So, what is the megapixel resolution of your favourite camera / phone / tablet camera? Leaving aside the questions of sensor size, pixel light bleed and so on, all of which influence the quality of images over and above mere megapixel count, people seem to take great pride in the camera’s megapixel resolution; so is it 16, 20, 24, 30? Well, how about 3200 megapixels?
That’s the resolution of the world’s most powerful digital camera. Not only that, but its sensor system is so large (64 cm (2 ft) across) it can ensure every single pixel produces the absolute minimum in light-bleed for those around it, ensuring the crispest, deepest capture possible per pixel. This camera is called The Legacy Survey of Space and Time (LSST) camera – which is a rather poetic and accurate name for it, given that in looking out into deep space it will be looking back in time – and it has been 20 years in the making. It is the final element of a major new stellar observatory which will soon be entering full-time service: the Vera C. Rubin Observatory, and it will lie at the heart of the observatory’s primary telescope, the Simonyi Survey Telescope.
The observatory is located 2.682 kilometres above sea level on the El Peñón peak of Cerro Pachón in northern Chile, a location that is already the home of two major observatories: Gemini South and Southern Astrophysical Research Telescopes. Originally itself called the LSST – standing for The Large Synoptic Survey Telescope – the observatory was first proposed in 2001, and work initially commenced through the provisioning of private funding – notably from Lisa and Charles Simonyi, who put up US $20 million of their own money for the project (and hence had the telescope named for them), and a further US $10 million from Bill Gates.
By 2010, the potential of the observatory was such that it was identified as the most important ground-based stellar observatory project by the 2010 Astrophysics Decadal Survey – a forum for determining major projects in the fields of astronomy and astrophysics which should receive US funding in the decade ahead. This led the National Science Foundation (NSF) to provide an initial US $27.5 million in 2014, as the first tranche of funding via the US government, while the US Department of Energy was charged with overseeing the construction of the observatory, telescope and the primary camera system, with the work split between various government-supported / operated institutions and organisations.
Whilst originally called the LSST, the observatory was renamed in 2019 in recognition of both its core mission – studying (the still hypothetical) dark energy and dark matter by a number of means – and in memory of astronomer Vera Rubin (July 1928 – December 2016); one of the pioneers of dark matter research. It was her work on galaxy rotation rates which provided key evidence for the potential existence of dark matter, and laid the foundation upon which later studies into the phenomena could build.
As well as this work, the observatory and its powerful camera will be used for three additional major science tasks:
- Detecting transient astronomical events such as novae, supernovae, gamma-ray bursts, quasar variability, and gravitational lensing, and providing the data to other observatories and institutions for detailed follow-up, again to increase our understanding of the universe around us.
- Mapping small objects in the Solar System, including near-Earth asteroids which might or might not come to pose a threat to us if their orbits around the Sun are shown to intersect with ours, and also Kuiper belt objects. In this, LSST is expected to increase the number of catalogued objects by a factor of 10–100. In addition, the telescope may also help with the search for the hypothesized Planet Nine.
- Mapping the Milky Way. To increase our understanding of all that is happening within our own galaxy.
To achieve this, the telescope is a remarkable piece of equipment. Comprising an 8.4 metre primary mirror – putting it among the “large” – but not “huge” earth-based telescope systems – it has a mechanism capable of aligning it with a target area of the sky and allowing the LSST camera capture an image before slewing the entire multi-tonne structure through 3.5 degrees, and accurately pointing it for the next image to be captured in just 4.5 seconds (including time needed to steady the entire mount post-slew). This means the telescope will be able to survey the entire visible sky above it every 3-4 days, and will image each area of sky surveyed 825 times apiece, allowing for a comprehensive library of images and comparative data to be built over time.
In turn, to make this possible, the LSST camera is equally remarkable. Operating a low temperatures, it has a primary lens of 1.65 metres in diameter to capture the light focused by the telescope’s unique set of three main mirrors (two of which – the 8.4 metre primary and the 5.0 metre tertiary – are effectively the “same” glass, being mounted back-to-back). This light is then direct through a second focusing lens and a set of filters to screen out any unwanted light wavelengths, to no fewer that 189 charge couple devices (CCDs).
These are arranged in a flat focal plain 64 cm (2 ft) across, and mounted on 25 “rafts” which can be individually fine tuned to further enhance the quality of the images gathered. In use, the focal plain will be able to capture one complete, in-depth, time-exposed image every 15 seconds, allowing it to capture the light of even the faintest objects in its field of view. Combined with the speed with which the telescope can move between any two adjacent target areas of the sky – each the equivalent of a gird of 40 full Moons seen from Earth – this means that the camera will produce around 20-30 terabytes of images every night, for a proposed total of 500 petabytes of images and data across its initial 10-year operational period.
As noted, the LSST camera is the last major component for the telescope to arrive at the observatory. It was delivered from the United States on May 16th, 2024, and will be installed later in 2024. As it is, all of the core construction work at the observatory – base structure, telescope mount, telescope frame and dome – has been completed, with the telescope delivered and mounted between 2019 and 2023. In 2022, a less complex version of the LSST camera, called the Commissioning Camera (ComCam) was also installed in preparation for commissioning operations to commence.
Most recently – in April 2024 – work was completed on coating the primary and tertiary mirror assembly with protective silver, so it is now ready for installation into the telescope (the 8 metre secondary mirror is already in place). This coating work could only be done at the observatory and once all major construction work have been completed, meaning the three mirrors have been carefully stored at the site since their respective arrivals in 2018 and 2019.
Commissioning will see the ComCam used to assist in ensuring the mirrors correctly moments and aligned, and to allow engineers make physical adjustments to the telescope without putting the LSST camera at risk. Commissioning in this way also means that issues that may reside within the LSST camera are not conflated with problems within the mirror assembly. Once science teams and engineers are confident the telescope and its mirrors are operating exactly as expected, the ComCam will be replaced by the LSST camera, which will then have its own commissioning / calibration process.
If all goes according to plan, all of this work should be completed by 2025, when the observatory will commence the first phase of its science mission. However, there is one slight wrinkle still to be ironed out.
As a result of growing concern among astronomers about the growing light pollution caused (particularly) by the 4,000+ SpaceX Starlink satellites, the European Southern Observatory (ESO) carried out a survey on behalf of AURA – the Association of Universities for Research in Astronomy, which is now responsible for managing the observatory’s operations – to measure the potential impact of Starlink overflights on the Vera Rubin’s work.
Using the La Silla Observatory, located in the same region as the Vera C. Rubin and at near enough the same altitude, ESO replicated the kind of 15-second image exposure the latter will use when operational, and found that during certain periods of the Vera C. Rubin’s daily observation times, between 30% and 50% of exposures could be impacted by light trails formed by the passage of multiple Starlink satellites overhead.
SpaceX has promised to do more to “darken” their satellites in the future (the first attempts having had mixed results), but AURA is also considering whether or not to make updates to the LSST camera’s CCDs and control system to allow the camera to overcome image pollution from these satellites. Such work, if proven viable, will need to be carried out ahead of the LSST’s installation into the telescope, and thus might result in the start of operations being pushed back.
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