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  • Writer's pictureMatt Russell

#162 - Dr Doreen Boyd - Athena

This week we talk about how Space can be used to track modern slavery with Dr Doreen Boyd. A rundown on an ESA future big mission to space, Athena, and a quick rundown on the news,

“Your reward will be the widening of the horizon as you climb. And if you achieve that reward, you will ask no other.”

Cecilia Payne-Gaposchkin born in 1900 December 7th

Professor Doreen Boyd (Geography) leads the Rights Lab's Data and Measurement Programme. Her current work uses satellite imagery and her expertise in remote sensing to map slavery from space for the first time. She is also working on an extensive analysis of the relationship between slavery and environmental destruction. She was the recipient of the Vice Chancellor's Medal in 2018 for her Rights Lab research and leadership. 

Brick Kilns in India, a sign post of Slavery ©2019 DIGITALGLOBE

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Space Mission of the week

Last week we reported the ESA Space19+ committee had approved the largest ESA budget ever, and this gave the green light to a bunch of missions and the one I want to talk about today is Athena.

Not to be confused with Poster shops, Athena family of rockets, or the proposed NASA Pallas flyby mission of the same name but.

The Advanced Telescope for High ENergy Astrophysics (ATHENA) The second of the large class in the ESA Cosmic Vision program. The Cosmic Vision will be 10 missions (small, Medium, Large and Fast), One of which is the first Small class (S1) mission up next CHEOPS, an exoplanet examiner! that will hopefully Launch later this month!!! The first medium (M1) mission the Solar Orbiter hopefully launches in February, The first Large mission (L1) JUICE (Jupiter Icy Moon Explorer), a mission to the Jupiter system launch planned for 2022, the first non American mission to the outer Solar system and finally a Fast mission (F1) the Comet Interceptor in 2028 recently funded as well.

So mission L2 - Athena is an X-ray telescope now under development for launch in 2031 on an ariane 6

So why do we need this thing? the objective is answering two questions from astrophysics:

  1. how ‘ordinary’ matter assembles, along with the invisible dark matter, to form the wispy ‘cosmic web’ that pervades the Universe?

  2. how supermassive black holes at the centre of galaxies form and evolve?

Athena will also Investigate other High Energy Astrophysical events.

“Athena is going to measure several hundreds of thousands of black holes, from relatively nearby to far away, observing the X-ray emission from the million-degree-hot matter in their surroundings,” says Matteo Guainazzi, “We are in particular interested in the most distant black holes, those that formed in the first few hundred million years of the Universe’s history, and we hope we’ll be able to finally understand how they formed.”

It will replace the XMM-Newton which was the 2nd large mission of the Horizon 2000 Program launched 20 years ago almost to the day on the 10 December 1999.

Back in the early 2000’s ESA, JAXA and NASA were all working on replacements for their X-ray telescopes, ESA had XEUS, NASA had Constellation-X. These were merged to form The International X-ray Observatory (IXO), with all 3 space agencies getting stuck-in in 2008.

Unfortunately NASA was having budget constraints and pulled out in 2012, possibly to JWST overruns.!!

ESA carried on and ATHENA was born, the science team appointed in 2014. vibration testing of a silicon pore optics mirror module took place in August 2014

Soon after JAXA had a nightmare with the Hitomi space X-Ray telescope that span itself to death about 4 years ago, soon after launch.

The Athena telescope will use ESA-developed silicon pore optics providing a combination of a large field of view and high angular resolution

This ‘mirror module’ – formed of 140 industrial silicon mirror plates, stacked together by a sophisticated robotic system – is destined to form part of the optical system of ESA’s Athena X-ray observatory.

Energetic X-rays don’t behave like typical light waves: they don’t reflect in a standard mirror. Instead, they can only be reflected at shallow angles, like "ducks and drakes" stones skimming along water. So multiple mirrors must be stacked together to focus them:

Focusing X-rays with glancing reflection in a Wolter Type-1 optical system

XMM-Newton has three sets of 58 gold-plated nickel mirrors, each nestled inside one another. But to see at Athena resolution you would need tens of thousands of densely-packed mirror plates.

Mirror module and petal in context of IXO aperture; the main technology demonstrations address the mirror modules, whereas the petal and optical bench can be implemented base-lining state of the art technology

The lens, based on a Wolter-I type double reflection grazing incidence angle design, will be very large (~ 3 m in diameter) to meet the science requirements of large effective area (1-2 m2 at a few keV) at a focal length of 12 m. To meet the high angular resolution (5 arc seconds) requirement the X-ray lens will also need to be very accurate.

A new technology had to be invented: ‘silicon pore optics’, based on stacking together mirror plates made from industrial silicon wafers, which are normally used to manufacture silicon chips.

Each new ESA Science mission observes the Universe in a different way from the one before it, requiring a steady stream of new technologies years in advance of launch. Long-term planning is crucial to realise the missions

Invented by and ESA employee and built by Cosine (also useful in the medical and materials world)

The wafers have grooves cut into them, leaving stiffening ribs to form the ‘pores’ the X-rays will pass through. They are given a slight curvature, tapering towards the desired point so the complete flight mirror can focus X-ray images. Each pore in the SPO acts as a very small section of a Wolter I telescope. Two reflections from the inner surfaces of the pore bring the X-rays to a common focus. The pores have a cross-section of only a few mm², and around 1.5 million pores will be used to provide the required collecting area.

