Wouldn’t it be interesting if camera sensors could see more of the light spectrum than our eyes could see? It would open up whole new worlds to our eyes, worlds that have been heretofore unseen and unexplored, and yet they’ve been right under our noses all along.
Tag Archives: research
Chasing RFI Waves – Part Seven
Here is part seven (the final part) of my non-fiction work about the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia. You can also read parts one, two, three, four, five and six.
The NRAO fleet
The cars used on the NRAO campus are different from what you might expect. You’ll see photos of them below, and in case you’re wondering why they look so old, let me explain.
Gasoline-powered cars generate more RFI than diesel-powered cars because they have spark plugs. That meant that NRAO had to purchase diesel cars when they bought their original fleet, and by the way, these cars are part of that original purchase. When NRAO wanted to renew their fleet, they found out they couldn’t, because the newer diesel-powered cars on the market were all using chips and various other electrical equipment (seat belt buzzers, door buzzers, etc.) that generated unwanted RFI. Any electrical ark (spark plugs, power lines, bad thermostats, etc.) generates broadband radio signals, at various frequencies throughout the spectrum but mostly at the lower frequencies, below 2 GHz or so. So that meant they had to stick with their original fleet, whose diesel engines used no computer chips whatsoever and generated little RFI. You may look at these cars and call them clunkers but to NRAO technicians and scientists, they’re reliable modes of transportation that do not interfere with their research.
You may see newer cars in the parking lot, but they’re not used on campus. Only these blue diesel cars can go under and around the telescopes without causing problems.
Because they have no new technology to warm up the engine block on cold mornings, they keep them plugged in whenever they’re parked, to make sure they can be started right away and to keep down on the wear and tear on the engines.
We were ferried around the NRAO campus in one of these cars by Mr. Sizemore, and they’re quite comfortable.
One thing I can’t get used to in these old cars is the gear shifter. It’s so long and seems so awkwardly placed…
More on the telescopes
One of the telescopes on site is used as a teaching instrument. NRAO, being involved in both research and educational efforts, brings groups of school-age children on-site to teach them about radio astronomy. The telescope is not a fancy, cryogenically cooled machine but a simple wire-mesh dish with simple control and monitoring gear that the kids can play with. It’s fully functional though, and it does pick up many radio waves. It’s sufficient to teach radio astronomy and galactic coordinate systems and such.
The National Youth Science Camp is just up the road from NRAO. For two weeks each summer, groups of teachers (high school and college) come to NRAO for an intense course in radio astronomy. The staff turn on the knowledge firehose and “really pour it on them”, as Mr. Sizemore puts it. They have classes during the day and then do research at night with the telescopes. He says it’s not unusual at the end of two weeks to see them walking around the campus, muttering to themselves.
After they complete the course, they can bring their own students to NRAO (for a day or so) and use the 40-foot learning telescope to teach them about radio astronomy without much intervention from NRAO Staff.
As the young researchers sit and wait by the telescopes for the stars to come into position, they have nothing to do, so they doodle or draw. Sue Ann Heatherly, the NRAO Education Officer, loves to collect the better ones and she puts them up on the walls of various NRAO corridors.
As we drove around, Mr. Sizemore pointed to a dish and told me it was a polar mount, and that I will never see a dish built like that again. It’s mounted on the plane of the galaxy (Milky Way) not the earth coordinate system. It’s a right ascension and declination mount. If you were to stand on the axis of the telescope and look at the sky, you would be looking directly at Polaris, the North Star. (By comparison, the GBT (Green Bank Telescope) is mounted as an elevation and azimuth drive system, which is an earth based system. ) The reason this telescope was built like this in the 1950s is because computer power at that time wasn’t fast enough to translate between the coordinates of the galaxy and the solar system in realtime. Now even a pocket calculator can do it.
Although the telescope has been sitting unused for 10 years, they recently brought it back online in order to do atmospheric research studies with MIT. The study involves bouncing radio signals off the satellites around the Earth, then measuring those signals to see how they were perturbed by the atmosphere. The MIT researchers brought their own trailer on-site, with their own receiver and computer equipment. After some work mitigating RFI leaks from the trailer, they were ready to go and NRAO was happy to see the telescope back in action.
When it comes to the GBT (Green Bank Telescope) one of the things NRAO doesn’t want to do with such a large telescope is to set up vibrations in the structure when it’s started and stopped. The way they handle that is to mount both forward and reverse motors at each drive wheel. In order to stop or start it, all the technicians have to do is to increase the current on the motors that move in the direction they need, and the structure will stop or start as fast or as slow as they want it. When you think about this and other precision equipment mounted on the dish, like the laser leveling equipment and the motors that power each plate in the dish, Mr. Sizemore likened the GBT to “building a battleship with the precision of a Swiss watch”.
Even the track of the telescope is leveled to within 1/5,000th of an inch, and the rest of the structure is comparable to that all the way up. What about the land settling over time, I asked? There are no such problems, he replied, because they went all the way down to bedrock when they laid the foundation (about 40 feet).
The local cement contractor had no competition when it came to the contract for laying the foundation. The closest competitor was about 40 miles away, on the other side of the mountain, so he got the contract and had to rent three additional cement mixer/pouring trucks in order to keep up with the demand. For the entire period (three or four weeks) that it took to pour the foundation, the man kept grinning as his trucks pulled into the construction site, because he stood to make a lot of money.
The NRQZ monitoring station
While I was on-site, Mr. Sizemore showed me his “hiding place” – his monitoring station. It’s a big trailer that can be hauled from place to place, but has been made stationary and hooked up to the power lines. That’s where he does most of his work. Here he monitors the gross violations of the Quiet Zone and also looks at the local environment: powerline noise, illegal use of radios, etc.
For example, at the time of my visit there, the amateur radio bands were being used improperly by a group of people and the signal was strong enough to overload the 140-foot telescope, so it became a serious problem. Wesley told me that the problem will likely be taken care of long before I write up about it, and the likely action taken will be that he calls the FCC in to enforce the rules in place. After 20 years on the job, Wesley has built up a network of contacts he can call upon when he needs help. One of those contacts is the man in charge of the Enforcement Bureau at the FCC, whom Wesley knew when he was still a satellite technician.
While I was recording our talk, I asked Wesley if he could see the interference generated by my recorder, and he worked up a quick setup to find the noise it created. Sure enough, he tuned into the noise generated by my iPod as it was recording our conversation within a couple of minutes.
