Armadillo Completes Test Flight

Image credit: Armadillo Aerospace
The new actuator covers worked out great. We made these by hand, but we also finally got around to getting a sheet metal roll / brake / shear for the shop to make this type of thing easier in the future.

There was intermittent rain around Dallas today, but we decided to head out to our test site and hope for the best anyway. We taped over all the exposed holes in the vehicle, but it turned out that we only caught a few drops on the way over, and the test site was fine. Since we had a test out there only two and a half weeks ago, we already had some of the gear ready, and we didn?t forget anything this time. We had the vehicle loaded up and ready to go within 30 minutes of arriving.

We pressurized the tank to 300 psi, which is a little high for the threaded end closures on these tanks, and we could hear a small pressure leak as the O-ring unloaded a bit.

The engine warmed up predictably, adding further evidence for the benefit of a compressed hot catalyst pack (although we did lose some thrust after compressing it). Something that we noticed this time was that there was still some cloudiness in the exhaust while I brought it up to temperature, but after it had sat for a couple seconds before I started it back up again for the launch it was completely clear. It is likely that there is some path that was channeling enough propellant to self cool at steady state, but after letting it heat soak a bit from the surrounding catalyst, it was uniformly at operating temperature. We can probably use this effect to shorten our warm-ups by warming for a few seconds, then pausing for a couple seconds.

I changed the liftoff procedure slightly, opening the valve to the warmup level and holding it there while engaging the boost command. Previously, I would warm the engine, then let it shut completely down for an inertial reset, then just engage boost mode, which pushes the throttle open as fast as it can. This lets more propellant flow into the engine than it would get if there was already chamber pressure, resulting in a brief period of higher than normal thrust and stress. This was quite noticeable in the test on Saturday, which had a momentary kick of nearly one G. Boosting from warmup made the flow completely predictable.

The flight parameters were set for 1.8 seconds of boost, -4 m/s^2 minimum acceleration (slightly more than negative one half G) during the stabilization phase, 3 m/s^2 acceleration in the landing phase, 1 m/s target touchdown velocity, and a 3 m uncertainty margin for the GPS altitude. I increased the minimum acceleration during stabilization because of concerns about throttling the ball valve at small open fractions and low chamber pressures. This wastes more propellant during the flight, but this vehicle can carry so much more propellant than we can use without our burn time waiver that it doesn?t really matter.

The flight was perfect. It went 131 feet high, and landed less than one foot from the launch point.

Analyzing the telemetry told us the following:

This engine didn?t run as well at full throttle with the increased pressure, giving an acceleration during the wide-open-throttle that cycled from 15 to 20 m/s^2. We really need to build a brand new engine to replace this one that has been cut open and modified a half dozen times.

The acceleration prediction that I added to smooth out the hunt-for-acceleration modes helped the stabilize mode, but not as much as it smoothed out the hovering in the test on Saturday. You can clearly hear the pulsations in the flight video. This is understandable, because the flow curve is changing faster at the lower ball valve opening. I should be able to either increase the acceleration prediction, or slow down the ball valve movement at smaller openings. I also realized that I can develop this on the test stand, because hunt-for-chamber-pressure will be effectively the same thing as hunt-for-acceleration on a vehicle.

We knew our chamber pressure signal was messed up, so we didn?t get that in the data logs this time. When we got back to the shop we investigated, and found that the porous pressure snubber in front of the transducer was blocked up. We had this happen once before on a test stand transducer, so we are going to change up from 1 micron to 7 micron filter size. A little bit of peroxide probably starts enough surface corrosion on the 303 SS to clog it up.

The auto-land worked perfectly. I had tried several algorithms on the simulator before settling on this one, and it behaved exactly the same in reality, which is always a pleasant surprise.

We were planning on doing more tests, but the burn time on the first one was 14 seconds, so we really didn?t have much room under the 15 second burn time limit. I could have trimmed the stabilization acceleration and GPS uncertainty, but risking the vehicle to go another 50 feet higher didn?t seem worthwhile, and we called it a day. (Neil, Phil, Tommy, John Carmack, Russ, John Carr, Matt) Joseph was sick today, and James teaches class on Tuesday nights, so they missed it?

