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Sat Apr 13, 2019, 07:21 AM

49 Years Ago Today; "Houston, we've had a problem..."


The Apollo 13 crew photographed the Moon out of the Lunar Module overhead rendezvous window as they passed by. The deactivated command module is visible.

Apollo 13 was the seventh manned mission in the Apollo space program and the third intended to land on the Moon. The craft was launched on April 11, 1970 from the Kennedy Space Center, Florida, but the lunar landing was aborted after an oxygen tank exploded two days later, crippling the service module (SM) upon which the command module (CM) had depended. Despite great hardship caused by limited power, loss of cabin heat, shortage of potable water, and the critical need to make makeshift repairs to the carbon dioxide removal system, the crew returned safely to Earth on April 17, 1970, six days after launch.

The flight passed the far side of the Moon at an altitude of 254 kilometers (137 nautical miles) above the lunar surface, and 400,171 km (248,655 mi) from Earth, a spaceflight record marking the farthest humans have ever traveled from Earth. The mission was commanded by James A. Lovell with John L. "Jack" Swigert as Command Module Pilot and Fred W. Haise as Lunar Module Pilot. Swigert was a late replacement for the original CM pilot Ken Mattingly, who was grounded by the flight surgeon after exposure to German measles.



Mission Operations Control Room during Apollo 13's fourth television transmission, on the evening of April 13, 1970. Lunar Module Pilot Fred Haise Jr. is seen on the screen.

Approaching 56 hours into the mission, Apollo 13 was approximately 205,000 miles (330,000 km) from Earth en route to the Moon. Approximately six and a half minutes after the end of a live TV broadcast from the spacecraft, Haise was in the process of closing out the LM, while Lovell was stowing the TV camera. Houston flight controllers asked Swigert to turn on the hydrogen and oxygen tank stirring fans in the service module, which were designed to destratify the cryogenic contents and increase the accuracy of their quantity readings. Two minutes later, the astronauts heard a "pretty large bang", accompanied by fluctuations in electrical power and the firing of the attitude control thrusters; the crew initially thought that a meteoroid might have struck the lunar module. Communications and telemetry to Earth were lost for 1.8 seconds, until the system automatically corrected by switching the high-gain S-band antenna, used for translunar communications, from narrow-beam to wide-beam mode.

Immediately after the bang, Swigert reported a "problem", which Lovell repeated and clarified as a "main B bus undervolt", a temporary loss of operating voltage on the second of the spacecraft's main electrical circuits. Oxygen tank 2 immediately read quantity zero. About three minutes later, the number 1 and number 3 fuel cells failed. Lovell reported seeing out the window that the craft was venting "a gas of some sort" into space. The number 1 oxygen tank quantity gradually reduced to zero over the next 130 minutes, entirely depleting the SM's oxygen supply.

Because the fuel cells generated the command and service module's electrical power by combining hydrogen and oxygen into water, when oxygen tank 1 ran dry, the remaining fuel cell finally shut down, leaving the craft on the command module's limited-duration battery power and water. The crew was forced to shut down the CM completely to save this for reentry, and to power up the LM to use as a "lifeboat". This situation had been suggested during an earlier training simulation, but had not been considered a likely scenario. Without the LM, the accident would certainly have been fatal.

Crew survival and return journey
The damage to the service module made safe return from a lunar landing impossible, so Lead Flight Director Gene Kranz ordered an abort of the mission. The existing abort plans, first drawn up in 1966, were evaluated; the quickest was a Direct Abort trajectory, which required using the service propulsion system (SPS) engine to achieve a 6,079-foot-per-second (1,853 m/s) delta-v. Although a successful SPS firing at 60 hours ground elapsed time (GET) would land the crew one day earlier (at 118 hours GET, or 58 hours later), the large delta-v was possible only if the LM were jettisoned first, and since crew survival depended on the LM's presence during the coast back to Earth, that option was "out of the question." An alternative would have been to burn the SPS fuel to depletion, then jettison the service module and make a second burn with the LM Descent Propulsion System (DPS) engine. It was desired to keep the service module attached for as long as possible because of the thermal protection it afforded the command module's heat shield. Apollo 13 was close to entering the lunar sphere of gravitational influence (at 61 hours GET), which was the break-even point between direct and circumlunar aborts, and the latter allowed more time for evaluation and planning before a major rocket burn. There also was concern about "the structural integrity of the Service Module," so mission planners were instructed that the SPS engine would not be used "except as a last-ditch effort."

For these reasons, Kranz chose the alternative circumlunar option, using the Moon's gravity to return the ship to Earth. Apollo 13 had left its initial free-return trajectory earlier in the mission, as required for the lunar landing at Fra Mauro. Therefore, the first order of business was to re-establish the free-return trajectory with a 30.7-second burn of the DPS. The descent engine was used again two hours after pericynthion, the closest approach to the Moon ("PC+2 burn", to speed the return to Earth by 10 hours and move the landing spot from the Indian Ocean to the Pacific Ocean. A more aggressive burn could have been performed at PC+2 by first jettisoning the service module, returning the crew in about the same amount of time as a direct abort, but this was deemed unnecessary given the rates at which consumables were being used. The 4-minute, 24-second burn was so accurate that only two more small course corrections were subsequently needed.

Astronaut John L. Swigert, at right, with the "mailbox" rig improvised to adapt the command module's square carbon dioxide scrubber cartridges to fit the lunar module, which took a round cartridge

The "mailbox" at Mission Control during the Apollo 13 mission

Considerable ingenuity under extreme pressure was required from the crew, flight controllers, and support personnel for the safe return. The developing drama was shown on television. Because electrical power was severely limited, no more live TV broadcasts were made; TV commentators used models and animated footage as illustrations. Low power levels made even voice communications difficult.

