Late Agena B / Agena D missing ullage RCS thrusters

[CAPFlyer]

I've noted that the Agena B & Agena D equipment racks lack provision for RCS-based ullage thrusters. Per available documentation, the later Agena B and all Agena D had RCS-based ullage thrusters instead of the solid rocket-based ones.

See - http://www.b14643.de/Spacerockets_2/United_States_4/Agena/index.htm (Section called "Agena B, D, & D+)

Agena B with integrated Ullage Thrusters/Rockets - http://www.b14643.de/Spacerockets_2/United_States_4/Agena/B_3.jpg

Agena D with integrated Ullage Thursters/Rockets - http://www.b14643.de/Spacerockets_2/United_States_4/Agena/D_1.jpg

I also found this which mentions "secondary propulsion" which I would take to be the Ullage Thrusters -

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=16154.0;attach=315794;image

[mountainparrot]

I also found this which mentions "secondary propulsion" which I would take to be the Ullage Thrusters -

The secondary propulsion system was a thruster package attached to the sides of the Agena D aft rack and is included in the mod. You can see the packages either side of the main engine in this image: https://upload.wikimedia.org/wikipedia/commons/2/2f/Gemini_and_Agena_D.jpg

[CAPFlyer]

Yes, but the reference image listed "secondary propulsion" for AGENA B under "Ancilliary Devices" and not AGENA D. Agena B had a different equipment rack.

[CobaltWolf]

I can actually see that little green thruster being a nice part to have. I'll see if I can bash something together some time!

[Pappystein]

Agena D did not need Ullage. The whole point of the upgrade from the B to the D was twofold. A) Digital electronics replaced analog clock-based electronics saving weight and length (approximately 4 inches) and B) The new sump system allowed for zero Ullage in low/no gravity.

This is all called out here: https://ntrs.nasa.gov/search?q=19720013179

The document is actually focused on the Ascent Agena but it coroberates many other agena documents all in one simple pdf.

[CAPFlyer]

Sorry to be so long responding to this. I don't agree with your assertion Pappy. The document you linked doesn't make a blanket statement like you did. In point, there is this from Page 1-4 - "...and devices were implemented as each major block of vehicles was manu-factured," and this lists the development of the advanced ullage control after that statement, suggesting it was an improvement created within Agena D production, not as part of the Agena B -> Agena D improvements. My links suggest this as well, that the ullage improvement was something introduced in the mid/late Agena D production run, and thus the need for the small thruster configuration seen on many of the early Agena D launches and most especially on the Reconnaissance and Intelligence flights.