NASA's next big Mars mission will have to wait a couple of years due to a faulty piece of equipment that won't stay fixed. The space agency announced today that the launch of the Interior Exploration using Seismic Investigations Geodesy and Heat Transport (InSight) lander mission scheduled for next March has been scrubbed due to a persistent vacuum leak in the lander's primary science instrument. A new launch date has yet to be determined as the lander is returned from Vandenberg Air Force Base in California to the Lockheed facility in Denver.

NASA says the launch was abandoned due to a continuing fault with the lander's Seismic Experiment for Interior Structure (SEIS). Built by France's Centre National d'Études Spatiales, this is a seismometer that is able to detect ground movements on an atomic scale thanks to three main sensors sealed in a vacuum.

This seal has been giving engineers problems since a leak in the seal was detected earlier this year. This was repaired and the instrument was declared fit for flight, but when it was tested on Monday in extreme cold reaching minus 49º F (-45º C), the seal failed again. Though not irreparable, NASA says that there isn't time to fix the SEIS and make the launch deadline.

Unlike missions to Earth orbit, which have launch windows that can recur every day, and ones to the Moon that can recur monthly, planetary missions involve a complex ballet of two bodies revolving about the Sun. For missions to Mars, the best conditions only appear during a period of a few weeks every 26 months. This means that InSight will be returned from Vandenberg Air Force Base in California to the Lockheed facility in Denver while scientists revisit their calculations for the next opportunity.

The InSight stationary lander is based on NASA's Phoenix lander, which set down at the Martian North Pole in 2008, and is designed for a 720-day primary mission near the Martian equator.

It has a robotic arm for placing instruments, including hammering a heat-flow meter up to 15 ft (4.5 m) into the ground. Its purpose is not only to study Mars, but also to gain insights into the formation of rocky planets in the inner Solar System.

"Learning about the interior structure of Mars has been a high priority objective for planetary scientists since the Viking era," says John Grunsfeld, associate administrator for NASA's Science Mission Directorate. "We push the boundaries of space technology with our missions to enable science, but space exploration is unforgiving, and the bottom line is that we're not ready to launch in the 2016 window. A decision on a path forward will be made in the coming months, but one thing is clear: NASA remains fully committed to the scientific discovery and exploration of Mars."

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