Tuesday, July 14, 2015


After a nine-year long journey covering 3 billion miles NASA's New Horizons probe has reached Pluto. Great coverage from EarthSky dot org:

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"Pluto nearly fills the frame in this image from the Long Range Reconnaissance Imager (LORRI) aboard NASA’s New Horizons spacecraft, taken on July 13, 2015 when the spacecraft was 476,000 miles (768,000 kilometers) from the surface. This is the last and most detailed image sent to Earth before the spacecraft’s closest approach to Pluto on July 14. The color image has been combined with lower-resolution color information from the Ralph instrument that was acquired earlier on July 13. This view is dominated by the large, bright feature informally named the “heart,” which measures approximately 1,000 miles (1,600 kilometers) across. The heart borders darker equatorial terrains, and the mottled terrain to its east (right) are complex. However, even at this resolution, much of the heart’s interior appears remarkably featureless—possibly a sign of ongoing geologic processes.
Credits: NASA/APL/SwRI"

There's an absolutely great series of short, easily understandable explanatory videos out there, Pluto in a minute. Here are a couple of them:

More from EarthSky.org:

"NASA’s New Horizons spacecraft is at Pluto.

After a decade-long journey through our solar system, New Horizons made its closest approach to Pluto Tuesday (July 14, 2015), about 7,750 miles above the surface – roughly the same distance from New York to Mumbai, India – making it the first-ever space mission to explore a world so far from Earth.

Per the plan, the spacecraft currently is in data-gathering mode and not in contact with flight controllers at the Johns Hopkins University Applied Physical Laboratory (APL) in Laurel, Maryland. Scientists are waiting to find out whether New Horizons “phones home,” transmitting to Earth a series of status updates that indicate the spacecraft survived the flyby and is in good health. The “call” is expected shortly after 9 p.m. tonight (July 14).

The Pluto story began only a generation ago when young Clyde Tombaugh was tasked to look for Planet X, theorized to exist beyond the orbit of Neptune. He discovered a faint point of light that we now see as a complex and fascinating world.

John Grunsfeld is associate administrator for NASA’s Science Mission Directorate in Washington. He said:

Pluto was discovered just 85 years ago by a farmer’s son from Kansas, inspired by a visionary from Boston, using a telescope in Flagstaff, Arizona. Today, science takes a great leap observing the Pluto system up close and flying into a new frontier that will help us better understand the origins of the solar system.

New Horizons’ flyby of the dwarf planet and its five known moons is providing an up-close introduction to the solar system’s Kuiper Belt, an outer region populated by icy objects ranging in size from boulders to dwarf planets. Kuiper Belt objects, such as Pluto, preserve evidence about the early formation of the solar system.

New Horizons’ almost 10-year, three-billion-mile journey to closest approach at Pluto took about one minute less than predicted when the craft was launched in January 2006. The spacecraft threaded the needle through a 36-by-57 mile (60 by 90 kilometers) window in space – the equivalent of a commercial airliner arriving no more off target than the width of a tennis ball.

Because New Horizons is the fastest spacecraft ever launched – hurtling through the Pluto system at more than 30,000 mph, a collision with a particle as small as a grain of rice could incapacitate the spacecraft. Once it reestablishes contact, it will take 16 months for New Horizons to send its cache of data – 10 years’ worth – back to Earth...."

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Some general info on the New Horizons probe, slightly adapted from Wiki:

* it hurtles through space in one of two "modes", either spin-stabilized mode (for cruising) or and three-axis stabilized mode (for science experiments). Both modes are controlled with hydrazine monopropellant. Post launch there was an additional delta-v of over 290 m/s (1,000 km/h; 650 mph), which was fueled by a 77 kg (170 lb) internal tank. Helium is used as a pressurant, with an elastomeric diaphragm assisting expulsion. And now that we are talking about hydrazine, that's N2H4, and it was first used as a propellant fuel in Nazi Germany's Me163B rocket interceptor, where it was called "B-Stoff". It's a colourless highly toxic flammable liquid, and I recall that back in the eighties, every time an F-16 had an accident (the BAF operated far more F-16's then than it does now, and one of the reasons is that there were so many accidents in the beginning), there was a huge fuss about hydrazine contamination at the crash site. But I digress.

* New Horizons has 16 thrusters: four 4.4 N (1.0 lbf) and twelve 0.9 N (0.2 lbf) plumbed into redundant branches. The four "large" ones are used primarily for trajectory corrections, and the small ones (the types were also used on the Cassini and Voyager spacecraft) are used mainly for attitude control and spinup/spindown maneuvers. Two star cameras are used to measure the spacecraft attitude. They are mounted on the face of the spacecraft and provide attitude information while in spin-stabilized or 3-axis mode. In between the time of star camera readings, spacecraft orientation is provided by dual redundant miniature inertial measurement units. Each unit contains three solid-state gyroscopes and three accelerometers. Two Adcole Sun sensors provide attitude control. One detects the angle to the Sun, whereas the other measures spin rate and clocking.

* Power supply: check out the cylindrical radioisotope thermoelectric generator (RTG) protruding in the plane of the triangle from one vertex of it. A radioisotope thermoelectric generator is an electrical generator that uses an array of thermocouples to convert the heat released by the decay of a suitable radioactive material into electricity by the Seebeck effect, which describes the conversion of temperature differences directly into electricity. Therefor, an RTG has no moving parts. NH's RTG will provide about 250 W, 30 V DC at launch, and is predicted to drop approximately 5% every 4 years, decaying to 200 W by the time of its encounter with Pluto/Charon in 2015. The RTG, model "GPHS-RTG," was originally a spare from the Cassini mission. The RTG contains 10.9 kg (24 lb) of plutonium-238 oxide pellets. Each pellet is clad in iridium, then encased in a graphite shell. It was developed by the U.S. Department of Energy at the Materials and Fuels Complex, a part of the Idaho National Laboratory. Less power than the original design goal was produced because of delays at the United States Department of Energy, including security activities. The mission parameters and observation sequence had to be modified for the reduced wattage; still, not all instruments can operate simultaneously. New Horizons carries no batteries and RTG output is relatively predictable; load transients are handled by a capacitor bank and fast circuit breakers.

The amount of radioactive plutonium in the RTG is 10.9 kg (24 lb), about one-third the amount on board the Cassini–Huygens probe when it launched in 1997. That launch was protested by some. The United States Department of Energy estimated the chances of a launch accident that would release radiation into the atmosphere at 1 in 350, and monitored the launch as it always does when RTGs are involved.

* The NH probe's Flight computer comprises two computer systems: the Command and Data Handling system and the Guidance and Control processor. Each of the two systems is duplicated for redundancy, thus there are actually four navigating computer. The processor used for its flight computers is the Mongoose-V, a 12 MHz radiation-hardened version of the MIPS R3000 CPU. Multiple clocks and timing routines are implemented in hardware and software to help prevent faults and downtime. To conserve heat and mass, spacecraft and instrument electronics are housed together in IEMs (integrated electronics modules). There are two redundant IEMs. Including other functions such as instrument and radio electronics, each IEM contains 9 boards.

Oh to be part of such a magnificent undertaking!


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