Apollo’s do-or-die: Last 100 feet to moon key to Apollo fate
By Marvin Miles, Aerospace Writer – Los Angeles Times (July 16, 1969)
HOUSTON — Success and disaster will hang in the balance for Apollo 11 Sunday during the last 100 feet of the descent to the moon, and again Monday in the first few seconds of the launch back into lunar orbit.
Near touchdown, the lunar module (LM) could run out of time for an emergency abort maneuver in case of rocket failure. The descent engine must function perfectly to prevent a crash or a damaging impact and the astronauts’ final decision on the safety of the landing site must be correct.
During the launch from the moon 21 hours, 27 minutes later, the first 10 seconds should indicate whether the crew will die on the surface or escape into lunar orbit, although the ascent engine must fire for 438 seconds to reach orbit.
There will be other critical periods: the cautious two-hour, 40-minute, exploration of the moon’s surface and the rocket burn that must ram the command ship free of lunar gravity Monday night for the return to earth.
But landing on the moon and blasting away from it — particularly the few heartbeats nearest the surface in each maneuver — will be extremely critical for the Apollo 11 crew.
No backstop for rocket
Normally the later escape from lunar orbit by the command module would be considered as crucial as the launch from the moon—and for good reason, there is no backstop for rocket engine failure in either case.
If the two landing astronauts should be stranded on the lunar surface or if three crewmen should be locked in orbit around the moon there will be no hope of escape or rescue.
Astronauts Neil A. Armstrong and Edwin E. Aldrin Jr., would face death within about 24 hours if they could not launch from the surface. Or, they would crash within minutes if their ascent rocket failed midway in its long burn.
Engine failure at the point of transearth injection (after the landing team has returned to the command module) would mean the spacecraft could not leave moon orbit and would doom all three astronauts, including Michael Collins, to perish in a 12-day agony of helplessness.
Or if their service rocket should fail to accelerate them to the minimum necessary speed for lunar escape—a burn of at least 109 to 120 seconds—their command ship would falter, fall back into lunar orbit and perhaps crash into the moon.
Yet despite the identical hazards of possible engine failure, the deorbit maneuver is regarded as less critical than the lunar launch because of the flawless performance to date of the big Aerojet-General service rocket that is to hurl Apollo home.
Tested thousands of times on earth without failure, the rocket also has blasted its 20,500 pounds of thrust 25 times in space bursts of a half-second to more than six minutes and accelerated both Apollo 8 and Apollo 10 safely home from the moon.
While the ascent rocket in the landing craft also has been tested exhaustively on earth and several times in space, it has yet to burn in a maneuver where a failure would spell catastrophe for Apollo crewmen.
A critical mission
Why is landing on the moon considered so critical? Because this maneuver is a first in space flight experience. It will involve crucial judgment and quick decisions in an extremely hostile environment that itself could cause a catastrophe.
True, in case of engine failure, Armstrong and Aldrin could abort their approach at any time down to within 100 feet of touchdown by dumping LM’s descent stage and firing their ascent rocket to climb back into lunar orbit.
But this will not be done unless the descent engine (or another vital system) fails or unless the terrain within LM’s landing zone is for some reason too menacing for a safe touchdown.
There is always the chance, however, that the descent engine might falter too low to permit abort staging and cause a crash or a hard landing that could damage the LM and perhaps maroon its crew.
Here again, the chance is remote. The throttleable engine has been tested 3,781 times on earth and fired eight times in space, including three burns on Apollo 9 and two on Apollo 10 near the moon.
But there is also the possibility that one (or more) of the LM’s four landing pads might settle on a rock or dip into a crater deep enough to give the landing craft a tilt angle that could endanger the launch.
However, the bulbous lunar module has been designed to accept rough landing conditions.
But with all the design precautions, all the computer calculations, all the study and thought, the testing and training, mission officials such as Christopher Kraft, director of flight operations, know only too well that the unexpected can happen.
At the time of the Apollo 10 mission in May, Kraft said there was a 90% chance that Apollo 11 would make the landing this month, and a 100% chance the United States would achieve the historic goal before New Year’s Day.
“We’ve learned everything we can down, to the powered descent,” he said. “Now we have to learn if we have the guidance equations designed right. We have to learn if the descent engine will throttle and perform properly.