One of the teaching tools he uses with school groups that visit NRAO is a metal trashcan (a Faraday cage with an antenna and amplifier mounted inside the lid). He takes his spectrum analyzer, connects it to the antenna and amplifier assembly, then gets a student volunteer to put in their phone or laptop or MP3 player, then he shows the whole group the interference those devices create. The only thing the antenna sees is the RFI generated by the device put in the trash can, because it’s a Faraday cage. Everyone is invariably wowed by this.
As we drove around the NRAO campus, we came across a car with a “cantenna” (a directional waveguide antenna for long-range WiFi), and I immediately pointed it out to Mr. Sizemore, as I knew he’d be on the lookout for WiFi transmissions in the area. Smirking, he admitted that was his service car, and he told me the story behind it. The FCC had donated it to NRAO, who had been using it to sniff out illegal transmissions. The car actually had antennas built into its roof and was already fitted with equipment for sniffing out radio transmissions. Mr. Sizemore outfitted it with WiFi “sniffing” equipment as well: a laptop with NetStumbler and a bunch of other apps, a GPS device for marking the location of RFI-causing WiFi and a “cantenna” on the roof, that he could rotate and point at various WiFi sources.
Before retiring from NRAO (years after my interviews with him), Mr. Sizemore outfitted a new Dodge Ram extended cab truck as an RFI vehicle, a feat which was written up in USA Today.
NRAO and the community
As we drove around the campus, Mr. Sizemore pointed to the farmhouses that surrounded NRAO. When the government took over the land, they invoked the right of imminent domain, forcing the farmers to move. That generated animosity toward the observatory, because the land was fertile and it was good for farming.
With time, things got better, to the point where there was only one farmer left who couldn’t stand NRAO and wouldn’t ever let them step on his property. All of the powerlines and phone lines for NRAO were routed around his property. At one point, the man chased Mr. Sizemore’s predecessor off with a stick. If NRAO staff ever had to go visit him, they’d take a deputy sheriff with them. When Mr. Sizemore began working there, he knew to steer clear of the farm.
One day though, he got a call from the man. He had an outside TV amplifier, a tube-type amplifier made by a company called Blonder-Tongue, which had been struck by lightning. The old man couldn’t find anyone to repair it and he didn’t want to spend money to get a new one. He called the only one whom he knew could help. Mr. Sizemore was of course glad to do it, because he’d finally be able to atone for the bad blood between NRAO and the farmer.
He drove out to the man’s place, where he had to wait off the property for the amplifier to be brought to him (he still wasn’t allowed on the farm) and took it back to the lab to see what he could do.
He called Blonder-Tongue and was told they hadn’t made that amplifier model in 20 years, and they hadn’t serviced it for 10 years. They didn’t think they could help. Mr. Sizemore insisted he speak with a supervisor and as luck would have it, the repair supervisor was an elderly guy who remembered working on them when he’d started with the company. He said, “Send it to me, and I’ll show these young technicians how things used to be.” Mr. Sizemore explained the entire situation to the man, about NRAO and the farmer, then mailed off the amplifier to the repair supervisor.
The amplifier came back repaired and it didn’t cost anything either. The old farmer was elated when he got it back. He put it back up and everything was fine until a week later, when he called Mr. Sizemore. You know the old saying about lightning not striking twice? Not true for the old man. His amplifier had been struck again.
He didn’t want to let Mr. Sizemore examine his property, to see if the lightning strikes could be prevented, so all he could do was to mail it off to Blonder-Tongue once more. Sure enough, it came back repaired as new again, at no charge. Thankfully, to the day of the interview, the amplifier evaded other lightning strikes so things were fine between NRAO and the old man.
Thanks to Mr. Sizemore’s efforts, NRAO enjoys a very good relationship with the community. Being an isolated rural community, where all they have is each other, they tend to pull together and help each other.
For example, some people had learned to recognize the interference from awry TV amplifiers, which would show up as a herringbone pattern on their sets, and would call Mr. Sizemore to let him know. They also knew what powerline interference looked like, because it would show up on their sets once again, generating a specific noise pattern.
The NRAO site is basically a wildlife preserve. They let the animals live and roam free. The only practice they instituted a few years back was a controlled deer hunt, because the deer population had gotten out of control. Before they began, the Wildlife Management Institute wanted to do a headcount of the deer, so they fitted a plane with thermal imaging equipment and started to fly over the NRAO site one night.
Because they hadn’t publicized this, the local people didn’t know what was happening and all they could see was a plane which kept circling over NRAO at night. They thought the plane was in trouble, so they all pulled together, drove to the local airport (next to NRAO) and shone their headlights on the landing strip, to help it land. Well, after a while, they figured out the plane wasn’t in trouble and went home, but let’s just say that the next time WMI decided to do nighttime wildlife studies, they publicized it widely, to make sure everyone knew what was going on.
The NEACP encounters
As we talk about flyovers, another good story is that of the NEACP encounters. When the Cold War was going on, the US Military always had an aircraft in the air at all times, an airborne command post (NEACP: National Emergency Airborne Command Post). There were multiple such aircraft in service and one was in flight at all times. One would take off before one would land.
When they would fly over NRAO, all the radio equipment on board those planes (they used 1,000 Watt transmitters) would overload NRAO’s equipment with RFI. Mr. Sizemore found the number for CMOC (Cheyenne Mountain Operations Center) and spoke to one of the people involved with NEACP. He introduced himself and said, “You have this aircraft, using this callsign, operating at this frequency, at this location.” They got upset right away, because they didn’t want anyone to know what their routes were. They started questioning Mr. Sizemore about the source of his information, to which he simply replied, “I used a 300-foot telescope and I looked at your aircraft.” Then he continued to explain: “I have to track this source of interference down. That is my job. I have a solution. Let me send you my observing schedule every month, to tell you what frequencies I’ll be observing on what days and tell you my station, and then you’ll be able to avoid me. And if you can’t avoid me, you can let me know, and I’ll tell the astronomers to take a coffee break.”
As a result of that phone call, Mr. Sizemore got the NEACP to avoid the Green Bank area, and when they couldn’t avoid it, he got a few calls from them when they had to pass over NRAO, after which he would quickly tell the astronomers to take a break, as their equipment would soon get overloaded, making the data unusable.
That’s the end of part seven and the series. As mentioned at the start, this work is unfinished, and that’s why you don’t see a nice story arc with good closure, but I hope that what I’ve published has proven enjoyable and interesting for you and has sparked your interest in radio astronomy and NRAO. You can also read parts one, two, three, four, five, and six.
I’d like to once again thank Wesley Sizemore, without whom this text would not be written (or edited properly). Thank you Mr. Sizemore!
