Apollo 13

The splashdown of Apollo 13 is only a little over an hour away, and the spacecraft is now down to the final component that remains, the Command Module. The damaged Service Module is gone, as is the Lunar Module Aquarius that successfully supported them all the way back from the Moon. The tired crew of Apollo 13, Jim Lovell, Jack Swigert and Fred Haise; and the equally exhausted men in Mission Control have done everything they can to ensure that the spacecraft can make a safe return. The math says the batteries will last all the way to landing. Their trajectory is solid. Recovery forces are standing by in a global readiness to pick up the crew and render assistance to them. Families are wishing and hoping.

Should the Command Module end up splashing down unexpectedly far away from the primary recovery ship, the long range rescue aircraft can drop down survival equipment to them, including a large sea anchor that will slow down the drift of the Command Module and make it easier to reach by other recovery forces heading to its location.

The star check is one for the Entry PAD, with them sighting Antares through the optics.

Very long comm break.

17,970 kilometres to go, velocity, 5,640 m/s.

The distance to go is 16,856 km, and their speed is 5,776 m/s. With their ever-faster fall towards the Earth, they have travelled a thousand kilometres in four minutes, and gained 136 m/s in velocity.

To save power, they will make the rest of the way down without recycling the onboard atmosphere.

The data passed up for their very last entry PAD is interpreted as follows:
Purpose: Entry.
Landing target: Mid-Pacific, Primary Recovery Area
IMU gimbal angles required for trim at 0.05g: Roll, 000°; pitch, 152°; yaw, 000°.
Time of the horizon check: 142 hours, 38 minutes, 19 seconds GET.
Spacecraft pitch at horizon check: 178°. This will be a Moonset and moon-check
Predicted splashdown point (Noun 61): minus 21.66° latitude, minus 165.37° longitude.
Maximum number of g's during entry: 5.2.
Velocity at Entry Interface (400,000 feet altitude): 36,211 feet/second (meters/second).
Entry flight path angle at Entry Interface: 6.20°.
Range to go to splashdown point from 0.05g event: 1,119.7 nautical miles. To set up their EMS (Entry Monitor System) before re-entry, the crew need to know the expected distance the CM would travel from the 0.05 g event to landing. This figure will be decremented by the EMS based on signals from its own accelerometer.
Predicted inertial velocity at 0.05g event: 36,291 feet/second. This is another entry for the EMS. It is entered into the unit's Delta-V counter and will be decremented based on signals from its own accelerometer.
Time of Entry Interface: 142 hours, 40 minutes, 46 seconds GET.
Time from Entry Interface to 0.05g event: 0:30 (seconds).
Planned drag level (deceleration) during the constant g phase: 4.00g.
Time from Entry Interface until their velocity slows sufficiently to allow a circular orbit around the Earth: 02:20.
The practical implication of this is that this is the "capture point" where the CM will no longer be able to skip off the atmosphere. Since the spacecraft will already be within the Earth's sensible atmosphere at this point, drag will continue to slow the spacecraft and the return to Earth is assured.
Time from Entry Interface that the communications blackout begins: 0:19. (seconds)
Time from Entry Interface that the communications blackout ends: 03:38. (minutes and seconds)
Time from Entry Interface that the drogue parachutes will deploy: 07:59. (minutes and seconds)
Lift vector at Entry Interface: Up. Since the direction of the lift vector is towards the crew's feet, they will re-enter in a heads-down attitude.
GDC Align stars: The stars to be used for GDC Align purposes are 31 Arcturus and 33 Antares. The align angles are roll, 41°; pitch, 45°; yaw, 24°.
Comments in addition to the PAD:EMS non-exit pattern will be used. Maintain mooncheck attitude until moonset. Constant g entry is performed by maintaining roll to right. Instructions have been given on power-down should battery power become critical during reentry procedures.

Very long comm break.

Distance is now but 13,120 km, and their velocity is up to 6,331 m/s.

As Odyssey approaches very close to Earth and then enters the atmosphere, they move below the line of sight of the radio and tracking stations, hence the ARIA aircraft are needed to allow for maximum coverage at this very last phase of the mission.

Distance, 12,237 km velocity is 6,450 m/s.

To ensure that their guidance for the reentry is as accurate as possible, they update the state vector, the accelerometer data and the onboard clock.

Long comm break.

Altitude, 10,856 km; velocity, 6,732 m/s.

Comm break.

With the minutes ticking down, they are now but 9,508 km away and moving at 7,017 m/s.

Very long comm break.

The power they estimate to remain in the batteries is incidentally very close to the amount that was transferred from the LM to the Command Module, meaning that without the battery charge, they would have most likely ended up running out.

With less than half an hour to go, they are now at 7,547 km away and speeding in at 7,504 m/s.

They decide not to use the suit compressors to recirculate the air, hence saving some power. They can now make it down quite comfortably without.

Comm break.

Distance, 6,491 km; velocity, 7,831 m/s.

