tinue to penetrate deeper into space and to utilize nearby space more completely, we can reasonably expect that use of RTG's will increase.

Last year was one of solid accomplishment in the development and flight of radioisotopic generators. Figure 2 shows the Pioneer spacecraft launched last March and powered entirely by four RTG's producing in excess of 120 watts of electrical power. The spacecraft is over halfway to its encounter with Jupiter which will occcur in December of this year. It has safely passed through the asteroid belt between Mars and Jupiter, is now about 450 million miles from earth and will encounter Jupiter this December at slightly over 500 million miles. The RTG's and the spacecraft are functioning very well as indicated by the higher than specification performance shown. A second Pioneer spacecraft was launched early this month on April 5, 1973. The four RTG's aboard this spacecraft are also functioning according to design expectations-with the initial power level being approximately the same as that of the RTG's on the first launch. This second spacecraft will reach Jupiter approximately 1 year after the first spacecraft has passed its destination and is headed on out into space.

In December, as indicated in figure 3, we completed the Apollo/SNAP-27 program. In all, five generators and the experimental packages that they power bave been emplaced on the surface of the Moon and are continuing to operate well. The oldest has been in operation for over 3 years as compared to the original requirement of 1 year. The RTG-powered ALSEP units by themselves and in conjunction with other spacecraft elements have produced information about the structure of the Moon, its composition and its origins and continue to be one of the most essential and productive of the science efforts of the Apollo program. These nuclear-powered scientific stations on the Moon are expected to to continue to supply useful data for many years. The AEC-industry team responsible for the SNAP-27 development has received the NASA distinguished service award for these accomplishments.

In September the Navy Transit satellite shown in figure 4 was successfully launched. The Transit is an experiemental navigational satellite powered by a 30-watt RTG. The spacecraft was successfully orbited and the RTG is working properly. Most of the onboard experiments continue to function properly and the spacecraft has accomplished its primary function of demonstrating the "DISCOS" in-orbit maintenance system. However, a computer failure has hindered the spacecraft's ability as an operational navigation device.

The past year and the early part of this year then have added five new RTG-powered missions to the overall history shown in figure 5. Since 1961 there have been 16 RTG-powered spacecraft launched-three experienced launch vehicle failures not associated with the RTG in anyway and 13 have achieved operational status. Throughout this history there have been no failures of RTG's in spaceflight.

I would like to turn now from past accomplishments to future plans. Figure 6 shows the three future spacecraft for which we are currently preparing RTG power systems. Pictured on the left is the NASA Viking lander of which two are scheduled for launch in 1975 and will land on the surface of Mars in 1976. The landers will be powered by two modified RTG units of the type used in the Pioneer program which I have previously discussed, The fiscal year 1974 effort will concentrate on electrically-heated engineering test units and isotopically fueled prototype generators. Work will also proceed on the safety analysis and testing which is required to obtain launch approval.

The second spacecraft is the Air Force Lincoln experimental satellite which is an Air Force mission scheduled for 1974 launch. The third spacecraft is for the NASA Mariner/Jupiter/Saturn mission which is scheduled for launch in 1977 and will utilize a Mariner-type spacecraft derived from the family of spacecraft such as recently completed a highly successful exploration of Mars. This craft will continue the exploration of Jupiter and extend that exploration to Saturn and beyond.

The LES and the MJS missions require greater power, lower specific weight and longer life than have been possible in any past RTG designs. To meet these requirements we have under development the Multi-Hundred Watt (MHW) RTG shown in figure 7. This design produces 125 watts of power at 5 years with a weight of about 85 pounds. The first use of the Multi-Hundred Watt RTG is expected to be with the LES mission in 1974. The development work has been proceeding well and the performance and structural validity of the converter design have been established. Although we have not yet accumulated sufficient data to confirm all of the endurance requirements, we expect that the objectives and flight date will be met.

In fiscal year 1974 for the LES 8/9 program, we will fabricate and deliver the two ETG's to Lincoln Laboratory and complete the fabrication of all flight hardware for the LES mission.

For the MJS mission during this period we will evaluate the environmental and safety requirements that may affect the modification of the MHW design. After this evaluation is completed, the design and fabrication of an engineering unit will begin.

In addition to the flight programs I have described, we are also requesting support for a minimal technology program looking toward the possibilities of substantial cost reductions in future RTG's. This work in fiscal year 1974 will concentrate primarily on the potential for cost reductions of the radioisotope fuel.

Isotope powered generators continue to fill a vital need for nuclear electric powered spacecraft for both NASA and DOD missions. I believe that this committee and the AEC can take pride in the accomplishments of this program, particularly in the past year in which we have made possible highly important missions which would not have been practical any other way.

TABLE 1.-SPACE NUCLEAR SYSTEMS PROGRAM-OPERATING COSTS