Launch of a Russian Progress cargo ship loaded with 2.9 tons of supplies and equipment bound for the International Space Station was aborted at the last second Thursday when the engine start sequence failed to engage after an otherwise flawless countdown.
The Progress MS-07/68P supply ship perched atop a workhorse Soyuz booster had been set for takeoff at 5:32 a.m. EDT (GMT-4; 3:32 p.m. local time), just 29 seconds before the space station passed over the Baikonur Cosmodrome.
The launch was timed to permit a fast two-orbit rendezvous with the lab complex, a procedure the Russians hope to use later with piloted Soyuz crew ships. But as the countdown ticked toward zero, the booster's engines did not ignite. The station passed overhead 29 seconds later and the rendezvous opportunity was lost.
Assuming the problem, whatever it was, can be resolved in time, the next launch opportunity will come Saturday at 4:46 a.m. EDT. But the station's trajectory and the subtleties of orbital mechanics will preclude a two-orbit rendezvous. Instead, the spacecraft will fly a 34-orbit approach, reaching the station two days after launch.
The 34-orbit rendezvous procedure was the norm for unpiloted Progress and Soyuz crew ships during the early years of station operations. But in recent years, the Russians shortened the rendezvous sequence to just six hours, or four orbits, to reduce the time crews spend cooped up in the cramped ferry craft.
The 34-orbit procedure is still available as an option -- it will be used on the next piloted Soyuz launch Dec. 17 -- but the Russians hope the two-orbit rendezvous will prove feasible when orbital mechanics permits.
As it now stands, the next chance to test the procedure will be delayed to next year. The first Progress flight of 2018 is scheduled for launch Feb. 13, but it's not yet known if that flight is an option.