The time finally came for the expedition to Mars to begin. In August 1975, almost exactly 10 years after plans for Voyager were initiated, Viking 1 stood tall on Pad 41, ready for launch. The first attempt was scrubbed because of a valve failure in the launch vehicle, and, while awaiting another try, the batteries in the spacecraft discharged. This resulted in the substitution of the second spacecraft while the first was checked to make sure no anomalies had occurred, reversing the planned order of spacecraft launches.
Amid these preparations were periods of anxious waiting for final word on the problem assessment tests. Flashbacks of the long hours of planning, meetings, and frustrations over Voyager occurred, as glimpses of the evolutionary steps toward Viking were recalled. I even had a brief mind-trip back to 1957, when I was an engineer at North American Aviation's Missile Development Division. About the time Sputnik 1 was being launched, we were engaged in a study of a Mars reconnaissance expedition employing ion-propelled spacecraft. Efforts being coordinated by the corporate office involved the Missile Development, Rocketdyne, Atomics International, and Autonetics Divisions. Our ambitious proposal envisioned multiple spacecraft-as many as four-to be launched during the 1964 Mars opportunity, to fly around Mars, gather data, and return to the vicinity of Earth. I led a small team concerned with spacecraft performance, trajectories, and propulsion integration; this study was my first exposure to the excitement of planning a visit to Mars and the beginning of a longing that has yet to be fully satisfied.
After all the years of exposure to missile and space launches, I could not help but think of the launch as the key milestone in any project. Committing to launch meant releasing the precious hardware and all direct control over it to prior judgments; after a missile launch there was nothing one could do to influence the mission, and not much more could be done for the early lunar and planetary spacecraft. For Viking, however, the launch was more like a  commencement exercise for a college graduate. It was the end of a long period of programmed experiences and hard work, yet just the beginning of a new and uncertain life. Of course the launch was still critical to success, but by now confidence in launch technologies was high, whereas technologies for landing on another planet were relatively unproven.
For those project members whose special skills had been applied to the engineering, design, and test of the launch vehicle, the trial was over as soon as a good orbit was reported. To be sure, there were data to be analyzed, reports to be written, and post mortems to be conducted, but the victory celebration came first and could be savored without reservation. Soon it would be necessary to concentrate on the tasks for the next vehicle that had gotten behind because the current launch demanded attention, but that was understood and to be expected.
For the spacecraft engineers, the launch had a variety of meanings. In fact, there were so many different possibilities for those who had been involved in spacecraft design, development, and testing that it was not entirely appropriate to think of them as a single class. For the hands-on hardware people, the work was over with the launch, just as it was for the launch vehicle people. Whether the mission succeeded or failed, they had completed the assigned tasks necessary to bring their efforts to conclusion. For some, Viking launches meant the end of a known career; they had been so busy for several years that there had been little place in their minds for thoughts of the future. Suddenly, almost catastrophically, their Viking jobs ended.
For others, the launch meant simply that their jobs would change: some would continue in the same manner, and some were to start a new type of work, with the thread of continuity being provided by intimate knowledge of the hardware or software they had helped to develop. A few were "born operational types" who worked alongside the hardware and software engineers during the development phases, giving counsel, conducting operational studies, and providing planning to support the developments as they went along. For them, Viking really came to life after launch, when, in a real sense, it became a different creature.
An entirely new organization chart was prepared; a number of names reappeared, but there were significant differences. For many who had been involved in the project from the outset, changed assignments meant new titles and work with new groups having different objectives and procedures. Returning to their home center or to JPL after being displaced for weeks or even months at the Cape also meant adjusting to new office environments, as  well as to new associates and assignments. Project management officials had wisely begun a transition to the operations phase by reassigning a core group to join the full-time operations experts well before launch. Those already comfortable in this new phase were able to help others adjust to the challenge of conducting flight operations.
A frightening aspect of this, at least to me, was the fact that during the 10 months or so the spacecraft were to be on their way to Mars, a sobering amount of work had to be done in order for the missions to be performed as planned. There had not been time or manpower to "engineer" all the planetary operations until after the launches. The systems had been designed and built with the flexibilities and programming capabilities to allow en route preparation for planetary operations; we would not know how well that goal had been achieved until after the cut-and-try process of simulations or actual operation. Needless to say, the discovery of design deficiencies after the hardware was millions of miles away would not have been very satisfying.
Although there had been a certain amount of new activities and operational training during the cruise periods of the Mariners, their limited capabilities left far fewer options after launch. Furthermore, there were never to be more than two machines operating in the vicinity of Mars at the same time, even if both were totally successful. With both sets of Viking spacecraft on the way, we could look forward to juggling people and facilities to accommodate arrival times, orbital injections, site selections, deboost maneuvers, communications relay periods, and critical orbiter and lander experiment timelines for four very sophisticated spacecraft, all arriving at Mars and requiring careful attention within a few days.
