 OFFICE DES NATIONS UNIES A VIENNE
OFFICE FOR OUTER SPACE AFFAIRS
2 November 1998
Ms. Selma Brackman Dear Ms. Brackman With reference to your letter dated 24 September addressed to the Secretary-General of the United Nations, I wish to inform you that the United Nation Committee on the Peaceful Uses of Outer Space (COPUOS) is well aware of the problems associated with the safe use of nuclear power sources (NPS) in outer space. This item had been on its agenda since 1978. Through deliberations among the Member States of the Committee (currently numbering 61 countries) have led to the preparation of legal Principles Relevant to the Use of NPS in Outer Space. These principles were finally agreed by consensus of the Committee at its session in 1992, and adopted by General Assembly Resolution 47/68 of 23 February 1993. The principles recognize that the use of NPS may be essential to some space missions, though such use involves some risk of accidental exposure of the public to radiation or radioactive material. The principles provide that missions using NPS should be designed with inter alia malfunction correction systems and redundancy, physical separation, functional isolation and adequate independence of their components in order to prevent or minimize exposure of the public to radiation. The principles also provide that a State launching NPS should make a safety assessment of the system publically available. The United Sates of America provided this information to the United Nations before the launch of the Cassini mission (UN Document A/AC.105/677 of 4 June 1997). The question of the safety of the Cassini spacecraft flyby near the earth covered, in detail, in this assessment. One of the safety provisions is that the spacecraft, at its present trajectory, would pass at a distance of over a thousand kilometres from the Earth. While the original flight plan called for the Cassini fly 700 kilometres above the Earth surface on 18 August 1999, the current proposal is for a distance of 1160 kilometres. The United States has thus provided the necessary information requested by the United Nations according to the Principles relevant to the use of NPS in outer space to provide assurances of the sufficient degree of nuclear safety of the Cassini spacecraft. With best wishes
 N. Jasentuliyana Deputy to the Director-General, United Nations Office at Vienna, and Director, Office for Outer Space Affairs |