Multiplexer

Mariner 1 was the first spacecraft of the American Mariner program. A range safety officer ordered its destructive abort at 09:26:16 UT, 294.5 seconds after it was launched on July 22, 1962 as a Venus flyby mission. According to NASA's current account for the public:

The booster had performed satisfactorily until an unscheduled yaw-lift (northeast) maneuver was detected by the range safety officer. Faulty application of the guidance commands made steering impossible and were directing the spacecraft towards a crash, possibly in the North Atlantic shipping lanes or in an inhabited area. The destruct command was sent 6 seconds before separation, after which the launch vehicle could not have been destroyed. The radio transponder continued to transmit signals for 64 seconds after the destruct command had been sent.

What NASA's website describes as "improper operation of the Atlas airborne beacon equipment" caused the booster to lose contact with one of the guidance systems on the ground, setting the stage for an apparent software-related guidance system failure. The role of software error in the launch failure remains somewhat mysterious in nature, shrouded in the ambiguities and conflicts among (and in some accounts, even within) the various accounts, official and otherwise. Mariner 1 was launched by an Atlas-Agena rocket.

The probe's mission was later completed by Mariner 2. The cryptic nature of the problems that led to the decision to abort Mariner 1, as well as the confusion in various reports on the incident, gave rise to an urban legend of sorts. Indirectly, this confusion also contributed to some software-engineering folklore about the role of supposed Fortran code in the guidance systems. This folklore persisted at least as late as 2006, despite a lack of evidence that Fortran was even in use for real-time guidance computations for the Mariner missions. Many accounts, instead, note a "missing hyphen" when a weak radio-guidance signal triggered the rare use of error-recovery software which lacked a hyphen in an equation, causing miscalculation or truncation of the remainder of the equation, which then pointed the rocket downward.

Spacecraft and subsystems

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The Mariner 1 spacecraft was identical to Mariner 2, launched 27 August 1962. Mariner 1 consisted of a hexagonal base, Template:Convert across and Template:Convert, which contained six magnesium chassis housing the electronics for the science experiments, communications, data encoding, computing, timing, and attitude control and the power control, battery, and battery charger, as well as the attitude control gas bottles and the rocket engine. On top of the base, was a tall pyramid-shaped mast on which the science experiments were mounted which brought the total height of the spacecraft to Template:Convert. Attached to either side of the base were rectangular solar panel wings with a total span of 5.05 meters and width of 0.76 meters (Template:Convert). Attached by an arm to one side of the base and extending below the spacecraft was a large directional dish antenna.

The Mariner 1 power system consisted of the two solar cell wings, one Template:Convert and the other, Template:Convert, with a Template:Convert dacron extension (a solar sail) to balance the solar pressure on the panels. Those panels powered the craft directly or recharged a 1,000-Watt-hour sealed silver-zinc cell battery, which was to be used before the panels were deployed, when the panels were not illuminated by the Sun, and when loads were heavy. A power-switching and booster regulator device controlled the power flow. Communications consisted of a 3 Watt transmitter capable of continuous telemetry operation, the large high gain directional dish antenna, a cylindrical omnidirectional antenna at the top of the instrument mast, and two command antennas, one on the end of either solar panel, which received instructions for midcourse maneuvers and other functions.

Propulsion for midcourse maneuvers was supplied by a monopropellant (anhydrous hydrazine) 225 N retro-rocket. The hydrazine was ignited using nitrogen tetroxide and aluminium oxide pellets, and thrust direction was controlled by four jet vanes situated below the thrust chamber. Attitude control with a 1 degree pointing error was maintained by a system of nitrogen gas jets. The Sun and Earth were used as references for attitude stabilization. Overall timing and control was performed by a digital Central Computer and Sequencer. Thermal control was achieved through the use of passive reflecting and absorbing surfaces, thermal shields, and movable louvers.

The scientific experiments were mounted on the instrument mast and base. A magnetometer was attached to the top of the mast below the omnidirectional antenna. Particle detectors were mounted halfway up the mast, along with the cosmic ray detector. A cosmic-dust detector and solar plasma spectrometer/detector were attached to the top edges of the spacecraft base. A microwave radiometer and an infrared radiometer and the radiometer reference horns were rigidly mounted to a Template:Convert diameter parabolic radiometer antenna mounted near the bottom of the mast.

In addition, a small 91 × 150 cm (3-by-5-foot) United States flag was folded and stowed onboard Mariner 1 (and Mariner 2), before it was mated to the Agena.

Program error

"The most expensive hyphen in history"

The most consistent account was that the error was in hand-transcription of a mathematical symbol in the program specification, in particular a missing overbar. Yet the story persists of a "missing hyphen" ('-'), either in the data or in the computer instructions, or even somehow in the equations. Several factors contributed to the "missing hyphen" narrative and its longevity, even in official accounts from technical cognoscenti at JPL and NASA. Among the factors cited (or obvious enough):

• The overbar's resemblance to a hyphen ('‾' versus '-').
• The difficulty of explaining the real error to the American public and its elected representatives.
• External political pressures and internal schedule pressures, as the mission was
  • an expensive failure of a three-way collaboration (JPL, NASA, USAF),
  • legitimized within the narrative of the US-USSR space race,
  • very high profile, as America's first planetary mission,
  • on a very tight schedule, as it was planned with a narrow launch window (45 days), leaving little time for inquiries, investigations or recriminations before the launch of Mariner 2. The official accounts (which included mentions of a missing hyphen) were the results of an inquiry conducted in less than a week.

