“Without phasing, there’s no real reason to build the GMT.”
The biggest optical/infrared telescope in world will be the Giant Magellan Telescope, which will be built on a nearby mountain peak within sight of the Clay and Baade telescopes at Las Campanas. The telescope will have 7 primary mirror segments and 7 adaptive secondary mirrors, similar to the Magellan AO system.
If we could build any optic we wanted for the primary of the GMT, we would probably build a monolithic 30 meter diameter (or larger) mirror made of a single piece of glass, with a thin face sheet and a honeycomb lightweight structure on back. However, at the moment, the largest mirrors in the world are built in the Steward Observatory Mirror lab under the bleachers of the football stadium at the University of Arizona and are limited to a diameter of 8.4 meters. Depending on who you ask, this 8.4 meter limit comes from either the distance between the columns underneath the stadium bleachers, or the size of an underpass on the highway leading from Tucson.
Because of this limit, the GMT is designed to take 7 of the largest mirrors that can be made and combine them to form one giant 25.5 meter primary. For this to be possible, the seven 8.4 meter segments must be “phased” to a fraction of a wavelength. That is to say, they must be aligned to each other so that they act as if they are one large continuous mirror.
To achieve the phasing of the GMT segments using off-axis natural guide stars, SAO and our collaborators at GMTO and Flat Wavefronts have designed a sensor that creates dispersed interference fringes using subapertures spanning the 12 segment boundaries. Phase shifts across the segment boundaries manifest themselves as tilts in the fringes.
To test this sensor technology, SAO has built a phasing prototype that simulates 6 of the GMT segment boundaries working in conjunction with the Magellan AO system. Our three nights at the end of the MagAO run turned out to be a success.
We obtained phasing data both on-axis and off-axis, with AO on and off, and at two different wavelength bands (I and J). This data, and data that we gather during another run possibly in February, will inform the design of the GMT phasing sensor, scheduled for first light in the next decade.
Lastly, a “song of the run:” Phazing, by Dirty South:
If you read carefully between the lines of yesterday’s blog post (which were mostly complaints about me trying to do science – hmph!), you may have noticed that we didn’t say anything about using Clio. Because we didn’t. At all. All night long.
We didn’t want to panic any of our upcoming observers, but Clio was down for the count yesterday. We started with mild instrument shaming to try and get her back up and running.
Unfortunately, it appears that Clio is insusceptible to shame.
The good news is that since we’re fessing up on the blog, that means we fixed it eventually! There were a few rabbit holes and false starts, but in the end we were able to bypass a faulty motor controller and get Clio back to work. Here are a few highlights from the process, which involved taking apart most of the motor control box and using tools of various levels of sophistication to test communications between the six Clio motors.
Once Jared and Katie identified the faulty motor (I mostly held stuff and made coffee, but it was fun for me to learn about hardware… and software… and firmware… and motor instruction manuals), they were able to bypass it and get all the other motors spinning again. The bypass makes operating Clio a bit more of a hassle in that Katie now has to run out to the platform and move the field stop wheel by hand. Luckily, this is one of the less common motor moves for Clio.
At this point, I feel that it is my duty to point out to all future observers that Jared and Katie have gone to heroic efforts to keep MagAO up and running in 2015A. Since I arrived, they’ve foregone sleep and breakfast (which involves fresh squeezed juice, so is a tough thing to give up!) most days to ensure that we maximize time on sky. And they’re only a third of the way through a loooooong run of loooooong winter nights. So take this as my admonition to be nice and to be grateful when you arrive. Perhaps signs of gratitude are in order. They claim to be all set on wasabi peas and instant coffee, but I’m sure you can think of something.
I’d also like to correct my statement from yesterday. Jared doesn’t hate science. He just hates MY science. Because tonight, when it came down to one of HIS targets, he changed his tune quite a bit about the wind. So here’s another “find the problem” blog challenge. I will happily mail a MagAO sticker to the first blog reader who e-mails to tell us what’s wrong with this picture.
In other news, it was empanada Sunday today, so that brightened things up considerably.
We ended the night with some astrometric calibrations, which included taking very pedagogically interesting images like these. So here’s another sticker-winning opportunity. Tell us what (a) camera we’re using, (b) observing mode we’re in and (c) star we’re guiding on (the right one or the left one?). If you get 3/3, we’ll send you a sticker!
I’m headed home tomorrow, which is bittersweet. It’s always a lot of fun to be here, and I got some awesome data, but I’m anxious to get home to this guy.
So here is the song that he wakes up singing every morning, which has been blissfully out of my head for a few days, and is solidly reimplanted now that I decided to post it to the blog.
