17 April 1970, 12:52:51 UTC, T plus 137:39:51.5

Omega Speedmaster Professional Chronograph worn by Jack Swigert during the Apollo 13 mission.

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 Space Technology Laboratories (TRW) VTR-10 Descent Propulsion System engine. The DPS engine produced 10,500 pounds of thrust (46.71 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.

Omega Speedmaster Professional “Moon Watch.” (Omega)

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.

Description of the Omega Speedmaster Professional Chronograph in a NASA Manual. (NASA)

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.

Astronaut Jack Swigert prepares to board the Apollo 13 Command Module. He is wearing his Omega Speedmaster Professional Chronograph on his left arm. NASA space suit technician Clyde Teague is at left. (NASA)

© 2019, Bryan R. Swopes

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9 thoughts on “17 April 1970, 12:52:51 UTC, T plus 137:39:51.5

  1. I read somewhere long ago (and haven’t been able to find it since) that one reason the course correction was required was that the original calculations assumed a cargo of moon rocks (which obviously weren’t aboard).

    1. Well yes, but also, the Lunar Module would have been undocked in Lunar Orbit prior to the Trans-Earth Injection maneuver. Its 36,200 pounds (16,420 kilograms) (at launch) far exceeded that of the rock specimens that were not carried.

      1. Bryan,

        No worries. I know from example that you strive for completeness of the story. You do fantastic work.

        BTW, I lived on Calle La Granada in the old Camarillo off-base housing for several years in the 1990s while serving as an F-14 test pilot at Point Mugu. Loved the area and the work.

        1. Thank you very much Ed. very kind of you. I wonder if we crossed paths out on the range? You were with VX-30, right? From ’84 to ’96, I was a civilian contract helicopter pilot flying for various projects out there. I would sometimes carry cinematographers and hover at around 5,000′ somewhere out by San Nicolas Island and wait for a QF-4 or an F-14 to come screaming by at Mach 36 or whatever you guys were doing, or some weird who-knows-what-that-might-have-been go zooming past. The c/o of one of the squadrons, Captain Lewis, I think, had me hover at 500′ over the numbers at the departure end of Runway 21. An allied military was launching. . . um. . . things, you know, from the beach just to the east, and Captain Lewis in his F-14 along with an F-4 wingman came blasting toward me in full afterburner, set up to pass me on either side. The captain called, “Don’t move!” and four afterburning engines passed within half-a-runway-width of me. 🙂 Oh, the good old days. 🙂

  2. CAPT Lewis was my first boss there for a short time in 1994, just before VX-30 was stood up.

    We did many interesting things, and zorched San Nicolas quite a bit in F-14Ds. Chase included drone QF4s, cruise missiles, glide weapons, and some surface-to-air projects.

    Nice to establish a connection like this. Cheers!

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