ESA Integral manoeuvres to improve future observations

Credit: ESA

ESA’s Integral observatory is able to detect gamma-ray bursts, the most energetic phenomena in the Universe.

Since 2002, ESA’s Integral spacecraft has been observing some of the most violent events in the Universe, including gamma-ray bursts and black holes.

While it still has years of life ahead, its fuel will certainly run out one day.

Integral, one of ESA’s longest-serving and most successful space observatories, has begun a series of four thruster burns carefully designed to balance its scientific life with a safe reentry in 2029.

That seems far off, but detailed planning and teamwork now will ensure that the satellite’s eventual entry into the atmosphere will meet the Agency’s guidelines for minimising space debris.

Making these disposal manoeuvres so early will also minimises fuel usage, allowing ESA to exploit the valuable satellite’s lifetime to the fullest.

This is the first time that a spacecraft’s orbit is being adjusted, after 12 years in space, to achieve a safe reentry 15 years in the future, while maximising valuable science return for the subsequent seven to eight years.

“Our four burns will use about half of the estimated 96 kg of fuel available,” says Richard Southworth, spacecraft operations manager at ESA’s Space Operations Centre, ESOC, in Darmstadt, Germany.

“This will influence how Integral’s orbit evolves, so that even after we run out of propellant we will still have a safe reentry in February 2029 as a result of natural orbit decay.

“No further manoeuvres are required between now and then and Integral can continue to operate.”

Debris Mitigation
The latest ESA debris guidelines require that a satellite must be disposed of in such a way that it poses no risk to other satellites in protected orbital regions for more than 25 years.

Although Integral’s early launch date, in 2002, means it is not required to stick to the guidelines, they were followed for planning the disposal.

“We have done a great deal of modelling for Integral’s reentry in 2029,” says Klaus Merz of ESA’s Space Debris Office.

“We’re confident that this month’s manoeuvres will put it on track for a future safe reentry at latitudes in the far south, reducing risk far below guideline levels.”

Without these firings, the fuel supply would run out in perhaps 12–16 more years, after other essentials such as power end Integral's working life, but the satellite would not reenter for up to 200 years, which would present a hazard to other missions.

El Hierro Volcano research improves algorithms used by EO satellites

Image taken by the satellite WorldView-2 in October 2011. 

The bright green waters indicate high concentrations of volcanic material flowing from the brown zone, which is where the volcano is located. 

On the right, the ‘diffuse attenuation coefficient’ has been applied, this is an indicator of the water roughness level. 

The areas shaded in black are clouds. 

Credit: Institute of Oceanography and Global Change (ULPGC)

Information provided by satellites on the amount of chlorophyll-A and the roughness of the sea following the eruption of the underwater volcano off the island of El Hierro (Spain) did not coincide with the actual data collected in situ by vessels carrying out oceanographic studies.

The models have been corrected by researchers at the University of Las Palmas de Gran Canaria, who have for the first time processed very high resolution images of this kind of natural phenomenon captured from space.

The image of the Canary Islands which won the prize this year of NASA's Earth Observatory was captured by one it its satellites, 'Terra', with the Moderate Resolution Imaging Spectro-radiometer (MODIS) instrument.

This sensor also travels in the US space agency's satellite 'Aqua' as well as alongside the Medium Resolution Imaging Spectrometer (MERIS) in the European Space Agency's satellite Envisat, and they have helped to understand the evolution of the underwater volcano which emerged in 2011 beneath the waters surrounding the island El Hierro, in the Canary Islands.

However, the information supplied by MODIS and MERIS was incorrect with regard to certain marine parameters, according to measurements taken in situ by oceanographic research vessels of the Spanish Institute of Oceanography (IEO).

This has now been confirmed by researchers of the University of Las Palmas de Gran Canaria (ULPGC) in a study published by the 'International Journal of Applied Earth Observation and Geoinformation'.

