I had a chance recently to take a tour of the Big Chamber at NASA's Johnson Space Center. A big thank-you to Eric Chan and Mary Halligan, facility managers for the building that houses the Big Chamber, or as it's officially known, Chamber A.
The building is unique because it's the only one where they built the equipment inside, and then put the building up around it. It was built in 1963, soon after JSC was established, and it was used for thermal and vacuum testing for the space program. It uses various pumps and cryogenic cooling to create an incredible vacuum inside the chamber and to chill the chamber down to 3 degrees Kelvin, or -435 degrees Fahrenheit. Absolute zero is defined as 0 degrees Kelvin. It's the temperature where all molecular activity is stopped.
This is the first thing you see when you walk into the high bay area. The first word out of every single person's mouth is "Wow!"
This is my office mate, Dave, standing in front of the door to the Big Chamber. The door is 40 feet in diameter and weighs 40 tons. In spite of the weight, two people can push the door closed.
Here we are inside Chamber A.
This gives you an idea how thick the door is.
It has an internal diameter of 55 feet, and an external diameter of 65 feet. It's 90 feet to the top, and it goes down another 30 feet underneath the chamber floor. In the Apollo program, they would actually put the Lunar Transfer Vehicle and the Luner Excursion Module inside the Chamber, pump it down and leave it exposed to space conditions for over 14 hours. During that time, the astronauts would be inside the vehicle in their space suits. It's the only time that the Big Chamber has had human test subjects in it.
In order to prepare the chamber for testing, they first use roughing pumps to get as much of the air out of the chamber as possible. Then they switch to a combination of diffusion pumps and liquid nitrogen, which gets them down to around a tenth of a torr. One torr is equal to one millimeter of mercury. At sea level, the atmospheric pressure is 760 torr or 760 mm Hg, so you get the idea that there's very little pressure in the chamber at this point.
The cryogenic system is really neat. There are radiator fins running the entire length of the chamber and placed every couple of feet around the outer wall. In the fins are small tubes that they use to pump liquid nitrogen. The nitrogen cools the chamber down to around 77 K. However, they're not done yet.
There are extra radiator fins with tubes, and they run liquid helium through these. This is how they cool the chamber down to 3 Kelvin. It's so cold that the remaining molecules of air (nitrogen and oxygen) freeze out as snow against the panels holding the liquid helium. At this point, the pressure in the chamber is down to one-millionth of a torr. It's now as close to space conditions as you can get on the planet Earth, excepting the whole gravity thing.
It takes just 14 hours to go from atmospheric normal to cold vacuum in the chamber.
Here we are outside the Big Chamber.
The light silver wall is the outer chamber wall. The dark gray cylinder with all the rings is one of 20 diffusion pumps. When you walk through the building, it's hard to believe engineers can build something so complex. There are pipes running every which way, systems to handle air, nitrogen, helium and ammonia, dozens of immense pumps and control systems. And because the facility is so old, some of the systems aren't being made any more. If a pump part goes bad, they may have to look for a long time to find a replacement.
Here's our tour guide, Eric Chan, explaining the pump control system in the man-lock.
They tested the Apollo space craft and dozens of other satellites in the chamber. I asked if they tested the Hubble Space Telescope in there, and the answer was no. That's interesting, because one of the main problems they had with Hubble early on was a wobble in the solar panels caused by thermal stress as the telescope went into and out of earth's shadow. They're looking at a new test in the chamber for the next generation of the space telescope. It's still a few years off though.
Eric took us outside to see the liquid nitrogen storage tanks.
There are 6 tanks that hold 28,000 gallons of liquid nitrogen each. If you've seen a cryogenic semi-truck going down the interstate, each of those holds about 6,000 gallons. When the Big Chamber is running, they take a delivery truck of liquid nitrogen every 6 hours.
After Hurricane Katrina, they had a big problem. They were in the last week of a test, and even though Johnson Space Center hadn't been hit by the hurricane, Interstate-10 was destroyed, and the liquid nitrogen supply companies couldn't get their supplies to Texas. In a heroic effort, in just three days they managed to write a new contract for liquid nitrogen. If you know anything at all about government contracting, that's unbelievably fast. They managed to complete the test and get all the data they needed.
We went back inside, and Eric showed us Chamber B, or the little chamber.
This chamber is used for small tests and for human testing. The top slides sideways and they use cranes to lower the equipment inside. People enter through an airlock on the side. They can get the same temperature and vacuum conditions as in the big chamber.
This airlock door is the one where the astronauts enter. The space suits weigh around 150 pounds, so they use a spring-loaded system suspended from an overhead track to carry the weight of the space suit, allowing the astronaut to move around the chamber more easily.
When we saw the facility, they had the Little Chamber set up to do testing on space shuttle tile repair in orbit. Here you can see the tiles set up on the table.
It was a really cool tour, and Eric and Mary were great to work with. So far, I've managed to see the Neutral Bouyancy Lab (the big swimming pool where the astronauts train), and land the space shuttle (simulator). Now all I need to see is Mission Control.
