 Welcome to this edition of NASA Images. I'm Lynn Bondrant. During this show, we're focusing on historic NASA film showing electric rockets and more recent videotapes showing how we may someday explore Mars. First, let's go back to 1965 to see most of the film electric propulsion. Though made in the mid-1960s, much of the film is still current. A concept showing how electric rockets could be used to fly space travelers to Mars is included. Imagine for a moment that this is the period of the 1970s and 1980s, a period of amazing explorations in space. Imagine that the distant planet Jupiter is to be investigated scientifically by a spacecraft that will fly close by. At the correct place in its orbit, its conventional chemical engines are fired to accelerate it to the velocity needed to get to Jupiter. Imagine also that nine and a half months later, a craft with advanced engines is launched. It slowly accelerates until it escapes Earth's gravity one year after the conventional craft started. Of course, the first craft is well on its way. Since leaving Earth, it has been coasting and its velocity has continuously decreased. But constant thrust is applied to the second craft for six months, which continuously increases its velocity. Even though it escaped Earth a year later, it reaches Jupiter about eight months ahead of the conventional craft and carries three times the payload. What could make this possible? Electric propulsion as used in the hypothetical second spacecraft and it is now under active research and development. Since the advent of the space age, the roaring flaming spectacle of the chemically fueled rocket has become a common occurrence, carrying space vehicles into Earth orbit and deep space. The weight of such a payload is extremely small compared to the lift-off weight of the entire rocket because a chemical booster can put only two to three percent of its weight into orbit. This lifting ratio cannot be improved significantly. Yet today, the chemical rocket is the only means of launching a payload from Earth. Once a vehicle is in Earth orbit, a chemical engine can send only about one-third of its orbital weight to the moon or the near planets. Two-thirds is fuel and engines. The craft quickly burns the fuel of its final stage to accelerate the payload to a high velocity, which then coasts the rest of the way. This coasting flight takes considerable time to cover large distances, but many deep space missions can be performed better by applying small amounts of thrust during most or all of the trip. Over long distances, this continuous thrusting will accelerate spacecraft to very high velocities and shorten overall travel time. When perfected, electric propulsion will provide the continuous thrust needed to reduce travel time to distant points and will use fuel so effectively that a larger fraction of the Earth orbit weight will be delivered as useful payload. If the goals for electric propulsion are achieved, the entire solar system will be open to versatile exploration. The most difficult space mission of this decade will be the landing of men on the moon and getting them back safely. Man in space must be transported in the shortest possible time. Today, only an all-chemical propulsion system can do this job of moon exploration. But what lies beyond? To establish and maintain a scientific base on the moon will require the delivery of large amounts of supplies and equipment, a very expensive operation. To send large manned spacecraft and unmanned probes to Mars and beyond will require the propelling of very large payloads over great distances. Just to lift these heavier payloads into deep space with all chemical systems will require either building bigger and bigger launch vehicles or launching several vehicles into Earth orbit carrying engines and fuel and then assembling them to provide the propulsion needed. Both alternatives are extremely expensive. So a propulsion system is needed that will use fuel more economically. In a propulsion system, fuel economy can be increased by speeding up the exhaust gases. In chemical rockets, the exhaust velocity is limited by the temperatures obtainable from combustion. So methods other than combustion have to be used to speed up propellant gases. One way is to use the heat of a nuclear reactor to increase the exhaust velocity of a light gas such as hydrogen. This velocity is about two and one half times that of chemical engines. Therefore, nuclear rockets will use fuel two and a half times as effectively as chemical rockets. Another way to increase exhaust velocity is to use electrical energy instead of heat to accelerate the propellant gas up to 20 times or more than in chemical rockets. These high exhaust velocities in the electric engine increase the effectiveness of the fuel 20 times and more as well, resulting in much more work per pound of fuel. With this high fuel effectiveness and with the ability to apply continuous thrust, the electric engine is a promising candidate for true space propulsion. It cannot