Iran entered the exclusive club of nations capable of putting things in Earth orbit on February 2, when it launched a small satellite using a homegrown rocket for the first time. Called Omid, or “Hope”, the satellite is a 40 cm wide cube with a mass of 27 Kgs.
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.
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 programs of Iran and other countries, including China and Russia.
David Wright of the Union of Concerned Scientists in Cambridge, Massachusetts, has posted the results of his calculations online.
For the calculations, Wright relied on the size and mass of Safir-2 reported in the Iranian media, which gave it a length of 22 metres, a diametres of 1.25 metres and a mass of 26 tons. He also determined the relative sizes of the two stages from photos of the rocket posted online.
Given the rocket's volume, its reported mass is consistent with a type of hydrazine called UDMH, which has long been used by China in its space launch vehicles, Wright says.
Assuming the fuel had the efficiency of UDMH, Wright also calculated the rocket's thrust and specific impulse, a measure of how much momentum a rocket can provide per kilogram of fuel burned. The calculated figures are enough to give a payload like Omid a speed of 7.6 Kms per second at an altitude of 240 Kms, which is about right for the orbit Omid is observed to be in.
“I don’t know for sure that that’s what they did, but (this) would seem to give Iran the capability to do this with two stages, and the reports coming out of Iran all seem to be pretty definite that it was two stages,” Wright told New Scientist.
If Iran really has developed more advanced rockets that can burn more efficient fuel, then it is a step closer to launching people into space, Forden says. Reza Taghipour, head of Iran's Aerospace Industries Organization, has said this is a goal Iran hopes to achieve.
The Long March rockets that China uses to put its taikonauts in orbit burn UDMH, although these are much larger and more powerful than the Safir-2.
“(Iran) could get a person up into low-Earth orbit certainly within a decade, at the rate they're going," Forden says. "Whether or not the guy can return safely is another question. A lot of things have to go right.”
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March 2009 |
