Shuttle, Houston

by Paul Dye

  The Ku band communication system was used to transmit large amounts of data from the Shuttle, primarily to support payload operations but also to provide TV coverage. The Ku band antenna was a pointable dish that was deployed after the payload bay doors were open on orbit. It could be easily blocked by the Orbiter because it needed a direct line of sight to the relay satellites that we used to communicate with the vehicle. For most of the Shuttle program this is the system we used. Attitude negotiations were always going on between the various users of the Shuttle and with Shuttle systems experts who needed to maintain communication and have particular attitudes for thermal control or micrometeoroid protection. It was the Flight Director who had to referee such discussions and make the final decisions—knowing that someone was always going to go away less than happy.

  INCO was also responsible for controlling and pointing the video cameras situated in the Orbiter payload bay. The crew had primary control, of course, but once they went to bed, and unless the cameras were dedicated for a particular payload activity, the INCO could “drive” them around to look at stuff on the Orbiter or on Earth. The original space camera that INCO controlled was the camera on the Apollo lunar rover, and the flight controller who drove it during moonwalks, Ed Fendell, became famous as Captain Video. Fendell was still doing the job in the early Shuttle days, and he handed over the duty to other generations of controllers later on. Many of the great views of Earth that people all over the world have enjoyed have come from an INCO-pointed, space-based camera.

  All of those digital systems were useless without electrical power, of course. Electrical power on the Orbiter was provided by fuel cells that used liquid hydrogen and liquid oxygen to generate power. They produced significant amounts of water as a by-product. Most people have heard of electrolysis, which is a process where you can produce hydrogen and oxygen by passing electricity through water. Well, fuel cells do the same thing in reverse. The good thing about them is that the water they produce is extremely pure and can be used for drinking, cooling, or other purposes. The bad news is that the fuel cells always provided more water than was needed, so the excess had to be dumped. Once the ISS was around, the Shuttle gave that excess water to them. The ISS was a vehicle that was “water poor” because it got its electricity from solar panels. The panels power the ISS with free energy from the sun, but unfortunately they don’t provide the water you get from fuel cells.

  The electrical generation and distribution system was essential to every system on the vehicle. It was looked after by the console operators known as Electrical Generation and Illumination (EGIL). The EGIL was another console position that dated back to the early days of US human spaceflight, and its operators were proud of the fact that they had been around forever. They always had a bronze eagle on the console to show their pride—until, of course, some other discipline decided to one up them and kidnapped the eagle. As I recall, ransom notes started appearing for the next year or so with pictures of the blindfolded eagle statue being delivered at random. I think it eventually came back, but not before at least one picture had it deep underwater in the Neutral Buoyancy Lab pool, with its own little scuba tank.

  EGIL was not only responsible for the fuel cells, they had to watch over the entire power distribution system of the Orbiter. If the DPS was the heart of the Orbiter, the electrical system was the power grid. Organized into more than a hundred individual buses, the main arteries split into smaller distribution buses then split again, and again. Each bus can be thought of like an individual circuit in your house, each with its own circuit breaker. Hundreds of circuit breakers spread through the cockpit protected the buses, along with some fuses and automatic relays. When a bus went down, it generally took multiple sets of equipment with it. As a result, every flight control discipline would be affected. It was easy to know what capability you had lost when one bus went down. It got more complicated when two went down, because now you had to analyze a two-dimensional matrix to make sure that you hadn’t lost critical redundancy. When a third bus was lost, along with a flight control channel, things really got interesting. That is where the EGIL lived… right at the point where all of these failures combined.

  Simulations were always busy for the EGIL, serving somewhat like the power company on a stormy night. With buses going up and down, and limited ability to troubleshoot (because you didn’t just want to close a popped circuit breaker without a dire need—you could start a fire if a short circuit had caused it to pop), the EGIL oftentimes couldn’t make anyone happy and just had to settle for the least bad of all levels of unhappiness.