be used as a launch engine, but once in space, it can take over. After the high thrust chemical booster has given the space vehicle sufficient velocity to overcome the main effects of gravity, the electric engine is started. This small thrust applied intermittently or continuously for months or years will result in a very high velocity. The effect of a very small thrust applied over a long time is the same as a very large thrust applied for a very short time. Thrust multiplied by the time it is applied is called total impulse. A million pounds of thrust applied for 30 seconds will deliver 30 million pound seconds of total impulse. The same as a pound of thrust applied for 30 million seconds, which is roughly a year. Each flight in space requires a certain total impulse. The goal of deep space propulsion is to use the least amount of fuel for a given total impulse. In space propulsion, fuel economy of a rocket engine is discussed in terms of specific impulse, which is defined as the total impulse generated per pound of fuel used. The higher the specific impulse, the longer in seconds one pound of fuel will deliver one pound of thrust. For convenience, specific impulse is expressed in seconds. Chemical rockets are limited to specific impulses of about 450 seconds, and relatively little improvement can be expected. Solid fuel nuclear rockets are expected to deliver up to about 1,000 seconds of specific impulse. Electric engines, however, are now operating at specific impulses from around 800 to 10,000 seconds and higher in laboratory vacuum chambers. The higher the specific impulse, the higher the fuel economy. But unfortunately, as specific impulse increases for the same thrust, the electric power needs increase, and power plant weight goes up even more. So an optimum value must be found for each mission. But even with this compromise, for many manned and unmanned interplanetary missions, the electric engine appears to be the propulsion system to deliver significant payloads within a reasonable time. For missions to Pluto, for example, the electric engine is the only device that can deliver any payload at all. The power source for electric engines will be either a nuclear reactor or solar cells or heat concentrators, depending upon how much power is needed. Waste heat is rejected to space by a radiator. Heat from the power source drives an electrical generator. The electrical power is conditioned and controlled to provide the necessary voltages and currents. The typical propulsion system also includes propellant storage and feed devices, which lead to the engine itself. Three types of electric engines are under development. They differ primarily in the way the propellant is accelerated. The electrothermal engine uses an electric arc or resistance element to heat a propellant gas to a very high temperature, which produces a high exhaust velocity. Specific impulses from 800 to in excess of 2,500 seconds are possible with these engines. The electrothermal engines have demonstrated good performance in vacuum chamber tests. However, laboratory work must continue in order to improve performance. In electromagnetic engines, a fast-moving ionized gas is generated and used as the propellant. This gas is a plasma of ions and electrons. Electric and magnetic fields then speed up the charged particles to much higher exhaust velocities. A specific impulse range of 800 to in excess of 10,000 seconds appears to be possible. These electromagnetic devices are the least developed at this time. However, there are many promising designs under laboratory investigation. In the third type, the electrostatic or ion engine, cesium or mercury fuel is ionized and the resulting electrons removed. The ions being positively charged are accelerated to very high velocities by a high negative voltage electrode. These engines will operate at specific impulses from 3,500 to 10,000 seconds or more. Electrostatic ion engines are the most advanced electric type, but much work remains to develop larger, more efficient and reliable engine systems. Electric engines has been underway only since 1959. Great progress has been made in government and contractor laboratories. Thrust levels approaching a pound have already been obtained. Yet enormous strides must still be taken before larger, reliable engines are available. Goals for electric systems include achieving power supply weights of less than 40 and an ultimate goal of 20 pounds per kilowatt with lifetimes of more than 10,000 dollars. Development of the engines themselves strives for smaller weight and size per unit thrust and higher overall effectiveness. Eventually, the entire engine system must operate continuously for up to four years. By grouping engines together as building blocks, power levels up to 40 megawatts and total thrusts of over 450 pounds may be obtained. In addition to this laboratory work, electric engines must be flight tested. Space conditions cannot be totally simulated even in these advanced vacuum chambers. And there may be influential