Regardless of whatever may have given rise to initial reports of a "missing hyphen", the simplest and most consistent-sounding explanation that the public and Congress would accept would probably have been preferable to those who simply wanted to get on with the job of a Venus fly-by mission. The stories had contradictions, perhaps, but they were so technical that nobody who could have interfered with Mariner-program progress was likely to care about them or even notice. (After all, even in one later NASA account, the supposed "hyphen" is reported as missing from instructions at one point in the text, and from equations at another).

Ambiguity of error location

The New York Times, reporting on the results of a review board, said that the error stemmed from "the omission of a hyphen in some mathematical data" . The same report also said the hyphen was

a symbol that should have been fed into a computer, along with a mass of other coded mathematical instructions.

This sort of inconsistency or ambiguity was seen in many subsequent variations on the story, official and otherwise. "Missing hyphen" versions of the story gained from official support before the month was out. NASA official Richard B. Morrison testified before Congress that the supposed hyphen

... gives a cue for the spacecraft to ignore the data the computer feeds it until radar contact is once again restored. When that hyphen is left out, false information is fed into the spacecraft control systems. In this case, the computer fed the rocket in hard left, nose down and the vehicle obeyed and crashed.

(Note that Morrison says the spacecraft "crashed", not that it was intentionally destroyed). In a NASA account submitted to Congress in 1963, the hyphen is described as missing in two different ways:

NASA-JPL-USAF Mariner R-1 Post-Flight Review Board determined that the omission of a hyphen in coded computer instructions transmitted incorrect guidance signals to Mariner spacecraft boosted by two-stage Atlas-Agena from Cape Canaveral on July 21. Omission of hyphen in data editing caused computer to swing automatically into a series of unnecessary course correction signals which threw spacecraft off course so that it had to be destroyed.

In the same 1963 report to Congress, Morrison's testimony from the previous year is recounted differently:

In testimony before House Science and Astronautics Committee, Richard B. Morrison, NASA's Launch Vehicles Director, testified that an error in computer equations for Venus probe launch of Mariner R-1 space-craft on July 21 led to its destruction when it veered off course.

JPL's Mariner Venus Final Project Report in 1965 noted that, at 4 minutes and 25 seconds into the flight, there was an "[U]nscheduled yaw-lift maneuver":

...steering commands were being supplied, but faulty application of the guidance equations was taking the vehicle far off course.

Arthur C. Clarke wrote several years later that Mariner 1 was "wrecked by the most expensive hyphen in history".

In a NASA report published in 1985, Oran Nicks offered another slightly differing account, but with the software-related error still identified as a missing "hyphen":

The guidance antenna on the Atlas performed poorly, below specifications. When the signal received by the rocket became weak and noisy, the rocket lost its lock on the ground guidance signal that supplied steering commands. The possibility had been foreseen; in the event that radio guidance was lost the internal guidance computer was supposed to reject the spurious signals from the faulty antenna and proceed on its stored program, which would probably have resulted in a successful launch. At this point a second fault took effect. Somehow a hyphen had been dropped from the guidance program loaded aboard the computer, allowing the flawed signals to command the rocket to veer left and nose down. The hyphen had been missing on previous successful flights of the Atlas, but that portion of the equation had not been needed since there was no radio guidance failure.

NASA's website now says the problem was:

... apparently caused by a combination of two factors. Improper operation of the Atlas airborne beacon equipment resulted in a loss of the rate signal from the vehicle for a prolonged period. The airborne beacon used for obtaining rate data was inoperative for four periods ranging from 1.5 to 61 seconds in duration. Additionally, the Mariner 1 Post Flight Review Board determined that the omission of a hyphen in coded computer instructions in the data-editing program allowed transmission of incorrect guidance signals to the spacecraft. During the periods the airborne beacon was inoperative the omission of the hyphen in the data-editing program caused the computer to incorrectly accept the sweep frequency of the ground receiver as it sought the vehicle beacon signal and combined this data with the tracking data sent to the remaining guidance computation. This caused the computer to swing automatically into a series of unnecessary course corrections with erroneous steering commands which finally threw the spacecraft off course.

Other punctuation

In other versions of the legend, the bug consisted of:

• a period typed in place of a comma, causing a FORTRAN DO loop statement to be misinterpreted (although there is no evidence that FORTRAN was used in the mission), of the form "DO 5  K=1. 3" interpreted as assignment "DO5K = 1.3" There are anecdotal reports that there was in fact such a bug in a NASA orbit computation program at about this time, but it was a program for Project Mercury, not Mariner, and the claim was that the bug was noticed and fixed before there could be any serious consequences.
• a missing comma
• an extraneous semicolon

Overbar transcription error

The error had occurred when a symbol was being transcribed by hand in the specification for the guidance program. The writer missed the superscript bar (or overline) in

${\bar {{\dot {R}}_{n}}}$

by which was meant "the nth smoothed value of the time derivative of a radius R". Without the smoothing function indicated by the bar, the program treated normal minor variations of velocity as if they were serious, causing spurious corrections that sent the rocket off course. It was then destroyed by the Range Safety Officer.

References

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External links

• NASA's article about the Mariner I
• Mariner 1 Mission Profile by NASA's Solar System Exploration
• RISKS Digest detail about the Mariner I failure

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