by Paul Dye
“Okay, everyone, it looks like we’ve got a fairly large leak. Not sure where it is yet, we’ll wait until we get the hatches closed to see whose side it’s on. If it’s on the ISS, we’ll see what they need for us to do to help; if it’s on our side, ah—EECOM, can you give me an idea with this size T-Rez? Uh… what does that translate into for Shuttle time on orbit—if it’s on our side?”
“I’ll work on that, Flight.”
“Okay, and FIDO, have we got any landing sites underneath us right now? I guess I’m really asking, let’s see… I’d guess a couple of hours to undock and clear, then a reasonable deorbit prep. What have we got out a couple of revs?”
FIDO was our Flight Dynamics Officer—essentially our navigator in Mission Control. FIDOs kept track of trajectories, where Atlantis was, and where it was going. They also computed maneuver and deorbit burns—so they were the ones who could find us a landing site when we needed one. TIG (time of ignition), another of their responsibilities, was when we’d have to do the burn—in this case, to drop us out of orbit. A rev was a quick term for a “revolution about the earth”—essentially a single orbit, around the planet.
With one of the largest back rooms in the Control Center, FIDOs sat in the front row of the FCR, over on the left side. They had a lot of computing power at their disposal and spoke in a language of vectors and targets that few outside their discipline understood. In the front room, we looked at the back of their heads most of the time, but when it was important—like now—they would stand up and talk directly at me—even though they still talked over the loops so that everyone else around the world knew what they were telling me. An experienced FIDO, Dan, had been through drills a thousand times, and he knew that it was too early to get excited about something as routine as a cabin leak. He looked me in the eye and I could see a little smile in his eyes, as if to say, “Sure, I can tell you the trajectory score, but we know EECOM will solve this.”
“Flight, FIDO. We’ve got two West Coast opportunities in a row, Northrup and Edwards on the first, Edwards on the second. They are about three-and-a-half to TIG, and then a rev later.”
“FIDO, get me those exact times, and give me clocks to TIG—we’ll figure an hour after TIG for touchdown. Why don’t you give us clocks for both TIG and touchdown for both opportunities—we’ve got the room up there.”
“Roger Flight.”
Up on top of the big screens in the front of the Control Room, there were slots for about eight different clocks. One always displayed Greenwich Mean Time, while another showed the total Mission Elapsed Time (MET). The others could be configured as stop watches or timers, counting down to a specific event, or counting up from when something had happened. Putting a clock up helped everyone focus on time—the single absolutely unrenewable resource that we had. Time always marched forward, and countdown timers always counted to zero, and no amount of pleading could change that fact.
“Okay, folks, in case the leak is on our side, I am thinking that if it’s stable, and we can get on the ground with an hour’s reserve, we’re going to be coming down. I just don’t want to cut it too close, so EECOM, I am going to be looking at you for a recommendation on…”
I was interrupted before I could finish the thought.
“Flight, EECOM. We just saw a big jump in the rate—I think the hatch is closed, and the leak is on our side—I’ll get a number for you.”
“CAPCOM, Flight. Let’s see where they’re at and…”
Once again, someone else was ahead of me, and this time it was the crew. They, of course, couldn’t hear what we were saying on the Flight loop, and everyone was trained to instantly stop talking when the crew came on air-to-ground—they were the reason we were there, so they always had priority.
“Houston, Atlantis, Space to Ground One. We’ve got everyone on our side, and closed the hatch, and I guess you can see that we’re still leaking. We’re going to the Orbit Pocket, page 4-3…”
“Okay, CAPCOM—copy that, we’re following them to the Pocket. EECOM—is that where you want ’em?”
“Flight, EECOM. Yes Orbit Pocket, page 4-3.”
I turned slightly toward Shannon and nodded my head—a quick signal for her to pass those words up to the crew. It was faster than me having to verbalize it.
“Atlantis, Houston. We copy you in the Orbit Pocket, and we’re looking at the leak on the ground!”
