Lunar Landing (Part 1)!

Let’s learn a little about Lunar Landing. This is the first week of a two part blog posting about landing on the lunar surface. In an earlier blog post we learned about the turbulent history of the surface of the Moon scarred by craters caused by meteorite impacts. Well, meteorites weren’t the only objects to impact the lunar surface. In fact, early human exploration of the Moon also included many “impact” missions to the Moon. The first lunar exploration vehicles of the 1950s were primitive pioneers. However, technology developed so rapidly that only about a decade separated the first flyby forays and Neil Armstrong's history-making steps on the Moon's surface.

It started in January 1959, when a small Soviet sphere named Luna 1 flew by the Moon at a distance of some 3,725 miles (5,995 kilometers). Though Luna 1 did not impact the Moon's surface, as was likely intended, its suite of scientific equipment revealed for the first time that the Moon had no magnetic field. The craft also returned evidence of space phenomena, such as the steady flow of ionized plasma now known as solar wind.

First Lunar Landings (or Impacts)

Later in 1959 Luna 2 became the first spacecraft to land on the Moon's surface when it impacted near the Aristides, Archimedes, and Autolycus craters. A third Luna mission subsequently captured the first blurry images of the far side of the Moon.

In 1962 NASA placed its first spacecraft on the Moon — Ranger 4. The Ranger missions were ‘kamikaze’ missions; the spacecraft were engineered to streak straight toward the Moon and capture as many images as possible before crashing into its molten core. Unfortunately Ranger 4 was unable to return any scientific data before slamming into the far side of the Moon. Two years later, however, Ranger 7 streaked toward the Moon with camera shutters snapping and captured more than 4,000 photos in the 17 minutes before it smashed onto the surface. Images from all the Ranger missions, particularly Ranger 9, showed that the Moon's surface was covered with craters. The photos highlighted the challenges of finding a smooth landing site on the Moon’s surface.

In 1966 the Soviet spacecraft Luna 9 overcame the Moon's topographic hurdles and became the first vehicle to soft-land safely on the surface. The small craft was stocked with scientific and communications equipment and photographed a ground level lunar panorama. Luna 10 launched later that year and became the first spacecraft to successfully orbit the Moon.

The Surveyor space probes (1966-68) were the first NASA crafts to perform controlled landings on the Moon's surface. Surveyor carried cameras to explore the Moon's surface terrain, as well as soil samplers that analyzed the nature of lunar rock and dirt (regolith). In 1966 and 1967 NASA launched lunar orbiters that were designed to circle the Moon and chart its surface in preparation for future manned landings. In total, five lunar orbiter missions photographed about 99 percent of the Moon's surface.

Man on the Moon

These robotic probes paved the way for a giant leap forward in space exploration. On July 20, 1969, Neil Armstrong and Edwin 'Buzz' Aldrin became the first humans to reach the Moon when their Apollo 11 lunar lander touched down in the Sea of Tranquility. Later Apollo missions carried a lunar rover that was driven across the satellite's surface, as astronauts spent as long as three days on the Moon. Five other missions and a dozen men had visited the Moon before the Apollo project ended in 1972.

After the dramatic successes of the 1960s and 1970s, the major space programs turned their attention elsewhere for a few decades. But in 1994, NASA again focused on the Moon. The Clementine mission succeeded in mapping the Moon's surface in wavelengths other than visible light, from ultraviolet to infrared. Later, the Lunar Prospector (1999) orbited the Moon in search of possible evidence of ice at the lunar poles. The prospector also explored the Moon's gravitational field and remapped its surface. The mission's end was spectacular—the craft was intentionally crashed into the Moon in the hopes of raising a plume that could yield evidence of water ice, but none was observed.

Recently, NASA deliberately crashed an upper Centaur stage and the ‘shepparding’ spacecraft into the surface of the Moon. The mission objectives of the Lunar Crater Observation and Sensing Satellite (LCROSS) include confirming the presence (or absence) of water ice in a permanently shadowed crater at the Moon’s South Pole. In 2009, LCROSS excavated the permanently dark floor of one of the Moon’s polar craters (Cabeus) to test the theory that ancient ice lies buried there. Moving at a speed of more than 1.5 miles per second, the Centaur upper stage hit the lunar surface shortly after 4:31 a.m. PDT on October 9, 2009, creating an impact that instruments aboard LCROSS observed for approximately four minutes. The impact ejected material from the crater’s floor to create a plume that the specialized instruments were able to analyze for the presence of water (ice and vapor), hydrocarbons and hydrated materials. LCROSS then impacted the surface at approximately 4:36 a.m. PDT. The mission accomplished its objectives by revealing the presence of water from yet another successful lunar impacting mission. I guess we can say that the LCROSS mission created a crater within a crater inside the Cabeus crater. So, it’s pretty fair to say that there are quite a few ‘man-made’ craters on the Moon too.

Now let’s look at a few famous ‘soft landings’ on the surface of the Moon and how they were accomplished.