  The EGIL was also responsible for the cryogenic (cryo) storage tanks that held the liquid oxygen and liquid hydrogen that fed the fuel cells, as well as the heaters that warmed the gases in those tanks so that they would generate pressures to feed the cells. Back in Apollo, the cryo tanks actually had motor-driven stirring paddles that helped mix the ultracold mixture of liquid and gas so that the oxygen and hydrogen would flow from the tank. No EGIL ever forgot that it was a cryo tank stir on Apollo 13 that ignited the oxygen tank when one of those motors short-circuited and caused a spark. Using the heaters in our tanks was a similar process. Even though the lesson was learned and design steps ensured that the same thing couldn’t happen with the Shuttle system, there was always a little catch of caution when turning on cryo heaters—and that caution lasted throughout the entire program.

  During major power bus or fuel cell problems, the Flight Director looked at the EGIL to give him as much power as possible in as safe a manner as he could. The EGIL was also fairly deeply involved in mission direction decisions, as the cryo was one consumable that you simply couldn’t live without. You never wanted to run out of cryo, or you had a dead vehicle—so managing cryo and power generation became the primary job of an EGIL Officer. They had a lot to do in the planning phase of a mission, defining who got what in terms of kilowatt hours at what times of the mission. Never tick off the EGIL—he could easily make your life miserable.

  The other critical system for crew survival was, of course, life support. Now you can seal human beings into a hermetic capsule, and they will survive on the air and water you gave them at the start (this is how the earliest Russian spacecraft worked). But it is usually better to provide a way to supply oxygen, get rid of carbon dioxide, provide water (and remove humidity), and control the temperature for comfort. In short, you need to maintain a habitable environment for the crew. On the Shuttle this was done with a number of specialized life support systems managed in Mission Control Center (MCC) by the EECOM. During the Apollo program and early Shuttle days, EECOM stood for Electrical, Environmental, and Consumables Manager. But when the electrical job was split off to the EGIL, the EECOMs kept the acronym but changed the first E to stand for Emergency—for they were always in the middle of any environmental emergency situation that might develop.

  Responsible for maintaining a breathable atmospheric pressurization, water supply and humidity control, and thermal control, the EECOMs operated a busy console position that watched over systems spread throughout the Orbiter. Many of their essential functions were things that the average person never even considered. While it is obvious that you need to provide air for an astronaut to breathe, it is not so obvious that one of the most essential systems on any spacecraft is the thermal control system. In short, you have a system generating electrical power, and every other system in the vehicle uses that electricity—but electrical boxes are notoriously inefficient users of power. They generally generate more waste heat with that power than they actually use. In an atmospheric vehicle, it is easy to dissipate that heat into the surrounding air. Because you don’t have that air in space you have to radiate the heat away if you can, or get rid of it in other ways. Think of the entire Shuttle as a heat generator. The computers, the communication systems, the fuel cells—and the astronauts themselves—all generate heat.

  To manage all that heat, the first thing you need to do is collect it. Heat collec
tion was done using water loops and heat exchangers—you heated water by running it through plates on which a computer or another electronics box was mounted. The electronics heated up the water running through those plates, and the heated water was then carried to a heat exchanger where the waste heat was transferred to a Freon-based cooling system. This Freon was then run through large radiators mounted to the inside of the payload bay doors, which were opened once you got into space. Since black space is extremely cold, the radiators would shed the heat from the Freon, run the cold Freon back to the heat exchanger, and pick up more heat from the water—and the cycle continued.

  But what did you do if the radiators weren’t yet deployed or were stowed for entry… or if a radiator developed a leak or a blockage? The heat wasn’t going away by itself, and heat was probably the biggest killer of systems if you let it get out of hand. You could manage a cabin leak by adding more oxygen or nitrogen from the tanks, but heat had to be rejected. So a secondary cooling system was developed called the Flash Evaporator (FES). The FES worked the same way that splashing water on hot skin cools you down on a warm day—the water is sprayed on a surface heated by your blood (or the hot Freon, in the case of the Orbiter) and the heat is released by the vaporized water. As a result, the working fluid (blood or Freon) cools down. In order to do this in the Shuttle, we used a supply of water and a flash evaporator surface that had heated Freon running through it. The resulting steam was vented overboard.

