Why 20 Starlink Satellites Fell After Falcon 9 Failure
Twenty Starlink satellites were lost on July 11, 2024, because the Falcon 9 rocket’s second stage suffered a liquid oxygen leak during its final burn, leaving the satellites in too low an orbit to survive. The leak caused the engine to underperform, so the stage could not raise the satellites to a stable altitude; atmospheric drag then pulled them back to Earth, where they burned up. This article explains the sequence of events, why the orbit was fatal, and what it means for SpaceX and the Starlink constellation.
Background: The Falcon 9 and Starlink Mission Profile
SpaceX’s Falcon 9 is a two-stage orbital rocket. The first stage boosts the vehicle through the lower atmosphere, then separates and lands for reuse. The second stage, with a single Merlin Vacuum engine, takes over to accelerate the payload to orbital velocity. For Starlink missions, the second stage performs a series of burns to place the satellites into a low orbit, typically around 300 km, before the satellites use their own ion thrusters to climb to their operational altitude of about 550 km.
This two-phase approach is deliberate: it reduces fuel needed on the rocket and lets the lightweight satellites do the final positioning. However, it means the initial orbit must be high enough that atmospheric drag won’t pull the satellites down before their thrusters can raise them. On July 11, 2024, the second stage failed to reach that safe altitude.
What Went Wrong: The Liquid Oxygen Leak
During the second burn of the Falcon 9’s upper stage, a leak developed in the liquid oxygen (LOX) system. Liquid oxygen is the oxidizer that combines with RP-1 kerosene fuel in the Merlin engine. A leak of LOX can cause several problems: it reduces the amount of oxidizer available for combustion, it can create ice or thermal stress on nearby components, and it can lead to engine performance degradation.
In this incident, the leak caused the engine to underperform, meaning it did not produce the expected thrust for the duration of the burn. As a result, the second stage ended up in an orbit with a perigee (lowest point) of only about 135 km, far lower than the intended 300 km circular orbit. At that altitude, the atmosphere is dense enough to create significant drag, rapidly slowing the satellites.
Why the Satellites Couldn’t Save Themselves
Each Starlink satellite is equipped with a Hall-effect thruster that uses krypton gas as propellant. These thrusters are efficient but very low-thrust—they accelerate slowly over weeks or months. To raise a satellite from 300 km to 550 km, the thrusters fire for an extended period. But from 135 km, the atmospheric drag is so strong that the satellite would need to fire its thruster continuously at maximum output just to maintain altitude, let alone climb.
Additionally, the satellites were still stacked in their deployment mechanism when the failure occurred. They were released from the second stage but had not yet separated into individual units. In that stacked configuration, they present a larger cross-section and are harder to maneuver. Even if they had separated, the drag would have overwhelmed their thrust capability. Within days, the satellites re-entered the atmosphere and burned up, posing no threat to the ground.
Immediate Aftermath and SpaceX Response
SpaceX confirmed the loss of 20 satellites in a statement shortly after the incident. The company said the satellites were designed to burn up completely on re-entry, and no debris was expected to reach the ground. The failure triggered an investigation by the Federal Aviation Administration (FAA), which grounded Falcon 9 launches until the cause was identified and corrected.
SpaceX traced the leak to a crack in a sense line—a small tube that measures pressure in the oxygen system. The crack allowed oxygen to escape, causing the engine to run lean and eventually shut down early. The company implemented a fix by removing the sense line and its associated sensor from future flights, simplifying the system and eliminating the failure point. The FAA approved the return to flight on July 27, 2024, and Falcon 9 launched again successfully.
Impact on the Starlink Constellation
The loss of 20 satellites is a minor setback for the Starlink network, which at the time had over 6,000 satellites in orbit. The constellation is designed to be resilient to individual satellite failures; new satellites are launched weekly, and the network can operate with gaps. However, the incident highlighted the fragility of the low-orbit deployment strategy.
Starlink satellites are intentionally small and inexpensive, which allows SpaceX to launch them in large batches. But that cost-efficiency comes with a trade-off: they lack the propulsion and shielding of larger, more expensive satellites. A single launch failure can wipe out dozens of satellites, but the financial impact is manageable because each satellite costs a fraction of the launch cost. This business model is a key reason SpaceX can tolerate occasional failures.
Common Misconceptions: “Falling Satellites” and Space Debris
Many people assume that failed satellites become dangerous space debris. In this case, the opposite is true: the satellites burned up completely, adding no debris to orbit. The reason is their low altitude. Objects in low Earth orbit (below about 600 km) experience enough atmospheric drag that they naturally decay within months or years. The Starlink satellites were placed so low that they re-entered within days.
Another misconception is that the satellites “fell” like a dropped object. In reality, they were in orbit but at an altitude where drag continuously slowed them, causing their orbit to spiral inward. The process is gradual, not a sudden drop. By the time they reached the dense lower atmosphere, they were traveling at several kilometers per second, and the frictional heating caused them to vaporize.
Frequently Asked Questions
How many Starlink satellites are in orbit now?
As of late 2024, SpaceX has launched over 7,000 Starlink satellites, with roughly 6,500 still operational. The constellation is constantly replenished with new launches, so the number changes weekly.
Could the failed satellites have been recovered?
No. Once the second stage failed to reach the target orbit, the satellites were doomed. Their thrusters were too weak to overcome drag at 135 km, and there was no way to refuel or boost them from the ground. Recovery was physically impossible.
Did the failure affect internet service?
No. The 20 lost satellites represent a tiny fraction of the constellation, and Starlink’s service continued without interruption. The network has built-in redundancy, so users did not notice any change.
Why didn’t SpaceX just launch the satellites to a higher orbit?
Higher orbits require more fuel, which means fewer satellites per launch or a larger rocket. The current design optimizes for cost and launch frequency. The low-orbit deployment is a calculated risk that has worked for hundreds of launches; this was a rare failure.
Is Falcon 9 safe to fly now?
Yes. The FAA cleared Falcon 9 for return to flight after SpaceX implemented the fix. The rocket has since completed dozens of successful missions, including crewed flights. The failure was traced to a single component, and the fix was straightforward.
What happens to the second stage after a normal mission?
In a normal Starlink mission, the second stage performs a deorbit burn to lower its own orbit, then re-enters the atmosphere and burns up over the ocean. This prevents the stage from becoming space debris. In the failed mission, the stage also re-entered, but it did so uncontrolled because the engine shut down early.
Related
Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.