From the Wikipedia Article: „Modified SR-71 Blackbird ejection seats and full pressure suits were used for the two-person crews on the first four Space Shuttle

From the Wikipedia Article: „Modified SR-71 Blackbird ejection seats and full pressure suits were used for the two-person crews on the first four Space Shuttle orbital test flights, but they were disabled and later removed for the operational flights.“[1]II-7 But I think this would not have helped the astronauts on the middle deck. [1]: Jenkins, Dennis R. (2016). Space Shuttle: Developing an Icon – 1972–2013. Specialty Press. ISBN 978-1-58007-249-6.