17 April 1970: Because of the unusual configuration of the Apollo 13 Command Module, Service Module and Lunar Module “stack” during the coast from the Moon back to Earth, an additional, unplanned, Mid-Course Correction burn, MCC-7, had to be carried out. The damage to the Service Module prevented the use of its 21,900 pounds thrust (97.42 kilonewtons) Aerojet General Service Propulsion System engine. It was necessary to use the LM’s Bell Aerosystems Ascent Propulsion System engine. The APS engine produced 3,500 pounds of thrust (15.57 kilonewtons). The maneuver had to be carried out manually by the astronauts from the LM’s cockpit.
Mission Commander Lovell visually aligned the spacecraft with the LM’s Reaction Control System thrusters, by sighting the Earth in his window of the LM. Once aligned, LM pilot Fred Haise conducted the burn, which was timed by CM pilot Jack Swigert.
Swigert timed the burn using his NASA-issued Omega Speedmaster Professional Chronograph, a very accurate manual wristwatch.
The Mid Course Correction ignition commenced at T+137:39:51.5 and the engine was cutoff at T+137:40:13.0 (12:52:51–12:53.13 UTC), for a duration of 21.5 seconds.
MCC-7 was performed at EI-5 hours (137:39 GET). The same manual piloting technique used for MCC-5 was used for control during MCC-7. This was manual crew pitch and roll control with the TTCA and automatic yaw control by the AGS. MCC-7 was performed with LM RCS using the +X translation push button. It steepened the flight path angle at EI to -6.49 degrees. After MCC-7, the crew maneuvered the spacecraft to the SM separation attitude. The CM re-entry RCS system was activated and a firing test of the thrusters was successful.
—“Apollo 13 Guidance, Navigation, and Control Challenges” by John L. Goodman, United Space Alliance. American Institute of Astronautics AIAA 2009-6455 at Page 23.
The Omega Speedmaster Professional Chronograph is a manual-winding analog wrist watch produced by Omega, a luxury brand of Société Suisse pour l’Industrie Horlogère, (SSIH) and now a part of the SWATCH Group. The case is made of stainless steel and has a diameter of 48 millimeters (1.89 inches). The Speedmaster Professional, which is also known as the “Moon Watch,” or “Speedy” to watch collectors, features a stop watch function and three sub dials for recording hours, minutes and seconds. The chronograph has a black dial with tritium-painted hands and hour marks. The bezel has a tachymeter for calculating speed based on time. When fully wound, the Speedmaster can run for up to 48 hours. The chronograph is water resistant to a depth of 50 meters (164 feet).
The Speedmaster’s crystal is not glass, but “hesalite,” a clear, scratch-resistant plastic. There had been concern that if a crystal broke during a space flight, glass fragments could be scattered throughout the weightless environment of the spacecraft, presenting a danger to the astronauts.
NASA provided Omega Speedmaster Professional Chronographs to Gemini and Apollo Program astronauts. Each watch was engraved with NASA’s two-digit serial number, and could be equipped with an adjustable length Velcro strap which allowed the watch to be worn on the outside of the space suit. NASA also assigned an equipment part number.
Jack Swigert’s watch, p/n SEB12100039-002, was NASA’s number 69. It is in the collection of the Smithsonian Institution National Air and Space Museum, as Catalog Number 1977-1181.000. In 2016, the watch was on display at the University of Colorado.
© 2019, Bryan R. Swopesby