Developing Lunar Orbiter

CHANGING HORSES

In January 1961 the Hughes Aircraft Company was selected to build the Surveyor spacecraft. With a planned mass of about 1,125 kg at translunar injection, it would require the Atlas-Centaur. The plan was for the orbital version to provide wide-area mapping and reconnaissance of potential landing sites for the surface Surveyors and, later, for Apollo. The mass at touchdown was expected to be about 340 kg, of which 114 kg would be scientific instruments which would not only transmit pictures but also provide data on the physical, chemical, mineralogical and biological properties of the surface material. The initial schedule called for the first flight in 1964. It was also envisaged that as the project matured, an orbital variant would be equipped to serve as a communications relay for landers investigating sites on the far-side of the Moon.

On 23 March the Lunar Science Subcommittee at the Office of Space Sciences recommended that the orbiter have a TV system which was capable of providing: (1) full coverage of the limb areas (highly foreshortened to terrestrial observers) and of the far-side at a resolution of 1 km, (2) wide-area reconnaissance at a resolution of 100 metres, and (3) stereoscopic pairs of selected areas with sufficient resolution to discern objects 10 metres in size. On 5 December Charles Sonett, Chief of Lunar and Planetary Sciences at the Office of Space Sciences, asked William Cunningham to determine the status of the orbiter. On 12 January 1962 Cunningham reported that JPL would not be able simply to adapt the vidicon system developed for Ranger; a new TV system would be required, the development of which had not yet begun.

NASA called for JPL to define the design requirements for the Surveyor orbiter, maximising its commonality with the lander, by 1 September 1962, but owing to the problems the laboratory was facing with Ranger the orbiter received little attention.

Meanwhile, on 15 June 1962 the Office of Manned Space Flight compiled a list of the data that it required the Office of Space Sciences to supply on the environment around the Moon and on its surface – i. e. Brainerd Holmes’s Requirements for Data in Support of Apollo. In view of the urgency to feed such information into the design

of the Apollo vehicles, the Office of Space Sciences asked JPL whether Ranger could serve as the basis for an orbiter. JPL in turn asked the Hughes Aircraft Company to consider the possibility of a 360-kg orbiter which could be launched by the Atlas – Agena. Hughes replied that in order to meet this mass limit, the scientific payload could not exceed 27 kg, which was unrealistic in view of the activity to be pursued. JPL calculated that if the solid-rocket motor that Surveyor was to use in the initial phase of its descent to the Moon were to be used to augment the Agena in the translunar injection, it would be possible to increase the scientific payload to 57 kg, but this was still too little. Even although the development of the Centaur stage was running behind schedule, the Office of Space Sciences decided to proceed with the Centaur-based orbiter.[26] To meet the Apollo requirements, the orbiter would require to provide photography of potential landing sites capable of revealing protuberances and pits as small as 1 metre in size and slopes as shallow as 7 degrees. But even the stereoscopic views from the Surveyor orbiter’s TV system would have a resolution no better than 10 metres. A photographic system employing film would be needed to meet the requirements of the Office of Manned Space Flight.

On 21 September 1962 Oran Nicks, Director of Lunar and Planetary Programs in the Office of Space Sciences, asked Lee R. Scherer to form a committee to evaluate proposals which had been submitted by the Space Technology Laboratories and the Radio Corporation of America for a ‘lightweight’ lunar orbiter compatible with the Atlas-Agena.

On 23 October Joseph Shea, the Deputy Director of the Office of Manned Space Flight, specified the relative priorities of the data that Apollo would require from the Office of Space Sciences. There was a greater need for the information which a soft – lander would provide, since this would feed into the design of the Apollo vehicles, whereas the information from an orbiter would not be required until later, in mission planning. Shea stressed that if funding was tight in Fiscal Year 1963, then the Office of Space Sciences should favour the lander over the orbiter.

