Lunar Lander games abound on every platform. Along with Tetris and Pac-Man, the game–in which your mission is to safely maneuver your lunar module onto the moon’s surface–is one of the most widely cloned computer games of all time. But did you know that game players began touching down on the moon in Lunar Lander just months after Apollo 11 astronauts Neil Armstrong and Buzz Aldrin did so on July 20th, 1969?

The descent from lunar orbit to landing was broken into three phases, and each of these phases had a specific computer program associated with it. Here’s the way it worked on all six lunar landings:

The descent began with the braking phase — the first and longest phase. It was flown entirely automatically by the computer (Program 63). Its goal was to slow the spacecraft from about 3,800 miles/hour to about 700 miles/hour, and to decrease the LM’s altitude from about 50,000 feet to 7,000 feet.
The approach phase began when the LM was about 7,000 feet in altitude and about 2 miles from the landing site. The computer was still doing all the flying (Program 64), but the crew could now see the landing site and offer adjustments to the computer.
The landing phase began around 500 - 700 feet in altitude. The Commander flipped a switch next to his left thumb, causing the computer to switch to Program 66. The computer was now in what was known as attitude hold. The Commander selected the spot where he wanted to land, and used his controls to tell the computer where to go. The computer was also responsible for keeping the LM upright. The landing phase ends with the LM on the lunar surface. //

Here are the times (in minutes and seconds) that each of the missions spent in the landing phase:

Apollo 11: 2:23

Apollo 12: 1:44

Apollo 14: 2:01

Apollo 15: 1:16

Apollo 16: 1:00

Apollo 17: 1:08

Apollo 11 had by far the longest landing phase — almost 2 and a half minutes. That’s how long it took Armstrong to find a suitable landing spot and guide the computer toward it.

At the other extreme was Apollo 16 — when it entered the landing phase, a suitable landing spot was right there and it took John Young only a minute to guide the computer through the last few hundred feet and onto the lunar surface.

All of these missions went through the same phases — they differed only in how long each phase lasted.

As far as Armstrong being the one to fly the LM, that was also the plan, and again, it was the Commander who guided the LM during the landing phase on all six lunar landing missions. The job of the LMP (Lunar Module Pilot) was to provide crucial support during the landing, monitoring systems and calling out numbers throughout the landing phase. If you listen to the audio of any of the lunar landings, the voice you hear calling out numbers is the LMP.

Andrew Swenson
MS in Space Systems Engineering, US Naval Postgraduate School (Graduated 1993)May 14

Why does NASA not allow anyone to inspect the lunar module (lunar excursion module) that traveled to the Moon during Apollo missions?

Which one would you like to inspect and how would you get there? Here are the locations of each one….good luck with your inspection:

Apollo 5- Destroyed in Earth's Atmosphere.
Apollo 9- Destroyed in Earth's Atmosphere.
Apollo 10- Heliocentric orbit
Apollo 11- released in lunar orbit, location unknown.
Apollo 12- Impacted Moon 20 November 1969 at 22:17:17.7 UT (5:17 PM EST) 3.94 S, 21.20 W
Apollo 13- Burned up in Earth's atmosphere.
Apollo 14- Impacted Moon 07 February 1971 at 00:45:25.7 UT (06 February, 7:45 PM EST) 3.42 S, 19.67 W
Apollo 15- Impacted Moon 03 August 1971 at 03:03:37.0 UT (02 August, 11:03 PM EDT) 26.36 N, 0.25 E
Apollo 16- Released around moon, impact site unknown. Orbited for about a year.
Apollo 17- Impacted Moon 15 December 1972 at 06:50:20.8 UT (1:50 AM EST) 19.96 N, 30.50 E

Despite a higher risk of a fire, pure oxygen also has some advantages.

First, the internal pressure of the vessel is only a fifth of a normal breathing mix, allowing less structural load on the hull of the spacecraft. The resupply system is also simplified, because a system including nitrogen must have an extra tank for the nitrogen. (If you had them mixed, you end up with a higher and higher nitrogen pressure over time). A small mass saving is therefore achieved. For a minimal spacecraft where you simply open the hatch and vent the cabin air when performing an EVA, pure oxygen simply means less air wasted. Nitrogen narcosis seems to not be an issue, as I find it difficult to imagine an accident of increase in the pressure.

