From NASA Goddard Space Flight Center (US) : “NASA Provides Laser for LISA Mission”

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From NASA Goddard Space Flight Center (US)

By Karl B. Hille
NASA’s Goddard Space Flight Center in Greenbelt, Md.

Media contact:
Claire Andreoli
(301) 286-1940

Finding the biggest collisions in the universe takes time, patience, and super steady lasers.

In May, NASA specialists working with industry partners delivered the first prototype laser for the The European Space Agency [Agence spatiale européenne][Europäische Weltraumorganisation](EU)-led Laser Interferometer Space Antenna, or LISA, mission.

The first prototype of a laser sits on a testbed at the Swiss Center for Electronics and Microtechnology (CSEM), headquartered in Neuchâtel, Switzerland. CSEM will test and characterize the laser, which will be used to conduct gravitational wave experiments in space for the LISA mission.Credits: European Space Agency/CSEM

This unique laser instrument is designed to detect the telltale ripples in gravitational fields caused by the mergers of neutron stars, black holes, and supermassive black holes in space.

Anthony Yu at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, leads the laser transmitter development for LISA.

“We’re developing a highly stable and robust laser for the LISA observatory,” Yu said. “We’ve leveraged lessons learned from previous missions and the latest technologies in photonics packaging and reliability engineering. Now, to meet the challenging LISA requirements, NASA has developed a system that produces a laser transmitter by using a low-power laser enhanced by a fiber-optic amplifier.”

The team is building upon the laser technology used in NASA’s GRACE mission. “We developed a more compact version as a master oscillator,” Yu said. “It has much smaller size, weight, and power consumption to allow for a fully redundant master oscillator for long-duration lifetime requirements.”

The LISA laser prototype is a 2-watt laser operating in the near-infrared part of the spectrum. “Our laser is about 400 times more powerful than the typical laser pointer that puts out about 5 milliwatts or less,” Yu said. “The laser module size, not including the electronics, is about half the volume of a typical shoe box.”

The Swiss Center for Electronics and Microtechnology (CSEM), headquartered in Neuchâtel, Switzerland, confirmed receipt of the lasers and will begin testing them for stability.

LISA will consist of three spacecraft following Earth in its orbit around the Sun and flying in a precision formation, with 1.5 million miles (2.5 million kilometers) separating each one. Each spacecraft will continuously point two lasers at its counterparts. The laser receiver must be sensitive to a few hundreds of picowatts of signal strength, as the laser beam will spread to about 12 miles (20 kilometers) by the time it reaches its target spacecraft. A time-code signal embedded in the beams allows LISA to measure the slightest interference in these transmissions.

Ripples in the fabric of space-time as small as a picometer – 50 times smaller than a hydrogen atom – will produce a detectable change in the distances between the spacecraft. Measuring these changes will give scientists the general scale of what collided to produce these ripples and an idea of where in the sky to aim other observatories looking for secondary effects.

These gravitational wave fluctuations are so small they would be obscured by external forces such as dust impacts and the radiation pressure of sunlight on the spacecraft. To mitigate this, the drag-free control concept – demonstrated on the LISA Pathfinder mission in 2015 – uses free-floating test masses sheltered inside each spacecraft as reference points for the measurement.

LISA expands on work by the National Science Foundation’s (US)3 Laser Interferometer Gravitational-Wave Observatory (LIGO), which captured its first recording of gravitational waves in 2015.

Since then, the pair of ground-based observatories in Hanford, Washington, and Livingston, Louisiana, have captured four dozen mergers.

Thomas Hams, program scientist for LISA at NASA Headquarters in Washington, said the precision laser measurements will allow us to zoom in on the gravitational wave signatures of these mergers and enable other observatories to focus on the right part of the sky to capture these events in the electromagnetic spectrum.

NASA’s Fermi Gamma-ray Space Telescope picked up the first such multimessenger observation just seconds after LIGO detected a merger of two neutron stars through gravitational waves.

“With LISA, the hope is you will be able to see these things develop before the merger actually happens,” Hams said. “There will be an indicator that something is coming.”

Industry Partnership

To achieve the required stability, the team brought Fibertek Inc. in Herndon, Virginia, and Avo Photonics Inc. in Horsham, Pennsylvania, to develop the laser, oscillator, and power amplifier, and an independent optical engineer in San Jose, California.

Avo Photonics built the laser for the observatory.

“Here you have the challenges of spaceborne ruggedness needs, on top of submicron-level optical alignment tolerance requirements. These really push your optical, thermal, and mechanical design chops,” Avo Photonics President Joseph L. Dallas said. “In addition, the narrow linewidth, low noise, and overall stability needed for this mission is unprecedented.”

