Tag: spacecraft

NASA’s SMAP is ready to get launched

NASA’s SMAP is ready to get launched



Scheduled for launch on Jan. 29, 2015, NASA’s Soil Moisture Active Passive (SMAP) instrument will measure the moisture lodged in Earth’s soils with an unprecedented accuracy and resolution. The instrument’s three main parts are a radar, a radiometer and the largest rotating mesh antenna ever deployed in space.

Remote sensing instruments are called “active” when they emit their own signals and “passive” when they record signals that already exist. The mission’s science instrument ropes together a sensor of each type to corral the highest-resolution, most accurate measurements ever made of soil moisture — a tiny fraction of Earth’s water that has a disproportionately large effect on weather and agriculture.

To enable the mission to meet its accuracy needs while covering the globe every three days or less, SMAP engineers at NASA’s Jet Propulsion Laboratory in Pasadena, California, designed and built the largest rotating antenna that could be stowed into a space of only one foot by four feet (30 by 120 centimeters) for launch. The dish is 19.7 feet (6 meters) in diameter.

“We call it the spinning lasso,” said Wendy Edelstein of NASA’s Jet Propulsion Laboratory, Pasadena, California, the SMAP instrument manager. Like the cowboy’s lariat, the antenna is attached on one side to an arm with a crook in its elbow. It spins around the arm at about 14 revolutions per minute (one complete rotation every four seconds). The antenna dish was provided by Northrop Grumman Astro Aerospace in Carpinteria, California. The motor that spins the antenna was provided by the Boeing Company in El Segundo, California.

“The antenna caused us a lot of angst, no doubt about it,” Edelstein noted. Although the antenna must fit during launch into a space not much bigger than a tall kitchen trash can, it must unfold so precisely that the surface shape of the mesh is accurate within about an eighth of an inch (a few millimeters).

The mesh dish is edged with a ring of lightweight graphite supports that stretch apart like a baby gate when a single cable is pulled, drawing the mesh outward. “Making sure we don’t have snags, that the mesh doesn’t hang up on the supports and tear when it’s deploying — all of that requires very careful engineering,” Edelstein said. “We test, and we test, and we test some more. We have a very stable and robust system now.”

SMAP’s radar, developed and built at JPL, uses the antenna to transmit microwaves toward Earth and receive the signals that bounce back, called backscatter. The microwaves penetrate a few inches or more into the soil before they rebound. Changes in the electrical properties of the returning microwaves indicate changes in soil moisture, and also tell whether or not the soil is frozen. Using a complex technique called synthetic aperture radar processing, the radar can produce ultra-sharp images with a resolution of about half a mile to a mile and a half (one to three kilometers).

SMAP’s radiometer detects differences in Earth’s natural emissions of microwaves that are caused by water in soil. To address a problem that has seriously hampered earlier missions using this kind of instrument to study soil moisture, the radiometer designers at NASA’s Goddard Space Flight Center, Greenbelt, Maryland, developed and built one of the most sophisticated signal-processing systems ever created for such a scientific instrument.

The problem is radio frequency interference. The microwave wavelengths that SMAP uses are officially reserved for scientific use, but signals at nearby wavelengths that are used for air traffic control, cell phones and other purposes spill over into SMAP’s wavelengths unpredictably. Conventional signal processing averages data over a long time period, which means that even a short burst of interference skews the record for that whole period. The Goddard engineers devised a new way to delete only the small segments of actual interference, leaving much more of the observations untouched.

Combining the radar and radiometer signals allows scientists to take advantage of the strengths of both technologies while working around their weaknesses. “The radiometer provides more accurate soil moisture but a coarse resolution of about 40 kilometers [25 miles] across,” said JPL’s Eni Njoku, a research scientist with SMAP. “With the radar, you can create very high resolution, but it’s less accurate. To get both an accurate and a high-resolution measurement, we process the two signals together.”

SMAP will be the fifth NASA Earth science mission launched within the last 12 months.

