Oct. 23 (UPI) -- A tweet from Elon Musk christened the burgeoning Starlink satellite constellation this week, which he plans to grow to 12,000 satellites.
It's an ambitious plan to boost Internet service around the world. It will also contribute to growing congestion in Earth's orbit, where tens of thousands of satellites and debris are in danger of colliding.
A close call last month put a spotlight on the hazards: Bigelow Aerospace's Genesis II experimental habitat and Russia's defunct Cosmos 1300 satellite nearly collided.
Cosmos 1300 is one of roughly 3,000 inoperative satellites that orbit Earth. They're joined in low Earth orbit by more than 2,000 active satellites.
Defunct satellites account for the vast majority of space junk mass, but even small pieces of debris can do serious damage. Some 14,000 pieces of space debris larger than 10 centimeters across exist. Scientists use tracking data and probability models to help active satellites avoid pieces of junk.
"We track objects [that are] anything about 10 centimeters and above -- about the size of a softball," John Crassidis, a professor of mechanical and aerospace engineering at the University of Buffalo, told UPI.
"We use our models to predict where we think they're going to be and we can do a probability of where the things around it will be to predict the chance of collision," Crassidis said.
Pieces of debris smaller than 10 centimeters also can cause damage.
"There could be up to 600,000 objects that are between 1 and 10 centimeters. That's the stuff we're really worried about -- the stuff we can't see," Crassidis said.
Near-space getting crowded
The growth of the private space industry and the shrinking of satellite technology has made it cheaper and easier to launch a satellite than ever before. Every year, hundreds of new satellites are sent into space.
"The space environment has become more congested and complex as our knowledge of the debris environment improves and the number of space actors and unique missions increases at an unprecedented rate," said Diana McKissock, the space situational awareness sharing and spaceflight safety lead at the Air Force's 18th Space Control Squadron.
Data collected by the U.S. government shows congestion in low Earth orbit gets worse every day.
"We're at a tipping point right now," Crassidis said.
Even without new satellites, some space junk experts suggest low Earth orbit, LEO, could become overwhelmed by space debris within 50 years.
"The Air Force has not established a specific timeline for when LEO will become untenable for new entrants to space," McKissock said. "Rather, the DoD [Department of Defense] focuses on working with inter-agency, allied, industry and academic partners on preserving the safety of the space environment through transparency and information-sharing to ensure long-term safety, sustainability and security."
Collisions cause space junk
Most smaller pieces of space junk are created by violent breakup events. But collisions also supply new pieces of debris. With each collision, the population of space debris increases, thereby increasing the odds of collisions.
In 1978, NASA scientist Donald J. Kessler predicted that space debris collisions would trigger a cascade effect, rendering low Earth orbit activities untenable for decades.
A decade ago, the inactive Russian satellite Cosmos 2251 smashed head-on into the active U.S.-based communication satellite Iridium 33 above Siberia. The Kessler Syndrome posits that it's only a matter of time before another collision further congests low Earth orbit.
"The Kessler Syndrome, in simple terms, is explained as the effect in which flux of space debris will increase with time exponentially by successive collisions, even if there are no more launches into space," said Anirudh Sharma, CEO of Digantara Research and Technologies, an Indian space engineering company focused on debris mapping and analysis.
"Although this effect has been exaggerated by many people, analysis and research have shown that we are now in the beginning of the time where the space environment will be increasingly controlled by random collisions," Sharma said.
Limited prevention effort
Life for satellites is likely to become increasingly precarious, and scientists aren't sure how a cascade of collisions might play out if nothing is done to limit the impact of future launches.
International guidelines exist for satellite launches. Owners must show that their satellite will have enough fuel left after its lifespan to conduct deorbiting maneuvers and burn up in the atmosphere. While space agencies and satellite makers in the United States and Europe typically abide by such guidelines, many nations do not.
"There is no international treaty for any of this stuff," Crassidis said. "There are just guidelines."
