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Composites, computers, & sensors boost the space station

DN Staff

September 8, 1997

13 Min Read
Composites, computers, & sensors boost the space station

After well over a decade of thinking and rethinking, design and redesign, one of the largest construction projects on--or off--Earth is about to "break ground." The first elements of what is now called the International Space Station (ISS) have been delivered to the Kennedy Space Center for placement in orbit next year. But, as the average home owner knows when hiring contractors for even a small job, someone usually has a problem in meeting the schedule.

In his 1984 State of the Union address, President Reagan charged NASA with building a space station along with this country's allies. The effort was altered over the years in light of changes in Shuttle flight rates and safety concerns--stemming from the Challenger accident in 1986--as well as continuous efforts to cut program costs. Meanwhile, by the early '90s, the Soviet Union had dissolved and the resulting individual states became potential partners. By 1993, after another cost-cutting push by the newly installed Clinton administration, NASA selected Boeing as the prime integration contractor to pull the whole shooting match together. NASA also tapped the aerospace giant to build the US-furnished laboratory and habitation modules, six-port connecting nodes, and the environmental-control and life-support system.

While international participation is spreading the work and expense, such cooperation does not come cheap. That's especially true when building a million-pound orbiting facility that's as long as a US football field and one-and-a-half times as wide. In addition to $11 billion in development money spent before 1993, Boeing is coordinating for NASA a program projected to cost the US $17.4 billion through completion sometime after 2002. US costs also include funding Russian contributions to the station. The European Space Agency is kicking in $5.2 billion, Japan $3.1 billion, and Canada $900 million. In all, fifteen nations, and more than 100,000 people, are working on the project.

When assembled, a pressurized volume the equivalent of a Boeing 747 (43,000 ft3) will be afforded astronauts and re-searchers. Three launch vehicles, the Space Shuttle and Russian Proton and Soyuz boosters, will make 45 flights to assemble the ISS. In orbit, elements of tens of thousands of pounds will maneuver into place, with astronauts making the final hook-ups of cables, tubes, and fittings. Sixteen 100-ft long solar panels, the largest ever built, will generate 110 kW of electricity that will be distributed, used, and stored in a system made by Rocketdyne, now a unit of Boeing Space Systems. Doug Stone, Boeing space station program manager, sums up the enormity of the task: "When you consider all the people, in all the manufacturing facilities, all producing one-of-a-kind space hardware that must come together out there in space and work perfectly the first time, it is phenomenal. This is definitely outside the experience any of us have ever had before."

Clarence Howard, Boeing's lead engineer for vehicle integration says, "The ability to do design by CAD/CAM made all the difference in the world in producing a close-tolerance and lighter station." One such tool was an "electronic design-fixture," a virtual representation that allowed "building" the station a piece at a time without a physical mockup. Engineers could detail and "test" interfaces between station elements such that a component launched late in the assembly sequence will be matched to the piece it mates with that's been in place for years. From CATIA to Unigraphics, virtually all software packages available were used in station design.

Howard notes the actual assembly process will be geared for automation. Robotic grapples will position elements for joining and automated AlliedSignal Aerospace (Teterboro, NJ) motor-bolts will tighten to predetermined torque levels. He adds that the joining flexure between modules, designed by McDonnell Douglas and now part of Boeing,"has a radial give so if thermal distortion between modules is present, they can still mate."

To build an experience base before assembly begins, what is termed Phase I is now well underway. This includes Shuttle missions docking with the Russian Mir space station to test approach and docking techniques, and the Russian docking system. The flights also validate the ability of the Shuttle to control the attitude of large structures in space and prove spacewalk hardware and methods.

Boeing not only heads up integrating the International Space Station, but furnishes the US laboratory and habitation modules, and connecting nodes for expansive research facility.

Delving in the details. While quarterbacking the ISS effort and building several station modules, Boeing is also turning its expertise to the nuts-and-bolts level of engineering that future station users will experience directly. In just the US, by 2000, NASA sees the station supporting more than900 investigators. Their payloads must be designed, built, launched, and installed in the ISS, and astronauts trained to operate them. And communications between all researchers and their payloads and crew on the station have to be coordinated. To ease this integration, Boeing's Huntsville, AL operation has built an experiment-equipment rack to Expedite the Processing of Experiments to the Space Station (EXPRESS).