Quotes of the Day:
various unrepeatable comments about Clio
“I’m just going to go move the telescope” -Alberto, running out into the dome
“Wait, WHAT?” – Jared
“Is he gonna push it?” -Katie
“USNO is a Joke! …. The catalog, not the organization” -[former naval officer] Jared Males
[4:52:54 AM] Vanessa Bailey: i’m headed home. thanks so much to all of you for working so hard to get the motors working! i hope the magao uptime clock is monotonically increasing from here on out!
[4:53:09 AM] Jared Males: uh no
[4:53:14 AM] Jared Males: we just broke the telescope
[4:53:28 AM] Vanessa Bailey: oh no, really???
[4:53:31 AM] Jared Males: yep
[4:53:48 AM] Vanessa Bailey: i’m sorry
[4:54:07 AM] Jared Males: at least we don’t have to troubleshoot this one
[4:54:11 AM] Jared Males: it’s kinda nice to get to watch
[4:54:19 AM] Vanessa Bailey: i know the feeling
[4:54:30 AM] Vanessa Bailey: guilt and relief at the same time
[4:54:48 AM] Jared Males: Unbelievably, this is possibly Clio’s fault. It all started when KT went out to hard reset the electronics.
[4:55:01 AM] Vanessa Bailey: bah
[4:55:09 AM] Vanessa Bailey: she just walked too loudly
[4:55:49 AM] Jared Males: this is kt – no i didnt!
[4:55:59 AM] Jared Males: we were transiting at like 89.2 deg and the limit is 89.3
[4:56:18 AM] Vanessa Bailey: that’s pretty damn high
[4:56:58 AM] Vanessa Bailey: https://imgflip.com/i/lnfvg
[4:58:09 AM] Vanessa Bailey: well, i hope it gets resolved quickly
[4:58:16 AM] Vanessa Bailey: good luck!!
[4:58:36 AM] Jared Males: thanks. we’re back. Alberto just told us he had to use [redacted content]
[4:58:40 AM] Jared Males: this is getting awesome
[4:58:47 AM] Vanessa Bailey: heck yeah
We’ve had a few meetings lately to prepare for our upcoming 2014B run in Oct–Dec. This will be our second regular science run, and our operations are becoming more smooth and efficient, so we are going to have a more streamlined personnel plan. It will also be our longest run yet (37 nights!).
We are laying in for spares and planning improvements in our operations. One spare Phil has gotten for Clio is a spare pump for pumping on the liquid nitrogen chamber in the dewar to bring the temperature of the detector from 77 K (liquid nitrogen) down to 55 K (solid nitrogen) by lowering the pressure. This spare pump is coming to us from the LBT where it used to be a vacuum pump, and while it is no longer strong enough to deliver a true vacuum, it is strong enough to lower the pressure to solidify the nitrogen in the dewar. It is a Leybold Oerlikon EcoDry M 30 Dry Piston Vacuum Pump.
New Clio pump technical info, from Phil:
The current Clio pump is specified to reach an ultimate vacuum of 5 Torr (7 mbar). This allows the solid N2 vessel to be at 50-51 K. We typically regulate ~5 K above this or 55 K. The new EcoDry pump has an achieved lab pressure of 0.11 Torr. This will put the solid vessel at ~42 K. This suggest we could regulate as low as 47 K on the detector.
Therefore, on this next run, we will explore new setpoints and the effect on detector performance. Thanks Phil!
Today was a busy day, and we began splitting MagAO’ers into day and night crew. See Derek’s awesome post for the bulk of the day’s tasks: aligning the CRO and ASM.
The next major happening was mounting Clio to the NAS. Even though we didn’t play the theme from Top Gunas we did it (sorry Phil!), it was an exciting moment. This is the first time our infrared camera officially met our optical camera and our AO system! They are together at the telescope at last!
LCO crew were busy as always, making everything work smoothly for the run. Here, Mauricio brings up LN2 to fill Clio’s dewar, and Pato optimizes the PID loop that rotates the Nas while the telescope tracks and slews:
Alfio: “What is this mirror cover?”
Laird: “Oh you’re so cute Alfio.”
Phil: “I don’t lean on Clio.”
Phil: “Used to be, we only had 1 actuator.”
Povilas: “Can 14 mm be considered a shim? That’s more like a structural member.”
Katie: “Hey Jared, how’s it going with the CRO?”
Jared: “I dunno. It’s all in Italian.”
Jared: “The number of Illuminati asking me questions is daunting.” (That would be Simone Esposito himself, as well as suspected members Laird, Phil, and Armando — see our paper for more info.)
Jared: “I’m pretty sure I would throw myself off the catwalk if Armando thought it would help.“