Wondrous encounters
The achievements of the twin Voyager craft are a space triumph that nearly wasn’t.
THE Voyager 1 spacecraft is the first human-made object to venture into interstellar space. Even if defined only by distance, the Nasa/Jet Propulsion Laboratory twin Voyagers are America’s greatest space adventure. They’ve been flying successfully for more than 36 years and are billions of kilometres from home. What isn’t widely known is that they almost never made it out there.
The first proposed mission in the late 1960s was for four spacecraft to take advantage of a rare alignment of the four outer planets of the Solar System; Jupiter, Saturn, Uranus and Neptune would all be on the same side of the sun. However, in December 1971, Nasa decided it couldn’t afford the billion-dollar pricetag for a 12-year “grand tour” mission with four spacecraft.
This alignment happens only every 176 years, and the next launch opportunity was just five years away, in 1977. To avoid missing the opportunity, JPL engineers quickly devised a plan to send two simpler spacecraft on fouryear flights to Jupiter and Saturn, with the hope of continuing on to Uranus and Neptune.
But exploring space is hard. If something breaks, you can’t send out a mechanic. Because of the hours it takes radio signals to travel to the spacecraft, ground controllers can’t fix anything in real time. So JPL engineers had to build the smartest spacecraft yet designed, using “fault protection” software in their small computers to spot any problems and take action.
The autonomy of the two spacecraft was essential to their capability and longevity, but that also made it difficult during the first few months to learn how to fly them.
Voyager 1 was on a shorter, faster trajectory, so Voyager 2 was launched first, on Aug 20, 1977. Soon after launch, Voyager 2’s fault protection was put to the test. The spacecraft was tumbling and in a state of mechanical vertigo. The computer began exchanging primary systems for backups, following its faultprotection sequences.
Although some engineers wanted to reboot the computer, a key engineer realised that a WHEN facing oncoming floodwaters, ants use their helpless babies as floating life-preservers – by sticking them at the very bottom of the life-rafts that they build with their own bodies.
The findings, described in a paper published in PLOS One, reveal that ant rafts have a fascinating internal structure – one that maximises the group’s buoyancy and thus, their chances of survival. But it puts the young ant brood at the very bottom of the boat, exposed to hungry fish and the risk of drowning.
“It was an interesting contribution. No one had really looked at this idea of the brood as a flotation device,” said David Hu, a mechanical engineer at the Georgia Institute of Technology, who was not involved in the study. “It adds a level of sophistication to the rafts that was previously not understood.”
Researchers have long marvelled at the incredible organising powers of ant colonies. Like beehives and termite nests, these so-called super-organisms exhibit what’s known as “swarm intelligence”, able to act quickly in coordinated ways.
Ants may be tiny alone, but they’re a formidable foe in large numbers. They build bridges with their bodies that others can then walk over, they surround intruders and “microwave” them to death with their body heat, and when a flood hits, they can link up and form “rafts” that can float to higher, drier ground. One study even found that the invasive fire-ant Solenopsis invicta actually traps air pockets to form a protective layer that helps keep them afloat.
But researchers at the University of Lausanne in Switzerland wondered if there was even more complex organisation to these ant rafts. After all, who were the unlucky ants forced to the bottom of the raft? Was there a reason they were chosen for the job? Were they submerged underwater, and thus at higher risk of drowning?
The researchers also wondered whether the ants would place the most valuable or vulnerable members, like the queen and the young brood, away from the water. The queen is important because she’s the mother of the colony, and the brood – made up of young ants in larval or pupal form, unable to fend for themselves and can’t really move around on their own and likely require extra protection. reset would be fatal because Voyager 2’s sun sensor had to locate and lock onto the Sun to orient itself. The engineers nervously watched the data as the spacecraft righted itself and stabilised. As someone put it, Voyager 2 was “smarter than we were”.
Two weeks later, Voyager 1 had its own launch adventure but rode it out in blissful ignorance. The first-stage rocket underperformed, requiring a longer burn by the second
To test their hypothesis, the scientists went to Formica selysi ant colonies along the bank of the Rhone River and picked up a bunch of worker ants, brood ants and queens. They took them back to the lab, put them in groups of 60 workers with queens and gave some of them 10 young brood ants to care for. That’s when they started to slowly raise the water level, and watched how these mini-colonies reacted.
Sure enough, the worker ants placed the queen in the centre of the ant raft, protected from the water on all sides. But, to their surprise, the ants took the young, helpless brood – the larval and pupal ants – and lined their bodies along the base of the raft, where they would be most exposed to the water.
This seemed counterintuitive; shouldn’t the ants try to protect their young? After submerging both adult ants and their brood young in the water, the scientists found that the pupae and larvae were actually more buoyant than the adults.
This played out in the overall success of the broodbottomed rafts, which seemed to do better than rafts held together only by adult worker ants. Once the rafts disembarked, the ant rafts with no brood took less time to disassemble, but they had more “non-responsive” workers that needed reviving, the authors found.
