Juno Arriving at Jupiter!
One of the primary goals of Juno is to learn the recipe for solar systems, said Scott Bolton, a scientist at the Southwest Research Institute in San Antonio who is the principal investigator for the $1.1 billion mission. How do you make the solar system? How do you make the planets in our solar system?
Interactive Feature
Spinnable maps of Jupiter and the Galilean moons.
Jupiter is the titan among planets called the gas giants, with more than three times the mass of Saturn, the next largest. But it is far more than a bland ball of hydrogen and helium.
What particularly piques scientists interest are the small amounts of heavier elements like lithium, carbon and nitrogen.
Jupiter is enriched with these elements compared to the sun, Dr. Bolton said. We dont know exactly how that happened. But we know its really important. And the reason its important is the stuff that Jupiter has more of is what were all made out of. Its what the Earth is made out of. It is what life comes from.
On July 4, as the main engine on the spacecraft fires, in the control room at NASAs Jet Propulsion Laboratory in Pasadena, Calif., there will be nothing to control, and all anyone there will be able to do is wait and watch.
Photo The Juno spacecraft captured this image of Jupiter, the yellow planet on the right, and several of its moons on June 21. Credit NASA
If anything goes wrong, there is no way for anyone to intercede. The radio signals take 48 minutes to travel from Jupiter to Earth. By the time engineers receive word the engine firing has begun, the engine should have already switched off, with the spacecraft in orbit.
If the engine shuts off prematurely, Juno might still end up in orbit, albeit in the wrong orbit. If the engine fails, we dont end up in a very exciting spot, Mr. Nybakken said.
We havent studied that too much in terms of where we end up, because were focused on success and not failure.
In other words, Juno would zip right past Jupiter and end up in a useless orbit around the sun.
Through the evening of July 4, mission control will receive only a series of radio tones three-second bursts at different frequencies telling the sequence of operations the spacecraft is performing. To point the engine in the correct direction, the main antenna will not be pointed at Earth, preventing more detailed telemetry. The spacecraft will also not send back any photographs or data from the instruments, which will be shut down on Wednesday, five days before its arrival, and will not be turned back on until a couple of days after its arrival. (NASA is holding back a series of photographs taken during the approach that it plans to release as a movie on July 4.)
Photo Juno in 2010 during its assembly and testing phase. Credit Patrick H. Corkery/Lockheed Martin
Juno is to make a series of 37 highly elliptical orbits passing over Jupiters north and south poles over 20 months.
At its farthest, it will be about two million miles from Jupiter. For each orbit, it will accelerate inward, reaching 128,000 miles per hour, and pass within 3,100 miles of Jupiters cloud tops. The slight fluctuations in Jupiters gravitational pull, measured by shifts in the frequency of Junos radio signals, will tell the density of the planets interior and whether there is a rocky core within, where pressures might reach half a billion pounds per square inch.
We dont really know if there is a core in the middle of Jupiter, Dr. Bolton said. If there is, it tells you sort of when and how and a little bit of where Jupiter must have formed.
Junos science instruments include one to measure Jupiters powerful magnetic fields and an infrared camera to observe the glowing auroras around the poles. At depth, increasing pressures transform hydrogen from a gas into a liquid. At even greater depths, the hydrogen issqueezed so tightly that the electrons squirt out, changing it into a metal. It is probably the churning of liquid metallic hydrogen that generates the magnetic fields.
Photo Scott Bolton, the principal investigator for the $1.1 billion mission, with a model of the solar-powered spacecraft. Credit SwRI
Juno also carries a camera for taking the usual kind of photographs, not as part of its prime science mission but as a way to attract public participation. Anyone can sign in to the Southwest Research Institutes Mission Juno website and suggest where the camera should be pointed and then vote on the choices.
Its really a public camera, Dr. Bolton said. They can engage in the debate of which things are most important to photograph.
Also on board Juno are three Lego custom minifigures made of spacecraft-grade aluminum. One is Jupiter, the king of the Roman gods. The second is Juno, wife and sister of Jupiter in Roman mythology, and the third is Galileo Galilei, the Italian astronomer who discovered the four large moons of Jupiter through a telescope he made.
We put these Lego minifigures on Juno in order to inspire and motivate and engage children, to help them share the excitement of space exploration, Dr. Bolton said.
Photo Lego figurines aboard Juno representing, from left, the Roman G*d Jupiter, his wife and sister Juno, and Galileo Galilei. Credit NASA/JPL-Caltech/KSC
After the first two orbits, during which engineers will check if the spacecraft and instruments are working properly, Juno is to fire its engine again to move into the orbit for making its scientific measurements.
Although the craft are very different in appearance, much of Junos electronics and programming are based on the design of Mars Reconnaissance Orbiter, an earlier spacecraft also built by Lockheed Martin. Its just configured in a different format, Guy Beutelschies, the director of interplanetary missions at Lockheed Martin, said in an interview.
Instead of developing electronic circuits that could operate in Jupiters intense radiation, Lockheed Martin used the same circuitry as Mars Reconnaissance Orbiter but shielded it within the half-inch-thick walls of a 400-pound titanium vault measuring about one yard on each side.
Unlike earlier missions to the outer solar system, Juno is powered by sunlight, not plutonium. Three solar panels 30 feet long with a total of 18,698 solar cells gather the dim sunlight to produce about 500 watts.
Even if everything goes better than planned, the mission will not last much beyond the planned 20 months. Despite the titanium armoring, we know the radiation is going to kill us, Mr. Beutelschies said.
Juno is expected to receive a radiation dose equivalent to more than 100 million dental X-rays.
One planet farther out, at Saturn, NASAs Cassini spacecraft is being readied for what its managers have called the grand finale. Almost 12 years after it arrived, Cassini is, through some slingshots past the moon Titan, swinging its orbit out of the plane of the moons and rings.
Beginning next April, Cassini will begin a series of 22 close flybys of Saturn, threading a narrow gap between the planet and its innermost ring, measuring Saturns gravitational and magnetic fields. Saturn is thought to have a rocky core perhaps as massive as Earth or perhaps several Earths. Cassini will also take stunning close-up images of the rings. Its like having a brand new mission, said Linda Spilker, Cassinis project scientist.
Then, on Sept. 15 next year, with its maneuvering fuel almost used up, it will shift its trajectory and end its 20-year mission with a death dive straight into Saturn, sending back data about the atmosphere until it is torn apart.
Five months later, Juno is scheduled to be similarly disposed at Jupiter. Then, for the first time in more than two decades, no NASA spacecraft will be orbiting any of the outer planets. The next mission to Jupiter, still on the drawing board, is to take a closer look at Europa. If it is built, it may not get there for a decade.
Continue reading the main story
Source: http://www.nytimes.com/2016/06/28/science/nasa-jupiter-juno.html