21 November 2007 ESA's Rosetta spacecraft performed an Earth swing-by on 13 November 2007. One of the instruments on board Rosetta, the Standard Radiation Environment Monitor (SREM), measured the energetic particle activity in the Earth’s radiation belts as the spacecraft passed through it. In order for Rosetta to reach and rendezvous with its target comet, the spacecraft has to gain a lot of velocity. Swing-by manoeuvres are the only way to gain the required amount of energy. Multiple planetary swing-bys are being used to accelerate Rosetta so as to eventually match the velocity of the target comet. The recent swing-by was the second of three around the Earth, with one swing-by also having been performed around Mars. At its closest approach, Rosetta passed 5 295 km from the Earth’s surface, travelling at around | ||||||||||||||||||||||||||||||||||||||||||||||||
The Standard Radiation Environment Monitor (SREM) was developed and manufactured by Contraves Space AG, now Oerlikon Space AG (CH), in cooperation with the Paul Scherrer Institut (CH) under a contract with ESA. SREM performs a wide range of radiation monitoring and alert functions during its host spacecraft’s mission and downloads the results via the spacecraft telemetry system to a user on ground. It is designed as a standard item of equipment, compatible with all common spacecraft interfaces and mission constraints. The Space Environments and Effects Section of the Electromagnetics and Space Environments Division, together with the Radiation Effects Section of the Components Division, both within ESA’s Directorate of Technical and Quality Management, facilitate the incorporation of radiation monitoring on ESA spacecraft. Measurement of the radiation environment experienced by a spacecraft is important because exposure to energetic particles can lead to interference and anomalies in systems and payloads, can damage electronic components such as integrated circuits or degrade the performance of sensors and solar generators. SREM has flown on Proba-1 and Integral, as well as Rosetta. It is scheduled to fly on GIOVE-B, Herschel and Planck. Of the spacecraft already launched, Rosetta is the only mission to have travelled beyond Earth orbit. | ||||||||||||||||||||||||||||||||||||||||||||||||
The Earth’s radiation belts (Van Allen belts) are torus shaped regions of energetic charged particles surrounding the Earth and held in place by Earth's magnetic field. The inner of these belts extends to an altitude of about 6 000 km above the Earth's surface at the equator, and contains high concentrations of protons with energies in the range 10 to several hundred MeV. Further out, with its peak intensity at an altitude somewhere between 15 000 and 20 000 km and extending beyond geostationary orbit, is a highly variable region populated mainly by electrons with energies between 0.1 and 10 MeV. | ||||||||||||||||||||||||||||||||||||||||||||||||
| The plot of SREM count rates versus time, which can be enlarged by clicking on it, shows two main peaks. Initial analysis has concluded that these were caused by two passages through the outer radiation belt. | ||||||||||||||||||||||||||||||||||||||||||||||||
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| While the primary purpose of SREM on Rosetta is to monitor the radiation dose received by the spacecraft, the swing-by offered an interesting chance to use the instrument for additional experimentation. For further information, contact Petteri Nieminen, (Space Systems Senior Analyst, Space Environments and Effects Section, ESA-ESTEC). | ||||||||||||||||||||||||||||||||||||||||||||||||
Wednesday, November 21, 2007
ESA : Rosetta monitors Van Allen belt during Earth swing-by
ESA : Solar outburst pulls a magnetic slingshot
With Cluster data, scientists now have evidence that solar outbursts can generate conditions that slingshot matter in Earth’s magnetic environment to speeds higher than 1000 km/s.
The outburst responsible in a recent study was a Coronal Mass Ejection (CME), a massive cloud of charged particles coming from the Sun. The study compares observations from the four satellites of the ESA’s Cluster mission with global simulations of the magnetosphere.
While the Sun continuously loses a small fraction of its mass via the solar wind, a CME is a massive, one-off ejection of matter at high speeds, carrying up to 10 thousand million tonnes of charged particles, or plasma, into the solar system. Most CMEs travelling towards Earth are harmless, but some can affect orbiting satellites or even power grids. Understanding how CMEs impact Earth’s magnetic environment – and consequently space- based and terrestrial technologies – is an active field of research.
On 11 January 1997, the 200 million dollar AT&T Telstar 401 satellite suddenly fell silent, cutting TV coverage to millions of viewers. Six days later, after no contact, it was declared permanently out of service. The most likely cause of this failure is that Telstar 401 was hit by a CME.
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Artist's impression of the four Cluster spacecraft |
On 25 November 2001, during the passage of a CME at Earth, the four Cluster satellites were skimming the border of the magnetosphere, in a region called the magnetosheath, when they detected plasma accelerated to speeds of 1040 km/s, while the speed of the solar wind was only 650 km/s.
This sort of acceleration has been observed in the past with or without the presence of a CME. Usually, it is a sign of magnetic reconnection, but on 25 November 2001, this was not the case.
