Random question here. SpaceX attaches their reaction frame to the transporter, but the Russian's don't. (see below) Any ideas about why each of them made the choices they did? The Russian approach, to me, seems like it has one less fluid/electrical connection to worry about.
One possibility is that FH will have a different reaction frame (which I believe is true?), so having it permanently installed is not an option.
Correct me if I'm wrong but older models of Soyuz didn't roll, so the table turned to set the azimuth. Is that the correct term? Therefore the table and it's turning mechanisms needed to be static. I can't provide a reference but it may have been Anatoly Zak.
Quote from: Grandpa to Two on 05/11/2017 11:45 pmCorrect me if I'm wrong but older models of Soyuz didn't roll, so the table turned to set the azimuth. Is that the correct term? Therefore the table and it's turning mechanisms needed to be static. I can't provide a reference but it may have been Anatoly Zak.Most versions of Soyuz rockets can't perform a roll maneuver. That is still true for some versions still flying today. Only the most recent versions can perform a roll on their own and don't require the launch platform to negate the need for it.
How does Soyuz achieve roll stability?And, how do they manage to avoid being able to roll? All that's needed is multiple independently gimballed rocket motors. At liftoff, those five clusters are obviously independent, and if they can't be gimballed at all, how does the rocket achieve guidance?Once the boosters are gone, the core still has the four smaller, independently gimballed steering motors, right? So why can't it use those to roll?
Quote from: IainMcClatchie on 05/13/2017 08:38 pmHow does Soyuz achieve roll stability?And, how do they manage to avoid being able to roll? All that's needed is multiple independently gimballed rocket motors. At liftoff, those five clusters are obviously independent, and if they can't be gimballed at all, how does the rocket achieve guidance?Once the boosters are gone, the core still has the four smaller, independently gimballed steering motors, right? So why can't it use those to roll?I think it has to do with the analog flight computers the older versions use(d). Unable to iterate fast enough to control the complex motion and independently gimbaled engines, perhaps? Some who is a rocket scientist might have to explain.
I think it has to do with the analog flight computers the older versions use(d). Unable to iterate fast enough to control the complex motion and independently gimbaled engines, perhaps? Some who is a rocket scientist might have to explain.
Quote from: cppetrie on 05/13/2017 08:44 pmI think it has to do with the analog flight computers the older versions use(d). Unable to iterate fast enough to control the complex motion and independently gimbaled engines, perhaps? Some who is a rocket scientist might have to explain.Soyuz-FG still has it. and if i am not mistaken it was(still?) manufactured in Kharkiv (Ukraine) only Soyuz-2 has new all digital russian manufactured flight computers.
Quote from: drzerg on 05/17/2017 11:55 pmQuote from: cppetrie on 05/13/2017 08:44 pmI think it has to do with the analog flight computers the older versions use(d). Unable to iterate fast enough to control the complex motion and independently gimbaled engines, perhaps? Some who is a rocket scientist might have to explain.Soyuz-FG still has it. and if i am not mistaken it was(still?) manufactured in Kharkiv (Ukraine) only Soyuz-2 has new all digital russian manufactured flight computers.Yes. With the recent retirement of the Soyuz-U, the only remaining version with analog computers is the Soyuz-FG. Oddly enough, it is also the only currently man-rated rocket in service. Seems kinda crazy that the only rocket we'll send people to space in is using analog computers.
Quote from: cppetrie on 05/17/2017 11:59 pmQuote from: drzerg on 05/17/2017 11:55 pmQuote from: cppetrie on 05/13/2017 08:44 pmI think it has to do with the analog flight computers the older versions use(d). Unable to iterate fast enough to control the complex motion and independently gimbaled engines, perhaps? Some who is a rocket scientist might have to explain.Soyuz-FG still has it. and if i am not mistaken it was(still?) manufactured in Kharkiv (Ukraine) only Soyuz-2 has new all digital russian manufactured flight computers.Yes. With the recent retirement of the Soyuz-U, the only remaining version with analog computers is the Soyuz-FG. Oddly enough, it is also the only currently man-rated rocket in service. Seems kinda crazy that the only rocket we'll send people to space in is using analog computers.Actually not that crazy. If you look at the resiliency of these analog systems - especially in respect to cosmic radiation events - and compare that to modern CMOS technology, the difference is fundamental.In an analog computer the rad event causes a momentary spike in a voltage level, but not significant enough to affect the accumulated voltage in capacitors. It's basically just static noise, which won't significantly affect the computation result.In a digital system, a rad event can cause a gate to flip and turns a 1 into a 0 or the other way around - effectively altering memory in a persistent way - and depending where that happens (worst case the most significant bit in an accumulator) it can have drastic results on the control output. The system is no longer inherently tolerant, as such you need much more complex external redundancy (like SpaceX multiple computers checking each other) or use shielding and hardening of the component to make radiation less likely to flip bits.The advantage of digital systems, they are cheaper and much more capable. Digital system are also much easier to test and certify in simulation.Because of that, effectively no one in their right mind would design a new rocket with an analog system these days. But if you have a flight proven* rocket with all the required functionality already in it, with hundreds of launches flight-heritage, that would actually be a very safe system to fly. They might be extremely antiquated, but they also have unmatched robustness.A bit similar to the question: How do you certify your space rated checklist-tablet to operate in an emergency situation?a) extra batteries under the seatb) solar cells and an emergency hand-crank on a dynamo to rechargec) the tablet uses paper and comes with a pencil on a stringEdit: *Due to recent events and to prevent confusion, I think the attribute "flight-proven" should only be used in the context of individual rockets, not rocket families. The term "flight-heritage" fits better.