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.
Starliner Launch Slips Again; May Fly Without Fix
The planned launch of Boeing’s new crew-carrying orbital “space taxi”, the CST-100 Starliner, has been pushed back yet again – but its is not as bad at it seems.
In sort, and as noted in my previous Space Sunday, when work was underway to fix an issue with the Centaur upper stage of the launch vehicle, Boeing engineers noted a small but potentially troubling helium leak in the Starliner’s Reaction Control System (RCS) / Orbital Manoeuvring and Attitude Control (OMAC) systems, causing NASA to delay the launch from a planned May 21st lift-off to May 25th. However, on May 22nd, the decision was taken to push the launch back to no earlier than June 1st, 2024 to give additional time for investigations to be concluded.
Subsequent to my previous update, Boeing, working with the RCS / OMAC manufacturer Aerojet Rocketdyne, was able to confirm that the leak was linked to a single manifold valve within one of the four “doghouse” clusters of thrusters mounted on the exterior of the Starliner, and affecting just a single thruster. This is actually not as bad as had been thought, and not a real impediment to flight – the thruster with the questionable valve can be disabled without impacting vehicle operations. However, Boeing asked NASA for additional time so the company can carefully work through the entire batch of 27 RCS / OMAC thrusters on the vehicle to make sure there are no signs of the issue being replicated elsewhere.
As a result, and assuming no further issues are found, NASA is prepared to fly the vehicle without the thruster being swapped out, and the crew of Suni Williams and Butch Wilmore are familiarising themselves with additional certified procedures to deal with any further valve / thruster issues whilst in orbit.
Currently, NASA plan to review the situation with Boeing on May 29th, and use that as a basis to decide whether to aim for a June 1st launch or hold off a little longer. Should the June 1st target not be possible, NASA has indicated the vehicle could launch on June 2nd, or on June 5th or 6th as near-term dates.
SpaceX Seeks June 5th Starship Launch
SpaceX has stated it is seeking to make a fourth orbital attempt with its behemoth Starship / Super Heavy combination on Wednesday, June 5th. However, this is dependent on the Federal Aviation Administration (FAA) granting a license for the launch attempt.
As I reported in Space Sunday: starships, volcanoes and Voyagers, the previous flight of the craft, on March 14th, 2024 in what was called Integrated Flight Test 3 (IFT-3) resulted in the loss of both vehicles, the booster exploding before it could splashdown in the Gulf of Mexico, the starship vehicle being lost during atmospheric re-entry, with both incidents triggering mishap investigations and the suspension of SpaceX’s launch license.
The March 14th launch was initially seen as broadly successful immediately after the fact, even allowing for some of us carefully qualifying the level of success based on the exceptionally limit natures of the tests. However, more in-depth analysis of the flight suggest there were more issues than had had been noted at the time, and the flight was, overall, far less successful than had been credited.
Most particularly, the analysis indicated that there appeared to be significant issues with the “Pez” door on the payload bay – which was supposed to cycle open and shut in a demonstration oof how it will be used to dispense Starlink satellites. Whilst the call was given that the payload bay door has been commanded to open around 12 minutes into the flight, it did not actually appear to respond for a further 3-4 minutes, the command having to be repeated; even then, the video suggests the door partially opened and jammed.
As the door opened, a significant amount of atmospheric gasses trapped within the vehicle’s payload bay were seen to escape through the evolving opening. The analysis of this event suggests that such was the force imparted by the exiting gases (Newton’s third law), it was directly responsible for starting the vehicle rolling (and almost tumbling), rather than the roll being any kind of controlled thermal activity (a so-called “bbq roll” designed to prevent any one side of the vehicle being heated by the Sun whilst the other side stays much colder), as had been thought at the time.
If correct, this analysis would explain why the vent thrusters on the vehicle struggled mightily to try and correct the roll / tumble: had it been a planned event, it should have been more manageable. It’s not clear if the “Pez” door was successfully closed prior to atmospheric re-entry, and thus may have contributed to the vehicle loss, but given the thrusters (and flap system) were just about getting the vehicle’s gyrations under control, it is possible that the atmospheric venting from the payload bay may have contributed to the vehicle’s loss.
SpaceX has not commented on these unofficial post-flight analyses. Certainly, issued with carious mechanisms on the vehicle are to be expected; as such the “Pez” door issue will likely be addressed. However, the fact that the vehicle was allowed to fly with a significant volume of atmospheric gases in the payload bay does point to something of a failure on SpaceX’s part to understand basic Newtonian physics. Given the current nature of the payload bay, getting it airtight and to a near vacuum pre-launch isn’t going to be easy; as such, and given the fact the up-coming launch of IFT-4, observers are going to be watching closely for any signs of a repeat issue, or whether SpaceX has taken steps to try to mitigate the impact of escaping gases from the payload bay.
Inara Pey: Living in a Modemworld 