PEARL HARBOR IN SPACE
Shining in almost continuous sunlight, the satellites in geosynchronous orbit (GEO) seem to float motionless, like ships at anchor. But the fleet is active. It sends billions of bits of information every hour to and from the earth, 22,300 miles away. To a traveler in GEO, the blue-green planet would appear delicate and beautiful, a treasure shining against the flat darkness of space. And many of the more than 100 sentinels at their posts in GEO are programmed to protect the verdant ball with all of their computerized resources.
The fleet is a vital communications and control link in our defense system. And its very distance from Earth would appear to make it invulnerable to enemy attack. But some new studies of geosynchronous orbit suggest that our satellites at GEO may be as vulnerable as were the ships in that other distant and sunny American outpost, Pearl Harbor, in December 1941.
The blackboard studies indicate that with a bold, long-distance mission -- involving a trip to the moon and back-potential enemies could wipe out our fleet. It would take but a single vehicle, making a single pass after its lunar voyage. The attack would be over in less than 12 hours. It would require no nuclear weapons. It would render the Western world blind, deaf, dumb -- and open to a full-scale missile attack.
The lines of this frightening scenario -- certainly already well known to Soviet scientists--surfaced during some recent informal investigations conducted by space engineers and others. The findings were by-products of research into a different space mission--one with benign intentions. Its objective would be to send humans into geosynchronous orbit, almost 25 times farther from Earth than we have ever orbited before. One major goal: to fix ailing satellites the way astronauts repaired Solar Max last April.
The astronaut's-eye view of Earth comes in two varieties. In the more common, witnessed by more than 100 men and four women, the planet is seen from an altitude of several hundred miles. Solar Max, a satellite that observed the sun for ten months until it blew a set of fuses, circled approximately 300 miles up. From this height, landmarks stay in sight for no more than a minute or two before passing far astern.
In the other view, experienced by only 21 men and not likely to be repeated much before the turn of the century, Earth is a full, round disc, seen from the porthole of a moon- or Earth-bound Apollo spacecraft.
Both views elicit different reactions. From low Earth orbit, or LEG, space crews remark on the wide expanses of Earth's surface and the inconsequentiality of the works of humankind From lunar trajectories -- passing through GEO--the astronauts were struck by the contrast between the brilliance of Earth and the blackness of space.
The visionary Russian theorist Konstantin Tsiolkovsky outlined the theory of geosynchronous orbits in the Twenties. The principle is simple: At 22,300 miles above the equator, satellites following circular orbits go around the earth at the same speed our planet rotates. So to any point on Earth's surface, GEO satellites appear to hang motionless in the sky. In 1947 Arthur C. Clarke proposed placing radio relay satellites in GEO. And in 1961 the first such device -- called Syncom, for synchronous communication -- was launched. Today more than 100 active satellites and an equal number of derelicts are strung along the full "great circle" in a man-made ring around Earth's equator.
Besides communications relay satellites, surveillance satellites for both military and civil purposes are also operating in GEO. Infrared sensors hang continuously above the Indian Ocean, peering northward for a clear, constant view of the entire Eurasian landmass, waiting to monitor Soviet and Chinese rocket launchings. At other points, meteorological monitors send back full-disc imagery of an entire hemisphere's cloud cover.
The road to GEO has recently appeared rocky. Satellites such as NASA's Tracking and Data Relay Satellite (TDRS), along with payloads for Western Union and the Indonesian government, went astray in 1983 and 1984 because of booster malfunctions during their journeys from LEO to GEO.
A satellite jettisoned from the space shuttle is moving at approximately 25,000 feet per second about 180 miles above Earth's surface. To boost itself into a transfer orbit arcing out to GEO's altitude, the satellite must gain an additional 8,100 feet per second from an attached rocket stage. Upon reaching the high point in the new elliptical orbit, the satellite would begin falling back toward Earth unless a second rocket burn, adding 5,900 feet per second, were performed. That burn circularizes the satellite's new orbit. It also "turns the corner," or changes the plane of the orbit from that of the transfer orbit (usually equivalent to the latitude of the launch site) to a perfectly equatorial one.
The conditions at GEO are quite different from those closer to Earth. Space may seem the same all over. But it's not.
