 Welcome to FuturePath. I'm Amarico Forresteri, the Director of External Affairs at the NASA Lewis Research Center. In this series, we are exploring research and technology programs that may affect our lives. This show deals with the present and the future. In a little while, we'll see how an advanced propeller aircraft engine now under test may replace conventional jet engines. But first, let's take a look at the Space Station. Here at Lewis, we have had an ongoing program to design power systems for future spacecraft. Before Lewis began to work on a power system for the Space Station, however, many years of research went by. Throughout the 30-year history of space exploration, there has been an evolution in our understanding and use of space. We began with exploration, pioneering kind of missions. We've demonstrated some initial space operational capability with the shuttle. We now want to make space a place where we live and work permanently. So Space Station, we believe, is the next logical step in that evolutionary process. The next logical step. We have visited space for short periods. We now have the capability and resources to make it a place to go to stay permanently, a place where we go to work and to do useful tasks. A Space Station is a logical place in which to do this. The main horizontal keel will have solar-powered electrical generating systems and pressurized crew in laboratory modules. The Space Station is being designed to serve a variety of users. Many experimenters have been identified. These will be earth viewing, space viewing experiments, many microgravity experiments. Space Station will be used for assembly of large structures, servicing of satellites and other payloads, and as a transportation node in the sense that payloads will be taken off of the space shuttle and put onto some other rocket to go into interplanetary space or to higher earth orbit. Space Station will be a research laboratory to conduct science and to develop new technologies. A permanent observatory enabling us to look down at earth and up at the stars. The station will be a servicing, manufacturing, and assembly plant, as well as a storage depot and a staging base. There are many other uses. The bottom line is that Space Station will be a multi-purpose facility, very much unlike the spacecraft that NASA has designed in the past, which were designed for essentially one mission. Space Station will be very different, it will be multi-purpose, and it will be very long-lived compared with previous spacecraft in the sense that Space Station is designed for approximately a 30-year lifetime. You contrast that with single-purpose satellites which might be designed for a few years at most. The role of Lewis Research Center in the Space Station program is to design the electrical power generating, conditioning, and storage systems. Power, the use of power for a civilization is a measure of its development. If you chart the usage of power on earth, you find that the more advanced societies use more and more electric power. The less advanced you are, the less you use. In space, we've been absolutely primitive in the first 25 years of the space program, scarcely using more than 10 kilowatts. To put that in perspective, your house uses about 25 kilowatts. So we're limited in what we can do, and that means we can't really flex our muscles in space. We can't utilize it. We can't understand it well. So we're power poor, and so we can't explore it. Power is vital to Space Station. Without power, the station could not work. Other space missions use a small amount of power in comparison to Space Station's needs. Communication satellites use up to about 10 kilowatts of power. Previously, the largest user of power in near space was Skylab. It used about 15 kilowatts of electricity. Space Station may use more than 20 times that, or nearly 300 kilowatts. To make that much electricity, Space Station will eventually rely on hybrid or combination of both solar cells and a solar dynamic system. The system to be used first is a solar cell system. Solar cells in large panels or solar arrays collect sunshine and convert it directly into electricity. The hardware to be launched first by the shuttle will be solar panels. They've been used to power spacecraft now throughout the history of the space program, and we have great confidence that they will work, that we will be able to manufacture, test, and verify their performance to a very high level of confidence. Early solar array panels are about 7 percent efficient, but now new improved solar arrays run at about 10 percent efficiency. Solar panels have a drawback. To produce about 300 kilowatts, 30,000 square feet of panels are needed. That's a lot. At first, two complete solar panels will be orbited for Space Station. Each unit will be about 110 feet long by 33 feet wide. Another problem created by the large size of the panels is atmospheric drag. Even though Space Station will orbit at about 250 miles, there are enough atoms of air at that altitude to impact on the panels and cause the station to slow down ever so slightly, so the station must be periodically boosted back into its original orbit. NASA is designing a system with a smaller area to reduce atmospheric drag. This system is the Solar Dynamic System. The Solar Dynamic System uses a concentrating mirror to collect and focus the sun's energy into a receiver that accepts that energy in the form of heat. That's very different than solar cells, which convert sunlight directly into electricity. Solar Dynamic Systems operate on heat. Use that heat to heat a fluid that runs through a turbine, causing it to rotate. The turbine, of course, is attached to a generator, which actually converts the mechanical energy of rotation into electrical energy. That circulating fluid is then reused in a closed system. Solar Dynamic Systems take sunlight, convert it to heat. That is transformed into mechanical energy and then finally into