"The algorithms used with the data from the NASA and ESA satellites made mistakes when determining the concentration of chlorophyll-A (a variable that indicates the biological productivity in marine ecosystems) as it showed concentrations that were greater than actual ones as measured by the research ships," explained Francisco Eugenio, co-author of the study and researcher at the Institute of Oceanography and Global Change at the ULPGC, to SINC.

Members of this institute have developed new mathematical algorithms that correct the incongruities detected with chlorophyll-A as well as what is known as the 'diffuse attenuation coefficient' - an indicator of the sea turbulence in terms of dissolved material.

This parameter had also been over-estimated when applied to the data from the satellites.

"In any case, the images processed from these remote sensors have proven to be a very powerful tool for monitoring effects associated with underwater volcanic activity, such as the change of colour of the water, the presence of floating matter and volcanic plumes," Eugenio underlined.

The researcher also pointed out that, for the first time, very high resolution images have been obtained to follow this kind of geological phenomenon.

These are the images obtained from the private satellite Worldview-2, which has a pan-chromatic resolution of 46 centimetres -in black and white- and 1.85 metres in 8 multi-spectral bands. New algorithms have also been used with these.

In the case of these images, as with the low-resolution images obtained from MODIS and MERIS, the researchers have been able to work out the chronology of the atmospheric, oceanographic and biological parameters in the ocean since the volcano erupted three years ago at a depth of 300 metres below the ocean surface.

This data has been supplemented with the samples retrieved from all round the island in the project called 'Vulcano', which was most recently conducted last March.

For its part, the IEO's underwater robot Lirupos 2000 has also captured the growth of the underwater volcano's structure and the rapid rate at which the marine ecosystem is recolonizing the area.

"Currently, the volcano's main crater is at the same depth as it was in October 2013, which is 88 metres below the ocean surface," explains Eugenio.

He goes on to confirm: "The waters around El Hierro are fine, and, with the exception of a small area within a 200-metre radius around the main crater, no physical or chemical anomalies have been detected at any point around the periphery of the island, from the ocean surface to depths of 1,200 metres."

More information: F. Eugenio, J. Martin, J. Marcello, E. Fraile-Nuez, "Environmental monitoring of El Hierro Island submarine volcano, by combining low and high resolution satellite imagery," International Journal of Applied Earth Observation and Geoinformation, Volume 29, June 2014, Pages 53-66, ISSN 0303-2434, dx.doi.org/10.1016/j.jag.2013.12.009.

NASA Van Allen Probes observations helping to improve space weather models

NASA's Van Allen Probes orbit through two giant radiation belts that surround Earth. 

Their observations help improve computer simulations of events in the belts that can affect technology in space. 

Credit: John Hopkins University Applied Physics Laboratory /NASA

Using data from NASA's Van Allen Probes, researchers have tested and improved a model to help forecast what's happening in the radiation environment of near-Earth space, a place seething with fast-moving particles and a space weather system that varies in response to incoming energy and particles from the sun.

When events in the two giant doughnuts of radiation around Earth, called the Van Allen radiation belts, cause the belts to swell and electrons to accelerate to 99 percent the speed of light, nearby satellites can feel the effects.

Scientists ultimately want to be able to predict these changes, which requires understanding of what causes them.

Now, two sets of related research published in the Geophysical Research Letters improve on these goals.

By combining new data from the Van Allen Probes with a high-powered computer model, the new research provides a robust way to simulate events in the Van Allen radiation belts.

Geoff Reeves

"The Van Allen Probes are gathering great measurements, but they can't tell you what is happening everywhere at the same time," said Geoff Reeves, a space scientist at Los Alamos National Laboratory (LANL), in Los Alamos, N.M., a co-author on both of the recent papers.

"We need models to provide a context, to describe the whole system, based on the Van Allen Probe observations."

Prior to the launch of the Van Allen Probes in August 2012, there were no operating spacecraft designed to collect real-time information in the radiation belts.

Understanding of what might be happening in any locale was forced to rely mainly on interpreting historical data, particularly those from the early 1990s gathered by the Combined Release and Radiation Effects Satellite (CRRES).

