Pale Blue Dot - Carl Sagan [34]
Earth-observing satellites, especially a new generation soon to be deployed, monitor the health of the global environment: greenhouse warming, topsoil erosion, ozone layer depletion, ocean currents, acid rain, the effects of floods and droughts, and new dangers we haven’t yet discovered. This is straightforward planetary hygiene.
Global positioning systems are now in place so that your locale is radio-triangulated by several satellites. Holding a small instrument the size of a modern shortwave radio, you can read out to high precision your latitude and longitude. No crashed airplane, no ship in fog and shoals, no driver in an unfamiliar city need ever be lost again.
Astronomical satellites peering outward from Earth’s orbit observe with unsurpassed clarity—studying questions ranging from the possible existence of planets around nearby stars to the origin and fate of the Universe. Planetary probes from close range explore the gorgeous array of other worlds in our solar system, comparing their fates with ours.
All of these activities are forward-looking, hopeful, stirring, and cost-effective. None of them requires “manned”* spaceflight. A key issue facing the future of NASA and addressed in this book is whether the purported justifications for human spaceflight are coherent and sustainable. Is it worth the cost?
But first, let’s consider the visions of a hopeful future vouchsafed by robot spacecraft out among the planets.
VOYAGER 1 AND VOYAGER 2 are the ships that opened the Solar System for the human species, trailblazing a path for future generations. Before their launch, in August and September 1977, we were almost wholly ignorant about most of the planetary part of the Solar System. In the next dozen years, they provided our first detailed, close-up information on many new worlds—some of them previously known only as fuzzy disks in the eyepieces of ground-based telescopes, some merely as points of light, and some whose very existence was unsuspected. They are still returning reams of data.
These spacecraft have taught us about the wonders of other worlds, about the uniqueness and fragility of our own, about beginnings and ends. They have given us access to most of the Solar System—both in extent and in mass. They are the ships that first explored what may be homelands of our remote descendants.
U.S. launch vehicles are these days too feeble to get such a spacecraft to Jupiter and beyond in only a few years by rocket propulsion alone. But if we’re clever (and lucky), there’s something else we can do: We can (as Galileo also did, years later) fly close to one world, and have its gravity fling us on to the next. A gravity assist, it’s called. It costs us almost nothing but ingenuity. It’s something like grabbing hold of a post on a moving merry-go-round as it passes—to speed you up and fling you in some new direction. The spacecraft’s acceleration is compensated for by a deceleration in the planet’s orbital motion around the Sun. But because the planet is so massive compared to the spacecraft, it slows down hardly at all. Each Voyager spacecraft picked up a velocity boost of nearly 40,000 miles per hour from Jupiter’s gravity. Jupiter in turn was slowed down in its motion around the Sun. By how much? Five billion years from now, when our Sun becomes a swollen red giant, Jupiter will be one millimeter short of where it would have been had Voyager not flown by it in the