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Exceptional Seeing At Dome C in Antarctica
Michael Ashley writes "A paper published in Nature
today reports on the exceptional
astronomical seeing conditions at Dome C (Coral link)
in Antarctica. Obtaining the data posed some significant technological
challenges, given that Dome C is uninhabited over winter. The
experiment was controlled by a PC/104
computer system that had to survive temperatures down to -85C, and
supervise the generation of its own electricity using a jet-fuel
powered stirling engine. The computer, running Linux, communicated with
the outside world using an Iridium
phone. The results are also covered in New
Scientist, and the Sydney
Morning Herald. Disclaimer: I'm a co-author."
Look at this photo. It is the author's Kyocera mobile phone with a web page showing the temperatures, memory usage and free disk space. Says battery temperature is -34.5 (is that C or F?)
2bits.com, Inc: Drupal, WordPress, and LAMP performance tuning.
What is "seeing"?
"Seeing" is a term that astronomers use to quantify the turbulence in the atmosphere and how it affects observations from the ground. The stars appear to twinkle because of the effect of this turbulence. In conditions of bad seeing, the stars appear to twinkle vigorously, and the images that you take with your telescope are blurry. In conditions of good seeing, the stars appear more stable, and you can take very sharp images.
You'd think they'd have a cooler word for that...
The link that the submitter provided to himself doesn't work. The correct link is: Michael Ashley
A PC/104 is just a form factor. And provides standards for things such as environmental operating parameters.
CPU boards usually have an intel clone processor MACH86 or VIA Athena.
So they can run any OS your desktop can.
Harder.. Better.. Faster.. Stronger
While colder can often mean faster, sometimes a signal requires some minimum delay to work correctly. This is especially true of the minimum hold times required on inputs after a clock transition. So it's possible that some signal might go out of spec if you drop the temperature too far. It only takes a single bad signal to hose the whole system.
Unlike just dropping the temperature of the CPU chip which will have relatively uniform characteristics, getting the whole system cold might cause a wider range of timing variations. Moreover, even dropping the external heat sink of a CPU to extreme cold doesn't mean the chip itself is in the cryogenic range. They usually run at temps well above the bulk of the heatsink.
PC/104 is a form factor and external bus specification, not a CPU type. It could have had any of many embeddable cpus on it.
Just stick .nyud.net:8090 on the end of your domain name (before the /) and it'll grab the content and cache it -- any future queries will return their cache instead of downloading from the original page. The coral links also work like your web browser and update the content when it is out of date.
Dude, I used to live in Alaska. The solution to the tongue problem, at least according to the neighborhood experts, is to urinate on it until it gets unstuck.
BTM
That was the turning point of my life--I went from negative zero to positive zero.
Computing equipment *loves* cold, as long as you don't have to worry about condensation.
Ah, not so! *processor cores* love cold, not electronics in general. Specifically, electrolytic capacitors freeze and fail below their rated temperature, and it's really tough to find any that are rated to temps that low. Also, because of resistance, capacitance, and crystal frequency value changes at low temps, oscillators and filters tend not to behave. This doesn't even consider the issue of thermal expansion coefficient differences causing BGA chips to pop off the circuit boards! Making anything electronic operate in that environment is highly non-trivial.
I am a geek attorney, but not your geek attorney unless you've already retained me. This is not legal advice.
From the article in case it get's slashdotted:
To operate our experiments over winter, when there was no one at Dome C, we had several problems to address:
1. For hardware reliability, we wanted to remove all moving parts in the computers, i.e., no disk drives, and no fans. So we used a small PC/104 form-factor computer system with solid-state disk drives.
2. We had to generate our own electricity. We took two approaches to this:
1. One experiment, ICECAM, relied entirely on a 5 kg pack of lithium thionyl chloride batteries. The batteries had to provide power for a year, so minimized the power consumption of the computer. The experiment only needed to take data every two hours, so we built a CMOS oscillator to power-up the computer for 30 seconds every two hours. We used MS-DOS 6.22 for the PC/104 computer since it boots quickly and was able to average 10 frames from the CCD camera and store them to CompactFlash disk.