As for the decision making process in the early US space programme, the slightly higher complexity of a nitrogen system must have felt a little redundant. The early US Mercury and Gemini also used pure oxygen, but the early Soviet spacecraft, like Vostok, used a normal atmospheric breathing mix. Note that modern EVA suits do still use pure oxygen. ///

At 5 PSI there is not enough atmosphere to support fire, even with 100% oxygen atmosphere.

Q:

I am curious what aspects of the Apollo program were impressive/advanced from an engineering perspective, in the 1960s and 1970s. That is, what would have made an educated engineer say, “Wow, they solved that problem?”

I ask the question because I know that as an engineering layperson I know I have very poor intuitions about what is technically difficult in spaceflight. For instance, I only learned from this website that maintaining 1 atm of pressure in a spacecraft isn't very difficult. Also, some technologies like pressure suits and rocket engines had already been developed. So it is not obvious (to me) what the actual innovations and engineering achievements of the program were.

A:

There was no one breakthrough that made it possible. The "big deal", in the mind of the world, was just that an obviously very hard thing was accomplished. And, if you doubted how hard it was, people can point out that no one has done it again in more than fifty years.

However, there are some good examples of challenging problems that had to be solved.

Problem 1: Rocket Size. Before Apollo, everyone thought we would send the top of a multi-stage rocket to the moon, it would land on its tail and launch again to return to earth. When you run the numbers on that, you end up with a pretty big lander requiring a lot of fuel, and a huge launcher to send it on its way; much larger than Saturn. The trick ended up being to only send down a little bug, and even leave part of that behind on the moon. If we had stuck with the giant lander we would never have been ready in time.

Problem 2: Rendezvous. The new method required being good at approaching and docking with another spacecraft. That's a hard enough problem that, even though the physics was well understood, they didn't really see the issues until they actually tried it. (I always get annoyed when characters in science fiction stories fail to foresee problems that the science should have told them beforehand, but sometimes that's how it works.) Wisely they tried it in Gemini in low earth orbit and had the hang of it by Apollo.

Problem 3: Rocket Size (Again). Even with the trick (called Lunar Orbit Rendezvous) used to solve Problem 1, they needed a much bigger rocket than anyone had built before. And so they built it. To get it to the launch pad, they built the crawler transporters, some of the largest land vehicles built up to that time, and to have a protected place to stack the stages, they built the Vehicle Assembly Building, one of the largest buildings by open volume in the world. I think seeing a tower the size of a 36-story skyscraper rise into the sky made a lot of people say, "Wow, they solved that problem?" I was too young at the time, but it was the initial uncrewed Apollo 4 launch of the Saturn V that made my dad think, "Huh, they might actually pull this off!"

There are many many more, but it was really the cumulative effect of solving thousands of hard problems that was the big deal. //

Number 2 is a small example of the large original research involved. A guy, later known as "Doctor Rendezvous", did his Ph.D. thesis at MIT on it in 1963. His next job was to fly it! Here's Buzz Aldrin's thesis: dspace.mit.edu/handle/1721.1/12652 –
Adam
May 19 at 1:38

The "slow down to catch up, speed up to slow down" stuff of orbital rendezvous was reportedly very confusing to the non-engineer test pilots and required someone like Buzz Aldrin to truly figure out. It's one thing to draw the equations out on paper but a whole other thing to actually do it in the cockpit. –
Jörg W Mittag
May 17 at 19:48

@JörgWMittag I think its still confusing to a lot of people today, mainly because of the terms "slow down" and "speed up" in that phrase are ... wrong, but appropriate? –
Moo
May 17 at 21:32

@Moo - If you go faster, you also go higher. Now that you're higher, you've got farther to go, so you're actually going slower –
Richard
May 18 at 18:36 //

A:

what has ALWAYS impressed the heck out of me is the sheer magnitude of scale involved... not physical size (although its size was truly impressive) but rather the huge number of complex problems that needed to be all solved in a complex optimization matrix to arrive at a suitable overall solution. This was the largest systems integration project ever to date and on a tight timeline. Project management on an unheard of scale and scope. That to me was the "Wow... they solved THAT problem" thing.

