Stardust's bonus flight by Comet Temple-1 - on Monday

This is a second flight to the same comet. The last time it was the Deep Impact spacecraft in 2005, and in the meantime it managed to orbit the sun once. It is also a new mission for a spacecraft that has already encountered another comet and brought gas samples from it to Earth

A bonus round is something more associated with TV entertainment, not a pioneering spaceship into deep space. "We're definitely in the bonus round," says Stardust Next Project Manager Tim Larson at NASA's JPL Center in Pasadena, California. This spacecraft has already flown by an asteroid and a comet, returned dust samples to Earth and now, almost twice its planned lifespan, it is moving toward an encounter with another comet.

The Stardust spacecraft was launched on February 7, 1999 to study a comet. Before Stradust, seven spacecraft from the USA, Russia, Japan and the European Space Agency visited the comets - they held short meetings and collected data and sometimes pictures of the comet nucleus during the flight.

Like the comet hunters before him, Stardust passed near a comet, collecting data and taking pictures, but he also had the ability to return home and carry cometary material with him - particles from the comet itself. Along the way, the payphone-sized spacecraft (anyone else remember what that is?) made a few more milestones and a few more times than it did the first time.

In the first round, on its original mission, Stardust made observations of the Anne Frank asteroid, altogether the sixth asteroid in history to be photographed up close. After that, she marked a few more firsts in the study of your behavior. She was the first to fly by a comet and collect particles from its dust, passing behind it at a speed of six kilometers per second. After that, she was the first spacecraft to return to Earth after reaching beyond the orbit of Mars in a two-year journey, a distance of 1.2 billion kilometers. When the Stardust spacecraft dropped the dust samples from Comet Wilt 2, Hexpaula was the fastest man-made object to enter the atmosphere.

The spacecraft was also the first to provide cometary dust samples that would allow scientists to uncover comet secrets for years.

Although some of its components have been retired, and the return chamber weighing 45 kg is on display in the main hall of the Smithsonian Museum in Washington. However, the rest of the ingredients are still there - and there is still work to be done.

"We put Stardust on a parking orbit that would bring it back to Earth within two years and in the meantime we asked the scientific community for suggestions on what to do with the spacecraft that still has fuel and its instruments are still working," says Jim Green, director of NASA's Planetary Science Division.

In January 2007, out of a selection of proposals and ideas, NASA chose the Stardust Next project. It was a plan to revisit Comet Temple 1 at one-tenth the price of getting a new spacecraft. Comet Temple 1 was of interest to NASA. This was the first mission of a previous NASA spacecraft in July 2005 - the Deep Impact mission placed a copper projectile weighing about 300 kg on a collision course with the comet and watched the results of the collision using cameras on the main spacecraft and on Earth.

"The plan was to get closer to Comet Temple 1 for a friendlier visit than our predecessor," says Joe Worka, principal investigator at Cornell University's Bankest. It is supposed to approach to a distance of about 200 kilometers from Temple-1 and see the changes that have taken place in it in the last five and a half years.

This time period is significant for Temple-1 as the comet orbited the Sun once. Not much happens during the transit through the cold regions of the outer solar system, but as the comet approaches its perihelion (closest point to the Sun) things start to change.

"Comets are spectacular when they get close to the Sun, but we still don't understand them as well as we should," says Warka. "They are also messengers from the past. They can tell us how the solar system formed and understand how comets themselves have changed since their formation.

So the spacecraft that moved far from all its predecessors was sent again in the name of scientific opportunity. In the meantime, she covered over a billion kilometers for four and a half years. and passed several obstacles along the way.

"One of the challenges of launching a spacecraft on a mission it was not originally designed for is that you don't start with a full fuel tank," says Larson. "Almost every deep space mission starts with enough fuel for the mission, and some reserves for change maneuvers and adjustment of direction and other uncertainties. Fortunately, the mission navigation team did a good job, the spacecraft worked well and there was enough emergency fuel on board after the main mission to allow the re-approach, but just barely.”

"We estimate that only less than 3% of the original fuel with which the mission was launched remains," Larson said. "This is only an estimate because no one has invented an accurate fuel gauge for spacecraft. There are some good techniques we have adopted to make the assessments, but they are still assessments.”

One of the ways to estimate is to look at the history of the spaceship, how long its engines have been operated. When this was done with Stradust, it turned out that this had been done about half a million times in the last 12 years.

"There is always a plus or minus in every combustion, when you add them all you get a range of how much fuel was used" said Larson.

Another problem is that the passage of a comet near the Sun may ignite jets of gas and dust that can cause its trajectory to change, sometimes in unexpected ways, which affects the accuracy of calculating the position for the encounter. Then there is the question of distance. Stardust will pass by Temple-1 almost on the opposite side of the Sun from Earth, which will make communication with Earth difficult. To this must be added the Stardust spacecraft itself. Launched when Bill Clinton was president, it boiled and froze countless times in its journey through the outer and inner solar system. She also caught quite a bit of radiation in sun storms. And while her gas is almost gone, that doesn't mean there's nothing left in the gas tank.

"All these challenges have been difficult. We believe that our team and the spacecraft will meet them all, and we look forward to seeing what Temple 1 looks like these days.

Researchers and the rest of the world will have the opportunity, starting a few hours after the encounter on Monday, February 14 at approximately 16:56 Israel time, to view the first of 72 images of Comet Temple 1.

All the pictures will be taken by the spacecraft's navigation camera - which itself was a backup camera intended for previous missions in case their camera was not working. Voyager (launched in 1977), Galileo (launched in 1989) and Cassini (launched in 1997). It will take 15 minutes to transfer each image. It will take about ten hours for all the data to reach the ground.

For information on the NASA website