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The Hubble Gets a Low-Power ASIC

June 28, 2009 on 1:35 am | In Hubble, Low-Power, Space | No Comments

As I watched Space Shuttle Atlantis pull away from a refurbished Hubble Space Telescope after a spectacular series of EVAs, I realized that it’s now time to look away from the spectacular in-orbit repair efforts of the astronaut/mission specialists and turn my attention to a bit of low-power high technology that went into Hubble during the repairs. Astronauts John Grunsfeld and Drew Feustel replaced four circuit boards in the Hubble’s disabled Advanced Camera for Surveys (ACS) with a new electronics module and an external low-voltage power supply. The existing 15V power supply, a dc-dc converter that had operated far beyond its MTBF rating, failed early in 2007. However, the ACS repair didn’t just replace the failed supply with a new external box; the astronauts also upgraded the ACS imaging system with a low-power ASIC.

Now ASICs are almost always designed for high-volume applications where the cost of the ASIC’s design can be amortized over a large number of chips. Almost always, but not always. In the case of the Hubble, the repair of the power supply required the replacement of the CEB (CCD Electronics Box), which includes the A/D conversion circuits for the ACS’ Wide-Field Channel (WFC) CCD imager. Markus Loose at Teledyne Scientific & Imaging realized that this repair was a prime opportunity for a low-power ASIC that he’d developed for other telescope imaging applications.

The ASIC is called SIDECAR (System for Image Digitization, Enhancement, Control And Retrieval). SIDECAR contains 36 analog digitizing channels for converting analog CCD signals into digital data streams. Each analog conversion channel on the SIDECAR ASIC consists of an analog preamp, a 16-bit/100KHz A/D converter, and a 12-bit/5MHz A/D converter. The AISC also contains a 16-bit, radiation-hardened microprocessor, memory, interfaces, digital I/O pins, and 20 DAC-driven analog output channels to bias the analog CCDs. Here’s a block diagram of the SIDECAR ASIC:

: SIDECAR ASIC Block Diagram

And here’s what the SIDECAR ASIC looks like in its Hubble packaging:

SIDECAR ASIC used in Hubble upgrade

In low-power mode, the ASIC draws a mere 11 mW. Now low power is the omnipresent watchword for earthbound applications these days but it’s even more important for the SIDECAR ASIC’s intended platform—the infrared James Webb Space Telescope—where it will be used in the Webb’s Near Infrared Camera (NIRCam) and the Near Infrared Spectrograph (NIRSpec). A hot conversion chip radiating IR cannot be tolerated in applications where sensitive imagers are trying to resolve a few infrared photons from faint, distant stars. The SIDECAR ASIC will also be used in the Webb’s fine guidance sensors. It’s a versatile chip design; The hallmark of a good ASIC. It’s the low-power, low-weight, and space-saving aspects of SIDECAR that make the ASIC attractive for space applications, not its cost. NRE amortization doesn’t play a role here.

Although originally designed for the James Webb telescope, Teledyne’s SIDECAR ASIC has now found its way into the Hubble. In addition, four SIDECARs were installed in early 2007 into the imaging system of the University of Hawaii’s 2.2 meter telescope on Mauna Kea. Like all well-designed ASICs, the Teledyne SIDECAR seems to have established itself as the standard part for high-end scientific imaging applications. When it’s fully tuned up inside of Hubble, it’s possible that the SIDECAR ASIC will pull more and better images from the ACS’ Wide-Field Channel CCD with less noise. Let’s hope so.

Here are some links if you want to get much more detained info on the SIDECAR ASIC and the ACS Repair (ACS-R) mission:

Amazing Miniaturized ‘SIDECAR’ Drives Webb Telescope’s Signal

Updates on ACS-R, PowerPoint presentation by Marco Sirianni

Imaging Sensor Technologies for Astronomy, Planetary Exploration & Earth Observation, PowerPoint presentation by James Beletic

SIDECAR ASIC Product Brief