Apollo Expeditions to the Moon: Chapter 13

Apollo Expeditions to the Moon

CHAPTER 13.3

FIFTEEN MINUTES OF POWER LEFT

With only 15 minutes of power left in the CM, CapCom told us to make our way into the LM. Fred and I quickly floated through the tunnel, leaving Jack to perform the last chores in our forlorn and pitiful CM that had seemed such a happy home less than two hours earlier. Fred said something that strikes me as funny as I read it now: "Didn't think I'd be back so soon." But nothing seemed funny in real time on that 13th of April, 1970.

Blast-gutted service module was set adrift from the combined command module and lunar module just four hours before Earth reentry. Mission Control had insisted on towing the wrecked service module for 300,000 miles because its bulk protected the command module's heat shield from the intense cold of space. The astronauts next revived the long-dormant command module and prepared to leave their lunar module lifeboat.

There were many, many things to do. In the first place, did we have enough consumables to get home? Fred started calculating, keeping in mind that the LM was built for only a 45-hour lifetime, and we had to stretch that to 90. He had some data from previous LMs in his book -- average rates of water usage related to amperage level, rate of water needed for cooling. It turned out that we had enough oxygen. The full LM descent tank alone would suffice, and in addition, there were two ascent-engine oxygen tanks, and two backpacks whose oxygen supply would never be used on the lunar surface. Two emergency bottles on top of those packs had six or seven pounds each in them. (At LM jettison, just before reentry, 28.5 pounds of oxygen remained, more than half of what we started with.)

We had 2181 ampere hours in the LM batteries. We thought that was enough if we turned off every electrical power device not absolutely necessary. We could not count on the precious CM batteries, because they would be needed for reentry after the LM was cast off. In fact, the ground carefully worked out a procedure where we charged the CM batteries with LM power. As it turned out, we reduced our energy consumption to a fifth of normal, which resulted in our having 20 percent of our LM electrical power left when we jettisoned Aquarius. We did have one electrical heart-stopper during the mission. One of the CM batteries vented with such force that it momentarily dropped off the line. We knew we were finished if we permanently lost that battery.

The jettisoning of elements during the critical last hours of the Apollo 13 mission is shown in this sequence drawing. When the lifesaving LM was shoved off by tunnel pressure about an hour before splashdown, everyone felt a surge of sentiment as the magnificent craft peeled away. Its maker, Grumman, later jokingly sent a bill for more than $400,000 to North American Rockwell for "towing" the CSM 300,000 miles.

Water was the real problem. Fred figured that we would run out of water about five hours before we got back to Earth, which was calculated at around 151 hours. But even there, Fred had an ace in the hole. He knew we had a data point from Apollo 11, which had not sent its LM ascent stage crashing into the Moon, as subsequent missions did. An engineering test on the vehicle showed that its mechanisms could survive seven or eight hours in space without water cooling, until the guidance system rebelled at this enforced toasting. But we did conserve water. We cut down to six ounces each per day, a fifth of normal intake, and used fruit juices; we ate hot dogs and other wet-pack foods when we ate at all. (We lost hot water with the accident and dehydratable food is not palatable with cold water.) Somehow, one doesn't get very thirsty in space and we became quite dehydrated. I set one record that stood up throughout Apollo: I lost fourteen pounds, and our crew set another by losing a total of 31.5 pounds, nearly 50 percent more than any other crew. Those stringent measures resulted in our finishing with 28.2 pounds of water, about 9 percent of the total.

Carbon dioxide would poison the astronauts unless scrubbed from the lunar module atmosphere by lithium hydride canisters. But the lunar module had only enough lithium hydride for 4 man-days - plenty for the lunar landing but not the 12 man-day's worth needed now. Here Deke Slayton (center) explains a possible fix to (left to right) Sjoberg, Kraft, and Gilruth. At left is Flight Director Glynn Lunney.

Fred had figured that we had enough lithium hydroxide canisters, which remove carbon dioxide from the spacecraft. There were four cartridge from the LM, and four from the backpacks, counting backups. But he forgot that there would be three of us in the LM instead of the normal two. The LM was designed to support two men for two days. Now it was being asked to care for three men nearly four days.