The rafts with brood, on the other hand, took a little more time to disassemble, but there were far fewer on their crew who needed CPR.
There were a few caveats, Hu pointed out: For example, their lab rafts were far smaller than those in the wild, which can carry a whole colony of 100,000 or so members. And 10 brood for 60 adults was a pretty high ratio for an ant colony, he added.
Still, the research gives insight into how ants play to each of their members’ strengths. The adult ants link jaws to limbs and move around to give the raft its structure; the brood can’t move, but their buoyant bodies (perhaps because they have more fat content, Hu said) help keep everyone afloat.
The ant young seemed to suffer no long-term ill effects from being put to work like this, the researchers found. They successfully reached adulthood at the same rate as brood that weren’t rafted. – Los Angeles Times/ McClatchy-Tribune Information Services stage to achieve the speed needed to reach Jupiter at the prescribed time. It did the job with only 3.5 seconds of fuel left; if it had run out of fuel, it would have been late for its rendezvous with Jupiter.
Wondrous encounters with Jupiter ensued in 1979. Thanks to the spacecrafts’ cameras, the Voyagers let everyone marvel at Jupiter’s orange moon Io as it spouted eight volcanic plumes, revealing it as the most geologically active object in the Solar System.
Encounters with Saturn in 1980 and 1981 entranced us with images of its majestic rings and many moons. Scientists knew that its planet-size moon Titan had an atmosphere, but they didn’t know it was mainly nitrogen and much denser than Earth’s.
In 1981, the continuation of the Voyager journey beyond Saturn, as well as Nasa’s other planetary programmes, were in dire danger of cancellation. But, aware of strong public interest buoyed by the illuminating images and unexpected discoveries, the White House agreed to continue the planetary programme and Voyagers’ mission to Uranus.
Five years later, Voyager 2 flew past Uranus. Finally, in 1989, Voyager 2 reached Neptune, finding its winds among the fastest and strongest even though it’s the farthest from the heat of the Sun.
Before Voyager 1’s cameras were turned off (to save power and memory), they looked back toward the Sun, taking a photograph of tiny Earth in the black distance, the famed “pale blue dot”.
Without the Voyager mission, we wouldn’t have been able to see the diversity and splendour of our Solar System up close, to answer that haunting, persistent question, “What is it like out there?” The adventure that almost didn’t happen will continue as Voyager 2 joins Voyager 1 in exploring the space between the stars, until about 2025, when power runs out. They will journey on, carrying golden records, which are time capsules of Earth where their great adventure began. – Los Angeles Times/ McClatchy-Tribune Information Services
Edward C Stone, a former director of Nasa’s Jet Propulsion Laboratory, is the project scientist of Nasa’s Voyager mission and a professor of physics of Caltech. WHEN stars explode, it’s a messy but useful business, the massive blasts seeding the universe with such key elements like calcium, iron and titanium.
And with the help of a new high-energy X-ray telescope, Nasa said last week that astronomers are closer than ever to seeing just what’s going on.
“This is helping us untangle the mystery surrounding how stars explode,” said Fiona Harrison, principal investigator on NuSTAR, or the Nuclear Spectroscopic Telescope Array.
Combined with images from another Nasa X-ray observatory, Chandra, NuSTAR has created the “first ever map of radioactive material in the remnants of a star that exploded”, she told reporters.
One of the biggest surprises was that stars, which are spherical objects, do not explode in a circular manner, she said.
Rather, it appears that the blast is more lumpy and distorted from the very beginning.
“Prior to the explosion, the core of the star literally sloshed about,” said Harrison, a scientist at the California Institute of Technology.
Astronomers based their findings on the observations of Cassiopeia A, or Cas A for short, a remnant of a supernova 11,000 light-years away.
The star exploded around 350 years ago, blowing off outer layers with an extreme heat that created even more elements.
Cas A has been expanding since the year AD1670, propelling debris at a speed of about 16 million kilometres an hour, but never before have scientists been able to glimpse the radioactivity that was produced inside the explosion.
“With NuSTAR, we have a new forensic tool to investigate the ashes left behind when this star exploded,” said Brian Grefenstette, an astronomer at Caltech.
NuSTAR launched in 2012 on a two-year mission, joining the Nasa fleet that also includes the Hubble Space Telescope.
It is the first orbiting telescope to focus on the high-energy X-rays of the electromagnetic spectrum.
Although the Chandra Observatory remains the world’s most powerful X-ray telescope, NuSTAR can monitor a range the older orbiting telescope can’t see.
Robert Kirshner, an astronomer at the Harvard-Smithsonian Center for Astrophysics, described the radioactivity map NuSTAR produced as “pioneering science”.
“You should care about this,” said Kirshner, who was not involved in the project.
“Stars perform a kind of alchemy where they turn one element into another. The Earth itself is something that is the residue of this astronomical process.”
Star explosions played a key role in the iron used to make cars, the calcium in our bones and the titanium used to manufacture hip replacements, he explained.
“So we are all star dust and NuSTAR is showing us where we came from, including our replacement parts.” – AFP