Jack's comment confirms that they've started the computer-guided reentry sequence by choosing Program 61. One of its displays is Noun 60, which indicates the predicted maximum g forces experienced, the predicted velocity, and the entry angle. They will go through Programs 62 and 63 before the actual reentry, still.

Noun 63 displays the range to go from Entry Interface, the predicted velocity at the time, and the time from Entry Interface.

Comm break.

Battery C was the first one brought online, supporting the Command Module RCS heating and other Main Bus A loads while the rest of the systems were powered from the Lunar Module.

Their velocity is 8,398 m/s.

Very long comm break.

Comm break.

This could be a gentle jibe, or acknowledgment of the astronauts' famous aversion towards the medical profession.

Long comm break.

A very cheeky Joe Kerwin suggests that the party could be improved by Jack Swigert passing along contact information to eligible guests. This is a clear reference to Swigert's infamous bachelor lifestyle, which was even mentioned by Jim Lovell in the Apollo mission history published later.

Lovell, from Apollo Expeditions to the Moon (NASA SP-350, 1975): "Only when we reached Honolulu did we comprehend our impact: there we found President Nixon and Dr. Paine to meet us, along with my wife, Marilyn, Fred's wife Mary (who, being pregnant, also had a doctor along just in case), and bachelor Jack's parents, in lieu of his usual airline stewardesses."

Although the PAO updates earlier mention many dignitaries and astronauts taking seats in the VIP viewing room overlooking Mission Control, it is the astronauts who have performed various crucial duties during the mission who have come into the Mission Control room itself. Wouldn't want to be anywhere else, surely.

Long comm break.

Very long comm break.

The speed of the spacecraft entering the atmosphere causes a shock wave to form a short distance ahead of the heatshield. The enormous compression of the air molecules at this point converts the energy of their motion into heat to a degree that they are ionized into plasma. This not only creates the plume of fire that will surround the spacecraft, but will also block radio waves and leave them outside radio contact for a few minutes.

As the comms blackout begins, they are just about to experience the 0.05g event - when the first hints of deceleration due to atmospheric re-entry occurs. It is at this point that the EMS display will either start automatically, or will be started manually by the crew (as is the case of Apollo 13's landing). From then on the EMS display, based on its own internal accelerometer, will use a moving Mylar scroll to display their entry profile. The digital numeric display shows their velocity. This information could be used to make a manually controlled landing should the automatic computer guidance fail. This not being the case, they are now being flown by the computer running Program 64 'Entry Post 0.05G'.

The Entry Monitoring System should have started automatically at this point. Due to the .05g light not illuminating at the predicted moment, Jack hits the switch to start it up manually.

As they hit Earth's atmosphere, the Command Module undergoes deceleration as a result of the thickening air offering resistance to the fast-moving object that is the CM. The resulting shockwave generates the fearful heat that threatens to melt down the skin of the vessel falling from space. The heat is strongest at the so-called stagnation point.

The reentry is not merely a passive event where the capsule hurtles down from space and the crew holds on and hopes for the best. The main forces affecting their trajectory are the drag generated by them hitting the thickening air with a very high speed, as well as lift produced by the hull of the spacecraft acting as a lifting wing-like surface. With the center of mass carefully positioned inside the spacecraft, the Command Module is designed to enter the atmosphere at a somewhat lopsided angle. This will create a usable lift to drag ratio (the relationship between their deceleration, and the lift provided by the air flowing around them). This way, not only will the deceleration slow them down, but the lift will also carry the blunt capsule onto their desired destination. To manipulate this further, the Command Module RCS jets are fired either automatically by the CMC or manually by the crew while consulting the EMS for information on their decceleration and estimated speed and landing location. The RCS jets are used to rotate the spacecraft around its central X axis, thus changing the direction that the lift vector is pointed. This allows them to manipulate their trajectory to a limited degree.

The EMS has an arrow-like display that indicates the needed direction for the lift vector for each situation. By manipulating the lift direction, the computer - or the crew if doing a manual re-entry, using the EMS as guidance - can control the Command Module's flight path through the atmosphere. For instance, if they are coming in too steeply, the resulting high deceleration can cause intolerable g forces upon the crew and the spacecraft. By aiming the lift vector upwards, they can keep the CM in the thinner parts of the atmosphere, reducing the deceleration on the spacecraft while also making it fly further along and thus extending its flight path. The same way, a too shallow an angle could cause them to overshoot their landing site. In extreme circumstances, the CM could even leave the atmosphere, perhaps going for an extra circle around Earth before re-entering once more. In such a situation, aiming the lift vector down would cause the spacecraft to dig into the denser atmosphere, increasing the drag and shortening their flight path. The guidance also gives them some crossrange capacity of moving their trajectory left and right, to help even further in aiming their landing spot.

A long Mylar plastic scroll is printed with the various entry patterns. Upon EMS start, a motor starts to move the scroll to provide a visual indication of the deceleration effects of their present flight path.

