Studying interstellar dust from a balloon

In just a few days, the Pilot astrophysics experiment will be launched under a stratospheric balloon from Alice Springs in central Australia. Its aim is to observe the polarized emission of dust particles found in the interstellar medium of our galaxy and nearby galaxies.

With a mass approaching one metric ton, Pilot uses the largest balloons ever launched by CNES, the French national space agency. The experiment was developed by the Research Institute in Astrophysics and Planetology (CNRS/CNES/Paul Sabatier University), the Institute of Space Astrophysics (CNRS/Paris-Sud University), and the Institute of Research into the Fundamental Laws of the Universe (CEA-Irfu).

The first Pilot flight was launched from Canada in September 2015; the forthcoming flight will thus be its first flight in the southern hemisphere sky, which contains more features of interest for Pilot than the northern hemisphere.

Studying interstellar dust from a balloon

The emission of dust particles in the interstellar medium of our galaxy and nearby galaxies is slightly polarized, as the particles are elongated and aligned with the magnetic field that prevails in the interstellar medium. The measurements obtained by Pilot will help scientists understand the nature of dust particles and why they are aligned in this way. The measurements will also be used to map the geometry of the magnetic field, which plays an important part in contracting the gas in the interstellar medium, a phenomenon that leads to the formation of new stars.
This emission is also an obstacle for experiments that seek to accurately measure the polarization of the cosmic microwave background, and Pilot’s measurements will shed more light on it, and thus improve the interpretation of the results obtained with this type of experiment.
The Pilot experiment will observe this emission in the far infrared region. It is equipped with 2,048 individual detectors, cooled to a temperature of 300 millikelvin, i.e. close to absolute zero. Polarization is measured using a rotating blade and a polarizer that separates two orthogonal polarizations on the two focal planes of the experiment. Apart from the primary mirror of the telescope, all the optics is maintained at a cryogenic temperature (2 kelvins or -271°C) inside a cryostat, cooled with liquid helium, to limit the instrument’s own emission.
The experiment was conceived and built by CNRS scientists and engineers at the Research Institute in Astrophysics and Planetology (CNRS/CNES/Paul Sabatier University) and IAS (CNRS/Paris-Sud University), with major contributions from the CNES Balloon Division in Toulouse, the ESA, the CEA (Saclay), which developed the focal plane and its electronics, La Sapienza University in Rome (Italy), and Cardiff University (United Kingdom). The whole project is backed by CNRS laboratories and CNES funding.
In a few days, Pilot will be launched by CNES as part of a campaign comprising three flights with different gondolas from Alice Springs, in central Australia. Pilot weighs nearly one metric ton and will have to climb to an altitude of nearly 40 km. It therefore requires the use of an open stratospheric balloon, approximately 100 m in diameter (the largest open balloon ever launched by CNES), and a payload chain as tall as the Eiffel Tower.
The flight will take place during one of the two annual reversals of stratospheric winds, which is a prerequisite for any hope of performing observations for more than 30 hours at the ceiling altitude. Although Pilot has already been launched in the past – its first flight was from Canada in September 2015 – this new flight will be in the southern hemisphere, thus providing an opportunity to observe outstanding astrophysical sources, such as the Magellanic Clouds, satellite galaxies of our own galaxy, or inner regions of the Milky Way, that cannot be observed from the northern hemisphere.

Thanks to Phys Org for this article on studying interstellar dust from a balloon.

Another great article I found is also from Phys Org……….

NASA team explores using LISA Pathfinder as ‘comet crumb’ detector

LISA Pathfinder, a mission led by ESA (the European Space Agency) with contributions from NASA, has successfully demonstrated critical technologies needed to build a space-based observatory for detecting ripples in space-time called gravitational waves. Now a team of NASA scientists hopes to take advantage of the spacecraft’s record-breaking sensitivity to map out the distribution of tiny dust particles shed by asteroids and comets far from Earth.

