Astrophoto Interference on Mauna Kea

Mauna Kea is simply a great place to shoot astrophotos from. Dark, clear skies with typically good seeing. Unlike some mainland locations there is a distinct lack of aircraft overhead. I am not sure how many shots I have had ruined by the bright anti-collision strobes crossing through the frame when shooting from locations in Arizona.

There are hazards to shooting photos here that do not commonly exist elsewhere. I was unpleasantly surprised when reviewing the take the next morning to find brilliant yellow lines through a hour and a half of exposures taken of the Cygnus region. The material is otherwise great, the makings of a nice shot, except for this one little issue. There are ways of suppressing artifacts like this when processing, but the beam is so bright I am not certain they will work all that well.

Worse, I checked the schedule, the offending laser is coming from Keck 2 AO, a system I work on.

The observatories have a system in place to deal with this issue. There are four operational lasers on the mountain, Keck 1 and Keck 2, Subaru and Gemini. Each optical observatory using a laser maintains a server that posts their laser location, status, and calculates the position of each beam in the sky. This can be queried by the other observatories to check if the beam crosses the field of view. A set of rules has been negotiated to determine who has right of way, usually who is on target first.

Obviously this computer system does not take into account my little telescope shooting photos from Hale Pohaku. If I had known I could have called Heather and asked her to shutter her laser, I was on target first. Being the kind soul she is, she would probably laugh with me.

Cygnus and Laser
Rough processing of a single frame, Cygnus region, with the Keck 2 Adaptive Optics laser crossing through the frame

Private Foundations Fund New Astronomy Tool

W. M. Keck Observatory press release

The W. M. Keck Observatory has been awarded two major grants to help build a $4 million laser system as the next leap forward in a technology which already enables ground-based telescopes to exceed the observational power of telescopes in space. The new laser, when installed on the current adaptive optics system on the Keck II telescope, will improve the performance of the system and advance future technology initiatives.

First Target of the Night
The Keck 2 AO Laser attempting the first target of the night with the light of sunset and a setting Moon behind
In early July the Observatory received a $1.5 million grant from the W. M. Keck Foundation, adding to a $2 million grant from the Gordon and Betty Moore Foundation awarded eight months prior for the multi-year project. Keck Observatory is charged to raise the remaining funds needed from its private supporters over the next two years.

“Ever since Galileo, astronomers have been building bigger telescopes to collect more light to be able to observe more distant objects,” said Peter Wizinowich, who leads the adaptive optics developments at Keck Observatory. “In theory, the larger the telescope the more detail you can see. However, because of the blurring caused by Earth’s atmosphere, a 10-inch or a 10-meter telescope see about the same amount of detail.”

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Transponder Based Aircraft Detection

When you shine a powerful laser into the sky, someone is likely to notice.

That someone is likely to be the Federal Aviation Administration, who, for some reason, seem to be concerned about the possibility of our illuminating a passenger airliner with an AO laser.

Both Keck lasers in operation
Both the Keck 1 and Keck 2 lasers in operation under a nearly full Moon
We currently use laser spotters to insure this does not happen. Yes, some poor soul must sit outside all night long and watch the skies for aircraft near the beams. When the weather is nice this is not a problem. It is seldom that nice, a bitterly cold wind is the usual condition. I have done this duty, for about an hour, and really do not need to do it again. After a night in the cold, is a person really an alert observer? An automated system that removes the human element from the equation is really a better solution.

Enter TBAD, the Transponder Based Aircraft Detector. All commercial and most civil aircraft carry a 1090MHz ADS-B transponder that identifies the aircraft and provides basic data. The transponder is part of an aircraft tracking system now used by air traffic control centers around the world to supplement, or in some cases replace, radar systems. An idea… Create a directional antenna that can determine if a 1090MHz transmitter is in the beam of the antenna and mount that antenna to the telescope. With such a system we can detect an aircraft approaching our beam and shutter the laser. The idea was conceived by Tom Murphy and Bill Coles at the University of California San Diego. Thus TBAD can alternately mean Tom and Bill’s Aircraft Detector.

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Laser Return Photometery

A different use for amateur astrophotography gear.

An amateur CCD camera can do more than take pretty pictures. There is no reason why any decent telescope, however small, and a CCD camera can not be used to do real science, or real engineering in this case.

The goal of the night was to perform proper photometry on the laser returns with independent equipment. We want to quantify the performance of the Keck adaptive optics laser systems. We launch two powerful lasers into the sky, one from each telescope, to allow analysis of the atmospheric distortions through which the telescope is observing. Using the data the system can correct for this atmospheric distortion and create much sharper images of distant stars and galaxies.

The lasers pass through a layer of sodium atoms about 90km (55miles) above the ground. There the 589nm yellow light excites these sodium atoms creating a glowing beacon, what we call the laser return. This return is what we look at to analyze atmospheric distortion. A brighter return allows better data and better performance of the system.

Both Keck lasers in operation
Both the Keck 1 and Keck 2 lasers in operation under the light of a nearly full Moon

Amateur astrophotography gear is perfectly capable of doing this task. A portable telescope, a proper CCD camera, combined with care to acquire calibrated images. All that I needed to add to the setup was a photometric V filter.

It was a perfect night for it, clear, dry and cold. Best of all, there was no wind to bounce the telescope around and chill anyone working outside. The winds are nearly constant atop at 14,000ft peak, calm nights are unusual, I was lucky indeed.

I setup the telescope atop a crust of ice and snow. The snow was convenient as it allowed me to set down gear on a cleaner surface than the gritty volcanic cinder underneath, keeping everything quite a bit cleaner. The altitude and cold made setup and breakdown a slow, laborious process, and added unique difficulties. I had to be very careful moving the heavy gear, so as not to slip on the icy snow. When I went to move the telescope tripod I found it frozen into the snow and cinder! I had to heave hard to break it free.

