Outposts on the Frontier: A Fifty-Year History of Space Stations (Outward Odyssey: A People's History of Spaceflight)

by Jay Chladek

  The cooling system used by the ISS would be ammonia based, with the primary coolant lines running completely outside the habitat areas. Ammonia is a very good coolant and more efficient than the glycol-based coolants used on Salyut and Mir, which is why it is used in industrial refrigeration units on Earth. However, its vapors can also be toxic to astronauts in smaller amounts than glycol. For the internal cooling loops inside the modules, a nontoxic fluid was used instead, and redesign work was done to the coolant lines to help safeguard them against corrosion over the service life of the station.

  Zarya

  The decision to use an FGB module for the ISS came about because of delays in development of the RSM. The Zarya FGB included its own solar arrays along with guidance and propulsion systems, so it could act as the nucleus of a station until the RSM was ready to fly. Even though Energia was in a little healthier state financially by the late 1990s, work delays and bureaucracy were still the order of the day, leading to slippages in work schedules. Thankfully, the Zarya module was not under Energia’s direct control, as it was built by the Khrunichev State Research and Production Space Center.

  Khrunichev was a merger of two of the older Soviet factories that had ties to Chelomei’s OKB-52. The former Myasishchev factory in Fili, which became part of TsKBM and later NPO Energia in the late 1970s when the DOS and OPS Salyut programs were combined, became an independent group in 1988 known as the Salyut design bureau with responsibilities over module development for the Mir program. The second group was the Khrunichev factory, which manufactured Proton boosters while also maintaining its manufacturing responsibilities for Energia and other firms. The two companies merged together to become the Khrunichev State Research and Production Space Center in 1993.

  While Energia’s problems were causing so many headaches for NASA during the 1990s, Khrunichev was having more success. The four-stage version of Chelomei’s Proton booster had become a very popular launch vehicle, winning several contracts for lofting communications satellites. The fall of the Soviet Union made it possible for Western companies to deal directly with providers of launch services in Russia, and Proton was the most capable booster in their arsenal. Today, Khrunichev continues to build on its successes as part of the International Launch Services (ILS) partnership with Lockheed Martin in the United States.

  While technically Khrunichev was a major subcontractor on the Russian Service Module, that particular project was managed by Energia. On the other hand, Khrunichev was the prime contractor for the Zarya, and the group coordinated its work with both Boeing, which was the prime U.S. contractor for the American side of the ISS, and NASA directly. So while the RSM fell behind schedule, the Zarya FGB was delivered on time and on budget. All parties involved considered the partnership between Khrunichev and the Americans to be a harmonious one compared to some aspects of the Energia partnership.

  As part of the revised construction sequence of the ISS, the Zarya module was launched first and would be joined in orbit by the first American segment, the Unity node, on shuttle mission STS-88. The original plan was for the Zarya and Unity complex to independently operate from six to eight months before the arrival of the RSM. But ultimately, the RSM would not be ready to fly for nearly two years. Thankfully, Khrunichev built their module well, as the FGB performed its job as the early brain of the ISS with very few problems.

  Unity Launches!

  On 4 December 1998 the space shuttle Endeavour sat on the launchpad at KSC in preparation for launch on mission STS-88, the first shuttle mission dedicated to construction of the ISS. At 03:35 EST the exhaust plumes from Endeavour’s SRBs turned night into day as the shuttle climbed into orbit. In its payload bay was the first U.S. module, the Unity node of the ISS. A node module is essentially an intersection module, featuring an attachment port on both ends as well as four radial ports. Each port is known as a Common Berthing Mechanism (CBM) and would allow for other station modules designed in the United States, Europe, and Japan to attach to the node like a giant construction toy.

  Being more than a simple docking port, CBMs also allow a module to be plugged in to the station’s power and cooling grids, as they include electrical and support system connections that are linked inside after docked modules are firmly secured together. By allowing the modules to dock this way, the connecting hatch passageways are free of obstructions, and the hatches themselves can be shut quickly in the event of an emergency. The CBMs themselves are round, but the transfer hatches are much larger and square in shape compared to a typical round docking hatch. This was done in part to allow large equipment racks to be floated through the station’s hatchways as needed.

