NASA/Agence France-Presse - Getty Images
Technicians at the Johns Hopkins University Applied Physics Laboratory prepared the Messenger spacecraft for its seven-year journey through the inner solar system. 
Posted on 07/28/2004 7:37:55 PM PDT by neverdem
The great unknown can be far away and nearby. This is true of the solar system, with the planets farthest and nearest the Sun remaining virtually uncharted by inquisitive humans while spacecraft send back mountains of data on the bodies in between.
Mercury, the planet closest to the Sun, will be getting its chance to become more scrutable starting next week when an instrument-crammed spacecraft called Messenger is to take off on a seven-year journey. Following a circuitous trip through the inner solar system, the craft will become only the second to visit mysterious Mercury and the first to orbit it for long-term study.
Meanwhile, Pluto, the smallest and most distant planet, has to wait until at least 2015 for its first visit from Earth if the planned New Horizons spacecraft meets its scheduled 2006 launching.
As with many aspects of this tricky mission, timing will be important. Messenger is scheduled to lift off for Mercury from Cape Canaveral, Fla., on Monday atop a Boeing Delta II rocket, but engineers will have only a 12-second launching period that day and, if something goes wrong, over each of the next 12 days.
Mercury, a small, rocky body slightly larger than Earth's moon, is difficult to study with spacecraft because of its proximity to the heat and brightness of the Sun. The planet's size and solar orbit also make it hard to slow a speeding spacecraft enough to be captured by its gravity for orbital studies.
Three decades ago, the National Aeronautics and Space Administration sent its Mariner 10 spacecraft to Mercury on a pioneering mission. Looping around Venus and the Sun, the craft made three swift flybys of Mercury during 1974 and 1975, sending back almost 1,000 pictures that mapped only 40 percent of the surface of the heavily cratered planet. Mariner found iron-laden Mercury to be the densest planet in the solar system and the only inner planet besides Earth with a global magnetic field, but left scientists wanting to know more.
"For nearly 30 years we've had questions that couldn't be answered until technology and mission designs caught up with our desire to go back to Mercury," said Dr. Sean C. Solomon of the Carnegie Institution of Washington, Messenger's principal investigator. "Now we are ready."
Since Mariner 10, ground-based observations have shown that Mercury is surrounded by an immense sodium cloud, but no one knows how it is being sustained. And radar probes from Earth show highly reflective areas in the polar regions that some scientists suggest may indicate some form of ice in cold, permanently shadowed craters.
"Studying Mercury's surface, tenuous atmosphere and magnetic field are a key to understanding the evolution of the inner solar system, including Earth," said Dr. Daniel N. Baker of the University of Colorado, a lead investigator for one of Messenger's seven scientific instruments.
Messenger is one of NASA's lower-cost, rapidly executed Discovery Program robot missions designed to go from planning to flight in about three years. It uses a relatively small, inexpensive launching vehicle. Pulling off the $427 million mission requires getting gravitational boosts from planetary flybys to get the spacecraft to Mercury and maneuver it into orbit.
Engineers are sending Messenger on a 4.9-billion-mile journey that takes it past Earth once, Venus twice and Mercury three times. The spacecraft will swing by Earth a year after launching for a boost to Venus, which it will fly by in October 2006 and June 2007 for course changes that take it past Mercury in January and October 2008, and again in September 2009.
Dr. Solomon said the Venus passes would be used to test Messenger's instruments and, he hoped, gather new scientific information, while the Mercury flybys would be used to map the previously un-imaged parts of the planet and gather other data critical to planning the orbital phase of the mission.
The importance of timing to the mission is illustrated by an 11-week delay that added almost two years to getting the spacecraft into Mercury orbit. Messenger was originally scheduled for launching around May 11, but NASA delayed the flight to resolve software issues and spacecraft testing. The change meant scrapping a flight plan that involved no Earth flyby, three trips around Venus instead of two and two passes past Mercury instead of three that would have put the craft in orbit in July 2009 instead of March 2011.
Engineers and scientists at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., had to design and build a special spacecraft to survive the rigors of the environment around Mercury. The planet orbits at an average distance of 36 million miles from the Sun during its 88-day year, about 50 million miles closer than the Earth, and is subjected to sunlight 11 times as intense.
David G. Grant, project manager at the laboratory, from which the mission also will be directed, said designing a spacecraft hardened against the heat, solar radiation and brightness of the nearby Sun was a challenge. "We're doing something no one has ever tried before," he said.