environmental factors in space unknown at this time. Small electric engines already being developed may perform early missions. The first application may be to control a synchronous communication satellite. These engines can deliver small, accurate bits of thrust for months or years using only small amounts of fuel. Solar cells will furnish the power. Another solar-powered application could be the raising of an advanced communication satellite from a low Earth orbit to its final 22,300 mile orbit. Solar-powered electric engines may also be used to slowly spiral out a scientific satellite to make a detailed study of the Van Allen Belt. Flight tests and early missions will provide data that will help perfect the larger electric engines needed for more ambitious projects. Large electric propulsion systems, when perfected, may take large amounts of supplies and equipment to the moon and do it much cheaper than all chemical systems. Chemically-propelled boosters will place the freight into Earth orbit. The spacecraft may incorporate a small chemical engine. An electrically-propelled lunar freighter will rendezvous with the craft, take it to the vicinity of the moon, and place it in a lunar orbit. The chemical stage will lower the freight-loaded craft to the lunar surface, while the electrically-driven freighter returns to Earth orbit for another load. It will continue to shuttle back and forth with periodic fuel replacement as long as its power supply lasts. Of course, the electric freighter will take longer to get to the moon, but for most freight, the longer travel time is not an important consideration. For the same amount of freight, this system will need far fewer expensive Earth-launched boosters than an all-chemical system would require. On small vehicle missions to the near planets, Mars and Venus, electric engines can deliver much more payload by taking a slightly longer time. A three-stage chemical rocket now being studied could get a 2,500-pound payload into an orbit around Mars in about 210 days. An electrically-propelled spacecraft substituted for the third stage could do as well in the same time, but by using a higher specific impulse engine and taking only 40 more days, it can deliver twice the payload. To those planets beyond Mars and Venus, electric propulsion gives both a payload and time advantage. It appears to be the most promising means of sending scientific probes from Earth orbit into the asteroid belt beyond Mars to Jupiter and farther. The greater the distance, the greater the advantages of electric propulsion. Looking toward the day when large power supplies from 20 to 40 megawatts and large engines of proven reliability are available, scientists have developed a concept for a manned Mars expedition with electrically-propelled vehicles. The concept suggests the expedition will consist of five space ships which will be assembled in a low Earth orbit before departure. The completed ships will each weigh 360 tons and will carry a payload of 40 tons. At one end of the vehicle, there will be a 40 megawatt nuclear power supply. Next will be power converter equipment. There also will be radiators to give off waste heat and cesium fuel tanks. At the other end will be a three-man crew compartment. There will be a total of 15 men to perform all the mission objectives. Three of the ships will carry piggyback Mars landing vehicles, while the other two will carry extra fuel for the return to Earth. Five vehicles will be used for safety purposes. If one or more fail, the men would be transferred to the other ships to continue the flight or return to Earth. After checkout and placing the flight crew aboard, the electric engines would spiral them continuously for 56 days until they escape the Earth's gravity. Then they would enter a transfer orbit around the Sun, traveling toward Mars. The ships would take 148 days to make the trip to the vicinity of the planet. Once near Mars, they would spiral into a low orbit. This would take an additional 21 days. Once in this orbit, one of the piggyback chemical vehicles would go down to the surface without men to land equipment. Then one manned craft would land to explore the surface. After 29 days, the party would board the landing craft and rejoin the ships. Then the landing craft would be abandoned and the fuel equalized between ships for the return trip. They would reverse their original flight path and head back to a low Earth orbit. This would take another 318 days, making a total of 572 days for the round trip. By applying thrust continuously over vast distances, travel time will be greatly reduced. Be used so effectively that a much bigger weight fraction of the space vehicle will be devoted to useful payload. Reduce travel time to the distant planets. Larger, useful payloads. These are the goals of electric propulsion, which will allow numerous missions to be carried out that would otherwise be impractical or impossible. Our next film is more recent from 1987. It's also about exploring Mars. Mars, commonly