SURVEYOR IN THE NATIONAL AIR & SPACE MUSEUM —Jack Fisher

The following material, text and photographs, was received in an e-mail from the Smithsonian on March 20, 2017 and is reprinted here with permission of the NASM.

THIS MONTH IN HISTORY

 WHAT’S UP IN APRIL

Hello! How Have You Been Doing Up Here on the Moon?

On April 17, 1967, the Surveyor 3 spacecraft was launched toward the Moon. It was one of five Surveyor landers that touched down on the Moon. The Surveyor program confirmed that the lunar surface could support a spacecraft and that astronauts would be able to walk on the Moon. In 1969, during the Apollo 12 mission, astronauts Charles Conrad Jr. and Alan Bean landed near enough to Surveyor 3 to visit it and remove its television camera, surface sampler, and some tubing, which they brought back to Earth for analysis.

          The artifact in the collection is an engineering model, S-10, used for thermal control tests. It was reconfigured to represent a flight model of Surveyor 3 or later, since it was the first to have a scoop and claw surface sampler. After receipt in 1968 it was displayed in Smithsonian’s Arts & Industries Building and then was moved to its present location in Gallery 112, Lunar Exploration Vehicles, in 1976.

The Surveyor series was designed to carry out soft landings on the Moon and provide data about its surface and possible atmosphere. These were the firs U. S. probes to soft-land on the moon. Once landed they provided detailed pictures of the surface by means of a TV camera carried on each of the spacecraft. Later Surveyors carried the instrumented soil mechanics surface scoop seen on the artifact. These were used to study the mechanical properties of the lunar soil. Some of the spacecraft were also equipped to perform simple chemical analyses on lunar soil by means of alpha particle scattering. There were seven Surveyor launches starting in May, 1966, all launched by the Atlas Centaur rocket. All but two successfully achieved program goals returning over 88,000 high resolution photographs and invaluable detailed data on the nature and strength of the lunar surface.

Surveyor (1966-1968)

The Surveyor probes were the first U. S. spacecraft to land safely on the moon. The main objectives of the Surveyors were to obtain close-up images of the lunar surface and to determine if the terrain was safe for manned landings. Each Surveyor was equipped wotj a television camera. In addition, Surveyors 3 and 7 each carried a soil mechanics surface sampler scoop which dug trenches and was used for soil mechanics tests and Surveyors 5, 6, and 7 had magnets attached to the footpads and an alpha scattering instrument for chemical analysis of the lunar material. The following Surveyor missions took place.

Surveyor 1

Launched 30 May 1966

Landed 02 June 1966, 06:17:37 UT

Latitude 2.45 S, Longitude 316.79 E – Flamsteed P

Surveyor 2

Launched 20 September 1966

Crashed on Moon 22 September 1966

Vernier engine failed to ignite-southeast of Copernicus

Surveyor 3

Launched 17 April 1967

Landed 20 April 1967, 00:04:53 UT

Latitude 2.94 S, Longitude 336.66 E – Oceanus Procellarum

Surveyor 4

Launched 14 July 1967

Radio contact lost 17 July 1967

2.5 minutes from touchdown – Sinus Medii

Surveyor 5

Launched 08 September 1967

Landed 11 September 1967, 00:46:44 UT

Latitude 1.41 N, Longitude 23.18 E – Mare Tranquillitatus

Surveyor 6

Launched 07 November 1967

Landed 10 November 1968, 01:01:06 UT

Latitude 0.46 N, Longitude 358.63 E – Sinus Medii

Surveyor 7

Launched 07 January 1968

Landed 10 January 1968, 01:05:36 UT

Latitude 41.01 S, Longitude 348.59 E – Tycho North Rim

 

 

 

 

Surveyor Flight Path Analysis and Command (FPAC)–John Gans

Surveyor mission operations were conducted in JPL’s Space Flight Operations Facility (SFOF) in Pasadena.   Technical support groups in the SFOF included the Flight Path Analysis and Command (FPAC) Group, the Space Performance and Command (SPAC) Group, and the Space Science Analysis and Command (SSAC) Group. FPAC and SPAC were the responsibility of Hughes.

The FPAC organization chart for Surveyor 6 is shown below. For earlier missions Mal Meredith was the FPAC director. FPAC was organized into five groups:  Computer Support, Tracking Data Analysis, Orbit Determination, Trajectory and Maneuver Analysis. Computer Support, Tracking Data Analysis and Orbit Determination were manned by JPL personnel. For earlier missions John Ribarich was the head of the Maneuver Analysis group.