  To dock with the Russian Zarya module and shuttle, each end of the Unity node was equipped with a Pressurized Mating Adaptor (PMA). A PMA essentially turns a CBM into a docking port capable of accommodating a spacecraft equipped with an APAS-style docking port, such as the shuttle, a properly equipped Soyuz, or other spacecraft that were still on the drawing board in 1998. The reason for not using a CBM as a standard docking port was related to the size of the hatch and the requirement for extremely tight tolerances. An RMS arm is needed to position a module on a CBM. A PMA also has some built-in shock-absorbing capability, should it see a rougher-than-normal docking.

  In cross section, a PMA looks sort of like an offset cone with a squared-off skinny end. The offsetting was done to provide the proper clearance issues with the space shuttle’s docking port. One PMA was permanently attached to allow Unity to join with a docking port at the end of the Zarya module. The second PMA would only be attached temporarily for shuttle dockings, and it would be relocated to make room for additional modules on later flights. Since PMAs can be docked with other CBMs, they can either be used as active docking ports or stored temporarily out of the way as needed.

  After reaching orbit, the Unity module was attached to Endeavour’s docking port with the shuttle’s RMS; after three days of flight, the shuttle caught up with the Zarya module. Instead of trying to dock something as massive as a shuttle with a module to a relatively lightweight FGB, the shuttle RMS was used to grasp Zarya and berth it to the PMA on top of Unity. The two modules were docked with one another early on the morning of 7 December. The reason for the unusual hours of operation was so that the two modules could be docked over Russia’s tracking stations during daylight hours.

  At docking, the new ISS weighed thirty-five tons and measured seventy-six feet long (twenty-three meters) from one end to the other. From that point on, it would only get bigger. After docking, shuttle mission specialists Jerry Ross and James Newman conducted space walks over the next two days to hook up power and data cables between Zarya, the PMA, and Unity. These tasks would become commonplace in the coming years of ISS construction, along with other tasks such as hooking up ammonia coolant lines. On the second space walk, the pair removed launch restraints and covers from Unity’s exposed CBMs.

  On 11 December, hatches between the shuttle and the ISS were opened for the first time by mission commander Bob Cabana and Russian mission specialist Sergei Krikalev. For the next few days until undocking, the shuttle crew spent their time unstowing equipment inside Unity from prelaunch storage containers. Some equipment was changed out as the two modules were given a thorough checkout in preparation for the first crew. In Krikalev’s case, he would be revisiting the ISS as a crewmember on Expedition 1, once the RSM was ready to fly. A third space walk was conducted a day later to install additional communications and docking antennae on the outside of both modules. After six days of joint flight, Endeavour undocked from the ISS, allowing it to fly free. Its new communications capabilities and activated systems would allow controllers on the ground in both Houston and Moscow to monitor its systems and operate them remotely as needed.

  In addition to the normal equipment transfers, astronaut Bob Cabana also carried up a couple of interesting items of significance. The first was a logbook for the station. This book was the brainchild of fellow pilot-astronaut Jeff Ashby
, who felt that having a logbook in the finest tradition of seafaring ships of old would be a way to help record its history. Unlike the great creations found on planet Earth, such as the pyramids of Egypt, one day the ISS will eventually be deorbited, leaving no other permanent record for future generations to look back on. Ashby approached the National Naval Aviation Museum in Pensacola, Florida, and recruited them to custom make and donate a logbook to the cause, which they did entirely on their own at no cost to NASA. On the front of its metal cover were printed the words “International Space Station One” (which in hindsight Ashby says is not entirely accurate, since Mir was technically the first international space station). On the back cover was printed an appropriate quote by English poet T. S. Eliot: “We shall not cease from exploration, and the end of all our exploring will be to arrive where we started and know the place for the first time.”

