Will the Soyuz-2 rocket carrying the Progress MS-35 (or MS-36) ISS cargo resupply mission launch from Baikonur Cosmodrome (Site 31) on its currently scheduled date of September 9, 2026?

probability: 86%

rationale:

Current Schedule and Designation Official scheduling from both NASA and Roscosmos confirms that the September 9, 2026 launch from Baikonur Cosmodrome is the Progress MS-35 resupply mission (NASA designation 96P). Multiple official and independent sources target liftoff for approximately 16:10 UTC 3 sources. Because this launch window is situated comfortably in the middle of the UTC day, there is virtually no risk of a minor timing adjustment pushing the launch across the date boundary. An older, third-party schedule from July had listed a September 18 launch date spider.seds.org, but recent updates from NASA and Russian tracking sources comprehensively reinforce the September 9 target 2 sources.

Hardware Processing at Baikonur Preparations at Baikonur are progressing nominally and on schedule. The spacecraft has been undergoing final ground processing at the Site 254 assembly-test facility since late June 2026 prospect.com.ru. On August 11, Roscosmos officially announced that Progress MS-35 successfully completed critical vacuum-chamber leak testing, with no hardware anomalies or technical holds reported roscosmos.ru. The remaining three weeks of the standard processing flow—which involves fueling, booster integration, and rollout—are proceeding without any reported impediments. Furthermore, Baikonur's Site 31 has been fully operational since March 2026 following repairs to a collapsed service platform russianspaceweb.com, mitigating concerns about pad readiness.

ISS Traffic and Phasing The current ISS Visiting Vehicle schedule aligns perfectly with a September 9 cargo mission. Progress MS-33 is scheduled to undock from the station's Poisk module on September 7, deliberately freeing a docking port just prior to MS-35's arrival r4uab.ru. Additionally, the next crewed mission, Crew-13, is targeted to launch no earlier than September 12 2 sources. This sequencing indicates a highly deconflicted traffic plan, heavily incentivizing both NASA and Roscosmos to maintain the current launch date to avoid awkward reshuffling of crew and cargo arrivals.

Remaining Uncertainties While the evidence strongly supports an on-time launch, a roughly 14% chance of a delay remains appropriate at this stage. Progress missions and Soyuz rockets have excellent on-time records when hardware is in final testing, but they are not immune to technical or weather-related disruptions. The primary risks involve a late issue during fueling, rocket integration, or rollout, as well as a rare day-of technical scrub. Additionally, if the upcoming Crew-13 launch experiences delays, it could prompt sudden adjustments to ISS traffic phasing. Nonetheless, the convergence of successful hardware testing, official scheduling, and clear ISS logistics makes a September 9 launch highly likely.