Tag: telescope

Pushing Steel

A snippet of overheard conversation. I was in Keck 2 control talking with the operator when a few words drifted over the video conference link from Keck 1. Some sort of trouble. I headed for the other end of the building.

Sniffen, our night attendant was looking for the cause of a drive fault. For some reason the computer refused to move the telescope, displaying a drive fault error. It would not move manually either, drive power would not come on. As he explained this to me I was a bit worried. This could be really simple, or really bad. Possibly something that would cost us the night.

Fisheye Keck 1
The Keck 1 Telescope awaiting lights out and release for the night
Opening the doors to the drive electronics cabinet I began decoding the cryptic status and error LED’s on the interlock control boards. Dozens of unlabeled indicators with a chart pasted to the door, a bit of 1980’s tech we still have to deal with, upgrade scheduled for the year after next. It takes a few moments… Right Final Limit error?

Sniffen and I looked at each other… How had the computer driven into a limit? This was not supposed to be possible. While we occasionally put the scope in a limit during maintenance, I had never heard of this occurring during the night. Was it really in the limit? The computer was indicating we were well clear of the limit. Something was lying to us.

Walking out into the dome and looking up confirmed we actually were on the limit switch. The telescope had driven as far around in azimuth as it could go, stopping just before the hard stop, a massive steel assembly that will definitely stop the telescope.

Oh !#%$! We have to push.

Yes, it is possible to push 300 tons of steel when it is floating on a film of oil. I have never had a chance to do it myself, but years ago someone had shown me how to do it. With Sniffen pressing a pair of pencils into the electrical contactors to release the brakes, I shoved the telescope out of the limit.

It moves surprisingly easy. I had braced my back against the laser enclosure and put my feet against the steel rails used to move the instruments. One good shove and it was moving. I really did not need to brace so well, just a good hard lean against the railings would have done it.

Once you get 300 tons of steel moving, it keeps moving. After I stopped pushing it continued to glide for another few degrees. Low friction creating a clear example of Newton’s first law of motion.

A surreal experience… 2am, in a darkened dome with stars overhead, pushing one of the world’s largest telescopes by hand. Life is interesting sometimes! Twenty six minutes of precious dark lost, but with a quick reinitialization of the telescope we were back on-sky.

A Very Dark Night

Planning a night of observing is a challenge. There is the choice of equipment, setting up observing lists of objects to target. And then there is deciding where to go.

Finding a dark spot can be a challenge in Hawai’i. Almost every bit of land is gated and tied up in bureaucratic rules. We often use the area around the Mauna Kea VIS to observe. Located at 9,000ft on the south side of Mauna Kea the area has much to recommend it for amateur astronomy. This land is under the administrative control of OMKM, who actively support astronomy, both professional and amateur. But the area does have a number of lights, and there is regular vehicle traffic, even in the middle of the night. Thus I have been actively looking for other places.

Ready for Dark
The 18″ setup at 9000ft on the side of Mauna Kea
The area around the MK VIS is state land, under the control of the State of Hawaii Department of Land and Natural Resources. Just below the VIS is the start of a back road that almost entirely circles the mountain, R-1, also part of the Na Ala Hele trial system, a road designated for public access. Perfect! All I need is a place just enough out of the way to avoid any lights or activity in the night.

State land is an interesting issue in Hawai’i. No camping is allowed outside of designated sites, period. But, according to the DLNR administrative rules it is not camping unless you are… “in possession of a backpack, tents, blankets, tarpaulins, or other obvious camping paraphernalia, any time after one hour after sundown until sunrise in a forest reserve” (Section §13-104-2 Hawai’i Division of Forestry and Wildlife). I made certain I had no “camping paraphernalia” with me. I am merely picnicking… in the middle of the night.

Continue reading “A Very Dark Night”

Just a Little Nudge

One of the tasks I have helped with on the K1 AO Laser is aligning the Launch Telescope Assembly (LTA). This is not so much an electrical engineer’s task, but a mechanical one. So how did I end up with the task? Simple, I was present the first time it was done. Since the mechanical engineer who was first responsible has now left the observatory, I get the job by default. Just the way things work around here.

The launch telescope is a small telescope, about 0.5 meter in aperture, that projects the laser into the sky. Mounted behind the secondary mirror of the Keck 1 telescope, it must be precisely aimed to exactly the same spot in the sky the main telescope is aimed.

Launch Telescope Adjustments
Adjusting the mounting of the K1 Launch Telescope
The procedure is not all that difficult. Mount two dial indicators in place, restrain the motion by using wooden wedges or a really big c-clamp, loosen the bolts, make the adjustment, tighten the bolts. No problem, right? The challenge is to move the large assembly just a few thousandths of an inch and have it stay exactly where you want it while re-tightening the bolts.

In practice this adjustment is about one to two hours crouched in the secondary assembly of the Keck 1 telescope. Each time the bolts are tightened the assembly moves about 10-15 thousandths of an inch. Thus I have to guess how much to offset the measurement so it ends up correct when the bolts are tight. It takes anywhere from three to five repetitions to get right sometimes.

This is where I curse the mechanical engineer who dreamed up the mounting for the launch telescope. I look at the dial indicators, shift my stance against the cold steel to stop the cramping, loosen the bolts and try again.

The last adjustment was a mere 0.004″ (four one-thousandths of an inch) to move the pointing about 30 arc-seconds on the sky. I am now only about 10 arc-seconds from the optical axis. Keep in mind that a single arc-second is 1/60th of an arc-minute, which is in turn 1/60th of a degree. Ten arc-seconds is pretty good, but we want closer. Here I go one more time…

A Few Grams of Aluminum

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.

