"Space is hard." But why?
Every time a spaceflight failure occurs, the phrase “space is hard” will invariably be uttered in response. The sentiment typically being expressed is one of disappointment tinged with begrudging acceptance that spaceflight is challenging and not all attempts will succeed.
This was certainly the case last week with Beresheet, the first private Moon mission. It was led by SpaceIL, an Israeli nonprofit that was originally competing for the Google Lunar X Prize. Launched on a SpaceX Falcon 9 rocket on February 22, 2019, the spacecraft operated nominally during cruise but failed its attempt at a soft landing on April 11, 2019.
Recognizing the boldness of the attempt, the space community’s reaction was one of overwhelming support and acknowledgement that “space is hard”:
Any large, high-stakes project carries a risk of failure, especially if it’s on the cutting edge of technology. Infamous examples of technical failures include the sinking of the Titanic, Hindenburg airship explosion, Tacoma Narrows Bridge collapse, Chernobyl nuclear reactor disaster, and BP oil spill in the Gulf of Mexico. What makes space even more challenging?
While there’s no shortage of technical problems to tackle here on Earth, spaceflight presents a unique set of conditions that make the margin between success and failure particularly narrow. Here are just a few of the reasons why space is so hard:
Propellant volatility. Rocket launches are controlled explosions in the most literal sense. The combustive power of liquid oxygen and hydrogen, alcohols, and kerosenes leaves little room for error. Harnessing that energy into usable thrust requires carefully designed combustion chambers, nozzles, and other components capable of withstanding extreme heat and pressure. Hydrodynamic instabilities are so complex and difficult to predict that the early rocketeers relied on experimentation rather than empirical modeling to perfect their designs.
Launch vibration. Rocket engines cause intense vibration during launch, which both rockets and their payloads (including humans!) must survive. Space-bound components and systems must be thoroughly tested on Earth to ensure that they can withstand the launch environment. Vibration testing often reveals anomalies that can be addressed on the ground before the real thing, such as a problematic latch that was discovered during testing of the James Webb Space Telescope.
Cleanliness standards. During assembly on Earth, dust, fluids, and other contaminants will settle to the bottom of a spacecraft or collect in spots with little air flow. In zero gravity, those particles can become airborne (so to speak) and damage electrical components, shorting them out. This is why spacecraft are assembled in clean rooms—it’s to protect the spacecraft from humans, not the other way around.
Temperature control. The temperature extremes of space require a system that either has robust temperature control or can safely operate within that range. The fact that heat cannot dissipate in a vacuum makes thermal design for space systems particularly challenging compared to Earth, where engineers can use air to move heat.
Radiation. Beyond the protective shell of Earth’s atmosphere and the Van Allen belt, electronic equipment (computers and microelectronics in particular) is sensitive to the harms of ionizing radiation, which in space comes from sources such as high-energy particles and cosmic radiation.
Automated sequencing. Spacecraft and rockets stand in sharp contrast to aircraft because the sequence of steps to operate a airplane can occur within the reaction time of a human—a pilot. In contrast, “[r]ocket stage separation required precise synchronization of the electrical signals that fired the pyrotechnic charges with the signals that governed the fuel values and pumps controlling propellant flow” (Johnson 2002). This challenge extends today to complex, autonomous operations such as delivering rovers to Mars or landing rocket boosters on ocean platforms.
Reliability. Unlike most projects on Earth, where engineering mistakes can be fixed as they arise, a space system has to operate correctly the first time since repairs are impossible after launch. (The Hubble Space Telescope is a notable exception; its first repair to fix a faulty primary mirror and other components cost $293M in 1993 USD.) The reliability, or dependability under stated conditions for a set period of time, of a space system must be quantified and well-understood before it even gets to a launchpad.
This is not an exhaustive list; spacecraft and rockets are adept at finding new ways to self-destruct. Yet each failure is an opportunity to learn from mistakes and to feed that knowledge forward through lessons learned. Just as space scientists and engineers stand on the shoulders of giants, successful missions in modern spaceflight operate thanks to the failures of their predecessors.