Photonics pioneer Tom Kane invented the monolithic laser oscillator technology that Goddard used to stabilize the frequency of the laser light. “Your average laser can be very messy,” Kane said. “They can wander all around their target frequency. You need a ‘quiet’ laser that’s exactly one wavelength and a perfect beam out to 15 decimal places of accuracy.”

His oscillator technology uses feedback loops to keep the laser burning at such precision. “The wavelength ends up becoming the ruler for these incredible distances,” Kane said.

The high-power, low-noise amplifier came from Fibertek.

Fibertek also contributed to NASA’s Ice Cloud and Land Elevation Satellite (ICESat) 2 and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), which has been operating a laser pointed at Earth for 15 years.

Including time for testing on the ground and potential mission extensions, LISA’s lasers must operate without skipping a hertz for up to 16 years, Goddard’s Yu said.

“Once launched, they will need to be in 24/7 operation for five years for the initial mission, with a possible six to seven years of extended mission after that,” Yu explained. “We need them to be stable and quiet.”

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NASA/Goddard Campus

NASA’s Goddard Space Flight Center, Greenbelt, MD (US) is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.

GSFC also operates two spaceflight tracking and data acquisition networks (the NASA Deep Space Network(US) and the Near Earth Network); develops and maintains advanced space and Earth science data information systems, and develops satellite systems for the National Oceanic and Atmospheric Administration(US) .

GSFC manages operations for many NASA and international missions including the NASA/ESA Hubble Space Telescope; the Explorers Program; the Discovery Program; the Earth Observing System; INTEGRAL; MAVEN; OSIRIS-REx; the Solar and Heliospheric Observatory ; the Solar Dynamics Observatory; Tracking and Data Relay Satellite System ; Fermi; and Swift. Past missions managed by GSFC include the Rossi X-ray Timing Explorer (RXTE), Compton Gamma Ray Observatory, SMM, COBE, IUE, and ROSAT. Typically, unmanned Earth observation missions and observatories in Earth orbit are managed by GSFC, while unmanned planetary missions are managed by the Jet Propulsion Laboratory (JPL) in Pasadena, California(US).

Goddard is one of four centers built by NASA since its founding on July 29, 1958. It is NASA’s first, and oldest, space center. Its original charter was to perform five major functions on behalf of NASA: technology development and fabrication; planning; scientific research; technical operations; and project management. The center is organized into several directorates, each charged with one of these key functions.

Until May 1, 1959, NASA’s presence in Greenbelt, MD was known as the Beltsville Space Center. It was then renamed the Goddard Space Flight Center (GSFC), after Robert H. Goddard. Its first 157 employees transferred from the United States Navy’s Project Vanguard missile program, but continued their work at the Naval Research Laboratory in Washington, D.C., while the center was under construction.

Goddard Space Flight Center contributed to Project Mercury, America’s first manned space flight program. The Center assumed a lead role for the project in its early days and managed the first 250 employees involved in the effort, who were stationed at Langley Research Center in Hampton, Virginia. However, the size and scope of Project Mercury soon prompted NASA to build a new Manned Spacecraft Center, now the Johnson Space Center, in Houston, Texas. Project Mercury’s personnel and activities were transferred there in 1961.

The Goddard network tracked many early manned and unmanned spacecraft.

Goddard Space Flight Center remained involved in the manned space flight program, providing computer support and radar tracking of flights through a worldwide network of ground stations called the Spacecraft Tracking and Data Acquisition Network (STDN). However, the Center focused primarily on designing unmanned satellites and spacecraft for scientific research missions. Goddard pioneered several fields of spacecraft development, including modular spacecraft design, which reduced costs and made it possible to repair satellites in orbit. Goddard’s Solar Max satellite, launched in 1980, was repaired by astronauts on the Space Shuttle Challenger in 1984. The Hubble Space Telescope, launched in 1990, remains in service and continues to grow in capability thanks to its modular design and multiple servicing missions by the Space Shuttle.

Today, the center remains involved in each of NASA’s key programs. Goddard has developed more instruments for planetary exploration than any other organization, among them scientific instruments sent to every planet in the Solar System. The center’s contribution to the Earth Science Enterprise includes several spacecraft in the Earth Observing System fleet as well as EOSDIS, a science data collection, processing, and distribution system. For the manned space flight program, Goddard develops tools for use by astronauts during extra-vehicular activity, and operates the Lunar Reconnaissance Orbiter, a spacecraft designed to study the Moon in preparation for future manned exploration.