Forty-one years after its launch, NASA’s Voyager 2 probe has exited the heliosphere – the protective bubble of particles and magnetic fields created by the Sun, and entered Interstellar space. Its twin, Voyager 1, made a similar crossing in 2012.
The crossing of the heliosphere took place around on Nov. 5 and was determined by comparing data from different instruments aboard the spacecraft. The Plasma Science Experiment (PLS) instrument observed a steep decline in the number and speed of the solar wind particles on Nov. 5. Further evidence was provided by three other instruments – the cosmic ray subsystem, the low energy charged particle instrument and the magnetometer – which showed an increase in inter-stellar cosmic particles.
The PLS had stopped working on Voyager 1 in 1980, long before that probe crossed the heliopause. Voyager 2 will continue to provide the first direct measurements from this region of space.
The Heliosphere
The heliosphere is the vast bubble-like region of space surrounding the Sun, created by the plasma (charged particles) "blown" out from the outer layers of the Sun, known as the solar wind. This bubble is shaped like a long wind sock as it moves with the Sun through interstellar space. The bubble presses outwards against interstellar plasma, which permeates our galaxy.
The solar wind flows outward from the Sun for billions of kilometres, far beyond even the region of Pluto, until it encounters the termination shock, where its motion slows abruptly.
The boundary between the solar wind and interstellar wind is the heliopause, where the pressure of the two winds are in balance. This balance in pressure causes the solar wind to turn back and flow down the tail of the heliosphere.
The space between the termination shock region and the heliopause is known as the heliosheath.
As the heliosphere plows through interstellar space, a bow shock forms, similar to what forms as a ship plowing through the ocean.
Voyager 2
Voyager 2 was launched by NASA on Aug 20, 1977, to study the outer Solar System. Its twin Voyager 1 was launched 16 days later. The Voyager 2 mission included flybys of Jupiter, Saturn, Uranus and Neptune. Voyager 2 is the only spacecraft to have visited Uranus and Neptune. Its primary mission ended with the exploration of the Neptunian system on October 2, 1989.
A few vital statistics -
PARAMETER |
VALUE |
Distance from Earth |
18 billion km |
Distance from Sun |
119 AU (17.8 billion km) from Sun
AU = Astronomical Unit = average Earth-Sun distance = ~150 million km
|
Communications Delay (one-way) |
16.5 hours |
Distance traveled |
30 billion km |
Current speed |
15.341 km/s relative to Sun
55,227 km per hour
484 million km per year
|
Launch Date |
Aug 20, 1977 |
Power |
3 radioisotope thermoelectric generators
470 W at launch time
Will run out of power around 2025
|
Computers |
3 subsystems, each with a pair of processors
Custom 16-bit designs
|
RAM |
69.63 kilobytes, across all 6 computers. www.wired.com/…
(A smart phone has 1 to 2 Gigabytes of RAM)
|
Flight Data computer Processor speed |
81,000 instructions per second
(A smart phone does around a few billion instructions per second)
|
Communications link speed |
160 bits per second
(A FIOS connection runs somewhere between 25 and 100 Mbps)
|
Secondary storage |
Digital ½ inch 8-track tape :-)
Capacity = 536 million bits
Stopped working in 2007
|
See voyager.jpl.nasa.gov/… for some more fun facts about Voyager.
Here is a diagram of Voyager 1 and 2 and their instruments -
Here is an animation showing the trajectory of the two Voyager spacecraft -
The images below show the locations of Voyager 1 and 2 from 2013 to 2018. Voyager 1 headed North of the plane of the orbits of the planets after its flyby of Saturn, while Voyager 2 headed South after its encounter with Neptune.
Here is a video highlighting Voyagers' epic journey through the solar system -
The 8-track Tape System
From ntrs.nasa.gov/… —
The data-storage subsystem can record at two rates: TV pictures, general science and engineering at 115.2 kbps; general science and engineering at 7.2 kbps; and engineering only at 7.2 kbps (engineering is acquired at only 1,200 bps, but is formatted with filler to match the recorder input rate). The tape transport is belt-driven. Its 1/2 in. magnetic tape is 328 m (1,076 ft.) long and is divided into eight tracks that are recorded sequentially one track at a time. Total recycleable storage capacity is about 536 million bits -- the equivalent of 100 TV pictures. Playback is at four speeds -- 57.6; 33.6; 21.6 and 7.2 kbps.
hackaday.com/… has a good article on the Voyager digital tape drive.
The Future of Voyager 2
It will be a long time before Voyager 2 exits the Solar system, whose boundary is considered to be beyond the outer edge of the Oort Cloud, a collection of small objects that are still under the influence of the Sun’s gravity. It will take about 300 years for Voyager 2 to reach the inner edge of the Oort Cloud and possibly 30,000 years to cross it.
Voyager 2 is not headed anywhere in particular, but in roughly 40,000 years, Voyager 2 should pass 1.7 light-years from the star Ross 248. And if undisturbed for 296,000 years, Voyager 2 should pass by the star Sirius at a distance of 4.3 light-years. Voyager 2 will go quiet around 2025.
But, we never know ...
Music
Here is a selection of music to go with the dairy. Select one and play it as you read the diary!
After 41 years, each Voyager spacecraft is still going strong, having survived the rigors of space over its 20+ billion km journey. Made possible by the ingenuity and hard work of its designers and mission personnel. A mission that has inspired generations of engineers and scientists. We need more investment of minds and dollars in such programs, not less. Our future depends on it.
To paraphrase D. H. Lawrence,
They say space is cold, but space contains
the hottest blood of all, and the wildest, the most urgent
All the spaceships in the wider orbits, hot are they, as they urge
on and on, and dive between the planets.
The Voyagers, the Pioneers, the New Horizons, the Cassinis,
there they blow, there they blow, hot wild white breath out of the vacuum!
What memories do you have of the time when the Voyager spacecraft were launched? And what do you see in the future of humankind?
References
- NASA’s Voyager 2 Probe Enters Interstellar Space — www.nasa.gov/...
- Voyager program — en.wikipedia.org/…
- Voyager 2 wiki — en.wikipedia.org/...
- Voyager NASA site — voyager.jpl.nasa.gov
- Computers in Spaceflight: The NASA Experience- history.nasa.gov/…
- Voyager backgrounder — ntrs.nasa.gov/…
- Voyager 1 Thrusters Fired Up After 37 Years of Deep Sleep — www.dailykos.com/…
- Why Go To Mars? And other Planets and Moons. — www.dailykos.com/...