Until the phone rings… The caller ID shows K1 Control.
Noooo!! It is Christmas Day!
What is wrong now? Time? 4 pm, daycrew should be doing final checks before releasing the telescope, just the time things usually go wrong. ACS?!? It has been creating a lot of trouble lately. Autofill? My usual problem child… No, I checked that already today. HIRES? Tonight’s instrument that I really know nothing about. Nothing to do but answer the phone…
Just Robert calling to say everything is fine and Merry Christmas.
I am actually rather surprised it had not happened to me before. Given the number of times I have dodged animals along Saddle Road. Pigs, sheep, mongoose, feral cats, francolins, quail… I had hit a turkey a few years back, but this was my first encounter with a larger animal.
I really prefer to avoid killing, but luck was not with me or the poor mouflon sheep this time.
It came into the headlights from the side at a full run, I had no real chance of avoiding the collision. Fortunately it did not hit square on, as it was a fairly big ram. It struck a glancing blow under the passenger side headlight, with a dull thud I can still remember vividly.
Damage on the front quarter of a Ford Explorer due to a Mouflon SheepThe results were pretty ugly, bits of sheep across the road, blood and guts sprayed down the side of the vehicle. What was left of the unfortunate ram was left wrapped around a fencepost, thrown well clear of the collision. Yes, I have a photo. No, I am not posting it here. It is rather gory.
I did have one bit of luck, there was no critical damage, allowing me to continue on to headquarters in the middle of the night. I was a bit concerned when I found fluid leaking from under the vehicle, but it didn’t look yellow enough to be antifreeze. Further inspection showed it to be wiper fluid, the reservoir is just above the wheel and had taken a hit. In my flashlight beam it was slowly draining onto the road.
I inspected the tire, the brake line and everything else in the impact zone before continuing my journey. As I pulled out there was a chime and a message in the dash… “Wiper Fluid Low”… as if I was worried about wiper fluid!
Mike, our company mechanic, places the damage at about $4k in a quick guess. I suspect he is about right. Given the size of the ram and the speed I am really surprised it was not worse. I did do Mike a favor, I hosed the vehicle down before leaving it parked it in front of our little shop. With the contents of the sheep all down the side, it was pretty rank!
I always feel bad about killing a wild animal like this. My only solace is that feral mouflon are a species that represent a problem, with a population that is growing to the point it is damaging the mountain. I recall a few years ago when sighting sheep was a rare occurrence along Saddle Road, for the last year it has been difficult not to see them, with large herds a common sight.
I am not the first to hit a sheep in an observatory vehicle lately. This will not save me from the inevitable ribbing I will receive. There will be jokes, and I will just have to laugh along.
A telescope relies on the quality of the primary mirror. The shape must be exquisite perfection, with errors measured in millionths of a meter. The reflective coating must also perform to high standards, reflecting well over 90% of the light across a wide region of the spectrum.
A Keck mirror segment after stripping and cleaning, ready to place in the chamber to receive a new reflective coatingKeck observatory carefully monitors each primary mirror to insure it is performing accurately. Instruments can detect small variations in the shape, indicating where there may be trouble in the support structure and active positioning of the segments. The coating is tested for reflectivity, to insure as much precious starlight goes to the instrument as possible.
Keck uses pure aluminum to coat the surface of each mirror segment, chosen for its excellent reflectivity in the visible and infrared parts of the spectrum. It takes only 20.5 grams of aluminum to coat an entire Keck primary mirror. This thin layer of aluminum degrades with time, losing several percent of it’s reflectivity each year. Eventually it must be replaced.
Re-coating a mirror is a painstaking process of stripping the old coating, carefully cleaning the mirror, the placing the mirror in a vacuum chamber to deposit a new metal coating onto the glass. The process takes about a week per segment, with one full time technician dedicated to the task, with a little help to handle some of the more intense parts of the process.
An advantage of a segmented telescope is that individual segments may be swapped in a single day. Telescopes utilizing monolithic mirrors must shut down for weeks to remove the primary mirror, strip clean and re-coat. With spare segments available the maintenance crew can perform the task of re-coating on a reasonable schedule, without taking the telescope off sky for an extended period.
