From: vince@offshore.ai (Vincent Cate) Newsgroups: sci.space.tech Subject: Re: Unguided orbital insertion (cheap upper stages) References: <9186edb5.0311101839.1d56c610@posting.google.com> <9186edb5.0311151754.68720ff8@posting.google.com> NNTP-Posting-Host: 207.42.133.230 henry@spsystems.net (Henry Spencer) wrote in message news:... > A while back, I wrote: > >...My guess is that the very fast spin of the Juno upper stages > >was to even out possible performance differences between the solids in > >each stage. > > Confirmed. In fact, they would have liked a still higher spin rate -- > they grumbled about how they couldn't really do precision orbit insertion > because of dispersion due to motor non-uniformities -- but the motors > just couldn't take it. And Henry earlier: >You need to model possible disturbing >torques, and decide how much gyroscopic stability you need to handle them. >Spin rates for comsats with solid-fuel apogee motors are not high, tens of >RPM at most. So if each stage was a single solid, instead of a cluster of solids, there would be less disturbing torques. Also, if we are starting at 90+ km high then there is less disturbance from air than a lower air launch like NOTSNIK. So an orbital launch from an X-prize vehicle could be done with a more moderate RPM. Cool. -- Vince