Saturday, December 18, 2010

Iran Launched Safir Satellite

On February 2, 2009 Iran launched a satellite weighing 27 kilograms using the Safir Omid two-stage rocket. Iran describes the Safir as a space-launch vehicle. Photographs of the Safir upper rocket stage used to inject the satellite into orbit suggest that the Safir could not be used as a ballistic missile to carry nuclear warheads to significant ranges. The rocket motors used in this upper stage do not have enough thrust to efficiently offset the additional gravitational force that would act on the upper stage when it carries a heavy warhead payload (in this case, payloads of 500 to 1000 kg, rather than 27 kg).

The inability of the upper stage's low-thrust rocket motors to offset gravitational forces and the very light construction of the stage, would likely limit the ability to accelerate the upper rocket stage and its heavier payload to the higher speeds needed to achieve significant range increases over a one-stage vehicle. However, as noted earlier in this chapter, Iran has demonstrated that it could develop a new or modified upper rocket stage based on SCUD rocket technology that would make it possible for the Safir to deliver a 1000 kg warhead to ranges of about 2000 km.

The first stage of the Safir launch vehicle is derived from the Shahab 3 airframe. The first stage fuel and oxidizer tanks are extended to increase the fuel load of the first stage by about 60 percent relative to that of the Shahab 3. Photographs released by Iran of the second stage propulsion section shows what appears to be two vernier rocket engines and a turbopump exhaust nozzle that look like they have been salvaged from a dismantled Russian SS-N-6 submarine-launched ballistic missile. These photographs suggest that the upper
stage of the Safir uses a powerful and energetic fuel combination, N2O4 and UDMH (Nitogen Tetroxide and Unsymmetrical Dimethyl Hydrazine), which allows for rocket motors with high exhaust velocities relative to those based on SCUD technology. Information derived from Iran’s successful launch of a satellite
weighing 27 kg makes it possible to estimate possible performance characteristics of this upper stage.

Additional photographs published by the Iranian Space Agency show that the satellite was powered by three banks of 15 standard D-sized batteries. It also had an onboard computer module, separate UHF transmitter and receiver modules, and other circuitry, all of which appear to have been constructed from electronic
components manufactured by Western companies. For example, two Dallas Semiconductor Corporation 64 kb static random access memory chips (SRAM) and microwave signal splitting devices from the Mini-Circuits company can be readily identified from the photographs. This satellite is therefore derived from commonly available commercial electronic components, none of which could possibly be manufactured by Iran. A very rough estimate of the weights of these different components leads to the conclusion that the satellite might well weigh the 27 kg reported by Iran.

We have reasonable estimates of the performance characteristics of the first rocket stage, which is basically derived from the technologies used to build the Nodong missile and its variants (like, for example, the Shahab-3M). The first stage carries a heavy payload during its powered flight (the fully fueled second stage and the satellite) and burns out at a relatively low altitude and velocity (about 2.1 km/s at an altitude of 68 km). As a result, the exact performance characteristics of the first stage do not strongly affect the overall ability of the two stage rocket to place the satellite into orbit (the required orbital speed for the satellite is roughly 7.7 km/s). If the rocket can place the satellite into orbit, almost all of the velocity needed to achieve this result must come from the second stage.

Hence, the information about the orbital characteristics of the Omid satellite makes it possible to estimate the total velocity capability of the second stage. This then makes it possible to estimate the performance characteristics of the upper rocket stage. These estimates can then be used to determine the possible range and payload of this rocket, or its variants, if it is employed as a ballistic missile.

At this time, there is still considerable uncertainty about the configuration of the second stage of the Safir and the actual engineering components that were used in it. In 200512 Iran reportedly bought 18 disassembled SS-N-6 (R-27) Soviet submarine launched ballistic missiles from North Korea. The R-27 utilizes Soviet
rocket technologies that were first developed in the 1960s. The propulsion system of the R-27 uses a single rocket motor that generates a thrust of 23 tons and two steering rocket thrust chambers that together generate 3 tons of thrust. The powered flight-time of the R-27 is about 120 seconds.

The two steering rocket thrust chambers are fed by a single turbopump and the fuel used by the R-27s rocket motors is Nitrogen Tetroxide and Unsymmetrical Dimethylhydrazine (N2O4 and UDMH). This propellant is much more powerful than that used by missiles based on SCUD technology. The R-27 airframe is also constructed from highstrength Aluminum alloys, which have a density almost one third that of steel.

Assuming the photographs of the Safir upper stage are not misleading, the motor would have to operate for about 274 seconds, roughly two and a half times longer than the time it is supposed to operate when used as part of the R-27. Calculations also indicate that if the Safir upper stage is capable of launching a satellite, it must have a very low empty-weight. Such a low empty-weight would almost certainly require that the stage's airframe be constructed from light-weight high-strength aluminum alloy rather than from heavy steel. The R-27 is constructed using these same materials. Such a light aluminum airframe would likely only be able to support a very light-weight payload. In addition, if payloads of hundreds of kilograms or more could be mounted on this upper stage, the lowthrust of the rocket motors could not initially offset the pull of the Earth's gravity
on the vehicle, and it would continuously lose vertical velocity during the early part of its powered flight.

These observations lead to the conclusion that the current Safir upper rocket stage is not readily adaptable to carrying a warhead of a thousand, or even hundreds of kilograms. Thus, if our observations about the Safir
upper stage are correct, the upper rocket stage used to launch the Omid satellite is only useful for launching a very light satellite into a low-earth orbit. Any further advances towards launching heavier satellites to low earth orbits, or lighter satellites to higher orbits, will require an entirely new rocket with first and second stages that are considerably larger than those used by the Safir.


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