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InSight lander
An artist’s conception shows the InSight lander on the surface of Mars. The SEIS instrument is the light-colored dome at lower left. (Credit: NASA)

NASA says it’s putting off next year’s scheduled launch of its InSight lander mission to Mars until at least 2018, due to a persistent leak in the spacecraft’s main seismic-sensing instrument.

Mission managers had been working for months to track down a series of small leaks in the vacuum seal for the instrument, known as the Seismic Experiment for Interior Structure, or SEIS. The instrument was being built and tested for NASA under the direction of France’s space agency, the Centre Nationale d’Etudes Spatiales, or CNES.

Up until Monday, managers had high hopes they could fix all the leaks in time for next March’s liftoff atop a United Launch Alliance Atlas 5 rocket from Vandenberg Air Force Base in California. But the results from a low-temperature vacuum test at a facility near Paris were so discouraging that they scratched the launch off the schedule.

“It’s a very close decision,” Marc Pircher, director of CNES’ Toulouse Space Center, told reporters during a teleconference.

SEIS is one of the two key instruments for the InSight mission, which is aimed at monitoring seismic activity deep beneath the Red Planet’s surface. “InSight” is a quasi-acronym, standing for Interior Exploration Using Seismic Investigations, Geodesy and Heat Transport. The other instrument is the Heat Flow and Physical Properties Package, or HP3, a German-built probe that’s designed to burrow up to 16 feet (5 meters) underground.

The SEIS instrument’s three main sensors are designed to measure movements as small as the diameter of an atom. But the sensors have to be enclosed within a vacuum-sealed sphere that insulates them from Mars’ harsh conditions. Vacuum chamber tests in France showed that the sphere couldn’t hold a seal under Mars-like conditions.

Pircher was confident that the leak can be fixed. “It’s a question of a few months,” he said. However, because of the orbital mechanics for flights between Earth and Mars, affordable launch opportunities come around only every 26 months.

2016’s opportunity extended from March 4 to March 30. The negative results from Monday’s test led NASA and CNES to conclude that they ran out of time for 2016’s opportunity. The next one comes in May 2018, said John Grunsfeld, NASA’s associate administrator for science. “The 2018 opportunity is actually energetically more favorable, so it might mean a little bit wider launch window and opportunities for us,” he said.

Grunsfeld said InSight’s science mission would have been ruined if SEIS had been sent in its current condition. “In some sense, we don’t have a decision to make, because we’re not ready to go,” he said. “In another sense, I think it’s much better that we have this discussion now, rather than send it to Mars and wishing we had the opportunity here on Earth to fix something.”

He said that NASA would weigh its options in the coming weeks. The space agency hasn’t yet committed itself to a launch in 2018, but the preferred path was clearly to go with a postponement rather than cancellation. “I see this as a minor setback rather than a disaster,” said InSight’s principal investigator, Bruce Banerdt of NASA’s Jet Propulsion Laboratory. “It’s not a disaster. It’s just a hiccup on our path to getting this kind of science, and this kind of understanding of our solar system and our place in the universe.”

It’s not the first time such a setback has delayed a Mars mission: NASA’s launch of the Curiosity rover mission, also known as Mars Science Laboratory, had to be postponed two years due to technical difficulties. That added hundreds of millions of dollars to the mission cost, boosting the total price tag to $2.5 billion.

Jim Green, director of NASA’s Planetary Science Division, said the total mission cost for InSight was budgeted at $675 million. So far, $525 million has been spent, he said. Green said it was too early to estimate the effect of the two-year delay on mission cost.

While work continues to fix the leak in the SEIS instrument, the car-sized InSight spacecraft will be returned to its Colorado-based manufacturer, Lockheed Martin, for storage.

Grunsfeld said InSight is a “stand-alone Discovery mission” that does not affect the tempo for sending other spacecraft to the Red Planet, leading up to potential human journeys to Mars and its moons in the 2030s. The European Space Agency is still on track to launch its ExoMars orbiter next March, and will send out an ExoMars rover in 2018. Meanwhile, NASA is readying yet another rover for launch to Mars in 2020.

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