Deformable Mirrors in Space: Key Technology to Directly Image Earth Twins - UNIVERSE (The Search for Alien Earths - How Coronagraphs Find Hidden Planets)

PROJECT:

Deformable Mirror Technology development

SNAPSHOT

Deformable mirrors enable direct imaging of exoplanets by correcting imperfections or shape changes in a space telescope down to subatomic scales.

Credit: NASA Jet Propulsion Laboratory.

Finding and studying Earth-like planets orbiting nearby stars is critical to understand whether we are alone in the universe. To study such planets and assess if they can sustain life, it is necessary to directly image them. However, these planets are difficult to observe, since light from the host star hides them with its glare. A coronagraph instrument can be used to remove the glare light from the host star, enabling reflected light from the planet to be collected.  A deformable mirror is an essential component of a coronagraph, as it can correct the tiniest of imperfections in the telescope and remove any remaining starlight contamination.

Detecting an Earth-like planet poses significant challenges as the planet is approximately 10 billion times fainter than its parent star. The main challenge is to block nearly all of the star's light so that the faint light reflected from the planet can be collected.  A coronagraph can block the starlight, however, any instability in the telescope’s optics—such as misalignment between mirrors or a change in the mirror’s shape—can result in starlight leakage, causing glare that hides the planet. Therefore, detecting an Earth-like planet using a coronagraph requires precise control of both the telescope and the instrument’s optical quality, or wavefront, to an extraordinary level of 10s of picometers (pm), which is approximately on the order of the size of a hydrogen atom.

Deformable mirrors will enable future space coronagraphs to achieve this level of control. These devices will be demonstrated in space on a coronagraph technology demonstration instrument on NASA’s Roman Space Telescope, which will launch by May 2027. This technology will also be critical to enable a future flagship mission after Roman recommended by the 2020 Decadal Survey in Astronomy and Astrophysics, provisionally called the “Habitable Worlds Observatory” (HWO). 

What is a deformable mirror and how do they work?

Deformable Mirrors (DM) are devices that can adjust the optical path of incoming light by changing the shape of a reflective mirror using precisely controlled piston-like actuators. By adjusting the shape of the mirror, it is possible to correct the wavefront that is perturbated by optical aberrations upstream and downstream of the DM. These aberrations can be caused by external perturbations, like atmospheric turbulence, or by optical misalignments or defects internal to the telescope.

DM technology originated to enable adaptive optics (AO) in ground-based telescopes, where the primary goal is to correct the aberrations caused by atmospheric turbulence. The main characteristics of a DM are: 1) the number of actuators, which is proportional to the correctable field of view; 2) the actuators’ maximum stroke – i.e., how far they can move; 3) the DM speed, or time required to modify the DM surface; 4) the surface height resolution that defines the smallest wavefront control step, and (5) the stability of the DM surface.

Ground-based deformable mirrors have set the state-of-the-art in performance, but to lay the groundwork to eventually achieve ambitious goals like the Habitable Worlds Observatory, further development of DMs for use in space is underway.

For a space telescope, DMs do not need to correct for the atmosphere, but instead must correct the very small optical perturbations that slowly occur as the space telescope and instrument heat up and cool down in orbit. Contrast goals (the brightness difference between the planet and the star) for DMs in space are on the order of 10^-10 which is 1000 times deeper than the contrast goals of ground-based counterparts. For space applications total stroke requirements are usually less than a micrometer; however, DM surface height resolution of ~10 pm and DM surface stability of ~10 pm/hour are the key and driving requirements.

Another key aspect is the increased number of actuators needed for both space- and ground-based applications.  Each actuator requires a high voltage connection (on the order of 100V) and fabricating a large number of connections creates an additional challenge.

Deformable Mirror State-of-the-Art

Two main DM actuator technologies are currently being considered for space missions. The first is electrostrictive technology, in which an actuator is mechanically connected to the DM’s reflective surface. When a voltage is applied to the actuator, it contracts and modifies the mirror surface. The second technology is the electrostatically-forced Micro Electro-Mechanical System (MEMS) DM. In this case, the mirror surface is deformed by an electrostatic force between an electrode and the mirror.

Several NASA-sponsored contractor teams are working on advancing the DM performance required to meet the requirements of future NASA missions, which are much more stringent than most commercial applications, and thus, have a limited market application. Some examples of those efforts include improving the mirror’s surface quality or developing more advanced DM electronics.

