A crewman’s favourite sight: red and white

With only 3.000 metres of altitude remaining, another barometric sw itch operated to fire mortars that deployed three pilot chutes into the smooth air stream, which in turn pulled the three main parachutes out from their bays around the tunnel. These were a welcome sight to the crews and became familiar to the public as the impressive 25-metre red-and-white canopies that featured clearly on colour television coverage of an Apollo’s return to Earth.

Both the main and drogue chutes were deployed in a reefed condition; that is. they were inhibited from inflating properly for the first 10 seconds by a line that ran around the edge of the canopy in order to reduce the mechanical shock of their deployment. A timed pyrotechnic device eventually cut the reefing line to allow the canopies to fully open.

“Going to free fall.-’ called Conrad as the drogue chutes disappeared.

“There go the mains!” yelled Gordon when he saw1 them replaced by the three glorious main parachutes.

“Hang on,” said Conrad. “We’ve got all three. A good show.-’

“They’re not dereefed yet,– warned Gordon. They couldn’t slow – enough until at least two canopies were fully inflated.

“There they go,” said Bean. "They’re dereefed.”

“A couple of them are,” said Gordon. “One of them isn’t yet. There they go,” as the last reefing cord let go. “Hello, Houston; Apollo 12,” he yelled to mission control. “Three gorgeous, beautiful chutes, and we’re at 8,000 feet on the way down in great shape.”

When things are occurring rapidly all around, events can appear to happen in slow motion. Collins was watching the deployment of the parachutes intently. “It seemed to me there was quite a bit of delay before they dereefed. All three chutes were stable and all were reefed and they kept staying that way until I was just about the point where I was getting worried about whether they were ever going to dereef; then they did.”

The fully deployed main parachutes rapidly slowed the spacecraft’s descent to just

8.5 metres per second.

While the service module had been attached, spacecraft communications on the VHF system had used two scimitar antennae mounted in semicircular housings on either side of that module. For VHF communication with the recovery forces, two small antennae stored beneath the apex cover popped up automatically soon after the main parachutes had been deployed. To use them, the crew had to manually switch the output of the VHF electronics across to the ‘Recovery’ position.

Engineers wisely allowed a generous margin by designing the main parachutes to enable the CM to land safely with only two inflated canopies. This precaution was

The Apollo 15 CM descends with one of its three main parachutes uninflated. (NASA)

justified when one of the canopies that should have been lowering Endeavour. the Apollo 15 CM to the ocean, failed and uselessly streamed beside its two functioning counterparts. The impact speed only rose from 8.5 to just less than 10 metres per second. Apollo 15‘s CMP Л1 Worden noted that all three chutes had inflated properly when first deployed so blame was put on the crew s next task, their propellant dump.

The propellant tanks for the RCS thrusters still contained much highly noxious propellant, especially hydrazine fuel. As such hazardous substances could not be on board when swimmers were clambering all over the spacecraft after splashdown, the excess was dumped by firing all their thrusters until the tanks were depleted as the spacecraft descended on its three main parachutes. Before doing so. the crew – closed the cabin pressure relief valve to prevent RCS fumes from entering the cabin, and instead, released fresh oxygen from the surge tank into the cabin. When Endeavour’s thrusters fired, its oxidiser tanks had emptied before its fuel tanks so that for a few seconds, unburnt hydrazine was leaving the engines. As hydrazine can burn in air, it has been blamed for damaging the parachute. On subsequent flights, engineers biased the propellant load towards the oxidiser and altered the liming of the burn to try to avoid the problem.

The timing of Apollo 8’s arrival meant that it re-entered just before dawn over the recovery site, so when the RCS tanks started emptying as the spacecraft descended on its main parachutes, the crew were treated to a sight which, though spectacular, was somewhat worrying. ‘The ride on the mains was very smooth,’’ said Borman afterwards, "and we could not. of course, see the mains because of the darkness until we started dumping the fuel. When we dumped the fuel, we got a good chute check, but there was so much fire and brimstone around those risers that we were really glad to see the fuel dump stop.”

Once the RCS propellant tanks had been emptied, the system’s plumbing was purged with helium gas to drive out as much trace propellant as possible.

At 1,000 metres altitude, with the RCS dump completed, the cabin pressure relief valve was reset to its dump position, which allowed the cabin’s air pressure to fully equalise wfith the outside atmosphere. It was finally closed 250 metres up, to prevent water entering the cabin at impact. For a short Lime, the spacecraft would be partially submerged when it hit the water and there was a good chance that it might be upside-down for a few minutes. The parachutes suspended the command module at an angle of 27.5 degrees to the horizontal with the main hatch facing upwards. This caused the hull to hit the water ‘toe first’, in a fashion that spread the final deceleration over the longest possible time. Also, the periphery of the CM structure was formed by shaped ribs. Those opposite the hatch, where the spacecraft would contact the water first, were designed to be crushable to help to reduce the force of impaet. They were primarily intended for the undesirable contingency of a land impact but could deform to help to reduce the shock of a conventional sea landing.

The moment of Apollo 15’s splashdown. (NASA)