Thank you for reading!
Chasing RFI Waves – Part Six
Here is part six of my non-fiction work about the National Radio Astronomy Observatory in Green Bank, West Virginia. You can also read parts one, two, three, four, five and seven.
The NRAO site is around 2,700 acres. It runs along the crest of the adjoining mountains. One big current problem, that will only get bigger in time, are wireless routers folks are starting to use in their homes. Mr. Sizemore has actually gone out and identified every wireless router in the area. At the time of writing there were 45 such routers.
The NRQZ (National Radio Quiet Zone) gives the NRAO the right to file comments to the federal frequency regulation bodies (FCC and NTIA) for permanent, fixed, licensed radio transmitters wishing to be installed in the NRQZ. The NRAO does not have any “power” to regulate radio use. However, the FCC and NTIA “determine”, in most cases, that it is in the public interest to uphold the NRQZ protection requests. However, there is a West Virginia state law that provides protection within a 10 mile radius of a radio telescope from any source, licensed or unlicensed, that causes interference. A wireless router, like a garage door opener, is an unlicensed device and thus falls under the state law.
Still, each case of interference has to be treated individually, and it is in everyone’s interest that it’s resolved it in a friendly way, for the sake of community relations. At the time of writing, Mr. Sizemore was working with the NRAO lawyers and local legislators to see how the problem of wireless routers could be addressed. They’re a real problem when it comes to interference, and they’re unlike past problems, where faulty equipment was to blame, which could be fixed or replaced. Well-functioning routers will emit interference and cause significant problems to NRAO’s daily work.
Of the 45 routers mentioned above, 26 were provided by the local telecommunications company to their customers free of charge, with the contract, so they could be removed by the telecommunications company itself. The rest were privately owned, and NRAO was naturally pursuing a voluntary removal approach with the router owners.
In the office space above the control rooms are the offices of the scientists and staff at NRAO. It’s a long hallway, part of the new construction, cleanly carpeted. The walls are filled with research posters.
Mr. Sizemore and I stopped to talk about one of the posters. Before, folks thought of the galaxy as a fairly uniform soup of fog. With the GBT (Green Bank Telescope), Jay Lockman, one of the senior scientists at NRAO, was able to discern that this fog was more like clouds. To the layperson, this may not seem like a lot, but to astronomy, that’s a big piece of the puzzle. Now they can try to figure out how the clouds work, what they’re made of, how they move, etc. This discovery could not have been made until the GBT was online.
As we continue to walk, one side of the hallway draws particular attention. Framed photos of the various Jansky lecturers are mounted there. Every year one is chosen, and he gives a lecture on a subject of his choosing. A lot of them are Nobel prize winners. Grobe Rieber was one, of course. Frank Drake (the Drake equation) is also one. Arno Penzius and Bob Wilson are also on the wall. They are Nobel Prize winners for their early work on background microwave radiation. They are the two scientists that discovered background radiation.
There’s an interesting story behind their work. In October of 2005, Mr. Sizemore met the technician who did the hands-on work for their experiments. The man and his wife visited NRAO one day, and Mr. Sizemore showed them around. The man acknowledged that he was scared for his life at times, as he worked with them. They had no sense of the practical or common sense, and would often ask him to do very dangerous experiments. Penzius, for example, could not figure out how to unbuckle his seatbelt. The technician had to do that for him. He couldn’t figure out how it worked, and yet he won a Nobel prize for theoretical work in physics!
Mr. Sizemore showed me his old office, the Quiet Zone office. That’s where the administrative work for the NRQZ is done. He used to be responsible for that, but he’s thankfully gotten help in that area in late 2005, when NRAO hired an NRQZ Administrator and let him focus more on chasing down interference. While he was in that office, he conducted more than 10,000 propagation studies. Paulette Woody, the new NRQZ Administrator, started on the 17th of October, 2005.
As we drove on the NRAO campus, Wesley stopped to show me his “hiding place” – his monitoring station, where he does his RFI hunt-work. It’s a big trailer that can be hauled from place to place, but has been made stationary and hooked up to power lines. Here he monitors the gross violations of the Quiet Zone and also looks at the local environment – powerline noise, illegal use of radios, etc. For example, at the time of my visit there, the amateur radio bands were being used improperly by a group of people and the signal was strong enough to overload the 140-foot telescope, so it became a serious problem. Wesley told me that it will likely be taken care of long before I write up about it, and the likely action taken will be that he calls the FCC in, to enforce the rules in place. After 20 years on the job, Wesley has built up a network of contacts he can call upon when he needs help. One of those contacts is the man in charge of the Enforcement Bureau at the FCC, whom Wesley knew when he was still a satellite technician.
Depending on the sorts of studies performed, the data collected by NRAO in a single day can get to be as much as 50 GB (nowadays it’s probably more than that). The data is usually written to LaCie portable drives and either handed out or shipped out to scientists responsible for the studies. The data isn’t archived locally. It’s recorded for the individual astronomers. Once it’s shipped out, it’s someone else’s data and they are responsible for it. If they lose the drive containing the data, they need to re-run the study. NRAO simply doesn’t have the money or the staff to act as a data warehouse for the data. Astronomers, like most scientists, also guard their data quite jealously and consider it proprietary until they decide whether they can publish it.
The sewer system on site is unique. Because NRAO has to worry about interference, they didn’t want any pumps on-site. What happens is that waste fluids from the sewer system flow into a series of sediment ponds that are built on a gentle slope. They are gravity-fed and include absolutely no motors. NRAO actually won an award for this design. As the water flows through the ground from pond to pond and through vegetation, it gets purified and is ready to be discharged into the adjoining streams of water.
The telescopes and their research
Mr. Sizemore had a story to tell about the motors that run the individual plates of the GBT. NRAO ordered a few samples, saw they worked alright, then ordered a whole batch, about 1,500 or so. When they started to do live testing, the motors ran out after a few days. They opened one up to see why and discovered that the carbon brushes were completely burned out. They’d disintegrated. Upon contacting the manufacturer, they found out that he’d switched the type of carbon brush from the harder ones they specified to softer brushes, which were a few cents cheaper per brush. They were basically cheating NRAO. NRAO’s Business Office sent back all the motors and had the brushes replaced. Add to this experience countless similar others over the years and one can see why they’re wary when dealing with contractors and manufacturers.
There are other radio telescopes on the NRAO Campus, all of which are involved in ongoing research. For example, the 45-foot dish is doing a project on solar radio burst spectrometry. They’re looking at the Sun and measuring the bursts of radio noise from it (solar flares and the like).