Imagine if meteorologists wanted to predict the temperature on March 5, 2014, in Washington, D.C. but the only information available was from a handful of measurements made in March over the last seven years up and down the East Coast.

That's not exactly enough information to decide whether or not you need to wear your hat and gloves on any given day in the nation's capital.

Artist's rendition of the Van Allen Probes in orbit. Credit: NASA

Thankfully, we have much more historical information, models that help us predict the weather and, of course, innumerable thermometers in any given city to measure temperature in real time.

The Van Allen Probes are one step toward gathering more information about space weather in the radiation belts, but they do not have the ability to observe events everywhere at once.

So scientists use the data they now have available to build computer simulations that fill in the gaps.

The recent work centers around using Van Allen Probes data to improve a three-dimensional model created by scientists at LANL.

The project was called DREAM3D, the Dynamic Radiation Environment Assimilation Model in 3 Dimensions. Until now the model relied heavily on the averaged data from the CRRES mission.

The Dynamic Radiation Environment Assimilation Model (DREAM) was developed at LANL to understand and to predict hazards from the natural space environment and artificial radiation belts produced by high altitude nuclear explosions.

DREAM was initially developed as a basic research activity to understand and predict the dynamics of the Earth's radiation belts. 

It uses Kalman filter mathematical techniques to assimilate data from space environment instruments with a physics-based model of the radiation belts.

DREAM can assimilate data from a variety of types of instruments and data with various levels of resolution and fidelity by assigning appropriate uncertainties to the observations.

Data from any spacecraft orbit can be assimilated but DREAM was originally designed to work with input from the LANL space environment instruments on geosynchronous and GPS platforms.

With those inputs, DREAM can be used to specify the energetic electron environment at any satellite in the outer electron belt whether space environment data are available in those orbits or not.

Even with very limited data input and relatively simple physics models, DREAM specifies the space environment in the radiation belts to a high level of accuracy.

DREAM is currently being tested and evaluated as we transition from research to operations.

Space Weather model selected to improve US warning system

A University of Michigan space weather model beat out four other contenders for a spot in the national Space Weather Prediction Center's forecasting toolbox.

It is the first time that computer models based on a firm understanding of physics have overtaken simpler, statistics-based models to predict magnetic disturbances due to space weather.

The new model can also give information about where the effects of a geomagnetic storm will be weaker or stronger around Earth.

Space weather forecasts are important for protecting satellites, predicting when GPS signals become unreliable, and in the worst case, preventing far-reaching and long-term electrical power outages.

Most of the time, Earth's magnetic field unflinchingly deflects most of the charged particles shed by the sun, known collectively as the solar wind.

Yet every now and again, the sun ejects a chunk of material—still charged particles but a lot more of them.

"You can have eruptions like coronal mass ejections or solar flares, and these propagate all the way from the sun to the earth," said Gábor Tóth, a research scientist in atmospheric, oceanic and space sciences and one of the model's main developers.

In a gale-force solar wind brought on by these eruptions, Earth's magnetic field shakes.

The main fear is that this shaking could knock out the big transformers in the electrical grid.

Simulation results show the solar wind in gray with Earth's magnetic field in shades of blue and yellow, corresponding to different pressures. 

The white ball is 2.5 times the size of Earth. 

Credit: Visualization created by Darren De Zeeuw, Dept. of AOSS

"These power grids always operate on the edge, and if you put an extra load on, they can fail," Tóth said.

As Earth's magnetic field moved, it would create its own currents in the high-voltage cables that carry electricity across hundreds of miles.

At substations, where transformers convert the electricity to lower voltages for delivery into cities and towns, that extra current would likely push transformers over the edge.

Since crisscrossing the Earth with high-voltage cables and sending satellites into orbit, humans haven't experienced space weather that could cause worldwide disruption.

The last event of that magnitude was in September 1859. Only the telegraph system was around to preview how Earth's roiling magnetic field can fry long-distance electrical systems.

Because large transformers take between five months and five years to build, a modern version of that storm could mean prolonged, extensive blackouts.