Source : http://www.nasa.gov/smap/

Curiosity readings point to mysterious, pulsing source of methane on Mars

Curiosity readings point to mysterious, pulsing source of methane on Mars



Levels of the organic gas methane are periodically spiking at the Gale Crater on Mars—suggesting something, possibly something alive, is creating the substance, scientists say.

Most of Earth’s methane production has a biological origin, but there are other ways methane, the simplest organic molecule, can arise naturally. Organic molecules are carbon-based and are essential ingredients for life.

The new findings, from the NASA Mars rover Curiosity, are published this week in the research journal Science.

Investigators said the findings suggest that the methane level in Mars’ atmosphere at the 154-km (96 mile) wide crater is generally lower than models predict, but that it spikes often. This implies the gas arises periodically from some nearby source, they added.

The scientists, from the NASA Jet Propulsion Laboratory in Pasadena, Calif. and other institutions, used 20 months of data collected by instruments on Curiosity to gauge levels of the gas at crater, near where the rover landed.

Their study found that the stable, background level of atmospheric methane is less than half of what was expected from known processes, such as the light-induced breakdown of dust and organic materials delivered to Mars by meteorites.

However, the researchers also found that this background level of methane spiked about tenfold, sometimes over the course of just 60 Martian days, which was surprising because the gas is expected to have a lifetime of about 300 years. The results suggest that methane is occasionally produced or vented near the crater, which is near the Martian equator, they added.

NASA originally chose Gale Crater, which has a mountain in the middle of it, as a landing site for the rover because there were signs of water in the area. The crater is believed to have formed with a meteor hit Mars in its early history, about 3.5 to 3.8 billion years ago.

The announcement comes just weeks after another report concluding that a Martian meteorite called Tissint contains organic molecules of possible biological origin.


source: http://www.world-science.net/

Data from Rosetta spacecraft yields secrets about comet’s water

Data from Rosetta spacecraft yields secrets about comet’s water


Comet 67p

A comet studied close-up by the European Space Agency is yielding surprising secrets about its water, scientists say.

The new data from the agency’s Rosetta spacecraft suggest most of Earth’s water came from asteroids, not comets, and that comets closer to our part of the Solar System have more diverse origins than previously suspected.

Rosetta found the water vapor from Comet 67P/Churyumov–Gerasimenko to be very unlike Earth’s, in measurements made in the month following the spacecraft’s arrival at the comet on Aug. 6.

One of the leading hypotheses on Earth’s formation is that it was so hot when it formed 4.6 billion years ago that any original water content should have boiled off. But, today, two thirds of the surface is water, so where did that come from?

Scientists think the water came later from impacting asteroids and comets—two different types of objects that orbit the Sun. (They have different makeups and asteroids lack tails, for instance.)

But how much water came from each type of object is debated.

Scientists believe a key to determining where a particular body of water originated is the levels, within it, of a type of hydrogen known as deuterium, as compared to normal hydrogen. Simulations show that during the first few million years of the Solar System, deuterium levels should change with distance from the Sun and with time. Therefore deuterium levels in a particular body of water can reveal something about where and when it originated.

Comets in particular are considered unique tools to study these origins, since they harbor material directly left over from the dust cloud that gave rise to the planets.

But this isn’t straightforward because many comet orbits have gotten mixed up since long ago. “Long-period” comets, a type that is more distant from the sun, are thought to have originally formed closer in, in the area of the planets Uranus and Neptune. And “short-period” comets, which now inhabit inner regions—like Rosetta’s—were thought to have formed further out, in the Kuiper Belt beyond Neptune.

Previous measurements of other comets’ deuterium levels have varied widely, researchers say. Of the 11 comets for which there are measurements, only the short-period Comet 103P/Hartley 2 was found to match Earth water in makeup, in observations made by the European Space Agency’s Herschel mission in 2011. The levels now measured by Rosetta are more than three times greater.

This suggests two things, mission scientists said.

“This surprising finding could indicate a diverse origin for the Jupiter-family comets – perhaps they formed over a wider range of distances in the young Solar System than we previously thought,” said Kathrin Altwegg, lead author of the paper reporting the results in the journal Science this week.

