ONE evening in January 1997, scientists and historians gathered in the basilica of St Anthony in Padua, the Italian city where Galileo taught, for a concert of 16th-century organ music.
The occasion was , a meeting dedicated to the man, and the spacecraft and telescope named after him. The highlights were to be a presentation of the first results from the spacecraft, which, against all odds, had recently completed its primary mission in orbit around Jupiter.
The organist invited to perform that evening was Les Deutsch, a musician from the California Institute of Technology in Pasadena. However, most of the audience were more familiar with Deutsch’s talents as a mathematician and communications specialist, for he and his colleagues had masterminded one of the most spectacular space rescues in history. Were it not for them, the conference might never have taken place. In fact, the Galileo spacecraft could have been lost entirely.
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Rescuing vehicles in space is hard for obvious reasons. “It’s not as if you can go and get them back,” says Deutsch. And fixes are needed more often than you might think. Space is a harsh environment, where temperatures can soar to over 100 °C in the full glare of the sun, only to fall seconds later to -70 °C in the shade. Spacecraft are also bombarded with radiation, which can play havoc with their electronics. “There has never been a long-duration deep-space mission that did not have unexpected problems,” says Deutsch. So missions are designed with flexibility in mind. Minor repairs and fixes are bread and butter to ground-control teams – it’s what they are trained to do.
Occasionally, though, problems arise that threaten an entire mission. Think of Apollo 13: when an oxygen tank exploded during the spacecraft’s journey to the moon, the three men on board were short of fuel, oxygen and power, and had only hours to live. They made it back thanks to the ingenuity of their ground-based colleagues in a story made famous by countless retellings and a Hollywood movie.
Apollo 13 is merely the most famous of the great space rescues. Less well known are many stories of multibillion-dollar missions left teetering on the brink of failure by unforeseen catastrophes. They are not as memorable because they involved no crew, so no lives were at risk. Yet the stakes are still massive: a mission that fails is not just a financial loss but can threaten livelihoods, ruin careers and hold back the progress of science and technology for decades. These are the stories of just a few, like Galileo, that were brought back from the edge, against all the odds.
Perhaps the unluckiest was . When it was launched into geostationary orbit in July 1989, the satellite represented the future of telecommunications. As the largest civilian telecoms satellite ever built, Olympus was designed to carry conventional transatlantic TV broadcasts and test novel services such as high-definition TV and inter-satellite communications.
Problems began in January 1990, when one of its solar panels stopped tracking the sun, dramatically reducing the power supply. Then in May, a series of incorrect commands shut down the satellite’s propulsion, electrical and thermal control systems, causing it to tumble wildly and its temperature to plummet to -60 °C. Luckily, engineers at the European Space Operations Centre in Darmstadt, Germany – mission control for the European Space Agency (ESA) – were able to grab back the reins: they used the spacecraft’s attitude-control system to stop the tumble, and oriented the craft towards the sun to reheat it and generate electrical power. The process took over a year but eventually Olympus-1 re-entered service in August 1992.
A year later, however, disaster struck again. On 12 August 1993, a meteor smashed into the spacecraft during the annual Perseid shower. It began to tumble and, in the struggle to rescue it, engineers exhausted the satellite’s fuel supply. Olympus-1 was finally dead. The ESA team parked the spacecraft in a safe orbit where it remains to this day.
Lunar rescue
Meteor hits are rare but malfunctions are not. Rocket failures in particular can doom a spacecraft. In 1998, a telecoms satellite called Asiasat-3 was declared a total loss after a booster failed, leaving it in a highly elliptical orbit, and engineers quickly calculated that the spacecraft did not have enough fuel to achieve its intended geostationary orbit directly above Earth’s equator.
With nothing to lose, they began an ambitious plan to salvage the craft using the moon’s gravity. The technique they developed was to fire Asiasat-3’s on-board rocket briefly to accelerate the spacecraft just before it reached its closest approach to Earth. This gradually increased the eccentricity of its orbit, sending it further away from Earth each time round. Engineers calculated that after one final fly-by the moon’s gravity would briefly capture the craft, sending it behind the moon, correcting its inclination and returning it earthward, where it could be stabilised in a geostationary orbit. The plan worked: though Asiasat-3’s fuel was depleted, the craft had enough to operate as a communications satellite as originally planned, albeit for a reduced lifespan.
Solving such problems is how innovative engineers on the ground earn their keep. Yet while fixing minor hiccups is routine work, ground controllers can sometimes make things much worse. The Solar and Heliospheric Observatory (SOHO), a joint mission between NASA and ESA to study the sun, is a good example.
Launched in December 1995, SOHO transmitted spectacular pictures of the sun until one of the gyroscopes that controlled its attitude malfunctioned on 25 June 1998. The craft’s on-board computer program should have switched on a back-up gyroscope, but it didn’t. To make matters worse, when ground controllers stepped in, they mistakenly switched off the good gyro while keeping the faulty one working. The spacecraft began spinning, its solar panels ended up pointing edge-on to the sun and its on-board batteries emptied. SOHO seemed doomed.
During the weeks of silence that followed, engineers made desperate attempts to locate and contact the spacecraft. Then Alan Kiplinger, a physicist at the National Oceanic and Atmospheric Administration in Boulder, Colorado, suggested looking for the spacecraft using radar. His idea was to use the giant 300-metre radio telescope in Arecibo, Puerto Rico, to transmit a powerful radio signal in SOHO’s direction and for one of NASA’s radio telescopes to listen out for the echo.
