Turn right at Alamogordo, pass High Rolls, and 9000 feet up into New Mexico’s Sacramento Mountains, turn right again and go 15 miles along a narrow switchback two-lane, turn off on the Apache Point road, pass a pond, and hit the dead end at Apache Point Observatory, a cluster of utilitarian buildings. Inside one building is a little 2.5 meter telescope. The telescope sits on a man-made ledge that’s cantilevered off the side of the mountain and looks out at the White Sands Missile Range; the white sands are gypsum that dusts the telescope and mirror. The telescope, dedicated to the biggest digital survey of the sky, has been up there since the mid-1990’s, and every year its mirror has to be taken off and cleaned. In the digital survey business, astronomers get all the glory but my personal true loves are the guys who take the mirror off the telescope.
“Guys” is generic, men and women both, six or so of them. They live not less than 45 minutes away. “This is a good job for out here,” they say, and they feel lucky to be working on a telescope and not the cooling units for refrigerated trucks. Age range is from 20 to around 60. Dress is workshoes, leather gloves, jeans, t-shirts, flannel shirts, sweatshirts, worn in multiple layers to be taken off and put on, depending on the quickly-changing cloud:sun and clear:rainy ratios. They work pretty much in the open: the building in which the telescope sits has effectively two open ends, one of them overlooking a view the size of Massachusetts. They’re aware of safety — “don’t put your finger in that nitrogen unless you want it frozen off” – and “if someone gets hurt and can’t be fixed with a Leatherman and duct tape, just roll ‘em off the front of the telescope and let the coyotes get ‘em.”
- Subject: 2.5m Day Log 20070705
- From: Dan Long
- Submitted: Thu, 5 Jul 15:59:17 -0600
- Summer Shutdown:
- The telescope was disassembled to the point of pulling the primary (wind baffle off, M2 off, M2 truss off, wind baffle counterweights reconfigured to balance the telescope, primary light baffle and common corrector off). The primary comes out tomorrow. Cheers, Dan
The primary is the 2.5 meter work mirror. It weighs one ton and has been polished to 100 nanometers, that is, no roughness higher than 0.0000039 inches. That smoothness makes it uncanny– you can’t tell what’s real and what’s reflection – and because the mirror curves, the reflection is in slightly the wrong place. Dan, who’s in training to be the crew chief, says “mirrors mess with your mind.” Divested of trusses and baffles, the mirror rests on its back, nested in its cell, looking up. French, the crew chief, crawls under it and stands up through the hole in its center, up to his shoulders in mirror which, just breathing, he’s steamed up. “I’ve never seen this mirror so dusty,” he says. The dust has to be removed by specialists in Tucson. The least damage to that mirror, and the crew is out of work until it’s repaired, for months. Diana, one of the crew, says to French, “You nervous?” “Any time you’re over the mirror,” says another crew member, “is prayer time.” They’ll need to lift it out of its cell, then move it to a triangle stand that French designed that looks like tinkertoys with padded stools at each corner. Meanwhile, they attach a hard cover plate over the mirror, plate rim to mirror rim. The next morning, French says, “Now. Let’s go pull a mirror.”
The crew sets up the triangle stand, figuring it out as they go, asking each others’ opinions, alert, on the jump. Diana can’t account for an allen wrench – tools need to be accounted for in case, in spite of the hard cover, they end up on the mirror – and makes everybody search their pockets. French gives them explicit directions: we’ll pick up the mirror by the loop on its hard cover with a hook, attach a dynamometer to the hook, lift the whole thing out slowly; four people will be on ladders over the mirror, watching the numbers on the dynamometer like hawks, making sure it doesn’t get hung up.
The dynamometer is new to them, and they cluster around it, figuring out how the meter works, what the units are. French has the controls for the lift: “I’m the only guy who can say ‘up,’ but anybody can say ‘stop.’” One of the crew is Chinese; his English is good but not perfect. “How do you say ‘stop’ in Chinese?” French asks. The guy tenses his whole body and yells, “chiiiiing.” They empty their pockets and ask French more questions. Diana says to the guys climbing the ladders to their watching points over the mirror, “Anything in your pockets?”
The dynamometer with its hook underneath moves over the mirror. The crew up on the ladders are hunched over. The hook latches to the loop on the hard cover. “Ok,” says French, “Up we go,” and presses the controls, and a loud groaning starts then stops immediately. “Ok,” he says, “the other up.” It’s a physicist joke: up is down to the minus one, so down is just the other up. French has a BA in physics which took him 20 years to get.
Dan reads out the numbers on the dynamometer: “2300,” he says; the mirror in its housing weighs 2300 pounds, so the dynamometer is carrying the full weight. The guys on the ladders check to see if the mirror is clearing the first set of earthquake bumpers. “Stop. Feels like it’s hung up.” “Ok, start.” Stop, start. Clear the first set. Clear the second set. Pick up speed — though it still moves almost imperceptibly.
Then the mirror hangs free over its cell. It’s a flat, honeycombed cylinder of glass; 2.5 meters is small for a telescope but this looks huge. French says, “We’re going east.” For the first time, the crew is absolutely silent; mirrors don’t belong floating in the air. “Ok, coming down,” says French. The mirror hovers a foot above the padded tops of the stools, then settles down. “Stop.” Hook and dynamometer, now reading 0, are removed. It’s been a long day and it’s only 9:30 a.m.
By the next day, French and the crew have taken mirror off the triangle and set it into a padded wooden box on a palette, then covered it with more padding, then screwed a wooden top on the box. They lower the box onto the flatbed of a truck and drop a tarp over the box. They bungee-cord the tarp to the truck, then fasten the box to the flatbed with wide tapes and chains. The truck should take about six or seven hours to get to Tucson. The crew stands around the truck, telling stories. Another telescope mirror was left on a flatbed in the Arizona heat and it cracked. Once another truck carrying this mirror lost its brakes on the incline by High Rolls. The truck should have two escorts, one in front and one in back; the front one warns of upcoming potholes; the back one picks up the glass.
- Subject: 2.5m Day Log 20070706
- From: Dan Long
- Submitted: Fri, 6 Jul
- Summer Shutdown:
- The primary was removed, and since the truck had arrived and the weather was cooperating, it was put in its crate, ready to go to Tucson. Cheers, Dan
It was back within a week. The astronomers relying on data from the telescope hardly notice the downtime; they have lots of data, so meticulously taken and analyzed that astronomy is being revolutionized. French’s crew shows up early and puts the shiny mirror back where it belongs.
- Subject: telescope eng report
- From: French Leger
- Submitted: Fri, 13 Jul
- The Primary Mirror has returned.
- The boys got in last night about 7:30 pm. We will remove it from its crate today as soon as the humidity and weather permits. Cheers, French
For more about the crew and the survey: my book.
Photo credits, in order:
a bigger, parabolic telescope mirror: with kind permission from Enrico Pinna
2.5m primary mirror still on telescope + French, Dan: Astrophysical Research Consortium, Apache Point Observatory
honeycombed back of another mirror at Apache Point: with kind permission from Ellarien
crew hand: Astrophysical Research Consortium, Apache Point Observatory