We have about 25 hops on this set of jet vanes now, and they have taken on an interesting coloration pattern:

We probably won?t fly this vehicle again until we build a completely fresh engine and develop the low throttle hunting algorithm a bit more, but we are submitting some changes to our burn time waiver request to allow us to do initial flights with the small vehicle before flying the big one. It can easily do flights three times as long, which may show up some problems before we hit them with the big vehicle. If the big engine isn?t burned from the leaking valve problem, we should have the big vehicle hovering under the lift this Saturday, so we may be out next Tuesday doing a boosted hop with it.

Speaking of next week? I think Space Ship One has good odds of success in the single-person-to-100km flight. I only see two real issues they may hit: The extended burn above the atmosphere may run into some control issues as the nozzle ablates, which will be hard to correct with only cold gas attitude jets. This would be a fairly benign failure, with the pilot just shutting off the main engine if he can?t hold the trajectory. The dangerous part of the test will be the reentry with a significantly bigger drop than the previous test. At this point, I hope Burt has everything work out and he is able to make the X-Prize flights soon, because our prospects are pretty dim for getting everything working perfectly in the big vehicle in five months and having permission to fly it. I certainly don?t want the insurance company to keep the prize money. If Space Ship One crashes, we will probably throw ourselves at an attempt, but it will be a long shot. No, I don?t think any of the other teams are close.

Original Source: Armadillo Status Report

Saturn’s Southern Storms

Image credit: NASA/JPL/Space Science Institute
Cassini continues its vigil as Saturn?s atmosphere churns and morphs through time. Four large, dark spots, or storms, form a symmetrical pattern in the mid-southern latitudes as these features squeeze past each other. Further observations will show whether these storms merge or spawn new spots of their own. North of the features, some latitudinal bands exhibit a bumpy or scalloped pattern, probably indicative of planet-scale wave motions in the atmosphere.

The image was taken with the narrow angle camera on May 15, 2004, from a distance of 24.7 million kilometers (15.3 million miles) from Saturn through a filter centered at 750 nanometers. The image scale is 147 kilometers (91 miles) per pixel. Contrast in the image was enhanced to aid visibility.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit and the Cassini imaging team home page,

Original Source: CICLOPS News Release

MOST Measures the Pulse of a Star

Image credit: Canadian Space Agency
MOST, Canada?s first space telescope, is shaking up the way astronomers think about stars — and putting a new spin on the life story of our own Sun — by allowing astronomers to see in unprecedented detail how stars shake and spin.

The first results from MOST, a Canadian Space Agency mission which was also the first scientific satellite to be launched by Canada in over 30 years, include the detection of a strong ?pulse? in a young adult star called eta Bootis, and a bad case of stellar acne and hyperactivity in a ?pre-teen? version of the Sun, kappa 1 Ceti. These data offer a unique perspective on what our own Sun may have been like in its youth.

?All this talk of stellar pulses and hyperactivity must sound like ER Meets Star Trek,? admitted MOST Mission Scientist Dr. Jaymie Matthews of the University of British Columbia, who presented the findings today in a keynote address to the annual meeting of the Canadian Astronomical Society in Winnipeg. ?But we really are doing diagnostic check-ups of stars at different points in their lives, by placing them under intensive observation for weeks at a time.?

Matthews made the presentation to a gathering of physicists, astrophysicists, and medical physicists at a unique conference of Canadian physics societies (CAP/CASCA/COMP/BSC CONGRESS 2004) hosted by the Department of Physics and Astronomy at the University of Manitoba in celebration of the Faculty of Science’s 100th anniversary.

These are ambitious results from a Canadian-built and -operated orbiting observatory which is no bigger than a suitcase but can monitor the brightnesses of stars with unmatched precision and thoroughness. MOST, which stands for Microvariability and Oscillations of STars, was launched into orbit last summer and has been collecting data for the last few months.

?MOST is a major advance in the way astronomers study stars, made possible by innovative Canadian technology,? noted Canadian Space Agency President, Dr. Marc Garneau. ?It is the world?s most precise light meter, capable of recording variations as small as one ten thousandth of a percent in the brightness of a star.?

How small is that?

?If all the lights in all the offices of the Empire State Building were on at night,? explains Dr. Garneau, ?you could dim the total light by 1/10,000th of a percent if you pulled down just one window blind by only one centimetre.?

