ESA’s Luca Parmitano got to station just 5-1/2 hours after launch, corresponding to 4 orbits, on 29 May – why is ATV-4 taking 10 days?
The short answer is, it can – or, from a basic orbital physics standpoint, it could. But, as with many things related to space flight, this simple question requires some background to answer.
First off, read our earlier post: “Ten days launch to docking,” in which ESA’s Jean-Michel Bois explains that the nominal ‘connect’ time for any ATV is five days (it’s ten days in the case of ATV-4, but that’s due to factors related to docking port availability rather than fundamental physics). Jean-Michel says:
This ‘5-day’ strategy allows a standard set of manoeuvres from the orbital injection point (by Ariane at 260km altitude) and the ISS orbit, which is at between 390-410 km, independently of the launch date and of the ISS position on its orbit.
Next, read the excellent post from Dr Rhett Allain, “Why does it take so long to rendezvous with the ISS?” explaining the basic physics behind how any two spacecraft can meet up in orbit.
OK – now that you’ve got the background, we passed this question to ESA’s Markus Landgraf, one of the mission analysts at ESA/ESOC.
He says that, yes – Ariane can indeed loft ATV into an orbit right from lift-off that, if carefully timed with respect to the ISS’s position, would bring ATV to a rendezvous within just a few orbits, like the Soyuz fast-track approach.
But that’s not how ATV is designed; it fact, the ATV-series are meant to perform a deliberate, automated docking in which safety is paramount.
Listen to his full answer here:
PS: The Progress vessels also can do fast-track; but they, too, don’t do an automated docking.