The lunar module consumables were intended to sustain two people for a day and a half, not three people for four days. Oxygen was the least critical consumable because the LM carried enough to repressurize the LM after each surface EVA. Unlike the command and service module (CSM), which was powered by fuel cells that produced water as a byproduct, the LM was powered by silver-zinc batteries, so electrical power and water (used for equipment cooling as well as drinking) were critical consumables. To keep the LM life-support and communication systems operational until reentry, the LM was powered down to the lowest levels possible. In particular, the LM's Abort Guidance System was used for most of the coast back to Earth instead of the primary guidance system, as it used less power and water.

Availability of lithium hydroxide (LiOH) for removing carbon dioxide presented a serious problem. The LM's internal stock of LiOH canisters was not sufficient to support the crew until return, and the remainder was stored in the descent stage, out of reach. The CM had an adequate supply of canisters, but these were incompatible with the LM. Engineers on the ground improvised a way to join the cube-shaped CM canisters to the LM's cylindrical canister-sockets by drawing air through them with a suit return hose. NASA engineers referred to the improvised device as "the mailbox".

Another problem to be solved for a safe return was accomplishing a complete power-up from scratch of the completely shut-down command module, something never intended to be done in-flight. Flight controller John Aaron, with the support of grounded astronaut Mattingly and many engineers and designers, had to invent a new procedure to do this with the ship's limited power supply and time factor. This was further complicated by the fact that the reduced power levels in the LM caused internal temperatures to drop to as low as 4 C (39 F). The unpowered CM got so cold that water began to condense on solid surfaces, causing concern that this might short out electrical systems when it was reactivated. This turned out not to be a problem, partly because of the extensive electrical insulation improvements instituted after the Apollo 1 fire.

The last problem to be solved was how to separate the lunar module a safe distance away from the command module just before reentry. The normal procedure was to use the service module's reaction control system (RCS) to pull the CSM away after releasing the LM along with the command module's docking ring, but this RCS was inoperative because of the power failure, and the useless SM would be released before the LM. To solve the problem, Grumman called on the engineering expertise of the University of Toronto. A team of six UT engineers, led by senior scientist Bernard Etkin, was formed to solve the problem within a day. The team concluded that pressurizing the tunnel connecting the lunar module to the command module just before separation would provide the force necessary to push the two modules a safe distance away from each other just prior to reentry. The team had 6 hours to compute the pressure required, using slide rules. They needed an accurate calculation, as too high a pressure might damage the hatch and its seal, causing the astronauts to burn up; too low a pressure would not provide enough separation distance of the LM. Grumman relayed their calculation to NASA, and from there in turn to the astronauts, who used it successfully.

Reentry and splashdown

Apollo 13 splashes down in the South Pacific on April 17, 1970

As Apollo 13 neared Earth, the crew first jettisoned the service module, using the LM's reaction control system to pull themselves a safe distance from it, instead of the normal procedure which used automatic firing of the SM's RCS. They photographed it for later analysis of the accident's cause. It was then that the crew were surprised to see for the first time that the entire Sector 4 panel had been blown off. According to the analysts, these pictures also showed the antenna damage and possibly an upward tilt to the fuel cell shelf above the oxygen tank compartment.

Finally, the crew jettisoned the lunar module Aquarius using the above procedure worked out at the University of Toronto, leaving the command module Odyssey to begin its lone reentry through the atmosphere. The reentry on a lunar mission normally was accompanied by about four minutes of typical communications blackout caused by ionization of the air around the command module. The blackout in Apollo 13's reentry lasted six minutes, which was 87 seconds longer than had been expected. The possibility of heat-shield damage from the O2 tank rupture heightened the tension of the blackout period.

Odyssey regained radio contact and splashed down safely in the South Pacific Ocean, 2138′24″S 16521′42″W, southeast of American Samoa and 6.5 km (3.5 nmi) from the recovery ship, USS Iwo Jima. The crew was in good condition except for Haise, who was suffering from a serious urinary tract infection because of insufficient water intake. To avoid altering the trajectory of the spacecraft, the crew had been instructed to temporarily stop urine dumps, which forced them to invent ways of storing all urine for the rest of the flight.

The lunar module and service module reentered the atmosphere over the South Pacific between the islands of Fiji and New Zealand.

Mission Control celebrates the successful splashdown of Apollo 13

The crew of Apollo 13 on board the USS Iwo Jima following splashdown


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Reply 49 Years Ago Today; "Houston, we've had a problem..." (Original post)
Dennis Donovan Apr 13 OP
JoyBugaloo Apr 13 #1
MarianJack Apr 13 #2
bobbieinok Apr 13 #3
paleotn Apr 13 #4

Response to Dennis Donovan (Original post)

Sat Apr 13, 2019, 08:21 AM

1. Thank you for posting this!

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Response to Dennis Donovan (Original post)

Sat Apr 13, 2019, 08:25 AM

2. I was almost 15 at the time.

I went to an anti Vietnam war demonstration in Washington that day. My mother, who was still pro war at the time, was SO pissed at me when I got home because she equated going to the protest as being, among other things, disrespectful to the astronauts. We had one hell of a fight over that.

She didn't change her mind about the war until I was almost 17...go figure.


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Response to Dennis Donovan (Original post)

Sat Apr 13, 2019, 08:45 AM

3. I remember the extreme worry. The whole world was paying attention!

My son was almost a year old.

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Response to Dennis Donovan (Original post)

Sat Apr 13, 2019, 09:54 AM

4. Wow! 49 years....

I was a precocious 6 in the spring of '70 and had been glued to the TV for every broadcast I could watch from Apollo 11 on.

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