The Story of Chandra

In the year 1976, two brilliant minds — Riccardo Giacconi and Harvey Tananbaum — came up with a space telescope that could study X-rays. They proposed this to NASA and it was called the Advanced X-ray Astrophysics Facility (AXAF).

In the heart of the Marshall Space Flight Center and the Smithsonian Astrophysical Observatory, AXAF took root. Engineers and scientists toiled, shaping mirrors — Wolter-type 1 mirrors, polished to perfection promising unprecedented resolution.

And on July 23, 1999 — the Space Shuttle Columbia finally cradled AXAF in its arms. The countdown reverberated across Kennedy Space Center, and the shuttle roared to life. As the Earth fell away, AXAF unfurled its wings — a colossal 13.8 meters by 19.5 meters — and rose with its gaze on the stars.

Renamed the Chandra X-ray Observatory as part of a contest held by NASA in 1998, it embarked on its mission to unveil the unseen. Chandra pays tribute to Subrahmanyan Chandrasekhar, the Indian astrophysicist who unravelled the fate of massive stars.

And thus began the legacy of Chandra.

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The Chandra X-ray Observatory essentially allows astronomers to observe the hot regions of the universe.

Unlike optical telescopes, which cannot see vast clouds of hot gas, Chandra’s huge, precisely shaped mirrors are equipped to capture X-rays. Chandra orbits at an altitude of 10,000 km above Earth and is one of NASA’s Great Observatories alongside the Hubble Space Telescope, Spitzer Space Telescope, and the now-deorbited Compton Gamma Ray Observatory.

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Some distinguishing features of this very cool telescope:

1. Mirrors and X-ray Detection:

• As mentioned, unlike optical telescopes, which rely on visible light, Chandra is designed to capture X-rays. These high-energy photons penetrate mirrors a lot like how bullets might hit a wall.
• Chandra’s telescope system consists of four pairs of nested mirrors that are meticulously shaped to focus incoming X-rays onto a tiny spot on the focal plane.
• The mirrors have eight times greater resolution than any previous X-ray telescope and can detect sources more than 20 times fainter due to their high angular resolution.

2. Instrumentation:

Chandra carries four science instruments:

• Advanced CCD Imaging Spectrometer (ACIS) which captures X-ray images and provides information about their position, energy, and arrival time.
• High-resolution camera (HRC) that complements ACIS by capturing high-resolution X-ray images.
• High Energy Transmission Grating Spectrometer (HETGS) which enables high-resolution spectroscopy by diffracting X-rays based on their energy.
• Low Energy Transmission Grating Spectrometer (LETGS), a grating array for precise energy determination.

3. Space-Based Observations:

• Earth’s atmosphere absorbs most X-rays — this renders them invisible to ground-based telescopes. Chandra, positioned 10,000 km above Earth, escapes this limitation.
• Chandra’s wings which span 13.8 meters by 19.5 meters, allow it to focus on X-ray sources without atmospheric interference.

The Chandra X-ray Observatory is truly a feat of engineering. Its true brilliance lies not just in its purpose, but in the ingenious selection of materials used in its construction.

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At the heart of Chandra’s structure lies a remarkable material — Carbon Fiber Reinforced Plastic (CFRP).

This composite boasts an unbeatable combination of properties. CFRP is incredibly strong, exceeding the strength of steel in many applications. Yet, it defies gravity by being remarkably lightweight.

Now, this lightweight prowess is crucial for Chandra as every ounce saved during launch translates to more scientific equipment reaching its destination.

By minimizing its weight, CFRP allows Chandra to be lofted higher — why this is particularly effective is because it aids in escaping the distorting effects of Earth’s atmosphere. This weight reduction also translates to lower launch costs, which is always desirable.

However, once launched, there’s a constant barrage of high-energy radiation that could cripple Chandra’s delicate instruments.

To combat this threat, a group of metals are used in tandem.

Nickel serves as the primary structural material for the spacecraft’s body. It offers a good balance of strength and weight, making it ideal for the harsh environment of space. However, for superior radiation shielding, heavier metals like tantalum and tungsten are strategically placed around the science instruments. These heavyweights act as a shield, absorbing the harmful radiation and ensuring the delicate detectors within remain protected.