On 23 July, SOHO’s location was pinpointed, and the radar echoes revealed that it was spinning slowly, in a way that was gradually tilting the panels back towards the sun. Once basic communications with the spacecraft had been re-established, the team waited until there was enough on-board power to begin simple operations. Over the next few weeks, SOHO was coaxed back to life. As power became available, the team reset the on-board computer and then checked out the craft’s instruments to ensure that extreme cold or heat had not damaged them. Four months later, SOHO was back at work.
Deutsch has spent time analysing the lessons learned from SOHO, but his great triumph came with Galileo. In April 1991, two years after Galileo’s launch, engineers sent the spacecraft a command to open its main communications antenna. The mechanism jammed, preventing the antenna from unfurling and forcing NASA to rely on the craft’s smaller secondary antenna. NASA later concluded that one of the antenna’s support struts had become cold-welded in place.
The loss of the main antenna was a crippling blow for a spacecraft that was intended to be NASA’s most advanced deep-space mission and, at $1.5 billion, its most expensive. Galileo’s on-board camera was designed to send back 5-megabit images of Jupiter and its moons. To cope with this, and data from the other on-board experiments, the main antenna broadcast at a rate of over 100,000 bits per second. By comparison, the small antenna broadcast at a mere 10 bits per second. Unless something could be done, Galileo would be almost useless.
“At first, there was hope that the main antenna could be unstuck,” recalls Deutsch, who works on NASA’s Deep Space Network of radio telescopes. “But a few of us began to make other plans just in case.”
Deutsch co-led a team that came up with a plan to increase the data output rate. First, they upgraded NASA’s Earth-wide Deep Space Network of radio antennas to make them more sensitive. They also developed a technique called “arraying” in which they routinely used several dishes simultaneously pointing at Galileo to amplify the detection of its signal.
The team then created an entirely new generation of radio codes for sending and receiving signals from the spacecraft, so-called error-correcting codes, that allow data to be transmitted more efficiently. Together these improvements increased the data rate by a factor of 10. They got a similar improvement by arranging to compress images aboard Galileo before they were sent, using a technique similar to the JPEG compression common in earthbound digital photographs.
Finally, they used a neat trick to get more data back. The main antenna had been designed to transmit data as it was gathered, in real time. Instead, the team commandeered Galileo’s on-board data-storage system – a tape recorder – to store information during busy times such as fly-bys of Jupiter’s moons. It then beamed the stored data back slowly during quieter periods.
By the time Deutsch gave his concert at St Anthony’s in 1997, the several gigabits of data Galileo had sent back to Earth were already revolutionising scientists’ understanding of Jupiter and its satellites, the largest of which had first been observed by Galileo Galilei himself four centuries earlier. When his organ recital finished that evening, the academics filed back to their hotels in the city. Over the next few days, they were kept busy digesting the latest secrets of the great gas giant sent back by the spacecraft. Given the money, science and careers at stake, Galileo’s stands as one of the great space rescues to date.
Yet its legacy is much broader. NASA’s Deep Space Network of radio telescopes had a decent overhaul, making them much more sensitive. Other spacecraft have also benefited from the techniques developed by Deutsch and his colleagues. After all, as Deutsch points out, spacecraft design is conservative by nature: “Nobody wants to try new ideas. But once they’ve been proven, everybody wants them.” Versions of the error-correcting codes developed for Galileo are now used routinely on deep-space probes. “Image compression had never been used before Galileo. Now it is routine,” he says.
Today, the Galileo rescue is a mere footnote in the history of a mission that exceeded all expectations – and which eventually ended in flames. After the Three Galileos conference, NASA extended the spacecraft’s mission. It continued until September 2003, when mission controllers sent the ageing spacecraft to a fiery death in the Jovian atmosphere.
A comedy of errors
Not all problems with spacecraft are the result of the harsh conditions of space. Often the errors are made back on Earth, sometimes on the drawing board or during the design phase. These are what space engineers call, in technical terms, cock-ups, and their enormity can sometimes be breathtaking.
Perhaps the most famous is the debacle surrounding the . When it was launched in 1990, astronomers were dismayed to find that the $2.5 billion instrument had a serious problem with its optical system, giving the telescope blurred vision. NASA discovered that the main mirror was the wrong shape, the result of equipment that had been wrongly assembled by the mirror’s maker, the optical company PerkinElmer.
Later, astronauts flew the space shuttle to the telescope to fit error-correcting lenses to the telescope. The cost? An extra $630 million.
Other problems have been easier to fix. For example, a serious one emerged during the Cassini mission to Saturn, which carried a probe called Huygens designed to parachute onto the surface of Saturn’s moon Titan. During the descent, Huygens was supposed to transmit its data to Cassini, which would relay it back to Earth.
However, a routine review of the mission after it was launched revealed a problem with the radio system linking Huygens and Cassini. The relative speed of the two spacecraft would cause a Doppler shift in the wavelength of the transmissions, but this had not been properly factored into the design. Once Huygens was on its way, the two spacecraft weren’t going to be able to talk.
In the end, the fix was straightforward, says Les Deutsch, the organ-playing communications expert with NASA’s Deep Space Network. The team designed a new trajectory that minimised the relative velocity of the two craft and so reduced the Doppler shift. Consequently, Huygens went on to send back spectacular images of the surface of Titan.
Some errors come to light only when it is too late to fix them. In 1992, an orbiting space shuttle began unreeling a giant conducting cable 20 kilometres long. It was supposed to generate an electric current as it moved through the Earth’s magnetic field. Unfortunately, after just 256 metres had been paid out, the $200 million tether snapped. NASA and the Italian Space Agency, which built the tether, later found that a bolt added just before launch had cut the cable. “The lesson to be learned is there is no substitute for good engineering design and judgement, review and – when possible – rigorous testing of the total system,” said a NASA safety panel in its review of the failure.