They also have calibrators, which are rock-solid sources of radio waves. They always emit at the same frequency and strength. Researchers point their equipment at them to see if their equipment is reading correctly and make any needed adjustments.
One of the telescopes on site is used as a teaching instrument. NRAO being involved in both research and educational efforts, brings groups of school-age children on-site to teach them about radio astronomy. The telescope is not a fancy, cryogenically cooled machine, but a simple wire-mesh dish with simple control and monitoring gear that the kids can play with. It’s fully functional though and it does pick up many radio waves. It’s sufficient to teach radio astronomy and galactic coordinate systems and such.
The fastest telescope at NRAO is a 20-meter dish which will go from horizon to horizon in 90 seconds. It’s not being used at the moment. In the past, the most popular program at NRAO was universal time and polar motion.
Time is not a naturally occurring thing. It’s a man-made contrivance. Time is nothing more than your position relative to something else at a given instance. We keep time by the rotation of the earth on its axis, and the rotation around the sun. Einstein said time is all relative depending on your motion and such. In order to keep accurate time, not only do we have to know the rotation of the Earth on its axis and around the Sun, but we have to know the wobble. Because the Earth is a spinning body, just like a spinning top, it tends to wobble.
There’s a plaque next to the telescope, with a plot of the position of the North pole of the Earth over 5 years. You’ll see that it wonders around, it doesn’t stay in one place. In order to have accurate time, we must know what that wobble is. How do you do that? There are quasars. They are quasi-stellar objects. We think they’re the black holes at the centers of galaxies. They’re very far out there, and they’re very strong, so they can act as a point source. Even though the distance to them is enormous and they’re moving relative to us, because of that distance to them, their movement is insignificant compared to the movement of the Earth itself. When we look at those quasars and we see any apparent shift in their position, we can determine what the Earth’s wobble is. That’s a use of radioastronomy that most people can grasp: timekeeping.
NRAO used to conduct regular time studies. Wesley actually started out at NRAO as an interferometer operator. The program running on the interferometer at that time was the universal time and polar motion. They fed that data into the master clock of the Naval Observatory. If you’ll remember, at the end of 2005, there was some discussion in the news because a leap second would need to be added to clocks. Wesley would take out leap seconds from atomic clocks. It would be done over time, with microsecond increments. NRAO was a major contributor to time-keeping for the US.
We can use those same quasars to monitor tectonic plate movement, geodesic work. This is also documented on a plaque there. There are several major tectonic plates on the Earth’s crust. If you put a radiotelescope on one plate and one on another plate, then look at a quasar, any apparent shift in their position will be due to the movement of the crustal plates. That means we can use radio astronomy for geodesic-type work.
The Howard E. Tatel Telescope was also the first telescope involved in the search for extra-terrestrial intelligence. Dr. Frank Drake, working on Project Osma, used it for his studies. That sort of work isn’t done by NRAO anymore. It’s not part of their primary mission. Now this sort of work is done through private organizations like the SETI (Search for Extra-Terrestrial Intelligence) Institute in California. You, dear readers, can participate in the study if you want, by downloading an application that will let your computer crunch through the data gathered from space in the search for signs of ET intelligence. The processing power of your computer will only be harnessed when your screensaver is active. This is a good example of distributive computing, where the power of many varied computers is put to work on a single task.
The HET Telescope is not being used currently. It’s part of a three-element interferometer. The second element is another 85-foot dish on the NRAO site, and that’s now used to do pulsar studies.
What are pulsar studies? Well, it starts with the sun, which is supposedly a fairly old star. It is hypothesized that in a number of significant years in the future (we’re talking billions), the physical nature, the make-up of the sun will start to change. It will collapse and throw off its outer shell, being left with a big hot center called a white dwarf. Now, if you have a star that is several times larger than the sun, like 6-8 times, when it’s in its death throes and its gravitation collapses, it blows off the outer shell, the nucleus will collapse to a very dense neutron star. A typical neutron star is several miles in diameter.
If we were to compare what’s going to happen to the Sun in Earth-terms, It’s like collapsing our planet to the size of a golf ball. A teaspoon of that sort of matter will weigh hundreds of thousands of tons. It would have an enormous magnetic field, so the only radiation that will escape from that neutron star will be through the poles of the magnetic field. Since the rotational axis and the magnetic poles do not have to align, the star could be spinning on its axis and the magnetic fields could be perpendicular to that axis, so that it will act as a sort of magnetic lighthouse. Every time it will sweeps its magnetic pole in the direction of the Earth, we will get a pulse of energy, hence the word pulsar.
Why are pulsars interesting? Because the spin of certain pulsars is as accurate as we can time it with an atomic clock. What’s a second? 1/60th of a minute? No! It’s over 9 billion vibrations of a Cesium electron at a certain pressure and temperature. That’s the official definition. The pulsars that NRAO looks at spin at millisecond time intervals. A big research topic now is using the timing of pulsars to prove gravitational waves.
There are certain time standards kept in cities throughout the world, such as Paris, Moscow, DC, but they are susceptible to destruction from natural or terrorist events. With pulsars, we have out of this world time standards that cannot be destroyed. They also serve as perfect navigational beacons, if we will ever do space travel.
The question that’s been asked in the past is, why don’t pulsars slow down? Well, they exist in binary pairs, two of them orbiting each other. Our Sun is an oddity, because it’s alone out there. There can also be trinary star systems, but gravity usually kicks the third star out. You know what they say, three’s a crowd… So, these pulsars are in binary orbit with other stars like red giants, white dwarfs, or other some such thing. They feed off the energy of their companion, and they don’t slow down, they stay in a constant rotation, or at least as constant as we can time it.
There are platforms out in the field at NRAO. They’re actually crossed dipoles. One of the big questions in astronomy is reionization. The dominant theory of the creation of the universe is the Big Bang. When it occurred, that primordial soup was extremely hot, so everything was fragmented into elemental particles, such as quarks, muons, etc. As things cooled down, particles came together and created molecules, then stars, etc. When the stars started to fire up and generate ultraviolet light, they re-fragmented some of the elemental hydrogen left over from the big bang that had not yet coalesced. That hydrogen was re-fragmented to its elemental particles, and sometime later, it re-congealed. NRAO is looking at that reionization process. They’re looking at this cycle of heating and cooling that takes places as the universe expands. Don Backer, one of the astronomers at NRAO, is looking at that extremely red-shifted signal (meaning very big waves) to see if he can determine when the heating/cooling cycles occurred. The signal is somewhere between 125-226 MHz. They’re not sure where that signal is and what frequency they’ll find it at, so they’re hunting background radiation at the moment, trying to discern a “flashlight in a floodlight”. When they do find it, it’ll be interesting.
