U.S. Has Outsider’s Role : World’s Space Armada Keeps a Date With Halley
An international armada of spacecraft has begun its rendezvous with Halley’s comet, giving scientists their closest view yet of the most fabled wanderer in the solar system.
The first of five probes--the Soviet Union’s Vega 1--passed within 6,000 miles of the comet’s icy nucleus late Wednesday night, beginning what one astronomer calls “the greatest week cometary science has ever had.”
The week’s activities, culminating in a razor-close encounter by a European Space Agency probe next Thursday, will spotlight an extraordinary display of international cooperation, with the Soviet Union, Japan, Europe and the United States working closely together to ensure the safety of the fleet.
Success in that cooperative effort is essential if the European probe, called Giotto, is to have safe passage through the eye of a cometary hurricane next Thursday.
Each of the five probes has a specific and different mission. Together, they are carrying about 40 instruments.
Vega 1 took pictures with television cameras as it sailed past Halley late last night, and it checked the temperature of the comet and measured the size and distribution of dust particles in the cloud that surrounds the nucleus. Information from the spacecraft will be analyzed by Soviet scientists and released over the next few days, providing a dramatic scientific boost to Soviet progress in interplanetary exploration.
More than 100 foreign scientists, including about a dozen from the United States, are at Moscow’s Institute for Space Research to take part in the historic encounter. Several had high praise for the openness of the Soviet project.
“If you want, you can go into a lab, ask an experimenter what he’s doing, you can even twiddle the knobs and the dials, as long as you don’t pull the plug,” said Louis Friedman of Pasadena, executive director of the Planetary Society and one of the scientists in Moscow.
But despite the early focus on Vega 1, it is the European effort that has captured the most attention from scientists around the world because Giotto is to pass perilously close to the icy core of the comet.
If it survives its plunge next week through the dusty, gaseous cloud that surrounds Halley’s nucleus, Giotto will send back the first high-resolution photos ever of the nucleus of an active comet--a treasure some scientists have waited for all their professional lives.
Information Storehouse
All the participating nations have agreed to make the results of their missions available to scientists throughout the world, promising a storehouse of information that will easily eclipse all that has been learned up to now about comets, which are remnants of the solar system’s formation about 4.5 billion years ago.
“It’s the greatest week cometary science has ever had and is likely to have for quite some time,” said John Brandt, astronomy laboratory chief at the National Aeronautices and Space Administration’s Space Flight Center in Greenbelt, Md.
Giotto will approach Halley head on, and the tiny craft--less than 10 feet tall--is to pass within about 300 miles of the dirty snowball at the comet’s nucleus, estimated to be about four or five miles in diameter.
The spacecraft and the comet will pass one another at more than 150,000 m.p.h., a speed so great that a speck of debris from the comet could hit Giotto with the same kinetic energy as a small, speeding car, thus possibly destroying the probe.
Soviets Help on Safety
It will be partly up to the Soviets to ensure the safety of Giotto.
Both Soviet probes were launched in December of 1984 and paused to explore the atmosphere of Venus last year on their way to Halley.
Vega 2 is to arrive on the scene Saturday, and it is expected to pass the comet much closer than its twin, Vega 1. But the Soviets will wait until they know what happened to their first probe to decide how close to send their second.
Meanwhile, information relayed back to Earth by the Soviet probes will play a vital role in the effort to guide Giotto through harm’s way.
At that distance, about 93 million miles from Earth, the probes are flying blind in the sense that their courses cannot be changed at the last minute if the encounter gets too hazardous. And since comets behave somewhat erratically as they interact with the sun, no one is absolutely certain just where the comet will be at any given moment. Thus navigation becomes the ultimate challenge.
Erratic Course
As comets like Halley approach the sun, solar winds activate the nucleus, causing it to radiate ionized gases that spew millions of miles into space from the surface of the comet. These sudden bursts act like small rockets on the surface of the comet, changing its course slightly and causing it to wobble as it whips around the sun. And at that speed, it does not take much of a wobble to wipe out what engineers call the “miss distance” between the spacecraft and the comet.
Japan also is making a significant plunge into space exploration with two spacecraft--Suisei and Sakigake--that will pass the comet far enough away to be of minimal scientific value, but close enough to demonstrate that Japan is serious about developing its own space program.
The United States, which abandoned plans to send its own spacecraft to Halley because of high costs and bickering within NASA, has found itself in the unfamiliar position of being on the sidelines, although it still will play a crucial role in helping the other nations maintain a safe “miss distance.”
The Soviets will supply U.S. scientists with telemetry data from their Vega probes and NASA will track both probes with its worldwide system of antennas, called the Deep Space Network, which is used to monitor spacecraft throughout the solar system.
Precise Positioning
“We can determine the positions of the spacecraft precisely,” said Charles T. Stelzried of NASA’s Jet Propulsion Laboratory in Pasadena.
