From Apollo to Artemis

May 4, 2024

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Earth has but one Moon. Here are some stats;

  • The Moon’s mass is approximately 1.2% of the mass of the Earth [0.012 Earth masses]
  • It’s diameter of 3476 km so it’s radius is half that at 1738 km [0.27 Earth radii]
  • The Moon’s temperature that varies between -153 and +120 degrees celsius [20-400 kelvin]
  • It’s gravitational field strength (g) of 1.6 metres per second squared [0.17 times Earth’s gravitational field strength]
  • The apparent magnitude is -13 at full moon.
  • The Moon is in an elliptical orbit, it is 363300 km from Earth at perigee and 405500 km from Earth at apogee. Average radius of 384400 km and average orbital speed of 1 km per second.
  • The Moon is in a synchronous orbit which means that the time it takes to orbit once around the Earth is the time that it takes to spin once on its axis. This means that the Moon always has the same side facing the Earth. 
  • We do see a little more than 50% of the Moon’s surface due to librations.
  • It takes 27.32 earth days for the Moon to rotate and to orbit the Earth. Just as a bit of myth busting here, this time period of 27.32 days is NOT the length of the cycle for the phases of the Moon. The phases are dependent upon the Moon’s position in Earth’s sky with respect to the Sun. It takes 29.53 earth days for the Moon to get back in the same position in Earth’s sky with respect to the Sun so that is the length of the phase cycle and also the length of the lunar day.
moon 1
Credit: NASA/GSFC/Arizona State University

How did the Moon form?

The best current theory for how the Moon was formed is based on a huge Mars-sized asteroid colliding with Earth when it was younger. The Mars-sized object has been given the name Thea and when it hit it is supposed to have knocked off some matter from the Earth which then formed a ring of material around the Earth. This material then cooled and came together (over time) and formed the Moon. 

Structure of the Moon

The structure of the Moon is thought to comprise a crust, mantle and core (according to our most recent theories). The crust is made up of rock and is heavily cracked due to impacts, the mantle is rocky and studies indicate it could have a small iron core. We get information about the inside of objects by using density measurements of bodies and by using a field of study called seismology. This is the study of how waves propagate through bodies. The way in which the wave travels and the time it takes can tell us something about the material that it’s travelling through. For example, a sound wave travels much faster through a solid than a liquid. The atmosphere of the Moon is very thin. The Moon is not massive enough to keep a substantial atmosphere. The thin atmosphere it has is composed of neon, helium, hydrogen and argon.

Lunar Exploration

The first sketches of the Moon came from Galileo in 1609 shortly after he made his first telescope. He was able to use shadows of craters to make statements about the elevation of certain features. The first photos of the Moon started to emerge in around 1840. An absolutely huge step forward was in 1959 when a USSR spacecraft [Luna 3] photographed the far side of the Moon. The near side and the far side look very different. Flurry of activity from the USSR and USA from 1959 onwards to see who could get to the Moon first. Over a period of about 13 years, sent many missions to orbit, land on and explore the Moon. There were lots of images taken, landers landed, rovers drove on the surface and people walked on the Moon. From 1966-67, NASA sent lunar orbiters to photograph most of the lunar surface hunting for landing sites. In 1966, Luna 9 made the first soft landing on the Moon confirming that the Moon’s surface could support lander and human exploration. 

Apollo Program (in brief)

There were 6 successful missions to the lunar surface with the Apollo Program (11, 12 ,14, 15, 16 and 17).

Apollo 7 – 1968 was the first successful crewed spaceflight of the Apollo program.

Apollo 8 – Orbited the Moon and saw the Earth rise from orbit around the Moon for the first time. 

Apollo 11 – 1969 saw the first steps on the Moon, and Armstrong and Aldrin spent 21 hours on the Moon collecting samples and taking pictures. 

Apollo 12 – Precision landing in Ocean of Storms. Set up experiments; seismometer, solar wind and atmosphere equipment. Collected parts of the Surveyor 3 craft to see how the lunar surface had affected it. Brought back rock samples. 

Apollo 14 – Landed near Cone Crater near Imbrium basin (many missions were near the Imbrium basin). Deployed experiments, used an equipment trolly, found huge boulders and collected samples. 

Apollo 15 – Landed at Hadley Rille, near Apennine mountains near Imbrium rim. Used a lunar rover for the first time, photographed the region, did deep core samples, found some important lunar rocks (Genesis and Seatbelt). The lunar module explored the topography of the Moon and deployed a satellite to lunar orbit.

Apollo 16 – Landed in the Descartes highlands and used a lunar rover to explore. Set up experiments to explore seismology, heat emission, solar wind, cosmic rays. They took a small telescope to make observations and collected samples. 