One of the things you’ll notice at NRAO is that there are no powerlines on-site. All of the power cables are underground. There’s a main cable that feeds the site, which NRAO runs through a generator where the power is conditioned, mostly in its frequency. The cables that run to each building are all buried. It’s easy to understand why. They don’t want any arcing of power lines above ground.
A couple of years back, one of their lines went dead and they started digging around, looking for the cause. It turned out to be a black snake which had crawled across two contact points and shorted itself and the lines. He was still there, unable to move, because he’d been fried!
And that’s the end of part six. You can also read parts one, two, three, four, five and seven.
Chasing RFI Waves – Part Five
Here is part five of my non-fiction work about the National Radio Astronomy Observatory in Green Bank, West Virginia. You can also read parts one, two, three, four, six and seven.
Senator Robert Byrd
Senator Byrd (1917-2010) was a consummate politician. He was from a very poor state – West Virginia. He served in the Senate for over 50 years. He was the longest-serving senator and the longest-serving member in the history of the United States Congress. While in office, he used his seniority to help his home state. As such, there are a lot things in West Virginia named after him. He was directly responsible for obtaining the funding for the GBT.
The actual shovel used during the groundbreaking ceremony for the GBT by Senator Byrd is encased in a display box in one of the NRAO lobbies. If you happen to see it and notice it’s a bit short and also very shiny, here’s why: Senator Byrd used a normal, brand new shovel at the ceremony; afterwards, NRAO chromed it and also had the handle shortened, so it could fit in the display case.
I’ll let Mr. Sizemore tell what happened at the ceremony, as it portrays Senator Byrd quite nicely:
“Senator Byrd went up to the podium and gave his dedicatory speech. He is a very good speaker. He frequently cites the Bible during his speeches. While you sit there, wondering where he’s going with all the stuff he talks about, he draws it all together in the end and it starts making sense to you. The National Science Foundation dignitaries were gathered there, as well as some of the local politicians, and also all of the NRAO big wigs.
A public reception was held at the site after the ceremony, where the local population was invited. All of the suits gathered quickly around the Senator at the reception, trying their best to hobnob. The Senator’s reaction was priceless. He laid his hand on the NRAO Director’s shoulder, and said, “George, take all these people away and leave me alone!” He would not let any politician or dignitary come within 20 feet of him the rest of the day. He stood in the sun, on the pavement, for 2 hours, and shook hands with every local person that was there. Meanwhile the suits went over to a table set up for them and pouted. Well, as the reception drew to a close, Senator Byrd pulled out his fiddle and played with one of the NRAO employees, then stood up and left.
The night before, he stayed at one of the local hotels. The old gentleman got up at 5 in the morning, and went down and had breakfast with the kitchen staff. Now, can you imagine whose votes he got? “Hey, mom, guess who I had breakfast with this morning!” He got their votes, and their families and friends’ votes! The man is a consummate politician!”
The total funding for the telescope came to 75 million. Fifty-five million went to the contractor for building it to the NRAO specs, and NRAO got the rest of the money to build the receivers, monitors, and other equipment that went along with it. After the telescope was built, NRAO needed to go into binding arbitration because the contractor wanted more money – 20 million more to be exact. In the end, they got almost 4 million – not their ridiculous figure – thanks to the arbitrator.
Here’s Mr. Sizemore’s take on basic research and general politics:
“The main problem with basic research, not just radio astronomy but physics, chemistry, mathematics, is the mindset of society. People want immediate gratification. They’re not willing to put in the long-term effort required for projects on which the return is 20, 30 or even 40 years. We are very short-sighted. We can’t see past the next election.”
The GBT Control Room
The whole room is enclosed in copper sheeting and copper fabric – the walls, ceiling, floors and even windows have copper over them. The room is what they call a Faraday Cage. It attenuates signals inside by 60 dB at 1 GHz. That’s not sound waves, it’s radio waves. You can also measure radio waves in decibels.
The windows have a thin brass wire lattice, so light can penetrate. Here we get into some more murky ground. To most radio waves, the lattice wire is a solid wall. The smaller the wavelength, the more likely it is that the radio signal will pass through. As computer processors increase in power, the wavelength of their radio signals gets smaller, since the frequency of the processors increases. That means that soon enough the wire lattice for the windows won’t suffice anymore to block out the radio waves generated by next-generation computers.
Even the door is made of copper and has a brass doorstep, on which Mr. Sizemore cautioned me not to step – apparently they need a tight seal and brass is pliable. Stepping on it would dent it. There are also copper “fingers” between the door and the doorstep. They need good contact between the two, and denting or dirt from your soles will prevent it — that’s another reason why it’s best to step over it as you enter or exit the room.
The reason for this is that the equipment generates radio interference. Since there’s a direct line of sight from the control room to the GBT, the only way to minimize that is to make the room into a Faraday Cage.
Here’s a tale of woe about the windows. The contractor “screwed up the execution of the design in any way possible”. One of the main problems was the use of copper fabric on the walls. They applied it to the wall with a water-based adhesive. Now the fabric is slowly turning green. The copper is turning into copper oxide, which is not as conductive and is also poisonous. Around the windows, they don’t have that problem, they have another, which is worse.
The contractor put copper and zinc together in the framing. The metal parts were zinc-plated. When you put those two elements together and add a little moisture from the sweating of the windows, you get a battery! The windows immediately corroded. You couldn’t just plug your Walkman into the windows and run it off the electricity generated, but they did have a lot of corrosion, so that was a major problem that needed to be taken care of immediately. In Wesley’s words, “watch contractors, they’ll mess it up in any way possible.”
Nathan, one of the technicians, and Mr. Sizemore had to re-do all of the windows. They had to take all of the windows apart down to the metal and send all of the framing off to have it nickel-plated. They also replaced the copper fabric on the walls around the windows with nickel fabric. If you put nickel and copper together, the electrolytic action isn’t as bad and it doesn’t corrode.
When they were refitting the windows in the GBT control room to do away with the “battery effect”, they had to do a lot of banging. As they started away in the morning, they banged at the frames for about a half hour or so, until Phil Jewell, the Deputy NRAO Director, whose office was directly underneath, walked in to see what was going on, with a confused look on his face. Nathan couldn’t resist: “Hey Phil, did we wake ya?” he spouted, a huge grin spreading across his face. Wesley was quiet as a mouse, not knowing how Phil would react to Nathan. Thankfully, Mr. Jewell just grinned and walked away.
