Quote from: mmeijeri on 05/25/2009 04:25 pmQuote from: Danny Dot on 05/25/2009 03:36 pmThe "winner" is a ballistic ascent abort entry and ballistic lunar entry. I read that a normal lunar reentry is mostly ballistic anyway, with only the RCS being used for attitude control. Is this true? And if so, how much difference does the attitude control make?A guided entry uses roll to put the lift vector largely up. In a ballistic entry with a capsule, roll is set to a constant value and the end result is no effective lift.
Quote from: Danny Dot on 05/25/2009 03:36 pmThe "winner" is a ballistic ascent abort entry and ballistic lunar entry. I read that a normal lunar reentry is mostly ballistic anyway, with only the RCS being used for attitude control. Is this true? And if so, how much difference does the attitude control make?
The "winner" is a ballistic ascent abort entry and ballistic lunar entry.
Nit: A capsule with an offset CG performs a ballistic entry by setting roll *rate* to a constant, so that the direction of the lift vector averages out.
Quote from: Jorge on 05/25/2009 09:39 pmNit: A capsule with an offset CG performs a ballistic entry by setting roll *rate* to a constant, so that the direction of the lift vector averages out.Ah, so does ballistic mean "as if there were no atmosphere and no propulsion" instead of "without propulsion" in this context?
Quote from: Danny Dot on 05/25/2009 09:27 pmQuote from: mmeijeri on 05/25/2009 04:25 pmQuote from: Danny Dot on 05/25/2009 03:36 pmThe "winner" is a ballistic ascent abort entry and ballistic lunar entry. I read that a normal lunar reentry is mostly ballistic anyway, with only the RCS being used for attitude control. Is this true? And if so, how much difference does the attitude control make?A guided entry uses roll to put the lift vector largely up. In a ballistic entry with a capsule, roll is set to a constant value and the end result is no effective lift.Nit: A capsule with an offset CG performs a ballistic entry by setting roll *rate* to a constant, so that the direction of the lift vector averages out.
A ballistic entry has zero lift. The only thing you can control is the angle of entry into the atmosphere. The astronauts would experience at least 17g's. NASA considered that to be not survivable.The Apollo entry was close to ballistic but with a small change to generate some lift: the CG was offset resulting in a small trim attitude. The lift kept the CM in the upper atmosphere long enough so the astronauts would not experience much over 7g. The lift vector could only be controlled by rotating the CM.Source: http://www.mae.usu.edu/aerospace/publications/Reno_rev_whitmore.pdfhttp://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060045567_2006144506.pdf
I would imagine a 20 g force on a launch abort would be very short in duration -- only in the moments after the initial firing. Sorta like an ejection seat on some fighter jets. Correct?
You do get a big g-pulse at LAS firing, but don't forget about the subsequent re-entry, which will be steeper than normal due to the lower horizontal velocity.
Quote from: Jorge on 05/26/2009 04:13 amYou do get a big g-pulse at LAS firing, but don't forget about the subsequent re-entry, which will be steeper than normal due to the lower horizontal velocity.I was only thinking about an escape at launch.
I guess the system could be used all the way up to orbit.
I'm embarassed to ask this but I never knew, are ELV stages recovered for burial or recycle or any other use (excepting reuse of course)
20+G for how long. snip
Quote from: C5C6 on 05/27/2009 09:14 pmI'm embarassed to ask this but I never knew, are ELV stages recovered for burial or recycle or any other use (excepting reuse of course)The only ones I know of are some solids on the Ariane that land on land and sometimes they take one down on chutes that land on water. Not to reuse, but to look at for problems in the design or manufacturing process.Danny Deger
Quote from: Danny Dot on 05/27/2009 10:13 pmQuote from: C5C6 on 05/27/2009 09:14 pmI'm embarassed to ask this but I never knew, are ELV stages recovered for burial or recycle or any other use (excepting reuse of course)The only ones I know of are some solids on the Ariane that land on land and sometimes they take one down on chutes that land on water. Not to reuse, but to look at for problems in the design or manufacturing process.Danny Degerso the ones that don't have chutes and crash on land or water are not recovered not even for cleanup??? I really find it hard to believe they keep throwing rocket stages to some places and are not removed....you'd have a pile of rocket stages in the atlantic only because of KSC launches.....another embarassing question: most of second or third stages burn up on reentry don't they?? first stages do not acquire enough speed for a destructive reentry do they???