Final Report Issued on Mars Observer Loss

An independent investigative board presented its final report on the failure of the Mars Observer mission to NASA Administrator Daniel Goldin on January 5. Communication with the spacecraft, which had been launched in September 1992, was lost on August 21, 1993, as NASA controllers prepared it to enter Mars orbit.

Though hampered by the lack of communication at the time of the catastrophe, the Mars Observer Mission Failure Investigation Board, chaired by Naval Research Lab Director of Research Timothy Coffey, looked at 60 failure scenarios during its investigation. According to its report, the Board “first identified technically possible failure scenarios, eliminated those deemed implausible, and then categorized the remaining scenarios as either `possible’ or `most probable.’”

While “unable to find clear and conclusive evidence pointing to a particular scenario as the `smoking gun,’ . . . the Board concluded through a process of elimination that the most probable cause of the loss of downlink from the Mars Observer was a massive failure of the pressurization side of the propulsion system, [and] the most probable cause of that failure was the unintended mixing of nitrogen tetroxide (NTO) and monomethyl hydrazine (MMH) in the titanium tubing. . . [This is] believed by the Board to have been enabled by significant NTO migration through check valves during the eleven-month cruise phase from Earth to Mars.”

This scenario envisions that premature mixing of the NTO and MMH caused ignition and rupture of the tubing, spilling propellant and forcing the spacecraft into a spin, as well as damaging electrical components.

The investigation found that pressurization of the Observer’s fuel tanks was originally planned for five days after launch. However, reports of problems due to early pressurization in other spacecraft led managers to decide, in February 1992, to delay pressurization of the tanks until the Observer approached its intended Mars orbit. The Board suspected that the check valves, intended to work for five days in proximity to Earth, allowed some leakage of NTO during the eleven-month, 450 million-mile journey to the much colder climate near Mars.

Although mentioned briefly within the body of the report, this management decision is not included in the summary, which Coffey claims was “an oversight.” The report notes, however, that “the organization and procedural `system’ that developed Mars Observer . . . failed to react properly to a program that had changed radically from the program that was originally envisioned. Too much reliance was placed on the heritage of spacecraft hardware, software, and procedures, especially since the Mars Observer mission was fundamentally different from the missions of the satellites from which the heritage was derived.”

Copies of the report summary can be obtained from Donald Savage, NASA Headquarters, (202) 358-1547.