NASA Marshall Space Flight Center's Payload Projects Office developed the EXPRESS payload system. The Boeing-built rack, made of composites, provides multiple smaller payloads with fast, simple integration by allowing standardized hardware interfaces. The "plug-in and go" rack will allow the experiments to be easily transferred to the station laboratories from Shuttle delivery flights. The standard interfaces will allow researchers to have an experiment in operation on the station in about 11 months from signing an agreement. Currently, the rise time from signing to space is three years and up.

There is room in the 570-lb rack for up to eight Shuttle-type middeck lockers and two standard interface rack drawers. Experiments are controlled on-board from the experiment itself or the rack's laptop computer, or remotely via uplink from the ground. In addition to a power distribution and protection system, the rack has a subsystem to supply cooling air for electronics. A communications system links the experiments, the station data system, and ground controllers.

The EXPRESS Rack made its first flight as part of a Shuttle cargo-bay Spacelab mission flown in April of this year, and continued in July after the initial mission was cut short. The rack contained four middeck lockers, the space for the other four lockers, and the drawers. One experiment was installed in the rack after the Shuttle arrived on orbit to simulate a late-access payload. Ted Davis, EXPRESS Rack manager for Boeing, notes, "This pathfinder rack was developed in just two years with a small multi-disciplined team. One of the biggest challenges was being the first to take a piece of space-station-developed hardware off the production line, and integrating it with the Spacelab interfaces and requirements." Eight racks are currently planned for the ISS.

Howard also mentions that all station racks will be equipped with an Active Rack Isolation System. This prevents high-frequency vibrations caused by crew movements from affecting microgravity experiments. Sensors on the rack detect such vibration and drive small electric actuators to cancel the motion.

Gift from the sea. In addition to a research facility such as the space station, Boeing is also looking into the hard commercial prospects of space systems and has partnered with worldwide firms to exploit the demand for satellite launching services. Here the name of the game is to deliver payloads to orbit--geosynchronous for many communications satellites--while minimizing the cost of getting there. The result is Sea Launch, a Boeing-led partnership that uses "tried and true technology" for a unique commercial launch system. It's the first system to conduct such launches at sea from directly on the equator in the Pacific.

The modular EXPRESS Rack will allow hundreds of space-station researchers worldwide to quickly obtain orbital access and furnishes data via standardized interfaces. The setup shown was flown on the first test missions earlier this year in the Spacelab carried in the Shuttle cargo bay on flights in April and July.

Equatorial launching, from about 1,000 miles southeast of Hawaii, takes maximum advantage of the Earth's rotation to impart energy to the booster and satellite. Two special vessels will provide the system infrastructure. The first is a modified 31,000-ton North Sea oil-drilling rig that serves as a self-propelled, semi-submersible launch platform for the three-stage Zenit booster rockets. Shipbuilding concern Kvaener (Oslo, Norway), a partner in the venture, modified the platform with an extra pair of supporting legs and extended underwater pontoons on each side. The company is also completing an Assembly & Command Ship (ACS) that will be the floating rocket assembly plant and mission control center.

Other members of the concern are Yuzhnoye/Yuzhmash (Dnipropetrovsk, Ukraine), which makes the two-stage Zenit booster, and RSC-Energia (Moscow, Russia), supplying the third-stage Block DM-SL--a modified Proton rocket DM fourth stage with more than 150 successful flights. In addition to oversight, Boeing is building the composite payload fairing structure that serves to encapsulate and protect the payload from integration until orbit is reached. Saab-Ericsson Space (Goteborg, Sweden) furnishes the spacecraft-to-booster adapter and separation system.

Liquid Fly-back Booster: Liquid rocket boosters for the Space Shuttle have been proposed in the past. Now Boeing is looking at such boosters again. This time there is a twist-small jet engines that deploy after separation from the Shuttle, allowing the two boosters, connected with a winglike structure, to fly back to the launch site. Liquid boosters would increase performance and permit checking all engine functions prior to committing the Shuttle to a lift off.

SBIRS: The Space Based Infrared System Low now under development by Boeing for the Air Force is the low-Earth orbit component of a complete space-based infrared missile warning system. These satellites will furnish mid-course tracking of targets for any future defense system as well as be used for "intelligence" purposes, such as missile-test monitoring.

Navistar Global Positioning System: Rockwell, now Boeing, has furnished 40 of the US Global Positioning System satellites. Boeing will also build 33 of the next generation GPS satellites.