The first difference is the radiation environment. Above most of Earth's magnetosphere, satellites at GEO are subjected to the full force of solar and cosmic radiation and charged particles. These are not weakened by the earth's magnetic field; so space vehicles are bathed in unadulterated interplanetary radiation. The solar high-energy particles can induce electrical-charge buildup across the structures of the vehicles, leading to sparking in electronics systems. In the Sixties many such satellites were lost when spurious computer commands were caused by such signals. If humans were to venture here, they would need "storm shelters" against solar flares. And they could not tarry unprotected in the face of the continuous high-level radiation.
Sunlight is also stronger at GEO than at LEO, not because the vehicles are closer to the sun but because for months at a time the sun never sets. Since Earth's equator is inclined 23 degrees to its orbital plane, a satellite circling high over the equator seldom passes through Earth's shadow.
So the environment at GEO is unique. Conditions there cause design problems. But the advantages are worth the trouble.
The view is new and spectacular: Earth fills an arc 20 degrees across the sky (about the same size as a basketball held at arm's length), and our home planet runs through its phases, from new to full to new again, every 24 hours. When new, the unlit Earth is hardly visible in the bright sunlight bathing the geosynchronous satellite. When full, the earth is spectacular, casting shadows 5.000 times brighter than the full moon casts on Earth. During the occasional eclipses (occurring in groups six months apart), the whole Earth is surrounded by a luminescent ring of light refracted through the atmosphere. A passenger in such a satellite could continuously watch weather patterns develop over hours and days. Earth would appear to be living and breathing with the slow-motion grace of a beautiful giant's head.
Unmanned spacecraft operating in GEO will grow larger and more complex in the future. Very wide antennas and large optical devices require extremely fine adjustments and alignments. Already there have been suggestions that future GEO platforms serving dozens of users on Earth will be assembled by shuttle crews and then gently pushed out toward their operating altitudes.
Once they are in GEO, any future servicing (such as refueling or replacement of electronic boxes) could be done by robot "monkeys" sent up from LEG. But such operations are difficult. For one thing, it takes more than a quarter of a second for a signal from Earth to reach GEO, an agonizingly long time to wait for a mechanical monkey to jump into action. Problems like this mean that someday people will have to venture out to GEO, too. Some repairs are going to be just too complex for robots.
NASA engineers in Houston recently completed a study on just how such a servicing mission could be conducted. The basic flight plan called for two astronauts to spend several days at GEO. They would be launched from the payload bay of a shuttle and would coast upward for five hours. Then they would rendezvous with the target space platform. Several days later they would fire onboard rockets to fall back toward Earth, where they would skim through the upper atmosphere to kill off excess speed and would change plane as required to swoop alongside the still-orbiting shuttle. After more maneuvers to complete a rendezvous, the crew would transfer to the shuttle for return to Earth. The GEO ferry capsule would remain in orbit for future use.
The engineers discovered that the mission could be accomplished with a five-ton Apollo-class command module atop an uprated Centaur rocket stage. The command module would either have to be already in orbit or brought up on a different flight; one entire shuttle mission would have to be dedicated to carrying the fully fueled Centaur rocket alone.
The old Apollo landed in mid-ocean, where it was cushioned by parachutes and water. But the seawater precluded reusing the craft. (The original Apollo design called for three reflights of the hardware, but this plan was abandoned when the splashdown mode was selected) If the proposed ferry to GEO were stripped of parachutes and flotation gear and loaded with extra maneuvering fuel, a precision guidance system could steer it into a retrievable "parking orbit" near the waiting shuttle instead of relying on a surface-impact trajectory. This was the route chosen by the NASA engineers: "Aerobraking eliminates the development for water-landing systems and water-recovery operations," their report concluded.
The engineers estimate that such a mission could be flown by 1990 at a comparatively low cost of about $1.5 billion. Each subsequent flight would cost about a tenth as much as the inaugural mission.
A companion vehicle to the GEO sortie tug would be the "line shack." This 12-ton module would remain near GEO and would contain spartan living quarters for visiting teams of astronauts. Most standard tools and the heavy airlock could be left attached to the line shack. So the home base in GEO would help keep the weight of the ferry capsule down. But the line shack would cost another $1.5 billion to build and launch.
In late 1983 the study results were presented to NASA headquarters in Washington. Reportedly, Washington thought that the research was nice, thank you very much, but the project was too dangerous and too expensive for any mission in the next ten years.