By the time of the launches, Viking's primary missions had been defined and basic arguments settled concerning the scientific objectives and the manner in which the spacecraft would perform. These objectives had evolved in concert with hardware development; this moderated original desires to coincide with hardware and software capabilities. To ensure that the teams and individuals involved all used the same list, the Project Office very plainly spelled out scientific objectives and mission strategies for operational use. There was a general set of these for the two orbiters and a set for both landers. Later, more specific tasks were to be assigned to each, but the pairs of spacecraft were designed to be interchangeable and thus shared the same broad guidelines for mission objectives.
The primary purpose of the orbiters was to obtain pictures, surface temperatures' and water vapor readings. While these data obviously had  scientific value in their own right, all were to be used in selecting landing sites for the Viking landers, as the first requirement of every Viking element was to help ensure that landers had the best possible chance of landing safely and conducting worthwhile experiments. The orbiters' scientific instruments therefore had to serve the good of the entire mission before they were to concentrate on important scientific functions. We have already mentioned how the orbiters served as buses for interplanetary transportation, as launching platforms, and as communications relay links.
The second objective for orbiters was to continue the photographic surveys begun by Mariner 9, repeating some coverage of the planet and adding thermal and water vapor measurements during the lifetimes of the landers. Orbital coverage of landing sites and similar areas would be used to extend the meaningful coverage of local lander data, adding emphasis to landing site studies.
The third objective for the orbiters was prescribed with the future in mind, for it specified obtaining images and thermal and water vapor data to help planners in the site selection process for subsequent missions. No one supposed that the first landers would do the complete job of exploring Mars with just two landings, particularly considering the importance of choosing the most hospitable sites for the first landings rather than the most hospitable sites for life to exist. Can you imagine how incomplete your impression of Earth would be if you could observe it only from two flat, smooth spots that had been chosen because they looked like safe landing fields?
The fourth objective specified clearly that orbiters were to obtain images and thermal and water vapor information to be used in the study of the dynamic and physical characteristics of the planet and its atmosphere. At last, thought some scientists, science for the sake of science! Although much data would be gathered in regard to the first three objectives, not until the chores were done in behalf of the whole expedition would priorities rest with the scientists. The objectives list was a reminder of an everyday rule of life we must ensure our survival before we can achieve higher goals.
There was also a very important fifth objective for orbiters; it called for scientific investigations using radio system data. We think of radios in conjunction with communications, but because the electromagnetic energy transmitted at various wavelengths is affected by the media through which it passes, measuring and analyzing these effects on radio signals as the spacecraft passed behind Mars also allowed scientists to make many deductions. Earlier flyby experiments had generated respect for this "by-product"  application of the radio signals for studies of the ionosphere, the atmosphere, and the interplanetary constituents. Viking's use of two frequencies to transmit signals from Mars to Earth would provide a measure of the electron concentration in interplanetary space, enhancing our understanding of communications capabilities for future systems. Radio tracking of the spacecraft transponder during approach and orbit would produce data for calculations of the orbit and mass of Mars, to be deduced from the gravitational influences of Mars on spacecraft trajectories. Finally, the analysis of radio signals as the spacecraft and Mars orbited the Sun would provide information to verify Einstein's theory of relativity.
These goals took into account the fact that Viking orbiters and landers were expected to continue operating over a significant portion of a cycle of seasonal change on Mars. Although it may seem that more than one photograph or water survey of a planetary site would merely be repetitious, this was not the case for Mars, for it experiences seasonal changes very much like Earth, with winter "frost" storms, dust storms with blowing sand, and other phenomena, such as erosion by wind, that bring continuous changes. In fact, major scientific gains might depend on synoptic studies of regions of interest.
Compared with the primary scientific objectives of the orbiters and landers, expectations for the entry science experiments were very briefly stated. The Primary Mission Summary document said simply, "Entry: Determine the atmospheric structure and composition." Easy to say, but to learn these things about a new planet during rapid passes through its tenuous atmosphere at two locations! What was meant to happen was an attempt to define the physical and chemical state of the Martian atmosphere and its interaction with the solar wind. In the upper atmosphere, the composition and abundance of neutral species were to be measured, along with the ion concentration and ion and electron energy distributions. In the lower atmosphere, pressure, temperature, density, and mean molecular weight were to be determined by direct pressure and temperature measurements together with data from the lander guidance systems. These data were all good scientific input, but would also serve in evaluating the design criteria and performance of the entry systems, in addition to lending valuable insight for the engineering of future missions.
The lander's scientific objectives had neither the mystique of the orbiter objectives nor the simplicity of those for the entry science experiments. They were straightforward, giving scientific priorities to the burning questions an  "objective" scientist might have asked had he personally set foot on the strange new planet:
The order of these objectives took into account not only their scientific relevance as determined by the science teams and project officials, but also the time-critical aspects of learning as much as possible as soon as possible in case difficulties arose. The missions were planned to continue for months, but there was always that haunting possibility of premature truncation for any one of a variety of reasons. Both Vikings were launched from Pad 41 on the last days of their preferred launch opportunities. For mission 1, this allowed encounter dates on or before June 18, 1976, and for mission 2, a nominal encounter date of August 7. These dates were important to permit a good match of the retropropulsion requirements and performance limits and to stay within acceptable landing site lighting angles at the time of arrival. Since the first and most important task for the orbiters was to help the landers by providing site selection data, it was desirable that they begin these tasks immediately upon arrival at Mars.