Keck 2
Looking into the optics of the Keck 2 telescope
Each 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.

Primary Gecko

In the tropical climate of Hawaiʻi small creatures are commonly found among one’s belongings. Spiders, centipedes, scorpions and more are a fact of life and can be found in anything that has not been carefully stored. Telescopes are often housed in the garage, particularly the large dobsonians that are too large to easily be carried into the house.

Primary Gecko
A gecko in the center of a 24″ telescope mirror
In the process of setting up telescopes at the Mana Kea VIS we found another critter that had sought a home. Upon unpacking the 24″ scope belonging to Cliff Livermore we were all amused to find a gecko atop the primary mirror when opening the cover of the box.

One can only imagine the poor creature’s predicament. A seemingly nice quiet, warm and dark place now subject to a great deal of motion and upheaval. Then the cover is removed to allow admission of cold mountain air. Hardly the safe refuge expected when the animal crawled into the box.

Primary Gecko
A gecko in the center of a 24″ telescope mirror
The discovery of this poor creature evoke an immediate response, a crowd of laughing humans quickly gathered round the mirror box.
It was notable that everyone’s reaction was the same. Not the revulsion that finding a cockroach or centipede would have caused in the same situation. A gecko is almost universally liked, the results were laughter and amusement.

Instead of being hunted down and squished, this gecko was carefully caught to be given a ride back down the mountain to the warm tropical climate of Waikoloa. The next day he was released into the new rock wall I am building in the back yard for a vegetable bed. With the voids among the rock, this wall is a perfect gecko habitat.

Telescope Maintenance

At the Mauna Kea Visitor Information Station telescopes are available every clear night for the public to enjoy the wonders of the night sky. Every evening a set of telescopes ranging from 102mm to 16 inches is setup in the patio beside the VIS. The gear is used heavily, every night of the year, the wear on the telescopes does exact a toll. The abuse is constant, kids hanging on the eyepiece, volunteer operators who have never used a telescope, rain, fog, blowing cinder dust. Conditions that were never foreseen by the designers and far beyond what most telescopes encounter. Sometimes the condition of the equipment is embarrassing, dirty eyepieces, groaning mounts that refuse to track, much of the gear just looks worn and tired.

Dirty Primary
An 8" telescope mirror covered with a ridiculous amount of dust
It is hard for me to see this, but at least I can do something about it, I do, after all, fix telescopes for a living. It is not unusual for me to spend an evening repairing a telescope and I have made a point of getting some more extensive maintenance accomplished.

My first effort last year was to clean and repair the small dobsonians used by visitors every night. Two eight inch, a six and a 4.5″ Orion dob are put out for anyone to use, from adults to children. After years of use they were in horrible shape, bearings and focusers were coming apart, collimation gone, moisture dissolving the woodwork, a finder attached with duct tape, the mirrors so covered with dust it is surprising there was much of an image to see. One of the eight inch scopes and the 4.5 inch were in pieces in the warehouse after a fix attempt by another volunteer. It took a few days of work to put all to right. Stealing parts from an older scope, repairing what could be saved, cleaning and pounding out a couple dents. Clean, re-install and re-collimate the optics. Four dobs back in service and in better shape than they had been in quite some time.

Losmandy Teardown
Parts of a Losmandy G-11 telescope mount spread across a table top
The 16″ Meade LX200 should be the flagship of the equipment used at the VIS. But for all too long it refused to work properly, it would not track. A trip back to the manufacturer failed to correct the problem, despite nearly a thousand dollars in shipping fees for factory service the telescope still would not work most of the time. Most volunteers would not use it, having given up in frustration. Surprisingly the issue was obvious, just listening to the scope indicated gears not fully meshed and grinding on one another. An hour’s worth of dismounting the scope, opening the bottom panel and re-seating a motor mount had the telescope back on sky and slewing from target to target. The scope has failed since, but the problem was even simpler, a loose connection found after a half hour of poking around.

Currently, one of the three Losmandy G-11 mounts belonging to the VIS is in my garage, spread across the table in many parts. I spent a few hours yesterday dismantling the mount and cleaning the grease and cinder dust out of the bearings. It is in pretty good shape, a good cleaning, re-seat the worm gears and some new clutch pads and it will be ready for a few more years of service. I need to get some more grease before I can reassemble the mount, but otherwise everything is ready to put back together. Finish this one and there are two more like it in sore need of maintenance.

One thing at a time, of course by the time I get through it all it will be necessary to start over again…

TMT versus Space Based Alternatives

There is an article on the TMT in yesterdays’s Honolulu Advertiser. While the article shows growing community awareness of the Thirty Meter Telescope project and puts forth some of the basics, it concentrates on some of the political issues. Those are, as typical for Hawai’i, rather fractious, showing the very polarized nature of political discourse in the state.

TMT Rendering
An overhead view of the proposed Thirty Meter Telescope, credit TMT Observatory Corporation
It is the comments that make the most interesting reading. These show the wide range of feelings in the community. There also seems to be a misunderstanding about the roles of large telescopes in general. The last two decades has seen an enormous advance in our understanding of the universe and its history. We now know the age of the universe, we have discovered planets around other stars, we have learned that ordinary matter makes up only a small fraction of the universe. These represent huge leaps in our understanding and these revelations have come, to the greater degree, from ground based astronomy. Many of these discoveries have been made, or greatly assisted, by the telescopes atop Mauna Kea.

One of the themes that popped up in the comments several times was the idea that space telescopes are where to put the money and the belief that ground telescopes were “obsolete’, thus projects like TMT are not needed. This could not be further from the truth. Yes there are advantages to space telescopes with respect to interference from the atmosphere. But space telescopes face several severe and inherent disadvantages.

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