2. For the experiment that obtained the seeing results, the AASTINO, we needed much more power, up to 400W, and we had to operate continuously, so we used stirling engines running on jet fuel. For software reliability we chose Linux, Redhat 9 to be precise. Software and hardware watchdog timers helped to ensure that the system would recover from most failure modes.
3. The ambient temperature at Dome C reaches a low of -85C during winter. Computers, and electronics in general, are not designed to operate at these temperatures. We took two approaches:
1. With ICECAM we had no reserves of power for heating, so we buried the computer in a crypt seven meters below the ice surface, at which point the temperature is stable at the yearly average of -57C. This is still outside the computer's specfication. Fortunately, a test in a low-temperature fridge showed that the computer and solid-state disks worked reliably at these temperatures. ICECAM's camera, a Watec 902-HS, had to remain outside, and tests shows that it was able to operate flawlessly down to at least -80C.
2. With the AASTINO, the stirling engines produced up to 6 kW of waste heat, which we utilized to maintain a comfortable operating temperature of about -10C.
4. Internet connectivity was provided by an Iridium phone, which acts like a 2400 baud modem.
5. The hardware and software had to be carefully designed so that we could recover from most problems remotely. There were no reset buttons to press, and no prompts to "click OK to continue".
The PC/104 computers we used were made by DSP Design, however it in unclear whether the company still exists, since all our attempts (using e-mail and filling out their laborious on-line enquiry form) over the past 6 months to have a simple technical question answered have received no response.
"Leo Fender was in a 'state of grace' when he designed the Stratocaster." -- Paul Reed Smith
The CPU is called the VIA C3 and the chipset is the VIA Eden. The "Athena" in your post refers to a Diamond Systems product name for the board which uses this CPU, not the name VIA calls their own CPU.
;-)
The "Mach86" you're thinking of is the ZFMicro ZFx86 chip. They are battling National Semiconductor, who produced these CPUs under contract for ZFMicro until ZFMicro was no longer able to pay their bills. Intel is not involved at all.
The other big PC/104 CPU vendors are Transmeta, STMicro (STPC), and AMD (Geode). Recently the Pentium 4-M have been popular for boards which don't need to support extended temperature.
PC/104 rocks for applications like this. Disclaimer: I work for a PC/104 company.
The US Military.
TANSTAAFI: There Ain't No Such Thing As A Free iPod.
Okay I'm interested in seeing this jet-fuel stirling engine. How well does it work in extreme cold?
For those of you who may not know much about stirling engines, here's some information.
"You can't just fly down there to replace broken parts."
You can actually, but I guess cost/benefit comes into it.
I live near Christchurch, New Zealand and once or twice a winter a fully loaded hercules takes off for an emergency trip to Antarctica to rescue some poor bastard that has broken an appendage etc.
Iridium is a nobel metal like palladium or platin and *not* radioactive.
want to know more? see ... http://www.scs.cs.nyu.edu/coral/
No moving parts to freeze? Can you say Hard Drive? Keyboard? Power Switch?
Last but not least. The user. You got to have some damn heavy mittens for -85C.
The article specifically says that they used solid-state hard drives. The system was operated remotely so I imagine no keyboard was used.
In addition, -85C was only the exterior surface temperature. One computer was installed under the surface with an average operating temperature of -57C. Another experiment was warmed by waste heat from the stirling engine.
Some electronics operates below its specified minimum operating temperature, and some doesn't. For example, we had some solid-state disks that were rated to -40C, but that failed at -20C. Mostly we have found that PC/104 computers, memory, etc work fine at -60C. M-Systems solid-state disks have been very reliable.