Second, she said, “our finding… adds weight to models that place more emphasis on asteroids [than comets] as the main delivery mechanism for Earth’s oceans.” Altwegg is principal investigator for an instrument called Rosina (Orbiter Spectrometer for Ion and Neutral Analysis) on the spacecraft, which made the measurements.

“As Rosetta continues to follow the comet on its orbit around the Sun throughout next year, we’ll be keeping a close watch on how it evolves and behaves,” added Matt Taylor, the space agency’s Rosetta project scientist.

Mars rock shows traces of biological activity

Mars rock shows traces of biological activity



Did Mars ever have life? Might it still? A meteorite identified as coming from Mars has reignited the old debate. A study published this month argues that the rock contains traces of carbon with a likely biological origin, like coal, which comes from remains of long-ago plants.

“So far, there is no other theory that we find more compelling,” said study co-author Philippe Gillet, stressing that he’s open to being proven wrong.

Gillet and colleagues from China, Japan and Germany argue that the carbon could have gotten into the rock through contact with fluid rich in organic material. The study appears in the journal Meteoritic and Planetary Sciences

Thrown off Mars after an asteroid hit its surface, the meteorite, named Tissint, fell on the Moroccan desert on July 18, 2011, in view of several witnesses, the scientists said. Studies found the rock had small fissures filled with organic, carbon-containing matter.

The researchers carried out several analyses to conclude that the rock didn’t originate on Earth and that the carbon got into it before it left Mars. They took issue with a previous proposal that the carbon traces originated through the high-temperature crystallization of magma, or molten rock. Gillet and colleagues argue that more probably, liquids containing organic compounds of biological origin infiltrated Tissint’s “mother” rock at low temperatures, near the Martian surface.

These conclusions are supported by several properties of the meteorite’s carbon, such as its levels of so-called carbon-13 compared to carbon-12, they explained. This was found to be significantly lower than the ratio of carbon-13 in the carbon dioxide of Mars’s atmosphere, previously measured by the Phoenix and Curiosity rovers. Moreover, this difference corresponds perfectly with what is seen on Earth between a piece of coal and the carbon in the atmosphere, the scientists argue.

The researchers say the organic matter could also have reached Mars when very primitive meteorites, called carbonated chondrites, fell there, but probably not, because such meteorites contain very low levels of organic matter.

“Insisting on certainty is unwise, particularly on such a sensitive topic,” said Gillet, who directs the Earth and Planetary Sciences Laboratory at the École Polytechnique Fédérale de Lausanne, a Swiss institute of technology. “I’m completely open to the possibility that other studies might contradict our findings. However, our conclusions are such that they will rekindle the debate as to the possible existence of biological activity on Mars – at least in the past.”

Spacecrafts speed up without following the law of gravity

Spacecrafts speed up without following the law of gravity



The laws of gravity don’t seem to be working exactly as they should around Earth—and it’s affecting our own space probes, though not seriously, a new report observes.

When space agencies send probes to explore the Solar System, they often use its planets and moons to help move those crafts along. Yet the paper notes that there’s a tiny discrepancy in the expected effect, versus the actual effect, at least when Earth itself is used for such maneuvers.

The use of planets and moons to adjust a craft’s motion is called a “gravity assist.” It’s like bouncing a spacecraft off a planet. Because every planet is in motion, this procedure will change the speed of the bounced object—much as a ball, tossed at the front of a speeding train, would bounce back faster than the speed you threw it at.

In the case of a “gravity assist,” the “bounce” isn’t quite the familiar kind of bounce. The spacecraft doesn’t actually touch the planet. Instead, it flies close by. But the planet’s gravity provides a similar effect to a bounce. In fact, the math is quite similar.

And it works quite well. The problem is that the real-life effect seems to differ a bit from what calculations, based on the known laws of physics, predict. The new paper, published in the August issue of the research journal Advances in Space Research, reviews the issue, and concludes that physicists still haven’t come up with a satisfactory answer. Only measurements near Earth have been precise enough to clearly detect the effect, according to author Luis Acedo Rodríguez, a physicist at the Polytechnic University of Valencia in Spain.

