Century In just 40 years, humanity has moved from dreaming of the moon and planets to landing on our satellite and sending spacecraft to all but one of our neighboring worlds.
Unless some economic collapse or popular backlash against space exploration cuts funding for the world's space programs, the coming century will certainly bring even more dramatic achievement and discoveries. Within several decades, engineers could be launching spacecraft toward the nearest stars.
If NASA meets its most optimistic scheduling goals, by the end of the coming decade, the agency will have completed its two highest priorities -- assembling the
International Space Station, and bringing back samples of martian soil. Also, the
next generation space telescope will likely be in position to take the most detailed astronomical images ever seen, and the Cassini spacecraft will have revolutionized our understanding of Saturn and its many moons.Beyond these, the space agency will be moving in several directions. Officials at NASA are now finalizing a set of broad goals for the second decade of the 21st century. A special team of experts is charged with NASA's "next-decadal planning," to set the top priorities for the next wave of space programs.
"If we can even think about going to hundreds of AU or thousands of AU, we can get to Mars real quick."
Lewis Peach, former director of advanced projects in NASA's office of spaceflight, saw the list of ideas being considered for this future roadmap. In its very preliminary stages, Peach said, the planning team was considering the architecture for a system of robotic outposts throughout the solar system, strategizing about the best way to help jump-start commercialization of space travel, and studying ideas for sending astronauts to the moon or Mars.
The study group is still evaluating NASA's options, Peach said, but it should make some decisions within the next few months that will then be evaluated at the top levels of NASA and the Clinton Administration.
Other planners at NASA are imagining a host of missions for the middle of the 21st century, ranging from poking at the boundaries of the solar system to reaching the nearest stars. Within a few decades, the agency may be ready to send astronauts to Mars, and it could even begin building some variation of a telescope that can image the surface of
planets around other stars.Bursting out of the solar system's bubble
The first step toward such far-out missions will be in the Interstellar Probe -- a proposed mission being developed at NASA's Jet Propulsion Laboratory. It aims to launch the first spacecraft that will escape the boundaries of our solar system.
Even though Voyager will have had a 30-year head start by the time this proposed probe launches, the Interstellar Probe could catch up to Voyager within several years to become the first craft to exit the solar system.
The sun and its entourage of orbiting planetary debris moves through the interstellar medium at about 58,000 m.p.h. (93,000 kilometers per hour). The sun's magnetic field and charged particle radiation create a bubble around the solar system called the heliosphere. As this bubble flies through the interstellar gas and dust it is compressed at its leading edge and trails out at the rear.
Scientists have a host of questions about the heliosphere: where it ends, just what the interstellar medium that surrounds it is made of and what the solar system beyond Pluto looks like. The Interstellar Probe will answer a lot about the evolution of the solar system, said Paulett Liewer, the study scientist for the probe mission.
"As you go farther out, you're sort of going back in time in terms of the evolution of the solar system," she said. "The solar system evolves through collisions, and collisions are much less frequent out there because everything's farther apart and everything's moving slower around the sun, so it's in an earlier stage of evolution."
The Interstellar Probe would study the outer solar system and study the interstellar medium that exists beyond it, which would help answer questions about what existed before the solar system was even around. With a target launch date somewhere between 2010 and 2015, the spacecraft would have to rely on some of the most cutting-edge technology being developed.
The craft's goal is a point some 200 times farther from the sun than Earth is. Mission developers want the probe to reach that target within 15 years of launch. The average distance between Earth and the sun -- about 93 million miles -- is known as an astronomical unit, or AU. In order for the interstellar probe to reach 200 AU in the only several years, it will have to reach a cruising speed of about 15 AU per year, or 160,000 m.p.h. (257,495 kilometers per hour).