The main body of the spacecraft, made of a lightweight, heat-tolerant graphite composite material, is covered with multilayered insulation and peppered with radiators and heat pipes to channel heat away. The craft, powered by two electricity-generating solar panels, weighs 2,424 pounds at launching, half of that rocket fuel for its maneuvering engine and control thrusters.
The most distinctive feature of the spacecraft is a large, highly reflective, heat-resistant sunshade attached to the front on a titanium frame. Measuring eight feet tall and six feet across, the quarter-inch-thick shield is made of front and back layers of Nextel ceramic cloth surrounding inner layers of Kapton plastic insulation.
Temperatures on the front of the white shield could reach 700 degrees Fahrenheit when Mercury is closest to the Sun, engineers said, but the spacecraft on the shady side should operate at a room temperature of 68 degrees. Messenger is programmed to keep the shade between itself and the Sun at all times.
Messenger is to circle Mercury for one Earth year in an oval-shaped orbit that takes it 124 miles above the surface at the nearest point and 9,420 miles out at the farthest. Cameras will send back images many times sharper than Mariner's, showing features as small as 60 feet across; a battery of spectrometers will identify the elements and compounds on the surface; a laser altimeter will map landforms and distances; and other experiments will study variations in the planet's gravity and magnetic field.
NASA/Agence France-Presse - Getty Images
Technicians at the Johns Hopkins University Applied Physics Laboratory prepared the Messenger spacecraft for its seven-year journey through the inner solar system.
PING
I wonder if ion engines could cut the 7 year journey in some way...
Aren't there rocks here on earth that could be studied for a lot less money?
Yes - but until they turn up as being from Mercury, this'll have to do. ;-)
Is mecurey part of bushs war on terror ?
Are ion engines practical yet?
The official Hayabusa web page from JAXA.
It's hard to believe, but we are way behind in ion propulsion technology, even though we developed the original idea; in fact, in 1998, we had a craft testing ion propulsion, and even now we have a long-running ion engine in one of our labs. But we have let Japan leapfrog us on this important technology; the Hayabusa uses a very advanced version called microwave ion propulsion.
Speaking of leapfrogging, here's another advance from Japan's space agency:
The mechanical spider is actually a prototype space spider rover that is not wheeled... so no more worrying just because the rover rolls downhill, it might not come back uphill. It probably wouldn't do for it to accidentally fall over on its back, though.
Thanks for the links. Do you have any references to how ion propulsion works? I didn't notice any with a quick perusal.
The ion engine is the first to ionize the propellant xenon by electrical discharge and to accelerate the ions by electrodes biased at 1.5kV. The ions are then mixed with separately produced electrons and are ejected as high-speed plasma beams. The plasma-state xenon glows purple. This “microwave-discharge-type ion engine” electric propulsion system developed by ISAS entirely eliminates the need for limited-durability discharge electrodes.
Visuals always help me:
That's a picture of two engines running here on Earth. If memory serves, the specific impulse is quite low, but these things can run a very long time, and a little acceleration for a long time is a lot of velocity.
Those idiots don't like anything.
I believe that NASA also wouldn't have to have used half of the space on the craft for fuel; it would probably would have been closer to 13% rather than 50%, from looking at JAXA's website.
Thanks for the info.
Leftists should know. Leftists are from URANUS.That is where their brains are. And don't we all know, too, that the sun, the moon, and the stars shine out of the liberals' backsides! Those idiots DO like a lot of things - provided they are not normal.
Wasn't deep space one (headed for a comet or something) an ion-propelled craft?
It might be if we painted it in camoflage and mounted a couple o' machine guns on it. ;-)
How's the cost factor on ion propulsion versus conventional propulsion?
But I believe that this mission only cost Japan $200 million for actual production and launch (not running costs or r-and-d), so the propulsion unit must be less than $200 million, maybe a lot less since Hayabusa's navigation system and the retrieval "gun" system are very sophisticated units also. This is an extraordinarily bold adventure, certainly the boldest going, and maybe the boldest since we put men on the moon and brought them back with a sack of moon rocks.
If it has any commercial value, Toyota will commercialize it (Prius, for example) and you will be able to buy all the fun parts in Akihabara long before you buy a Toyota "Prius-the-Space-Version".
Is there room for TeREEEEHHHYzaaa onboard????
I WOULD MAKE AN ORBITING URANUS JOKE HERE, BUT I'M TOO CLASSY.
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