Last Thursday, three astronauts aboard the International Space Station (ISS) took emergency shelter in their Soyuz vehicle. For nearly an hour, the crew remained in their capsule with hatches closed over concerns that a piece of orbital debris would pass alarmingly close to the Station.
Thousands of man-made debris objects orbit around the Earth. They include derelict satellites, broken up rocket stages, solid rocket motor effluent and even paint that has flaked off old spacecraft. In the past, these kinds of objects have collided with operating spacecraft creating even more debris fragments. Since collisions take place at hypervelocities (10 km/s), the consequences can be catastrophic.
Mission Control Centres in Houston and Moscow are normally informed a day or two in advance of a potential collision between the International Space Station and a piece of debris. Flight controllers then plan evasive action. On several occasions, the ISS main engines have been fired strategically to maneuver the 400 ton Station out of harm’s way.
On less frequent occasions (such as last Thursday), a close pass isn’t identified in time or the tracking data isn’t precise enough to plan a ‘debris avoidance maneuver’. In this worrisome situation, the best course of action is for the crew to take shelter in their Soyuz vehicle until the debris passes by. If the Station were to be hit and irreparably damaged, the crew would be prepared to leave the Station in their Soyuz.
Metal shielding can protect vulnerable parts of the ISS against tiny debris objects and micrometeoroids. Spacewalking astronauts have noted many small debris hits on the external structure and on solar arrays.
If the International Space Station would be hit by a larger piece of debris (> 1 cm), the hull could be breached and the Station would lose internal atmospheric pressure. Astronaut crews are trained to deal with such contingencies. As the Station gradually depressurizes, we would work quickly to locate and isolate the leaking module by closing hatches. At a later time, we would patch the hole and re-pressurize the module.
And, heaven forbid, if the Station would ever be hit by a massive object – really bad things could then happen. A one kilogram piece of debris at orbital velocity would impact the Station with the same collision energy as a tractor-trailer rig travelling at 190 km/h. Following impact, shrapnel would fly about and structures would fail. Large pressure waves propagating throughout the Station would cause further damage. Astronauts would hopefully have time to get to their Soyuz vehicles and close the hatches before the Station depressurizes. Not a fun scenario.
It’s naïve to think that a catastrophic impact with a habited spacecraft will never happen. In fact I am surprised, but also relieved, that in the 15 years that the ISS has been inhabited, there has not been a significant debris impact.
Prior to the launch of Sputnik in 1957, low Earth orbit was pristine. As humans have ventured into this new frontier, we have unfortunately brought along our bad habits and spread our mess.
The debris problem is getting worse. Objects that could pack a dangerous punch (> 1 cm dia.) number in the hundreds of thousands.
Guidelines, voluntary measures and national policies about orbital debris have been insufficient to halt the rate of growth. The number of debris objects in orbit continues to grow by 2 – 5% a year. If nothing else is done, I foresee a time later in this century when low Earth orbit will be uninhabitable or even impassable – an indictment of humanity’s mindset. In my opinion, it is a privilege to access low Earth orbit for our benefit. If we wish to make continued use of the new frontier for utilitarian and economic purposes, then we have a stewardship responsibility to care for it.
I am aware that there are many smart people who are currently considering the debris problem and that there are significant technical and economic obstacles to cleaning up the existing mess. However, orbital debris is a world problem that is escalating in magnitude and significance. We need to markedly raise the level of international commitment and collaboration to tackle it. It is a matter of principle and resolve.
I was concerned for the safety of Gennady, Scott and Mikhail. All of them are friends. Thank goodness the debris (an old Russian weather satellite of unknown size) passed by harmlessly. In a real sense, the crew and the space community dodged another bullet.