Last week NASA canceled the program to create the first lunar rover under the name VIPER (Polar Exploration Rover Investigating Volatiles) due to budget issues, despite $450 million already being spent on the project.

The news has shocked many experts. Scientists have written an open letter to the US Congress, demanding that lawmakers reject the “unprecedented and inexcusable” cancellation of the mission NASAMore than 1,000 people signed the document.

“VIPER was intended to be a groundbreaking American project and the first NASA mission to study the origin and distribution of water ice on and below the lunar surface,” the letter said.

NASA says the skyrocketing costs of the VIPER rover are jeopardizing other commercial missions to deliver payloads to Earth’s natural satellite, designed to demonstrate capabilities offered by private partners ahead of a manned lunar mission.

But many experts do not believe NASA’s explanation: they emphasize that the goals of the VIPER mission are too important to ignore.