Thomas Zurbuchen, the head of NASA’s Science Mission Directorate, has cancelled an instrument that was being developed for the Europa Clipper mission because of persistent cost overruns. Instead, he wants to find a way to include a simpler, less complex instrument that can provide similar data. He also restated NASA’s commitment to the project overall.

Europa Clipper is intended to study Europa, a moon of Jupiter believed to have a liquid ocean under an icy crust. Fissures in the ice are thought to allow geysers to erupt, spewing the watery contents above the surface where they can be studied by a spacecraft passing by. Life as we know it requires liquid water so scientists want to investigate any location in the solar system where it exists in case it might harbor microbial organisms.

Priorities for NASA’s planetary exploration program are set by Decadal Surveys conducted under the auspices of the National Academies of Sciences, Engineering, and Medicine every 10 years (a decade). The most recent planetary science Decadal Survey in 2011 did not select a Europa mission as its top priority for a “flagship” mission because of its expected $4.7 billion cost. Instead, it chose a set of missions to return a sample of Mars to Earth as the number one priority.

However, the report said that if the cost came down, and more resources were made available, a Europa mission might rise in priority. NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, CA redesigned the mission to lower the cost to about $2 billion. Instead of orbiting Europa, the new Europa Clipper will orbit Jupiter and swing by Europa 45 times, an easier mission profile. John Culberson, who then chaired the House Appropriations Commerce-Justice-Science (CJS) subcommittee, added the money year after year. A Republican from Texas, Culberson is a planetary science enthusiast who is convinced there is life in Europa’s ocean and was determined to fund missions to find it. However, he lost his reelection race last year and no longer is in Congress to promote and defend the project.

Zurbuchen explained in the Planetary Exploration Newsletter today that the Interior Characterization of Europa Using Magnetometry (ICEMAG) instrument has been experiencing cost growth since last year. In fact, cost growth began affecting the entire Europa Clipper payload so much so that in 2017 NASA established “triggers” for each instrument to keep higher levels of program management informed.

In March 2018, ICEMAG began approaching its trigger and “three months later exceeded it,” Zurbuchen wrote today. Despite efforts to stem the growth, the trigger had to be repeatedly raised and “cost growth continued to outpace increases to the cost trigger.” During a February 14, 2019 review, the cost was pegged at $45.6 million, $8.3 million above the most recent trigger set in January 2019 and $16 million more than the original trigger set in February 2017. “Altogether this represents a cost approximately three times the cost estimate presented in the original ICEMAG proposal,” which is “not acceptable.”

“As a result, I decided to terminate the ICEMAG investigation.”

Zurbuchen has directed Lori Glaze, director of SMD’s Planetary Science Division, to present a plan in the next two weeks on how to include a “simpler, less complex magnetometer.”

NASA explains that a magnetometer will measure Europa’s magnetic field and help confirm the existence, salinity and depth of Europa’s ocean and constrain the thickness of its ice shell. All of those measurements are important to determining if Europa is habitable. “Even without ICEMAG aboard, Europa Clipper’s suite of science instruments can help scientists understand the ocean’s properties and ice shell thickness. With a simpler magnetometer, these objectives are all the more likely to be met.”

Culberson also directed NASA to build a spacecraft to land on Europa. Although it was not finalized until last month after he departed Congress, the FY2019 Consolidated Appropriations Act requires, by law, that NASA launch Europa Clipper in 2023 and Europa Lander in 2025, specifying the Space Launch System (SLS) as the rocket to send both of them on their way. Sen. Richard Shelby (R- AL) chairs the Senate Appropriations Committee and represents Marshall Space Flight Center, which manages the SLS program.

The FY2019 bill allocates $545 million for Europa Clipper and $195 million for Europa Lander.

Zurbuchen confirmed NASA’s commitment to Europa Clipper today, but not the Lander and not the launch dates. NASA said only that Clipper would launch “in the 2020s.”

NASA’s FY2020 budget request will be released next Monday. How much is included for Clipper and Lander will reveal the Trump Administration’s level of commitment. Then it will be up to Congress to decide how far to go in protecting the goal of exploring Europa now that Culberson is gone.