Apollo 13

This is Apollo Control at 96 hours. At the present time the discussions here in the Mission Control Room about the midcourse correction, are beginning to firm up toward a definite time, heretofore, the times under discussion were 10 ... 104 hours and 113 hours. Right now it's shaping up to look like we'll do the midcourse correction to bend the trajectory back to the entry corridor with a vacuum perigee of around 20 nautical miles. The burn would be at 105:30 ground elapsed time; descent propulsion system burn 7.6 feet per second; 14.8 seconds duration. This burn would be ... is being timed to coincide with the estimated time that the burst disk in the supercritical helium in the lunar module will give way, so that the effects on the trajectory would be lessened in having both the burn and any perturbations in the trajectory come at the same time. The vent from the supercritical helium now is non-propulsive, that is, there's a T in the line and it should cancel out any Delta-V added by the venting, however, there's somewhat ... a certain amount of uncertainty in this regard. At any rate, having the burn and the burst disk event near the same time frame gets both of these events out of the way and it gives a good long bit of tracking to pin down what the new trajectory will be. We're now showing 0.1 millimeters in mercury partial pressure carbon dioxide in the lunar module. So, apparently the shade tree engineering using the Command Module lithium hydroxide canisters in the plastic bag and the suit hoses, is working out all right. And at 96 hours, 3 minutes ground elapsed time, this is Apollo Control."

This is Apollo Control at 96 hours 15 minutes ground elapsed time. There's some white sacks with sandwiches being brought into the room by a young lady. Getting back to midcourse correction in the trans-Earth coast phase here in Apollo 13, the current thinking is to do a descent propulsion system maneuver at about 105 hours 30 minutes ground elapsed time 7.6 feet per second. The burn time of 14.8 seconds. Apollo 8, back in December 1968, did a similar burn in about a similar time. However, it was a Command Module or service module RCS burn of 4.8 seconds ... 4.8 feet per second at 103:58. The burn is intentionally timed to the estimated time frame in which the lunar module super critical helium burst disc is supposed to let go. It's not anticipated that this burst disc, the venting of the super critical helium will cause any perturbations to the trajectory and that vent outlet has a T on it and thereby cancels out any propulsion. It's called an non-propulsive vent. Having the burn and the burst disc take place in the same time frame will allow the tracking after these events to provide a good handle on spacecraft trajectory for refining the ... into the recorder and calculations towards entry. There's quite a bit propulsion available out of the spacecraft up to some 28 feet per second still available with the vehicle that weighs in the neighborhood of 87,000 pounds. For the small RCS thrusters on the Lunar Module, 28 feet per second available out of that system. Still a great deal of propulsion available in the descent propulsion system and one as yet untapped system. That's the ascent propulsion engine in the upper stage of the Lunar Module which likely won't even be used at all. Rather quiet now in the air to ground circuit. Taking a lunch break here in Mission Control. Sandwiches were brought in as mentioned earlier and most of the people are taking this opportunity to have a mid-afternoon snack. At 96 hours 18 minutes and standing by, this is Apollo Control.

This is Apollo Control 96 hours 53 minutes ground elapsed time. Spacecraft communicator Vance Brand has relieved Joe Kerwin at that post, the spacecraft communicators on a different shift schedule than the rest of the Flight Controllers. To go back again, once over lightly with the midcourse correction upcoming. Repeat the current thinking is to do a midcourse correction burn at 105 hours 30 minutes ground elapsed time, the descent propulsion system of the Lunar Module would do the burn ... the velocity change would be 7.6 feet per second. This burn would place the Apollo 13 spacecraft back on the entry corridor for entry into the South Central Pacific. Another aspect of timing the maneuver at 105:30 instead of the earlier discussed 104 hours, is that it is expected that super-critical helium burst disk in the Lunar Module descent stage is likely to let go at about ... about this time frame 105:30 and by doing the maneuver and the ... and having the burst disk rupture at this time would put both of these events close together so it wouldn't be expecting the burst disk to go which in turn may or may not affect the trajectory as far as tracking concerns, so this would get them both behind and an accurate tracking state vector of the spacecraft could be measured. It's expected that the new thinking on the midcourse correction will be passed up to the crew before too long.

