斯科特凯利的最后任务是着名的“双胞胎研究”的一部分。为此，他花了将近一年的微重力，而他的兄弟马克，现在是一名退休的宇航员，留在了地球上。科学家设计了这项实验来研究延长微重力对斯科特的影响，并比较两者在任务过程中及其后的变化。该研究还提供了有关宇航员如何在月球和火星的长期航行中生活和工作的宇航员受到影响的宝贵信息。 2015年3月27日，当他与俄罗斯宇航员米哈伊尔·科尔尼延科（Mikhail Korniyenko）一起从地球爆炸时，他开始执行任务。凯利参加了两次任务，并担任第二次任务的指挥官。他于2016年3月11日返回地球。除了双胞胎研究之外，马克还在车站上与俄罗斯同事一起工作，并在部分逗留期间担任该任务的指挥官。他乘坐俄罗斯火箭和太空舱前往火车站。在其他活动中，凯利与宇航员蒂莫西科普拉进行了一次舱外活动，修理了该站的移动运输车。他还与Kjell Lindgren一起为该站的几个部分提供了EVA服务，包括Canadarm 2和安装对接设备，以供SpaceX和NASA机组人员进行未来任务。
Scott Kelly’s final mission is part of the famous “Twin Study”. To this end, he spent nearly a year on microgravity, and his brother Mark, now a retired astronaut, stayed on the earth. The scientists designed the experiment to study the effect of prolonging microgravity on Scott and comparing the changes between the two during and after the mission. The study also provides valuable information about how astronauts are affected by astronauts living and working on the long-term voyages of the Moon and Mars. On March 27, 2015, when he exploded with the Russian astronaut Mikhail Korniyenko, he began his mission. Kelly participated in two missions and served as the commander of the second mission. He returned to Earth on March 11, 2016. In addition to the twin study, Mark also worked with a Russian colleague at the station and served as the commander of the mission during part of his stay. He took the Russian rocket and space capsule to the train station. In other activities, Kelly and the astronaut Timothy Copra conducted an extravehicular activity and repaired the station’s mobile transporter. He also worked with Kjell Lindgren on EVA services for several parts of the station, including the Canadarm 2 and installation docking equipment for future missions for SpaceX and NASA crews.