Roger Mark Boisjoly (/ˌboʊʒəˈleɪ/ BOH-zhə-LAY;[2] April 25, 1938 – January 6, 2012) was an American mechanical engineer, fluid dynamicist, and an aerodynamicist.

He is best known for having raised strenuous objections to the launch of the Space Shuttle Challenger months before the loss of the spacecraft and its crew in January 1986.

Boisjoly correctly predicted, based on earlier flight data, that the O-rings on the rocket boosters would fail if the shuttle launched in cold weather.

[6] He subsequently worked for companies in California on lunar module life-support systems and the moon vehicle.

[7] He later worked for Morton Thiokol, the manufacturer of the solid rocket boosters (SRBs) for the Space Shuttle program.

Boisjoly wrote a memo in July 1985 to his superiors concerning the faulty design of the solid rocket boosters that, if left unaddressed, could lead to a catastrophic event during launch of a Space Shuttle.

It was found, however, that flight dynamics caused the joints in the SRBs to flex during launch, opening a gap through which rocket exhaust could escape.

Cold weather made the rubber hard and less flexible, meaning that extrusion took more time and more blow-by took place.

In late 1985, Boisjoly advised his managers that if the problem was not fixed, there was a distinct chance that a shuttle mission would end in disaster.

NASA officials strongly questioned the recommendations, and asked (some say pressured) Morton Thiokol to reverse its decision.

At 58 seconds after launch, the shuttle was buffeted by high-altitude winds, the ash seal collapsed, and hot gases streamed out of the joint in a visible blowtorch-like plume that burned into the external hydrogen tank.

After President Ronald Reagan ordered a presidential commission to review the disaster, Boisjoly was one of the witnesses called.

[12] After leaving Morton Thiokol, Boisjoly founded a forensic engineering firm and was frequently invited to speak on leadership ethics.

[6] For his honesty and integrity both leading up to and directly following the shuttle disaster, Boisjoly received the Award for Scientific Freedom and Responsibility from the American Association for the Advancement of Science in 1988.