You want to avoid spinning up a hard disk at -85C though! The altitude (4000m equivalent) also tends to be rough on hard disks (both due to the cooling problems and the smaller head-gap), which is why we avoid hard disks in critical applications. Actually, one of our experiments is running on a Dell laptop with a normal 2.5-inch IDE drive and RT Linux. It has worked fine for two years now.
There is no part of the sky that the HST can't look at, though obviously at any given time its choices are more limited (e.g. it can't point within 50 degrees of the Sun, but the Sun moves wrt the stars...) The key point about this work is that it would be much, much, much cheaper than HST. Moreover, it's looking at the moment as though the JWST, HST's successor, as well as being very expensive to the US taxpayer, will be restricted to the infrared. A ground-based optical telescope with high resolution could clean up at that point. Pity we can't have another one in the northern hemisphere, though.
We're building a sub-mm polarimeter (Clover)to go to Dome-C (Dome-C is the best site in the world for sub-mm, being high, dry, cold and calm) starting now.
The total budget is 4.3M GBP, including new detector development, and the telescope will be collecting data from Austral winter 2007 onwards. This telescope will have better results on CMB B-mode polarisation than the Planck satelite mission, before Planck reports results, for about a tenth to hundredth of the cost. The Planck project has a 15 year head start. Admittedly Planck isn't designed to only make the measurements we are trying to make.
When something goes wrong, we'll be able to send someone out to fix it, and if someone invents better detectors, we can send some out to be installed.
Hubble is limited to the resolution of its 2m mirror, while optical telescopes on the ground are now reaching 10m (Keck), with sub-mm telescopes reaching 50-100m (LMT and GBT).
Hershcel/First will be the sub-mm equivalent to Hubble, and is limited to a single 3m mirror, while ground based sub-mm telescopes are using 64 15m mirrors spread across 60 km of the Atacama desert, simulating the resolution of a 60 km mirror.
Magdelena Ridge Observatory, New Mexico will be 14 1.4 m telescopes in a 400m baseline array. MRO has pretty good seeing in the optical.
I think he means you don't get an "idle" process running HLT instructions like in linux/windows (meaning the cpu is using a lot of power doing nothing).
as others have said, PC/104 is a board form-factor, but it's more than just a size (roughly 4" square). It also dicates the bus. PC/104 uses .1"x2 stackable headers for the ISA 8-bit and another, smaller, .1"x2 header for the ISA 16-bit bus. The two headers are stuck right next to each other. So you can have non-x86 processors on PC/104 but they must be able to read/control the ISA bus. So chips like the StrongArm must include a little glue logic as a bridge.
Additionally, there is PC/104+ which includes the 32-bit PCI bus in a 4x2mm stackable connector on the opposite side as the ISA headers.
There are more features to PC/104 but the size and bus signals are the most important.
"The Thing from another world", or just "The Thing"
Original: http://www.imdb.com/title/tt0044121/
John Carpender's excellent remake: http://www.imdb.com/title/tt0084787/
(Sorry - don't know how to make the "html-syle" hyperlinks)
You can view the health reports (temperature etc.) that that telescope sent back via Iridium here.
There may be other tasties too -- I haven't dug too much.
Freezing point of mercury is -38C (which is just about -38F) ... so it would be solid through much of the Antarctic winter.
When I froze mercury in the lab, it made a surface that wasn't optically useful -- lots of tiny bumps.
Also of interest: the century old Mt. Wilson 100-inch telescope used mercury bearings for the polar axis. In the 1970's, mercury pollution worried the operations staff; I don't know what was done about it.
This is off-topic, but in html, a link is made by Free gmail invites!. Clicking on "Free gmail invites" would then take you to http://www.goatse.cx.
The 'a' I believe stands for 'anchor', and 'href' for HTTP Reference. Note the '/' before the 'a' in the closing tag, it's important.
Why a stirling engine and not a thermoelectric
generator? Because ordinary bismuth telluride
modules running as a Seebeck generator are no
more than 3%, and in practice more likely 1.5%
efficient. That's why.
AC