They still had a problem with the sweating on the windows, which they needed to alleviate, since they were still made of metal that could corrode over time, though at a much slower rate than before. Some of the scientists on-site got together and offered a bunch of “solutions”. One of them was to put Plexiglas over the windows to keep air circulation to a minimum. But then another decided to drill holes in the Plexiglass to keep the air circulating through, since the sweating still occurred. They then used a fan to blow air over the windows to cut down on the circulation. Not very practical!
The final solution was offered by one of the technicians, who happened to live in a mobile home. For those of you who haven’t had this experience – including me – windows sweat a lot in mobile homes. He went to the general store in town and got a little window kit from 3M. It’s film that is applied to the windows and shrunk with a blowdryer. After the fix was proven, the 3M film was replaced with plexiglass with a resealable access hole to allow desiccant packs to be inserted between the window and plexiglass covers.
Each window now has a round hole at the bottom that is used to exchange the dessicant packs once in a while, and also a moisture indicator that points out the approximate time when the packs need to be changed.
Sometimes it’s a little hard to see the forest for the trees. It helps to stop over-analyzing things sometimes. It certainly becomes less of a headache when the problem is far less complex than originally thought!
In the Control Room, the GBT operator constantly monitors the equipment from the Control Console. The operator is responsible for two main things: the safe operation of the telescope, and the implementation of the different observing programs that various astronomers use. The observation is done in various modes. Normally most astronomers come and “babysit” their programs to make sure they’re getting the data they need, although the trend nowadays is to observe more and more by remote access. The advantage with being there is they can change their program on the fly if adjustments need to be made. Other programs are run over and over, so there’s no need for the astronomer to be there. NRAO operators record the data and ship it off to the astronomers.
In some cases, people that do research there win the Nobel Prize. In other cases, there are people who look at their data then chuck it to the circular file and try again. Some of the research pans out and some of it doesn’t. NRAO is a basic research institute and that means a lot of effort is put in to look at things that only matter down the road.
In the computer control room, separated from the main area by a glass wall, the collective whir of each of the computers adds up to a somewhat deafening noise. The interesting thing about NRAO is that it has a good mix of both old and new technology. Nowhere is this more apparent than in this room. Most of the equipment in there is one of a kind. The pictures here are worth a thousand words. The synthesizer filters, the front panels, the painting of these panels, is all done in-house.
All of the fiber lines from the GBT come right into the equipment room, where the optical signal is converted back into a radio signal.
The spectral processor is another big piece they have in the room. Wesley told me to think of it as nothing more than a big radio. It takes the radio signals it receives and splits them into 1,024 different channels. Then if they have interference on one channel, they can drop it and still reclaim part of the data, provided the interfering signal is not strong enough to overload the first amplifier. The newer spectral process has over 250,000 channels and the technology gets better with each year.
If the signal is strong enough to overload the cryogenic amplifier, and drives it into a non-linear portion of its amplification, then everything in the entire band is lost. The data has to be collected again once the interference is done away with. If the interference is there but not strong enough to overload the first amplifier, then they may be able to drop that interference provided it doesn’t occur precisely on the astronomical signal you’re looking at: same frequency/wavelength. That’s what the spectral processor is good at.
Inside the spectral processor you’ll find another oddity that’s part of that mix of unique, old and new equipment. The circuit boards aren’t printed (they don’t have the circuits embedded into them) but they are wire-wrapped. The cards have little posts sticking out of them, and wires are run from post to post to post. It’s very old technology, but it works great. It’s something NRAO has a lot of experience with, it’s very robust, and it’s cheap to do one card that way. If they were going to do dozens of cards, they would ship them out and have them done as printed circuits.
They also have equipment manufactured by other organizations. For example, they have a CalTech Pulsar machine. They get very picky about the equipment brought on-site. They have to be careful that it doesn’t interfere with the other equipment there, and especially not with the telescopes.
NRAO operates frequency and time standards on the site. Because of the sensitivity of their work, they have to have very accurate frequency standards. They operate a hydrogen maser, a machine that gives them very accurate 5 MHz readings that are piped all over the site. Everything then gets slaved to that signal.
They also operate an atomic clock on site that gives a very accurate time standard. The clock may go away in the future, since a time signal just as accurate can be obtained from the GPS satellites.
Here Mr. Sizemore pointed out a common point of confusion for many people. Stores sometimes sell atomic clocks or watches. They aren’t atomic clocks as scientists define them. A real atomic clock has a Cesium atom movement in it. The movement of those atoms is used to drive it. The clocks one can buy at Radio Shack or Sharper Image are normal digital clocks with a radio receiver built-in that can tune into the time signal transmitted by our government and set itself. Not quite the same thing.
One of their research efforts involves trying to excise interference from the astronomical data, provided, of course, that the amplifier isn’t overloaded. They are looking at a real-time solution, one that would involve an antenna that receives and records only the interference, and the normal dish would record all of the signals. The two recordings would then be spliced together and the interference would be excised. It sounds simple, but it gets more complicated in practice. At any rate, one of the NRAO scientists is working on that very project.
And that’s the end of part five. You can also read parts one, two, three, four, six and seven.
Chasing RFI Waves – Part Four
Here is part four of my non-fiction work about the National Radio Astronomy Observatory. You can also read parts one, two, three, five, six and seven.
A Walk Through the Jansky Lab
This is the place at NRAO where all of the circuitry is put together for the observatory. It was named after Karl Jansky.
First, let’s understand their particular kind of telescope. We normally think of a lens-based device when we hear the term “telescope” but in NRAO’s case, a telescope refers to a large radio antenna that helps them “see” radio signals that are emitted far away.
A radio telescope operates in two different fashions. In the first, radio signals come from space, hit the main reflector, the sub-reflector, and are then are beamed down to the receiver room. For the second type, a boom is swung out above the dish, and the signal is reflected directly into the receiver that gets mounted on the boom. For both types of telescopes, the signal is fed into a receiver through a feed horn that’s machined out of aluminum and anodized. The receiver is housed in a vacuum.
The observatory has a complete machine shop, where they make their own circuits and components. The feedhorn is a funnel for radio signals. It’s ridged, and there’s a very good reason for that. The explanation is complicated – too complicated for me to understand – but the net effect is that it clarifies the radio waves; it breaks up different modes of propagation within the feed horn itself. The point is that you want to funnel the signal without affecting it. Mr. Sizemore’s droll statement about feed horns is as follows: “I’m not a feed engineer, I don’t want to be a feed engineer, there is entirely too much math involved.”