The cruise phase of the Viking missions was defined as the period from the launch of the first spacecraft to 40 days before it was to be injected into orbit about Mars. At that time, the approach phase, which lasted through Mars orbit insertion of the second spacecraft, officially began.
Shortly after being launched from its parking orbit around Earth, each Viking spacecraft acquired the Sun and oriented its solar panels normal to it. About 80 minutes later, the biocaps that had provided hermetically sealed containers for the entry capsules were separated and allowed to float away so as to miss Mars entirely. About 2 days later, a 720° roll turn around the....
 ....Sun axis provided for a star map and tracker calibration sequence. Several days after this, and several times throughout the mission, gyro and accelerometer calibrations were performed to ensure that these components were working properly, as they would be needed for critical maneuvers.
An early midcourse maneuver was executed on each mission at the earliest opportunity following propellant warmup. These early maneuvers were to correct the major vehicle injection errors as soon as they were known. The first correction occurred after 7 days on mission 1 and after 10 days on mission 2. Such midcourse maneuvers were to be completed by about 30 days postlaunch, after which the orbiter propulsion system pressurants were to be shut off to prevent any possibility of leakage during cruise. Leaks of any sort would cause unwanted trajectory and/or attitude changes, much like the effects of firing small rockets.
During the early cruise periods until about 100 days after launch, communications with the spacecraft were generally maintained using the low-gain antennas, except for periods such as the midcourse maneuvers and the early scan platform and science instrument checkouts, when the high-gain modes were needed to return data. A number of engineering tasks and instrument calibrations were carried out during cruise, including venting of the gas chromatograph mass spectrometer (GCMS), battery conditioning, GCMS bakeout, and tape recorder maintenance.
Throughout the entire cruise period the Viking Flight Team on Earth was conducting personnel testing and training exercises, making sure that all players were ready for their duties when the planet was reached. A shorthand summary of the cruise activities as used by the Flight Team is included here to illustrate the manner in which the activities were integrated. There were also important interfaces with Helios and Pioneer operations; as these were occurring at the same time and sharing common DSN and SFOF facilities, close coordination between projects was necessary.
The approach phase, beginning 40 days before Mars orbit injection, signaled the start of the intense period of rapid-fire activities associated with arrival at the destination. During this period, final adjustments were to be made to the trajectories, and all science instruments and equipment that could be checked out were exercised. One midcourse maneuver had been planned for each spacecraft to finally align the flight paths and set times of closest approach; these were done about 10 days before orbit injection. The propellant supply valves that had been closed after the initial midcourse correction had to be reopened, of course, to enable the final correction to occur. When the valve was opened on the mission 1 spacecraft, a slight leak was  detected which would have led to an overpressure in the propellant system after a time, and possibly to an explosion of the propellant tank. It was decided that two large-magnitude midcourse corrections, compensating in the sense that their vector sums would achieve the equivalent of the smaller correction needed, would be performed to allow the bleed-down of pressure to a safe level. To perform such complex maneuvers so near the planet without much tracking time to assess results by the time of orbit injection was a risk, but more appealing than a possible blowup. This decision clearly points out how far confidence in propulsion and guidance and control technologies had progressed since Mariner 4; the capability to perform a second midcourse correction on Mariner 4 had been added after agonizing considerations, but everyone had felt a sense of relief when the first correction satisfied the gross flyby distance criteria and the second firing was not required.
In support of the two correction manuevers, extensive observations of Mars and adjacent stars were made that provided optical data to augment the radio tracking information. Much was learned about optical guidance techniques from this activity; later missions to Jupiter and Saturn involving flyby encounters with several moons were to employ similar techniques in their final guidance input.
As the Vikings approached Mars, many observations were made of the planet to aid in calibrating instruments and checking their operation before arrival. During the period from about 5 days out to about 1 day away, a complete set of science observations was made, including color photography and global-coverage infrared measurements. The last 3 days before injection were very exciting as Viking 1 pointed its TV cameras at the Martian moon Deimos, capturing the first close-up color images of that small, rocky object against a starry background. These images also provided final optical navigation data to help in designing the orbital injection maneuver.
Because of the leaky propellant valve on the first spacecraft, the valve on Viking 2 was not opened until just before the final midcourse correction. This time things went according to plan, and only one maneuver was required. As with Viking 1, a series of approach science and optical navigation observations were made. Since Viking 2 did not reach Mars until 50 days after Viking 1, the operations teams had much additional experience to apply to the approach and landing phases for the second encounter.
