Maybe someone with more specific knowledge in this area can say if this article should be merged with Ullage motor. Qutezuce 04:25, 9 January 2006 (UTC)Reply
Maybe someone with more specific knowledge in this area can say if this article should be merged with Ullage motor. Qutezuce 04:25, 9 January 2006 (UTC)
- Although ullage motors and ullage engines serve the same function, they can be of different designs. In most contexts, "ullage motors" use solid propellants and are therefore only fired once to push the propellants to the bottom of the tank. It appears that in the case of the Saturn V that they also used the term "ullage engine" separately to refer to the Auxillary Propulsion System (APS) which could operate in ullage mode on the 500 series version of the S-IVB (http://www.apollosaturn.com/s4b.htm). Compare this to the 200 series S-IVB on the Saturn 1b which used three solid ullage motors. The APS served as more that just a ullage engine, however, and provided RCS-like functionality for the S-IVB.
This article refers to eight ullage motors on the S-II, but page 11 of the SA503 Flight Manual (http://history.nasa.gov/ap08fj/pdf/sa503-flightmanual.pdf) says that there were just four. I think that the picture that accompanies this article has mislabelled the retro packages on the S-II, because there were four ullage motors and four retro rockets, which adds up to the eight motors that are labelled in the attached image. There is also an image on apollosaturn.com (http://www.apollosaturn.com/s143txt.htm) which clearly shows four ullage and four retro packages on the S-II.
If these articles are going to primarily reference the Saturn V ullage motors then it would be great if they included first-hand descriptions of the Apollo astronauts on their functions. There are many descriptions in many books where the astronauts refer to engine cutoff, in which case they were thrown forward in their seats, followed by the ignition of the ullage engines, which once again forced them back into their chairs. What happened to the astronauts was what happened to the fuel, and brings to life the action of the ullage motors.
A couple of other notes about ullage: ullage not only moves the propellants to the back of the tank so that they can be pumped, but the action of the motors can actually force the propellants into the plumbing of the engine. This is important because there's no lag time for the pumps to begin their action. It's nearly simultaneous with the ignition of the engines. Another note about ullage is that you'll sometimes see it refer to any propulsion which translates into positive movement in the z-axis. This is probably not a correct use of the term, but it's understandable given that ullage is obtained by initiating and sustaining forward momentum.
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