Yes. Apollo was a triumph of project management as much as, or maybe even more than, it was a technological feat. –
Wayne Conrad
May 18 at 2:40

I would argue that project management was born within the Apollo program. I don't think it even had a name beforehand. –
Vladimir Cravero
May 18 at 8:18 //

A:

It was fractally hard.

Everything they did was Voltroning hard problems together to solve other hard problems. And this was all done in a coordinated way on an incredibly tight timescale.

The long answer would fill a series of books. E.g. for a high level overview of the effort involved in the LEM alone, you can look at Tom Kelly's Moon Lander (and you should; it's great).

But to put a quick gloss on top of it, Apollo was not an aerospace engineering triumph, Apollo was a systems engineering triumph. Everyone solved hard problems in every field, but the real accomplishment was orchestrating those solutions in a way that led a seven-year program from zero to the moon.

Apollo systems engineering built upon Polaris (see en.wikipedia.org/wiki/UGM-27_Polaris). –
Jon Custer
May 18 at 20:42

@JonCuster Sort of, but it's more complicated than that. I'm not putting a history of SE in this answer though. Recommend Morris' "Management of Projects" from 1990 or so if you want an overview of the most relevant thread for Apollo/ –
fectin
May 19 at 0:55

A:

After depressurization of the cabin though there is, obviously, no environment to condition, and during repressurization fresh oxygen needs to be supplied at high flowrate from oxygen tank at cryogenic-temperature to fill the entire cabin. What heating mechanism was applied to heat up the supply of fresh cryogenic oxygen for CM cabin repressurisation?

P.S. In original question I asked about repressurization of both CM and LM, but it seems LM stored oxygen in compressed gas form rather than cryogenic liquid or supercritical fluid, therefore I have removed LM from the question.

A:

Unsurprisingly, it worked exactly like it did in shuttle.

To assure uniform flow, the capillary restrictors are coiled around a warm water-glycol line to increase the oxygen temperature.

Page 2.7-3

The aforementioned oxygen supply capillary restrictors are wound around the line routed to the space radiators and relief valves. The other line is routed to the mixing valve. To insure proper operation of the oxygen supply restrictors, in the line between the cryogenic O2 storage in the S/M to the surge tanks in the C/M during cabin repressurization, full water - glycol flow through the line to the space radiators is required. Sufficient heat must be available to prevent cryogenic oxygen entering the C/M oxygen system and preclude the possibility of freezing the water-glycol. To achieve this, the mixing valve must be manually placed to the full closed position 15 to 30 minutes before repressurization and remain closed until the surge tank returns to maximum pressure after repressurization of the C/M.

Q:

Does anyone know what the approximate Apollo cabin temperature and humidity was kept at? I am curious if the unusual 100% O2 atmosphere affected other aspects of the cabin air.

A:

From this NASA report:
https://history.nasa.gov/SP-368/s2ch5.htm

The design range for temperature and humidity control in the Apollo Command Module was 294° to 300°K (70° to 80°F) [i.e., 21 to 27 °C] with a relative humidity of 40 to 70 percent. Similarly, the design range for the Lunar Module was 291° to 300°K (65° to 80°F) [i.e., 18 to 27 °C] with a relative humidity of 40 to 70 percent.

AnechoicMedia @AnechoicMedia_

What an incredible rabbit hole. Margaret Hamilton, awarded the Presidential Medal of Freedom for "[leading] the team that created the on-board flight software" for the Apollo missions, wasn't even hired until after the completed software had already flown to the moon in Apollo 8!

How on Earth do you patch the software on a computer orbiting the Moon? Very carefully.

FRANK O’BRIEN - 1/30/2020, 12:30 PM

In the afternoon of January 31, 1971, the flight thundered away from the Kennedy Space Center on its Saturn V launch vehicle after only a brief 40 minute hold for weather. After restarting the S-IVB third stage for trans-lunar injection (TLI), the command module Kitty Hawk and her crew were on their way to the Moon. //

However, less than four hours before the scheduled landing, controllers noticed that according to the indications on their consoles in Mission Control, the LM's Abort pushbutton appeared to have been pressed. When asked via radio, Shepard confirmed that no one on board Antares had pressed the Abort button—which meant there was a short-circuit or other electrical issue somewhere inside the LM's complicated guts.