Finally, after a 10-month journey, Viking 1 was injected into orbit about Mars This began the phase designated planetary operations, signaling the beginning of the activities in orbit and on the surface of Mars. The so-called  Mission Profile Strategy for this phase was the top-level overall plan for the mission and had received a great deal of review and discussion among all interested parties, from administrators to technicians. In addition to being, menu for all activities, it was the basis for interactions among scientists engineers, and management officials who had worked together to plan the missions and who would now be carrying them out. The Viking systems allowed for a fair amount of flexibility in operations, but there were many possible actions which were irreversible. The physics of orbits, limitations or propellants, times when viewing conditions were affected by spacecraft position, time of day, and Earth-Mars-Sun relationships were just a few of the constraints that had to be considered. The operational interrelationships of both orbiters and both landers had to be carefully regarded from the outset to avoid conflicts when multiple operations would be required.
Key factors for orbiter strategies included four considerations: propulsive maneuvers, orbit walks to relocate the spacecraft orbital parameters, identification and relative positions of reference stars, and Earth and Sun occultations that would influence attitude control and communications. Any requirement for orbiter operations had to consider these basic factors, regardless of other considerations.
For the landers, the basic strategy for operations revolved around the biology analyses and the organic analyses; these were the principal priorities for the landing mission. It almost went without saying that they should enjoy the first consideration in protocol development.
From earlier data obtained primarily by Mariner 9, a region on Mars known as the Chryse Basin had been chosen as the target area for Viking Lander 1. The selection of the initial site was based on both safety and science considerations, with safety clearly coming first. If several sites appeared to be equally safe after being surveyed, then scientific interest would become the basis of choice. A backup site was chosen on the other side of the planet in another type of geological formation, within the same latitude band, in case the primary site appeared to be questionable, but it was not used.
The safety issues that might affect the success of landing were mainly the altitude of the site, the wind conditions, and local surface hazards such as boulders. Since the atmosphere was a prime factor in providing braking during descent, the higher density at lower altitudes made them favored choices. Wind conditions were estimated by observing streaks on the surface, a very indirect indication of existing conditions, but at least providing a clue of  some benefit. Areas with noticeable streaks were avoided, as were regions where surface changes had occurred since the Mariner 9 flyby. Since the best orbiter camera coverage only provided resolution of objects 100 meters in size, and since boulders greater than 22 centimeters in size could damage a lander, this hazard was dealt with by extrapolation of orbiter photos and interpretations or inferences from ground-based radar data.
While it had been hoped that the historic first landing on Mars could occur on July 4, 1976, the bicentennial of the Declaration of Independence, the 4 weeks required for reconnaissance resulted in a delay of the landing from July 4 to July 20. This was a good season to arrive, being near the beginning of summer in the northern latitudes of Mars. If organisms were present and growing, this should have been a good time to look for them.
One aspect of Mars that has always fascinated me is its similarity to Earth as a planet. It orbits the same Sun in nearly the same plane, with its rotation axis tilted 25° as compared with 23.5° for Earth, and with a rotation around its axis every 24 hours 39 minutes compared with 24 hours for Earth. This amazing coincidence (is it really?) means that Mars days are almost exactly the same as ours; but, more interesting, the tilt of its axis means that Mars undergoes seasonal changes in each hemisphere the same way they occur on Earth. Mars' orbit is farther from the Sun than Earth's; it takes about 687 Earth days for Mars to travel completely around the Sun. Thus the Martian year is almost twice as long as Earth's, which is the major difference in its general behavior as a planet.
The two approach midcourse correction maneuvers delayed the arrival of Viking 1 at Mars by about 6 hours. The site certification plan had called for the spacecraft to be over the preselected A-1 site in a synchronous orbit so that site surveys could begin immediately after injection into orbit, but the delay precluded that. An alternate plan was selected that involved an orbit with a period of 42.5 hours such that the craft would essentially overfly the A-1 site on the second orbit, allowing a retro maneuver to synchronize at that time. This alternate was executed as planned, and reconnaissance of A-1 began on the third revolution of Mars.
Although a successful orbit was a major milestone achieved, the first images of A-1 produced something of a jolt to the project team viewing them in Pasadena. When orbiter coverage of the originally chosen Chryse site was studied, many craters were evident, and it appeared that there had been extensive erosion activity and exposure of boulder fields as seen at the 100-meter resolution. The photos were more detailed than those from  Mariner 9 and showed many geologic features large enough to represent real hazards to landers. Common sense suggested that it was not a very good site.
The area to the south was known to be very rough, with deep channel beds, while images of the region to the east indicated that there had been an enormous amount of flooding in the ancient past. To the west was a vast area eroded by winds, and it almost seemed desirable to use the backup site on the opposite side of the planet.
Landing site selection (LSS) meetings had been planned all along, but they now took on a more serious character. On June 24, the first LSS meeting was held amidst exciting speculation about the preselected site; a room full of scientists and project personnel were present to see and discuss findings. Hal Masursky of the U.S. Geological Survey had been asked to lead the site selection studies, but it would finally be up to Tom Young, Mission Director, and Jim Martin, Project Manager, to decide. In addition to their own vibrations, they would rely heavily on input from Gentry Lee, responsible for mission analysis and design, and on Gerald Soffen, who, as Project Scientist, was official spokesman for the scientists.
