velocity of the engine. The only engine we had that could provide that was the service propulsion engine and it would have required dropping the lunar module. So that option was quickly deleted from our discussions.

The other option we had was to power down immediately since we were concerned about the amount of power and water the command module was using. We accepted the opportunity we had at hand and that was to do a midcourse maneuver relatively soon, get back on free return and plan a little more leisurely how we wanted to manage the remaining consumables in the lunar module. We decided to execute that at midcourse at about 61 hours and 30 minutes and address the problem of what would be our plan for the rest of the way back.

By about 2 hours from that time, we had gone through a series of discussions both in the Control Center and with the pilots in determining what our projected overall flight plan would be.

Next slide. (See fig. 8.) Very simply, after the start of the problem, we did the midcourse to free-return to the earth at about 61%1⁄2 hours. We now had a trajectory established-again it was the dark oneback to the earth. We did have a number of maneuvering opportunities in order to improve both the time it was to take to return to the earth and the area in the earth to which we would return. One of those opportunities is labeled up there, PC+2. That describes an opportunity 2 hours after pericenter, at the closest approach to the moon, which was one of the techniques that we would have used if we had to do an abort during the interim orbit. We had two midcourse corrections scheduled, midcourse 5 and midcourse 7. There is no midcourse scheduled six, because generally it occurs between those two and we did not do that in our budget scheduling.

CONSUMABLE STATUS

Next slide. (See fig. 9.) This is an important set of facts but there is a lot more that needs to be said than those facts up there. The

chart describes the amount of water, power, oxygen, and carbon dioxide removal capability we had in the lunar module at entry and what we had remaining when we jettisoned the lunar module.

One point I would like to mention is when we made our projection at about 7 hours after the problem occurred, we ended the flight with a set of consumables which were within about 2 percent of what we predicted back at 63 hours. So the view we took of the mission at 63 hours held very well.

We stuck to the plan that we had. We used only the power and the water and the oxygen that we had forecast and we were very close to predictions made almost 80 hours earlier.

The second point is that although this does show that we are running down to 28 pounds of water, we had not employed another series of procedures which could have been used to further stretch the consumables on board the lunar module. By that I mean we kept the lunar module communication system, the telemetry system, the environmental control system up all the way back. If the consumable posture we were in had worsened or if we had absorbed another failure in some of these areas like an oxygen tank, we would have had

to resort to scheduling communications times with the crew and gone on what we call a duty cycle operation, where we might turn the equipment on for 10 minutes or 20 minutes out of every hour. I only say that to give assurance that although we were probably within 12 hours to 24 hours of running out of our most critical consumable, which was water, had we proceeded into this other set of procedures entailing duty cycling the communications gear on board, we probably could have stretched that further.

The third point I would make was that with the lunar module environmental control system running full time, we knew that we would deplete the canisters in the lunar module which are used to remove the carbon dioxide from the air for the astronauts to breathe. We knew we had to find some way to use the CSM canisters in the module. There were a number of ways to do that. We finally selected the method represented by this configuration on my right. This is a canister designed to withdraw carbon dioxide by drawing the oxygen through it. This is a hose from the lunar module (indicating). This is connected to the lunar module ship and the fan; the compressor in the lunar module sucks the oxygen through there and cleanses it as it comes through.

That plan having been agreed upon, we then had a number of options for the maneuver that we were to perform 2 hours after passing behind the moon. The options were about three. One, we could have decided to try to come back in the absolute minimum time by dropping the service module, thus getting rid of about 50,000 pounds of weight. This would have enabled us to get a lot. more velocity with the LM engine and would have enabled us to return to earth sooner. However, we discarded that on the basis of the unknown thermal environment, the command module heat shield and the command module control system, propellant and jet control system we use for entry, would be in if we jettisoned the service module. Those systems are essentially at the lower end of the module and they are protected by the command module being attached. To remove it would have endangered the all-important heat shield for entry.

The second option we would have had would have been to try to land in the Atlantic. We would have been able to land about 9 hours earlier than we did. The problem with that was we would have used essentially all the propellants in the descent tank to accomplish that and it would not have allowed us to make the midcourse corrections subsequent to that posture. Second, there was the recovery posture we were in in the Atlantic. You know there was a fair amount of work going on to see what would have been arranged in the Atlantic. We would have certainly had a lot of aircraft and people to recover the module. There were a lot of ships going in the area. However, that option was also discarded because we would have run the lunar module propellant out. We chose to go on to the Pacific at a spashdown time of 79 hours, to almost 143 hours.

(See fig 10).

79:28

94:00

100:00

105:18

126:15

133:35

142:54

SUMMARY OF EVENTS (CONCL'D 2 OF 2)

DECISION, EXECUTION OF MANEUVER 2 HOURS AFTER CLOSEST APPROACH
TO MOON (PC+2)

CARBON DIOXIDE SUCCESSFULLY REMOVED WITH CSM CANISTER FIX

SIMULATOR-VERIFIED CHECKLIST READ UP FOR MCC BURN AT 105:18
MIDCOURSE CORRECTION FOR ENTRY CORRIDOR

SIMULATOR-VERIFIED CHECKLIST READ UP FOR ENTRY PHASE

BEGIN LUNAR MODULE POWER UP FOR ENTRY PREPARATIONS

SPASHDOWN

Figure 10

The carbon dioxide was removed from the canister here. We used up what sounded to the outside world like more numbers. We read up a checklist which was verified in the simulator by other sets of astronauts just running around the clock to perform the midcourse corrections we performed with the secondary guidance system. We had to aline it with the unique power saving technique that we had to discuss with Captain Lovell. It worked very well. The midcourse was burned at 105:18 approximately. The other checklist was read up at about 126 hours. You now recall at this stage of the flight, we were approaching the entry phase where we had, one, a lunar module with us that we wanted to use as long as possible. Two, we had a service module. which was essentially unpowered which we had to jettison. We also at some point had to jettison the lunar module. Third, we had a very critical or short supply of power in the command module and we could only stand a short number of hours in the command module with the pilots getting the vehicle ready for entry before we actually did enter. We also wanted to keep the tasks and the time length for the astronauts as simple as we possibly could. Those kinds of thoughts were in the work that we did, the check lists we got for the simulator and the checklists we read up. The other powers were for entry and splashdown.

SEQUENCE FOR ENTRY

Next slide (fig. 11) gives you an idea of the sequence for entry. We have the LM power up; the midcourse correction. We jettisoned the service module behind us. We have the command service module power up. This time we transferred the equipment from the lunar module to the command module. Later we jettisoned the lunar module. The entry altitude and attitude was reached and the landing was as predicted at 142:54.