Most of these particles have masses measured in micrograms, similar to a small grain of sand. But with speeds greater than 22,000 mph (36,000 kph), even micrometeoroids pack a punch. The new measurements could help refine dust models used by researchers in a variety of studies, from understanding the physics of planet formation to estimating impact risks for current and future spacecraft.
“We’ve shown we have a novel technique and that it works,” said Ira Thorpe, who leads the team at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “The next step is to carefully apply this technique to our whole data set and interpret the results.”
The mission’s primary goal was to test how well the spacecraft could fly in formation with an identical pair of 1.8-inch (46 millimeter) gold-platinum cubes floating inside it. The cubes are test masses intended to be in free fall and responding only to gravity.
The spacecraft serves as a shield to protect the test masses from external forces. When LISA Pathfinder responds to pressure from sunlight and microscopic dust impacts, the spacecraft automatically compensates by firing tiny bursts from its micronewton thrusters to prevent the test masses from being disturbed.
Scientists call this drag-free flight. In its first two months of operations in early 2016, LISA Pathfinder demonstrated the process with a precision some five times better than its mission requirements, making it the most sensitive instrument for measuring acceleration yet flown. It has now reached the sensitivity level needed to build a full multi-spacecraft gravitational wave observatory.
“Every time microscopic dust strikes LISA Pathfinder, its thrusters null out the small amount of momentum transferred to the spacecraft,” said Goddard co-investigator Diego Janches. “We can turn that around and use the thruster firings to learn more about the impacting particles. One team’s noise becomes another team’s data.”
Much of what we know about interplanetary dust is limited to Earth’s neighborhood, thanks in large part to NASA’s Long Duration Exposure Facility (LDEF). Launched into Earth orbit by the space shuttle Challenger in April 1984 and retrieved by the space shuttle Columbia in January 1990, LDEF hosted dozens of experiments, many of which were designed to better understand the meteoroid and orbital debris environment.
The different compositions, orbits and histories of different asteroids and comets naturally produce dust with a range of masses and velocities. Scientists suspect the smallest and slowest particles are enhanced in Earth’s neighborhood, so the LDEF results are not representative of the wider solar system.

“Small, slow particles near a planet are most susceptible to the planet’s gravitational pull, which we call gravitational focusing,” Janches said. This means the micrometeoroid flux near Earth should be much higher than that experienced by LISA Pathfinder, located about 930,000 miles (1.5 million kilometers) closer to the sun.
To find the impacts, Tyson Littenberg at NASA’s Marshall Space Flight Center in Huntsville, Alabama, adapted an algorithm he originally developed to search for gravitational waves in data from the ground-based detectors of the Laser Interferometer Gravitational-wave Observatory (LIGO), located in Livingston, Louisiana, and Hanford, Washington. In fact, it was one of many algorithms that played a role in the discovery of gravitational waves by LIGO, announced in February 2016.
“The way it works is that we come up with a guess of what the signal might look like, then study how LIGO or LISA Pathfinder would react if this guess were true,” Littenberg explained. “For LIGO, we’re guessing about the waveform, the peaks and valleys of the gravitational wave. For LISA Pathfinder, we’re guessing about an impact.”
To map out the probability of likely sources, the team generates millions of different scenarios describing what the source might be and compares them to what the spacecraft actually detects.
In response to an impact, LISA Pathfinder fires its thrusters to counteract both the minute “push” from the strike and any change in the spacecraft’s spin. Together, these quantities allow the researchers to determine the impact’s location on the spacecraft and reconstruct the micrometeoroid’s original trajectory. This may allow the team to identify individual debris streams and perhaps relate them to known asteroids and comets.
“This is a very nice collaboration,” said Paul McNamara, the LISA Pathfinder project scientist at ESA’s Directorate of Science in Noordwijk, the Netherlands. “This is data we use for doing our science measurements, and as an offshoot of that, Ira and his team can tell us about microparticles hitting the spacecraft.”
Its distant location, sensitivity to low-mass particles, and ability to measure the size and direction of impacting particles make LISA Pathfinder a unique instrument for studying the population of micrometeoroids in the inner solar system. But it’s only the beginning.
“This is a proof of concept, but we’d hope to repeat this technique with a full gravitational wave observatory that ESA and NASA are currently studying for the future,” said Thorpe. “With multiple spacecraft in different orbits and a much longer observing time, the quality of the data should really improve.”
LISA Pathfinder is managed by ESA and includes contributions from NASA Goddard and NASA’s Jet Propulsion Laboratory in Pasadena, California. The mission launched on Dec. 3, 2015, and began orbiting a point called Earth-sun L1, roughly 930,000 miles (1.5 million km) from Earth in the sun’s direction, in late January 2016.
LISA stands for Laser Interferometer Space Antenna, a space-based gravitational wave observatory concept that has been studied in great detail by both NASA and ESA. It is a concept being explored for the third large mission of ESA’s Cosmic Vision Plan, which seeks to launch a gravitational wave observatory in 2034.

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