At the June 26 LSS meeting, Gentry Lee began the discussion by announcing that the July 4 landing was in jeopardy and that a decision had to be made about whether to move the survey to alternate site A-2 or to move the search to the northwest, where scientists had hypothesized that a sediment basin might exist. Jim Martin explained that the geologic appearance of site A-1 as shown in orbiter images did not correlate well with findings from ground-based radar and that better correlation was necessary. Following considerable discussion, a vote was taken on whether to examine the northwest or to use site A-2; the result was overwhelmingly in favor of extending observations northwest toward a new site area called A-1NW.
As photomosaics of the new area were made, theories about the geology of the region seemed to be confirmed. However, the site had some rough areas, and it was not until Monday night, July 11, when the last mosaics were ready, that a site could be chosen. Jim Martin had stated that a decision had to be made the next day; he scheduled an LSS meeting to begin at 3:00 A.M. and continue until a decision was reached in the event that the issue was not resolved at the 11:00 P.M. meeting. Three sites in the A-lNW area were final candidates. After discussions of detailed studies and analyses, a unanimous vote allowed everyone to go home about midnight. Hal Masursky was able to announce to the press the next morning that the first Viking lander would be targeted for landing on the Golden Plain, Chryse Planitia, at  22.5° N, 47.5° W. Jim Martin praised the LSS process led by Masursky and the Orbiter Imaging Team, indicating that he was convinced that they had picked the safest site possible in a reasonable time.
After the landing site for Viking 1 had finally been chosen, a ground command was sent to initiate the separation and landing sequence. At this time, Mars and Earth were about 200 million miles apart, and the roundtrip time for communications amounted to some 40 minutes. The fully automated landing sequence began, first separating the lander and its aeroshell from the orbiter bus to which it had been attached for so long. After a gentle nudge by separation springs, the aeroshell-lander combination was oriented so that the deorbit rocket motor could be fired to begin the long descent from orbit to the surface. The lander then coasted for about 3 hours, gaining speed as it approached the Martian atmosphere. Meanwhile, it was sending data to the orbiter to be relayed to Earth. Just before arriving at the fringes of Martian atmosphere, some 300 kilometers above the surface, the aeroshell was reoriented for its aerodynamic entry. Its ablatable heat shield protected lander systems from the intense heat, decelerating the lander to a speed of about 250 meters per second so that a parachute could be deployed from a can by a small mortar. This device, 50 feet in diameter, had been packed into a small container well before the launch, much longer than the 90- to 120-day maximum normally specified before repacking is required for emergency parachutes. The parachute essentially pulled the lander away from the aeroshell, allowing it to drop to the surface, as it slowed the lander to about 60 meters per second some 1.5 kilometers above the surface.
At that height, a marking radar called for the firing of three retro rockets mounted directly on the lander spacecraft. These engines burned for about 40 seconds, being throttled by commands from the computer, based on sensor information from the radar system. The last 30 meters of altitude were covered with the spacecraft descending vertically in a gentle fall at about 2 meters per second. A switch on a landing footpad signaled shutoff for the rockets, and Viking landed.
Landing sites had to be elliptical in shape, about 100 by 300 meters in size, to allow for uncertainties in control over touchdown. Lander 1 touched down within 20 meters of the center of the chosen ellipse, so the "guesses" of the engineers must have been better than expected.
During the design and development period for the landing rockets, there was concern about the effects of jet blasts on surface materials. Simulation firings of motors in dust led to studies of multiple nozzle concepts and the....
 ...development of an 18-nozzle rocket that showed minimal effects from impingement on the surface. Many tests were run to determine temperature, chemical, and mechanical problems that might be induced by the motors. To make a long story short, the effects were well analyzed, the multiple-nozzle rockets were successfully developed, and no known problems occurred as a result of using rockets to achieve the soft landing.
During the descent through the upper atmosphere, entry science instruments in the aeroshell made measurements of the ions and electrons in the upper atmosphere and the neutral species in the lower atmosphere. Pressure, temperature, and acceleration measurements were also made during descent. All this happened in about 10 minutes, but it was another 20 minutes before those of us patiently waiting in the SFOF knew that it had been accomplished successfully.
During the entry and landing period, I was stationed in the "glass cage" shared by mission directors Tom Young and Bob Crabtree. The SFOF was crowded with the Viking project members who had to be there; with visitors like me from Headquarters, Langley, and corporations that had helped build Viking, the place was packed. Several "bullpen" areas housed engineering specialists with their tightly spaced desks, videomonitors, and telecom consoles. Surrounding these were the glass offices occupied by management officials and their special display and communication systems. The glass provided some shield from noise, but allowed almost all of the operating team to view the comings and goings of colleagues. It was a scene of high technology communications activities, but I was amused to see it occasionally augmented by a frantic wave, by pointing, or by some other primitive, human hand signal used as an expedient.