electrical energy. That sounds like a complex process, but the overall system efficiency there is greater than it is for photovoltaic devices. Besides having a smaller drag area, the Solar Dynamic System is more than 15 percent efficient and NASA is looking at other systems which are more than 30 percent efficient. They use different engines to drive generators. But what do you do if there's no sunlight? Communication satellites orbit at an altitude of 22,000 miles. These satellites rely on solar cells and storage batteries for power. Batteries supply electricity to the craft when it is in Earth's shadow. At 22,000 miles though, satellites rarely pass into the shadow of Earth. In low Earth orbit, space station will be in the shadow of Earth for about half of each 90-minute orbit. The initial space station, relying exclusively on solar cells, will require much larger batteries than previously used in space. But as Solar Dynamic Power Systems are added, energy storage will be a different matter altogether. In the case of the Solar Dynamic System, that energy is stored in the form of heat. The leading contender for storing that energy, that heat energy now, is some type of salt, a phase change material that converts from a solid to a liquid, and by virtue of doing that is able to store much greater amounts of energy. These salts, or phase change materials, are not like common table salts. The special salts melt at a very high temperature. When space station passes into the Earth's shadow, sunlight will no longer be focused onto the receiving cavity of the solar mirror. The salts will slowly cool and change from a liquid to a solid, giving off large amounts of heat to drive generators. Space station power systems will make a lot of electricity. Initially, more than 75 kilowatts, and more later, how will all this electricity be used? Probably the users will be the largest consumers of power. There is a class of experiments called materials processing that are estimating their needs in the tens of kilowatts. By far and away, that will be the single largest user of power. We also lump power into another category called housekeeping. By this, we mean electrical energy required to operate the environmental control and life support system for regenerating the air and water on board the space station. Housekeeping also includes lights, preparing food in the galley, entertainment devices, and so forth. Personal care devices that the astronauts might use, and communications and computer systems. All of that, we lump into housekeeping power. It will be not as large a user of electrical energy, but since we lump so much into that single category, it looks like a big number. The shuttle will first launch space station elements in the mid-1990s. Shuttle will be used in the assembly and checkout of the station. A number of launches will be needed, and there will be various phases of capability that the station will go through. It will be unmanned at first. Then, man-tended within a year and a half. Beyond that, the station is to be permanently manned. The ultimate benefit of space station to mankind will be to extend man's capability to explore the solar system. Space station will provide the necessary first step for future man missions in space. A permanent lunar base. A manned mission to Mars. A manned survey of the asteroids. Space station will enable the staging of future unmanned missions to the planets with the possibility of sample returns. But most importantly, space station will be the next logical step. Now, let's turn from the space station to a story about how propellers may again be back on passenger planes. In the late 1950s, jet aircraft entered into commercial service and essentially replaced the slower but more efficient propeller-driven aircraft. Then, in the late 1973, the oil embargo hit. NASA was mandated to explore all technologies that could significantly reduce commercial aircraft fuel consumption. The Lewis Research Center responded with the advanced turboprop program. What might look like a step backwards is actually two giant steps forward on the future path of advanced aircraft engines. Since 1941, the Lewis Research Center has developed an international reputation for its research on jet propulsion systems. However, in 1977, the researchers at Lewis began to take a new look at the propeller. Their challenge was to combine the efficiency of the propeller with the power of the turbine engine. What has evolved is ATP, the Advanced Turboprop Project. Keith Siebers, manager of the NASA Advanced Turboprop Project office at the Lewis Research Center. Back after World War II, jets were the coming thing. Propellers were very efficient in those days, but they couldn't go fast. They couldn't go to high altitudes. Quite frankly, they were not jazzy like jet engines, which gave way then to turbofan engines and high bypass ratio engines. When fuel was cheap, people didn't worry much about it, 10 cents a gallon. As long as they get speed, high altitude capability, which the air transport system required, propellers just kind of withered on the vine for 20 or 30 years. The Arab oil embargo of the early 70s not only hit American consumers at the corner gas station, but was also reflected at the airline ticket counter due to the soaring price of jet fuel. In 1973, the price of a gallon of jet fuel was 12 cents and represented one quarter of the direct operating cost of the jet. In 1981, the cost of jet fuel was over a dollar eight cents a gallon. With the rising fuel prices, a fuel-efficient propeller engine again became the object of an aeronautical propulsion research effort. The researchers' objectives were to develop a power plant that would be fuel-efficient, do .8 Mach, cruise at 35,000 feet, operate at a reduced noise level. Well, these propellers look a lot different. They're very highly swept. They're very thin compared to old propellers. And the thing that hits you first is there are