Indian space officials say they know what went wrong on the debut flight of the nation's new rocket last summer.
The 112-foot-tall (34 meters) Small Satellite Launch Vehicle (SSLV) lifted off for the first time ever on Aug. 6, 2022, carrying the EOS-02 Earth-observation satellite and a tiny student-built cubesat called AzaadiSAT skyward.
Everything went well at first. But instead of delivering the two satellites to their intended circular orbit 221 miles (356 kilometers) above Earth, the rocket ejected the payloads into a highly elliptical path that took them within just 47 miles (76 km) of Earth at the closest point, or perigee. Both spacecraft came crashing back to Earth in short order.
Six months later, ISRO officials have pinpointed what caused the failure of the SSLV, which consists of three solid-fuel stages topped by a "velocity trimming module," or VTM.
Analyses "revealed that there was a vibration disturbance for a short duration on the Equipment Bay (EB) deck during the second stage (SS2) separation," ISRO wrote in an update on Wednesday (Feb. 1).
This higher-than-expected vibration briefly saturated all six accelerometers in the rocket's navigation system. As a result, onboard software declared the accelerometers faulty and triggered a "salvage mission mode," in which the SSLV attempts to deploy payloads into a stable orbit despite a detected anomaly, ISRO officials explained.
The satellites were not successfully salvaged, however; deployment occurred when the SSLV was going about 125 mph (200 kph) slower than the required 17,209 mph (27,695 kph). The velocity shortfall is attributable, at least in part, to the fact that the VTM never fired up — a feature of salvage mode.
"VTM ignition was bypassed as programmed, since it could be a deterrent to the success of salvage option in some cases," ISRO officials wrote.
In addition, the SSLV conducted its salvage work without data from the accelerometers, because they had been declared faulty. Investigators have since concluded, however, that the accelerometers survived the vibrational shock in good shape; they were briefly saturated but not damaged.
The investigation also highlighted a number of measures that, taken together, should prevent the problems that doomed the SSLV's debut flight from cropping up again.
For example, designers have swapped out the second-stage separation system, installing one that's "proven to be generating lesser shock and is already used in the separation of third stage," the ISRO update reads.
In addition, salvage mode won't automatically lock out the VTM anymore.
"The propulsive capability of VTM will be considered in this salvage mode also, and thrusters will be operated to ensure the minimum required perigee for the mission," ISRO officials wrote.
These changes have apparently been incorporated already, for the SSLV, which can loft up to 1,100 pounds (500 kilograms) to low Earth orbit, is getting ready to fly again. ISRO is targeting the first quarter of this year for the rocket's second mission, which will carry the EOS-07 Earth-observation satellite and two smaller rideshare payloads.
Mike Wall is the author of "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or on Facebook.