I could think of no place I would rather be during the final minutes of the first landing on Mars. The two mission directors had as much real-time information available to them as anyone on the team, and I had developed the highest respect for their competence over the many years we had been working together. Bob Crabtree had been involved in the operations activities at JPL and at the Cape from the very early days of Mariners 1 and 2, quietly advancing to more responsible positions until he was leading Viking orbiter operations. I had watched Tom Young develop from a mission integration engineer during the successful Lunar Orbiter program to his present very critical position as Mission Director for Viking. We were sure to have the facts as soon as they were known, and I was proud to be with two of the key "Vikings" in this crucial period.
 Words seem inadequate to describe the last 10 minutes of the landing sequence. I may have been in a state of suspended animation, although I thought at the time I was just being cool. After all, I had been through this process seven times before during Surveyor landings on the Moon. I don't think Surveyor even entered my mind as the key events of chute deployment, aeroshell jettison, engine start, and velocity-altitude callouts occurred, followed finally by the indication that the telemetry bit rate had switched from 4000 to 16 000 bits per second. This signal, 10 seconds after touchdown, was the mark of survival; had the landing been destructive, the signal would not have been given. It seemed almost too good to be true, but then we were quickly caught up in the handshakes and backslapping of mutual congratulations. This made the time pass quickly, and before long the festivities were interrupted by the appearance on the monitors of the first linescan image of Mars' rocky surface and a Viking footpad, clearly resting solidly on the target planet more than 200 million miles away.
On the heels of the thrills that went with the successful landing and remarkable pictures came one other small personal experience I will not forget. It was a result of my wandering around visiting with friends everywhere in the SFOF during the long period between lander separation and entry into Mars' atmosphere. I entered a glass cage where Israel Taback of Langley, John Goodlette of Martin, and other systems experts were waiting for the next events. Taback had been a respected friend since Lunar Orbiter days and had functioned as chief engineer throughout the Viking effort. He met me with a broad grin, asking if I would like to get in the pool. I immediately recognized this as a sucker setup, with me as the sucker, but I naturally responded with, "What pool?"
"The blackout pool," he said, meaning a pool for guesses as to how long the radio blackout would last as the entry capsule passed through the atmosphere. Just as communications blackouts always occurred when spacecraft were returning to Earth, this same phenomena was expected to a lesser extent for Mars. Naturally these men had been thinking about this effect as part of their jobs and, for all I knew, had the benefit of some astute calculations to support their guesses. Nevertheless, since the amount of the "donation" was only a dollar or two, to enter into the spirit of things, I joined the pool.
When faced with the challenge of picking a number, I suddenly had a hunch that the very tenuous atmosphere and the conservatism of the communications engineers, who always had a surprising amount of margin in  their predictions, might just combine to result in no perceivable blackout at all. The rest you can guess; my "zero" blackout time won, and Taback sheepishly came to me with a handful of bills and the secret ballots that had been cast by "us ionospheric physics experts" who were confirming "prior" knowledge of conditions at Mars.
Almost like the chrysalis transition from a caterpillar to a butterfly, Viking became a different object upon landing. What had been, moments before, a flying machine of the most sophisticated sort, was now a scientific laboratory, immobile and wedded to the soil. Changed, too, were some of its masters, for there were no longer any tasks involving rocket or attitude control functions to perform, and those who had played such a vital role in getting to the surface of Mars were no longer needed. The Viking Lander 1 was now a laboratory dedicated to the conduct of premier scientific investigations of historic proportions. New masters came forward to command it.
There were still many engineering functions to be performed and monitored for the Viking laboratory, just as there are for laboratories on Earth, which demand engineering support to operate as effective facilities. Such functions were not unimportant; they simply assumed a different priority when the scientific investigations began.
The lander's presence on Mars also brought about a subtle change in our thoughts about time. The lander was now a creature of a new world where the days were 24 hours and 39 minutes long. Not much different from what it was used to, but enough to accumulate over a period of time and make the sunrises and noontimes change. If it was to operate as an entity studying the environs of this strange place, it would have to operate on local time, the same way you or I would adjust in a foreign land. And so, too, would its masters on Earth have to adjust.
To deal with operational time based on a Martian day, the term SOL was invented. For a long time I supposed it to be another acronym that I needn't bother to learn, but I haven't found anyone who knows how it came to be. As a substitute definition for a "Mars day," these SOLs became the units of time for planning all operations on Mars, even the work shifts of the people involved in lander operations. However, their days were so unroutine that there never was such a thing as a 9 to 5 shift geared to SOL. The entire operation was, at best, on flextime; realistically, it was probably more like continuous overtime.
While everyone else was gasping and exclaiming over the images coming in on their screens, the entry science team was pouring over the data they  had received concerning the atmosphere. A major question had arisen over argon content, primarily because of a Russian estimate that argon made up 35 percent of the atmosphere. If the Russian estimate had been correct, the GCMS instrument might have had difficulty. After a few hours of study, the results clearly showed that the argon concentration was only about 2 percent, a much more reasonable number and no cause for alarm.
