question: How was the Opportunity Rover able to have last words?
comment: Programmers choose the text for error messages all the time. When the logic is added to detect this situation, and send an error, the choice of messages was made. Programmers are deeply, deeply in love with the cryptic and poetic when it comes to messages that might never be seen.
passages: The Mars Exploration Rovers, "Spirit" and "Opportunity" landed on Mars to explore the Martian surface and geology, and searched for clues to past water activity on Mars. They were each launched in 2003 and landed in 2004. Communication with "Spirit" stopped on sol 2210 (March 22, 2010). JPL continued to attempt to regain contact until May 24, 2011, when NASA announced that efforts to communicate with the unresponsive rover had ended. "Opportunity" arrived at Endeavour crater on 9 August 2011, at a landmark called "Spirit Point" named after its rover twin, after traversing from Victoria crater, over a three-year period. After a planet wide dust storm in June 2018, the final communication was received on June 10, 2018, and "Opportunity" was declared dead on February 13, 2019. The rover lasted for almost fifteen years on Mars — although the rover was intended to last only three months.
   NASA stated they did not expect to resume communication until after the global dust storm subsided.
  
  Section::::Mission timeline.:2018.:After the storm.
  
  At the beginning of September 2018, the atmospheric opacity (tau) over the rover site was estimated to be below 1.5. This started a 45-day window that was expected to be the best time to re-establish contact with the rover. After more than three months without contact, NASA expected "Opportunity" to have most of its timers in fault state. To take this into account, as of September 19, 2018, "sweep and beep" commands are sent throughout the available transmission time.
   On November 10, Phoenix Mission Control reported the loss of contact with the "Phoenix" lander; the last signal was received on November 2. Immediately prior, "Phoenix" sent its final message: "Triumph" in binary code. The demise of the craft occurred as a result of a dust storm that reduced power generation even further. While the spacecraft's work ended, the analysis of data from the instruments was in its earliest stages.
  
  Section::::Mission highlights.:End of the mission.:Communication attempts 2010.
   On February 12, 2019, past and present members of the mission team gathered in JPL's Space Flight Operations Facility to watch final commands being transmitted to Opportunity via the 70 meter dish of the Goldstone Deep Space Communications Complex in California. Following 25 minutes of transmission of the final 4 sets of commands, communication attempts with the rover were handed off to Canberra, Australia.
   During the beginning of October 2015, "Opportunity" began its drive to northly-tilted slopes in Marathon Valley of the west rim of Endeavour creator in preparation for the Martian winter. By November 2, after attempting to use the rover's flash memory, "Opportunity" again suffered an "amnesia" event. and the decision was made to switch back to use RAM on November 11 (Sol 4195).
  
  Section::::Mission timeline.:2016.
   In April 2013, the rover passed through a three-week-long solar conjunction, when communication with Earth was blocked because of the Sun. The rover arm was positioned on a rock during that time so the APXS could collect data.
   At 08:30 local Mars time on Sol (May 14, 2008), they allowed "Opportunity" to direct as much current as possible to the warm, joint-1 azimuth motor in order to get the robotic arm into a usable position, in front of the rover. It worked.
  
  Because "Opportunity" will likely never again stow the robotic arm, engineers devised a strategy for driving the rover safely with the arm deployed in front.
  
  Section::::Mission timeline.:2008.:Departing Victoria crater.
   Before "Curiosity" landed on August 6, 2012, "Opportunity" sent special Ultra High Frequency radio signals to simulate "Curiosity" for a radio observatory in Australia. August activities for "Opportunity" included collecting data on atmospheric opacity, visiting "Sao Rafael" and "Berrio" craters, and achieving of driving on Sol 3056 (August 28, 2012). Also, on August 19, 2012 Mars Express orbiter automatically exchanged data with both "Curiosity" and "Opportunity" in one orbit, its first double contact.
   By Sol 415, "Opportunity" stopped by some soil ripples to investigate the differences between soil in the trough of a ripple and its crest. Various soil targets included "Mobarak" in the trough, named in honor of Persian New Year, and "Norooz" and "Mayberooz" on the crest. By Sol 421, the rover left the ripple for "Viking" crater.
   Compared to the previous "Hayabusa" mission, the spacecraft features improved ion engines, guidance and navigation technology, antennas, and attitude control systems. A kinetic penetrator was shot into the asteroid to expose pristine sample material that was later sampled for return to Earth.
  
