Mars InSight lander
An artist’s conception shows NASA’s InSight lander on Mars. The SEIS instrument is in the chamber shown to the left of the lander platform. (Credit: NASA / JPL-Caltech)

NASA has approved plans to fix a flaw on its InSight lander in time for a launch to Mars in 2018.

The flaw involves a leak in a vacuum seal for one of the lander’s main scientific instruments, known as the Seismic Experiment for Interior Structure or SEIS. InSight had been scheduled for launch this year, but last December, NASA put off the launch because the leak couldn’t be fixed in time.

Today NASA said it would spend an extra $153.8 million, on top of the mission’s previously budgeted $675 million, to redesign the instrument and cover other costs of the two-year delay.

“The additional cost will not delay or cancel any current missions, though there may be fewer opportunities for new missions in future years, from fiscal years 2017 to 2020,” NASA said in a statement.

NASA said it was targeting a 2018 launch back in March, but it wasn’t until this week that the agency’s Science Mission Directorate gave final approval for the revised mission plan.

The Jet Propulsion Laboratory will be responsible for redesigning SEIS’ vacuum container and the electrical connections that previously failed testing. Meanwhile, France’s space agency, the Centre National d’Études Spatiales, will focus on SEIS’ sensors as well as integration of those sensors into the container, and the integration of the complete instrument into the lander.

SEIS is meant to measure ground movements on Mars as small as half the radius of a hydrogen atom, but to do that, the instrument’s seismic sensors have to be held in a perfect vacuum.

“InSight” is a quasi-acronym, standing for Interior Exploration Using Seismic Investigations, Geodesy and Heat Transport. The seismic instrument plays a key role in InSight’s mission to study Mars’ deep interior, where astrobiologists say any life on Mars stands the best chance of surviving.

More broadly, data from InSight could shed light on the formation and evolution of rocky planets like Earth and Mars. “We’ve concluded that a replanned InSight mission for launch in 2018 is the best approach to fulfill these long-sought, high-priority science objectives,” said Jim Green, director of NASA’s Planetary Science Division.

The revised plan calls for InSight to be launched during a window that opens on May 5, 2018, with the Mars landing planned for Nov. 26 of that year.

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