The Hubble Space Telescopes extremely long service life and its string of amazing contributions to astronomy belie its distressed history. The parallel advancement of the Space Shuttle and the space telescope, which would eventually be named after American astronomer Edwin Hubble, resulted in design choices that would pay enormous dividends down the road. Hubble was designed from the beginning to be serviced, and particularly by area shuttle bus missions. The very first service objective to the Hubble, which went up on Endeavour in 1993 and made Story Musgrave and Kathyrn Thornton family names, included the COSTAR restorative optics package, which brought back Hubbles great focus and allowed it to check out the faintest and furthest items in the universe. The foresight Hubbles designers showed in acknowledging the requirement to switch out science bundles on Hubble affected their styles for other locations of the spacecraft.

Above It All
The concept of putting a telescope in area, high above the roiling atmospheric soup all of us live near the bottom of, was not precisely a new one even in the early 1960s, when humanitys very first tentative steps into area really made such an adventurous strategy feasible. Prior to they had even put a boot on the Moon, NASA aspired to put a large showing telescope in Earth orbit, with a tentative goal of making it occur by the end of 1979. They recognized that such a setup would require frequent visits to keep and upgrade it, and so the future space telescopes design proceeded along with NASAs designated replacement for the mighty expendable rockets of the Apollo era: the multiple-use space plane that would become understood as the Space Shuttle.
The parallel advancement of the Space Shuttle and the space telescope, which would become called after American astronomer Edwin Hubble, resulted in style decisions that would pay huge dividends down the road. Hubble was designed from the outset to be serviced, and particularly by area shuttle bus objectives. The spacecraft bring the telescope and all the different scientific instruments that can be changed into its optical path has abundant handholds, tether points, and quickly accessed compartments and hatches, all designed to make it easier for spacewalking astronauts to perform their tasks. Inside the spacecrafts numerous devices bays, instruments are connected with standardized fasteners created to be manipulated with gloved hands. Hubble even came with a total package of specialized tools, to be utilized by future service missions.
All the best cars come with a great toolkit. Hubbles customized service tools. Source: NASA
Ever mindful of the march of progress, Hubbles designers understood that the instruments they might believe up and integrate in the 1980s would pale in contrast to what would undoubtedly follow. To prevent built-in obsolescence, Hubble was particularly created with not just repair work in mind, however upgrades to its scientific plans. Really the only part of Hubble that has been constant over its service life has been the Optical Telescope Assembly, including the notoriously misground main mirror, a secondary mirror, and supporting structures like the trusses that keep them in positioning and the baffles to control reflections.
The instrument bay behind the primary mirror was created to accommodate 5 clinical instruments at a time. The very first service objective to the Hubble, which increased on Endeavour in 1993 and made Story Musgrave and Kathyrn Thornton home names, consisted of the COSTAR restorative optics bundle, which restored Hubbles great focus and permitted it to check out the faintest and outermost objects in the universe. A lots other spectrographs and cams have actually inhabited the equipment bays over the years, some being left in place for simply a few years; others have been permanent parts of Hubble, generating data given that the very start.
NASA Standard Spacecraft Computer: Built to be Modded
The insight Hubbles designers displayed in recognizing the requirement to swap out science packages on Hubble affected their designs for other locations of the spacecraft as well. As early as the mid-1970s, NASA recognized that building custom-made subsystems for each objective, which had actually worked so well for the manned area flights of Mercury, Gemini, and Apollo, would be a limitation to developing and fielding a broad variety of spacecraft to check out near space. To that end, the NASA Standard Spacecraft Computer-1 (NSSC-1) was developed, with the objective of standardizing the difficult organization of keeping pretty much any spacecraft that carried it steady and in orbit, as well as to run whatever science the objective planners could think up, and to do all of that with basically just software changes.
The Hubble SI C&DH. The NSSC-1s are called out as CPUs at the back of the tray, flanked by the stacks of main and backup memory modules. Source: NASA
NSSC-1 flew on a variety of objectives prior to finding its way into the Hubble devices bay. By contemporary requirements, the computer appears primitive, with discrete TTL chips and a simple 64k of 18-bit core memory (plated-wire memory was also utilized, and appears to be what was originally flown on Hubbles NSSC-1). But the style was robust, radiation-hardened, and redundant at the module level, and most importantly, it gave objective coordinators for the very first time what had actually largely been missing from prior spacecraft controllers: in-flight programmability.
On Hubble, the NSSC-1 forms the core of a subassembly called the Scientific Instrument Command and Data Handling Unit, or SI C&DH. This is a largish tray upon which the NSSC-1 module and other modules, like power regulators, user interfaces to the scientific instruments, and push-button control user interfaces are attached. Whatever is redundant, and the whole assembly is constructed to support being switched out by spacewalking astronauts. In truth, the last service call paid to Hubble in 2009 included the replacement of the SI C&DH with a new unit, one with the original core memory modules updated to CMOS. The video below programs the SI C&DH undergoing ground tests prior to heading upstairs.