  Obviously, this system only worked so long as you had water available—but as we said before, the Orbiter was water-rich because that is what the fuel cells generated as a by-product when making electricity. Water on the Orbiter was a commodity—you needed it to drink, use it for hygiene, make up dried food with it, use it for cooling—and it was EECOM’s job to keep track of where all the water was and where it was going to go. He or she needed to make sure that there was always enough water stored for cooling the vehicle during entry after the payload bay doors had been closed. This wasn’t as simple as knowing how much water you needed to cool the vehicle for the nominal timeline—they also had to plan for contingencies like going around an extra orbit or two on entry day so as to get to a different landing site—or calling off the landing and getting the doors back open to try for another day. This water management was just one of the consumables that went into the COM part of the EECOM’s name.

  EECOM also had to manage the atmosphere in the vehicle. They drew oxygen from the cryo tanks that EGIL was using to generate electricity—a peaceful exchange of consumables in which they got O2 and EGIL had a place to dump their water. Nitrogen was stored in pressurized bottles in the payload bay, but rarely did the cabin require a great deal of nitrogen gas during a mission. The Shuttle was designed with an automated system to sense the percentage of O2 in the cabin, and maintain it by adding oxygen when it dropped below a certain level. Interestingly enough, we discovered early in the program that human beings use a very predictable amount of oxygen in a given period of time, and it was just as easy to manage the percentages by opening a valve and sending a continuous “leak” of O2 into the cabin. We could always turn on the automatic system, if we needed, or open and close valves to manage it manually in emergencies—but this controlled leak was simple and usually kept the oxygen level right where it needed to be.

  Of course, as humans use O2 they produce CO2—a gas that becomes poisonous to our systems in sufficient quantities. So it had to be removed from the cabin continuously, using CO2 scrubbers—canisters of lithium hydroxide (LiOH), which attract the CO2 in the air. The canisters fill themselves up with CO2, which couldn’t be removed during a mission, so we flew many cartridges of LiOH and changed them out on a regular schedule based on the number of crewmembers and their sizes. LiOH was a consumable that had to be tracked—and EECOM had that job as well.

  Humans generate an extraordinary amount of humidity as well—they breathe out moisture and exude it as sweat. This all went into the atmosphere and had to be removed on a continuous basis. This was done using a centrifugal humidity separator that spun moisture out of the air and collected it for transfer into the waste water tank. The waste water tank also collected urine for the Waste Collection System (WCS)—otherwise known as the toilet. And it was another of EECOM’s responsibilities. If you’re beginning to realize that EECOM was a busy person, you’re right! Generally, they were at the center of any systems-level emergency or crisis—not the least of which was the case of a cabin leak, where they had to determine the leak rate and recommend ways to stop it. If they couldn’t stop it, then it was their job to maintain cabin pressure using the stored gases at their disposal to get the crew home safely.

  On a long mission, of course, waste water tanks filled up and needed to be dumped. In fact, the same thing often happened with the fresh water tanks before we began donating water to the Mir and ISS. Water dumps were conducted through special nozzles on the side of the Orbiter. It could be fascinating to watch as the liquid in the tanks sprayed out of the nozzles and instantly froze into a little snowstorm. It was fun, that is until it began to freeze to the nozzle and form ice blocks or blobs. These could plug the nozzle and/or form a debris hazard should they break off. The nozzles were heated to prevent freezing, but heaters could fail, or the amount of water dumped could overwhelm the heater—so water dumps were always treated with special care, and not a little trepidation. Once space station docking became the norm, we realized that dumping water would contaminate solar arrays and scientific experiments, so dumps became a thing of the past as a routine operation. Instead, we stored the water in special, collapsible bags. Of course, we usually had to dump some of the waste water we were holding when we got off the station—especially if we weren’t going to come home right away. No one liked hooking up bags of waste water because fittings invariably leaked a few drops of the nasty stuff. But sometimes the bags just couldn’t hold it all.