He suggests that the solution might lie in factors such as radiation from the sun, tides, or “dark matter”—an invisible goop that is believed to permeate galaxies throughout the universe, though it betrays its presence only through its gravity.

The tiny anomaly has been detected in near-Earth flybys thanks to monitoring stations such as that of the NASA in Robledo de Chabela in Madrid or that of the European Space Agency in Cebreros, Spain, Acedo said. Thus, when the Galileo space probe flew over Earth in 1990, instruments detected a change of speed of about one-hundredth of a mile or kilometer per hour compared to what was expected.

“These deviations do not seriously affect the trajectories,” Acedo told Spain’s Scientific Information and News Service. Yet it’s “very important to clarify” the causes, he insisted, “especially in the current era of precise space exploration.”

Scientists have proposed many hypotheses, he said. One points towards solar radiation being the cause of the change in speed. Others suggest an influence from magnetic fields, from tides, or from a blob of dark matter around Earth.

Acedo has proposed his own theory—though he himself admits it has problems. It involves a supposed “circulating gravitomagnetic field,” a force field that would follow the Earth’s parallels. The approach can be used to explain the majority of cases, he said, and “Einstein’s general theory of relativity predicts the existence of a similar field.” Yet some instruments that should have detected the effect have not.

If that is wrong, he wrote, the anomalous behavior “must originate in something that, although common, we have been unaware of to date, or in an error in the data analysis programs.”

Meanwhile, he said, space probes continue to challenge scientists every time they perform a “gravity assist.” One of the last was that of the spacecraft Juno in last October, from Earth en route to Jupiter. NASA hasn’t yet published data on this journey, but everything indicates that its speed as it flew over our planet was once again different from estimates, Acedo said.

Source :  www.world-science.net

Spacecraft gather dust that come from outside solar system

Spacecraft gather dust that come from outside solar system



Dust grains brought to Earth by NASA’s Stardust spacecraft probably originated in the interstellar dust stream, which comes from outside the solar system, researchers have concluded.

With the help of amateur participants, scientists said they identified seven dust particles and residues, more than a thousand times smaller than a grain of sand, whose characteristics are consistent with interstellar dust. Understanding what the grains are made of may shed light on the solar system’s formation, since this sort of material is believed to be what generates new stars and planetary systems.

The study, led by Andrew Westphal at University of California, Berkeley, is published in the journal Science. The Stardust spacecraft used giant tiles made out of aerogel and aluminum foil to collect the dust samples. Aerogel is an extremely lightweight synthetic material, sometimes described as “solid smoke.”

“We know from astronomical observations that there is a stream of particles that reaches our Solar System from interstellar space,” the vast areas between stars, Bridges said. “Our results show us what this stardust—from which our Solar System formed—actually is.

“Some of these grains formed in suns predating ours, so we are looking beyond our own Solar System when we study them,” he added. “We have also learnt a lot about how to collect and analyze these tiny grains, which are less than one millionth of a meter in size, which will be important in future missions.”

The findings are based on an analysis of specks collected by NASA’s Stardust mission launched in 1999 to collect dust samples from the comet Wild 2 and return them to Earth for study. Stardust also collected dust coming from the direction of the constellation Ophiuchus, or the Serpent Bearer.

All analysis was non-destructive of the particles, but subsequent tests will ultimately have to destroy some of the particles to confirm their origin conclusively, Westphal said. “We have limited the analyses on purpose,” he added. “These particles are so precious. We have to think very carefully about what we do with each particle.”

Source : world-science.net

Rosetta arrives at comet for a close-up look

Rosetta arrives at comet for a close-up look



A European Space Agency spacecraft has become the first to reach a comet for a close-up view, coming within 100 km (60 miles) on Aug. 6 and preparing for an even closer approach, scientists report.

The event follows a decade-long journey. “After ten years, five months and four days travelling towards our destination, looping around the Sun five times and clocking up 6.4 billion kilometres, we are delighted to announce finally ‘we are here,’” said Jean-Jacques Dordain, the agency’s director general, on Aug. 6.

