bach's Brandenburg Concerto No. 2 and Chuck Berry's Johnny B Goode.  Then President Jimmy Carter has a written message.
• Here is a nearly 2-hour long video of the entire contents.

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