NASA’s long-running Voyager 1 spacecraft is barreling its way toward the edge of the solar system.
Since 2004, the unmanned probe has been exploring a region of space where solar wind — a stream of charged particles spewing from the sun at 1 million miles per hour — slows abruptly and crashes into the thin gas between stars.
NASA said Monday that recent readings show the average outward speed of the solar wind has slowed to zero, meaning the spacecraft is nearing ever closer to the solar system’s edge to a boundary known as the heliopause.
“It’s telling us the heliopause is not too far ahead,” said project scientist Edward Stone of the NASA Jet Propulsion Laboratory.
Scientists estimate it will take another four years before Voyager 1 completely exits the solar system and enters interstellar space.
The latest milestone occurred in June when scientists noticed the solar wind speed matched the spacecraft’s. Just as wind velocity on Earth can vary, the team took measurements for several more months to make sure there were no changes.
“We knew this was going to happen. The question was when,” Stone said.
Voyager Squashes View of Solar System
Scientists using data from NASA’s Voyager 2 spacecraft have observed the bubble of solar wind surrounding the solar system is not round, but has a squashed shape, according to recent data published as part of a series of papers in this week’s (July 3) Nature.
The beginning of the transition zone between the heliosphere (the solar wind bubble) and the rest of interstellar space is known as the ‘termination shock’. Scientists report that Voyager 2 crossed this boundary closer to the sun than expected, suggesting that the heliosphere in this region is pushed inward, closer to the sun, by an interstellar magnetic field. These findings help build up a picture of how the sun interacts with the surrounding interstellar medium.
Interesting that Voyager 1 launched Sept 5, 1977 and it will still have electrical power from plutonium up until 2020 according to JPL.
“Voyager’s radioisotope power generators, which use heat from the decay of plutonium to produce electricity, have enabled the spacecraft to operate for this extended period of time, so far away from the sun.”
“It is estimated that both Voyager craft have sufficient electrical power to operate their radio transmitters until at least 2025, which will be over 48 years after launch.” – wik
Neat, but is it safe to launch plutonium into space? Image: Apollo 16 RTG.
… The failure of the Apollo 13 mission in April 1970 meant that the Lunar Module reentered the atmosphere carrying an RTG and burnt up over Fiji. It carried a SNAP-27 RTG containing 44,500 curies (1,650 TBq) of plutonium dioxide which survived reentry into the Earth’s atmosphere intact, as it was designed to do, the trajectory being arranged so that it would plunge into 6–9 kilometers of water in the Tonga trench in the Pacific Ocean. The absence of plutonium 238 contamination in atmospheric and seawater sampling confirmed the assumption that the cask is intact on the seabed. The cask is expected to contain the fuel for at least 10 half-lives (i.e. 870 years). The US Department of Energy has conducted seawater tests and determined that the graphite casing, which was designed to withstand reentry, is stable and no release of plutonium should occur. Subsequent investigations have found no increase in the natural background radiation in the area. The Apollo 13 accident represents an extreme scenario due to the high re-entry velocities of the craft returning from cislunar space. This accident has served to validate the design of later-generation RTGs as highly safe.
To minimize the risk of the radioactive material being released, the fuel is stored in individual modular units with their own heat shielding. They are surrounded by a layer of iridium metal and encased in high-strength graphite blocks. These two materials are corrosion- and heat-resistant. Surrounding the graphite blocks is an aeroshell, designed to protect the entire assembly against the heat of reentering the Earth’s atmosphere. The plutonium fuel is also stored in a ceramic form that is heat-resistant, minimising the risk of vaporization and aerosolization. The ceramic is also highly insoluble.
The most recent accident involving a spacecraft RTG was the failure of the Russian Mars 96 probe launch on 16 November 1996. The two RTGs onboard carried in total 200 g of plutonium and are assumed to have survived reentry (as they were designed to do). They are thought to now lie somewhere in a northeast-southwest running oval 320 km long by 80 km wide which is centred 32 km east of Iquique, Chile.
Many Beta-M RTGs produced by the Soviet Union to power lighthouses and beacons have become orphaned sources of radiation. Several of these units have been illegally dismantled for scrap metal resulting in the complete exposure of the Sr-90 source, fallen into the ocean, or have defective shielding due to poor design or physical damage. The US Department of Defense cooperative threat reduction program has expressed concern that material from the Beta-M RTGs can be used by terrorists to construct a dirty bomb.