MEMS DMs manufactured by Boston Micromachines Corporation (BMC) have been tested in vacuum conditions and have undergone launch vibration testing. The largest space-qualified BMC device is the 2k DM (shown in Fig. 2), which has 50 actuators across its diameter (2040 actuators in total). Each actuator is only 400 microns across. The largest MEMS DM produced by BMC is the 4k DM, which has 64 actuators across its diameter (4096 actuators in total) and is used in the coronagraph instrument for the Gemini ground-based observatory. However, the 4k DM has not been qualified for space flight.

Fig. 2: The Boston Micromachines Corporation 2k DM that has 2040 actuators with 400 um pitch. Credit: Dr. Eduardo Bendek

Electrostrictive DMs manufactured by AOA Xinetics (AOX) have also been validated in vacuum and qualified for space flight. The AOX 2k DM has a 48 x 48 actuator grid (2304 actuators) with a 1 mm pitch. Two of these AOX 2k DMs will be used in the Roman Space Telescope Coronagraph (Fig. 3) to demonstrate the DM technology for high-contrast imaging in space. AOX has also manufactured larger devices, including a 64 x 64 actuator unit tested at JPL.

Fig. 3: The Roman Space Telescope Coronagraph during assembly of the static optics at NASA’s Jet Propulsion Laboratory Credit: NASA

Preparing the technology for the Habitable Worlds Observatory

Deformable Mirror technology has advanced rapidly, and a version of this technology will be demonstrated in space on the Roman Space Telescope. However, it is anticipated that for wavefront control for missions like the HWO, even larger DMs with up to ~10,000 actuators would be required, such as 96 x 96 arrays. Providing a high-voltage connection to each of the actuators is a challenge that will require a new design.

The HWO would also involve unprecedented wavefront control requirements, such as a resolution step size down to single-digit picometers, and a stability of ~10 pm/hr. These requirements will not only drive the DM design, but also the electronics that control the DMs, since the resolution and stability are largely defined by the command signals sent by the controller, which require the implementation of filters to remove any noise the electronics could introduce.

NASA’s Astrophysics Division investments in DM technologies have advanced DMs for space flight onboard the Roman Space Telescope Coronagraph, and the Division is preparing a Technology Roadmap to further advance the DM performance to enable the HWO.

Author: Eduardo Bendek, Ph.D. Jet Propulsion Laboratory, California Institute of Technology.

The research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004).

ACTIVITY LEADS

Dr. Eduardo Bendek (JPL) and Dr. Tyler Groff (GSFC), Co-chairs of DM Technology Roadmap working group; Paul Bierden (BMC); Kevin King (AOX).

SPONSORING ORGANIZATION

Astrophysics Division Strategic Astrophysics Technology (SAT) Program, and the NASA Small Business Innovation Research (SBIR) Program  

Source: Deformable Mirrors in Space: Key Technology to Directly Image Earth Twins - NASA Science

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NASA One Step Closer to Fueling Space Missions with Plutonium-238 - UNIVERSE

Close-up of NASA’s Perseverance Mars rover as it looks back at its wheel tracks on March 17, 2022, the 381st Martian day, or sol, of the mission. Credit: NASA

The recent shipment of heat source plutonium-238 from the U.S. Department of Energy’s (DOE’s) Oak Ridge National Laboratory to its Los Alamos National Laboratory is a critical step toward fueling planned NASA missions with radioisotope power systems.

This shipment of 0.5 kilograms (a little over 1 pound) of new heat source plutonium oxide is the largest since the domestic restart of plutonium-238 production over a decade ago. It marks a significant milestone toward achieving the constant rate production average target of 1.5 kilograms per year by 2026.

Radioisotope power systems, or RPS, enable exploration of some of the deepest, darkest, and most distant destinations in the solar system and beyond. RPS use the natural decay of the radioisotope plutonium-238 to provide heat to a spacecraft in the form of a Light Weight Radioisotope Heater Unit (LWRHU), or heat and electricity in the form of a system such as the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG).

The DOE has produced the heat source plutonium oxide required to fuel the RPS for missions such as NASA’s Mars 2020. The first spacecraft to benefit from this restart, the Perseverance rover, carries some of the new plutonium produced by DOE. An MMRTG continuously provides the car-sized rover with heat and about 110 watts of electricity, enabling the exploration of the Martian surface and the gathering of soil samples for possible retrieval.

