That was fun to write.
Since a solid 2nd stage is less precise in placing a payload into orbit than a Liquid
Since a solid 2nd stage is less precise in placing a payload into orbit than a Liquid, I wonder how Cygnus compares to Dragon in delta V. It seems reasonable to expect that Cygnus will need more flexibility to reach ISS. The lack of precision in orbital insertion could also mean that the target "drop off" point for Antares is further from ISS than what Falcon 9 is permitted?
The ATK STAR-48BV stage is a thrust-vector-controlled motor offering a simple control system and higher performance than the spinning STAR-48B, which has been used in programs such as New Horizons. The STAR-48BV uses a loaded motor case from the flight-proven STAR-48B, with nozzle design qualified for the Conestoga program and a newly developed thrust vector actuator (TVA) control system currently being qualified to support vectorable nozzles across the STAR product line. The nozzle and thrust vector control system will be used on a STAR-37FMV in mid-2008, and the STAR-48BV upper stage currently is under contract and scheduled for a first flight as part of the Minotaur IV launch vehicle.
The Cygnus will act as a third stage and trim out any dispersions. It has an SM based on the STAR spacecraft bus. There will be a third stage or trim stage for other missions or the payload will have to handle the dispersions.But what does have one nozzle have to do with TVC not being helpful.
Quote from: Jim on 03/06/2013 03:52 pmThe Cygnus will act as a third stage and trim out any dispersions. It has an SM based on the STAR spacecraft bus. There will be a third stage or trim stage for other missions or the payload will have to handle the dispersions.But what does have one nozzle have to do with TVC not being helpful. Thanks for clarifying about the 3rd stage SM. TVC with 1 nozzle is perfectly capable of keeping a rocket pointed in the right direction. TVC with 2 or more nozzles could use Cosine losses to reduce effective thrust and hence orbital height. With just 1 nozzle, the only way I can see to use TVC as a means to adjust orbital insertion height is to "Tack" the entire rocket back and forth. IMHO, that sounds challenging to guidance, slow and cumbersome.
Does "a submerged design" mean the nozzle throat is actually touching/within the grain of the prop?
Quote from: Chris Bergin on 03/06/2013 03:05 amThat was fun to write.That was fun to read!
Thanks Jim. I'm not sure why submerging the nozzle helps--perhaps makes TVC that much easier (both the physics of steering, as well as housing the TVC hardware).I think it's safe to say the stretched casing carries more propellant as well as room for the nozzle (that is, they didn't just stretch to house the nozzle).I realize how silly it sounds to ask if the nozzle was up at the grain of the prop. Then again, it does cause me to ponder the interface between the top of the nozzle and the bottom of the prop on any srm.Speaking of prop, is there a dramatic difference between the chemical components of a solid used at sea level, and that used in vacuum? On a simplistic level, is it still PBAN? HTPB? Some significantly different variation?