After checking tunnel, latches, and docking probe, the crewmen had a light workload as they coasted toward the moon. They were grateful for even such small jobs as firing the thrusters to make slight corrections in spacecraft attitude, but this was so seldom necessary they began to wonder if the jets were working. On occasion, however, when nothing was firing, the whole stack shimmied. They later speculated that this may have been caused by fuel sloshing. When making optical navigational sightings, the crew had trouble acquiring enough stars for an accurate reading. Without the optics, the men could see no stars at all for a long time. Finally, Stafford spotted a few dim orbs after he had traveled 190,000 kilometers into space. But not much navigating was needed; the course was so true that the service module propulsion system was used only once, to add 15 meters per second to their speed, at 26 hours into the voyage. This firing put the spacecraft on a lunar path that would lead the crew over the exact spot where the first landing might be made. The rest of the time the astronauts studied the flight plan, slept, ate, and beamed five excellent television transmissions back to the earth.
Stafford, Cernan, and Young were the first Apollo pilots to be free from illness during the mission, although Cernan experienced a slight vestibular disturbance. Like all their colleagues who had flown before, once they unbuckled from the couches they had a stuffy feeling in their heads. This lasted for 8 to 10 hours for Stafford and Young; Cernan gradually lost the sensation over the next two days. He practiced "cardinal head movements" that the medics thought might help overcome his slight feeling of nausea. Although he was able to do the exercise for more than four minutes at a session by the seventh day of flight, when he returned to earth he lambasted the procedure, saying it must have been designed to bring on illness rather than to alleviate it.
The crew slept well, although thruster firing bothered Cernan the first night. Later, when they were circling the moon, the men were glad that McDivitt's crew had suggested they carry a sleeping bag apiece. The spacecraft grew cold once the windows had been covered to darken the cabin for sleeping.
One major complaint the astronauts registered was about their water supply. They were supposed to chlorinate it at night; because of an error in procedures passed to them by flight control, Stafford had a double dose of chlorine when he took a drink during the first breakfast of the trip. This was unpleasant, but it posed no major problem. Something else in the water supply did. When earlier crews had complained about gas in the water system, a new water bag was designed, with a handle the crew could use to whirl the bag around to separate the gas from the water. It did not work. The gas settled to the bottom of the bag and then remixed with the water when the crew members tried to drink. The gas worried them; they could envision getting diarrhea, which would have been difficult to cope with during flight. They did have gas pains and cramps but, fortunately, nothing more.
Poor water quality may have affected their appetites, for the astronauts on this flight were not big eaters. On occasion, they skipped meals. Stafford estimated they had enough food to last for 30 days. Not all the blame could be laid on the water, however; the food was still no epicurean delight. Back on earth in early May, Donald D. Arabian, chief of the Apollo Test Division, had tried a four-day supply of their rations. Arabian claimed to be "somewhat of a human garbage can," but even he lost his desire for food on this diet. The sausage patties, for example, tasted like granulated rubber and left an unpleasant taste. With all the difficulties of preparation, Arabian added, by the third day continuing the test was a chore. He did like the items that were closest to normal table foods. Stafford's crew also found some of the newer dishes that could be eaten with a spoon quite palatable. But the men dreaded reconstituting the dehydrated meals, knowing that the water contained so much gas.
Unlike Borman's crew, which could not see the moon with the unaided eye until the spacecraft was almost upon it, Stafford's group spotted it on the second day of flight. On the earth, it looked like a waxing crescent, but Stafford and Young, with the help of earthshine, could see almost a full moon. Although the moon was much bigger at 200,000 kilometers above the earth, landmarks on the lunar surface still could not be picked out. Cernan also asked flight controllers if they thought he could really recognize the S-IVB stage 5,600 kilometers away, because that was what he thought he was seeing. The CapCom told him that the men in the control room were nodding their heads yes and that the distance between the two vehicles actually measured 7,400 kilometers.