  Propulsion, navigation computation, communication, electrical generation, and life support—these comprised most of the essential systems needed to make the Orbiter a functioning vehicle. Most—but not all. For the remainder of the critical systems, a special console position was created—the Mechanical Maintenance Arm and Crew Systems (MMACS—pronounced “Max”). The MMACS position was created after the Challenger accident. Before then, its responsibilities were spread out over a number of disciplines. But once this position was formed it stayed through the life of the program. Mission Control Center positions changed over the program as mission needs changed, and as we learned more about the best way to organize teams.

  The Mechanical systems (the first M in MMACS) of the Orbiter were numerous and varied. Basically, anything that opened or closed with a motor was considered a mechanical system; this included the payload bay doors, the vent doors, and things like the doors that covered the star trackers for ascent and entry. The air data probes, used to sense airspeed and altitude on entry, were also swung in and out on motors. There were also nonmotorized mechanical systems—the hatches, for instance. They were manually operated—and if you ever see a movie of a Space Shuttle hatch operating with a push button, you now know that they got it wrong.

  The MMACS’s job also included one of the essential systems for ascent and entry—the Auxiliary Power Units (APUs) that drove the hydraulic pumps that powered the flight controls. The three APUs (one for each hydraulic system) lived in the aft compartment. Each generated about 120 horsepower from a 9-inch turbine wheel driven by decomposing hydrazine fuel over a catalyst bed. They spun very fast (about eighty thousand rpm) and were cantankerous little devils for the first ten years of the program. The hydraulic pumps supplied motive power to the flight control actuators that were necessary to fly, and you need at least two of the three of them to give full authority to fly the vehicle. Technically speaking, you still had limited control with only one running—but it was easy to run out of control if the wind conditions were anything but light. You need more control capability in gusty or strong
winds, and a single APU simply didn’t provide enough power in those cases.

  In addition to the critical APU/hydraulic systems, the MMACS Officer was responsible for the landing and deceleration systems—the landing gear, tires, wheels, brakes, nosewheel steering, and the drag chute. All operated electromechanically and in concert with the hydraulic systems. The landing gear deployed, for instance, using pressure from any of the hydraulic systems, and those same hydraulics powered the brakes and nosewheel steering. The drag chute was developed after the Challenger accident. It worked in concert with the brakes to slow and control the vehicle on landing. It fell in the MMACS bailiwick, as well.

  The final major mechanical system to come along and get dumped in the MMACS’s lap was the Russian Docking System (APDS). This system was clearly designed by elves using magic fairy dust and built by relatives of Swiss watch makers—the number of cables, latches, cams, and gears was frightening. Yet it pretty much always worked and connected the Shuttle to the Mir and ISS on every flight that went to a station. The MMACS worked with the Russians to understand and operate the system, and eventually they made it a routine part of the overall operation. The system was considered androgynous—there were no male or female parts, and any APDS could dock to any other APDS. This was a great improvement over the less flexible Apollo (or Soyuz) probe and drogue: with a male and female component, and only certain things could dock with other things.

  The second M in MMACS stood for Maintenance—specifically In-Flight Maintenance (IFM). IFM is when the crew is asked to fix or take something apart in flight that was never really intended to be fixed or taken apart in flight. The IFM guys were all top-notch mechanics who knew how to jury-rig systems and use tools and parts in ways that were never intended. Over the years of the program, they had the crew build things from paper, plastic, duct tape, and glue. They gave the crews procedures to jump-start computers, swap black boxes, and rework plumbing to send water where it was never intended, in an effort, for instance, to bypass a clog or a failed valve. Although the EECOM discipline owned the toilet, the IFM guys were the plumbers—and they were the ones who figured out how to fix it when it went wrong. Those IFM folks worked for the MMACS, who represented their work and products to the Flight Director.