Next Generation Space Telescopes Could Use Deformable Mirrors to Image Earth-Sized Worlds
Observing distant objects is no easy task, thanks to our planet’s thick and fluffy atmosphere. As light passes through the upper reaches of our atmosphere, it is refracted and distorted, making it much harder to discern objects at cosmological distances (billions of light years away) and small objects in adjacent star systems like exoplanets. For astronomers, there are only two ways to overcome this problem: send telescopes to space or equip telescopes with mirrors that can adjust to compensate for atmospheric distortion.
Since 1970, NASA and the ESA have launched more than 90 space telescopes into orbit, and 29 of these are still active, so it’s safe to say we’ve got that covered! But in the coming years, a growing number of ground-based telescopes will incorporate adaptive optics (AOs) that will allow them to perform cutting-edge astronomy. This includes the study of exoplanets, which next-generation telescopes will be able to observe directly using coronographs and self-adjusting mirrors. This will allow astronomers to obtain spectra directly from their atmospheres and characterize them to see if they are habitable.
NASA is pursuing the development of adaptive optics through its Deformable Mirror Technology project, which is carried out at the Jet Propulsion Laboratory at Caltech and sponsored by NASA’s Astrophysics Division Strategic Astrophysics Technology (SAT) and the NASA Small Business Innovation Research (SBIR) programs. The research is being led by Dr. Eduardo Bendek from JPL and Dr. Tyler Groff from NASA’s Goddard Spaceflight Center (GSFC) – the co-chairs of the DM Technology Roadmap working group – Boston Micromachines (BMC) founder and CEO Paul Bierden, and Adaptive Optics Associates (AOX) Program Manager Kevin King.
Directly Imaging Exoplanets
The field of exoplanet studies has exploded in recent years, with 5,539 confirmed candidates in 4,129 systems and over 10,000 more awaiting confirmation. Finding habitable planets among these many candidates is crucial to addressing one of the greatest mysteries of all time: are we alone in the Universe? Thanks to advances in instrumentation, advanced analytics, and data-sharing, the field has been transitioning from discovery to characterization. However, to date, most exoplanets have been discovered using indirect methods.
To do this effectively, scientists need to be able to observe exoplanets directly. This is known as the Direct Imaging method, where astronomers study light reflected directly from an exoplanet atmosphere and/or surface. This light is then analyzed with spectrometers to determine its chemical composition, allowing astronomers to constrain habitability. Unfortunately, it is very difficult to resolve smaller, rocky planets that orbit closer to their parent stars – which is where Earth-like planets are expected to be found – due to the overpowering glare from their stars.
This is likely to change with cutting-edge telescopes like James Webb, as well as next-generation arrays like the Extremely Large Telescope (ELT), the Giant Magellan Telescope (GMT), and the Thirty Meter Telescope (TMT). These ground-based arrays will combine 30-meter primary mirrors, advanced spectrometers, and coronographs (instruments that block out starlight). Deformable mirrors are an essential component of a coronagraph, as they can correct for the tiniest of imperfections in the telescope and remove any remaining starlight contamination.
This is essential since a misalignment between mirrors or a change in the mirror’s shape – i.e., which leads to instability in the telescope’s optics – can result in glare that obscures the detection of smaller rocky exoplanets. Moreover, detecting an Earth-like planet demands an extremely precise optical quality of 10s of picometers (pm) – about the size of a hydrogen atom. This requires very precise control of a telescope’s mirrors in real-time that can correct for any source of interference.
One of the Unit Telescopes (UTs) that make up the ESO’s Very Large Telescope is seen firing four lasers which are crucial to the telescope’s adaptive optics systems. Credit: ESO
Deformable Mirrors (DM) rely on precisely
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Japan’s New H3 Rocket Successfully Blasts Off
Japan successfully tested its new flagship H3 rocket after an earlier version failed last year. The rocket lifted off from the Tanegashima Space Center on Saturday, February 17, reaching an orbital altitude of about 670 kilometers (420 miles). It deployed a set of micro-satellites and a dummy satellite designed to simulate a realistic payload.
With the successful launch of the H3, Japan will begin transitioning away from the previous H-2A rocket which has been in service since 2001 and is set to be retired after two more launches. Several upcoming missions depend on the H3, so this successful test was vital.
The launch came after two days of delays because of bad weather. The H3 rocket, built by Mitsubishi Heavy Industries, is now set to become the main launch vehicle of Japan’s space program. The rocket’s first flight in March 2023 failed to reach orbit, which resulted in the loss of an Earth imaging satellite.
The successful launch and deployment of the satellites was a relief for JAXA and members of the project. A livestream of the launch and subsequent successful orbit insertion showed those in the JAXA command cheering and hugging each other.
“I now feel a heavy load taken off my shoulders,” said JAXA H3 project manager Masashi Okada, speaking at a press briefing after the launch. “But now is the real start for H3, and we will work to steadily improve it.”
H3 stands about 57-meter (187-feet) tall and is designed to carry larger payloads. The two microsatellites were deployed approximately 16 minutes and 43 seconds after liftoff. They included an Earth observation satellite named CE-SAT-IE, developed by Canon Electronics, and TIRSAT, an infrared Earth observation instrument that will observe the temperature of the Earth’s surface and seawater.
“We feel so relieved to be able to announce the good results,” JAXA President Hiroshi Yamakawa said at the briefing. Yamakawa added that the main goals of H3 are to secure independent access to space and allow Japan to be competitive as international demand for satellite launches continues to grow. “We made a big first step today toward achieving that goal,” he said.
