By Matthew Kresal
The eyes of many interested in space exploration have spent recent weeks focused once more upon NASA's Kennedy Space Center in Florida. At Launch Complex 39B sits Artemis I atop the Space Launch System (SLS). The mission is intended as an uncrewed test flight to prove the flight worthiness of spacecraft and rocket alike before taking the first human beings to the Moon in over half a century. It's a mission years in the making. A faulty sensor, followed by a fuel supply line leak, led to the delay of launch from its planned August 29th launch date in front of an estimated half a million people (including the author of this article) to instead a planned date of September 27th, as of this writing.
Such test flights help pave the way for taking crews into space. Nearly fifty-five years ago, a similar mission took place for Artemis's much-vaunted predecessor, Apollo. The Apollo 6 flight would prove to be an overlooked turning point of the race to the Moon, one that could have put the goal of landing on the Moon by the decade's end into further jeopardy.
The State of Play
The spring of 1968 was a less than a glorious moment for Apollo. Eighteen months earlier, things had been looking up for NASA. The Gemini program had overtaken the Soviet lead in space flight they'd held for much of the previous decade. With the first Apollo mission scheduled for February 1967, NASA seemed to be on track to make it to the Moon by some margin.
Then came the events of January 27, 1967. A flash fire during a launch pad test had killed the crew of Apollo 1. Having exposed flaws in the Command Module's design, the fire led to an extensive re-design of the craft, postponing the first crewed Apollo flights until late 1968. With 20 months until the deadline set by President John F. Kennedy in 1961, a crewed Apollo mission was still six months away.
One bright spot was the uncrewed test flights. Three previous launches had tested Saturn rocket components and the Command Module before the fire. Following it, and after considerable delays with testing of its Moon rocket, the November 1967 Apollo 4 had proven to be a successful first flight for the 363-foot-tall Saturn V, while the January 1968 flight of Apollo 5 had been the first flight of the Lunar Module in space (ironically lifted into Earth orbit by the Saturn 1B intended for Apollo 1).
By spring 1968, NASA was ready for the Saturn V's second flight. One that would see it launch both a Command Module and the Lunar Module Test Article first into Earth orbit and then conduct a Trans-Lunar Injection (TLI) burn using the Saturn V's third stage. With that objective accomplished, the Service Module's engine would bring the Command Module back to Earth, testing one of the planned abort options in the event of an issue early in the mission.
After delays, Apollo 6's launch date became April 6, 1968.
Of Pogoing & Engines
The five F-1 rocket engines of the Saturn V's first stage roared to life at 7:00 am Eastern that morning. Clearing the tower with its white painted Command Module and beginning the journey into orbit, all seemed well. The Saturn V was performing as predicted.
Until two minutes into the flight. Even as the first stage continued its ascent, pogo oscillations began making themselves felt. A design flaw in the first stage caused the center of the five F-1 engines to bend, causing a strain on the fuel lines. This unbalancing of thrust made itself felt through the pogoing, similar to the children's toy, and sending a series of vibrations through the length of the Saturn V’s 363 foot structure. The oscillations continued as the F-1s continued burning, eventually causing the loss of a panel on the Spacecraft-Lunar Module Adapter housing the Lunar Module Test Article. When the first stage, its tanks emptied of fuel, was separated, flight controllers and engineers responsible for the Saturn V might well have breathed a sigh of relief.
If so, they did so far too soon.
The pogoing had caused issues in the upper stages of the Saturn V. Damage inside the second stage, coupled with unforeseen problems with the ignitors for its five J-2 engines, led to one of the engines receiving a premature shutdown command. A cross-connected computer wire led to that command passed on to a second engine. Thus three engines did the job intended for five. The third stage, meanwhile, was forced to burn for an additional 29 seconds to help further compensate with its sole J-2 engine. The result put the third stage with its Command and Service Module and the Test Lunar Module Article into Earth orbit.
Then came the moment for TLI. Having conducted two orbits to check that the spacecraft and third stage were ready, mission control sent the order for the J-2 engine to relight and send Apollo 6 on a trajectory toward the Moon. Now was a crucial moment, necessary for any lunar journey to be possible.
The third stage’s sole engine failed to relight.
