SCUBA-2, being a revolutionary instrument and all, is still in the process of being commissioned at JCMT. It shipped with “engineering-grade” arrays, which are of lower quality than “science-grade” arrays. They have more dead pixels and the remaining pixels are noisier than the requested spec. They can still be used for commissioning, as they can detect photons, only not well enough to do proper science with.
Until June 9, when NIST researchers discovered that a vial of plutonium was cracked and some particles spilled from the vial. Understandably this has lead to the closure of the lab while cleanup and investigations are done. Unfortunately this lab had either parts of the arrays or the full arrays in it. They’re not expecting to get into the lab until August, when we find out if the radiation event caused any damage to the sensitive SCUBA-2 array electronics.
But full operation SCUBA-2 has just been pushed back again. How much is still uncertain, but a month is probably the lower limit.
*One of the more serious problems to date came when one of the groups was preparing the arrays for shipping and accidentally dropped a crate on or tightened a lid on one of them, crushing one of the corners. Whoops.
This week’s Weekly Science Video comes courtesy NASA. This is the second in a series produced to educate people about GLAST, the Gamma-Ray Large Area Space Telescope, which is due to launch on June 5.
Seriously, how can you come up with a picture cooler than this one:
What is it? It’s the Phoenix Lander parachuting down to the surface of Mars. Why is it cool? Because it was taken by the HiRISE camera on the Mars Reconnaissance Orbiter. It’s the first time that a spacecraft has taken a picture of another spacecraft descending to land on another planet. How cool is that? You can even see the tethers connecting the Phoenix lander to the parachute!
Three weeks ago, SCUBA-2 arrived in Hilo. Today, after putting it on the back of a truck and hauling it up Mauna Kea, the cryostat was successfully lifted into JCMT!
While this may not sound like that big a deal, for SCUBA-2 it is. Most astronomical instruments have cryostats that are relatively small, maybe a few cubic feet, and they typically get cooled with liquid nitrogen to temperatures in the tens of Kelvins (remember, zero Kelvin is absolute zero, or 273 degrees Celsius below zero, or 459 degrees Fahrenheit below zero). SCUBA-2’s cryostat is huge! It’s about 2.5 cubic meters (about 90 cubic feet) and weighs about 2500 kilograms (5500 pounds)!
Let’s put that another way: a typical hot tub holds about 450 gallons of water, which is about 1700 liters. 1700 liters is 1.7 cubic meters. SCUBA-2 is 2.5 cubic meters — larger than your typical hot tub. This happy coincidence wasn’t lost on the SCUBA-2 designers, as there’s a CAD drawing of the SCUBA-2 cryostat with four humans sitting inside it. SCUBA-2, the hot tub instrument!
And get this: the entire thing is cooled to four degrees above absolute zero!
To get the cryostat into JCMT, they had to roll back the protective Gore-Tex membrane, tip the dish over on its side, and use a giant crane to lift the cryostat in. This was a major effort and kudos to everybody involved!
Jonathan Kemp took a bunch of pictures of the installation. This pulled-back shot shows what I described in the previous paragraph — the membrane is rolled back, the dish is tipped over, and the crane is lifting the blue SCUBA-2 cryostat into place. This picture shows the scale quite nicely — compare the men to the blue cryostat. It’s huge!