An image sent back by a mini-probe shows Japan’s SLIM lander on its side on the lunar surface. (JAXA / Takara Tomy / Sony Group / Doshisha Univ.)
The successful launch comes after two other recent successes for JAXA last month where the H-2A rocket successfully placed a spy satellite into orbit, and just days later JAXA’s robotic SLIM (Smart Lander for Investigating Moon) made the first-ever precise “pinpoint” Moon landing – although unfortunately the lander came down on its side. However, during the final stages of the descent two autonomous rovers were successfully deployed: a tiny hopping robot and the other designed to roll about the surface. Both have sent back pictures and can continue exploring and sending back information even if SLIM cannot be operated.
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European Satellite ERS-2 to Reenter Earth’s Atmosphere This Week
One of the largest reentries in recent years, ESA’s ERS-2 satellite is coming down this week.
After almost three decades in orbit, an early Earth-observation satellite is finally coming down this week. The European Space Agency’s (ESA) European Remote Sensing satellite ERS-2 is set to reenter the Earth’s atmosphere on or around Wednesday, February 21st.
Trail Blazing Mission
Launched atop an Ariane-4 rocket from the Kourou Space Center in French Guiana on April 21st, 1995, ERS-2 was one of ESA’s first Earth observation satellites. ERS-2 monitored land masses, oceans, rivers, vegetation and the polar regions of the Earth using visible light and ultraviolet sensors. The mission was on hand for several natural disasters, including the flood of the Elbe River across Germany in 2006. ERS-2 ceased operations in September 2011.
Anatomy of the reentry of ERS-2. ESA
ERS-2 was placed in a retrograde, Sun-synchronous low Earth orbit, inclined 98.5 degrees relative to the equator. This orbit is typical for Earth-observing and clandestine spy satellites, as it allows the mission to image key target sites at the same relative Sun angle, an attribute handy for image interpretation.
ERS-2 tracks and ice floe. ESA
The Last Days of ERS-2
Reentry predictions for the satellite are centered on February 21st at 00:19 Universal Time (UT)+/- 25 hours. As we get closer, expect that time to get refined. The mass of ERS-2 at launch (including fuel) was 2,516 kilograms. Expect most of the satellite to burn up on reentry.
The orbital path of ERS-2. Orbitron
For context, recent high profile reentries include the UARS satellite (6.5 tons, in 2011), and the massive Long March-5B booster that launched the core module for China’s Tiangong Space Station in late 2022 (weighing in at 23 tons).
ERS-2 in the clean room on Earth prior to launch. ESA
ESA passed its first space debris mitigation policy in 2008, 13 years after ERS-2 was launched. In 2011, ESA decided to passively reenter the satellite, and began a series of 66 deorbiting maneuvers to bring its orbit down from 785 kilometers to 573 kilometers. Its fuel drained and batteries exhausted, ERS-2 is now succumbing to the increased drag of the Earth’s atmosphere as we near the peak of the current solar cycle.
Look at How Much the Sun Has Changed in Just Two Years
The solar cycle has been reasonably well understood since 1843 when Samuel Schwabe spent 17 years observing the variation of sunspots. Since then, we have regularly observed the ebb and flow of the sunspots cycle every 11 years. More recently ESA’s Solar Orbiter has taken regular images of the Sun to track the progress as we head towards the peak of the current solar cycle. Two recently released images from February 2021 and October 2023 show how things are really picking up as we head toward solar maximum.
The Sun is a great big ball of plasma, electrically charged gas, which has the amazing property that it can move a magnetic field that may be embedded within. As the Sun rotates, the magnetic field gets dragged around with it but, because the Sun rotates faster at the equator than at the poles, the field lines get wound up tighter and tighter.
Under this immense stressing, the field lines occasionally break, snap or burst through the surface of the Sun and when they do, we see a sunspot. These dark patches on the visible surface of the Sun are regions where denser concentrations of solar material prohibit heat flow to the visible surface giving rise to slightly cooler, and therefore darker patches on the Sun.
A collage of new solar images captured by the Inouye Solar Telescope, which is a small amount of solar data obtained during the Inouye’s first year of operations throughout its commissioning phase. Images include sunspots and quiet regions of the Sun, known as convection cells. (Credit: NSF/AURA/NSO)
The slow rotation of the Sun and the slow but continuous winding up of the field lines means that sun spots become more and more numerous as the field gets more distorted. Observed over a period of years the spots seem to slowly migrate from the polar regions to the equatorial regions as the solar cycle progresses.
To try and help understand this complex cycle and unlock other mysteries of the Sun, the European Space Agency launched its Solar Orbiter on 10 February 2020. Its mission to explore the Sun’s polar regions, understand what drives the 11 year solar cycle and what drives the heating of the corona, the outer layers of the Sun’s atmosphere.
Images from Solar Orbiter have been released that show closeups of the Sun’s visible surface, the photosphere as it nears peak of solar activity. At the beginning of the cycle, at solar minimum in 2019, there was relatively little activity and only a few sunspots. Since then, things have been slowly increasing. The image from February 2021 showed a reasonably quiet Sun but an image taken in October last year shows that things are, dare I say, hotting up! The maximum of this cycle is expected to occur in 2025 which supports theories that the period of maximum activity could arrive a year earlier.
Understanding the cycle is not just of whimsical scientific interest, it is vital to ensure we minimise damage to ground based and orbiting systems but crucially understand impact on life on Earth.
Source : Sun’s surprising activity surge in Solar Orbiter snapshot
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