This was potentially a mission-ending problem: if the button was pressed and the engine was firing, the LM would immediately begin its abort procedure as soon as the lunar descent started, making a landing impossible.

Under hard time pressure, the ground had to quickly figure out what was wrong and devise a workaround. What they came up with was the most brilliant computer hack of the entire Apollo program, and possibly in the entire history of electronic computing.

To explain exactly what the hack was, how it functioned, and the issues facing the developers during its creation, we need to dig deep into how the Apollo Guidance Computer worked. Hold onto your hats, Ars readers—we're going in. //

Once again the LM’s orbit carried it behind the Moon and out of communications, leaving the crew with just a smattering of procedures and few options. The normal work of finishing the system configurations continued, and the crew maneuvered to the descent attitude, tidied up the cabin, and put on their helmets and gloves. In the meantime, Don Eyles’ team was feverishly working to find a better solution to the Abort bit issue.

Working the problem involved unraveling a complex, daisy-chained series of events. The main landing program, P63, does not perform all of the landing computations itself. Rather, it orchestrates a large number of Jobs and Waitlist Tasks, each performing a necessary part of the effort. Another Job running concurrently was the SERVICER, which sampled attitudes and accelerations that fed into the guidance equations. SERVICER, in turn, scheduled Routine R11 as a Waitlist Task, running every 0.25 seconds. R11 first checked whether aborts are enabled (via the LETABBIT flag), and if so, it then checked the status of the Abort bit. With aborts allowed, and the abort signal set (presumably because the crew pressed the Abort pushbutton), P63 is terminated, the AGC's Major Mode switches to P70, and the abort process begins. //

This was the breakthrough. If R11 could be spoofed into believing that an abort was already in progress, then it didn’t matter if the Abort button was pressed or not—the button's state would be ignored.

But how did R11 actually inform itself about whether or not an abort was executing? The answer was in plain sight on the DSKY: The Major Mode display, under the label “PROG”. //

In less than two minutes after the descent to the Moon had started, the Abort pushbutton had been successfully disabled and the computer was happily managing the descent. All indications were that the next lunar landing would be successfully accomplished in eight more minutes. //

As Antares passed through 32,000 feet (about 9,700 meters), Mitchell became concerned and informed controllers that the radar hadn’t locked on. Houston replied with a suggestion to pull the circuit breaker for the radar, and then power the system back on, which did the trick. Solid radar data began flowing into the computer, and the crew quickly agreed to accept it. Just a few minutes later, Shepard made a smooth and on-target touchdown at the Fra Mauro highlands.

After the mission, when asked if he would have attempted to land without the radar, the notoriously hard-charging Shepard reportedly replied, “You’ll never know.” In Gene Kranz’s Failure is Not an Option autobio, Kranz recounts that Flight Director Jerry Griffin was convinced that Shepard would indeed make an attempt to land without radar, and would just as certainly have had to abort when fuel ran out. //

The idea that a single errant switch could derail a lunar landing attempt was unacceptable. After the mission, a new variable in the AGC code was introduced that allowed the crew to "mask out" (that is, to ignore) the Abort and Abort Stage pushbuttons. The scenario assumed that a failing switch would be recognized well before the descent began, and commands could be entered in time to prevent an inadvertent abort. Like the fix used for Apollo 14, this would make initiating an abort through a pushbutton impossible, and any urgent situation would have to be performed on the Abort Guidance System. //

The recovery from Apollo 14’s Abort switch failure can only be described as brilliant and heroic. But the most important enabler of this effort was that the software, while fiendishly complex, could be understood by a small team of developers. Modern hardware and software, with its extensive protection schemes, virtualization and dynamic program management simply would make such a simple hack impossible. Faced with a comparable problem today, even if the fix were trivial, the solution likely would require large amounts of code to be recompiled, tested and uploaded to the spacecraft. This may not be possible given the short timeframe necessary to save the mission.