“Rosetta is now the first spacecraft in history to rendezvous with a comet, a major highlight in exploring our origins. Discoveries can start.” Mission scientists plan to direct the craft closer over the next six weeks, putting it within half its current distance. Later plans include having it deposit a lander directly on the comet.

Comet 67P/Churyumov-Gerasimenko and Rosetta now lie 405 million km (250 million miles) from Earth, about half way between the orbits of Jupiter and Mars, rushing towards the inner Solar System at nearly 55,000 km (34,000 miles) per hour.

The comet orbits the sun once every 6.5 years. The path takes it from beyond Jupiter at its furthest point, to between the orbits of Mars and Earth at its closest to the Sun. Rosetta is planned to accompany it for over a year as they swing around the Sun and back out towards Jupiter again.

Comets are considered to be primitive building blocks of the Solar System and may have helped to ‘seed’ Earth with water, perhaps even the ingredients for life, according to scientists. But many fundamental questions about these enigmatic objects remain, and Rosetta is aimed at answering some of these.

Its journey to the comet wasn’t straightforward. Since its launch in 2004, Rosetta had to make three gravity-assist flybys of Earth and one of Mars to help it on course to its rendezvous with the comet. This complex course also allowed Rosetta to pass by asteroids Šteins and Lutetia, obtaining unprecedented views and information on these two objects.

Aug. 6 saw the last of a series of ten manoeuvres that began in May to adjust Rosetta’s speed and trajectory gradually to match those of the comet. Had any of these failed, the mission would have been lost, and the spacecraft would simply have flown by the comet.

The comet began to reveal its personality while Rosetta was on its way. Images taken between late April and early June showed that its activity was variable. The comet’s “coma” – a surrounding area of gas and dust – became quickly brighter and then died down again over those six weeks. Measurements suggested that the comet was losing water vapour to space at about 300 milliliters (1.3 U.S. cups) per second, and that its average temperature was about minus 70 degrees C (minus 94 degrees F), pointing to a “dark and dusty” surface, astronomers said.

Then, images taken from about 12,000 km (7,000 miles) away began to reveal that the nucleus, or core of the object comprises two distinct segments joined by a ‘neck’, giving it a duck-like appearance. Subsequent images showed more and more detail.

“Our first clear views of the comet have given us plenty to think about,” said Matt Taylor, the European Space Agency’s Rosetta project scientist. “Is this double-lobed structure built from two separate comets that came together in the Solar System’s history, or is it one comet that has eroded dramatically and asymmetrically over time? Rosetta, by design, is in the best place to study one of these unique objects.”

Eventually, Rosetta is to attempt a close, near-circular orbit at 30 km (19 miles) and, depending on the comet’s activity, perhaps come even closer.

“Arriving at the comet is really only just the beginning of an even bigger adventure, with greater challenges still to come as we learn how to operate in this uncharted environment, start to orbit and, eventually, land,” said Sylvain Lodiot, the agency’s Rosetta spacecraft operations manager.

As many as five possible landing sites are to be identified by late August. “In addition to characterizing the comet nucleus and setting the bar for the rest of the mission, we will begin final preparations for another space history first: landing on a comet,” said Taylor.

“After landing, Rosetta will continue to accompany the comet until its closest approach to the Sun in August 2015 and beyond, watching its behaviour from close quarters to give us a unique insight and real-time experience of how a comet works as it hurtles around the Sun.”

Scientists develop new method for finding aliens

Scientists develop new method for finding aliens



Scientists say they have de­vel­oped a pow­er­ful new mod­el to de­tect life on plan­ets out­side of our so­lar sys­tem, more ac­cu­rately than ev­er be­fore.

The new mod­el fo­cus­es on meth­ane, the sim­plest or­gan­ic mol­e­cule, widely ac­knowl­edged to be a sign of po­ten­tial life.

Re­search­ers from Uni­vers­ity Col­lege Lon­don in the U.K. and the Uni­vers­ity of New South Wales in Aus­tral­ia de­vel­oped a new meth­od to de­tect the mol­e­cule at tem­per­a­tures above that of Earth, up to 1220 de­grees Cel­si­us, some­thing not pos­si­ble be­fore.

