Small light‐weight satellites and space vehicles under development for future NASA missions have reduced thermal mass and are strongly affected by changes in orbital conditions, resulting in large temperature variations. Restrictions on payload weight and volume limit the usefulness of many thermal control technologies. One thermal control approach, being considered by NASA in both nano‐ and micro‐ spacecraft applications, involves the use of electrochromic (EC) variable emittance devices (VEDs). VEDs operating in the harsh space environment (UV radiation, atomic oxygen) must be properly protected if they are to reach their design operational life. In this paper, we discuss the design of an all‐solid‐state EC VED built on a silicon wafer. The silicon wafer serves as a window for IR radiation and protects EC layers from the space environment. This paper also discusses the expected limits of emittance modulation of the EC VED on the silicon substrate as well as possible impact of an antireflective coating on IR emittance modulation. © 2004 American Institute of Physics