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#11
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ISS-104-Soyuz records
In article ,
Danny Dot wrote: ...And the Zond tests were not nearly as successful as they looked from outside... The Zonds had a lot of ballistic entries that ended up in the Indian Ocean (v.s. the planned skipped entry into Russia)... Not really "a lot". Indeed, in a strict sense only one -- Zond 5, which was directed to a ballistic reentry because various equipment problems had made the chances of a successful skip remote, and was recovered from the Indian Ocean. Zond 4 had worse equipment problems, and likewise made a ballistic reentry, but didn't land. It was coming down far off course, near the coast of Africa, and its destruct charge was fired before parachute deployment to make sure it wasn't recovered by the US. Zonds 6 and 7 made perfect skip reentries with landings near Baikonur Cosmodrome, although Zond 6's cabin had depressurized earlier, which messed up its landing control systems badly enough that it crashed. And Zond 8 did come down in the Indian Ocean, but that was planned, the result of a new skip trajectory, going over the Northern Hemisphere rather than the Southern-Hemisphere path that 6 and 7 had used. (That improved tracking and control from the USSR, and had some other minor advantages.) (Zonds 1-3 were early-60s planetary probes, unrelated to the circumlunar Soyuz variant; for some reason, the Soviets reused the name.) The darn thing would pull 20G;s but apparently the human body can take this much for a short time. Yes, it's no fun but usually doesn't cause injury. A ballistic lunar reentry is pretty nasty, because there's a lot of energy to be shed in a short time in thick air. A lifting reentry is a lot less drastic, with deceleration peaking briefly at about 7G for an Apollo-class capsule. The reason for the Zond skip reentry wasn't lower deceleration -- other things being equal, it's no better than Apollo's less-drastic lifting reentry -- but greater distance covered during reentry, to put the landing in a better place and give more control of its location(*). Apollo was originally going to use a skip too, in its very early days when it had a requirement for land touchdown in the continental US. Apollo dropped it because relaxation of the landing requirements reduced the need, and while the primary guidance system could fly a skip, neither of the backups could, so planning and procedures were simplified by avoiding the skip. (* It turns out that a ballistic or non-skip lifting reentry ends up coming down at a point very nearly opposite where the Moon was in the sky at the time the return trip starts. The details of the return trajectory influence the ground track and the timing -- and timing determines landing longitude, since it determines which point on Earth has rotated to that point in space at landing time -- but give almost no control of landing latitude. So in particular, if you want a landing at a high-latitude site like Baikonur, you *must* use a skip. ) -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | |
#12
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ISS-104-Soyuz records
Thanks for the post. Lots of great information.
-- Danny Dot wrote: Look at my site and see how NASA treats a creative mind!!! The summary is "Not Very Well" :-) www.mobbinggonemad.org "Henry Spencer" wrote in message ... In article , Danny Dot wrote: ...And the Zond tests were not nearly as successful as they looked from outside... The Zonds had a lot of ballistic entries that ended up in the Indian Ocean (v.s. the planned skipped entry into Russia)... Not really "a lot". Indeed, in a strict sense only one -- Zond 5, which was directed to a ballistic reentry because various equipment problems had made the chances of a successful skip remote, and was recovered from the Indian Ocean. Zond 4 had worse equipment problems, and likewise made a ballistic reentry, but didn't land. It was coming down far off course, near the coast of Africa, and its destruct charge was fired before parachute deployment to make sure it wasn't recovered by the US. Zonds 6 and 7 made perfect skip reentries with landings near Baikonur Cosmodrome, although Zond 6's cabin had depressurized earlier, which messed up its landing control systems badly enough that it crashed. And Zond 8 did come down in the Indian Ocean, but that was planned, the result of a new skip trajectory, going over the Northern Hemisphere rather than the Southern-Hemisphere path that 6 and 7 had used. (That improved tracking and control from the USSR, and had some other minor advantages.) (Zonds 1-3 were early-60s planetary probes, unrelated to the circumlunar Soyuz variant; for some reason, the Soviets reused the name.) The darn thing would pull 20G;s but apparently the human body can take this much for a short time. Yes, it's no fun but usually doesn't cause injury. A ballistic lunar reentry is pretty nasty, because there's a lot of energy to be shed in a short time in thick air. A lifting reentry is a lot less drastic, with deceleration peaking briefly at about 7G for an Apollo-class capsule. The reason for the Zond skip reentry wasn't lower deceleration -- other things being equal, it's no better than Apollo's less-drastic lifting reentry -- but greater distance covered during reentry, to put the landing in a better place and give more control of its location(*). Apollo was originally going to use a skip too, in its very early days when it had a requirement for land touchdown in the continental US. Apollo dropped it because relaxation of the landing requirements reduced the need, and while the primary guidance system could fly a skip, neither of the backups could, so planning and procedures were simplified by avoiding the skip. (* It turns out that a ballistic or non-skip lifting reentry ends up coming down at a point very nearly opposite where the Moon was in the sky at the time the return trip starts. The details of the return trajectory influence the ground track and the timing -- and timing determines landing longitude, since it determines which point on Earth has rotated to that point in space at landing time -- but give almost no control of landing latitude. So in particular, if you want a landing at a high-latitude site like Baikonur, you *must* use a skip. ) -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | |
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