The NASA engineers weren't alone, however, in their ambitions to put humans into GEO. At Eagle Engineering, a consulting firm in Houston, Hu Davis has long been an advocate of the development of manned geosynchronous capability. But he sees little purpose in merely going out there to show it can be done. His plans involve developing a significant in-place work capacity.
"I want two things beyond a bare-bones demonstration." Davis told me early in 1984. First, "We need to be able to cover a significant fraction of the geostationary arc while we're there. And we need to stay for a week or more." Since no shuttle could tarry in orbit that long, the GEO ferry capsule -- in contrast to the vehicle envisioned by NASA engineers -- would have to contain its own Earth-landing system. This would probably be a parachute for a dry-land thumpdown.
Second, "I want at least one ton of discretionary payload," Davis demands. No stripped-down capsule could carry enough cargo to do anything useful once it got to GEO, he argues. But with a cargo capacity, sortie vehicles would be able to bring up hydrazine propellant, new batteries, spare apparatuses, and improved radio transponders for installation on degrading communications relay satellites. "These are useful payloads to enhance the value of orbital assets." Davis says.
The larger vehicle would need more launch power. For each GEO expedition, Davis foresees one full shuttle launch and one full launch of a "shuttle-derived vehicle," a heavy carrier capable of putting double-size payloads into orbit.
Such a capability would allow some really useful missions for flights at least once a year, Davis believes. "Most GEO satellites that die, starve," he says. Refueling with new propellants could restore such satellites to life.
Currently, most users of GEO satellites figure that after seven to ten years, the satellite's technology is so obsolete that it makes more economic sense to replace it entirely. "Sure, there's no incentive right now for repair missions," Davis points out, "because the communications-satellite manufacturing companies sell new satellites and replacement satellites.
Instead, Davis suggests that the older satellites could be sold to customers with less need for the latest technology. Or if high technology were the object, the satellites could have their radio transponders replaced, while leaving the still-serviceable power, command, and other systems.
Sooner or later, the large GEO platforms now being planned will demand this servicing capability, first by robot "teleoperators" and then by on-site humans. Davis predicts astronauts will visit GEO space, on service missions, as early as the end of the Nineties. "It's an implicit part of NASA's new space station program," he says, since the agency will be placing its permanent station at a 28 degree inclination--a convenient angle for voyaging deeper into space. "Washington has called for a bolder, more innovative, and broader-reaching space program." Davis recalls, "and this could be part of it."
Davis's eyes twinkle. "Besides," he says, "GEO sortie is a back door to the moon."
The cold numbers of space navigation show that Davis is right. It actually takes less fuel to go all the way to the moon, orbit 100 miles above it, and return to Earth than it does to reach and return from LEO. Sure, the lunar trip takes longer -- three days each way instead of six hours -- but any GEO-sortie ferry that is built to support astronauts for a week at GEO could just as easily support them on a return voyage to lunar orbit.
And Davis thought of one more reason for developing a manned geosynchronous capability. "You might need it to remove a threat," he says. What kind of threat? Davis first lists out-of-control derelicts interfering accidentally with neighbors. But other Threats -- some deliberate -- are possible.
With all these tempting targets lined up along the GEO are, how would an attacker design his flight plan? There is no need to be coy about the identity of the players: The primary targets in GEO are Western, and the leading (essentially only) candidate for attacker is the Soviet Union. The Soviets have no military assets in GEO. Their space vehicles there are presumably commercial communications and navigation systems; their military systems are in different orbits. So they have the freedom to fire against anything they want to shoot at.
The Soviets could use a large Proton booster to place one of their currently operational "killer satellites" into a GEO orbit. For LEO targets, they would use a smeller ICBM derivative, called the F-class. Skeptics point out that the Proton is five times bigger than the F-class and is correspondingly harder to launch. But the Soviets launch the bigger booster more often than the smaller one. So it would be no great problem to loft several killer satellites atop such boosters.
Once near the GEO arc, the weapons could drift along until they made radar contact with their targets. Under ground command, they would close in and execute their shrapnel attack.
Most experts have concluded that although the Soviets might be able to put three or four killer satellites into GEO, they could hardly make a dent in the American military assets there. This is all the more comforting because it would take a long time -- days or weeks -- to get into the proper attack approach path. And the endangered targets, under ground control,would be able to take evasive action.