  The second item carried up by Cabana was a ship’s bell. This was another idea from Ashby, with the intention of starting a second tradition on the ISS with its roots in nautical history. Its intent was to show good order and mutual respect. The bell could be rung each time there was a return of an ISS crewmember or a change of command. But what it is perhaps best known for is that each time a shuttle would arrive or depart, the bell would be rung twice to signify the event. Again, Ashby enlisted the assistance of the National Naval Aviation Museum in Pensacola to create the bell. To give the bell a connection with previous spaceflight endeavors, a small space was hollowed out in part of the bell, and inside it were placed shavings from the Naval Academy class ring of Mercury astronaut Alan Shepard; shavings from the ship’s bell of the nuclear aircraft carrier USS Enterprise; a screw from Mir; and by some mysterious circumstances, shavings from Ashby’s own naval aviator wings.

  The logbook was briefly brought back for refurbishment in 2006 before being returned to the ISS. However, the bell was replaced after a couple of years since the tone of its ring didn’t sound so good in orbit. It was replaced with a different bell that had a better sound. The original ISS bell is currently housed at the National Naval Aviation Museum.

  Like Mir, the orbital inclination of the ISS is 51.6 degrees, and this was needed due to how far north the Baikonur Cosmodrome is from Earth’s equator. Rockets launching from Baikonur can’t launch into lower-inclination orbits. There was some criticism that the orbit selected would prevent the ISS from being used as an effective launching platform for probes to the moon or other planets, but the orbit would also allow for much of Earth’s surface to be surveyed on an ongoing basis.

  Another problem with the orbit is that it limited the amount of cargo that can be carried up. In a lower-inclination orbit, a spacecraft can gain additional velocity due to the speed of Earth’s rotation. To compensate for a lack of this velocity assistance, NASA put the space shuttles Discovery, Atlantis, and Endeavour on a diet during their scheduled refits to help save a few hundred more pounds of weight for cargo. More powerful main engines had also been developed for the shuttles to give them a little more kick on the climb to orbit.

  The launch window from KSC to intersect with the orbit of the ISS is only about five minutes long, so shuttle flights to the ISS would require precise launch timing. During each day, the time that the ISS orbit passes over a certain point of the earth advances by about thirty-seven minutes. A missed launch opportunity means that a spacecraft launching from KSC has to wait about twenty-three and a quarter hours before it can make another launch attempt. Technically, the ISS orbit passes over Florida twice each day due to its ground track with one orbit being an ascending node trajectory (its path being from southwest to northeast) and the other being a descending node trajectory (northwest to southeast). While a spacecraft theoretically could be launched from KSC on either trajectory, launches toward the south are never done since the ascent path would take a rocket over Cuba.

  Data Transfer

  On the U.S. side of the ISS, the command-and-control computer boxes in each module, known as MDMs (Multiplexer De-Multiplexer), use 80386 processor chips, similar to what home computers used in the late 1980s. This may seem like an outdated technology, given that several generations of more sophisticated and powerful processors have been made over the past two decades. Even smartphones today have faster computing power, but NASA had some good reasons for doing this. First, an older technology is a well-understood technology, which means problems are less likely to develop if older systems are used. Second, microscopically compared to a current-generation processor chip, an 80386 chip set is big and not as densely packed with circuit pathways. So if a stray cosmic ray were to hit the chip directly, it would be less likely to hit a critical area and may pass completely through without doing damage at all. As for the computing power needed to run systems on the ISS, the processors are up to the task since they don’t need to run anything that requires a lot of calculations, unlike graphics found in modern computer games.

  The Russian side of the station still used its own computers based on Mir-type architecture. Three Russian computers were used for the station’s primary attitude control, while an additional three were used to handle other systems. One of the delays in getting the RSM ready for flight involved how to network them with the systems on the U.S. side. Part of that task fell to a recently selected astronaut named T. J. Creamer.