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Simulation of the magnetosphere |
“We have unambiguous proof that the strong plasma acceleration observed on 25 November 2001 by Cluster was not the result of magnetic reconnection, but because of conditions created by the CME”, said Dr Lavraud, lead author at Los Alamos National Laboratory, USA.
The presence of such high-speed flows has consequences on the interaction between the solar wind and the magnetosphere. It may increase wavy or viscous interactions at magnetospheric boundaries and lead to giant, spiral auroral features, as reported early this year by Lisa Rosenqvist from the Swedish Institute of Space Physics, Uppsala, Sweden.
“This result demonstrates that not only is Cluster data indispensable, but also there is great mutual benefit in comparing global MHD simulation results with Cluster measurements,” commented Philippe Escoubet, ESA’s Cluster and Double Star project scientist.
Notes for editors:
The paper ‘Strong bulk plasma acceleration in Earth’s magnetosheath: a magnetic slingshot effect?’ is by B. Lavraud, J. Borovsky, A. Ridley, E. Pogue, M. Thomsen, H. Rème, A. Fazakerley, and E. Lucek (2007), published in the Geophysical Research Letters.
The observed giant spiral auroral features were reported in ‘An unusual giant spiral arc in the polar cap region during the northward phase of a Coronal Mass Ejection’ by Rosenqvist, L., Kullen A., and Buchert S. published in the Annales Geophysicae on (2007).
ESA : Rosetta: Earth’s true colours
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20 November 2007
True colour images of Earth as seen by Rosetta’s OSIRIS camera are now available. The pictures were taken on 13 November during the swing-by, and on 15 November, as Rosetta left on its way to the outer Solar System, after the swing-by.
After its closest approach to Earth, Rosetta looked back and took a number of images using the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) Narrow Angle Camera (NAC). This particular image was acquired 15 November 2007 at 03:30 CET.
The image above is a colour composite of the NAC orange, green and blue filters.
At the bottom, the continent of Australia can be seen clearly.
During the swing-by, OSIRIS observed Earth’s night-side.
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Earth from Rosetta's position |
This image shows a simulated view of Earth as seen from Rosetta's position.
The same view was seen by the OSIRIS Wide Angle Camera (WAC). It is shown in false colour to emphasise city lights seen at night.
This image was acquired on 13 November 2007 at 20:30 CET using the WAC with a red filter.
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NASA : Bargain Basement Satellites
November 19, 2007: Looking for a cheap fare 'round the world? Your search is over. A NASA team has built a small, low-cost satellite called FASTSAT, and it's almost ready to fly.
Need some details before you sign up? Read on.
Why is it called FASTSAT?
It's not because it travels fast. It's because it was built in a hurry. The FASTSAT team built this prototype in a mere 10½ months for the relatively thrifty sum of 4 million dollars.
"That's unheard of," says Marshall Space Flight Center's Edward "Sandy" Montgomery, "to build something that will fly in space in that short time frame and for that amount of money. But that was part of our experiment – to see if it could be done." The full name says it all: Fast, Affordable, Science and Technology SATellite.
Right: Low-cost launch vehicles like SpaceX's Falcon 1 highlight the need for low-cost payloads like FASTSAT.
How did they do it?
Montgomery, the FASTSAT Project Manager, led a team already experienced in low-cost, quick turnaround balloon missions. "In the balloon program, people know how to take risks and do things more quickly," he says. "Quicker build time means less labor charges, and that's one of the keys to keeping costs down."
Balloon missions taught the team some specific ways to save time and money. For instance, they used commercial off-the-shelf components, which are readily available and cheaper than specially ordered parts.
"We also did some scrounging and got some items left over from other programs," says Montgomery. "There's nothing fancy on this satellite."They even built the satellite out of aluminum instead of expensive titanium. And they used a design so simple "even a cave man could do it." The design required few cuts in the metal, so fabrication was fast.
FASTSAT is safe as well as simple. Magnets provide its attitude control instead of jets, so there are no propellants onboard to offgas or explode. The satellite has no moving parts – no blades or momentum wheels whirring around. All of these factors add up to subtract cost. "We are kind of like the bargain basement of satellite building," jokes Montgomery.
Why did they do it?
A new class of very low cost launch vehicles (such as SpaceX's Falcon 1 and Kistler's K-1) has opened doors for inexpensive satellites and instruments.
"You wouldn't put an expensive payload on an inexpensive rocket – it's a risk issue. You'd use an inexpensive bus to fly an inexpensive instrument on an inexpensive rocket," says Montgomery.
For example, FASTSAT could be used for test demonstrations of new technologies. "It doesn't make sense to spend several hundred million dollars just to test a technology before a major mission when a FASTSAT can do it for so much less," states Montgomery. "That's the impetus driving this project."
What does FASTSAT look like?
A picture is worth a thousand words:
FASTSAT is 39.5 inches in diameter – not much larger than the dreaded exercise ball. It is hexagonally shaped and weighs 90 kg without a payload. A payload up to 50 kg can hitch a ride. These dimensions place FASTSAT squarely in the microsatellite category.