referred to as the Red Planet, is one of our closest neighbors beyond the moon. It has qualities that make it a potentially habitable outpost. Before all Martian exploration ended in November 1982, a handful of probes had made the year-long journey. Viking 1's orbiter completed nearly 1,500 picture-taking trips around the planet, while its lander studied samples and returned views from the surface. As a result, Mars is well mapped, but many questions remain. So researchers are designing systems to explore the varied Martian geography in anticipation of a return mission. On calm sunny mornings, Jim Burke can often be found flying this lightweight solar balloon in the courtyard at NASA's Jet Propulsion Laboratory in Pasadena, California. Mr. Burke views his study as an important stepping stone to a larger goal in gathering more precise information about the Red Planet. Now the Martian atmosphere is carbon dioxide, and if you put a black balloon that's light enough with a light enough payload into that atmosphere, the sun shining on the black balloon will warm it up like the heat inside a parked car with the windows shut, and it gets hot enough inside to become a hot air balloon. Scientists, students, and engineers from JPL and the California Institute of Technology have taken the concept a step further by testing the feasibility of this 30-foot diameter solar balloon that might be used to study Mars. In theory, the device could be blown around by local Martian winds during the day to collect data and take pictures. At night, it would cool down, lose buoyancy, and lower itself to the ground to survey the planet's surface. The small, clear balloon holds the larger one off the ground at night so it won't get damaged. There are many regions of Mars that could be explored this way, according to Jim Burke. One very interesting possibility is to put the balloon in the atmosphere, get it inflated, operating up in the polar regions, and let the circumpolar winds drift it down across the polar cap over the layered terrain, which is in the canyons that spiral out from the polar cap, then across the immense dune fields that surround the polar caps and on downward into temperate latitudes on Mars. To remotely explore the surface of Mars, a number of devices have been investigated. They include early roving vehicle prototypes designed to crawl or wheel their way across alien terrain. Rovers continue to be designed today, based on some of these models. University of Arizona's Lunar and Planetary Labs graduate students and faculty have recently built this gigantic two-wheeled prototype, Mars Roller. Another vehicle being developed is this robotic six-wheeled version, which is JPL's latest test bed for understanding the control and vision systems needed for a Mars mission. According to Brian Wilcox of the Robotics and Tele-Operators Research Group at JPL, sending commands to a rover on Mars would be difficult because of the 10-40-minute round-trip delay. You can't just sit there and steer in your armchair from a TV monitor and make the vehicle do useful things because of this long speed of light delay. So we've identified several techniques to maneuver a vehicle on Mars in such a way that you can go useful distances in a day in spite of the fact that the humans are this long speed of light delay removed from the action. A rugged vehicle has two TV cameras for eyes and is capable of climbing objects a third taller than its wheel height. The proposed mission vehicle would have robotic arms to make measurements and collect rock and soil samples. Using rover's onboard vision system, scientists can freeze three-dimensional images from its pair of television cameras. They can then designate the pathway to follow, continually updating commands from Earth so that the rover is able to avoid obstacles and hazards. As more sophisticated visual systems are developed, greater artificial intelligence can help the rover find its own way if given high-resolution imagery of the Martian surface and a list of targeted regions designated by Earthbound scientists. The hope is to someday send a manned mission to Mars, but a more detailed study of the planet is necessary first, and these pioneering steps can be made by roving vehicles and balloons. Again, Brian Wilcox. If you imagine an expedition at Lewis and Clark trying to survey the Louisiana Purchase, they basically made one track across a very small fraction of the land surface of the Earth. It took them years to do it, and yet they found incredible things all along the way. We could certainly have a dozen rover missions which yielded equally interesting results. The exploration of Mars, sending unmanned vehicles as pathfinders for the future. That's all we have for this edition of NASA Images. But before we go, let me remind you that you're cordially invited to see the displays here at the Visitor Center at the NASA Lewis Research Center. We're located near Hopkins International Airport in Cleveland. Until next time, this is Lynn Bonderant saying goodbye.