The Orbit Pocket—short for Orbit Pocket Checklist—contained all the immediate response procedures for things in Atlantis that needed to be worked immediately. They were the quick response steps used to make the system safe. The full malfunction checklist procedures could be dealt with after you stopped a leak and regained control, or had dealt with whatever emergency arose. The Joint Ops book told both the ISS and Shuttle crews what to do to get to their own vehicles and isolate themselves, and each crew then went to their own detailed book to solve their own issues. Ours was the Orbit Pocket.
Things were tricky with two spacecrafts. The Station was full of atmosphere—lots more than we had on Atlantis because of the comparative volumes. When the hatch between the two vehicles was closed, the leak rate picked up on the Orbiter because there was a smaller volume to leak out… and it was real trouble.
Now it was the EECOM’s turn to stand and face me. I could see that he wasn’t happy—he knew that all the focus was on him, and what he and his team could do would determine which path we’d be taking in the next few minutes. He wasn’t happy because his data weren’t solid—this was going to be a judgment call based on changing rates, which was getting awfully close to the definition of guessing—something that flight controllers never want to do.
“Flight, EECOM. My preliminary estimate is six hours to eight psi—we’re working to refine that—give me a couple of minutes.”
“Copy EECOM. Let’s get the numbers right, and I need to get a feeling of your confidence—is that leak going to be stable, or is it varying? I’m trying to figure out how much I can trust the time you’re going to get, ’cause that’s going to be really close getting all the way to the ground.”
Atmosphere on a spacecraft is life—but not just for the astronauts. Humans can survive at reasonably low atmospheric pressures (usually measured in pounds per square inch, or psi), especially if you can bump up the percentage of oxygen. Half of Earth’s atmospheric pressure is below you when you are at 17,500 feet in altitude, and people live at that elevation routinely. The top of Mount Everest is at just about a third of sea level pressure, and some hardy souls have climbed it without supplemental oxygen. So keeping the crew alive was not my most immediate concern—we could flow oxygen into the cabin for a while to keep them breathing. No, the bigger problem in this case was cooling the many critical avionics boxes in the vehicle. Computers are very good heaters—they use electricity to run, make calculations, and pass data back and forth, but most of the electricity they use is discarded as waste heat. Some of that heat goes into the water cooling system designed for the task, and some of it goes into the air. You need that air to cool the machines, or pretty soon you’ll start losing the primary General Purpose Computers (GPCs) needed to fly the Orbiter, or the many Multiplexer/Demultiplexers (MDMs) that collect data from the various systems, transfer that data to the GPCs (and the ground), and send control commands back to the machines. Without GPCs and MDMs, you couldn’t fly the vehicle—and without the various sensors, inertial measurement units, and display screens, you wouldn’t know where you were. All these boxes depended on the air in the cabin to keep them cool (to a point), and the lower the pressure, the fewer the air molecules available to carry that heat away. Thinner air, poorer cooling. Reentering with a leak means that the closer you get to the ground, the thinner the air in the cabin and, therefore, the less efficient cooling would become.
The bottom line was that we might have five hours to get to the ground—but the absolutely riskiest part of that entry was going to be the last ten minutes if the pressure kept dropping and the coo
ling kept getting worse and worse. There were no points for second best in this game, and my controllers knew it. It did no good to separate from the station, go through entry, and then lose the vehicle in the last few minutes because we had nothing left to fly it. This wasn’t going to be an easy call for my EECOM. I gave him a minute to watch his data, then pulsed him on the loop.
“EECOM, Flight. You seeing any progress on the Pocket?”
“Yes Flight. It looks like they’ve got the cabin pressure relief valves and the dump valves closed—let’s get them to close the airlock—there are a couple of other steps, but that’s our best bet.”
Before I could answer, an interruption came from the row in front of EECOM. It was common for controllers to slip in an additional call if something was going up to the crew, and we appreciated it because it was more efficient to make one call rather than two.
