Surveyor essay by Hamish Lindsay

The Surveyor Program

1966 – 1968.
Preparing the way for the Apollo Moon Landings.

By Hamish Lindsay.

The Surveyor Program originated in May 1959, from a thought bubble by rocket scientist Wernher von Braun. This was followed by a proposal submitted by the US Army called “Preliminary Study of an Unmanned Lunar Soft Landing Vehicle,” using the Apollo Saturn 1 rocket as a launch vehicle.

Contracts were awarded to four companies to study preliminary designs and, on 19 January 1961, NASA selected Hughes Aircraft Company to build seven Surveyor spacecraft. The first spacecraft was planned to launch in 1963.

The original concept, from scientists such as Eugene Shoemaker, was a purely scientific program. The planned spacecraft bristled with exciting experiments – three cameras; seismometers; magnetometers; gravity meters; radiation detectors; X-ray diffractometers; spectrometers; drills; soil processors; microscopes and even a roving vehicle.

Then the scientists watched the real world invade their program with inadequate launch vehicles, diminishing budgets, misunderstandings, and changing mission objectives, until the program was dragged reluctantly into supporting the Apollo manned missions.

With a hoped-for 20 missions reduced to 7; fewer experiments; 101 modifications to sort out hardware problems and two years behind schedule, the Surveyor program finally got under way. From June 1966 to January 1968, seven robotic spacecraft were sent to the surface of the Moon to prepare the way for the Apollo manned landings.

The program’s primary goal was to demonstrate the feasibility of soft landings on the Moon. The missions called for the spacecraft to travel directly to the Moon on an impact trajectory, on a journey that lasted 63 to 65 hours, and ended with a deceleration of just over three minutes to a soft landing.

The program was implemented by NASA's Jet Propulsion Laboratory (JPL), Pasadena, California, to prepare for the Apollo Program. The total cost of the Surveyor program was officially US $469 million.

Five of the Surveyor spacecraft successfully soft-landed on the moon, including the first one. Two failed: Surveyor 2 crashed at high velocity after a failed mid-course correction, and Surveyor 4 lost radio contact (possibly exploding) 2.5 minutes before its scheduled touch-down.

All seven spacecraft are still on the Moon; none of the missions included returning them, or any part of them, back to Earth. Some parts of Surveyor 3 were brought back to Earth by the crew of Apollo 12, which landed near it in 1969. The camera from this spacecraft is on display at the National Air and Space Museum in Washington, DC.

Objectives of the Surveyor Program.

The primary objectives of the Surveyor program were to support the upcoming manned Apollo landings by:
(1) Developing and validating the technology for landing softly on the Moon.
(2) Providing data on the compatibility of the Apollo design with conditions encountered on the lunar surface.
(3) Adding to the scientific knowledge of the Moon.

Launch considerations.

The launch azimuth constraint of 80° to 115° was imposed by the range safety consideration of allowing the initial launch phase only over the ocean, not over land. The time of flight from launch to landing was about 6l to 65 hours, mainly determined by the fact that Surveyor must reach the Moon during the viewing period of the prime Deep Space Network station DSS11 at Goldstone, California. The trajectory was also influenced by the landing site selection. This selection was based on several considerations.

One was that a limitation imposed on the first Surveyor flights of the spacecraft's angle of approach to the Moon must not exceed 20° off vertical. There was essentially only one point on the Moon for each launch day that a spacecraft could land vertically. The 20° consideration then, in effect, drew a constraining circle around this point. Surveyor had to land within that circle.

The landing sites were further limited by the curvature of the Moon. The trajectory engineer cannot pick a site, even if it falls within this 20° circle, if the curvature of the Moon will interfere with a direct communication line between the spacecraft and the Earth.

The other factors in landing site selection were smoothness of terrain and a requirement for Surveyor to land in the landing area selected for the Apollo manned lunar missions.

Lighting conditions on the Moon on arrival of the spacecraft at a given landing site were determined by the launch day, which, in turn, was controlled by the use of direct ascent trajectories, which limited the launch days available. In later missions, using a parking orbit, the launch day was picked to provide optimum light conditions.

The time span during each day that Surveyor could be launched (the launch window) was determined by the requirement that the launch site at launch time and the Moon at arrival time be contained in the Earth/Moon transfer orbit plane. With the launch site moving eastward as the Earth revolves, acceptable conditions occur only once each day for a given plane. However, by altering the plane as a result of changing the launch azimuth, or direction of launch from the launch site, between an allowable 80° to 115° East of North, the launch window can be extended up to as much as two hours.

The velocity of the spacecraft when it arrives at the Moon must also fall within defined limits, defined by the retro-rocket capability. The velocity relative to the Moon was primarily correlated with the flight time and the Earth/Moon distance for each launch day.

So, a further requirement on the trajectory engineer was the amount of fuel available to slow the Surveyor from its lunar approach speed of 11,000 odd kilometres per hour to nearly zero velocity, 4 metres above the lunar surface. The chosen trajectory must not reach velocities that are beyond the designed capabilities of the spacecraft propulsion system.

During the journey to the Moon the spacecraft’s flight path and velocity was also influenced by the gravitational attraction of the Earth and Moon, and to a lesser extent the Sun, Mercury, Venus, Mars and Jupiter. This also had to be taken into account.

It was not expected that the launch could be performed with sufficient accuracy to impact the Moon in exactly the desired area without a mid-course maneuver. The uncertainties involved in a launch usually yield a trajectory, or an injection velocity, that vary slightly from the desired parameters. These uncertainties are due to inherent limitations in the guidance system of the launch vehicle. To compensate, lunar and deep space vehicles have the capability of performing mid-course maneuvers, or trajectory corrections. To alter the trajectory of a spacecraft it is necessary to apply thrust in a specific direction to change its velocity. The trajectory of a spacecraft at a point in space is basically determined by its velocity.

Mid-course manoeuvres were usually planned to be over the Goldstone tracking station, the nearest station to the JPL mission control centre in Los Angeles. More than 250 ground commands were required to control Surveyor during its flight, and a successful landing on the Moon. About 300 persons were involved in flight control at peak times in the mission.

Bruce Window, one of the Operations Supervisors at DSS42, Tidbinbilla, remembers a trip to the Hughes factory,

“In early 1967, I was sent to JPL along with Operations Supervisors from the Cape, Madrid and Goldstone to write SOPs.

While we were in LA, some of the Hughes teams from different stations were there at the Hughes Plant for training on the upcoming Surveyor missions. Frank Hain from the Tidbinbilla Hughes team made contact and offered me and Jeff Newnham (also from DSS42) and a few others a tour of the Surveyor assembly area at the Hughes Plant (in El Segundo, I think). We had to get kitted out in dustproof suits, hats and shoe coverings and go through a dust vacuum airlock.

Frank led the way through to the Assembly Area and was explaining in his usual excitable, arm-waving manner what was new on this particular Surveyor spacecraft. He was about to touch something on the spacecraft to highlight what he was talking about when a booming voice from a supervisor nearby told him in no uncertain terms not to touch anything on that #@^%! assembly. Frank sheepishly backed off and continued his tour. There were about 4 or 5 Surveyors being built there at that time, and we had the good fortune to see them close-up. In time to come, we would be communicating with them on the Moon.”