At Keck there is a special storage facility for segments awaiting re-coating and those that are ready for installation back into the telescope. The process is continuous, once the last segment is finished, it is time to start the rotation again.
Glow discharge cleaning the mirror surface prior to aluminizingThe first step in replacing the old coating is to chemically strip the old coating. This is done in a special bay used only for this purpose. An acid solution dissolves the aluminum revealing the glass below. The mirror is the extensively cleaned to remove any remaining contamination. If the mirror surface is not perfectly clean, the new aluminum coating will not adhere properly. All of the chemicals used are caught in a closed system for proper disposal off the mountain.
Once cleaned the mirror is moves to a large vacuum chamber where the new coating will be deposited. Here the mirror is positioned face downwards. With the cover reinstalled on the chamber it will take most of a day to pump out the air and ready the chamber for coating.
Glow discharge is a method of cleaning a surface prior to vacuum coating it. A high electrical charge is placed on an electrode just below the mirror in a partial vacuum. The result is something like creating a storm of electrons to blow any remaining impurities off the surface of the mirror. It is also a very beautiful process, looking through the ports one can see a brilliant violet haze around the electrode with sparks flickering along it’s length.
The bright glow of coils of aluminum vaporizing in the coating chamberThe final step is to vaporize the aluminum itself. In the bottom of the coating chamber are arranged a number of electrodes, each made of pure aluminum. By electrically heating these electrodes a few ounces of metal is vaporized. In the vacuum this aluminum forms a cloud of metal that coats everything in the chamber, including the mirror segment positioned above the electrodes. An instrument measures the buildup of the layer and shuts off the current when the deposited layer reaches the desired thickness of 100nm.
The coating process takes only a few minutes once the electrodes are turned on. Peering in through the small view port a cheery red glow is seen from each of the electrodes at the bottom of the chamber. The view only lasts a few moments as the cloud of vaporized aluminum soon reaches the view port and the glow fades as the window is covered by a layer of deposited aluminum along with the mirror segment.
What emerges from the chamber is a mirror with a beautiful, reflective metal coating. A few tests will be performed to insure the coating meets specification. If all is well the mirror segment will be prepared for installation in the telescope. It will await another segment exchange when it will replace another segment that has become dull with years of exposure to the elements. That segment will then receive it’s turn in the coating chamber.
It is an observation I have made before, but one that continually amazes me… Each Keck telescope consists of three hundred tons of steel and glass, with one simple purpose, to hold a few grams of aluminum in the perfect shape necessary to collect the light from distant stars and galaxies.
Looking into the optics of the Keck 2 telescopeEach segment of the primary mirror is covered with a very thin coating of pure aluminum, about 100nm thick, this is 1/10,000 of a millimeter or 0.000004 inches. Aluminum is used in the Keck telescope as it reflects over 92% of the light across a wide wavelength range extending from the UV well into the infrared.
The layer is just thick enough to reflect nearly all of the light, any thinner and too much light would penetrate the mirror, any thicker and small variations in the coating would begin to distort the shape of the mirror.
How much aluminum?
Density of Al…
2.70g/cm³
Area of a Keck Primary…
36 x 2.598 x (0.9m)² = 75.75m²
Mass of Al…
2.70g/cm³ x 75.75m² x 100nm x 1,000,000cm³/m³ = 20.45g
20.45g = 0.71oz (if you prefer imperial)
Just how much aluminum is really on each Keck primary mirror? Simple enough to calculate… just multiply the surface area of thirty six hexagons by the thickness of the aluminum layer to figure the total mass of metal used.
The figures are found in the sidebar, and the answer is surprisingly little, about 20.5g. In comparison, an empty 12oz soda can weighs about 15g, thus it take a bit more than one soda can of aluminum to cover the Keck’s 10 meter primary mirror.
There is much more to a telescope than just one simple layer of aluminum. But that one component is critical. It is the mirror that gets a great deal of the attention. The primary mirror is what gives a large observatory the ability to capture light from the earliest eras of the universe, billions of years in the past.