The semiconductor industry has already made these wafers available at a ridiculously low price, while mastering the machinery and processes ESA need. They are really riding an existing wave of terrestrial R&D.

“We’ve produced hundreds of stacks using a trio of automated stacking robot,” explains ESA optics engineer Eric Wille. “Stacking the mirror plates is a crucial step, taking place in a cleanroom environment to avoid any dust contamination, targeting thousandth of a millimetre scale precision. Our angular resolution is continuously improving.

The stacking is the most innovative part of the manufacturing process, where most of our investment has gone – employing a robotic arm in a cleanroom environment to avoid any dust contamination, targeting thousandth of a millimetre scale precision.

Athena’s flight mirror – comprising hundreds of these mirror modules – is due for completion three to four years before launch, to allow for its testing and integration.

These mirror modules have to be mounted on an “optical bench”

Twin robotic arms will work together to construct what will be the largest, most complex object ever 3D printed in titanium

The first multi-axis robotic arm builds up each new layer of metal using a laser to melt titanium powder. The second robotic arm then immediately cuts away any imperfections using a cryogenically cooled milling tool

The optic bench aligns and secures around 750 mirror modules in a complex structure with many deep pockets that tapers out to a maximum height of 30 cm. Its overall shape needs to be precise down to a scale of a few tens of micrometres – or thousandths of a centimetre

“The optic bench’s complexity requires each addition to be milled immediately after printing,” comments André Seidel, overseeing the project at the Fraunhofer Institute for Material and Beam Technology. “Any subsequent modification could risk introducing contamination, weakening the space-quality titanium.

“Similarly, the entire process has been designed to minimise any risk of contamination. The titanium powder is swept into the laser using the noble gas argon that also prevents any contamination with air. And the milling tool is kept cool using liquid carbon dioxide that evaporates as it warms up, preventing any harmful deposition on the freshly-laid metal surface.”

The Mirror Assembly Module (MAM) will support the X-ray optics and the associated structure, and will include a straylight baffle, a thermal baffle and an expandable Sun protection baffle to maximise the field of regard. During ground operation and launch, the X-ray mirror will be covered by a door, which can also be used for Sun protection after deployment. To maintain the performance of the optics and simplify calibration, a thermal control system will be required for the mirror. Magnetic diverters will be implemented to deflect soft protons and electrons thereby reducing the particle background.

A fixed structure will connect the MAM to the Focal Plane Module (FPM), which will be part of the Service Module (SVM). The two instruments will be mounted on a moving platform that will position one or the other in the focal plane of the telescope.

USing this unparralled technology, Athena will look at the black holes which lurk at the centre of almost all galaxies by observing X-ray emission from very hot material just before it is swallowed by a black hole, measuring distortions due to gravitational light-bending and time-delay effects in this extreme environment. Athena will also be able to determine the spin of the black hole itself.

Athena's powerful instruments will also allow unprecedented studies of a wide range of astronomical phenomena. These include distant gamma-ray bursts, the hot gas found in the space around clusters of galaxies, the magnetic interplay between exoplanets and their parent stars, Jupiter's auroras and comets in our own Solar System.

Athena is also a powerful, general-purpose observatory, able to address a wide range of current astrophysical topics

The instruments comprise

— the X-ray Integral Field Unit (X-IFU) a cryogenic imaging spectrometer covering the 0.3 to 10 keV energy range with unprecedented energy resolution, over a field of view a few arcminutes across


— the Wide Field Imager (WFI) covering the 0.1 to 12 keV energy range, based on a silicon active pixel sensor. It features a large field of view, excellent spatial and energy resolution and count rate capabilities up to the Crab regime (2-10 keV flux ~10-8 erg cm-2 s-1).

During each sky observation, one of the two instruments will be placed on the focal plane of the X-ray telescope (focal length ~12m limited by the launcher fairing).

L2 Athena coincidently wil be launched into a halo orbit at the Sun-Earth L2 (2nd Lagrangian) point, 1.5 million KM from earth, L2 is ideal for astronomy because a spacecraft is close enough to readily communicate with Earth, can keep Sun, Earth and Moon behind the spacecraft for solar power and (with appropriate shielding) provides a clear view of deep space for our telescopes. The L1 and L2 points are unstable on a time scale of approximately 23 days, which requires satellites orbiting these positions to undergo regular course and attitude corrections. It is the home of Planck and will be the home of JWST

The real exciting bit is when this technology is combined with that of L3, LISA (Laser Interferometer Space Antenna), a space mission concept designed to detect and accurately measure gravitational waves at lower frequencies than Earth-bound detectors. Its launch is planned for 2034

Athena will predominantly perform pointed observations of celestial targets. There will be around 300 such observations per year, This routine observing plan will be interrupted by target of opportunity observations (for example, gamma ray bursts and other transient events) at an expected rate of twice per month.

The baseline mission duration for Athena will be four years, with consumables sized to allow a six-year extension to maximise the return from this ambitious mission. With a conservative observing efficiency of 85%, Athena will be able to achieve the science goals of the Hot and Energetic Universe theme during the baseline mission, while preserving around 20% of the available time for observatory science.

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