“Flight, MMACS. If they’ve got a spare hand, you can have them get out the leak detector and get that fired up. It’s in the IFM tool locker… that’s MA9F.”
The Mechanical Maintenance Arm and Crew Systems, or MMACS (pronounced “Max”), was a complicated position that handled all the Orbiter’s mechanical systems as well as the robot arm, maintenance, and crew systems. A catch-all position, they were responsible for all tools and loose equipment in the Orbiter. Today’s MMACS knew that if there was a leak to be found and patched, he would be the one responsible for helping the crew through that process, so he might as well get them started looking for equipment.
“Copy, MMACS. CAPCOM, make a note of that, but hold on.”
I wanted to check on more details before bothering the crew again.
“EECOM, Flight. We don’t want to open back up to ISS yet because…?”
“Flight, we need to isolate the airlock to see if that’s our problem, and…”
“Oh, duh—yeah, right, got it—let’s get the airlock closed up. CAPCOM, let’s expedite that!”
The airlock in the Orbiter was not used as an airlock during ISS docking missions—it was, in fact, the Orbiter end of the tunnel that led to the Space Station. It was mounted in the Orbiter’s payload bay, and was, therefore, a potential location for a leak—and we couldn’t reopen the tunnel to the ISS (to give ourselves more time with the larger volume of air) while still checking it for leaks.
“And Flight, EECOM. Let’s flow max N2. Open up the N2 Systems 1 and 2 to the cabin, if we could.”
“CAPCOM, let’s add that—N2 Systems 1 and 2 valves to open, and expedite closing the airlock to see if that’s our leak.”
“Atlantis, Houston. We need you to flow max N2, open up N2 Systems 1 and 2 to feed the leak, and we’d like to get the airlock isolated ASAP to see if that’s our leak.”
“Copy Houston. Flow max N2. Airlock hatch close is in work right now.”
By opening the nitrogen valves, located on the ceiling of the Orbiter’s Mid-deck, we would feed the leak to keep the pressure in the cabin from decaying to a level that might prove dangerous to the crew and equipment. We had lots of high-pressure nitrogen stored in bottles in the payload bay for just such an emergency. The Orbiter generally leaked a tiny amount on every flight, so we could make it up with the stored gas. Flowing maximum amounts of N2 from both systems gave us the best chance for keeping up the pressure while we searched for the leak.
“Shuttle Flight, Station Flight. Your loop.” Courtenay was listening in and watching our progress like a hawk.
“Go ahead, Station Flight.”
“Yeah, we see the leak is on your side. We’re standing by over here.” There was little that the ISS could do for us now, and Courtenay knew it. They’d have to watch as our crew fought the leak with what little help we could give them from the ground.
“Yep, we’re just about to close the hatch on the airlock. We’ll let you know what we find. We’ve got some landing opportunities, but they are going to be close, and frankly I’m not sure we’ve got stability on the leak—just hold on a couple of minutes, we may be back.”
This was my indication to the ISS Flight Director that we might not be able to stop our leak, and might not have a landing opportunity—and that our crew might just be coming back to the Station.
“Houston, Atlantis. Uhh, we’ve got the airlock hatch closed, and we still see the negative dP/dT. We’re opening up the N2 systems now.”
“Copy Atlantis. Stand by.” CAPCOM knew to give me a moment to talk with my team and have the crew stand by for whatever we could tell them.
“EECOM, have you got anything else up your sleeve?” I wanted to make sure we had covered all the bases so that we could understand our options.
“Uh, Flight, EECOM. We aren’t seeing much of a change in the overall leak rate, but it is a little unsteady—we’re having to sort of interpolate a little. The hole size is probably about a quarter inch. I think we should see if the crew can hear it, maybe get the leak detector out—see if they can pin it down.”
“Okay, CAPCOM. Let’s tell them that we are still seeing the leak, and see if they have any leads on where it might be—anything they can hear or see flowing in one direction. We think it’s about a quarter inch.”