From its vantage point in polar orbit, 820 km high, the tiny MOST space telescope can stare at stars without interruption for up to eight weeks. No other observatory or network of telescopes, including the Hubble, can do this. The unique combination of precision and time coverage enables MOST to look for subtle vibrations in stars that will reveal secrets hidden beneath their surfaces. It also gives MOST the best chance to detect light directly from planets outside our Solar System and study their atmospheres and weather.

MOST is a Canadian Space Agency mission. Dynacon Inc. of Mississauga, Ontario, is the prime contractor for the satellite and its operation, with the University of Toronto Institute for Aerospace Studies (UTIAS) as a major subcontractor. The University of British Columbia (UBC) is the main contractor for the instrument and scientific operations of the MOST mission. MOST is tracked and operated through a global network of ground stations located at UTIAS, UBC and the University of Vienna.

The MOST Canadian space telescope was launched from northern Russia in June 2003 aboard a former Soviet ICBM (Intercontinental Ballistic Missile) converted to peaceful use. Weighing only 54 kg, this suitcase-sized microsatellite is packed with a small telescope and electronic camera to study stellar variability.

One of its early targets was the star eta Bootis, a slightly more massive and younger version of the Sun. Astronomers had picked out this star as one of the best candidates for the new technique of ?asteroseismology? — using surface vibrations to probe the inside of a star, similar to how geophysicists use earthquake vibrations to probe the Earth?s core.

MOST monitored eta Bootis for 28 days without interruption, placing the star under a 24-hour scientific ?stake-out? that revealed behaviour that was hidden from the limited view possible for Earth-bound telescopes. Accumulating almost a quarter of a million individual measurements of this star, MOST reached a level of light-measuring precision at least 10 times better than the best ever achieved before from Earth or space.

The data reveal the star is vibrating, but at a pitch well below the range of human hearing. The stellar melody should allow the MOST team of scientists, including Dr. David Guenther of the Canadian Institute for Computational Astrophysics at St. Mary?s University, Halifax, to determine the age and structure of eta Bootis. ?We?re now in a position to explore new physics in stars, with observations like these,? said Dr. Guenther.

Before observing eta Bootis, while still in the shakedown phase of its mission, MOST was aimed for testing purposes at a fainter star called kappa 1 Ceti. Astronomers already suspected this was a younger version of our Sun, with an age of about 750 million years. The Sun?s age is about 4.5 billion years, and it?s just entering middle age. In terms of a human life, the Sun would be about 45 years old while kappa 1 Ceti would be eight years old ? barely a pre-teen.

Like many human kids, Kappa 1 Ceti is hyperactive, flaring up from time to time, and spinning with much more kinetic energy than sedate older stars like the Sun. It also has a severe case of acne — dark spots on its face which are much larger than those visible on the Sun’s surface. The MOST data, following Kappa 1 Ceti for 29 days, show in exquisite detail how the spots move across the visible side of the star as it spins once every nine days or so. And because a star is not solid, different parts of its gaseous surface spin at different rates. MOST has been able to measure this effect directly in a star other than the Sun for the first time. These results are being prepared for submission to The Astrophysical Journal.

Future targets for MOST include other stars representing the Sun at various stages in its life, and stars known to have giant planets. MOST is designed to be able to register the tiny changes in brightness that will occur as a planet orbits its parent star. The way in which the light changes will tell astronomers about the atmospheric composition of these mysterious worlds, and even if they have clouds.

?It?s like doing a weather report for a planet outside our Solar System,? says Dr. Jaymie Matthews, MOST Mission Scientist, of the University of British Columbia.

Original Source: UBC News Release

Spirit Reaches Columbia Hills

Image credit: NASA/JPL
NASA’s Mars rovers are delighting scientists with their extra credit assignments. Both rovers successfully completed their primary three-month missions in April.

The Spirit rover is exploring a range of martian hills that took two months to reach. It is finding curiously eroded rocks that may be new pieces to the puzzle of the region’s past. Spirit’s twin, Opportunity, is also negotiating sloped ground. It is examining exposed rock layers inside a crater informally named “Endurance.”

“Both rovers have begun exploring brand new places,” said Dr. Mark Adler, mission manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Opportunity has entered Endurance Crater. Spirit has arrived at the Columbia Hills. Both rovers are getting their second wind in bonus time, and we are very excited about the scientific potential we see at their new homes. Of course, the terrain at both locations is challenging, one up and one down. We are making certain that we proceed safely to keep these wonderful machines as healthy as we can for as long as we can.”

