Why are engines usually "chilled down" prior to startup? This strikes me as exactly the wrong thing to do. When the engine actually starts, it immediately gets extremely hot, going through a substantial change in temperature in a fraction of a second. Chilling down the engine would seem to drastically increase the amount of temperature change it undergoes. Most materials don't like wild and abrupt temperature swings; they will often fracture or deform or otherwise suffer substantial degradation. Anyone who has placed a hot glass on a cold counter and seen it shatter will be familiar with this.Obviously, since engines don't fracture upon startup from the thermal shock, there's a link in the sequence that I'm missing. Perhaps "chilldown" doesn't mean chill down in the usual sense?
I don't follow. Rockets are fueled over a long period of time (30 minutes or so, at least, based on the latest SpaceX launch), which means that the cryogenic components should reach cryogenic temperature gradually. But rocket engines go from ambient temperature to red-hot in a matter of seconds.
Well, I remember reading Wernher von Braun's popular book Space Frontier long ago. IIRC, the four cycles he described were pressure-fed, gas-generator (by which he meant monoprop gas-generator), bi-propellant (i.e., what we call GG around here), and topping (regenerative). So he seemed to regard it as a separate cycle.
I heard a report on Daily Planet on the Discovery Channel that said that CO2 was produced along with water vapour when the RS-25 was test fired.Is this true?
RS-25 burns Oxygen and Hydrogen.Where would the carbon come from?
Since the exhaust is hydrogen rich and hot, I imagine a number of compounds involving H, N and O would form, possibly including some nitric acid (HNO3).