In the end, Apollo 14’s fix truly represented the “Spirit of Apollo," where talented teams made the impossible happen.

The same question could well be asked of the LM's descent engine and the main engine on the Apollo service module, however, which did both need to fire in free-fall. In those cases, the smaller RCS thrusters on the LM or CSM were fired first, to "settle" the tankage and separate the fuel from the helium. In the LM case, this "ullage burn" was about 7.5 seconds. The first couple of service module burns -- typically for mid-course correction while en route to the moon -- generally didn't need an ullage burn prior, as the tanks would be full of propellant with little or no volume of helium. SPS burns later in the mission did require ullage burns. The RCS thrusters produced about 100 lbs of thrust each, and four would be used for the ullage burn, yielding roughly 1/200 g acceleration.

The same RCS ullage burn technique would also apply to a situation where the descent engine failed and the ascent engine needed to be used for abort from free-fall, or in flight testing of the ascent engine.

That, in turn, raises the question of how helium ingestion was avoided in the RCS thrusters, since they were also helium pressurized. In those cases, the helium was separated from the propellants by a teflon bladder, so the helium didn't mix with the propellants. This was more practical to do on the smaller scale of the RCS propellant tanks than it would have been for the larger engines.

The American astronauts calculated critical course-correction maneuvers on their HP-65 programmable hand-held during the rendezvous of the U.S. and Russian spacecraft.

Full-Scale Model of Apollo 11 12 13 14 Command Module Control Panel (CMCP)

All or nothing. This project will only be funded if it reaches its goal by Tue, September 21 2021 2:03 PM EDT.

Measuring a massive 82" wide, 33" tall, and 7" deep, all representing that same vision of teamwork, peaceful exploration, engineering accomplishment, and pioneering spirit.

"You can now take the controls of a historic NASA spacecraft — literally.

A team of Hollywood prop and visual artists are offering replicas of the Apollo command module control panel. The museum-quality reproduction features every switch, knob and indicator that was used on board the first three missions to land astronauts on the moon and to bring the Apollo 13 crew safely back to Earth.

"It is here where the impossible becomes possible," team leader Mark Lasoff, an Academy Award-winning artist whose credits include the 1995 feature film "Apollo 13," wrote about the control panel. "It is here where humans and machines interface. It is here where every vital operation, including navigation, propulsion, communication and life support is calculated, calibrated and controlled intricately."

"It is both an engineering feat and a work of art," Lasoff wrote of the flight deck." //

Measuring an expansive 82 inches wide, 33 inches tall, and 7 inches deep (208 by 84 by 18 cm), the replica control panel was designed using the original blueprints for the NASA spacecraft. Lasoff and his team also used 3D scans of the Apollo 11 command module produced by the Smithsonian's National Air and Space Museum to verify their details.

http://kck.st/36XvTlG

The Kickstarter campaign is offering the full-scale metal replica for $3,900.

With Collins' death, only 10 of the 24 humans who have flown into deep space remain alive: Collins' colleague on the Apollo 11 mission, Buzz Aldrin, as well as Bill Anders, Frank Borman, Charlie Duke, Fred Haise, Jim Lovell, Ken Mattingly, Harrison Schmitt, David Scott, and Tom Stafford.

Judith Love Cohen was a tenacious engineer. This fact check is just a tribute.

Fifty years ago this week, NASA astronaut Alan B. Shepard Jr. made space history when he took a few golf swings on the Moon during the Apollo 14 mission, successfully hitting two golf balls across the lunar surface. Space enthusiasts have debated for decades just how far that second ball traveled. It seems we now have an answer, thanks to the efforts of imaging specialist Andy Saunders, who digitally enhanced archival images from that mission and used them to estimate the final resting spots of the golf balls.

