Soon after witnessing the Sputnik spacecraft cross the Boston sky in fall of 1957, he became a part-time student employee for the Mars Probe project at the MIT Instrumentation Lab, and in early 1960s was staff physicist at the same Laboratory's project to develop the Apollo Mission's navigation and guidance system.
In 1968 Nordtvedt calculated how and to what degree the gravitational-to-inertial mass ratio of gravitationally compact bodies—bodies with significant gravitational binding energy—will generally differ from one in gravity theories other than general relativity, and he then showed how lunar laser ranging data could be used to measure that key ratio to significant precision for the Earth.
He was a board member and scientific advisor overseeing the joint NASA-ESA Space Test of Equivalence Principle mission.
His research was the subject of a Wall Street Journal article featured on the front page.
[4] Nordtvedt was elected to three terms in the Montana state legislature for a six-year period from 1979 to 1984, and there he wrote one of the first inflation indexing reforms of income tax law in the nation.