Mariner 1

The most detailed and consistent account was that the error was in the hand-transcription of a mathematical symbol in the program specification for the guidance system, in particular a missing overbar.

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

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

by which was meant "the nth smoothed value of the time derivative of a radius R". Since the smoothing function indicated by the bar was left out of the specification for the program, the implementation treated normal minor variations of velocity as if they were serious, causing spurious corrections that sent the rocket off course.[4][5][6] It was then destroyed by the range safety officer.[7]

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, led to other explanations in the popular press.

Many accounts note a missing "hyphen" ('-') rather than the overbar, in either the equations, the computer instructions or the data. For example, Arthur C. Clarke wrote several years later that Mariner 1 was "wrecked by the most expensive hyphen in history".[8]

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 bears a resemblance to a hyphen ('‾' versus '-').
• It would be difficult to explain the real error to the American public and its elected representatives.
• There were 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
  • and on a very tight schedule.

The narrow window (45 days) before the launch of Mariner 2 left little time for inquiries, investigations, or recriminations. 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[3]).

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".[9]

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 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.[10] (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. The omission of hyphen in data editing caused the computer to swing automatically into a series of unnecessary course correction signals which threw spacecraft off course so that it had to be destroyed.[11]

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.[12]

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.[13]

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, the 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.[3]

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.[14]

In other accounts, 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".[15] 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 any serious consequences resulted.[16]
• a missing comma [17]
• an extraneous semicolon [18]