I am going to assume you are only referring to only scientists and not engineers. People sometimes assume that scientists are engineers too. Also, I am going to answer from a NASA/Johnson Space Center perspectives.

The question depends on whether the scientist is doing only research or is on a project or both. Scientists that do pure research spend about 75–85% of their time doing research in their area of expertise. The other portion of the time is spent meetings, paper writing, review of university proposals for doing NASA research and sometimes educational outreach. Some spend their time writing proposals to get research funds to pursue their research.

The ones involved in projects spend a large portion of their time ensuring their part of the project is on track. They may participate in the design and testing and monitoring their scientific instruments during testing such as thermal testing. They may review the test data and get with the design engineers to make modification. Some scientists may do some of the engineering work such as writing software code for their instrument. The scientist may be able to do research on the side while supporting a project as the subject matter expert.