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Yeah, It Was One of Those Days

Can anything go smoothly? Please?

A simple job. Get an 80 pound optical interferometer back under the bench. Nothing like two guys setting the thing on my chest so I can worm my way underneath and heave this beast back onto it’s shelf. Then we have to bolt the fold mirror back in place, another thirty pound piece of awkwardness, just hold it in place to get the bolts in. I hold while Olivier tries to thread the bolts. We also have to replace the pellicle, a bit of ultra-thin optical film that will break if you touch it. Then there is an hour spent aligning the thing. chasing my tail trying to get a properly centered image of the deformable mirror. Sometimes optical alignments just go that way. I finally got a decent image, just to learn there was some vibration in the system. I adjusted some shims to reduce the issue, but there is more to be done.

Much of the remaining day is spent troubleshooting a simple optical shutter in the K1 laser. It fails to completely open. When it fails the safety system detects the failure and shuts down the entire laser. A couple hours of checks later has me convinced that the hardware is working, more or less. The design could have been better. The critical issue is the tight timing requirements. The circuit expects the mechanical shutter to actuate in 50ms, it used to, but as it has been used for a few years, it doesn’t any more. Why they did not simply allow a few hundred milliseconds I have no idea, dumb design, there is no issue with a longer timing window.

One of those days
One of those days on the summit in the K1 laser enclosure
Of course I can not simply change the timing. It is hard coded into a Xilinx CPLD. Give me a few days to setup the Xilinx software, another day or two to understand the code, then maybe I could fix it. I have one day, then the laser is scheduled to be on-sky. Great, time to use my hacking skills to dream up a solution in one day… Tomorrow.

There is a camera in the laser enclosure. We use it for tele-presence. As I worked, Pete, our laser engineer, was on the phone assisting from headquarters. He could run the software remotely and watch as I probed the system to measure the timing. Unbeknownst to me, Pete saved a couple images from the camera and sent them to me. The photo does reveal the day I was having. Thanks Pete… I think.

Lasers and Aircraft

Those of us who use green lasers for astronomy outreach are always worried about law enforcement cracking down on these devices. As the lasers get cheaper and more available they inevitably get into the hands of those who do not use them responsibly. Worse, the lasers are easily available at power levels that are truly dangerous.

Laser and Stars
Deb pointing out the star βPhoenicis to VIS volunteer Joe McDonough
The problem has continued to escalate, each year there are more reported incidents of aircraft being illuminated by the laser of some idiot (yes, the correct term) who thinks it might be cool to tempt fate and the law. In 2010 there were 2836 incidents reported to the FAA, up from only a few hundred a few years before. With this sort of trend it seems inevitable there will be some sort of official reaction.

Illuminating an aircraft with a laser can be prosecuted under federal law. Not because there is any specific statute addressing lasers, but as it is deemed “Interference with a Crewmember” using an interpretation of a pre-existing 1961 federal law, specifically 14 CFR 91.11.

The FAA has put together a new webpage on lasers and aircraft safety. The page organizes and links some informative resources. This includes a couple reports on the possible effects of laser illumination on aircraft crew, as well as the legal and regulatory recommendations of the FAA. I urge anyone who uses these devices to follow the link and do a little reading.

Used responsibly these lasers are extraordinarily useful in astronomy education. Nothing grabs the crowd’s attention so quickly as that brilliant green beam. Everyone can follow along without confusion as objects are pointed to across the sky. From the constellations to the Milky Way, satellites, planets and zodiacal light, on to star clusters and galaxies, everyone knows right where to look. I do prefer lasers in the 20-30mW range, bright enough to be seen by a crowd, even under moonlight. Not powerful enough to easily injure in the case of a brief exposure to the beam.

Postcard from the Summit – Laser Panorama

Assembling panoramas properly is not a trivial exercise. I have been attempting to master a program called Hugin and may have achieved some modest level of competency with it. It is surprising complex, and extraordinary powerful. Even more impressive as it is free software. Properly mastered it allows correction of tip, tilt and yaw in the camera, lens distortion, even translation of the camera’s position in x,y, and z. The task is made even more complex if the scene changes during the sequence, which is inevitable during the fifteen minutes it takes to sweep a moonlit scene on the observatory roof with one minute exposures. The stars move, the telescopes move, while I try not to shiver uncontrollably in the bitter wind.

Laser Panorama
A moonlit panorama from the roof of Keck during a night of laser engineering

Laser Susan

The old saying “Necessity is the mother of invention” has a certain truth to it.

In this case the necessity is created by the conditions. Sub-freezing temperatures, bone chilling wind, and the need to be outside under these conditions. The summit of Mauna Kea can be downright miserable for mere human beings. Yet, in order to operate the laser, someone has to watch and insure we do not illuminate some passenger aircraft on the way to Australia.

Thus we have laser spotters, a hardy crew indeed. Braving the conditions, spending hours watching the sky to insure we operate safely. We are attempting to introduce technological solutions to the problem. The FAA however is an extraordinarily conservative organization, rightly so when hundreds of lives are at risk on any given flight. It takes time, many years, to approve another method of insuring safe laser operation.

It is a cold job. I have done it for a few hours, just enough to instill a real respect for the guys who do it all night. You bundle up in many layers of insulation and attempt to get comfortable in a position that allows observation of the area of sky around the beam. Given the heavy clothing it is a pain to simply sweep the sky, and completely reposition each time the telescope changes target.

Given the problem, Doug Macilroy, one of our intrepid Keck crew, saw a solution. It took time, and a number of prototypes to get it right. But he now has a neat way to stay comfortable and warm while scanning the sky. Now we have the “Laser Susan”!

YouTube video for the Laser Susan