Scherer reported to Nicks on the issue of an Agena-based orbiter on 25 October. The proposal by the Radio Corporation of America was for a Ranger bus to make a lunar flyby, dropping off a 200-kg package which would insert itself into orbit. The orbiter would be 3-axis stabilised and use a vidicon system (no doubt a development of the camera the company had provided for Ranger Block II) to provide pictures at a resolution of 130 metres in the wide-angle coverage and 30 metres in the narrow – angle coverage. The Space Technology Laboratories had envisaged an orbiter with a mass of 320 kg. It would have a monopropellant engine which was capable of firing several times. In addition to a midcourse manoeuvre and orbit insertion, this engine would permit changes to the orbit. One mission profile would be to enter a circular polar orbit at an altitude of 1,600 km and map the entire Moon, resolving objects as small as 18 metres in size. Alternatively, it could be placed into equatorial orbit at an altitude of 40 km to photograph that zone with a resolution of 0.5 metre. It would be spin-stabilised, and use a ‘spin scan’ camera of a design similar to that proposed by the RAND Corporation in 1958. It would use film to obtain a higher resolution than was obtainable using a vidicon. Scherer reported that only the proposal by the Space Technology Laboratories offered the prospect of meeting the requirements set by the Office of Manned Space Flight for imaging resolution, and he recommended that the company further refine the concept so as to enable the Office of Space Sciences ‘‘to establish the confidence needed [to consider] a flight program of this type, should it be deemed preferable to a Centaur-based orbiter’’. In fact, once the viability of an Agena-based reconnaissance orbiter had been established, this in itself undermined the case for pursuing the Surveyor orbiter.

On 26 October, Clifford Cummings, unaware of Scherer’s study, wrote to advise Oran Nicks that JPL was about to conduct a study to refine the configuration of the Surveyor orbiter in order to specify how it would perform its mission. In his reply on 8 November, Nicks pointed out that the Office of Space Sciences was looking into the possibility of an Agena-based orbiter.

On 2 January 1963 Nicks asked Floyd L. Thompson, the Director of the Langley Research Center, to consider the possibility of his staff taking on the development of a lightweight orbiter. Thompson set up an internal feasibility study. After the Space Technology Laboratories had refined its concept, a review was held at Langley on 25 February involving representatives of the company, the Office of Space Sciences, the Office of Manned Space Flight, Langley and Bellcomm. Lee Scherer and Gene Shoemaker reported on a study they had undertaken for Nicks to determine how a lightweight orbiter might satisfy the photographic requirements of Apollo. Dennis Jones of Bellcomm reported an assessment made for Shea on the degree to which an orbiter might support the manned and unmanned exploration of the Moon. A second meeting on 5 March agreed that not only was a lightweight orbiter viable, it would also significantly support Apollo. Langley then sent a delegation headed by Clinton E. Brown to brief Robert Seamans and present the case for Langley taking on such a project; Seamans authorised planning to proceed.

In order to assist Langley draw up the request for proposals, in April 1963 the Office of Manned Space Flight refined its requirements. The critical needs were: (1) data on the radiation flux in lunar space over a typical 2-week period; (2) a summary and analysis of all efforts for short-term prediction of severe solar proton events; (3) measurements of particles capable of penetrating 0.01 cm and 0.1 cm of aluminium in an average peak 2-week period of micrometeoroid activity; and (4) photographic data capable of showing protuberances 3.5 metres tall and slopes of 15 degrees in an area of the lunar surface with a radius of 60 metres (to be provided by the autumn of 1965) and then equivalent data showing 50-cm protuberances and 8-degree slopes in an area with a radius of 1,600 metres. Other needs were: (1) measurements of the distribution of slopes greater than 15 degrees in areas of 3.5 metres radius; and (2) the greatest possible coverage of the zone within 5 degrees of the lunar equator with a resolution of 25 metres or better.

On 25 April Edgar Cortright put it to Homer Newell that since one successful orbiter could be worth “dozens of successful Ranger TV impactors”, the three new Rangers which had recently been funded in order to obtain high-resolution pictures and gamma-ray and radar reflectance data on the Moon should be cancelled. Newell accepted this reasoning and passed the recommendation to Robert Seamans, who concurred on 12 July. Later in the year, the second batch of rough landing Rangers was also cancelled.