An explosion on board a spaceship can be terrifying for astronauts and potentially hazardous to satellites nearby.
America watched in horror in January 1986 as the space shuttle Challenger exploded during liftoff, killing seven astronauts including Christa McAuliffe of NASA’s Teacher in Space program. A suitcase-sized piece of insulating foam fell from an external tank and struck the orbiter, leading to its fatal fate.
Causes
NASA and SpaceX are jointly investigating last week’s SpaceX launch at Cape Canaveral, when one of their rockets exploded. Although until recently kept secret, a photographer at a surfing competition captured images showing an orange plume rising into the atmosphere which forced both companies to acknowledge there had been an anomaly.
Search efforts are currently under way to locate any remains of the booster rocket. While this search effort may be among the largest ever carried out in space, it won’t be an easy one: most fragments are too small for ground tracking systems to detect; their masses and speeds vary widely as do their speeds of travel.
Shards may have come from the upper stages of spacecrafts, which burn up and shatter after propelled satellites into orbit. Such fragmentation events increase trackable debris populations but scientists remain unsure why or what causes it. Elon Musk recently suggested it might have been caused by multiple factors including an improperly loaded upper stage.
Damage
Explosions in space generate fragments with various masses and speeds, some entering our atmosphere before eventually returning back down again; others, however, enter higher orbits that may remain out for months at a time.
An Apollo 13 Service Module bay no. 4 cover fragment was dislodged during reentry and left one side open to space; astronauts monitored this damage using television cameras and quickly recognized that their spacecraft needed to be brought back down for repairs on Earth.
Engineers conduct an exhaustive risk analysis on every exposed component and how it responds to hypervelocity impact tests in order to predict how much debris a spacecraft might generate during reentry, known as ballistic limit equations, based on extensive damage prediction research and test data. These parameters serve as predictors when it comes time for reentry.
Detection
Human risk from space debris collision is minimal compared to that associated with being struck by lightning or dying in an automobile accident, but the accumulation of space junk is increasing costs and making operations harder in orbit. Purdue University professor Carolin Frueh is researching ways to prevent spacecraft fragmentation that poses threats to satellites and space stations from fragmenting into thousands of pieces that pose risks of impact with satellites or space stations.
Frueh’s lab analyzes data collected by terrestrial telescopes to assess if there is an imminent potential breakdown based on how objects reflect sunlight – known as light curves – as this helps pinpoint any changes to spacecraft components or spacecraft themselves over time, such as gold foil flaking off from satellites.
Her team examined telescope images of three upper stages that exploded and discovered that each had ruptured due to different causes – for instance, one may have experienced fuel burning due to an obstruction, while another was likely the victim of structural failure.
Prevention
Space debris comes from many sources – used rocket stages, satellites, separation bolts and instrument covers to name just a few. Some will eventually reenter Earth’s atmosphere and burn up; but only few objects big enough to track reenter annually. Collision avoidance maneuvers are now standard practice in low Earth orbit but more effective methods must be devised in order to limit future build-up of debris.
ESA’s Clean Space initiative seeks to address this problem through technologies for efficient passivation (which involve depleting all remaining energy sources at mission’s end via engine burns, fuel or pressurant venting and battery discharging etc), as well as active debris removal missions.
Though it is unlikely, major debris collisions remain possible. Computer models that track all objects larger than softball in low Earth orbit reveal that the odds of such an encounter increase exponentially with time spent there.