Interstellar space and Interstellar Probes ( Voyager and New Horizons Missions )
Interstellar Space:
Interstellar space is often called the space between the stars, but more specifically, it’s the region between our Sun’s heliosphere and the astrospheres of other stars.
Our heliosphere is a vast bubble of plasma – a gas of charged particles – that spews out of the Sun. This outflow is known as the solar wind. The bubble surrounds the Sun and stretches beyond the planets. Both Voyager spacecraft had to travel more than 11 billion miles (17 billion kilometers) from the Sun in order to cross the edge of the heliosphere. This bubble is moving through interstellar space as the Sun orbits the center of the Milky Way galaxy. As our heliosphere plows through space, it creates a bow wave, like the wave formed by the bow of a ship.
Kuiper Belt & Oort Cloud:
The Kuiper Belt is a doughnut-shaped ring of icy objects around the Sun, extending just beyond the orbit of Neptune from about 30 to 55 AU.
Similar to the asteroid belt, the Kuiper Belt is a region of leftovers from the solar system's early history. Like the asteroid belt, it has also been shaped by a giant planet, although it's more of a thick disk (like a donut) than a thin belt.
The Kuiper Belt shouldn't be confused with the Oort Cloud, which is a much more distant region of icy, comet-like bodies that surrounds the solar system, including the Kuiper Belt. Both the Oort Cloud and the Kuiper Belt are thought to be sources of comets.
The Oort Cloud is the most distant region of our solar system. Even the nearest objects in the Oort Cloud are thought to be many times farther from the Sun than the outer reaches of the Kuiper Belt.
Unlike the orbits of the planets and the Kuiper Belt, which lie mostly in the same flat disk around the Sun, the Oort Cloud is believed to be a giant spherical shell surrounding the rest of the solar system. It is like a big, thick-walled bubble made of icy pieces of space debris the sizes of mountains and sometimes larger. The Oort Cloud might contain billions, or even trillions, of objects.
Interstellar Probes:
Voyager Mission:
The twin Voyager 1 and 2 spacecraft continue exploring where nothing from Earth has flown before. Launched in 1977, they each are now more than three times farther away from Earth and the Sun than is Pluto. The Voyagers are involved in a mission to characterize the far outer heliosphere, the distant solar wind, and the interaction between the two. This phase of the mission has allowed us to explore the most distant reaches of our heliosphere and allowed us to take the first tentative steps in the transition regions between that region dominated by the Sun and interstellar space.
Voyager 1 and Voyager 2 have crossed the termination shock — where the solar wind is slowed abruptly due to the interaction with interstellar gas. Voyager 1 crossed the shock in December 2004 and Voyager 2 crossed in August 2007. Both spacecraft are sending information about their surroundings through NASA’s Deep Space Network.
Voyager 1:
Voyager 1 was launched on Sept. 5, 1977.
- Voyager 1 was the first spacecraft to cross the heliosphere, the boundary where the influences outside our solar system are stronger than those from our Sun.
- Voyager 1 is the first human-made object to venture into interstellar space.
- Voyager 1 discovered a thin ring around Jupiter and two new Jovian moons: Thebe and Metis.
- At Saturn, Voyager 1 found five new moons and a new ring called the G-ring.
- Voyager 2 is the only spacecraft to study all four of the solar system's giant planets at close range.
- Voyager 2 discovered a 14th moon at Jupiter.
- Voyager 2 was the first human-made object to fly past Uranus.
- At Uranus, Voyager 2 discovered 10 new moons and two new rings.
- Voyager 2 was the first human-made object to fly by Neptune.
- At Neptune, Voyager 2 discovered five moons, four rings, and a "Great Dark Spot."
New Horizons Mission:
New Horizons was launched directly into a hyperbolic escape trajectory, getting a gravitational assist from Jupiter en route. By March 7, 2008, New Horizons was 9.37 AU from the Sun and traveling outward at 3.9 AU per year. It will, however, slow to an escape velocity of only 2.5 AU per year as it moves away from the Sun, so it will never catch up to either Voyager. As of early 2011, it was traveling at 3.356 AU/year (15.91 km/s) relative to the Sun. On July 14, 2015, it completed a flyby of Pluto at a distance of about 33 AU from the Sun. New Horizons next encountered 486958 Arrokoth on January 1, 2019, at about 43.4 AU from the Sun.
The Heliosphere's termination shock was crossed by Voyager 1 at 94 astronomical units (AU) and Voyager 2 at 84 AU according to the IBEX mission.
If New Horizons can reach the distance of 100 AU, it will be traveling at about 13 km/s (29,000 mph), around 4 km/s (8,900 mph) slower than Voyager 1 at that distance.
It was launched on Jan. 19, 2006.
- It is the First spacecraft to explore Pluto and its Moons up close.
- It is the First spacecraft to explore a second Kuiper Belt Object up close – Arrokoth (2014 MU69)
The Deep Space Network - or DSN - is NASA’s international array of giant radio antennas that supports interplanetary spacecraft missions, plus a few that orbit Earth. The DSN also provides radar and radio astronomy observations that improve our understanding of the solar system and the larger universe.
The DSN is operated by NASA's Jet Propulsion Laboratory (JPL), which also operates many of the agency's interplanetary robotic space missions.
The DSN consists of three facilities spaced equidistant from each other – approximately 120 degrees apart in longitude – around the world. These sites are at Goldstone, near Barstow, California; near Madrid, Spain; and near Canberra, Australia. The strategic placement of these sites permits constant communication with spacecraft as our planet rotates – before a distant spacecraft sinks below the horizon at one DSN site, another site can pick up the signal and carry on communicating.
Solar cells are used to provide power to space crafts including International Space Station. But Solar Energy ( Solar Radiation ) which reach interstellar space is of very low intensity. At such a low intensity, it is impossible to use Solar Cells to provide electric power to space craft. To provide Electric Power to Interstellar Missions, Radioisotope Thermoelectric Generators (RTGs) are used.
About Radioisotope Thermoelectric Generators (RTGs): Radioisotope Thermoelectric Generators (RTGs) are lightweight, compact spacecraft power systems that are extraordinarily reliable.
RTGs provide electrical power using heat from the natural radioactive decay of plutonium-238, in the form of plutonium dioxide. The large difference in temperature between this hot fuel and the cold environment of space is applied across special solid-state metallic junctions called thermocouples, which generates an electrical current using no moving parts.
They are such a reliable power sources that their power output diminishes by a factor of 1 – (1/2)1/87.7, which is 0.787%, per year.
One example is the MHW-RTG used by the Voyager probes. In the year 2000, 23 years after production, the radioactive material inside the RTG had decreased in power by 16.6%, i.e. providing 83.4% of its initial output; starting with a capacity of 470 W.
Compared to RTGs, Solar Panels have life span of 25 to 30 Years.
RTGs work on the principle of Seebeck Effect.
About Seebeck Effect:
More than two centuries ago, a German scientist named Thomas Seebeck discovered an unexpected property of physics: Metals and some compounds are good conductors of electricity as well as heat. He found that when he combined two of these materials and then applied heat to one end while exposing the other end to cold, a small electrical voltage was created across the materials. This is called Seebeck Effect.
Issues with Radioisotope Thermoelectric Generators (RTGs):
If space craft containing RTGs fails within atmosphere, it could lead to nuclear fallout. It could spread dangerous radio active elements on human settlements. There are many incidents of Radioactive contamination due to failure of launch vehicle containing RTGs.
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