The Apollo Lunar Landers

The Lunar Module was originally designated the Lunar Excursion Module or LEM. Over the course of its development, the name was officially changed to Lunar Module (LM), eliminating the word 'excursion'. This was done because NASA was pushing to get funding for some kind of powered lunar surface mobility and they wanted to make it clear that such 'excursions' were beyond the capabilities of the lunar lander itself. (This new excursion capability was eventually realized with the Lunar Rover.) After the name change from 'LEM' to 'LM', the pronunciation of the abbreviation did not change, as the habit became ingrained among engineers, astronauts, and the media to universally pronounce 'LM' as 'LEM' which is easier than saying the letters individually.

The Apollo Lunar Module (LM) was the ‘Lander’ portion of the Apollo Moon missions built to carry a crew of two from lunar orbit to the surface and back. Six such crafts successfully landed on the Moon from 1969 to 1972. The LM, consisting of an Ascent stage and Descent stage, was ferried to lunar orbit by its companion Command/Service Module, a separate spacecraft of approximately twice its mass, which took the astronauts back home to Earth. After completing its mission, the LM was discarded.'

Here is a short video describing the design of the “LEM”:

At launch, the Lunar Module sat directly beneath the Command/Service Module (CSM) with legs folded, inside the Spacecraft-to-LM Adapter (SLA) attached to the S-IVB third stage of the Saturn V rocket. There it remained through Earth parking orbit and the Trans Lunar Injection (TLI) rocket burn to send the craft toward the Moon. Soon after TLI, the SLA opened and the CSM separated, turned around, came back to dock with the Lunar Module, and extracted it from the S-IVB. During the flight to the Moon, the docking hatches were opened and the LM Pilot entered the LM to temporarily power up and test its subsystems (except for propulsion). Throughout the flight, he performed the role of an engineering officer, responsible for monitoring the systems of both spacecraft.

After achieving a lunar parking orbit, the Commander and LM Pilot entered and powered up the LM, replaced the hatches and docking equipment, unfolded and locked its landing legs, and separated from the CSM. Flying independently, the Commander operated the flight controls and engine throttle, while the Lunar Module Pilot operated other spacecraft systems and kept the Commander informed on systems status and navigational information. After inspection of the landing gear by the Command Module Pilot, the LM was withdrawn to a safe distance, then the descent engine was pointed forward into the direction of travel to perform the 30 second ‘Descent Orbit Insertion’ burn to reduce speed and drop the LM's perilune (point closest to the Moon) to within approximately 50,000 feet (15 km) of the surface, about 260 nautical miles (480 km) up-range of the landing site.

At this point, the engine was started again for ‘Powered Descent Initiation’. During this time the crew flew on their backs, depending on the computer to slow the craft's forward and vertical velocity to near zero. Control was exercised with a combination of engine throttling and attitude thrusters, guided by the computer with the aid of landing radar. During the ‘braking phase’, the altitude decreased to approximately 10,000 feet (3.0 km), and then the ‘final approach phase’ went to approximately 700 feet (210 m). During final approach, the vehicle pitched over to a near-vertical position, allowing the crew to look forward and down to see the lunar surface for the first time.

The ‘landing phase’ began approximately 2,000 feet (0.61 km) up-range of the targeted landing site. At this point manual control was enabled for the Commander and enough fuel reserve was allocated to allow approximately two minutes of hover time to survey where the computer was taking the craft and make any necessary corrections. (If necessary, landing could have been aborted at almost any time by jettisoning the descent stage and firing the ascent engine to climb back into orbit for an emergency return to the CSM.) Finally, three-foot-long probes extending from three footpads of the lander touched the surface, activating the ‘contact indicator light’ which signals time for descent engine cutoff, allowing the LM to settle softly on the surface.

When ready to leave the Moon, the LM would separate the descent stage and fire the ascent engine to climb back into orbit, using the descent stage as a launch platform. After a few course correction burns, the LM would rendezvous with the CSM and dock for transfer of the crew and rock samples. Having completed its job, the LM was separated and sent into solar orbit or to crash into the Moon.

Let’s watch a simulation of the Apollo Lunar Landing sequence described above. Note the RCS (reaction control system) thrusters on the LM fire to ‘reorient’ the craft into the proper ‘attitude’ (pointing direction) for the ‘Descent Orbit Insertion’ burn:

Now let’s look at a video of the true story of the first humans, Neil Armstrong and “Buzz” Aldrin, landing the Lunar Module on the surface of the Moon. Listen for the astronaut call-out of the illumination of the 'contact light' and 'engine stopped':

Phew, that was a close one – they almost ran out of fuel! Next week we will continue this blog post with Part 2. Please join us again - we promise that you will have FUN!

See you next week!

Mystical Moon

'All one can really leave one's children is what's inside their heads. Education, in other words, and not earthly possessions, is the ultimate legacy, the only thing that cannot be taken away.' - Dr. Wernher von Braun

Thanks to NASA, MAGiC