Sailing by the light of the sun
The best chance to economically reach such high speeds is by using solar sails, said
Sarah Gavit, manager of the Interstellar and Solar Sail Technology Program at NASA's Jet Propulsion Laboratory. Solar sails would use the pressure of sunlight to propel a craft forward. Physicists have known for decades how much pressure is associated with photons of light from the sun, but the pressure is so low that harnessing it has remained a fantasy until recently.Technological developments in the past several years, such as the miniaturization of electronics that have made it possible to build small, lightweight spacecraft, as well as the development of materials suitable for use as sails, is putting the solar-sailing spaceship within reach.
"There have been some real breakthroughs within the last five years in having materials that are structurally rigid, but extremely lightweight and reflective all at the same time," Gavit said.
Just making a super-reflective, super-lightweight film that will not tear and will resist becoming extremely electrically charged is only one of the many challenges for the Interstellar Probe mission. While scientists say the physics behind the solar sailing is sound, most of the engineering problems of deploying and operating a solar sail in space have to be worked out. No project has yet demonstrated that a solar sail can actually be used for propulsion.
This artist's conception shows a deployed solar sail. The edges would be weighted and centrifugal force would keep the spinning sail open.
Gavit and others working on solar sails hope the first step might come in 2004 -- if a solar sail demonstration project is selected to fly as one of NASA's New Millennium missions. Such a project was proposed in 1999, but the cost was outside the New Millennium's budget, and a
cheaper mission was selected. Dana Brewer, NASA's New Millennium Program Executive, said that selection should in no way be interpreted as a selection against solar sails, which are very important to NASA."One of the far-reaching goals that [NASA Administrator Dan Goldin] has established is to go to the next 10 or 20 nearest stars and to leave our solar system. To make that cost efficient, we need to reduce the propulsion and launch costs, and that can be accomplished by reducing weight of propellant and spacecraft," Brewer said. Solar sails are by definition extremely light, and their propellant is free, so they seem extremely promising, he said.
Therefore, it is likely that a solar sail demonstration may be selected for an upcoming New Millennium mission.
After sails are demonstrated, the Interstellar Probe will be one of the first space missions to actually use them. It would use its sail to swing in close to the sun, taking advantage of the greater intensity of light to get the biggest possible push. It would then zoom outward toward the front edge of the solar system in the direction of the constellation Scorpius. By the time it gets to the line of Jupiter's orbit (about 5 astronomical units from the sun) the craft will have reached its target velocity, and will jettison the sail. (See mission map at the end of this story.)
The unique feature of the Interstellar Probe's mission that gives it wide ranging support is that it appeals to many different science disciplines, Liewer said. It will collect information about the origin of the solar system, the chemical evolution of matter in the galaxy, the structure of the heliosphere, and could even reveal something about the origin of organic molecules. "Its strength is that it is so interdisciplinary, and the fact that it will be the first exploration beyond our solar system," Liewer said.
A technological boost to all missions that follow
Apart from the discoveries that the probe makes, much of its significance will be that it is a sort of stepping stone to a range of future missions.
"What we're proposing is so much harder than what anybody else can conceive of right now, that just about anybody can benefit from whatever technologies we develop," Gavit said. "If we can make some progress in the solar sail area or the propulsion area, or in telecommunications, that would just open up the door for tons of other missions who probably wouldn't dare to think of things as big as we're thinking."
Demonstrating an extremely high-speed propulsion method, or a sort of autonomous navigation and decision-making capability, or a reliable, low-power means of
communicating across vast distances would enable true interstellar missions, ones that might reach neighboring stars. Seeing mountains on planets in other solar systems
One of the missions that is daring to think of things even bigger and farther out is the
Gossamer Spacecraft Initiative. The multi-decade effort to build an advanced space telescope that can zoom in on planets that orbit other stars kicked off in 1999. It is counting on the Interstellar Probe to develop many of the technologies it will need.The Gossamer program began its first fiscal year with some $6 million earmarked for technology-development projects. About half a million dollars of that money is being plowed into the Interstellar Probe's solar sail development work.
"We're trying to detect and image planets around nearby stars," said Chris Moore, who is the thrust-area manager for ultra-lightweight structures and space observatories at NASA's Langley Research Center in Hampton, Virginia.