  Section::::Mission overview.:Status.
  
  On 21 September 2018, the "Hayabusa2" spacecraft ejected the first two rovers, Rover-1A and Rover-1B, from about 55 meters altitude that fell independently to the surface of the asteroid. They functioned nominally and transmitted data. The MASCOT rover deployed successfully on 3 October 2018 and operated for about 16 hours as planned.
   BULLET::::- "Mars 3", "Prop-M" rover, 1971, lost when "Mars 3" lander stopped communicating about 20 seconds after landing.
  
  BULLET::::- "Sojourner" rover, Mars Pathfinder, landed successfully on July 4, 1997. Communications were lost on September 27, 1997.
  
  BULLET::::- "Spirit" (MER-A), Mars Exploration Rover, launched on June 10, 2003, and landed on January 4, 2004. Nearly 6 years after the original mission limit, "Spirit" had covered a total distance of but its wheels became trapped in sand. The last communication received from the rover was on March 22, 2010, and NASA ceased attempts to re-establish communication on May 25, 2011.
   During Sol 465 and 466 more drive commands were executed, and with each trial the rover moved another couple of centimeters. At the end of each movement, panoramic images were acquired to investigate the atmosphere and the surrounding dune field. The sand dune escape maneuver was successfully completed on sol (June 4, 2005), and all six wheels of "Opportunity" were on firmer ground. After studying "Purgatory" from Sol 498 to Sol 510, "Opportunity" proceeded southward toward "Erebus crater".
  
  Section::::Mission timeline.:2005.:Erebus crater.
   Section::::Mission highlights.:Surface mission.
  
  Section::::Mission highlights.:Surface mission.:Communications from the surface.
  
  The robotic arm's first movement was delayed by one day when, on May 27, 2008, commands from Earth were not relayed to the "Phoenix" lander on Mars. The commands went to NASA's Mars Reconnaissance Orbiter as planned, but the orbiter's Electra UHF radio system for relaying commands to "Phoenix" temporarily shut off. Without new commands, the lander instead carried out a set of backup activities. On May 27 the Mars Reconnaissance Orbiter relayed images and other information from those activities back to Earth.
   More than 835 recovery commands were transmitted since losing signal in June 2018 to the end of January 2019 with over 1000 recovery commands transmitted before February 13, 2019. NASA officials held a press conference on February 13 to declare an official end to the mission. NASA associate administrator Thomas Zurbuchen said, "It is therefore that I am standing here with a deep sense of appreciation and gratitude that I declare the "Opportunity" mission is complete." As NASA ended their attempts to contact the rover, the last data sent was the song "I'll Be Seeing You" performed by Billie Holiday.
   With word on February 12, 2019, that NASA was likely to conclude the "Opportunity" mission, many media outsides and commentators issued statements praising the mission's success and stating their goodbyes to the rover. One journalist, Jacob Margolis, tweeted his translation of the last data transmission sent by "Opportunity" on June 10, 2018, as "My battery is low and it’s getting dark". The phrase struck a chord with the public mind and became widely reported, including some news reports that mistakenly asserted that the rover sent that English message, inundating NASA with additional questions. Margolis wrote a clarifying article on February 16, making it clear he had taken statements from NASA officials who were interpreting the data sent by "Opportunity", both on the state of its low power and Mars's high atmospheric opacity, and rephrased them in a poetic manner, never to imply the rover had sent the specific words.
   By sol (August 29, 2011), "Opportunity" had continued to function effectively 30 times longer than its planned 90-sol mission, aided by solar cell cleaning events, and performed extensive geological analysis of Martian rocks and planetary surface features with its instruments.
  
