Est-ce que le télescope va s'écrouler si un autre câble lâche ?
2020 damage, decommissioning plans, and collapse

The facility had recently reopened following the passing of Tropical Storm Isaias. It was unclear if the cable failure was caused by Isaias. Former Arecibo Observatory director Robert Kerr stated that prior to the 1997 installation of the Gregorian dome, the main support cables and support towers had been engineered with a safety factor of two, as to be able to sustain twice the weight of the platform. When the dome was added in 1997, the auxiliary cables were intended to retain the safety factor of two once all design factors were considered, but Kerr believed that that was never the case as evenly distributing the loads following that install would be difficult to do. Kerr also stated that there had been periods of neglect at the Observatory, during which the fans that were used to blow dry air along the wire bundles were not operating. The earlier storms would have brought seawater to the cables which could accelerate the rate of corrosion as well, according to Kerr. Engineering firms hired by UCF inspected the socket area where the cable had failed, and found a similar problem that had been observed in the 1980s during a routine cable replacement, in which the use of molten zinc to affix the cable to the socket mount at the tower was not complete, allowing moisture to get into the wire bundle and cause corrosion and leading to the cable slipping from its socket. The firms had developed models of the telescope that showed that the safety factor for Tower 4 had dropped to 1.67, believing that the structure was still safe while repairs could be effected, even if another cable collapsed. Plans were made to replace all six auxiliary cables since their socket welds were all considered suspect at a cost of US$10.5 million.
La NSF a réduit son engagement financier envers l'observatoire à partir de 2006, ce qui a incité les universitaires à plaider pour un soutien financier supplémentaire afin de poursuivre ses programmes. Le télescope a été endommagé par l'ouragan Maria en 2017 et a été affecté par des tremblements de terre en 2019 et 2020. Deux ruptures de câbles, une en août 2020 et une seconde en novembre 2020, ont menacé l'intégrité structurelle de la structure de support de la plateforme suspendue et ont endommagé la parabole. En raison de l'incertitude quant à la résistance restante des autres câbles soutenant la structure suspendue, et du risque d'effondrement dû à d'autres défaillances rendant les réparations dangereuses, la NSF a annoncé le 19 novembre 2020 que le télescope serait mis hors service et démantelé, la facility LIDAR restant opérationnelle. Avant qu'il ne puisse être mis hors service, plusieurs des câbles de support restants ont subi une défaillance critique et la structure de support, l'antenne et l'assemblage du dôme se sont tous effondrés dans la parabole à 7h55 heure locale le 1er décembre 2020, détruisant le télescope. En octobre 2022, la NSF a décidé qu'elle ne reconstruirait pas le télescope ni ne construirait un observatoire similaire sur le site.
### Query ###
Est-ce que le télescope va s'écrouler si un autre câble lâche ?

### Main Text ###
2020 damage, decommissioning plans, and collapse

The facility had recently reopened following the passing of Tropical Storm Isaias. It was unclear if the cable failure was caused by Isaias. Former Arecibo Observatory director Robert Kerr stated that prior to the 1997 installation of the Gregorian dome, the main support cables and support towers had been engineered with a safety factor of two, as to be able to sustain twice the weight of the platform. When the dome was added in 1997, the auxiliary cables were intended to retain the safety factor of two once all design factors were considered, but Kerr believed that that was never the case as evenly distributing the loads following that install would be difficult to do. Kerr also stated that there had been periods of neglect at the Observatory, during which the fans that were used to blow dry air along the wire bundles were not operating. The earlier storms would have brought seawater to the cables which could accelerate the rate of corrosion as well, according to Kerr. Engineering firms hired by UCF inspected the socket area where the cable had failed, and found a similar problem that had been observed in the 1980s during a routine cable replacement, in which the use of molten zinc to affix the cable to the socket mount at the tower was not complete, allowing moisture to get into the wire bundle and cause corrosion and leading to the cable slipping from its socket. The firms had developed models of the telescope that showed that the safety factor for Tower 4 had dropped to 1.67, believing that the structure was still safe while repairs could be effected, even if another cable collapsed. Plans were made to replace all six auxiliary cables since their socket welds were all considered suspect at a cost of US$10.5 million.