Apollo 17 – The final Apollo mission landed in Taurus-Littrow valley, Mare Serenitatis. Used a lunar rover and had a mass spectrometer to explore composition. Collected samples and discovered orange glass on the lunar surface that was made in an ancient volcanic eruption. In lunar orbit they explored the temperature variation of the lunar surface. 

The surface itself. 

The surface of the Moon is incredibly dusty; it’s basically a huge pile of rubble from all of the impacts that have bombarded the Moon over billions of years. The Moon’s soil is called regolith and is made of fragmented rock of various sizes. There’s no wind or rain on the surface of the Moon so objects just stay where they are. Difference between the near and far sides. The near side has more mare due to lava flows. It has a thinner crust. The far side has a thicker crust and is more heavily cratered. Events that cause surface features include impacts which create craters and cause moonquakes. Lava from ancient volcanoes and eruptions made lava tubes. Can roughly discuss two areas of the Moon’s surface, the mare and the highlands. Mare are so called because earlier generations of humans looked at the darker patches on the Moon and assumed they were bodies of water (sea or oceans) like here on Earth. The mare are actually formed from ancient lava flows. They are made of basalt and samples from the Apollo mission confirm this and also some of the samples have little holes (thought to be formed by gas bubbles in the rocks) which is consistent with basalt volcanoes here on Earth. Highlands are lighter in colour. From samples the highlands are made of anorthosite. Also Apollo missions collected lots of breccias and impact melt rock. Olivine was also present in some samples. The lunar highlands are generally older and more cratered than the younger basalt seas. The repaving of the surface will have erased the cratering record of the mare regions. The older surfaces will have naturally been hit more with impacts.

The Moon is not a spent learning source

There is still much more that we can learn from the Moon and to do that we need to have the opportunity to study our natural companion up close. Widely interpreted as a new billionaire space race, the desire to get back to the Moon is actually rooted in some pretty worthy science reasoning. One of those reasons is water. 

Since the Apollo program, craft have visited the Moon in search of the water molecule. In 1998, Lunar Prospector travelled to the Moon to learn more about its gravity and to study the possibility of ice at the poles. After finding evidence to support that (in the form of large amounts of hydrogen at the lunar poles), it crashed onto the Moon. Later Chandrayaan-1 and LCROSS went back to the Moon and gathered data to confirm that this hydrogen was indeed water on the Moon. Chandrayaan is the lunar exploration programme by the Indian Space Research Organisation (ISRO). ISRO is making huge leaps in lunar exploration. LCROSS was a NASA mission. LCROSS was a spacecraft that had two parts; one part went barrelling straight into the Moon at a suspected site for water, and the other followed behind ensuring to go through the debris cloud created by the impact to analyse the molecular content. A simple, yet effective plan. The crater that they crashed the spacecraft into is likely to contain material that may not have seen direct sunlight for billions of years. The reason for this is that the Moon has very little tilt on its axis so the Sun never manages to reach the bottom of some of the impact craters at the poles of the Moon. As temperatures in these craters are low, they trap material, like water ice. 

The Artemis Program

In 2022, NASA conducted an extremely successful Artemis I mission – see previous blog for successes of this mission. 

NASA is now looking to the future with the follow up Artemis missions. The first crewed mission, (Artemis II) is scheduled for launch in September 2025. According to the NASA website, their plan with Artemis is to:

“… land the first woman and first person of colour on the Moon, using innovative technologies to explore more of the lunar surface than ever before. [They] will collaborate with commercial and international partners and establish the first long-term presence on the Moon. Then, [they] will use what we learn on and around the Moon to take the next giant leap: sending the first astronauts to Mars.”

NASA has a large number of missions in the Artemis program that are being prepared: Artemis II will be the first crewed flight beyond the Moon which will take humans the farthest they’ve ever been in space. The humans that are going on this mission will be Commander Reid Wiseman, Pilot Victor J. Glover, Payload Specialist Christina Koch, and Mission Specialist Jeremy Hansen. Artemis III will be the first crewed Moon landing mission since Apollo 17 in 1972 – a huge milestone for humanity. NASA plans to land the first female astronaut and first astronaut of colour on the lunar surface during this mission. The astronauts that take part in the Artemis III mission will spend about a week on the Moon conducting scientific experiments. These astronauts will return to Earth after the mission. Artemis VI and V will continue to bring humans and cargo to the surface of the Moon as well as start work on the lunar space station – Gateway.

NASA has partnered with a number of private companies for the Artemis Program. Notably they’ve worked with Aerojet Rocketdyne, an L3Harris Technologies Company, Boeing, and Northrop Grumman for the SLS rocket and Lockheed Martin for the Orion Spacecraft. Looking to future missions, they have contracted SpaceX to provide a Starship rocket to land humans on the Moon for Artemis III mission (and subsequent missions) and Blue Origin to make a lunar lander for Artemis V. 

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