To effectively collect and focus X-rays, Chandra relies on specialized glass mirrors with a super-smooth, ultra-reflective surface. These mirrors are made from a special type of glass called Zerodur (is it just me or does that sound like something from LoTR?), known for its exceptional thermal stability. Even in the vast coldness of space, Zerodur maintains its shape with remarkable precision, ensuring the collected X-rays are precisely focused onto the detectors.

How has Chandra revolutionised Astrophysics?

Chandra’s contributions to astrophysics have been nothing short of transformative!

Its high-resolution X-ray observations have yielded crucial insights into black holes, neutron stars, and the large-scale structure of the universe. Chandra has identified numerous stellar-mass black holes within the Milky Way and neighbouring galaxies, furthering our understanding of stellar evolution and the immense gravitational forces that shape galaxies.

Moreover, Chandra’s observations of neutron stars have revealed their ability to generate powerful jets of energetic particles, providing valuable data on the properties of ultra-dense matter within collapsed stellar cores. Significantly, Chandra has detected previously unknown clouds of hot intergalactic gas, contributing to our understanding of the large-scale structure of the cosmos, a network of filaments and voids where galaxies form and evolve.

And yet, the future of the Chandra X-ray Observatory, which has been a cornerstone of X-ray astronomy for over two decades, hangs in the balance.

The primary driver behind this potential shutdown stems from NASA’s proposed fiscal year 2025 budget. This proposal outlines a significant decrease in funding for Chandra, with a trajectory that effectively reduces operational capabilities to a bare minimum by the end of the decade. While budgetary constraints are a major factor, the decision is likely influenced by a confluence of other considerations.

Firstly, the age of the spacecraft itself plays a role. Launched in 1999, Chandra has surpassed its initial five-year mission lifespan considerably. While still operational, certain systems require increased management to maintain proper temperature ranges, potentially impacting scheduling efficiency and driving up mission costs.

Secondly, the emergence of next-generation telescopes with even more advanced capabilities presents a factor to consider. Telescopes like the Nancy Grace Roman Space Telescope, currently under development and planned for launch in 2027, promise to push the boundaries of observation in the infrared spectrum. While not a direct replacement for Chandra’s X-ray focus, such advancements may influence prioritization within NASA’s overall astrophysics budget.

Finally, the ongoing evaluation of operational costs associated with Chandra cannot be discounted. Maintaining a complex spacecraft in its operational orbit requires constant monitoring and resource allocation. As Chandra ages, the question of cost-effectiveness compared to newer technologies becomes a relevant part of the budgetary decision-making process.

Despite its impressive legacy in X-ray astronomy, Chandra’s future hangs in the balance. Yet, its potential for further discoveries remains.

Chandra’s story reminds us — the tools that unlock the universe’s secrets are precious, and their light must not be extinguished prematurely.

For 24 years and counting, it continues to orbit our Earth, capturing X-rays from distant realms.

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Referred sources:

• NASA Chandra X-ray Observatory Website: https://chandra.harvard.edu/index_students.html
• “Chandra: A Decade of Discovery” by Chandra X-ray Center: https://chandra.harvard.edu/resources/podcasts/by_category_hte.html
• “The Future of Chandra” by Chandra X-ray Center: https://chandra.harvard.edu/new.html
• “X-ray Astronomy” by NASA Science:
  https://science.nasa.gov/ems/11_xrays/
• “Great Observatories” by NASA:
  https://science.nasa.gov/universe/observatories/
• “Subrahmanyan Chandrasekhar” by Wikipedia: https://en.wikipedia.org/wiki/Subrahmanyan_Chandrasekhar
• “Wolter Telescope” by Wikipedia:
  https://en.wikipedia.org/wiki/Wolter_telescope
• “Advanced CCD Imaging Spectrometer (ACIS)” by NASA: https://chandra.harvard.edu/resources/illustrations/ACIS.html
• “High-Resolution Camera (HRC)” by NASA:
  https://chandra.harvard.edu/
• “High Energy Transmission Grating Spectrometer (HETGS)” by NASA: https://link.springer.com/chapter/10.1007/978-981-99-4409-5_3
• “Low Energy Transmission Grating Spectrometer (LETGS)” by NASA: https://cxc.harvard.edu/proposer/POG/html/chap9.html
• “Carbon Fiber Reinforced Plastic (CFRP)” by American Composites Manufacturers Association:
  https://acmanet.org/

Originally published at the contemplative elf on May 18, 2024.