Even fewer guidelines exist for CubeSats, which can't be easily deorbited as a result of their low fuel reserves. And because they're so small, it takes a long time for drag to pull the toaster oven-size satellites out of low Earth orbit.
Engineers have invented a variety of technologies -- including balloons that can be inflated at the end of a CubeSat's mission -- to increase the surface area of CubeSats and enhance drag, pulling them more quickly out of orbit.
In Europe, companies and space agencies that launch CubeSats must meet basic deorbiting requirements. The United States has failed to adopt strict regulations for CubeSat launches.
"You have to show that it will deorbit within 25 years and burn up in the atmosphere," Crassidis said. "Personally, I think 25 years is way too long with the amount stuff that's going up there."
Tracking crafts and pieces
Space-tracking efforts in the United States are led by the U.S. Space Command, a unified combatant command of the Defense Department. Space situational awareness data is shared publicly with registered users on the website Space-Track.org.
USSPACECOM and the 18th Space Control Squadron monitor active satellites daily, watching for close approaches, and delivering alerts and data to the appropriate satellite operators, McKissock said.
In early September, the U.S. military informed the European Space Agency there was a 1-in-1,000 chance its Aeolus Earth-observation satellite would hit one of SpaceX's Starlink satellites. ESA decided to adjust the orbit of Aeolus.
SpaceX is one of several aerospace companies with plans to launch and manage mega-constellations of small satellites, fleets of hundreds of synced spacecraft that will provide communication services to users on Earth. SpaceX has launched 60 Starlink satellites. Eventually, the company founded by Musk plans to put 12,000 satellites into orbit.
Guidelines are slowly emerging
Earlier this month, a newly established group of space industry leaders called the Space Safety Coalition published a list of best practices for spacecraft operators, guidelines for limiting the impact of new satellites and preventing the growth of space debris. The guidelines call on spacecraft operators to create improved deorbiting plans and for engineers to prioritize collision-avoidance capabilities.
"Spacecraft owners, operators and stakeholders should exchange information relevant to safety-of-flight and collision avoidance," the group wrote.
NASA and the Defense Department are working to update their guidelines for ensuring the sustainability of the space environment, the U.S. Orbital Debris Mitigation Standard Practices.
Many ideas are being floated for how to address the problem of space junk. Engineers even built a net that can be used to capture it, but none of the technologies is likely to prove economical anytime soon.
"You're going to spend millions of dollars to build and launch a satellite that collects a couple of pieces of debris," Crassidis said. "It's not worth it. It's not cost feasible."
Tracking and limiting
The best course of action, he said, is to improve tracking capabilities and limit the impact of new satellites. New satellites also can be outfitted with more and better sensors to help the spacecraft avoid collisions.
"It is probably cheaper to prevent the space debris from accumulating than to remove it, once it is there," said Sharma, whose company develops space junk-tracking technologies. "For the junk that has been already created in the space, the cost-effective methods include various ground-based techniques to map it."
Mitigation efforts will cost money, too, but if satellite makers don't take the necessary steps to ensure their products won't contribute to space junk, the increasing odds of a collision will raise satellite insurance premiums, making launches prohibitively expensive.
Though tracking space junk is easier and cheaper than collecting and getting rid of debris, it is not without challenges. More space junk-tracking telescopes need to be deployed and mathematical issues must be worked out.
"The classic problem for ground tracking is that computers confuse crossing objects. We need to solve this association problem," Crassidis said.
For now, satellite purveyors and space agencies will have to rely on tracking systems to keep their assets in low Earth orbit safe, and also work to prevent new missions from making the problem worse.
If low Earth orbit becomes too crowded for new launches and space travel -- "a situation far worse than what we have imagined," according to Sharma -- then space junk removal technologies like satellite-capturing projectile nets and laser vaporization devices, no matter how far-fetched they may sound, could be the only options.