<div class="htmlview paragraph">New goals set for the U.S. space program focus on reestablishing the human presence on the Moon and sending the first manned mission to Mars in the beginning of the 21st century. The necessary first step in the support of these goals is identifying requirements that drive the development of new technologies. Since extravehicular activity (EVA) will be an integral part of the establishment of both a lunar base and the exploration of the martian surface, this is an area where specific requirements for the EVA systems need to be determined.</div> <div class="htmlview paragraph">EVA on the lunar and martian surfaces presents unique conditions in which an extravehicular mobility unit (EMU) must operate. These conditions include environmental factors such as partial gravity, dust, thermal gradients, atmospheric conditions, lighting, and radiation. Not only must the suit and portable life support system (PLSS) be designed to accommodate these environmental factors, the system must also support the activities involved with exploration and the establishment of a permanent human presence on these surfaces. This paper will present basic design reference requirements applicable to EVA equipment on the lunar and martian surfaces.</div>