Yellow light, specifically light at 589nm, the yellow glow of excited neutral sodium. A color of light familiar to anyone who has stood under the soft glow of low pressure sodium streetlights. A laser shining at 589nm, aimed high into the atmosphere, will encounter a layer of sodium atoms at an altitude of 90km (60miles). When the yellow light strikes this sodium it will excite the atoms and cause them to glow, creating a dot of light, an artificial ‘star’ in the sky.
A sodium yellow laser propagating through the optics of the Beam Transfer Optical Bench
An artificial star, a useful thing if you want to analyze the distortion caused by the atmosphere. If you can understand these distortions you can use the information to correct the images of an instrument looking though the atmosphere, creating sharp views of stars and galaxies, views vastly better than were possible before the advent of adaptive optics. Such system are now routinely used on large telescopes across the globe to allow a clear view of the universe we live in.
The Keck 1 Laser piercing the sky for the first time on 28 Jan 2010
Adaptive optics systems are amazingly complex instruments. Hundreds of filters, lenses, mirrors and other optical surfaces interact with dozens of motorized stages and half a dozen cameras. Controlling the system are a horde of computers, some of which are specialized machines with impressive processing power. Everything must work in concert, the failure of one element can bring the whole system down.
A laser is not necessary for an operating AO system, but without it there is 70% of the sky that can not be observed, making a laser highly desirable. While the K2 AO laser has been operating for several years, Keck Observatory has never had a laser on the Keck 1 telescope.
A convoy of observatory vehicles heads up the summit access roadIt started when we arrived at the morning rendezvous and noted the number of vehicles waiting. Transportation sets up up as many vehicles as necessary based on the ride board, usually two or three vehicles are sitting by the door waiting to transport our crew to the summit. That morning there were five, and we all knew from the schedule that many more would be leaving later in the day. This was going to be a busy and crowded day.
At Hale Pohaku we were met by a film crew. Documentary film crews are an occupational hazard at Keck. I have appeared in more than one show. Not usually a problem, this day the crew would be yet one more complication.
For myself, things started to go bad with an email message, trouble with a key piece of equipment in AO. At the heart of the adaptive optics system is a thin flexible mirror that can change shape to correct the light, the DM or deformable mirror. In order to monitor this mirror a WYKO interferometer is used to image its surface. This device shines laser light at the mirror, the return light is interfered with itself, allowing the surface shape to be analyzed with incredible accuracy. This is used to calibrate the AO system at the beginning of each night. Gone was my plan of a simple day doing some documentation checks to prepare for some upcoming modifications to the system.
A big milestone arrived this week. The launch telescope arrived from the manufacturer. It is an impressive instrument itself, a half meter aperture, an extraordinarily short focal length, made to very exacting precisions, even for optics. It is a cassegrain design with an focal ratio of f/1. The primary is coated with a custom coating designed for maximum reflectance at the 589nm sodium D line, where the laser will operate. This gives the primary a notably orange cast that is quite beautiful. The entire telescope is enclosed in an airtight aluminum shell with the optics supported on a carbon fiber frame within.
Kenny Grace inspecting the Keck 1 laser launch telescope during incoming inspection after unpackingThis is one of the key components in creating a laser for the Keck 1 adaptive optics system. An enormous amount of work has gone into preparing for the laser… modifications to the structure of the Keck 1 telescope, cabling, electrical power and liquid cooling plumbing. An insulated room built on the side of the telescope to house the laser and a safety system to comply with laser safety regulations. All of this in preparation for the arrival of two key components, the laser itself and the launch telescope that will focus this light into a clean beam rising into the night sky over Mauna Kea.
The entire assembly will mount behind the secondary of K1. This is different than the current laser in Keck 2 that is emitted from a launch telescope along the side of the main telescope. Having the laser on the side creates some problems for the AO wavefront controller, the artificial guidestar can be elongated by parallax when seen from the other side of a ten meter telescope. Having the laser launched from the center of the main telescope is a far more optimal solution. But doing that takes a far more difficult to design and build launch telescope as it has to be extraordinarily compact.
