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Mercury spacecraft No. 18 was delivered to [[Cape Canaveral Air Force Station|Cape Canaveral]], Florida on November 15, 1961. While under checkout, the crew changed the periscope and also worked on the drogue parachute to prevent it from firing prematurely as had happened during the previous flight. In addition, a device known as a "low-level commutator" was added, to measure the temperature around the capsule, recording temperature data from 28 positions on the spacecraft.<ref name="history138">{{Cite book|url=http://www.hq.nasa.gov/office/pao/History/SP-4201/toc.htm|title=This New Ocean: A History of Project Mercury|last1=Swenson Jr.|first1=Loyd S.|last2=Grimwood|first2=James M.|last3=Alexander|first3=Charles C.|work=Published as NASA Special Publication-4201 in the NASA History Series|publisher=NASA|year=1989|editor-last=Woods|editor-first=David|chapter=13-8 MA-7 Preparations|format=url|access-date=17 December 2016|editor-last2=Gamble|editor-first2=Chris|chapter-url=http://www.hq.nasa.gov/office/pao/History/SP-4201/ch13-8.htm|archive-date=13 July 2009|archive-url=https://web.archive.org/web/20090713233748/http://www.hq.nasa.gov/office/pao/History/SP-4201/toc.htm|url-status=dead}}{{PD-notice}}</ref>
Changes made to Atlas 107D over Glenn's booster were minor. It had been agreed that the insulation blanket in the tank bulkhead was unnecessary and would be removed on subsequent Mercury-Atlas vehicles, although MA-7 would still retain it. The LOX tank skin was thickened still further due to the growing weight of the Mercury capsule as missions grew longer and more ambitious. A meeting of the Flight Safety Review Board on May 16 discussed the 12 Atlas flights since Glenn's launch and any anomalies on them that were of concern. There had been four major Atlas in-flight malfunctions during this stretch, but three were caused by random quality control defects unlikely to be a concern in the much more tightly supervised Mercury program. More concerning was Atlas 11F, which had exploded almost immediately at liftoff on April 9 and the static firing test of Atlas 1F, which exploded at Sycamore Canyon on May 13. The cause of these two mishaps was as yet unclear, but assumed to be the result of rough combustion, an old problem that had destroyed several previous Atlas vehicles. NASA ultimately decided a rough combustion failure was unlikely to be a concern as Mercury-Atlas vehicles had a three-second hold down prior to launcher release and a different engine start sequence than the Atlas F (as it turned out, the failures on 11F and 1F had an entirely different cause). The explosion of the first Atlas-Centaur shortly after liftoff on May 8 was also a momentary source of concern until postflight analysis found that the Centaur and not the Atlas had been at fault.<ref name="history138"/>
The temperature sensor installation and the correction of the drogue parachute circuit delayed the launch until May.<ref name="history138"/>
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