How long can probes stay in space

In the past, dense clouds might have so squeezed the heliosphere that even Earth sat outside the shield, exposed to cosmic rays that may have helped or hindered the origin of life. Although no one knows for sure, the comets may reach halfway to Alpha Centauri, the closest star system at 4. In that case, despite its swift speed, Voyager 1 is like a California-bound traveler who has walked just a few miles from the Atlantic seaboard.

Ask Smithsonian A Smithsonian magazine special report. Stamatios Krimigis, a space scientist at the Johns Hopkins University Applied Physics Laboratory and the principal investigator of the mission's low-energy charged particles experiment , explained that the devices were designed to last just four years, during which they would need to conduct , turns of a motor dubbed "steps" to take measurements.

Both versions of the experiment are still running. The Voyager spacecraft launched two weeks apart in , taking slightly different trajectories past Jupiter and Saturn. Then, the probes parted ways. Voyager 1 scouted out Saturn's moon Titan and then made a beeline out of our solar system; Voyager 2 took a more leisurely route, giving humans our only look at Uranus and Neptune. Their longevity has translated to speed and distance that are difficult to fathom.

On NASA's tracking page for the mission , each spacecraft's odometer ticks up by 10 miles 16 kilometers or more twice a second, a constant churn that makes the passage of time suddenly excruciating.

And yet, it takes nearly 17 hours for messages from Voyager 2 to travel back to Earth and more than 20 hours for those sent by Voyager 1. After all, even after we lose contact with all five, they will still be speeding away from the solar system toward distant stars.

When famed astronomer Carl Sagan spearheaded the effort behind that plaque more than 40 years ago, it was thought of as a greeting. The article was first published on October 23, Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue.

See Subscription Options. Go Paperless with Digital. Get smart. Total number of words among the six computers is about 32K. Computer Command System CCS - bit word, interrupt type processors 2 with words each of plated wire, non-volatile memory.

According to my calculations, that's a total of about 68KB, or small potatoes compared to today's microprocessors. We probably could perform all functions with one of today's boards and still have room for solid state data storage and much more fault detection software.

We would still need a second unit for redundancy. Today's microprocessors are also much faster than the chips used on Voyager and a comparative system would use less electrical power. On the other hand, software might be more complicated as opposed to that used in an interrupt type system, but it would be much more capable and more flexible. Let's look closer at the CCS. The CCS has two main functions: to carry out instructions from the ground to operate the spacecraft, and to be alert for a problem or malfunction and respond to it.

Two identical word memories contain both fixed routines about words and a variable section about words for changing science sequences. The CCS issues commands to the AACS for movement of the scan platform or spacecraft maneuvers; to the FDS for changes in instrument configurations or telemetry rates and to numerous other subsystems within the spacecraft for specific actions.

The FDS also keeps the spacecraft "time" and provides frequency references to the instruments and other spacecraft subsystems. The Voyager spacecraft computers are interrupt driven computer, similar to processors used in general purpose computers with a few special instructions for increased efficiency.

The programming is a form of assembly language. There is no clock chip, as such, in the spacecraft. The "clock" is really a counter, based on one of several electronically generated frequencies.

These frequencies, based on a reference, generated by a very stable oscillator, are converted and fed to different locations in the spacecraft as synchronization signals, timers, counters, etc. The "clock" signal is part of the information telemetered to the ground and it is with ground software that we convert to day of year, time of day Greenwich Mean Time. A typical instruction takes 80 microseconds, that is about 8, instructions per second.

To put this in perspective, a top-of-the-line smartphone runs at 1. Pioneer 10 is headed towards the constellation of Taurus The Bull. It will take Pioneer over 2 million years to pass by one of the stars in the constellation.

Pioneer 11 is headed toward the constellation of Aquila The Eagle , Northwest of the constellation of Sagittarius. Pioneer 11 may pass near one of the stars in the constellation in about 4 million years. In the year 40, AD, Voyager 1 will come within 1. Voyager 2 is also escaping the solar system at a speed of about 3. You asked about the Voyager plate. I'm assuming you mean the engravings on the aluminum record cover on each of the two Voyagers.

You can see the record cover installed on the spacecraft bus. Also, from Carl Sagan's book, "Murmurs of Earth", here is a description of the cover engravings: "In the upper left-hand corner is an easily recognized drawing of the phonograph record and the stylus carried with it. The stylus is in the correct position to play the record from the beginning.

Written around it in binary arithmetic is the correct time of one rotation of the record, 3. The drawing indicates that the record should be played from the outside in. Below this drawing is a side view of the record and stylus, with a binary number giving the time to play one side of the record - about an hour. The top drawing shows the typical signal that occurs at the start of a picture.

The picture is made from this signal, which traces the picture as a series of vertical lines, similar to ordinary television in which the picture is a series of horizontal lines. Picture lines 1, 2 and 3 are noted in binary numbers, and the duration of one of the "picture lines," about 8 milliseconds, is noted.

The drawing immediately below shows how these lines are to be drawn vertically, with staggered "interlace" to give the correct picture rendition. Immediately below this is a drawing of an entire picture raster, showing that there are vertical lines in a complete picture. Immediately below this is a replica of the first picture on the record to permit the recipients to verify that they are decoding the signals correctly. A circle was used in this picture to insure that the recipients use the correct ratio of horizontal to vertical height in picture reconstruction.

It shows the location of the solar system with respect to 14 pulsars, whose precise periods are given. The drawing containing two circles in the lower right-hand corner is a drawing of the hydrogen atom in its two lowest states, with a connecting line and digit 1 to indicate that the time interval associated with the transition from one state to the other is to be used as the fundamental time scale, both for the time given on the cover and in the decoded pictures.

The steady decay of the uranium source into its daughter isotopes makes it a kind of radioactive clock. Half of the uranium will decay in 4.

Thus, by examining this two-centimeter diameter area on the record plate and measuring the amount of daughter elements to the remaining uranium, an extraterrestrial recipient of the Voyager spacecraft could calculate the time elapsed since a spot of uranium was placed aboard the spacecraft. This should be a check on the epoch of launch, which is also described by the pulsar map on the record cover.