Ken Mattingly and John Young are prominent in this view of the astronauts waiting to hear from their comrades. CapCom Joe Kerwin has opted for a nervous puff on his pipe. Note the discarded CO₂ adapter prototype on the floor next to the console!

It has taken them longer than predicted to report in, only adding to the nervous waiting. Odyssey's unexpectedly shallow entry angle may have made the blackout period last longer than expected. Although this has been a favorite topic of speculation, the original reports do not pay any heed to it.

Long comm break.

Pyrotechnic devices are used to separate the forward heat shield - also known as the apex cover - a moment before the drogue chute deployment.

The circular compartment surrounding the docking tunnel holds the landing systems. This includes the two drogue parachutes, the three main parachutes, radio and strobe light beacons, a dye marker, and the three uprighting bags.

The apex cover is jettisoned pyrotechnically. Afterwards, pyrotechnic mortars shoot the drogues and their risers up into the air above the spacecraft before deployment. Reefers - ropes that prevent the parachute from being deployed completely at once and hence possibly be damaged - are used for eight seconds, after which pyrotechnic cutters cut these reefing lines and the chutes are allowed to open completely.

Noun 67 displays their range to go to their landing target, as well as their latitude and longitude. It would be the last thing displayed by Program 67 - 'Entry - Final Phase'. Once their chutes open, guidance is terminated and the computer goes dormant, its mission over.

At 10,000 feet (3,048 meters) the drogue chutes are released and at the same time, pilot chutes are deployed. They are little parachutes that are used to pull out the main chutes. Reefing lines prevent the main chutes from opening fully for the first 8 seconds, after which they are allowed to fully inflate for the final braking of their landing.

Comm break.

Gerry Griffin has raised his hand in a victorious thumbs up, next to Gene Kranz and and a beaming, applauding Glynn Lunney.

The remaining radio traffic and exchanges are provided via the PAO loop transcript that contained additional post-splashdown material.

Lovell, from 1970 Technical debrief: "The last thing that slipped out was the main chute after cold soaking for that time. After that, Fred fell asleep."

Stable 1 means that the Command Module is floating upright. Stable 2 would mean that a wave or a gust of wind on the parachutes has toppled them upside down. This occurred multiple times during the Apollo landings. A switch was pressed to cut the parachute free right after landing to prevent this, but it was not always on time.

Lovell, from 1970 Technical debrief: "The impact was as designed because the sea state was slow and we knifed in. It was less impact than Apollo 8 and we stayed stable I. Fred cut in on two circuit breakers and Jack jettisoned the chutes."

Haise, from 1970 Technical debrief: "I think I only had one in at the time he hit the button, but that's all it takes."

Lovell, from 1970 Technical debrief: "Everything worked exactly like the checklist worked."

Swigert, from 1970 Technical debrief: "We just went right down the checklist, item by item."

Lovell, from 1970 Technical debrief: "The only thing we forgot to do - I guess I forgot to punch to get lat-long out of the computer."

Haise, from 1970 Technical debrief: "The last time I saw, we had miss distance of 0.8 mile. the choppers asked us if we had lat-long laid out and at the time, we didn't have. It might be of interest to point out that, after we hit and had gone through this smoke and entry, we were all three sitting there on the couches, laying in that 81-degree water, blowing frosty smoke out of our mouths. It was still icy cold in the CM."

The recovery strobe beacon has activated automatically.

It is important for the rescue units to know whether the remaining Command Module RCS propellant has been dumped overboard. Should propellant remain in the system, particularly the hydrazine fuel, they might be exposed to these extremely toxic substances while approaching the spacecraft after landing.

The sea anchor will prevent the Command Module from drifting excessively. This will make all subsequent rescue efforts easier.

An inflatable flotation collar is attached by the rescue swimmers onto the circumference of the Command Module. It will provide extra security and stability during the crew recovery.

A specially designed inflatable raft is filled and attached to the flotation collar, to stand by to receive the crew from inside the Command Module.

The Command Module side hatch can be opened from the outside, as well as the inside.

The crew has been given some life jackets to wear. The normal recovery procedure would include the swimmer passing them flight suits and filtration masks to wear to prevent contamination of the recovery crew before the crew is transferred to the Mobile Quarantine Facility onboard the carrier. This is of course not needed now.

Sickly Fred gets the first ride off the sea and into the relative safety of the helicopter.

Lovell, from 1970 Technical debrief: "Egress was good and we had a good crew pickup."

This remarkable comment reveals the lengths taken to welcome the crew home - to allow them to get dressed for the occasion! The normal recovery plan would have had them get dressed in the Command Module before leaving it for the egress raft.

Comm break.

The crew steps out wearing bespoke flight suits that are adorned with NASA and Apollo 13 patches, as well as custom caps with their names. The Iwo Jima, being the primary recovery ship, would have been carrying these articles of clothing for them to wear for the landing.

Comm break.