Spirit began climbing into Columbia Hills late last week, and right away sent pictures of tantalizing rocks. “Some of the rocks appear to be disintegrating. They have an odd kind of rotting appearance, with soft interiors and resistant rinds or hulls,” said Dr. Larry Soderblom, a rover science-team member from the U.S. Geological Survey, Flagstaff, Ariz. “The strangest things we’ve encountered are what we’re calling hooded cobras, which are evidently the resistant remnants of some of those rocky rinds. They stand above the surface like small canopies.”

Another rock, dubbed “Pot of Gold,” appears to have nodules and resistant planes in a softer matrix. Scientists have chosen it as a target for Spirit to examine with the instruments on the rover’s robotic arm. Afterwards, controllers plan to send Spirit to an outcrop farther uphill.

“Although it’s too early to even speculate as to the processes these rocks have recorded, we are tremendously excited over the new prospects,” Soderblom said.

The Columbia Hills rise approximately 90 meters (about 300 feet) above a plain Spirit crossed to reach them. Scientists anticipate a complex blend of rocks in the hills, perhaps holding evidence about a broader range of environmental conditions than has been seen in the volcanic rubble surfacing the plain. The entire area Spirit is exploring is within Gusev Crater. Orbital images suggest water may have once flowed into this Connecticut-sized basin.

“Halfway around Mars, Opportunity has driven about five meters (16 feet) into stadium-sized Endurance Crater. “As we look back up toward the rim, we can see the progress we’ve made,” said Scott McLennan, science-team member from the State University of New York, Stony Brook.

Opportunity’s first target inside the crater is a flat-lying stone about 36 centimeters by 15 centimeters (14 inches by 6 inches) dubbed “Tennessee” for its shape. Opportunity will inspect it for analysis with the spectrometers and microscopic imager on the rover’s robotic arm. It is in a layer geologists believe corresponds to sulfate-rich rocks. The rocks are similar to those, in which Opportunity previously found evidence for a body of water covering the ground long ago.

“The next step will be to move farther down from this layer to our first close-up look at a different sedimentary sequence,” McLennan said. “Color differences suggest at least three lower, older layers are exposed below Opportunity’s location.”

“The interpretation of those lower units is in a state of flux,” he said. “At first, we thought we would encounter poorly consolidated, sandy material. But as we get closer, we’re seeing more-consolidated, harder rock deeper into the crater. If we can get to the lower units, this will be the first detailed stratigraphic section ever done on another planet. We’re doing exactly what a field geologist would be doing.”

Spirit is showing what may be the first sign of age and wear. “The right front wheel is drawing about two to three times as much current as the other wheels, and that may be a symptom of degradation,” Adler said. “There may be steps we can take to improve it. We’ll be studying that possibility during the next few weeks.”

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA’s Office of Space Science, Washington, D.C. Images and additional information about the project are available from JPL at and from Cornell University, Ithaca, N.Y., at

Original Source: NASA/JPL News Release

Did Comets Create the Earth’s Oceans?

Artist's conception of asteroids or comets bearing water to a proto-Earth. Credit: Harvard-Smithsonian Center for Astrophysics

Did the Earth form with water locked into its rocks, which then gradually leaked out over millions of years? Or did the occasional impacting comet provide the Earth?s oceans? The Ptolemy experiment on Rosetta may just find out?

The Earth needed a supply of water for its oceans, and the comets are large celestial icebergs – frozen reservoirs of water orbiting the Sun.

Did the impact of a number of comets, thousands of millions of years ago, provide the Earth with its supply of water? Finding hard scientific evidence is surprisingly difficult.

Ptolemy may just provide the information to understand the source of water on Earth. It is a miniature laboratory designed to analyse the precise types of atoms that make up familiar molecules like water.

Atoms can come in slightly different types, known as isotopes. Each isotope behaves almost identically in a chemical sense but has a slightly different weight because of extra neutrons in its nucleii.

Ian Wright is the principal investigator for Ptolemy, an instrument on Rosetta?s Philae lander. By analysing with Ptolemy the mix of isotopes found in Comet 67P/Churyumov-Gerasimenko, he hopes to say whether comet water is similar to that found in Earth?s oceans. Recent results from the ground-based observation of another comet, called LINEAR, suggested that they probably are the same.

