Within the framework of Cognitive Translation Theory, the paper aims to explore how students of science who do not specialize in English use and acquire various kinds of knowledge in the process of translating a scientific text from Russian into English, focusing on the problems they encounter and the strategies they use in order to solve these problems. The study is based on the assumption that with the numerous sources of information available today many of the knowledge gaps both linguistic and non-linguistic can be filled provided the translator uses the right sources at the right moment. The paper uses data obtained from an experimental study carried out using the think-aloud protocols technique. The translation process is described in terms of the cognitive-heuristic approach to translation, using such terms as the cognitive context, cognitive search, and auto-correction. The paper uses the term 'operational error' to denote the wrong strategy employed by the translator, which leads to a breakdown in the process of translation and eventually to an unsuccessful translation variant. Various kinds of operational errors specific to students of science are discussed using examples from the protocols. Special attention is paid to the importance of translation on the conceptual level and the use of auto-correction to ensure the naturalness of the target text. The experimental data obtained also allow identifying the areas of English grammar that cause the most problems for students of science.