  Section::::Mission timeline.:2011.:Endeavour crater arrival.
   On 22 November 2011, a signal from the probe was picked up by the European Space Agency's tracking station in Perth, Australia, after it had sent the probe the command to turn on one of its transmitters. The European Space Operations Centre (ESOC) in Darmstadt, Germany, reported that the contact was made at 20:25 UTC on 22 November 2011 after some modifications had been made to the 15 m dish facility in Perth to improve its chances of getting a signal. No telemetry was received in this communication. It remained unclear whether the communications link would have been sufficient to command the spacecraft to switch on its engines to take it on its intended trajectory toward Mars. Roscosmos officials said that the window of opportunity to salvage Fobos-Grunt would close in early December.
   There have been two "safing" events, that sent the spacecraft into safe mode:
  
  BULLET::::- On March 19, 2007, the Command and Data Handling computer experienced an uncorrectable memory error and rebooted itself, causing the spacecraft to go into safe mode. The craft fully recovered within two days, with some data loss on Jupiter's magnetotail. No impact on the subsequent mission was expected.
   Each sol, the Deep Space Network mission controllers sent a set of X-band "Sweep & Beep" commands. If the rover had experienced a mission clock fault and then had been awoken during the day, it would have listened during brief, 20-minute intervals during each hour awake. Due to the possible clock fault, the timing of these 20-minute listening intervals was not known, so multiple "Sweep & Beep" commands were sent. If the rover heard one of these commands, it would have responded with an X-band beep signal, updating the mission controllers on its status and allowing them to investigate the state of the rover further. But even with this new strategy, there was no response from the rover.
   BULLET::::- "Cassini–Huygens" download of the Iapetus flyby data was interrupted by a safing event September 10, 2007.
  
  BULLET::::- "New Horizons" entered safe mode March 19, 2007 due to an uncorrectable memory error in the primary Command and Data Handling (C&DH) computer.
  
  BULLET::::- "Odyssey" has broken the communications link between the Mars Exploration Rovers and Earth during several sudden safing events.
  
  BULLET::::- 2009
   Traveling at 6.9 kilometers per second, the entry capsule entered the Martian atmosphere at 20:10:00 UTC and was expected to land in the vicinity of in a region known as Planum Australe. Communication was expected to be reestablished with the spacecraft at 20:39:00 UTC after having landed. However, no communication was possible with the spacecraft, and the lander was declared lost.
  
  On May 25, 2008 the Phoenix lander arrived at Mars, and has subsequently completed most of the objectives of the "Mars Polar Lander", carrying several of the same or derivative instruments.
  
  Section::::Mission profile.:Intended operations.
   In December 2014, NASA reported that "Opportunity" was suffering from "amnesia" events in which the rover failed to write data, e.g. telemetry information, to non-volatile memory. The hardware failure was believed to be due to an age-related fault in one of the rover's seven memory banks. As a result, NASA had aimed to force the rover's software to ignore the failed memory bank; amnesia events continued to occur, however, which eventually resulted in vehicle resets. In light of this, on Sol 4027 (May 23, 2015), the rover was configured to operate in RAM-only mode, completely avoiding the use of non-volatile memory for storage.
   "Opportunity " studied Erebus crater, a large, shallow, partially buried crater and a stopover on the way south toward Victoria crater, between October 2005 and March 2006.
  
  New programming to measure the percentage of slip in the wheels was successful in preventing the rover from getting stuck again. Another "Purgatory"-like incident was averted on Sol 603, when onboard slip check software stopped a drive after slip reached 44.5%. It proceeded over many ripples and 'half-pipes', taking photographs after each sol's journey.
   In the fall "Opportunity" headed south, exploring Matijevic hill and searching for phyllosilicate minerals. Some data was sent to Earth directly using X-Band radio signals, as opposed to orbiter relays. Finally, the number of power cycles on the rover's Inertial Measurement Unit were reduced. Science work included testing various hypotheses about the newly discovered spherules.
  
  Section::::Mission timeline.:2013.
  
  Section::::Mission timeline.:2013.:Leaving Cape York.
   The retrieval of the first miner, Florencio Ávalos, began on Tuesday, 12 October at 23:55 CLDT, with the rescue capsule reaching the surface 16 minutes later. At 21:55 CLDT on 13 October, all 33 miners had been rescued, almost all in good medical condition, and expected to recover fully. Two miners had silicosis, one of whom also had pneumonia, and others had dental infections and corneal problems. Three of the rescued miners had immediate surgery under general anesthesia for dental problems.
  
  Section::::Survival.
  