If this is true, then scientists have solved another puzzle. However, if the comets are not responsible for Earth?s oceans, then planetary scientists and geophysicists will have to look elsewhere.

For example, the answer could be closer to home, through processes related to vulcanism. Also, meteorites (chunks of asteroids or comets that fall to Earth) have been found to contain water but it is bound to the minerals and in nothing like the quantity found in comets.

However, since the Earth formed from rocks similar to the asteroids, it is feasible that enough water could have been supplied that way.

If comets did not supply Earth?s oceans then it implies something amazing about the comets themselves. If Ptolemy finds that they are made of extremely different isotopes, it means that they may not have formed in our Solar System at all. Instead, they could be interstellar rovers captured by the Sun?s gravity.

Rosetta, Philae and Ptolemy will either solve one scientific mystery, or open another whole set of new ones.

Original Source: ESA News Release

Titan Targeted

Image credit: NASA/JPL/Space Science Institute
Cassini?s finely-tuned vision reveals hazes high in the skies over Titan in this narrow angle camera image from May 22, 2004. Here the northern hemisphere is notably brighter than the southern hemisphere. This trait was noticed in images returned by the Voyager spacecraft, but the effect is presently reversed, North to South, as Titan is currently experiencing opposite seasons from those during the Voyager epoch 23 years ago.

The image was taken from a distance of 21.7 million kilometers (13.5 million miles) from Saturn through a filter sensitive to strong absorption by methane gas (centered at 889 nanometers). The image scale is 129 kilometers (80 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit and the Cassini imaging team home page,

Ultra Cool Star Measured

Image credit: ESO
Using ESO’s Very Large Telescope at Paranal and a suite of ground- and space-based telescopes in a four-year long study, an international team of astronomers has measured for the first time the mass of an ultra-cool star and its companion brown dwarf. The two stars form a binary system and orbit each other in about 10 years.

The team obtained high-resolution near-infrared images; on the ground, they defeated the blurring effect of the terrestrial atmosphere by means of adaptive optics techniques. By precisely determining the orbit projected on the sky, the astronomers were able to measure the total mass of the stars. Additional data and comparison with stellar models then yield the mass of each of the components.

The heavier of the two stars has a mass around 8.5% of the mass of the Sun and its brown dwarf companion is even lighter, only 6% of the solar mass. Both objects are relatively young with an age of about 500-1,000 million years.

These observations represent a decisive step towards the still missing calibration of stellar evolution models for very-low mass stars.

Telephone number star
Even though astronomers have found several hundreds of very low mass stars and brown dwarfs, the fundamental properties of these extreme objects, such as masses and surface temperatures, are still not well known. Within the cosmic zoo, these ultra-cool stars represent a class of “intermediate” objects between giant planets – like Jupiter – and “normal” stars less massive than our Sun, and to understand them well is therefore crucial to the field of stellar astrophysics.

The problem with these ultra-cool stars is that contrary to normal stars that burn hydrogen in their central core, no unique relation exists between the luminosity of the star and its mass. Indeed, luminosities and surface temperatures of ultra-cool dwarf stars depend both on their age and their mass. An older, somewhat more massive ultra-cool dwarf can thus have exactly the same temperature as a younger, less massive one.

It is therefore a basic goal of modern astrophysics to obtain independently the masses of an ultra-cool dwarf star. This is in principle possible by studying such objects that are members in a binary system.

This is precisely what an international team of astronomers has now done in a four-year long study of a binary stellar system with an ultra-cool dwarf star, using a plethora of top telescopic facilities, including ESO’s Very Large Telescope, as well as Keck I and Gemini North in Hawaii and also the Hubble Space Telescope. This system – with the telephone number name of 2MASSW J0746425+2000321 – is located at a distance of 40 light-years.

The astronomers used high-angular-resolution imaging to see both stars in the binary system and to measure their motion over a four-year period. However, this is more easily said than done, as the separation on the sky between the two stars is quite small: between 0.13 and 0.22 arcsec. This corresponds to the size of a 1-Euro coin, seen at a distance of about 25 km.