Trouble Upstairs
The current concern with Hubble centers around the SI C&DH assembly, which the media have actually mercifully dubbed “the payload computer system.” On June 13, the NSSC-1 in the unit went into safe mode, which was the commonly reported “glitch”. Initial diagnostics led operators to think that one of the memory modules had actually deteriorated enough that the computer could not continue operating. Precisely how a single degraded memory module is triggering this problem is a bit of a secret; the NSSC-1 only requires one memory module at a time to work, leaving the other 3– as well as the 4 memory modules in the backup NSSC-1– in reserve. Provided the readily available data, it appeared like the most rational explanation.
The next action was to change the NSSC-1 to one of the three backup memory modules, however that command was satisfied with a failure. This and other diagnostics led NASA to believe that the problem may not lie in the NSSC-1 or its memory modules at all, but rather in other modules on the SI C&DH, specifically the Standard Interface (STINT) hardware, or the Central Processor Module (CPM).
Testing that hypothesis required an extreme action: turning on the backup NSSC-1 for the very first time in area. The backup had actually only ever been checked on Earth, and has been sitting dormant given that it was set up twelve years back. This step was handled June 23 and 24, and the information showed that the backup computer system suffered from the exact same fault as the main computer.
Its not likely in the extreme that both the main computer and a backup computer that has been sitting idle for more than a decade would fail in precisely the same way at precisely the same time, so that test supplied strong evidence that the fault lies elsewhere. Existing thinking is that some other piece of hardware on the SI C&DH, something shared by both computer systems, is really causing the fault, which the memory error is but a sign. NASA is looking at the Command Unit/Science Data Formatter (CU/SDF), which formats and sends commands to the different science instruments and information to the ground, as the most likely offender. The other suspect is the Power Control Unit, which conditions and regulates the different voltage rails needed around the SI C&DH.
Is This the End?
While it sounds like NASA has a good manage on whats going on with Hubble, provided everything the spacecraft has actually been through over the last 31 years, its hard to say that the chances of recovery remain in its favor at this moment. Thats a pity, since aside from the current issue, the spacecraft and instruments remain in great shape. However theres likewise the reality that given that the retirement of the shuttle fleet in 2011, Hubble is without the lorry it was created to be serviced by, and to enhance it to a higher orbit from time to time to combat climatic drag.
Whats even more threatening is one of the last modifications made to Hubble in the 2009 service call: attaching a gadget called a Soft Capture Mechanism to the aft end of the spacecraft. The SCM will enable NASA to manage reentry more specifically, giving Hubble a quick and dignified end to a decades-long career of unequaled clinical achievement.
It appears to us that a theoretical deorbit mission might simply as easily be an orbital increase objective, however that presumes NASA will be able to get and clear the present bug Hubble back to work. Heres hoping thats precisely what takes place, which the SCM does not have to be utilized one minute earlier than essential.
A huge thanks to [David Anders] for pulling together a bunch of outstanding sources on the NSSC-1 and SI C&DH and publishing it on Hackaday.io. It was invaluable in pulling this short article together.
[Main image via Wikimedia Commons]

The Hubble Space Telescopes remarkably long service life and its string of amazing contributions to astronomy belie its struggling history. Long prior to its launch into low Earth orbit in 1990, Hubble experienced style disputes, funding and financial pressures, and even the death of 7 astronauts. Long postponed, much modified, and incorrectly sent up with suboptimal optics, Hubble still handled to provide outcomes that have actually changed our view of deep space, and is perhaps responsible for more screensaver and desktop pictures than any other single source.
All of that changed on June 13 of this year, when Hubble suffered a computer system problem that interrupted the circulation of science data from the orbiting observatory. Its not yet clear how the present concern with Hubble is going to pan out, and what everything means for the future of this almost irreplaceable scientific asset. All of us wish for the finest, obviously, however while we wait to see what occurs, its worth taking the chance to dive inside Hubble for a take a look at its engineering and just what has gone incorrect up there.