“Copy, and Flight, do we want them to continue in the Pocket?” Shannon was always keeping track of what we had the crew doing… that was her job.
“EECOM?” With one word, I passed the question on to EECOM.
“No, Flight, we’ve pretty much got that done—uh, stand by.” I realized that standby probably wasn’t for me, but for EECOM’s back room. I knew his loops were buzzing, and because this was the focus of the failure, he was going to stay busy until we sorted this out.
I turned slightly to my right. “CAPCOM, just have them search for the leak for now.”
“Atlantis, Houston. We see that the leak is still there, we think it is about a quarter inch and, uh… we’d like to know if you can locate it by sound or anything?”
There was a slight pause as the crew digested this, then they came back. “We’ll check, Houston.”
Searching for leaks was always a long shot. A quarter-inch hole could be anywhere. It could be a micrometeoroid hit on the skin, but the crew couldn’t see the skin, not directly—everything in the cabin was covered with close-out panels or switch panels or lockers. And the leak might not be a hole in the skin—it could be a plumbing fixture that suddenly let loose—but those were mostly on the aft bulkhead, again, hidden from view by close-outs—or worse, down in the Lower Equipment Bay (LEB). The LEB was not an easy place to reach if it hadn’t already been opened up, and sending a crewmember down there was truly exploring the bowels of the ship with lots of plumbing, tanks, and pumps. The question in my mind was not just where the leak was—but did we have confidence that it would remain the same so we could make a dash for the ground?
“Flight, FIDO.”
“Go ahead, FIDO.”
“Flight, we’ve got the LSOs calling up Northrup and Edwards, but I really think it is going to be close to get the first opportunity. We’ve got to get undocked, and separated, then do the emergency deorbit—I’m guessing that if we started right now, we’d barely make it.”
The LSOs were the Landing Support Officers—basically our interface with the various landing sites around the world. Back in the days of capsules that splashed down in the oceans, they worked with the Navy and other military services to request the support we needed at any time. Since we now landed on runways, they worked with the airfields that we might use, including Edwards Air Force Base in the high desert of California north of Los Angeles, and Northrup Strip, a dry gypsum lake bed located within the White Sands Missile Range in central New Mexico. They had direct communication lines to both, as well as many more places we might have to land. Until we had ruled out an option, we wanted everyone to be ready—just in case.
It was simply a matter of geometry (and geography), that you had a landing opportunity at White Sands a rev before you had one to Edwards—often you’d have White Sands on one, both of t
hem on the next, and then Edwards alone on the third. A rev takes ninety minutes, and you can accomplish a lot in that time—enough to make a landing feasible versus dashing to the ground in hope that you’ll get all the procedures done in time.
“Yeah, I see your point—I agree with you FIDO—I don’t want to screw up the sep, or plume the station, or mess up the deorbit prep. Let’s shoot for the second opportunity—that’s just Edwards, right?”
“Yes Flight. Just Edwards.”
The sep, or separation burn, was the maneuver that backed the Shuttle away from the ISS, slowly and carefully to make sure that it didn’t bump into anything or disturb its attitude control system (which keeps the spacecraft pointed in the desired direction). Another concern was the possibility that the Shuttle jet plumes (or exhaust) were directed at a solar array, making it wave like a flag in a stiff breeze—a sure way to damage something. Pluming the station was one of the worst things we could do during an undocking, and rushing through the procedure was a great way to miss something and cause exactly that to occur. Never rush anything if you can possibly help it—a fundamental rule of flight operations.
I turned my attention back to EECOM. “Okay… uh, EECOM. How’s that rate looking—can you get me to the ground if that’s, say… four and a half hours away?”
EECOM looked at me as he juggled a pencil. I could see the pressure he was under—and I was the one causing it. “Well, Flight, our latest calculation shows we’re going to be down to… uh, Flight, it looks like that is going to be just about our limit—if we go to eight psi now, then start feeding the leak, we are only going to have about a fifteen-minute pad to the ground.”