The folded meteorology boom, carrying sensors much like those seen on a small Earth weather station, extended soon after launch. Right after the first look around with the cameras, Viking did what any new arrival would have done and observed the status of the weather.
The meteorology team gave their first Mars weather report early the next morning, telling us that there were "light winds from the east in the late afternoon, changing to light winds from the southwest after midnight. Maximum wind was 15 mph. Temperature ranged from -122° F just after dawn to -22° F [but this was not the maximum]. Pressure steady at 7.70 millibars." This was the first of a daily (SOLy?) series of reports from the Viking lab on the changing weather conditions on the surface of Mars. Quite a while later, a morning report told of a winter storm that was verified by camera images showing what appeared to be light snow covering the ground. The meteorology instruments worked well on both Viking landers, and we soon had enough seasonal data on Mars weather to joke about a Martian Farmer's Almanac.
The next instrument to be activated was a seismometer. While not a primary instrument in the search for life, it was expected to provide basic information about the origin and evolution of Mars. Efforts to uncage the instrument were disappointing, and troubleshooting did not succeed in getting it to work. Fortunately, its counterpart on Viking 2 performed flawlessly, so that data about Mars quakes were obtained. Mars appears fairly inactive seismically, and most of the disturbances measured were believed to be related to the effects of wind.
As if to prove its human qualities by showing that "nobody's perfect," a command to the surface sampler control assembly (SSCA) caused the collector head to retract too far, crunching a restraint or latching pin and inhibiting its release. This caused a stir in Mission Control, for the surface sampler was vital to the biology and chemistry experiments. The SSCA was the "arm and hand" that had to reach out and collect samples, pick them up, and load the hoppers of the "chemistry lab," whose exotic and unique instruments would have been useless without them. This brings to mind the dependence scientists must often place on technicians who serve loyally in  laboratories on Earth, as well as the fact that they are often taken for granted-until they do not respond as expected or make mistakes. A further object lesson of the Viking surface sampler experience came from the troubleshooting activities that were begun immediately, for they showed the problem to have been caused by an incorrect command, not an improper response.
A diligent effort on the part of a team led by Len Clark of Langley quickly determined where the trouble was and how to remedy it. This involved reworking the commands and checking them carefully on the prototype hardware used in simulations. When everything was ready, including new commands for pointing the cameras to observe pin release and the location of the sampler after it was dropped to the surface, the new instructions were sent and executed perfectly. All these unplanned activities meant that the SSCA was unable to perform until SOL 5 instead of SOL 2 as scheduled, but everyone was so relieved to have things right again that Clark was congratulated for his heroic effort.
The development of the surface sampler arm and hand involved a combination of electromechanical technologies and the fundamental physics of its human counterparts. It had to be capable of being stowed out of the way until after the landing, able to extend in the desired direction, reach surface features over a nearby circular arc, manipulate the surface, pick up samples, and place them in receivers that allowed the samples to be processed. We humans take our arms and hands for granted, but those who have contemplated the design of their replacements are well aware of the magnificent sophistication of the combination of sensors and the mechanical and control systems involved. Compared with the dynamic, adaptable qualities of a human arm, the SSCA was extremely simple; nonetheless, it was effective in the Martian environment.
The SSCA could extend 13 feet from its mount, reaching the ground from to 10 feet from the spacecraft. Its radius of operation was about 120°, giving it a surface area coverage of about 95 square feet. Normally it would be programmed to the desired azimuth, extended the desired amount, and lowered to the surface. It would then extend into the soil about 16 centimeters with its jaw open, acquire a sample, retract the collector head with the jaw closed, and then elevate and deliver the sample to the desired receiver. Of course it could be used in other ways: as a trenching tool, as a rock hammer, or to move a rock on the surface. In addition to its scoop and backhoe, it carried magnets and a thermocouple to determine magnetic properties and surface temperatures. Its motor load could be recorded to give an  idea of the cohesion of the soil or the forces required to scrape a sample. A vibrator was installed so that loose soil samples could be shaken loose from the collector head of necessary. Though limited to "feeling" Mars in a very narrow area, the surface sampler did provide this surrogate capability for the scientific explorers who commanded its actions on Mars, and it served its technician role faithfully as long as the commands given to it were appropriate to its basic capabilities.
