The evidence is mounting that the Iranian rocket recently used to launch a satellite was more powerful and advanced than initially thought.
Iran entered the exclusive club of nations capable of putting things in Earth orbit on 2 February, when it launched a small satellite using a homegrown rocket for the first time. Called Omid, or "Hope", the satellite is a 40-centimetre-wide cube with a mass of 27 kilograms.
But there has been much debate about whether the rocket that launched it was relatively crude and inefficient, operating at the limits of its capabilities, or a more advanced type that could eventually be upgraded to put astronauts in orbit. Iran has released few details about the rocket, called Safir-2, leaving outsiders to guess at its capabilities.
Initially, outside rocket experts thought the Safir-2 was based on scud missile technology, which Iran is known to have obtained previously from North Korea.
Scuds, and other rockets derived from them, pack less punch than more advanced rockets because they burn a relatively inefficient fuel - a mixture of kerosene and nitric acid.
Even a two-stage scud-type rocket, with the second stage separating and igniting after the first stage provided an initial burst of speed, would not be powerful enough to reach orbit.
So it was thought that Iran had mounted a very small, solid-fuelled third stage on this kind of launch vehicle to provide the final kick needed to get Omid to orbit.
But soon after Omid's launch, amateur satellite trackers reported that the final stage, which also reached orbit, appears much too bright to be a tiny third stage, hinting that it might be a two-stage vehicle using more advanced technology instead.
New calculations have reinforced this view, showing that a two-stage rocket the size of Safir-2 could get Omid to orbit if it had ditched the scud design in favour of engines that use more efficient hydrazine fuel.
"I think it's [now] much more likely that it really is a two-stage rocket," Geoffrey Forden of MIT told New Scientist. Forden analyses the rocket programmes of Iran and other countries, including China and Russia.