FPACorg

The Atlas-Centaur launch trajectories were designed to provide a lunar transit trajectory that will impact at the desired lunar landing site –as selected by NASA in the desired Apollo landing zone. Errors in the Atlas-Centaur boost resulted in missing the desired landing site.

The primary responsibility of FPAC was to determine these errors and correct them. Spacecraft range rate (doppler) and angle data were gathered by the three stations of the Deep Space Net located at Goldstone, California, Canberra, Australia and Johannesburg, South Africa.  JPL’s Orbit Determination Program (ODP) was used to process the tracking data using a weighted least-squares technique to generate an estimate of the spacecraft trajectory and produce a state vector.  The state vector consisted of position and velocity of the spacecraft defined in an Earth-centered Cartesian coordinate system at a defined epoch. The state vector provided the Trajectory Group the initial conditions for the calculation of a precision trajectory using the program JPL Trajectory software (JPTRAJ). to determine the resulting lunar landing location.

Using this trajectory the Maneuver Analysis Group determined a midcourse maneuver that will correct the landing location error and investigated parameters that might affect the probability of a successful terminal descent and landing. A computer program, Midcourse and Terminal Guidance Operations (MTGS), designed and built by Hughes was used for these analyses.

The earth-centered lunar transit trajectory upon approach to the moon resulted in a hyperbolic trajectory that can be described in a selenographic B, T, and R coordinate system. For a given trajectory the lunar impact location can be defined in terms of the two components B.T and B.R (vector dot products). This is a very useful concept as the miss vector is very nearly a linear function of changes in the initial conditions at the time of the midcourse correction.

A critical plane was determined so that ∆Vs in that plane only affect the landing location while ∆Vs normal to the plane affect only the velocity at lunar impact and not the landing location. The determination of the midcourse maneuver will then proceed in two stages: first the ∆V in the critical plane required to correct landing location errors will be determined and second using the ∆V normal to the critical plane as a parameter to improve the probability of a successful terminal descent.

A time of the midcourse correction is selected and a critical plane established with TRS coordinates:  the B vector was aligned along the spacecraft’s velocity vector and the T and R vectors comprised the critical plane which was perpendicular to the flight path.  Any thrust by the spacecraft in the critical plane would result in a change in the landing point on the moon. A  K-matrix was formed of partial derivatives in the critical plane which would then be used to find a suitable thrust vector (described by B.T and B.R). The use of a K matrix allowed MTGS to find the optimum thrust vector in a relatively quick fashion to change the trajectory to the desired lunar site in just a few seconds of MTGS IBM 7090 execution time.  Then the equations of motion were integrated to the moon (many minutes of MTGS execution time using the IBM 7090) to insure that the vehicle would land at the required site.

After the critical plane maneuver to correct the landing location was determined possible maneuvers normal to the critical plane are investigated as shown in the attached figure for Surveyor 6. This velocity increment, designated U3, was varied parametrically to determine the resulting flight time (compared to the Goldstone DSN rise and set times), the main retro solid rocket burnout velocity, vernier propellant reserve, and landing site dispersions as shown in the figure. For Surveyor 6 the critical plane maneuver was 1.18 m/sec and a maneuver of 10 m/sec normal to the critical plane was selected to reduce the main retro burnout velocity to 480 ft/sec. The total ∆V was 10.06 m/sec.U3ScanThis thrust vector was then used to determine the roll, pitch and yaw maneuvers to reorient the S/C for the course correction maneuver.  This information with the required vernier engine thrust duration was given to SPAC to generate the commands for transmission to the S/C.  Following the midcourse maneuver the S/C was again reoriented to its translunar attitude, tracked, and the trajectory determined and the landing site verified.  Then as the S/C approached the moon MTGS was again employed to calculate the thrust vector to slow the S/C for the lunar landing.  Roll, pitch and yaw maneuvers were determined, and a delay time in seconds calculated to fire the solid rocket motor and initiate terminal descent.  This delay time was computed based upon the 60 mile mark obtained by the S/C Altitude Marking Radar (AMR) sensor.  The maneuvers and the delay time, in seconds were transferred to SPAC for transmission to the S/C via the DSN.

This completed the actions by FPAC.  The S/C completed all maneuvers, fired the retro motor and the vernier engines to begin the gravity turn until the S/C was 12 feet above the moon’s surface. Following vernier engine shut down the S/C then free fell to the surface where it remains to this day.

Among other things we wrote and sang a ditty which went, ” B.T and B.R, How we wonder what they are, Way up in the sky so blue…”  Just a little bit of levity to relieve the tension in FPAC.