  We explore how astronomers take observational data from telescopes, process
them into usable scientific data products, curate them for later use, and reuse
data for further inquiry. Astronomers have invested heavily in knowledge
infrastructures - robust networks of people, artifacts, and institutions that
generate, share, and maintain specific knowledge about the human and natural
worlds. Drawing upon a decade of interviews and ethnography, this article
compares how three astronomy groups capture, process, and archive data, and for
whom. The Sloan Digital Sky Survey is a mission with a dedicated telescope and
instruments, while the Black Hole Group and Integrative Astronomy Group (both
pseudonyms) are university-based, investigator-led collaborations. Findings are
organized into four themes: how these projects develop and maintain their
workflows; how they capture and archive their data; how they maintain and
repair knowledge infrastructures; and how they use and reuse data products over
time. We found that astronomers encode their research methods in software known
as pipelines. Algorithms help to point telescopes at targets, remove artifacts,
calibrate instruments, and accomplish myriad validation tasks. Observations may
be reprocessed many times to become new data products that serve new scientific
purposes. Knowledge production in the form of scientific publications is the
primary goal of these projects. They vary in incentives and resources to
sustain access to their data products. We conclude that software pipelines are
essential components of astronomical knowledge infrastructures, but are
fragile, difficult to maintain and repair, and often invisible. Reusing data
products is fundamental to the science of astronomy, whether or not those
resources are made publicly available. We make recommendations for sustaining
access to data products in scientific fields such as astronomy.