Making the best of a bad situation situation, the team in mission control elected to repeat the earlier Apollo 4 flight. Using the Service Module's engine, Apollo 6 was put into a high orbit and brought down approaching speeds similar to a lunar return for its re-entry. Ten hours after launch, the Command Module splashed down in the Pacific Ocean, with recovery by the US Navy carrier USS Okinawa following.
The post-flight analysis would reveal much of what had gone wrong with Apollo 6's Saturn V. In its aftermath, efforts to "detune" the rocket followed on the part of an appointing “pogo task force,” preventing further violent pogoing that might injure a future crew. The cavities inside the stages using J-2 engines received a filling of helium before future launches, acting as a shock absorber to prevent damage similar to that experienced during Apollo 6. Testing firings of stages at NASA’s test site in Mississippi later that summer proved the concept as much as possible short of an actual flight.
Thanks to the effort of over a thousand NASA contractors, the flight of the next Saturn V eight months after Apollo 6 would take the crew of Apollo 8 on their historic mission around the Moon for Christmas 1968 with only very minor pogo issues. Two further crewed Apollo missions tested hardware first in Earth and then Lunar orbit in the spring of 1969. Having paved the way, the landing of Apollo 11 followed in July 1969, and seven further missions to the Moon until December 1972.
The exposure of flaws during Apollo 6's launch revealed issues in the Saturn V, some known, some not. Doing so made the rocket safer, with a resulting perfect safety record of crewed launches. Could things have gone differently that April morning in 1968?
What if the launch had gone even more wrong? The future of the Apollo program was riding on the Saturn V, the only rocket capable of getting a crew and their spacecraft beyond Earth orbit. A launch aborted in mid-flight, either through pogoing or by more extreme failures of the upper stages, would have been disastrous. While the post-Apollo 6 modifications were made with great speed and accuracy, could that have been accomplished with a less successful flight? Or would the disaster, coupled with still fresh memories of Apollo 1's tragedy, have further grounded or even ended NASA's sixties lunar ambitions?
Conversely, the launch being more successful could likewise have had devastating effects. The lack of design and system issues could have led to the next Saturn V launch, Apollo 8, suffering from many, if not all, of the same problems. Only with a crew onboard and with much publicity as the first crewed lunar flight. What the experience might have been like was re-imagined by Stephen Baxter as part of the disastrous Apollo-N mission in his novel Voyage, with the sequence dramatically dramatized in Dirk Maggs’ BBC radio adaptation. Back in December 1968, however, could the violence of the pogoing have injured, even killed, astronauts Frank Borman, Jim Lovell, or Bill Anders? Could Christmas 1968 not be remembered for their reading of Genesis and the famous Earthrise photograph but a year of tragedy finished off by the loss of the crew? Could a failure at this juncture, coupled with the Apollo 1 disaster, end Apollo for good without a lunar landing?
Such a possibility isn't without precedent. The Soviet equivalent of the Saturn V, the likewise massive N-1, had a complex and troublesome development and testing process. One made infinitely more so by the Soviet decision to forgo designing massive engines in favor of clustering small ones. The result was that despite four N-1 launches, none reached orbit, with a July 1969 test launch (shortly before Apollo 11) destroying the launch pad and causing an 18-month delay. If the Saturn V had gone the way of the N-1, the 1960s might have ended without human beings ever making the journey from the Earth to the Moon.
By an ironic twist of history, the less-than-stellar results of the Apollo 6 mission were lost among headlines under another event. As the Command Module recovery was underway in the Pacific, a shot rang out from near Lorraine Motel in Memphis, Tennessee. Fired by James Earl Ray, it mortally wounded Martin Luther King Jr., leading to days of rioting and anguish across the United States. How might the events of Apollo 6 have played out if the news cycle had been quieter and Ray had failed to take his shot?
More than a half-century later, as Artemis I and its SLS sits on the sister launch pad to that which Apollo 6 left from, the lessons of what Apollo Program Director Samuel C. Phillips called a " less than a perfect mission" remain. The importance of test flights to expose design faults and the need to work through them for the safety of future crews remains paramount among them. So too is the recognition that less than perfect missions help to define the outcome of endeavors as much as the successes. Apollo 6, after all, made it possible for three astronauts to travel to the Moon eight months after its near-catastrophic issues. A mission that might not have been without errors exposed and rectified.