Saunders, who has been working with the United States Golf Association (USGA) to commemorate Shepard's historical feat, announced his findings in a Twitter thread. Saunders concluded that the first golf ball Shepard hit traveled roughly 24 yards, while the second golf ball traveled 40 yards. //

Saunders, whose forthcoming book is entitled Apollo Remastered, estimates that a professional US Open golfer like Bryson DeChambeau could, in theory, hit a ball as far as 3.41 miles on the Moon, with a hang time of 1 minute 22 seconds—much farther (and longer) than Shepard's feat. As he told the BBC:

Unfortunately, even the impressive second shot could hardly be described as "miles and miles and miles," but of course this has only ever been regarded as a light-hearted exaggeration. The Moon is effectively one giant, unraked, rock-strewn bunker. The pressurized suits severely restricted movement, and due to their helmet's visors they struggled to even see their feet. I would challenge any club golfer to go to their local course and try to hit a six-iron, one-handed, with a one-quarter swing out of an unraked bunker. Then imagine being fully suited, helmeted, and wearing thick gloves. Remember also that there was little gravity to pull the clubhead down toward the ball. The fact that Shepard even made contact and got the ball airborne is extremely impressive.

And of course, the astronaut's legacy as the first human to play golf on the Moon remains secure.

At precisely 8:42:47 p.m. EST tonight (Sunday, 7 February), a new record will be set in the annals of U.S. human spaceflight, when Dragon Resilience—the vehicle which delivered Crew-1 astronauts Mike Hopkins, Victor Glover, Shannon Walker and Soichi Noguchi to the International Space Station (ISS), last November—passes 84 days, one hour, 15 minutes and 30 seconds in flight.

Video Credit: NASA
In doing so, the hardy little SpaceX ship will eclipse Skylab 4’s almost-five-decade-old achievement for the longest single mission by an American crewed orbital spacecraft. Current plans call for Dragon Resilience and her four-member crew to return to Earth in late April or early May, targeting a record-setting duration for a U.S. piloted vehicle of around 165 days in space.

When the Skylab 4 mission launched atop a Saturn IB rocket from historic Pad 39B at the Kennedy Space Center (KSC) in Florida at 10:01:23 a.m. EST on 16 November 1973, its three-man crew knew they were aiming for one of the longest orbital voyages ever attempted at that time. Two previous flights to America’s Skylab space station had recorded 28 and 59 days aloft, respectively, whilst the Soviet Union had achieved 23 days with its ill-fated Soyuz 11 crew.

Two trips, a decade apart, spanned the most exciting era in space history.

Of the original seven astronauts chosen by NASA in 1959, only one, Alan Shepard, made it to the moon. And he almost didn’t. More than two years after his pioneering Mercury-Redstone flight in May 1961, Shepard was in training to command the first two-man Gemini mission. Progress to the moon was planned in three steps: Mercury to prove that space travel was feasible, Gemini to demonstrate rendezvous and long-term spaceflight, and Apollo to go all the way. In 1963, Shepard was a fair bet to fly all three.

NASA chose the Apollo 11 landing site for engineering simplicity, but it had scientific benefits nevertheless.

This article considers the utilisation of modern image processing and enhancement to determine the impact of the catastrophic failure of Cryogenic Oxygen Tank 2, and it's subsequent impact on Bay 4 and critical systems on Apollo 13. The analysis also aims to aid visualisation and identify key components of the damaged Service Module.

Details of the original photographic analysis which formed a significant part of the 1970 investigation can be found in Apollo 13 document collection with particular reference to the following documents: //

Only around half a second separated the first vibrations detected in the accelerometers (caused by changing pressures in oxygen tank 2) and rapid pressure increase in Bay 4, leading to panel blow out. A calculated 60,000-pound force was effected on the CSM and 1.17g was recorded in the X-axis as the panel blew out and contacted the High Gain Antenna, although the actual total attitude change was small.

The shock loads closed several reaction control propellant isolation valves and the reactant valves in the fuel cell oxygen system leading to the loss of electrical power from fuel cells 1 and 3. The oxygen tank 2 feedline or pressure transducer wiring / plumbing was also severed leading to a zero reading on tank 2.

Damage to the adjacent oxygen tank 1 lead to a leak, and this venting oxygen caused attitude changes necessitating stabilisation from the attitude control system. However, some thrusters were assigned to main bus B which received electrical power from the now dead fuel cell 3 and as such were not functioning.

For the next 1.5 hours there were confusing firings of the attitude control thrusters. Lovell struggled to regain correct attitude manually, only re-assigning the thrusters to main bus A allowed Lovell to eventually regain control.