What is the significance of FASTSAT?
FASTSAT is just the right size for earth observing missions, space science missions, and technology demonstrations. Montgomery says, "We think we can do whole missions for less than 10 million dollars instead of the traditional 100s of millions, and that includes the launch vehicle, the satellite, and the widget you want to test. If you can do low-cost missions locally, at the center level, this has the potential to bring how NASA does its work to a whole new level of manageability. It would give centers more latitude on how to do things and lower management costs tremendously. If you don't have to have 100 people in the chain signing off on a project, you save time and money."
What is next for FASTSAT?
In late September, the team rolled out their masterpiece for an internal review, showing their audience proof-positive that a satellite can be built quickly and inexpensively. They're hoping for a little more money in order to test and do final integration activities once they have a specific payload in mind. But right now, FASTSAT is a horse without a cart. It has no payload.
"That's the next step," says Montgomery. "We've proven we can design it, and we've got it built. Someone who can afford the ride and has an instrument they want to fly will come along and find us."
Space.com : New Way to ID Stars in Night Sky Photos
 |  By Dave Mosher Staff Writer posted: 20 November 2007 07:02 am ET |
BALTIMORE - A new search engine will soon turn your night sky images into powerful research data and identify the twinkling objects in them with just the click of a button.
The Astrometry.net database will hunt down and name celestial objects in any amateur photo, pinpoint the region of night sky that was photographed and use the image to expand a detailed database of the cosmos for use by scientists
David Hogg, an astronomer at New York University and leader of the project, showed off the still-in-development tool at the recent Astrophysics 2020 conference here at Johns Hopkins University's Space Telescope Science Institute.
"Any individual can take a picture of the sky, plug it in and learn what stars, galaxies or other objects are in their image," Hogg told SPACE.com. "It's fun for people to do this, but more importantly it'll provide data we need to make that image searchable and useful to scientists."
'Wiki' the sky
The project's driving force is astrometry: a branch of astronomy that relies on star positions to explain how they got there. Although stars may look stationary, they move in a slow "proper motion" from our Earthly vantage point.
"To understand the physics of a star cluster, you need to know the proper motions of stars in it," Hogg said, mentioning the Beehive Cluster in the constellation Cancer as an example. "When you run the clock back, you see the stars came out of some huge formation event."
The best way for astronomers to pin down the celestial motions—as well as keep tabs on the latest supernovae—is to take many images over time, Hogg explained. Problem is, monitoring the sky tedious and expensive.
Meanwhile, armies of amateurs scour the sky every minute of every day around the world. But most don't tag their images with "meta-data" scientists need, such as the exact time the photo was taken and location of the photographer on Earth at the time.
Hogg wants to change that.
"Amateurs with first-class equipment could really revolutionize how we think about doing this kind of science," he said, noting the search engine's ability to automatically tag random celestial images with the crucial meta-data.
How it works
The Astrometry.net process begins with an image and software that performs "the most idiotic star identification possible" on it, Hogg said: circling stars and other points of light.
Computer code then connects the dots between four stars at a time and compares the pattern to those in a massive celestial database. When a good match appears, the Web-based tool not only visualizes what section of the night sky was photographed, but also lists the constellations, objects of interest and precise celestial longitude and latitude.
"If an amateur takes an image, says, 'Wow, I have a super cool image, what do I do with it?'," Hogg explained, "we can take that image and turn it into science-grade data."
Hogg said developers are also working toward finding out when a photo was taken by reversing the proper motions of stars in the most up-to-date celestial catalogues.
"We're building the catalogue at different times, because in principle there's also a best fit for year," Hogg said.
What's more, he explained, is that the database won't be a "greedy" repository that simply gathers images and gives nothing back to hard-working amateur astronomers—some of whom sell prints of their photographs for a living and worry about copyright issues.
"We want to give back services in exchange for their help," Hogg said. Such services might include recognition in scientific studies that use the amateur's image, or perhaps linking back to the contributor's Web site when other users stumble upon the image with Astrometry.net's search engine.
Growing pains
While computer scientists prepare the database for its public debut, tentatively set for spring 2008, Hogg said the entire operation currently is running off of a simple Web server.
"If we have tens of thousands of amateur astronomers pushing big images files through the server, I'm not sure we could handle that," he said.
To handle the heavy traffic, Hogg said has been speaking with Internet companies that could host the service. Eventually, he envisions simple desktop applications for the astro-curious public.
"We like the idea of a kid in a backyard looking up at the sky, asking 'What is that?' and having a parent be able to answer their question," he said. "All they would need is a decent shot of the part of the sky they're looking at."
While Hogg expects most users to query astronomical images with the database, he said a few will submit non-astronomy images for fun—perhaps to see if their grandmother's head might create a new constellation.
"Trying to find your granny in the sky isn't going to work. Our alpha testers have submitted some crazy pictures, but we rarely ever get a match," he said. "If it's not in the sky, the software won't find it."
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