eight to ten blades on these rather than three or four as you've been accustomed to in the past. And what the sweep does in the propeller in a thinness is to reduce the drag losses at the higher tip speeds and higher Mach numbers. It also helps to reduce the source noise of the propellers. The higher blade count, and we've loaded these blades up much higher than old propellers, so we can get a lot more power at a lot smaller diameter. And this saves weight on the propeller, saves weight on the engine, and it also packages better on the aircraft. These two turboprops were limited both in horsepower and in flight speed, mainly because of the compressibility effects that occur at the propeller tips. With the recent advances in computer design technology, we are now able to optimize the blade shape to minimize the compressibility effects occurring at the blade tips, allowing the planes to fly faster, up to 600 miles an hour, and at higher altitudes, up to 35,000 feet. As you approach the speed of sound, you run into a problem where the apparent pressure that you're trying to push through suddenly takes a quantum leap. And because the blades are very large in diameter, to 13 feet in diameter, the tip speed is upwards of 800 feet per second, which is just under Mach 1, or the speed of sound. As you try to push through that Mach 1 range, you run into this compressibility factor. It's almost like running into a brick wall with the blade. Blade construction is now a composite type arrangement where you have a metallic leading edge, such as aluminum and a graphite epoxy-resigned internal construction that allows the blades to be very lightweight. And because they're lighter weight, minimizes the centrifugal stresses that occur when the propeller system is rotated at 12,000 rpm. The ultimate goal is to save fuel, commercial aircraft and also military aircraft where it can be applied. And this fuel saving is very dramatic compared to the fuel burn that aircraft have today, such as a 727, 737, that type of aircraft. A pop fan driven airplane can do the same mission at like 40 to 50 percent of the fuel that they use today. If you look at just the US fleet existing today for medium to short range aircraft, and I'm talking 727s, 737s, DC-9s, MD-80s, those aircraft in a typical year burn about 5 billion gallons of fuel. If these aircraft were equipped with prop fans, they could do the same mission they're doing today and save two to two and a half billion gallons of fuel per year. Propeller driven airplanes have traditionally been noisy. Advanced turboprop researchers are tackling the problem of trying to build a turboprop to rival the relative quiet and smoothness of the jet. Well, we've had to look at the entire aircraft as a system. We didn't look just at sticking a new widget called prop fan on them. Had to look at what to do to the rest of the aircraft. And particularly we're concerned about passenger comfort. It doesn't matter how much fuel we save, if the people don't like it or they're uncomfortable, sound, vibration, they're not going to ride it. So it won't matter. So part of our project goal is to make sure that people have the same comfort that they're used to on today's wide-body aircraft. In addition, we're concerned about community noise. These things are allowed and we have to provide the technology so that they can live within the existing FAR 36 stage 3 regulations which are laws that we have to abide by around airports and communities. Most of the time, we really don't even know what's running inside the cockpit. It's that quiet. And we're only, what, 15 feet away from it. After several years of wind tunnel and static engine testing, a full flight test of the advanced propeller system was held on May 19th, 1987 at Lockheed Georgia Company in Marietta, Georgia. So far operation has been very good. Everything is about as predicted that the engineers had predicted from their initial assessment of the program. We haven't really had any big surprises, I should say. When you pull the prop fan in and add power to it, the pilot really knows it. But there again, this airplane wasn't really designed to fly with an engine out on the left wing. But again, what our engineers predicted is pretty much what's happening with the airplane. So I'd have to say so far it looks good. So far it looks very good. If all goes to plan, prop fans will probably be fitted on short to medium range aircraft. We hope to have, as a part of the project goal, to have the technology in hand by the end of the 1980s, so that industry, the engine people, the aircraft people can make marketing decisions because it involves a lot of private capital that makes or breaks their company. So the way things are proceeding right now, it looks like Boeing and McDonnell Douglas are aiming for new aircraft industry with prop fans in, say, the 1991, 92, 93 time frame. The Advanced Triple Prop Program that you just saw will help maintain the U.S. aircraft industry in a dominant world leadership position. Well, we've nearly come to the end of our show. But before we go, let's watch this NASA-Lewis Research Center overview. This segment will show you some of the high tech facilities and people who make it possible for Lewis to accomplish its mission, to develop advanced technology for high priority national needs. Six, we have main engineering mission. Three, two, one. And solid building ignition and liftoff. Liftoff of the faith operational space center mission with two satellites on board, and the shuttle has cleared the tower. What's the whole pitch program? First rule on the earth. Houston out-control emission control control. Thank you for spending some time with us. Please stop by and see the many displays and programs at the visitor center here at Lewis. We are located near Hopkins International Airport in Cleveland, Ohio. Admission is free and we are open every day. Until next time then, this is Amarico Forest Area saying goodbye.