Data from the NASA Rodent Research-1 (RR-1) mission showed that gene-expression levels in mouse livers are different depending on what tissue preservation protocol is used and that slow freezing is not an effective method for preserving signals in gene-expression data. In response to these and other observations the Rapid Freeze hardware was built for use on the International Space Station. The Rapid Freeze hardware freezes mouse tissues (Glovebox freezer) and whole carcasses (Cryochiller) at rates closely mimicking those attained with immersion in liquid nitrogen. Because this hardware will be used extensively on future rodent research missions it is crucial to understand whether or not it preserves signals in gene expression data in order to maximize the value of these rare and expensive spaceflight experiments. Therefore this study was designed with three goals: 1) To evaluate the temperature profile of the Cryochiller and Glovebox freezer cartridges (Rapid Freeze hardware) over time during mock on-orbit procedures; 2) To determine the freezing profiles of tissues and carcasses using Rapid Freeze hardware at both optimal and sub-optimal temperatures (to mimic on-orbit operations) compared with those frozen in liquid nitrogen (the laboratory gold standard) or frozen in at -80 C (the current standard method); 3) To identify gene expression changes in a) tissues that were frozen via the Glovebox freezer and b) tissues dissected from whole or partial carcasses that were frozen via the Cryochiller versus tissues that were frozen via control methods (liquid nitrogen or -80C slow freeze) to assess how the Rapid Freeze hardware compares with laboratory gold standard practices and our current standard methods.