I don't know. If I were in something that small with a soda-can sized bomb right under my butt, it'd be kind of hard to ignore it. But then, all of the Mercury astronauts were test pilots. They were used to riding in planes with ejection seats. Back before the invention of zero-zero ejection seats which use rockets, they used explosive charges to eject in an emergency. I guess they were used to the idea of explosive charges under their butts. They had much larger explosive charged just below their heat shield in the booster rockets. BTW: rockets don't use explosions but very controlled fast combustion.

If you're interested in computers in space, especially in regard to manned spaceflight, here's a good reference. For example, here are some tidbits about the Gemini computer with emphasis added by me:

Restrictions on size, power, and weight influenced the final form of the computer in terms of its components, speed, and type of memory. The shape and size of the computer was dictated by the design of the spacecraft. It was contained in a box measuring 18.9 inches high by 14.5 inches wide by 12.75 inches deep, weighing 58.98 pounds. An unpressurized equipment bay to the left of the Gemini commander s seat held the computer, as well as the inertial guidance system power supply and the computer auxiliary power supply. The machine consisted of discrete components, not integrated circuits. However, circuit modules that held the components were somewhat interchangeable. They were plugged into one of five interconnection boards, and it took 510 of the modules to build the logic section alone. The computer had no redundant circuits, which meant that failures in the computer canceled whatever activity needed to be controlled by it. For example, a failure in the power switch three quarters of the way through the Gemini IV mission caused cancellation of the planned computer-controlled re-entry. It was possible to fly the Gemini computer without a backup because whatever the computer did erroneously could be either abandoned (such as rendezvous) or handled. albeit more crudely, in other ways (such as re-entry using Mercury procedures).

The machine had an instruction cycle of 140 milliseconds, the time it required for an addition. Multiplication took three cycles, or 420 milliseconds, with division requiring double that time. The arithmetic bit rate was 500 kilocycles, and the memory cycle rate half that. The computer was serial in operation, passing bits one at a time, which explains the relatively slow processing speeds, slower than some vacuum tube computers such as the Whirlwind. Also, its fixed decimal point arithmetic unit design limited the precision of the calculations but greatly reduced complexity. The Gemini digital computer used ferrite cores for its primary memory. Core memories store one bit in each ferrite ring by magnetizing the ring in either a clockwise or counterclockwise direction. One direction means a one is stored and the opposite direction is a zero. Each core is mounted at a perpendicular crossing of two wires. Thousands of such crossings are in each core plane, consisting of rows of wires running up and down (the x wires) and others running left and right (the y wires). Therefore, to change the value of a bit at a specific location, half the voltage required for the change is sent on each of two wires, one in the x direction and one in the y direction. This way only the core at the intersection of the two wires is selected for change. All the others on the same wires would have received only half the required voltage. By the use of a third wire it is possible to "sense" whether a selected core is a one or a zero. In this way, each individual core can be read.

The ferrite core memory in the Gemini computer had a unique design. It consisted of 39 planes of 64 by 64-bit arrays, resulting in 4,096 addresses, each containing 39 bits. A word was considered to be 39 bits in length, but it was divided into three syllables of 13 bits. The memory itself divided into 18 sectors. Therefore, it was necessary to specify sector and syllable to make a complete address. Instructions used 13 bits of the word with data representations of 26 bits. Data words were always stored in syllables 0 and I of a full word, but instructions could be in any syllable. This means that up to three instructions could be placed in any full word, but only one data item could be in a full word.

To put that in perspective, even the Palm Pilot has about 1000 times the memory, many times the processing speed, fits in a shirt pocket, and has a far better user interface. It wouldn't be radiation hardened, but you can buy one for less than $100. Progress, indeed.