Picture this: you’re a wealthy billionaire who’s fuelling the space tourism industry by taking a flight to the Moon for a couple weeks. Launch from French Guiyana goes without a hitch, and within four days you’re within shitting distance of Earth’s largest satellite, orbiting until you’re ready to land. But then disaster strikes: a rogue fingernail scrapes at the circuitry controlling the engines, preventing your pilot from applying the braking thrusters for a soft landing. You’re on a crash course for the Moon’s surface as gravity takes over unhindered. The pilot is dead, along with all the other passengers. How do you safely get back to Earth?
As tempting as it might be, don’t attempt to fly the spacecraft back home: it takes years of training and mental conditioning to develop the skills and reflexes required to operate a vehicle designed to escape Earth’s gravity. Spaceships also require huge amounts of maintenance by entire teams of engineers to keep running, so given that your spacecraft is (most likely) a smouldering wreck on the Moon’s surface, you’re best off not trying to fix it if you somehow happen to be a space pilot.
Your best bet is to send a a distress signal back to Earth and wait for rescue teams to arrive, even if this means waiting several months while they build a state-of-the-art multi-billion-dollar spaceship to replace the one that you destroyed with your grooming routine. Either way, you’re looking at at least four days on the lunar surface assuming they dispatch a rescue ship immediately. Rummage through the wreck for a power supply and some lengths of cable to create a makeshift transmitter if the radio system didn’t survive the crash.
The lunar landscape is one of the harshest locations in the Solar System, with a complete lack of breathable atmosphere and little in the way of vegetation. Making things worse,when the Sun rises it will become unbearably hot, hitting up to 200C. If you’re lucky about where you crashed, there might be a crater whose shadow you can hide inside. If no such shade can be found, your priority will be to build yourself a shelter to hide from the elements. One thing the Moon has in ample quantities is dust – lunar soil. Mixing this with small quantities of your own urine will create a sort of clay that you can mould into bricks that will harden almost immediately thanks to the vacuum, which you can then use to build a makeshift hut.
You’re safe from the scorching heat, but as night falls you will have the opposite problem, as temperatures plummet to -170C. The barren landscape offers no fuel to burn for the night. However, you must look closer: the lunar surface is rich in helium-3, which in a pinch can be used as nuclear fuel in a fusion reaction that will produce ample quantities of heat to keep warm. Arrange your helium-3 in a pile, surrounded by some regolith bricks to provide containment to stop the reaction from fizzling out. Then you will need to find some sort of high-friction material from the spacecraft wreckage (ceramic plates from the heat shield will work for this), and rub together at roughly 10 percent of the speed of light to achieve the 100 million degree temperatures required to initiate nuclear fusion. You may be tempted to use water from your emergency supplies on the basis that hydrogen has a lower nuclear charge and therefore easier to fuse, but you’ll need that to stay hydrated. Besides, a pure H-H reaction proceeds via the weak interaction, taking billions of years which is time that you just won’t have.