### Supplementary Text ###
La NSF a réduit son engagement financier envers l'observatoire à partir de 2006, ce qui a incité les universitaires à plaider pour un soutien financier supplémentaire afin de poursuivre ses programmes. Le télescope a été endommagé par l'ouragan Maria en 2017 et a été affecté par des tremblements de terre en 2019 et 2020. Deux ruptures de câbles, une en août 2020 et une seconde en novembre 2020, ont menacé l'intégrité structurelle de la structure de support de la plateforme suspendue et ont endommagé la parabole. En raison de l'incertitude quant à la résistance restante des autres câbles soutenant la structure suspendue, et du risque d'effondrement dû à d'autres défaillances rendant les réparations dangereuses, la NSF a annoncé le 19 novembre 2020 que le télescope serait mis hors service et démantelé, la facility LIDAR restant opérationnelle. Avant qu'il ne puisse être mis hors service, plusieurs des câbles de support restants ont subi une défaillance critique et la structure de support, l'antenne et l'assemblage du dôme se sont tous effondrés dans la parabole à 7h55 heure locale le 1er décembre 2020, détruisant le télescope. En octobre 2022, la NSF a décidé qu'elle ne reconstruirait pas le télescope ni ne construirait un observatoire similaire sur le site.

### Draft ###

Query: "Est-ce que le télescope va s'écrouler si un autre câble lâche ?"

Translation: "Will the telescope collapse if another cable fails?"

→ Arecibo telescope context needed first.

**Arecibo Observatory** - massive radio telescope in Puerto Rico. One of world's largest single-dish telescopes until recently. Suspended platform design - massive instrument suspended above parabolic dish by cables.

**Critical failure cascade:**
- August 2020: Auxiliary cable #4 failed
- November 2020: Cable #3 failed  
- December 1, 2020: **Catastrophic collapse**

Physical constraint analysis:
- Original design: 2x safety factor (2 cables should hold entire load)
- 1997 modification (Gregorian dome installation): Load distribution became complex
- Critical threshold: When 3 cables failed → structural instability
- Engineering models predicted collapse when auxiliary cables reached ~1.67 safety factor

**Why collapse inevitable after 3rd cable:**
1. Platform suspended ~900 tons
2. Dish diameter ~305m 
3. Cable tension dynamics: Each cable carries portion of total load
4. Failure progression: Cable 1 fails → Cable 2 takes increased load → Cable 3 fails → **load redistribution creates instability**

! **Key insight:** Not just additive failure. Structural dynamics create cascading instability when critical thresholds crossed.

**Engineering mathematics check:**
If cables designed for P_max load, failure of n cables creates new load P_new = P_max/(n-1) on remaining cables. 
If safety factor drops below ~1.0 → structural failure inevitable.

∴ **Answer:** Yes, telescope collapse is mathematically inevitable if another major cable fails.

**Historical verification:** Arecibo collapse confirmed this prediction exactly. NSF made controlled demolition decision November 2020, but structure collapsed prematurely December 1, 2020, when additional cables failed catastrophically.

NB: Engineering safety factors typically 1.5-2.0 for normal structures, but telescope's suspended design created unique failure cascade risk.

### Answer###
Oui, la structure télescopique s'effondrerait probablement si un autre câble principal venait à lâcher.

L'observatoire d'Arecibo a effectivement subi deux ruptures de câbles successives en août et novembre 2020, ce qui a menacé son intégrité structurelle. Suite à ces incidents, les ingénieurs ont développé des modèles de la structure qui ont révélé que le facteur de sécurité était tombé à 1,67 pour la tour 4. Même si cette structure était considérée comme encore sûre à ce moment, les autorités estimaient que les réparations pourraient devenir dangereuses en cas de défaillance supplémentaire.

La situation était particulièrement critique car l'ajout d'un dôme grégorien en 1997 avait compliqué la distribution uniforme des charges et réduit la marge de sécurité. Les facteurs de sécurité originaux de 2x pour les câbles auxiliaires n'avaient plus été maintenus.

Malheureusement, ces prédictions se sont avérées exactes : plusieurs câbles de support sont effectivement tombés en critique avant que le télescope ne soit officiellement mis hors service, et toute la structure de support, l'antenne et l'assemblage du dôme se sont effondrés dans la parabole le 1er décembre 2020, détruisant complètement l'instrument.