The midcourse correction burn made earlier at 79 hours and 28 minutes transferred Apollo 13 from a hybrid nonfree return trajectory to a free return trajectory. The next maneuver at pericynthion plus two hours transferred back from one free return to another with a change in the landing point and landing time. We're continuing to stand by. The velocity now showing 4,068 feet per second as Apollo 13 continues to accelerate, now that it is back into the Earths sphere of influence. Some 172,937 miles out from Earth. At 96 hours 57 minutes ground elapsed time and standing by, this is Apollo Control.

This is Apollo Control at 98 hours 49 minutes. EECOM says that repress package pressure is good, it's about where he would expect to see it. He was pleased with that 820 pounds per square inch reading. The repress package consists of three one pound oxygen bottles, in the Command Module. It's used to quickly repressurize the Command Module after it has been depressurized. The name repress comes from repressurization. In addition to these three one pound bottles of oxygen in the Command Module, the surge tank contains an additional three pounds of oxygen for the Command Module. Flight Director, Gerry Griffin, and his Gold team have relieved Glenn Lunney and his Black team. He has no estimate yet on the time for the change of shift briefing. We'll continue to stand by for live air-ground transmission.

This is Apollo Control at 99 hours, 1 minute. Apollo 13 now is 167,992 nautical miles from Earth. Velocity 4,154 feet per second. As you heard on air-ground, we do intend to ... play the ignition time for the midcourse correction rather loosely. Basing it on the predicted supercritical helium tank burst disk going as the pressure in that tank rises to the point where it will burst the disk and vent the helium overboard. However, we burned the descent propulsion engine which is pressurized by this helium enough times now that ... we have enough helium entrapped in the propellant tanks ... known as blowdown capability or ullage capability, for 800 feet per second Delta-V so there will be no problem in ... in losing the ... the remainder of the helium from the helium tank. Based on a prediction of 106 hours at the present time for the helium tank relieving, we would expect to do the burn somewhere around 105-1/2 hours. If the helium tank relieves earlier than predicted, we would do the burn as quickly after that as operationally possible. We'd like to keep ... to do the burn within a half an hour of the tank pressure relieving, if possible. This is a non-propulsive venting, but it will probably cause some attitude excursions, and they would like to have the spacecraft powered up with the crew in control of the ... Aquarius when the venting occurs. The midcourse correction itself will be a straight forward maneuver, estimated right now that it will be on the order of 7 to 8 feet per second. About a 15 second burn, using ... the descent propulsion system. We'll use the AGS or the secondary guidance system backup guidance system of the Lunar Module for this burn. The AGS takes less power than PGNS and we would like to hold the power usage down. And this burn is well within the capability of the AGS as far as accuracy. We will probably burn on time rather than velocity achieved. It will be done with the throttle in the minimum position. The Flight Director Gerry Griffin has been taking a status report from his Flight Controllers. The CO₂ lithium hydroxide procedure worked out with the hoses and the ... the makeshift method to run the cabin air pass the Command Module, lithium hydroxide canisters appears to be working very well. The CO₂ in the cabin is now up to only 2/10 of a ... of millimeters of mercury. Based on present usage rates we have enough water to last until an elapsed time of 165 hours 14 minutes. The water rate will go up slightly during ... during burns. We expect to use about 7 pounds of water for midcourse. We have enough oxygen to last until an elapsed time of 273 hours 27 minutes, under the present usage rates. And enough electrical power for 209 hours, 8 minutes. We calculate we have enough lithium hydroxide for 100 ... for 164 hours from now, that is not a GET time, we have enough remaining for 164 hours. All of these consumables are well above what is required for a 142 hours elapsed time landing.

This is Apollo Control at 99 hours 17 minutes, Flight Director Glynn Lunney has left the Control Center for the Building 1 Auditorium and the News Conference. I repeat, Flight Director Glynn Lunney is on his way to the MSC Auditorium for the Change of Shift News Conference.