[X] My Assistant

[hal_9000]

From Space.com
BOULDER, Colorado -- A commercial remote sensing spacecraft has caught Chinese space workers readying their second piloted space mission.

The Ikonos satellite, operated by Space Imaging of Thornton, Colorado, took images of China’s human spaceflight launch complex on October 3 and October 9, with a shadow covering much of the rocket between two structures. The very tip of the rocket can be seen emerging from the shadow.....

http://www.space.com/missionlaunches/05101...unchcenter.html

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[djellison]

That brief burst of brown/red exhaust is something that the Titan 2 exhibited as well, i believe it's a small motor used to kick start the compressor turbine.

Doug

[GregM]

That brief burst of brown/red exhaust is something that the Titan 2 exhibited as well, i believe it's a small motor used to kick start the compressor turbine.

Doug

The rusty exhaust smoke and clear flame is a product of the fuel being used: hydrazine and nitrogen teteroxide. The charge that gets the turbopumps up and running briefly adds signifigantly to the colour of the smoke at ignition as well.

There are 3 basic types of liquid fueled rocket engines used in big launchers: cryogenic, storable-hypergolic, and petroleum-based. Most big Chinese space launch vehicles and military missiles use storable-hypergolic. This system has a few big advantages: the fuel/oxidiser can be used at room temperature, and the fuel and oxidiser ignite when contacting each other. This means that the fuel and oxidiser can sit in the launch vehicle for many days, weeks, or months if need be (unlike liquid oxygen, hydrogen, or methane). It also means that the engines do not require an ignition system – just pump the fuel and oxidiser into the combustion chamber and it flames away, resulting in a much simpler and foolproof engine!

One downside to this system is the horrible toxicity of these liquids. Very, very lethal for people to ingest, and handling them is expensive and problematic. This is why most newer launch systems shy away from these propellants. The other downside is the need to keep the fuel and oxidiser apart up till the moment they are mixed in the engine. This usually means that the vehicle body and tanks are double-walled and physically separated. The tiniest propellant leak can spell disaster for the launch vehicle and ground crew.

These propellants originally had their uses in military ICBM/IRMB/SLBM missiles. At one time, they were the propulsion system of choice for big military missiles. The ability of the fuel to sit for long periods of time in the missile allowed the missile to be pre-fuelled and then to stay ready and on alert to be fired at very short notice for many months. A simple(er) combustion system allowed for the missile’s greater ease of use in the field. Eventually, the storable-hypergolic fuels were supplanted by solid fuelled missiles, which had all the advantages of storable-hypergolic without the dangers and difficulty of handling. The Americans went all-solid fuel with their large missiles by the mid-60’s. The Soviets had a much harder time developing large solid fueled rocket motors and did not switch over till the early 1990’s. Up until then, all of their long-range missiles were storable-hypergolic (with the exception of the Semyorka). The Chinese however, are just getting there now.

Many space launch vehicles are derived from large military missiles, especially in the first 25 years of spaceflight. Because of that, many have used storable-hypergolic propellants. The Americans used them in the Vanguard, Titan 2, Titan 3, and Titan 4 (all of these vehicles are retired). The Soviets/Russians have used them in the Kosmos, Cyklone, and Proton launch vehicle families. I believe that the Chinese currently use them in all of their launch vehicles.

Although as time goes by and this family of propellants slowly fades out in use with large boosters, it still holds favour as the system of choice in spacecraft and in some upper stages of both long range missiles and space launchers. This is mainly due to their ease of restart in a vacuum environment and long-term internal storage. NASA’s announcement to abandon this fuel system in favour of ammonia and methane in the new Constellation family of manned spacecraft marks a significant departure from this standard operating practice.

[dvandorn]

One downside to this system is the horrible toxicity of these liquids. Very, very lethal for people to ingest, and handling them is expensive and problematic. This is why most newer launch systems shy away from these propellants. The other downside is the need to keep the fuel and oxidiser apart up till the moment they are mixed in the engine. This usually means that the vehicle body and tanks are double-walled and physically separated. The tiniest propellant leak can spell disaster for the launch vehicle and ground crew.

Another big downside, back during Apollo days, to using the hypergolics was they tended to be corrosive. You could keep them in aluminum tanks with no problems, but they ate away at gaskets and seals. You had to have all-metal seals from the fuel and oxidizer tanks into the feed lines, keeping the lines entirely clear of either propellant until you "armed" the vehicles for launch. At that point, you had roughly one month to launch the spacecraft before the propulsion systems were considered degraded. At that point, the fuels were drained and the seals and gaskets had to be replaced before they could fly. This was especially true of the LMs.

One of the biggest issues they had in adapting the Apollo CSM for SkyLab was to make the propellant systems "good" for at least three months after the main seals were cracked. The SPS and the RCS propellant systems were both upgraded with corrosion-resistant seals and gaskets. One of the results was a leak in the propellant lines in two of the RCS quads on the second SkyLab CSM -- the new corrosion-resistant seals and gaskets were apparently a little more prone to cracking than the older style, and sprung leaks.

One of the reasons why the Shuttle takes so much refurbishment is that it uses UDMH and nitrogen tetroxide in its OMS and RCS systems. After each flight, the gaskets and seals in the RCS and OMS propellant lines are cleaned and, often, replaced.

-the other Doug