“Is the landing radar going to work in its interface with the computer? Will the crewmen be able to see where they are relative to their altitude over the moon? Will they be able to pick out a reasonable landing site?
“Then there is the whole question of astronaut mobility in the one-sixth gravity of the moon… but the only way to find out all these things now is to go do them, perform the total mission.”
Like the low passes flown on the Apollo 10 mission, the descent of Apollo 11’s lunar module — call sign Eagle — will start when the docking latches mooring the landing craft to the command ship Columbia are released at 60 nautical miles and a speed of 3,600 m.p.h.
This is scheduled at 10:50 am. PDT Sunday after Armstrong and Aldrin have crawled through a connecting tunnel to ready LM for the descent, including extension of the awkward spacecraft’s quadruped landing gear.
The undocking should occur just before LM comes in view around the eastern edge of the moon, circling the lunar equator from right to left as seen from earth.
In undocking, the physical release of spring-loaded mechanisms will separate LM and the command ship slowly, at about half a foot per second.
Then, at a range of 40 feet, the two spacecraft will orbit in formation while the lunar module is rotated slowly for inspection of its landing gear by Collins, alone in the Apollo command craft.
Thirty minutes after undocking, Collins will burn the command ship’s Continued from 12th Page thrusters for a slight downward push (2.5 feet per second) and increase the distance separating the two spacecraft to 13,120 feet.
Half an orbit later, over the far side of the moon, ILM’s descent engine will be triggered for 28.5 seconds to slow the spacecraft to 3,600 m.p.h. and into a transfer orbit that will reach down to a perilune, or low point, of 50,000 feet.
On completion of the first descent firing, called the DOI burn (for descent orbit insertion), the LM will coast backward down to nine miles above the Sea of Fertility and 260 nautical miles short of the landing zone.
Landmark navigation
If a problem should develop at this point, Armstrong and Aldrin have only to continue their orbit back up to 60 miles for a quick rendezvous with the Apollo command ship.
But if Mission Control authorizes a “go”, the crew will trigger what is called the powered descent initiation, a 12-minute burn to slow LM through a long, shallow arc to the landing site on the Sea of Tranquility.
At a point 35,000 feet above the surface and about 100 miles from the landing site, the astronauts will rotate to a windows-up attitude so LM’s vital landing radar can come into play at about 02,000 feet.
Bouncing a continuous stream of signals off the surface and back, the radar will judge the space- craft’s diminishing height and through an on-board. computer, adjust its attitude jets and control its thrust, allowing for fuel consumption and decreasing weight.
Final assessment
The approach should become vertical at about 100 feet, and at this point, the descent can be shaded into hovering flight for about two minutes, if required, for final assessment of the landing site.
If Armstrong goes for the landing, 68-inch whisker probes extending beneath three of the L’s four landing pads will touch the moon first and signal the crew with a light in the cabin.
Armstrong will shut down the descent engine within one second and the robot-like landing craft should touch down at an impact speed of about 3 feet per second of slightly faster than 2 m.p.h., with virtually no horizontal velocity.
Climax to mission
In the hours after they receive authorization for the lunar stay, the two astronauts will eat, rest for four hours, eat again, then don their life support backpacks for the surface exploration that will climax the epic mission.
Not until 11:17 p.m. PDT Sunday will Armstrong set foot on the moon, with Aldrin following about 25 minutes later.
The whole 2-hour 40- minute span of extravehicular activity will be a tense period for the moon explorers, the controllers here and the world at large for the dangers are obvious.
Two men encased in pressurized spacesuits — walking spacecraft — will work in an incredible environment that could bring quick death if a system failure should occur, if a pressure suit should be ruptured by a fall, if unexpected physical disability should develop, if any one of many unknowns should happen.
Once back in their spacecraft, the astronauts will eat, rest again for four hours, eat once more, then prepare the LM for the lunar launch.
At the time of liftoff, the command ship, orbiting at 60 nautical miles, will have passed overhead and reached a point about 140 nautical miles downrange. Rendezvous maneuvers will follow, and docking of the two spacecraft should occur at 2:32 PM PDT Monday.
