“Everything is unfolding very quickly,” said Victoria Samson, Secure World Foundation’s chief director of space security and stability, in an interview.
Congested orbits
Samson noted that currently satellites are surrounded by relatively large “bubbles” used for collision monitoring. That’s due to uncertainty about exact positions and trajectories. Enhancing space situational awareness — like what SpaceX proposes with Stargaze — could tighten those buffers and reduce the number of potential collision alerts. However, that would introduce new risks.
“There’s obviously plenty of space,” Samson said. “But the issue is how much risk one is willing to accept?”
A technical specialist at The Aerospace Corporation, Marlon Sorge, told Ars that numerous unknowns about SpaceX’s planned megaconstellation of orbital data centers make it hard to evaluate collision risk. Questions include their dimensions (they’ll need very large solar arrays to collect sunlight) and the exact orbital locations where the satellites would be placed. The region roughly 800 to 1,000 km above Earth already contains substantial debris from past collisions, including the infamous 2007 Chinese anti-satellite missile test that created more than 3,000 pieces of debris the size of golf balls or larger.
There is less debris above that altitude, Sorge said. But at those heights objects can take centuries to deorbit naturally because the atmosphere is so thin.
“The core problem at those altitudes is that whatever is up there tends to remain up there,” Sorge said. “If you produce more debris or have mishaps, it won’t disappear, so you’re left with it.”
SpaceX tried to address these concerns in its regulatory filing, stating that each satellite would have “redundant maneuverability capabilities” to enable deorbiting into Earth’s atmosphere. The filing also appears to acknowledge emerging research indicating that aluminum vaporized during reentry can harm ozone levels. To address this, SpaceX is considering moving aging satellites into “high altitude Earth orbits or heliocentric orbits.”
