[AR] Re: Regarding Univerity solid rockets for cube-sat launch to orbit
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sat, 3 Mar 2018 15:44:10 -0500 (EST)
On Sat, 3 Mar 2018, Nels Anderson wrote:
The mass overhead can be substantial, and minimizing that requires
using reactive liquids (e.g. the N2O4 injection used in the Titan III
SRBs) which add handling hazards...
Aside from it already being available at the pad in the case of the
heavy Titans, was there particular reason for choosing N2O4?
To get maximum effectiveness -- greatest possible exhaust deflection for a
given injected flow rate -- you want something that reacts with the
exhaust to generate a large volume of hot gas. Since the SRB exhaust
stream was fuel-rich, this meant injecting an oxidizer, and N2O4 was the
obvious choice.
(If you look at a photo of a Titan IIIC on the pad, you'll see a slim
cylinder nestled in the groove between the core and one SRB -- that's the
N2O4 tank for that SRB.)
A subtlety of LITVC is that you want the injectant tank pretty much empty
at the end of the burn, since unused injectant is dead weight that hurts
payload. This is a little tricky if you're not quite sure how much you'll
need for vectoring! The simplest way would be to dump some occasionally
during the burn, getting rid of injectant that you're pretty sure you no
longer need. The Titan III designers decided to be clever instead: the
ring of injection valves is actually dribbling injectant into the exhaust
continuously, with vectoring done by sending more flow to one side and
less to the opposite side. Arguably more elegant, but it complicates the
valve system and may have contributed to the leak problems.
Henry
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