Three days after a dramatic launch abort, a SpaceX Falcon 9 rocket suffered a premature engine shutdown during the climb to space Wednesday but was still able to place another batch of 60into the planned orbit. The first stage, however, was unable to pull off what would have been its fifth landing, instead chalking up SpaceX's second unsuccessful recovery in the past three flights.
The launching from historic pad 39A at the Kennedy Space Center came just hours after NASA put its field centers on coronavirus "level 3" status, requiring civil servants to work from home and closing the bases to all but "mission-essential" personnel to slow the spread of the COVID-19 virus.
But the restrictions did not affect SpaceX workers or Air Force personnel who provide tracking and telemetry support, and the Falcon 9 thundered to life at 8:16 a.m. EDT, streaking away from pad 39A at the Kennedy Space Center along a northeasterly trajectory over the Atlantic Ocean.
A launch try Sunday was aborted as the booster's nine Merlin 1D engines were firing up when "out of family" data was detected during a last-second computer check. No details were provided, but the company was able to recycle for a second launch try Wednesday and this time around, the countdown ticked smoothly to blastoff.
The first stage, after boosting the second stage and its cargo of 60 Starlink satellites out of the thick lower atmosphere, attempted to fly itself back to fifth landing an off-shore droneship, firing three engines to slow down as it plunged back toward Earth.
But video from the rocket was lost about a minute before touchdown and a SpaceX commentator later confirmed "we were not able to land that stage today. We are obviously disappointed, but our primary mission ... is still on target."
The lost stage flew in July 2018, again in October 2018 and twice more in February and November 2019. The "block 5" stages are designed to fly at least 10 times without major refurbishment, a key element in SpaceX founder Elon Musk's drive to lower launch costs through "rapid reusability."
Video from a camera mounted on the booster showed a sudden, very brief change in the rocket's exhaust plume a few seconds before engine shutdown and stage separation. In a tweet, Musk said the booster experienced "an early engine shutdown."
"Shows value of having 9 engines! Thorough investigation needed before next mission," he said.
It was the second off-shore landing failure in the last three Falcon 9 flights. The company's stage recovery record stands at 50 successful landings and nine failures. More important, NASA plans to use a Falcon 9 to launch two astronauts to the International Space Station in May and any engine issue will need to be thoroughly understood before that long-awaited flight can be cleared for takeoff.
In a second tweet, Musk elaborated, saying the Sunday launch scrub due to an engine high power reading was "possibly, but not obviously, related to today."
"This vehicle has seen a lot of wear, so today isn't a big surprise," he said. "Life leader rockets are used only for internal missions. Won't risk non-SpaceX satellites."
The Starlinks are designed and built by SpaceX and the 60 launched Wednesday were released to fly on their own about 15 minutes after liftoff. In six flights to date, SpaceX has launched 360 of the internet relay stations.
SpaceX has regulatory approval to launch more than 12,000 Starlink satellites in multiple orbital planes to provide high-speed, uninterrupted internet access from any point on Earth using small pizza box-size terminals. The company plans to begin limited commercial service across the northern United States and Canada later this year.
Other companies also are planning large-scale broadband constellations, including Amazon and OneWeb, which now has 40 spacecraft in orbit. Another batch of 34 OneWeb satellites is scheduled for launch from Kazakhstan atop a Russian rocket on Saturday.
The constellations have raised alarm in the astronomical community that sunlight reflecting off multiple satellites above the horizon at any given moment, along with their radio traffic, could disrupt observations by the world's largest optical and radio telescopes.
Speaking last week at a satellite conference in Washington, Musk said the company is taking steps to minimize the reflectivity of the Starlinks and that he is "confident that we will not cause any impact whatsoever in astronomical discoveries. Zero. That's my prediction, and we will take corrective action if it's above zero."
He said the satellites are more easily visible when first deployed, before they have reached their higher, operational orbits. Once stable and on station, "I'll be impressed if somebody can actually tell me where all of them are."
"We are actually working with members of the science community and astronomers to minimize the potential for reflection of the satellites," he said. "We're running a bunch of experiments to, for example, just paint the phased array antenna black instead of white."
In addition, he said, "we're working on a sunshade because there are certain angles where if the sun gets sort of just right, and there's not like a little sunshade, then you can get a reflection. And so we're launching a sunshade, changing the color of the satellites, and otherwise minimizing the potential for any impact. This should not be an impact, I think."
He did not address concerns about interference with ultra-sensitive radio telescopes. And in any case, astronomers are not convinced. In a letter to Astronomy & Astrophysics, researchers reported initial results tracking the brightness of a Starlink satellite that had been "darkened" by SpaceX to test a non-reflective coating.
The team reported the so-called "Darksat" reflected 55 percent less light and was invisible to the unaided eye even under dark sky conditions.
"However, this reduction does not come close to the required amount needed to mitigate the effects that low orbital mega-constellation LEO (low-Earth orbit) communication satellites will have on ultra-wide imaging exposures from large telescopes, such as the National Science Foundation's Vera C. Rubin Observatory," the astronomers wrote.
To be effective, they continued, the satellites' "reflective brightness" would need to be just 7 percent of the brightness of an unmodified Starlink.