The feed horn isn’t made from layers, it’s a single machined piece, milled from the inside. Feedhorns vary in size, but they fulfill the same purpose every time: they funnel the radio waves into the receiver.
Inside the receiver, they’ve got a wave guide, which is nothing more than a metal conduit, but it’s a very special conduit, that drives the signals directly to the amplifier through the vacuum chamber, which is called a “dewar vessel”.
An ortho-mode transducer “straightens out” the radio waves. If you look at the antennas in your neighborhood, you might see they’re pointed either vertically or horizontally. Most of the man-made radio signals are transmitted with a linear polarization. They’re either horizontal or vertical. The ortho-mode transducer takes circularly polarized astronomical radio signals and splits them into horizontal and vertical radio signals. These transducers also vary in size depending on the telescope where they’re used.
All of the receivers are housed in vacuum chambers equipped with refrigerator pumps. All of the components are built in-house. The amplifiers, for example, are made in the Central Development Lab in Charlottesville, VA. Because the operations at the observatory are so unique, there are no companies making certain parts, and NRAO has to manufacture them. I gathered from talking to Mr. Sizemore that most every time they relied on outside contractors to do work at the observatory for certain projects, the results were much less than satisfactory, even with close supervision. In the end, more time, effort and money was spent with contractors, when it would have been quicker to do things in-house. The rule now is that they do everything they can do, unless it’s not feasible or practical.
NRAO has gotten more involved with fiber optics. Interference problems in the past weren’t necessarily caused by the feed from the receiver, but from the cables that connect the receiver to the control room. What NRAO now does is to convert the radio signals to optical signals and bring them to the control room that way, unaffected by line noise. It’s converted back to a radio signal there, without any loss.
Long cables act just like antennas, and pick up signals unwittingly. That’s why the quality of your cable TV signal improves if you use higher quality coaxial lines (thicker copper, more shielding). That’s also why Monster Cable is doing so well. They’ve managed to convince most folks that it’s worth it to pay extra for higher quality cables if you want less interference. Same concept. The difference there is that you experience little to unnoticeable interference for short cable runs like the ones from your TV to your amplifier, for example, so unless you’re using really poor cables, your signal will barely suffer.
Another analogy is the use of optical fiber lines to connect buildings on a common LAN (Local Area Network). The signal would simply die out or incur too much interference if it would be carried through regular CAT5 cables from building to building, especially if they’re spread apart, so what’s done is the electrical signals from the CAT5 cable are converted to optical signals in a switch room, then carried through a fiber optic line from one building to another, where they are once more converted to electrical signals in another switch room. What people have now started doing is to forgo fiber optic lines altogether and simply transmit the signal through laser from one building to another. It’s still an optical transmission; it’s like shining a flashlight and seeing the beam. Here you’d need a clear line of sight, and during inclement weather, the quality of the connection would decrease or drop out altogether.
Usually, an engineer and a technician are assigned as a team to take care of a receiver. This photo shows the work being done on the W band receiver, which is a high-frequency receiver. NRAO hopes to be able to receive the high-frequency band in late spring or early summer of 2006, which is when I hope this book will be published [sic]!
The higher in frequency folks get, the harder it gets to focus the waves, because they are so small that any irregularities in the dish shape can smear them, or put them out of focus. As work is being done on the higher-frequency receiver, they’ve got to be really careful about what they’re doing, or things won’t work properly.
Most of your current devices have something called Field Effect Transistors. NRAO uses High Electron Mobility Transistors, which are the next generation of transistors. NRAO happens to be the proving ground for new technology. The first transistor they used cost about $50,000. Its manufacturer, a company in Japan, gave it to NRAO for free, asking them to try it. If NRAO would be happy with it, they’d know everyone would be also. Why? Nobody works to the standards of NRAO, in terms of signal fidelity, clarity, etc. If an electronics company can satisfy NRAO, they’ve just satisfied everybody in the world. For that reason, it’s not seldom that companies contact NRAO and offer them products to try. All that they ask is for data in return. How did the product behave? What are its limitations? What can be improved? It works out very well for both parties. That’s one of the direct spin-offs for NRAO’s work. Everyone in the world benefits indirectly from the work they do.
Most amplifiers at NRAO start out as solid pieces of aluminum. They’re machined by them, on-site. Nowadays, the amplifiers are made at the Central Development Lab in Charlottesville, VA, also part of NRAO. Again, the rationale is very simple. That sort of a product simply can’t be bought commercially. It’s not available, just like most of NRAO’s components – they are one of a kind.
One of the other things that NRAO has gotten involved with is the surface-mount technology for different electronic components. Some of them are so small that if you were to sneeze around the technician, it would very likely mess up his work.
Each little cubbyhole, people are building different components. In one, folks are at work on the Alma Array, which is getting built in the Chilean Atacama Dessert. JD, a technician, and one of the engineers, are working on the little cards (circuits) that will process the signals received there. The Array will employ many telescopes and many cards will be needed.
It’s a good working environment at NRAO. It’s a rural area, so by nature people try to maintain good relationships. In Wesley’s words, “the guy you piss off may be the guy you need to help you get out of the ditch in the winter,” so there are extra incentives to maintaining friendly relationships. There are some downsides, as well. For major shopping, the closest towns are 1 ½ hours away, like Harrisonburg or Roanoke.
Interferometers and the GBT
The United States is not the only country involved in radio astronomy. There are observatories throughout the world. There are maps in one of the NRAO lobbies showing the locations of such observatories. The unique thing about the Greenbank observatory is that it is protected by the National Radio Quiet Zone. This is the only area where folks are compelled to coordinate all radio frequencies with NRAO. There are some other areas in the world such as Puerto Rico, where limited frequencies are controlled.
Incidentally, the Puerto Rico telescope was used in one of the James Bond movies. The NRAO folks are waiting (but not holding their breaths) for the Green Bank Telescope, the GBT, to be used in one of the science-fiction movies. It’s just so out of this world, in both its proportion and look, that it’s bound to end up in a sci-fi movie sooner or later.
Some of the telescopes are single dishes, and some are arrays. Why do you need an array of dishes? Well, why do you have two eyes instead of one? The answer is depth perception.
The term in radio astronomy is spatial resolution, but it’s the same thing. You want the large collecting area of the single dish in order to get the weak signals. You want the arrays of telescopes in order to get the depth perception. Ideally, NRAO would like to have an array of GBTs, but it’s not economically feasible. In those cases, the GBT can be used as one part of an interferometer – that’s another word for arrays. That way you can get the best of both worlds. You can have a large collecting area – for signal strength – and a remote telescope, somewhere else, that gives the astronomers the base line signal, for spatial resolution. The further your “eyes” are spread apart, the better you perceive “depth”.
