Science on This Day: December 2 | Nuclear Physics, Hubble’s Repair and the First Soft Landing on Mars
December 2 is a useful date for exploring a central idea in science: progress rarely comes from simply making a discovery. Scientists and engineers also need to control processes, solve unexpected problems and work out what the evidence really tells them. On this date in 1942, a team led by Enrico Fermi achieved the first controlled, self-sustaining nuclear chain reaction. In 1993, Space Shuttle Endeavour launched on a mission to repair the Hubble Space Telescope. And in 1971, the Soviet Mars 3 lander became the first spacecraft to make a successful soft landing on Mars, although it transmitted data for only a few seconds before contact was lost.
These three events offer opportunities to connect physics, chemistry, astronomy, engineering and the nature of scientific evidence. They also make good starting points for discussions about the benefits, risks and limitations of technological progress.
December 2, 1942: The First Self-Sustaining Nuclear Chain Reaction
Imagine a scientific experiment taking place beneath the stands of a university sports stadium. Instead of a modern laboratory filled with sophisticated equipment, the setting was a squash court at the University of Chicago. There, physicist Enrico Fermi and his colleagues were preparing to demonstrate that a nuclear chain reaction could be sustained and controlled.
The experiment, known as Chicago Pile-1, used uranium and graphite arranged in a large structure. When certain uranium nuclei split, a process called nuclear fission, they released energy and additional neutrons. Those neutrons could then cause further fission events. If enough neutrons continued the process, the reaction could sustain itself rather than dying away.
The challenge was to create the right conditions and control the reaction. Graphite slowed neutrons, making them more likely to trigger further fission, while control rods containing neutron-absorbing material could regulate the process. On December 2, 1942, Fermi’s team withdrew the final control rod far enough to achieve the first controlled, self-sustaining nuclear chain reaction. The team monitored the reaction and then stopped it by reinserting the rod.
This was a major milestone in nuclear physics, but it is important to understand what the experiment did and did not achieve. Chicago Pile-1 was not a commercial electricity-generating power station. It demonstrated that a nuclear chain reaction could be sustained and controlled, laying important groundwork for later nuclear technologies.
The discovery also occurred during the Second World War and formed part of the wider scientific effort that became the Manhattan Project. Nuclear fission would contribute to the development of atomic weapons, while subsequent research also enabled nuclear power generation and applications in medicine and scientific research. The same underlying physics could therefore lead to very different outcomes depending on how people chose to use it.
Classroom connection: Students can model a chain reaction using dominoes, counters or a simple computer simulation. Ask them what conditions allow a reaction to continue, what might cause it to stop, and how control rods change the behaviour of a reactor. The model is not a complete representation of nuclear fission, but it can help students distinguish between a process that dies out, one that sustains itself and one that grows.
A useful discussion question is: Does a scientific discovery have a moral value of its own, or does its value depend on how people use it? Students can consider nuclear medicine, electricity generation and nuclear weapons before developing an evidence-based response.
December 2, 1993: Endeavour Launches to Repair the Hubble Space Telescope
When the Hubble Space Telescope began sending back its first images in 1990, astronomers discovered that its primary mirror had a serious optical flaw. The telescope was still able to collect scientific data, but its vision was not as sharp as planned. A telescope designed to investigate distant galaxies, stars and other celestial objects needed a solution.
Rather than abandon the mission, NASA developed a repair strategy. On December 2, 1993, Space Shuttle Endeavour launched on STS-61, carrying seven astronauts on the first Hubble servicing mission. The crew would have to rendezvous with the telescope in orbit, secure it in the shuttle’s cargo bay and carry out complex repairs in the difficult environment of space.
Over the mission, astronauts completed five spacewalks. They installed corrective optics, replaced a camera with an improved version and carried out additional maintenance, including work on the telescope’s solar arrays. One important device, called COSTAR, provided corrective mirrors that compensated for the original mirror’s flaw in several of Hubble’s instruments.
The mission was a striking example of engineering under pressure. The astronauts could not simply bring Hubble back to Earth for repairs, and the work had to be completed while wearing bulky spacesuits and using tools designed for operation in orbit. The repair plan also had to account for the telescope’s existing systems and the risks involved in working around a large spacecraft.
The results justified the effort. Hubble’s corrected instruments returned the telescope to its intended capabilities, allowing it to produce sharper images and continue its scientific work. The mission also demonstrated the value of designing complex technology with maintenance and upgrades in mind.
Classroom connection: Give students a fictional instrument with a known fault, such as a telescope that produces blurry images or a sensor that records inconsistent measurements. Ask them to identify the evidence they would need before proposing a repair. They could then design a testing plan to check whether their solution worked.
This introduces an important feature of scientific and engineering practice: a problem does not always mean the entire project has failed. Sometimes the most useful response is to identify the cause, develop a correction and test the result. Hubble also offers a good example of why careful planning, teamwork and repeated checks matter in complex engineering projects.
Ask students: Should engineers design expensive technology to be repairable, even if that makes the original design more complicated or costly? The Hubble mission provides a real example for weighing the advantages of maintenance against the difficulties of designing and carrying out repairs.
