www.lesswrong.com/posts/fbrz9xhKpEeTKw5zL/irretrievability-or-murphy-s-curse-of-...
2 corrections found
and this produced an explosion when the engine was restarted (for course correction before orbital insertion).
NASA’s post-loss investigations put the likely failure during propellant-tank pressurization three days before orbit insertion, not during an engine restart for a course-correction burn.
Full reasoning
This sentence gets the timing and mechanism wrong.
NASA says Mars Observer lost contact on August 21, 1993, three days before Mars orbit insertion, after controllers had turned off the transmitter just before pressurizing the onboard propellant tanks. NASA/JPL’s 1994 summary says the leading failure scenario was that oxidizer leaked past a check valve and, during tank pressurization, was forced into lines containing fuel, causing the line to burst.
A later NASA technical history likewise summarizes the board’s conclusion as the inadvertent mixing of nitrogen tetroxide and monomethylhydrazine during the helium pressurization of the fuel tanks, which ruptured tubing and sent the spacecraft into a catastrophic spin. In other words, the likely failure was associated with the pressurization sequence before orbit insertion, not with an engine restart for a course correction.
It is also overstated to present an "explosion when the engine was restarted" as established fact. NASA described several possible scenarios and emphasized that telemetry was off at the time, so investigators could not determine a single conclusive event with certainty.
3 sources
- Potential Causes of the Loss of Mars Observer Identified | NASA Jet Propulsion Laboratory
Mars Observer had turned off its transmitter just before it pressurized its onboard propellant tanks on August 21. At the end of the tank pressurization, Mars Observer was supposed to turn its transmitter back on. One likely scenario was that oxidizer migrated past a check valve and, during tank pressurization, caused the line to burst.
- Mars Observer - NASA Science
End of Mission: Aug. 22, 1993, communication lost prior to orbit insertion.
- NASA/TP−20230005922
The board’s study concluded that the propulsion system failure most probably was caused by the inadvertent mixing and the reaction of NTO and MMH within titanium pressurization tubing during the helium pressurization of the fuel tanks.
With the lander's antenna no longer pointed at the orbiter, no further software updates beyond that point could be received.
By November 1982 the Viking 1 orbiter had already been shut down, and NASA says the lander could communicate directly with Earth. The issue was not that the antenna was no longer pointed at an orbiter.
Full reasoning
This description mixes up Viking 1’s communications setup at the end of the mission.
NASA’s Viking 1 mission page says the orbiter was shut down on August 7, 1980, after it ran out of attitude-control propellant. The faulty command that ended the lander mission was sent on November 11, 1982 — more than two years later. So the lander was not relying on a still-operating orbiter at that point.
NASA’s Viking spacecraft documentation also says the lander’s high-gain and low-gain S-band antennas allowed communication directly with Earth, and specifically refers to direct lander-Earth links. That means the corrupted antenna-pointing software could not have mattered because the antenna was no longer pointed at an orbiter that was already gone; the relevant communications path was the lander’s direct link to Earth.
So the historical problem is real — a faulty command interrupted communications — but the post’s explanation that the antenna was no longer pointed at "the orbiter" is inaccurate for November 1982.
2 sources
- Viking 1 - NASA Science
Key Dates: Aug. 7, 1980: Orbiter was shut down after running out of attitude-control propellant. Nov. 11, 1982: Lander stopped operating after getting a faulty command.
- Viking Spacecraft and Science - NASA Science
The Viking 1 Orbiter was powered down on Aug. 17, 1980. For the lander, both the high-gain and low-gain S-band antennas allowed for communication directly with the Earth, and the page also describes two-way direct lander-earth S-band links.