This separation is so small that it is normally not possible to differentiate the two stars due to the blurring effect of atmospheric turbulence (the “seeing”). It is therefore necessary to use the technique of adaptive optics. This wonderful method is based on the measurement of the image quality in real-time and sending corresponding corrective signals up to 100 times every second to a small deformable mirror, located in front of the detector. As the mirror continuously modifies its shape, the disturbing effect of the turbulence is neutralised. Applied at the VLT, this technique has resulted in images which are at least ten times sharper than the “seeing” and which therefore show many more details in the observed objects.

At the Very Large Telescope, the astronomers used the state-of-the-art adaptive optics NACO instrument. Says Herv? Bouy, principal author of the paper presenting the results described here: “NACO offers the possibility to work in the infrared and is therefore ideally suited for the study of ultra-cool stars, which emit most of their light in this wavelength range. With the combination of the high efficiency of NACO and the VLT, and the excellent atmospheric conditions prevailing at Paranal, we were able to achieve very sharp images of this binary stellar system, almost as good as if the telescope were located in space.”

Ultra-cool and on diet
During their four-year long study, seven different relative positions of the two components of the binary system were measured and Herv? Bouy and his co-workers were able to determine with good precision the stellar orbits. They find that the two stars revolve around each other once every 10 years and that their physical separation is only 2.5 times the distance of the Earth to the Sun – as astronomers say, 2.5 Astronomical Units. Using Kepler’s laws, it is then straightforward to derive the total mass of the system. The obtained value is less than 15 % of the mass of the Sun.

The astronomers then used the photometric data of each star obtained in several wavebands, as well as spectra obtained with the Hubble Space Telescope to study the two objects in more detail. Using the latest stellar models of the group of the Ecole Normale Sup?rieure de Lyon, they found that both stars have roughly the same surface temperature, around 1500 ?C (1800 K). For a star, this is ultra-cool indeed – by comparison, the surface temperature of the Sun is more than three times higher.

Using theoretical models, the team also found that the two stars are rather young (in astrophysical terms) – their age is between 500 and 1,000 million years only. The more massive of the two has a mass between 7.5 and 9.5% the mass of the Sun, while its companion has a mass between 5 and 7% of the solar mass.

Objects weighing less than about 7% of our Sun have been variously called “Brown Dwarfs”, “Failed Stars” or “Super Planets”. Indeed, since they have no sustained energy generation by thermal nuclear reactions in their interior, many of their properties are more similar to those of giant gas planets in our own solar system such as Jupiter, than to stars like the Sun.

The system 2MASSW J0746425+2000321 is thus apparently made up of a brown dwarf orbiting a slightly more massive ultra-cool dwarf star. It is a true “Rosetta stone” in the new field of low-mass stellar astrophysics and further studies will surely provide more valuable information about these objects in the transitional zone between stars and planets.

Original Source: ESO News Release

Cassini Passes Phoebe

Image credit: NASA/JPL/Space Science Institute
Images collected during the Cassini-Huygens close fly-by of Saturn’s moon Phoebe give strong evidence that the tiny moon may be rich in ice and covered by a thin layer of darker material.

Its surface is heavily battered, with large and small craters. It might be an ancient remnant of the formation of the Solar System.

On Friday 11 June, at 21:56 CET, the Cassini-Huygens spacecraft flew by Saturn’s outermost moon Phoebe, coming within approximately 2070 kilometres of the satellite’s surface. All eleven on-board instruments scheduled to be active at that time worked flawlessly and acquired data.

The first high-resolution images show a scarred surface, covered with craters of all sizes and large variation of brightness across the surface.

Phoebe is a peculiar moon amongst the 31 known satellites orbiting Saturn. Most of Saturn’s moons are bright but Phoebe is very dark and reflects only 6% of the Sun’s light. Another difference is that Phoebe revolves around the planet on a rather elongated orbit and in a direction opposite to that of the other large moons (a motion known as ‘retrograde’ orbit).

All these hints suggested that Phoebe, rather than forming together with Saturn, was captured at a later stage. Scientists, however, do not know whether Phoebe was originally an asteroid or an object coming from the ‘Kuiper Belt’.

The stunning images obtained by Cassini’s high-resolution camera now seem to indicate that it contains ice-rich material and is covered by a thin layer of dark material, probably 300-500 metres thick.

Scientists base this hypothesis on the observation of bright streaks in the rims of the largest craters, bright rays radiating from smaller craters, grooves running continuously across the surface of the moon and, most importantly, the presence of layers of dark material at the top of crater walls.