We expect delivery of the laser itself in May. Our laser engineer has been working with the laser manufacturer to insure it meets all specifications. Reports indicate it is not only meeting those specifications, but surpassing them. When we take delivery there will be a period of testing before the equipment is trucked to the mountain for installation in its final position.
The coming week will be fun, need to string a new set of cables to the Keck 1 secondary mirror. This means 150 feet of cabling from the Nasmyth Deck, up the tubular structure of the telescope and across the spider to the secondary. On a ten meter telescope this means a lot of high work from the personnel bucket of the jib crane among the girders of the telescope. This is going to be fun!
Monday I spent the day on the summit, I often choose Mondays, if I have a choice, as we often have a smaller crew and getting access to the various parts of the telescope is easier. There are fewer people trying to do fewer things at once. Monday turned out to be very good choice indeed, the first clear day at the summit since Christmas. We arrived at the summit to deep blue skies over a landscape of white. Poli’ahu has again blessed the summit of the White Mountain with deep snow.
Looking across at the Keck 1 dome from the top of Keck 2 with Mauna Loa in the backgroundA small crew does have a disadvantage as well, the chance of being drafted into whatever job needs being done. Not that I was unwilling, the job in this case was clearing snow and ice from the domes. This meant climbing to the top, one place in the facility I had not yet had a chance to go.
So after rigging myself in full safety harness I climbed the dome with the crew. The view from the top is stunning! A full 360 degree view of the summit on a perfectly clear sunny day. The entire summit is blanketed in a beautiful white coat of snow, one of the most dramatic scenes I have ever witnessed. The small Canon G9 camera fit in a breast pocket, small enough not to interfere. I began filling my memory card with many images of the view from the top, reveling in the spectacular vista.
Mike Dahler clearing snow from the edge of the Keck 2 shutterNot that it was all sightseeing, there was work to do, shoveling snow and chipping ice from the areas where it could interfere with operation of the telescope. Ice and snow coated the upper sections of the dome. Several inches of ice needed to be hammered free of the steelwork and drifts of snow, up to two meters (six feet) deep were packed into any corner and along the side of the shutter. Blocks of ice and shovelfuls of snow flew, crashing to the ground 30m (100ft) below. A crew worked each side of both domes for several hours to complete the task, made all that more difficult by the extreme altitude.
In the thin air there is only so much you can do before you are short of breath. Put down the shovel for a few moments and take a few more pictures. I have material from which to assemble a full panorama as well as dozens of individual images.
After much of the snow and ice had been cleared by hand there was one more step to accomplish. Clear the large drift of snow from the back of the shutter by using the shutter itself as a snowplow. This drift is many tons of snow, over 2m (6ft) thick at the top and about 12m (40ft) wide. When it came down it becomes an artificial avalanche, with huge blocks of snow falling to the ground far below.
I enjoyed moonrise tonight on the way home, and then enjoyed it again. The first was just after leaving Waimea, a golden full Moon rose over a band of clouds, a beautiful sight as I drove home from work. My drive then takes me deep into the shadow of Mauna Kea, the Moon disappearing behind the bulk of the mountain. A second moonrise found me about ten miles further down the road, with that golden orb rising over the summit. Two beautiful moonrises to grace the end of a long day.
Venus was visible in the golden glow of sunset, mercury right below if you knew to look for it. I saw no sign of Saturn which should have been a ways below the other two, it was probably hidden by a band of clouds that occupied the right spot.
Yes, I did say I was driving home from work on a Saturday. One of the guys on the crew is out with a bad back, and I worked a couple more days on the summit to cover. I was performing some procedures I had never done before, optical alignments in preparation for using the interferometer that night. As a result I will have spent five out of seven days on the summit, quite a bit more than my usual two days a week. I get a day off tomorrow, then back at it Monday. Even tomorrow will not be completely a day off, with an interferometer run in progress there will be some work I need to do from home to check the systems and insure they are ready for the night.
Hopefully the phone stays silent through the night.