To find out what re­mote plan­ets or­bit­ing oth­er stars are made of, as­tro­no­mers an­a­lyze the way in which their at­mo­spheres ab­sorb star­light of dif­fer­ent col­ors. They then com­pare that to a mod­el, or “spec­trum,” to iden­ti­fy dif­fer­ent mol­e­cules.

“Cur­rent mod­els of meth­ane are in­com­plete, lead­ing to a sev­ere un­der­es­tima­t­ion of meth­ane lev­els on plan­ets,” said Jon­a­than Ten­ny­son, a phys­i­cist at Uni­vers­ity Col­lege Lon­don. “We an­ti­cipate our new mod­el will have a big im­pact on the fu­ture study of plan­ets and ‘cool’ stars ex­ter­nal to our so­lar sys­tem, po­ten­tially help­ing sci­en­tists iden­ti­fy signs of ex­tra­ter­res­tri­al life.”

“The com­pre­hen­sive spec­trum we have cre­at­ed has only been pos­si­ble with the as­ton­ish­ing pow­er of mod­ern su­per­com­put­ers which are needed for the bil­lions of lines re­quired for the mod­eling,” added the stu­dy’s lead au­thor, Sergei Yurchenko, al­so of the uni­vers­ity.

“We lim­it­ed the tem­per­a­ture thresh­old,” he added, “to fit the ca­pa­city avail­a­ble, so more re­search could be done to ex­pand the mod­el to high­er tem­per­a­tures still. Our cal­cula­t­ions re­quired about three mil­lion CPU (cen­tral pro­cess­ing un­it) hours alone,” he said.

“We are thrilled to have used this tech­nol­o­gy to sig­nif­i­cantly ad­vance be­yond pre­vi­ous mod­els avail­a­ble for re­search­ers stu­dying po­ten­tial life on as­tro­nom­i­cal ob­jects, and we are ea­ger to see what our new spec­trum helps them dis­cov­er.”

The mod­el has been tested and ver­i­fied by re­pro­duc­ing the way meth­ane in failed stars, called brown dwarfs, ab­sorbs light, the re­search­ers added. The study is published in the journal Proceedings of the National Academy of Sciences.


IITan discovers new control logic for controlling spacecraft after actuator failure

The attitude, i.e. roll yaw and pitch of a satellite in space are controlled by three  actuators. In real satellites more then 3 actuators are kept, so that it can be controlled in case of any actuator failure. A student from IIT Kharagpur with his guide shows that the satellite can even be controlled by two actuators. Their research article was the top most viewed research article of the Journal for more then 9 months.

The abstract of their paper is as follows :

Micro-, nano-, and pico-satellite designs are constrained by small power budget, weight, and size. The power constraint is taken care of by ensuring that all the systems onboard are optimized for low power consumption. Weight and size can be made small by reducing the number of sensors and actuators. However, the attitude control system, which constitutes one of the most important components of the satellite, often requires redundancy to make the satellite fail to be operational; but for such small satellites, low power, weight, and size limit the accommodation of redundancy in the attitude control system. Such small satellites are often magnetically actuated. The under-actuation problem of a satellite magnetic control torque in the presence of three magnetic coils has been extensively studied since 1970s. Moreover, the attitude control of a satellite using two actuators and time-dependent feedback control has been developed, but the magnetic attitude control of a satellite, which is already an under-actuated system, in the post-failure scenario of one of the three magnetic actuators, has not been developed. Failure of any one of the magnetic coils may render a satellite dysfunctional if proper control reconfiguration is not provided, keeping in view that the redundant attitude control system is not available.

A new formulation for reconfiguring the control based on magnetic dipole moment modulation for the attitude control of Earth-pointing satellite has been presented in this article. In the post-failure scenario of one of the magnetic coils, the controlling capability of the system remains intact, which comes at the cost of high magnetic dipole moment in the functional magnetic coils but not at the cost of extra power.

Author : Santanu Das
Link : http://pig.sagepub.com/content/224/12/1309.abstract