  A little less than a year before the scheduled launch of the RSM, Creamer visited Russia to hash out details for a network. He had three plans for consideration: a primary plan, a backup plan, and a backup for the backup. Upon meeting with his Russian colleagues, he proposed his ideas. The first idea involved running a coaxial cable between the Russian and U.S. segments across the open hatchways. That idea was rejected since the Russians didn’t want to run any exposed cables between the hatches in the aftermath of the Progress collision with Mir and the criticism of that practice. The second plan would involve using a wireless network router. At this time (early in the year 2000), there was no accepted standard for router architecture. There were a couple of off-the-shelf wireless systems that could be used, but the Russians were concerned that the radio frequency interference would violate the EM (electromagnetic) and RF (radio frequency) constraints required for the scientific payloads planned for the station. So idea number two was rejected. The third idea involved line-of-sight transmission of the network signals with an infrared light system across the open hatchways. The use of infrared signals instead of radio signals is something commonly seen today with radio-controlled toys; in some applications, it is a nice alternative to using radio frequencies. But the Russians rejected that idea because it could set off the fire detectors in the station, since infrared energy is also heat. So in one meeting, all three of Creamer’s ideas were rejected.

  After a night at the hotel coming up with alternatives, T. J. Creamer went back the next day and asked the Russians if they had any unused data cable on the outside of the RSM. It turns out there was. After looking at the specifications for the cables, Creamer and the Russians hashed out a plan to use the cables on the outside with some adapters at each end to make them compatible with networking the American and Russian computers together. Since the cables were already built into the RSM, the cost to add the capability was reduced down to just creating the adaptors. Since the cables also ran outside of the hatchways, they wouldn’t get in the way in case a hatch needed to be closed in an emergency. So one issue of many was overcome.

  More Outfitting

  About five months after STS-88’s mission, the space shuttle Discovery was the next one to visit the station on STS-96. This time, the shuttle was packed with supplies in a Spacehab module to outfit the station’s interior in preparation for the first crew. Discovery’s cargo bay also included a new design of pallet rack known as the Integrated Cargo Carrier. It contained equipment that the crew would attach to the ISS during a pair of space walks. Among the equipment were parts for a Russian Strela crane similar to what Mir utilized and a smaller type of U.S. crane known as the ORU Tran
sfer Device. The Strela would be an important piece of equipment for use in EVAs conducted from the Russian side of the station using Orlan suits.

  After Discovery’s visit, the RSM was still not ready for launch, and it would be over a year before the next shuttle would visit. Part of the reason for this was mission scheduling, as the next three shuttle missions were dedicated to the launching of the Chandra X-Ray Observatory, a servicing mission to the Hubble Telescope, and a space radar topography mapping mission. Problems were also encountered during the launch of STS-93 as a short circuit shut down two of the space shuttle Columbia’s main engine controllers at liftoff, forcing the vehicle to switch to onboard backups. There was also a slight fuel leak in one of the shuttle’s main engines. Columbia made it into orbit and was able to deploy the Chandra observatory without any problems, but when the orbiter returned from its mission, an inspection revealed that the short was due to chaffed wires in Columbia’s engine bay caused by worn insulation. The rest of the shuttle fleet was grounded for inspections, resulting in a six-month delay before the Hubble and radar mapping missions could fly.

  The space shuttle Atlantis flew the next mission to the ISS on STS-101 in May 2000. Some EVA construction work was done to outfit the station’s Strela crane with another segment and fit additional EVA handholds, but the primary task was to give the Zarya module a tune-up, as some of its onboard batteries needed replacement. Air filters and fire extinguishers were replaced with fresher units, and some work was done to reconfigure how air circulated inside the station. Since the station’s internal electronics need air circulation to help with equipment cooling, it couldn’t be depressurized, so the filter replacements were necessary. Atlantis spent five days docked with the station before returning home. At a glance, everything seemed fine with the orbiter, but inspection of a wing panel after landing revealed that there was internal damage due to a small heat leak during reentry. The damage was logged and repaired in preparation for the next mission. The ramifications of this incident weren’t fully realized at the time.