“NASA’s Radioisotope Power Systems Program works in partnership with the Department of Energy to enable missions to operate in some of the most extreme environments in our solar system and interstellar space,” said Carl Sandifer, RPS program manager at NASA’s Glenn Research Center in Cleveland.

For over sixty years, the United States has employed radioisotope-based electrical power systems and heater units in space. Three dozen missions have explored space for decades using the reliable electricity and heat provided by RPS.

NASA and DOE are continuing their long-standing partnership to ensure the nation can enable future missions requiring radioisotopes for decades to come. 

Source: Promo sentence: NASA’s planned missions are one step closer to being fueled thanks to the Department of Energy’s shipment milestone of Plutonium-238.  

JWST detects water vapor, sulfur dioxide and sand clouds in the atmosphere of a nearby exoplanet

Artist impression of WASP-107b and its parent star. Credit: Illustration: LUCA School of Arts, Belgium/ Klaas Verpoest (visuals), Johan Van Looveren (typography). Science: Achrène Dyrek (CEA and Université Paris Cité, France), Michiel Min (SRON, the Netherlands), Leen Decin (KU Leuven, Belgium) / European MIRI EXO GTO team / ESA / NASA

A team of European astronomers, co-led by researchers from the Institute of Astronomy, KU Leuven, used recent observations made with the James Webb Space Telescope to study the atmosphere of the nearby exoplanet WASP-107b. Peering deep into the fluffy atmosphere of WASP-107b they discovered not only water vapor and sulfur dioxide, but even silicate sand clouds. These particles reside within a dynamic atmosphere that exhibits vigorous transport of material.

Astronomers worldwide are harnessing the advanced capabilities of the Mid-Infrared Instrument (MIRI) aboard the James Webb Space Telescope (JWST) to conduct groundbreaking observations of exoplanets—planets orbiting stars other than our own sun. One of these fascinating worlds is WASP-107b, a unique gaseous exoplanet that orbits a star slightly cooler and less massive than our sun.

The mass of the planet is similar to that of Neptune but its size is much larger than that of Neptune, almost approaching the size of Jupiter. This characteristic renders WASP-107b rather 'fluffy' when compared to the gas giant planets within our solar system. The fluffiness of this exoplanet enables astronomers to look roughly 50 times deeper into its atmosphere compared to the depth of exploration achieved for a solar-system giant like Jupiter. 

WASP-107b is a unique gaseous exoplanet that orbits a star slightly cooler and less massive than our sun. The mass of the planet is similar to that of Neptune but its size is much larger than that of Neptune, almost approaching the size of Jupiter. This characteristic renders WASP-107b rather 'fluffy' when compared to the gas giant planets within our solar system. The fluffiness of this exoplanet enables astronomers to look roughly 50 times deeper into its atmosphere compared to the depth of exploration achieved for a solar-system giant like Jupiter. Credit: Illustration: LUCA School of Arts, Belgium/ Klaas Verpoest (visuals), Johan Van Looveren (typography). Science: Achrène Dyrek (CEA and Université Paris Cité, France), Michiel Min (SRON, the Netherlands), Leen Decin (KU Leuven, Belgium) / European MIRI EXO GTO team / ESA / NASA

The team of European astronomers took full advantage of the remarkable fluffiness of this exoplanet, enabling them to look deep into its atmosphere. This opportunity opened a window into unraveling the complex chemical composition of its atmosphere.

The reason behind this is quite straightforward: the signals, or spectral features, are far more prominent in a less dense atmosphere compared to a more compact one. Their recent study, now published in Nature, reveals the presence of water vapor, sulfur dioxide (SO₂), and silicate clouds, but notably, there is no trace of the greenhouse gas methane (CH₄).

A dynamic atmosphere

These detections provide crucial insights into the dynamics and chemistry of this captivating exoplanet. First, the absence of methane hints at a potentially warm interior, offering a tantalizing glimpse into the movement of heat energy in the planet's atmosphere. Secondly, the discovery of sulfur dioxide (known for the odor of burnt matches), was a major surprise.

Previous models had predicted its absence, but novel climate models of WASP-107b's atmosphere now show that the very fluffiness of WASP-107b accommodates the formation of sulfur dioxide in its atmosphere. Even though its host star emits a relatively small fraction of high-energy photons due to its cooler nature, these photons can reach deep into the planet's atmosphere thanks to its fluffy nature. This enables the chemical reactions required to produce sulfur dioxide to occur.