"[NASA Administrator] Dan Goldin has challenged us to take a picture of the surface of an extrasolar planet," Moore said. While such a task is way beyond the capability of current technology the Gossamer initiative seeks to develop some of the most advanced and interesting ideas that astronomers, physicists and others are daring to imagine.
Pulling off such a feat might require an array of 100 space telescopes, each with a light collecting area about 83 feet (25 meters) in diameter, Moore said. The enormous instruments might fly in formation to focus the light to a single collector.
The technology for such an immense dream is only just now being conceived. "It may even be beyond the laws of physics, we're not even sure of that," Moore said, "but we need thousands of times more collecting area than the Hubble Space Telescope has."
Beyond the Interstellar Probe
After the Interstellar Probe, NASA is planning a series of missions that will go farther and farther out, said Glen Mucklow, NASA's program executive in the office of space sciences, who directs the office's advanced projects.
Some points could be useful for astronomy, Mucklow said, and future missions might take advantage of special places far away from the sun. "There's a point at around 550 astronomical units where the sun should form a gravitational lens," Mucklow said. "It's essentially the focal point of the sun as a gravitational lens," a point where the sun could naturally magnify and intensify the light from other celestial objects.
Taking advantage of such a phenomenon could yield a way to see very fine structures, or perhaps concentrate neutrinos, which could hold clues about the origin of the universe, he suggested.
"We're investigating what we might be able to do with it. There are a lot of systematic problems. You have to look very close to it, so it's very difficult," he said, "This is pretty far out stuff, but if it works, you could get fantastic resolution."
Blazing a trail to the stars
Following up a these missions might be what some at NASA are calling the Interstellar Trailblazer. The trailblazer, which would basically be a longer-range Interstellar Probe might be sent to a distance of 2,000 astronomical units, Mucklow said. "It would look at the plasmas and the heliosphere the galactic wind, that type of stuff," and perhaps also investigate the Oort cloud. That region is a proposed reservoir of comets that mathematical calculations predict exists at about 100,000 astronomical units from the sun.
The Interstellar Trailblazer would have to use some sort of advanced propulsion method, something that would have to be "pretty exotic," Mucklow said, such as antimatter propulsion.
Far before leaving the limits of the solar system, solar sails become useless because the sun's light is too dim to provide much thrust.
Some physicists are now considering ways to use intense solar-powered laser or microwave beams that could be aimed at a solar sail to shoot a spacecraft toward another star at perhaps 10 percent the speed of light. Such a system might use huge space-based solar concentrators to produce the beam.
Alpha Centauri
"By 2040 or so, we might actually have some breakthroughs that might allow us to consider destinations like Alpha Centauri," Mucklow said.
"Getting to the next star is going to take antimatter propulsion, [it] is the only known technology that we have that can do that, or some kind of exotic laser sail or microwave sail," but he also leaves room for propulsion methods that have not even been discovered. Mucklow credited the
Breakthrough Propulsion Physics Program at NASA's Glenn Research Center with investigating such ideas as gravity modification and quantum teleportation.Propulsion, though, is only one of the multitude of technologies that must experience a quantum leap before such far-ranging missions are possible, Mucklow said.
"If you could get out hundreds of astronomical units, suddenly you realize that you've got a communications problem. We're talking about several days for a command to travel from Earth to a spacecraft and back.
So the spacecraft has to have a level of intelligence and autonomy, and that requires much greater computing power.
"By looking out that far you identify things that you need to do in the short term," Mucklow said.
And even though a mission to Alpha Centauri is not likely to be return results during the lifetime of anybody alive today, Mucklow emphasized that there are practical benefits of such way-out missions.
"If we can even think about going to hundreds of AU or thousands of AU, we can get to Mars real quick. So the technology that we develop in looking at the interstellar regions, we can apply within the solar system to make things a lot easier," he said.
advertisement