Inspector: Along with Daimler-Benz and RSC Energia, Boeing is developing the Inspector free-flier to furnish auxiliary viewing and lighting external to the space station. It will also transport tools and replacement units and can be used for astronaut rescue and assistance. Boeing is also investigating advancedvehicles for emergency station crew return to Earth or station resupply and crew replacement.

Space Shuttle: By virtue of its takeover of Rockwell space operations, Boeing is the prime contractor for the Space Shuttle. It also furnishes the Inertial Upper Stage for Satellite deployment from the Shuttle and is a partner with Lockheed Martin in the United Space Alliance which conducts Shuttle operations for NASA.


Boeing picked the Zenit because of its high degree of automated checkout and servicing before launch. As the rocket pivots to the vertical on its erector, all utility lines and fueling couplings leading to connector "plates" are automatically mated to a matching fitting on the launch pad. About 3,500 electrical and 25 fuel lines are hooked up in 21/2 minutes. Computers and control personnel on the ACS then check systems and activate fueling. Plans are to initially conduct one launch for each sailing. Eventually, multiple launch missions may be undertaken with up to three boosters stored on the ACS for transfer by crane to the launch platform while at sea.

Home port for the two Sea Launch vessels is Long Beach, CA, convenient to both launch locations and communications-satellite manufacturers based in the state. Any polar-orbiting satellites could be launched from a northern Pacific spot. Allen Ashby, Sea Launch president says, "The mobility of the system, allowing us to best position ourselves for each individual mission, is a key feature. A very capable, relatively heavy-lift rocket, and processing facilities conveniently near to major satellite manufacturers also have proven to be strong selling points." As of this writing, 18 launches have been contracted--13 for Hughes Space & Communications and five for Space Systems/Loral. First launch will be for Hughes in the fall of 1998.

Space-station two step

Failure of the Russian government to timely fund the Russian Space Agency has caused a projected eight-month delay in construction of the space station's Service Module (SM) and dictated some quick thinking on the part of NASA, Boeing, and the other International Space Station partners. Being one of the first elements launched, the SM obviously directly affects all those scheduled immediately afterward in the assembly chain. But the module's functions required backstopping as well.

For starters, the first assembly-sequence flight has been pushed back from next November until June of 1998 when the Khrunichev (Moscow, Russia) Functional Cargo Block (termed by its Russian acronym FGB) will be lofted by a Proton booster. The FGB is a 20-ton pressurized spacecraft that supplies control propulsion, fuel storage, ground communications, and electrical power during early stages of construction. It will be used to rendezvous and dock to the SM. In July 1998, a Space Shuttle launches the second station piece--the Boeing fabricated Node 1, whose six ports will anchor station elements such as the Boeing laboratory and habitation modules, as well as the FGB.

When launched, Node 1 will have two McDonnell Douglas Pressurized Mating Adapters, one forming the interface and passageway with the FGB while the other provides a Shuttle docking port. The third flight, in December next year, is the scheduled delivery of the SM to mate with the FGB at its end opposite Node 1. The Service Module furnishes environmental control and life support functions, is the primary docking port for Russian Progress resupply and refueling ships, and provides propulsive attitude control and reboosting to maintain the station's orbital altitude.

Under Boeing's direction, to cover more bets, Khrunichev is adding an attitude control capability to the FGB. Other enhancements include Progress electrical power and on-orbit refueling hookups at a lower docking port for refueling in the absence of the SM, and upgraded avionics. "These modifications make the FGB a more robust vehicle," says Michael Wood, Boeing FGB deputy program manager, which also means they pull the schedule bacon out of the fire if the SM is further delayed. "Additional attitude control and avionics will maintain the station in the assembly [process] as components are added. Modifications to the aft port will allow docking of either the SM or an interim control module."

In a twist on the Cold War mentality in place when the space station was proposed under the name Freedom, an "interim control module" could be based on the US satellites used to spy on the former Soviet Union. Until the SM or substitute is attached, the FGB will control motion and station altitude. In the final station configuration, the FGB will serve as storage volume and a fuel depot.

Space

1998 sees the launch of the first components of the International Space Station. NASA long ago selected Boeing as the company to make that orbital research facility happen. But, while the space station may be one of the company's highest profile projects, Boeing is also involved in satellite-launching services, such as Sea Launch. It's the first system to launch at sea, from the equator.

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