[EMAIL PROTECTED] wrote: > Today's Topics: > 9. Re: Black Adder? \ Re: Aerospike engine flies at MTA > (Randall Clague) > ---------------------------------------------------------------------- > Message: 9 > Date: Sat, 04 Oct 2003 00:24:22 -0700 > From: Randall Clague <[EMAIL PROTECTED]> > Subject: Re: [ERPS] Black Adder? \ Re: Aerospike engine flies at MTA > > On Fri, 03 Oct 2003 21:56:23 -0700, David Masten > <[EMAIL PROTECTED]> wrote: > > >I think there is an unstated assumption here. The long burn time comes > >with lower acceleration. > > We were talking about CSXT's 100 km attempt, so I indeed assumed lower > acceleration for a longer burn time. Ignoring that pesky atmosphere > for a moment, a 15 second burn requires 10.04 g, 30 seconds 5.29 g, > and 60 seconds 2.94 g. Pretty significant difference. > > But I still don't see why that matters. OTOH, I see Dave W posted a > long reply, so I'll go read it. > > -R >
Doug Drummond here: There were several good descriptions about pertubations being corrected by active guidence (or not) so I won't waste time on that. One big problem with short burn times for CATS or XPF category rockets is the drag and resulting destructive forces due to high mach numbers at low altitudes. [ Q = rho * Vee ^ 2 ] To keep "Max Q" down to a low roar, 'Everybody' waits until rho is at least one fourth of see level, meaning at least 30-40 kilofeet. It is NOT a coincidence that jet aircraft also cruise in that altitude range. I'm using a very simplified atmospherical model, in which the density is down by half for every 20 kilofeet of altitude. This is a fairly good model up to 50-60 Kfeet. One 'cheat' we came up with for a CATS flight plan was a staged "stutter" with 3 5-sec burns at appropriate intervals. Obviously this required aerodynamic active control and perhaps thrust vectoring also. The first burn accelerated the vehicle to approximatly Mach One, then it coasted to about 20-25 Kfeet. The second stage did a similar burn and coasted. The max coast speed was high subsonic or low supersonic in both cases, with low drag. The last burn/stage was "GO! for it time" accelerating to serious Mach numbers at an altitude of 40-70 kilofeet and air density about 1/8 -- 1/10 of sea level. The bad news is that this is a very complex vehicle with either three stages or a restartable motor. BTW, the proposed motor for this exercise was a lot like the XCOR EZE-Rocket motor -- one of the reasons that I have always thought XCOR was on the right track. Sincerely Douglas E Drummond. _______________________________________________ ERPS-list mailing list [EMAIL PROTECTED] http://lists.erps.org/mailman/listinfo/erps-list