In some ways, the design and operation of the surface sampler presents an eerie parallel to applications of prosthetic devices. Its substitution for a human arm and its special requirements for control and manipulation required skill and learning. A mission status bulletin in October 1976 described the tricky process of pushing rocks 200 million miles away. This experience with Viking Lander 2 resulted from the desire to learn more about the nature of the rocks and Martian surface materials by moving some of the rocks near the lander. These had all been observed in their undisturbed state for a period of time; now it was reasonable to turn one over and to really see what it was like. Although it had taken longer to get this far in the exploration process because of the remote operations, the action was not different from that an explorer might have taken had he been able to use his own hands and tools. The account in the bulletin read as follows:
Returning to the problem with the surface sampler pin that was solved on SOL 5, it was SOL 8 before everything was ready and a trench was dug by the sampler. A sample of Martian soil was transferred to the chemistry lab, technically described as the biology, gas chromatograph, and X-ray sample processing and distribution assembly. The most interested "Vikings" gathered at 6:30 A.M to watch, as images of the trench dug by the sampler were returned slowly on the direct video link from the lander. The surface looked appropriately disturbed, and presumably the samples had been delivered. Engineering data showed that the biology instrument had obtained enough of a sample, but something had apparently gone wrong with the processing for the GCMS. Evidence initially pointed to a low level or insufficient sample size, but no one knew why that could have occurred. Needless to say, this caused a great deal of worry, and theories were developed about what had happened and how to recover. Three possibilities were considered: (1) no soil had been delivered to the distribution assembly, (2) the level-full indicator had not operated, or (3) some unusual quality of the soil had kept it from flowing through the distributor.
After much discussion, it was decided that a reasonable course of action was to collect another sample on SOL 14, disable the level-full no-go signal, and attempt to perform experiments on the available sample, even if the quantity was smaller than desired. Of course, the TV was used to observe the sample site, the processing and distribution assembly, and the dumped sample remaining in the collector head that did not pass through the sieve. Following this day of work, the spacecraft would be commanded to analyze the sample on SOL 15 and again on SOL 23. The limited amount of "equipment and expendables" contained in the Viking chemistry lab plus the extreme care necessary to ensure proper commands and interpretation of data made it prudent to proceed slowly.
Meanwhile, rumors flew as the scientists met on SOL 11, for the biology team had received its first data and was to report on the results. Vance Oyama from NASA Ames described his findings from the gas exchange  experiment, in which water vapor was released into the soil and evolved gases were analyzed to determine whether organisms would exhale exhaust products. His results indicated that the soil was active in some way, but he was cautious about the reason there seemed to be such a large amount of oxygen produced. This was the kind of happening to be expected if plants were growing, but . . .
Data from the labeled release experiment described by Pat Straat were even more exciting. In this experiment a radioactively marked nutrient that might be "devoured" by living organisms was introduced into the soil. By monitoring the amount of radioactive carbon dioxide produced, an idea could be obtained about the quantity of such organisms. Results from this experiment showed an incredible amount of activity. It was possible to interpret these results as indicators of both plant and animal forms of life, in significant abundance, but soon after these presentations another possible interpretation was offered by John Oro, a member of the Molecular Analysis Team. He suggested that it might be possible to obtain such results if Martian soil contained peroxides that were decomposing to release the oxygen detected in the gas exchange experiment. Such chemical constituents could also break down the formate and other organic ingredients of the labeled release nutrient, causing the large signal suggesting carbon dioxide. This somewhat unusual theory was reluctantly accepted as a possibility pending future analyses, but it dampened hopes enough to keep reports of life on Mars from being blown out of proportion in the newspapers.
There was hope that the matter might be settled by detailed analysis of data from the gas chromatograph mass spectrometer, which would be able to determine the presence or absence of organic compounds or carbon molecules. When, on SOL 14, the sampler again performed its task, the level-full indicator did show positive results; a sample had been delivered to the GCMS soil processor. Klaus Beimann presented bad news for the biologists, reporting no evidence of organic substances in the soil. This was the beginning of the negative results concerning evidence for life, as repeated experiments and analyses seemed to confirm the theory that chemical combinations-not expected based on Earth conditions-were responsible for the active biology indications.
Many of us were very disappointed. It had been a little like waiting for Christmas as a kid, only to find on Christmas morning that Santa didn't come through. All those years of talking about the possibility of life and planning to find out about it had built up the tremendous hope that exciting  results might be obtained. But after thinking about the negative results for a long time now, I have replaced those disappointments with other thoughts perhaps more exciting. Maybe the fact that there appears to be no life on Mars is better than finding that there were only some low forms of algae or distorted microbes of little significance. Mars may be a pristine site for future development through "planetary engineering"; perhaps we can make it an habitable and otherwise useful place for expansion. After all, the future residents of Mars might not have to worry about ants at their picnics or contend with viruses that have a long history of development.
Such biological speculations are far beyond my qualifications, but I will be ready to consider how we might create an atmosphere and satisfy other environmental requirements to enable a manned expedition to succeed. The fact that the planet represents a lot of real estate-not much more bleak than the deserts of Arizona-makes it a "place" to explore and examine for its intrinsic value. It has mountains, canyons, large volcanoes, and other features that are magnificently awesome. What little we have deduced about its history indicates that it has seen dynamic periods of flooding and erosion that might have been accompanied by spectacular developments-unimaginable, almost, until one reads about the continental drifts, the ice ages, the dinosaurs, and other stranger-than-fiction occurrences on our planet. What might we find if we could roam the Martian surface and dig around? After all, its land surface area of 55 million square miles is equal to about 40 percent of the land area of Earth, and we have only been able to scratch 180 square feet with our samplers.