Author Topic: ESA - LISA Pathfinder updates  (Read 22874 times)

Offline Star One

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ESA - LISA Pathfinder updates
« Reply #60 on: 02/07/2017 04:23 PM »
Scientists optimistic about prospects for LISA gravitational wave mission

A European consortium submitted to ESA in January a proposal for the development of the Laser Interferometer Space Antenna (LISA) mission for ESA’s third large mission, or L3, competition. LISA is widely considered the leading candidate to be selected for that mission for launch likely in the early 2030s.

LISA, as proposed, will consist of three spacecraft in a triangular formation, each 2.5 million kilometers from the other two in an orbit around the sun trailing the Earth. The spacecraft would shine lasers at each other, with interferometers on each spacecraft detecting minute distance changes caused by passing gravitational waves.

The three spacecraft, with a combined mass of about 6,000 kilograms, including payload adapter, would launch on an Ariane 6 and drift to their planned orbit over the course of a year and a half. LISA would have a planned mission lifetime of four years, but with sufficient propellant on each spacecraft to operate for up to a decade.

“LISA looks like it’s going to happen. It looks like it’s on a pretty firm track,” said David Shoemaker, a senior research scientist at the Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research, during a meeting of the American Physical Society (APS) here Jan. 29.

Shoemaker is chairman of the L3 Study Team, a NASA group looking at contributions NASA can make to the LISA mission. The LISA proposal submitted to ESA assumes NASA will cover 20 percent of the mission’s cost through instruments and other technologies.

Parth of the confidence of Shoemaker and other scientists is linked to the announcement a year ago of the first detection of gravitational waves, by the Laser Interferometer Gravitational-Wave Observatory (LIGO), ground-based gravitational wave detectors in Louisiana and Washington. That discovery removed any doubt that gravitational waves exist, creating confidence that a mission like LISA could also successfully detect and study gravitational waves, and do so at frequencies not possible with LIGO.

Another factor is the technical success of ESA’s LISA Pathfinder mission, a single small spacecraft launched in December 2015 to test technologies that could be used in a later LISA mission. The performance of the spacecraft, including a thruster system provided by NASA, exceeded expectations.

Those tests not only exceeded the stability expectations of the LISA Pathfinder mission, but also approached the requirements for the full-fledged LISA mission. “This was a successful demonstration of drag-free control at a level necessary for a LISA-type gravitational wave observatory,” said Charles Dunn of JPL, project technologist for the disturbance reduction system flown on LISA Pathfinder, at the APS meeting Jan. 28.

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« Last Edit: 02/07/2017 04:27 PM by Star One »

Offline Star One

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Re: ESA - LISA Pathfinder updates
« Reply #61 on: 04/17/2017 08:03 PM »
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.

In a proof-of-concept study, NASA scientists are exploring using ESA’s (the European Space Agency) LISA Pathfinder spacecraft as a micrometeoroid detector. When tiny particles shed by asteroids and comets impact LISA Pathfinder, its thrusters work to quickly counteract any change in the spacecraft's motion. Researchers are monitoring these signals to learn more about the impacting particles.
Credits: NASA's Goddard Space Flight Center
Download HD video and additional visuals from NASA's Scientific Visualization Studio
"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.

Banner image: An illustration of LISA Pathfinder on its way to Earth-sun L1. Credit: ESA/C. Carreau