For telescopes that are close together, technicians can use wave guides to gather signals from each, but for telescopes that are far apart, it becomes impossible. So what NRAO does is to use GPS signals. Each one of the telescopes records the data individually and marks it with GPS ticks from GPS satellites. The data then gets sent to the Array Operations Center, where all of the data is brought together and synced using the GPS timing ticks.
One of the first interferometers built was at Green Bank. It was a three-element interferometer. It worked great, so they got some money together and built the array in New Mexico, which is currently an array of 27 telescopes and will be expanded to 35-40 telescopes in the near future.
They got even more excited about the capabilities of interferometers and decided to make a very long baseline array of 10 telescopes. They used 8 telescopes in the US, one in the Virgin Islands, and one in Hawaii.
The long baseline array also worked very well, so they set to work on building an even bigger array. Unfortunately, the found out it couldn’t be done on the face of the Earth. If the telescopes are too far apart, they can’t see the same object at the same time. The solution to the problem is to put a radio telescope in orbit around the Earth. NRAO actually did a project with Japanese researchers, where they put a telescope in an elliptical orbit around the Earth, and NRAO used the GBT to get the best of both worlds. They had the large collecting area for signal strength and a huge baseline for spatial resolution.
Let’s carry the situation even further. “What about sticking one on the moon?” I asked Mr. Sizemore. “We would like to,” he said. There are plans to do that. Ideally, it should be located on the dark side of the Moon, because it’s never toward us – the Earth. It always faces toward space, and thus would incur significantly less interference from radio signals coming from the Earth than terrestrial telescopes. The stepping-stone to that would be to put a telescope at the LaGrange points, the gravitational balance points between the Earth and the Moon or the Earth and the Sun.
This is the 300 ft telescope that fell down some time ago. It was a perfectly calm night, there was no wind, no weather at all. When it collapsed, they decided to do a finite element analysis on it, and discovered (after the fact) that indeed it would have fallen down sooner or later. At the time it was built, it was designed to the best of the available technology. Unfortunately it simply reached the end of its useful age. Nobody was at fault. What actually happened was that a gusset (a joining place) cracked, and when it failed, it took about 12 seconds for the entire telescope to crash down. They were able to determine that from watching the temperature data on the receiver. The temperature went up as the telescope went down, and then the data simply stopped recording as the sensors and wires got destroyed. Remember, the receiver’s kept in a refrigerated vacuum, and it stopped functioning when the structure started coming apart. NRAO sold the telescope for $10,000 for scrap metal, then it cost them $30,000 to clean up the asbestos damage in the building. “We actually lost on that deal,” said Mr. Sizemore.
He went on: “Senator Byrd, bless his heart, was able to get an emergency one-time appropriation to rebuild the telescope. NRAO used that money to build the Green Bank Telescope (GBT), which is a very unique piece of machinery.”
The GBT has several innovations. The most obvious innovation is the offset feed. If you look at the other telescopes on site, you will see they all have the boom holding the receiver in the center of the reflector. Not so with the GBT – it has its receiver off-center. With a center-mounted feed, man-made signals will get reflected by the legs of the boom and cause interference. The GBT doesn’t have that problem. All of the astronomical signals get correctly reflected into the sub-reflector, then into the receiver, and from there get transported into the Control Room.
Another unique innovation about the GBT is that it’s fully adjustable. All of the panels – and there are over 2,000 panels – can be moved individually. The moving weight on the telescope’s track is about 17,000,000 pounds. NRAO believes the GBT is the largest moving object on ground, and no one has disputed that yet. The only larger moving object on Earth is a ship at sea. The tipping weight on the elevation axle this year is around 13,000,000 pounds.
When you tip that much weight, gravity will tend to sag the reflecting surface and distort it. NRAO needs to keep that reflector as accurate to a parabolic shape as possible, because that will dictate their efficiency at high frequencies, where the wavelengths are shorter.
The dish is built in such a way that they can adjust each individual panel to take out any deformations in the overall shape. The original plan for solving this problem was to use a laser ranging system. Twelve lasers were set up around the dish, giving them a known reference plane. They would then use additional lasers pointed at the dish, at the feed arm, and other different points on the structure. Any movement of the structure could be monitored that way. By doing this, they found out that the gravity deformation was not as serious as the thermal deformation. The structure was getting heated and cooled at different rates depending on where those parts were located. The chief culprit was the sun. It would shine only on certain portions and not on others, subsequently causing thermal expansion in those exposed parts. So NRAO stopped relying on the laser sensors, and started using thermal sensors. They mounted about 20 such sensors around the structure, in order to compute the thermal variations and use that data to correct the focus of the receiver and the positions of the individual plates in the dish. They are still working out the details of the thermal sensor monitoring and adjustment. Once they work this part out, they’ll go back to the laser sensors for the fine tuning. Their goal is to keep the 100-meter dish within 1/5,000th of an inch of the horizontal plane. That’s the thickness of a sheet of paper. Amazing, isn’t it?
Because of the fine adjustments they can make, they are able to advance to higher frequencies such as 50 GHz and soon, 100 GHz. They are doing science that hasn’t been done before. They are finding things that could not be found with any other instrument in the world.
Mr. Sizemore showed me photographs of the construction of the dish. What many people don’t know is that it was built three times! It was put together once, at the manufacturer site, then it was taken apart and shipped to NRAO. Once there, as many of the parts as possible were assembled on the ground. A large crane was then used to lift them into place.
One of the other unique innovations of the structure is that it is a continuously welded structure. There are no bolts supporting weight in the GBT. They will never build a structure like this that is bolted together, including bridges. When the 300-foot telescope collapsed, they did an analysis and found out that the collapse was caused by a tiny crack in the material that had gotten larger over time. Engineering studies have actually shown that any time one punches a hole in metal, one makes a stress fracture that will propagate over time. What one must then do to avoid these fractures is to never punch holes in metal that is supporting weight. It must be welded.
In building the GBT, over 50 tons of welding wire were used. About 300 welders tested for the job, and only about 30 of them passed. The welding needed to be very precise and very accurate. Some of the passes they had to weld involved dozens and dozens of back and forth welds to fill up large gaps. Of course, NRAO does constant testing of the structure. All of the welds are inspected, radiographs are also taken, and all of the constant maintenance ensures the structure remains in great shape.
That was part four. You can also read parts one, two, three, five, six and seven.