A transmission spectrum of the warm Neptune exoplanet WASP-107b, captured by the Low Resolution Spectrometer (LRS) of the Mid InfraRed Instrument (MIRI) on board JWST, reveals evidence for water vapour, sulfur dioxide, and silicate (sand) clouds in the planet's atmosphere. Credit: Michiel Min / European MIRI EXO GTO team / ESA / NASA

But that's not all they've observed. Both the spectral features of sulfur dioxide and water vapor are significantly diminished compared to what they would be in a cloudless scenario. High-altitude clouds partially obscure the water vapor and sulfur dioxide in the atmosphere.

While clouds have been inferred on other exoplanets, this marks the first instance where astronomers can definitively identify the chemical composition of these clouds. In this case, the clouds consist of small silicate particles, a familiar substance for humans found in many parts of the world as the primary constituent of sand.

"JWST is revolutionizing exoplanet characterization, providing unprecedented insights at remarkable speed," says lead author Prof. Leen Decin of KU Leuven. "The discovery of clouds of sand, water, and sulfur dioxide on this fluffy exoplanet by JWST's MIRI instrument is a pivotal milestone. It reshapes our understanding of planetary formation and evolution, shedding new light on our own solar system."

In contrast to Earth's atmosphere, where water freezes at low temperatures, in gaseous planets reaching temperatures around 1000 degrees Celsius, silicate particles can freeze out to form clouds. However, in the case of WASP-107b, with a temperature of around 500 degrees Celsius in the outer atmosphere, traditional models predicted that these silicate clouds should be forming deeper within the atmosphere, where temperatures are substantially higher. In addition, sand clouds high up in the atmosphere rain out. How is it then possible that these sand clouds exist at high altitudes and continue to endure?

Peering deep into the fluffy atmosphere of WASP-107b a team of European astronomers discovered not only water vapour and sulfur dioxide, but even silicate sand clouds. Credit: Illustration: LUCA School of Arts, Belgium/ Klaas Verpoest (visuals), Johan Van Looveren (typography). Science: Achrène Dyrek (CEA and Université Paris Cité, France), Michiel Min (SRON, the Netherlands), Leen Decin (KU Leuven, Belgium) / European MIRI EXO GTO team / ESA / NASA

According to lead author Dr. Michiel Min, "The fact that we see these sand clouds high up in the atmosphere must mean that the sand rain droplets evaporate in deeper, very hot layers and the resulting silicate vapor is efficiently moved back up, where they recondense to form silicate clouds once more. This is very similar to the water vapor and cloud cycle on our own Earth but with droplets made of sand."

This continuous cycle of sublimation and condensation through vertical transport is responsible for the enduring presence of sand clouds in WASP-107b's atmosphere.

This pioneering research not only sheds light on the exotic world of WASP-107b but also pushes the boundaries of our understanding of exoplanetary atmospheres. It marks a significant milestone in exoplanetary exploration, revealing the intricate interplay of chemicals and climatic conditions on these distant worlds.

"JWST enables a deep atmospheric characterization of an exoplanet that does not have any counterpart in our solar system, we are unraveling new worlds," says lead author Dr. Achrène Dyrek at CEA Paris.

Design and development of the MIRI instrument

Belgian engineers and scientists played a key role in the design and development of the MIRI instrument, including the Center Spatial de Liege (CSL), Thales Alenia Space (Charleroi) and OIP Sensor Systems (Oudenaarde). At the Institute of Astronomy at KU Leuven, instrument scientists tested the MIRI instrument extensively in special test chambers simulating the space environment in laboratories in the UK, at NASA Goddard and NASA Johnson Space centers.

"With colleagues across Europe and the United States we have been building and testing the MIRI instrument for almost 20 years. It is rewarding to see our instrument unravel the atmosphere of this intriguing exoplanet," says instrument specialist Dr. Bart Vandenbussche of KU Leuven.

This study combines the results of several independent analyses of the JWST observations, and represents the years of work invested not only in building the MIRI instrument but also in the calibration and analysis tools for the observational data acquired with MIRI," says Dr. Jeroen Bouwman of the Max-Planck-Institut für Astronomie, Germany.  

by KU Leuven

Source: JWST detects water vapor, sulfur dioxide and sand clouds in the atmosphere of a nearby exoplanet (phys.org)  

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