But suppose the tables were turned. Or rather, suppose the attacking Soviet satellite were at the same altitude as the GEO arc, but moving east to west instead of west to east, the direction in which the earth and the GEO satellites rotate. This so-called retrograde geosynchronous path is far more threatening. The Soviet orbital weapon would be running head-on through the space occupied by the necklace of satellites, like a car hurtling the wrong way on a superhighway. Accidental collision would be unlikely in space, however, since a cross section of the are is at least 100 kilometers across.
The hunter-killer vehicle could pick out one target on one pass, track its path precisely, and on the next pass 12 hours later, fire a small homing missile (of which it could carry a dozen or more). The missile could carry a miniaturized radar guidance system, with the radar transmitter on the main killer satellite. Alternately, a simple optical sensor would be more than adequate since the target is in full sunlight. Desired targets could be picked off one by one over a period of several days.
In another scenario, the Soviet killer satellite merely ejects a cloud of particles ahead of itself. At a combined speed of 16,000 feet per second, the target satellites and the particles -- grains of sand, for example -- would destroy one another. With a suitably thick cloud, the entire GEO are--including the Soviet communications satellites, which have little if any military use -- could be reduced to junk in 12 hours. A thinner cloud would merely take more passes--perhaps five, ten, or twenty -- to eventually turn GEO into a new asteroid belt.
If the Soviets wanted to reoccupy the orbit later, they could use plastic pellets, which would pulverize under solar ultraviolet and eventually blow away on the solar wind.
Could any of this happen? It's easy to dismiss the threat. After all, putting satellites directly into retrograde geosynchronous orbit is an almost impossible task. If the booster takes off from Earth westward instead of eastward, it loses at least a fifth of its total power because it must work against Earth's rotation. If the reversal burn occurs at the top of the long GEO transfer arc, swinging up from parking orbit to the point the second rocket burn must occur, then an enormous amount of fuel would be required to kill off the original motion and apply "full reverse" to get into a retrograde orbit. Little if any payload would be left for the warhead.
But unfortunately, these comforting arguments assume that anyone wishing to throw an object into retro-GEO is not very clever. Putting a hostile craft into "backward" orbit is actually comparatively easy.
The broad lines of the mission can be worked out on a blackboard. While the Soviets may be short of black boxes and esoteric gadgetry, they have plenty of blackboards -- and clever orbital mechanicians to write on them.
To get to retro-GEO the smart way, you merely pretend you are going to the moon. You actually perform a lunar flyby. The chosen path is very much like the free-return trajectories followed by Apollo lunar expeditions, except that the lunar flyby altitude is a little higher.
On the return to Earth, then, the enemy craft would fly by at an altitude of about 22,000 miles. At that point, after about a week of flight, instead of whipping on past and back up and out into the depths of interplanetary space, the vehicle would perform a rocket burn to enter retro-GEO.
The killer satellite could also get into position secretly. The initial launching would of course be detected. But Moscow could merely announce another scientific lunar probe. Something (a small transmitter, for example) could be dropped off in lunar orbit so eavesdropping American antennas would be satisfied. Or else Moscow could simply report that the probe had crashed. And as the killer satellite rounded the moon and headed for its rendezvous, no tracking system on or off Earth could follow it.
Even if it could, what could be done about such a retro-GEO threat? The worst defense the West could mount would be to blow up the weapon, because resulting fragments would merely carry out the original mission and destroy all the satellites.
The only feasible response would be a manned mission to retro-GEO, via the moon, to rendezvous with the killer satellite and disarm it. Presumably, if such a mission were at all feasible, the Soviets would booby-trap the satellite to explode if tampered with. So the tamperers would have to be very clever and very gentle because the jewels of the GEO necklace would be zooming past their heads at three miles per second.
Thrust, counterthrust, parry, and thrust ... the quest for the high ground goes on, even in the depths of space. With current boosters and warheads, such a mission is feasible already. But the nightmare may be prevented by the mere existence of effective countermeasures and by awareness of the threat. And countermeasures in turn provide unadvertised capabilities for much more beneficial space trekking.
In the nightmare, the moon is a back door to retro-GEO and destruction. In a more hopeful and benign dream, GEO will be a back door to the Moon and the stars.