“The imaging team is in hot debate at the moment on the interpretations of our findings,” said Dr Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, USA.

“Based on our images, some of us are leaning towards the view that has been promoted recently, that Phoebe is probably ice-rich and may be an object originating in the outer solar system, more related to comets and Kuiper Belt objects than to asteroids.”

The high-resolution images of Phoebe show a world of dramatic landforms, with landslides and linear structures such as grooves, ridges and chains of pits. Craters are ubiquitous, with many smaller than one kilometre.

“This means, besides the big ones, lots of projectiles smaller than 100 metres must have hit Phoebe,” said Prof. Gerhard Neukum, Freie Universitaet Berlin, Germany, and a member of the imaging team. Whether these projectiles came from outside or within the Saturn system is debatable.

There is a suspicion that Phoebe, the largest of Saturn’s outer moons, might be parent to the other, much smaller retrograde outer moons that orbit Saturn. They could have resulted from the impact ejecta that formed the many craters on Phoebe.

Besides these stunning images, the instruments on board Cassini collected a wealth of other data, which will allow scientists to study the surface structures, determine the mass and composition of Phoebe and create a global map of it.

“If these additional data confirm that Phoebe is mostly ice, covered by layers of dust, this could mean that we are looking at a ‘leftover’ from the formation of the Solar System about 4600 million years ago,” said Dr Jean-Pierre Lebreton, ESA Huygens Project Scientist.

Phoebe might indeed be an icy wanderer from the distant outer reaches of the Solar System, which, like a comet, was dislodged from the Kuiper Belt and captured by Saturn when the planet was forming.

Whilst studying the nature of Phoebe may give scientists clues on the origin of the building blocks of the Solar System, more data are needed to reconstruct the history of our own neighbourhood in space.

With that aim, ESA’s Rosetta mission is on its way to study one of these primitive objects, Comet 67P/Churyumov-Gerasimenko, from close quarters for over a year and land a probe on it.

The fly-by of Phoebe on 11 June was the only one that Cassini-Huygens will perform with this mysterious moon. The mission will now take the spacecraft to its closest approach to Saturn on 1 July, when it will enter into orbit around the planet.

From there, it will conduct 76 orbits of Saturn over four years and execute 52 close encounters with seven other Saturnian moons. Of these, 45 will be with the largest and most interesting one, Titan. On 25 December, Cassini will release the Huygens probe, which will descend through Titan’s thick atmosphere to investigate its composition and complex organic chemistry.

Original Source: ESA News Release

SpaceShipOne Set for Launch in a Week

In just one week Scaled Composite’s SpaceShipOne will make an attempt to become the first privately-built vehicle to reach space – an altitude of 100 km (62 miles). Thousands of people are expected to show up at the runway in California’s Mojave Desert to watch the launch and suborbital flight. This won’t be an official attempt to win the Ansari X Prize; however, but the company is planning to try for the $10 million prize if this flight is successful. Billionaire Paul Allen has contributed $20 million to the development of SpaceShipOne.

Close Up on Phoebe Crater

Image credit: NASA/JPL/Space Science Institute
This eye-popping high-resolution image of Phoebe’s pitted surface taken very near closest approach shows a 13-kilometer (8-mile) diameter crater with a debris-covered floor. Part of another crater of similar size is visible at left, as is part of a larger crater at top and many scattered smaller craters. The radial streaks in the crater are due to downslope movements of loose fragments from impact ejecta. Also seen are boulders ranging from about 50 to 300 meters (160 to 990 feet) in diameter. The building-sized rocks may have been excavated by large impacts, perhaps from some other region of Phoebe rather than the craters seen here. There is no visible evidence for layering of ice and regolith or a hardened crust in this region, as on other parts of this moon.

Some of the relatively bright spots are from small impacts that excavated bright material from beneath the dark surface. Images like this provide information about impact and regolith processes on Phoebe.

This image was obtained at a phase, or Sun-Phoebe-spacecraft, angle of 78 degrees, and from a distance of 11,918 kilometers (7,407 miles). The image scale is approximately 18.5 meters (60.5 feet) per pixel. The illumination is from the right. No enhancement was performed on this image.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit and the Cassini imaging team home page,

Original Source: CICLOPS News Release