Instruments aboard the Vegas will allow Soviet scientists to determine the exact position of the comet in relation to the probes. The Soviets and NASA will supply both sets of data--the positions of the spacecraft and the relative position of the comet--to the Europeans, who will then be able to calibrate exactly where the comet is in relation to Giotto.
That kind of exacting information will allow the Europeans to make a final course correction in the next day or so.
“That’s going to be hair-raising,” Stelzried said. “We’ve all been working on this for years, and they’ve got to do everything exactly right at the very end.”
An inaccurate course change could send the craft plunging into the comet’s core, or into the darkness away from the sun where the camera would be useless.
Amazon Forest Launch
Giotto was built by the Europeans for the European Space Agency, and was launched from the Amazon forest on its 465-million-mile journey atop a European rocket on July 2, 1985. It will be commanded from a control center in Darmstadt, West Germany.
This is the first effort at interplanetary exploration by the European Space Agency, and it is all that is left of what was to have been a joint U.S.-European effort. Early NASA plans called for the United States to provide a “mother ship” that would stay a safe distance from the comet, and the Europeans were to build a “daughter ship” that would make a close approach. The U.S. craft was to be loaded with navigational equipment to aid the Europeans during the close flyby.
According to scientists who were involved in the U.S. effort, European scientists sold the project to the member countries of the European Space Agency on the basis of support from the United States as a joint effort. But a fierce debate raged within NASA over how much of a commitment the space agency should make, and some scientists are still licking their wounds from that battle.
“The Europeans were left holding the bag when we dropped out,” one key American scientist said bitterly. “They didn’t have any choice but to go ahead.”
Going for Broke
And in the end, they decided to go for broke, making their debut in interplanetary exploration with a project that now threatens to steal the show.
American scientists, however, have not been cut completely out of the action. U.S. scientists have dust-gathering instruments aboard the Soviet probes, and Giotto carries an experiment from the University of California, Berkeley, designed to sample gases from the comet in an effort to learn about the earliest composition of the solar system.
The United States had planned to study the comet with two instrument packages aboard a space shuttle, but one of those was destroyed in the Jan. 28 Challenger explosion and the other was grounded, along with the entire shuttle fleet, after the tragedy.
Giotto’s moment in the spotlight should be spectacular, but brief. The relative speed at which the comet and Giotto will pass one another will be more than nine times faster than the speed of an orbiting space shuttle, for example, and that means that Giotto will have less than four hours to do its work. That opportunity could be even shorter if dust particles damage the craft.
Bullet-Proof Vest
Giotto is wearing a space-age bullet-proof vest that should shield it from the dust. Although some scientists have suggested that this is a suicide mission, the Europeans have predicted that the chance of safe passage is around 90%.
The protective system consists of two shields. The theory is that dust particles will penetrate the first shield and be trapped in a gap between the two shields, where they will be converted instantly to hot gases, thus spreading the impact over a larger area.
To maintain stability during flight, Giotto rotates 15 times per minute, and it will snap a picture each time the camera is pointed at the comet, thus providing 15 color pictures a minute. However, the prime time is only about 30 minutes, during the period of closest approach, and many of the photographs will probably prove unsatisfactory. The European Space Agency hopes to release at least five photographs next Thursday and Friday.
The resolution is expected to be sharp enough to allow scientists to study features the size of a small house, giving them their first close look at an object that has terrorized and fascinated the human race for thousands of years.
ENCOUNTER WITH COMET HALLEY. SPACECRAFT TRAJECTORY / EUROPEAN SPACE AGENCY GIOTTO SPACECRAFT.
The European Space Agency’s Giotto spacecraft and Halley’s comet will pass within about 300 miles of each other at a closing velocity of 151,000 miles an hour. That close approach makes Giotto the star attraction among the five probes now on their way to Halley. But at that speed, a speck of debris from the comet, weighing as little as 1/250th of an ounce, would have the same energy as a 1,300-pound object traveling at 62 miles an hour, giving rise to concern over the survivability of the spacecraft. Giotto will study the comet with 10 instruments during the encounter next Thursday, including a high resolution camera that will send back close-up photos of Halley’s nucleus, which has never been seen.
USSR VEGA SPACECRAFT
The Soviet Union has two identical spacecraft en route to Halley, one of which got there ahead of everyone else when it passed about 6,000 miles from the comet Wednesday night. Vega 1 and Vega 2, which studied VeNus last June on their way to Halley, carry television cameras and instruments to measure gas and dust particles and the magnetic field around the comet. The second Soviet prObe will arrive Saturday night, and how close it approaches the comet will depend on what the Soviets learn from their first probe.
JAPANESE SPACECRAFT
Japan marked its entry into interplanetary exploration with two spacecraft, one to study the comet Saturday from a safe distance of about 120,000 miles, and the other to monitor the solar winds that form Halley’s tail. The second craft will pass within a few million miles of the comet next Tuesday. Both of the Japanese probes were launched from Japan’s Kagoshima Space Center on the island of Kyushu.