December 2, 1971: Mars 3 Makes the First Soft Landing on Mars
Reaching another planet is difficult. Landing safely is harder still. A spacecraft travelling to Mars must survive the journey, enter the planet’s atmosphere at the right speed and angle, and reduce its velocity enough to reach the surface without being destroyed. It must then operate in an unfamiliar environment and communicate with Earth across millions of kilometres.
On December 2, 1971, the Soviet Union’s Mars 3 mission achieved a major milestone when its lander reached the Martian surface intact. It was the first spacecraft to make a successful soft landing on Mars. The mission included an orbiter as well as the lander, allowing the spacecraft to carry out different tasks around the planet and on its surface.
However, the landing did not lead to a long period of surface exploration. Mars was experiencing a severe planet-wide dust storm, and the lander transmitted a brief, unclear television image before communications stopped after roughly 20 seconds. The exact reason for the loss of contact remains uncertain. The storm may have contributed to the failure, but it is important not to treat a possible explanation as a proven cause.
The mission therefore produced a mixed outcome. The lander achieved its immediate goal of reaching the surface safely, but it failed to return the sustained observations its designers had hoped for. The accompanying orbiter continued to provide useful information, so the wider mission was not simply a failure.
Mars 3 is a valuable example of why scientific success is not always an all-or-nothing result. A mission can achieve one objective while failing to achieve another. The landing itself demonstrated that a spacecraft could survive the final stages of reaching Mars, while the short transmission highlighted how much could still go wrong once a lander reached the ground.
Classroom connection: Ask students to design a hypothetical Mars lander. What would it need to survive entry into the atmosphere, touch down safely, collect useful data and communicate with Earth? Students might consider parachutes, protective structures, power supplies, temperature, dust and the delay involved in communicating over such a large distance.
Then ask them to define success before evaluating Mars 3. Would they judge the mission by the successful landing, the short transmission, the data from the orbiter or the mission’s original scientific objectives? Their answers can lead into a discussion of how scientists assess evidence and report uncertain results.
The story also connects naturally with later Mars missions, including the Viking landers, which returned extensive images and scientific measurements from the surface in 1976, and modern robotic explorers that continue to investigate the planet.
Bringing These Events into the Classroom
The three events from December 2 work well together because they illustrate different stages of scientific and technological progress. Fermi’s experiment demonstrated how a physical process could be sustained and controlled. Hubble’s repair showed how engineers could correct a design flaw and restore a complex instrument. Mars 3 demonstrated both the difficulty of planetary exploration and the importance of separating what a mission achieved from what remains unknown.
For a short science lesson, introduce each event with a brief description and ask students to identify the main problem scientists or engineers were trying to solve. Students can then compare the evidence available, the obstacles encountered and the outcomes. This can be done as a class discussion, a short written response, a group investigation or a science-history starter.
For older students, the events also provide opportunities to discuss the relationship between science and society. Nuclear technology raises questions about energy, weapons and responsibility. Hubble illustrates the cost and value of maintaining major scientific instruments. Mars 3 raises questions about how much evidence is needed before scientists can draw a conclusion about an unfamiliar environment.
If you would like a ready-to-use way to bring these kinds of stories into your lessons, my December Science on This Day activity set includes 132 STEM events across all 31 days of December. It comes in interactive HTML, editable slides, a filterable spreadsheet and printable PDF formats, so you can choose events by date or subject and adapt them to your classroom. The slides include discussion questions, while the interactive version offers filtering and a classroom display mode.
You can also browse the Teaching Astrophysicist store for free and paid science resources to support lessons across physics, chemistry, biology, Earth science and space.
What Else Happened in Science History in December?
December 2 is only the beginning of a month filled with events that can connect science history to current classroom topics. On December 3, the first human-to-human heart transplant took place in Cape Town in 1967, while NASA’s Pioneer 10 spacecraft made its closest approach to Jupiter in 1973. These events offer contrasting ways to explore medical science and planetary exploration.
On December 4, the assembly of the International Space Station began with the connection of its Unity module to the Russian Zarya module in 1998. The same date also provides a link to DNA research through the birth of Alfred Hershey in 1908, whose later work helped establish DNA as the genetic material of viruses.
Later in the month, December 10 marks the first Nobel Prize awards in 1901, while December 11 recalls the Apollo 17 lunar landing in 1972. On December 14, Max Planck presented his quantum theory in 1900, opening a new chapter in physics. December 17 brings together the Wright brothers’ first powered flight in 1903 and the discovery of nuclear fission in 1938.
There are plenty of space-science connections too. Apollo 8 launched on December 21, 1968, becoming the first crewed spacecraft to travel to the Moon and enter lunar orbit. On December 24, its crew captured the famous “Earthrise” photograph. December 25 marks the launch of the James Webb Space Telescope in 2021, as well as the birth of Isaac Newton in 1642.
These anniversaries can be used as quick starters, research prompts, discussion activities or links between topics in a longer unit. A short story from science history can help students see that the ideas they study in class are connected to real people, practical challenges and discoveries that continue to shape the world.
Thanks for reading
Cheers and stay curious
Oliver - The Teaching Astrophysicist
