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Dragon2 test flight
On 19-03-02 11:17 , Rocket Man wrote:
"Jeff Findley" wrote in message ... ... From what I understand, Dragon 2 has a triply redundant computer system so any computer hardware problem shouldn't be an issue. [...] [...] Also, the astronauts don't have any control over Crew Dragon, it's completely autonomous. I believe that is not correct. At the pre-launch press conference it was evident that the Crew Dragon can be commanded from the ISS -- as long as the commanding system works, of course. The docking plan includes a "back away" command sent from the ISS (or so I understood) which will make the Crew Dragon move a certain distance away, and then a new command will let it approach again, and dock. If something goes wrong, there's nothing they can do to prevent a catastrophe. The risk is that the Crew Dragon malfunctions in a way that prevents commanding it. -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ . |
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On 19-03-03 16:54 , Jeff Findley wrote:
In article , says... "Jeff Findley" wrote in message ... From what I understand, Dragon 2 has a triply redundant computer system so any computer hardware problem shouldn't be an issue. I'd bet the updated computer hardware on Dragon 2 is at least somewhat based on what was done with Dragon, which has been successful in terms of its software used to approach and station keep near ISS so that the SSRMS can grab it. The difference is that Cargo Dragon is docked via a robotic arm, whilst Crew Dragon docks via the airlock. That's a significant difference. Also, the astronauts don't have any control over Crew Dragon, it's completely autonomous. If something goes wrong, there's nothing they can do to prevent a catastrophe. I watched the docking on NASA TV this morning. The crew were definitely monitoring the approach and even had a display from the Dragon 2 on one of their laptops. Could they have commanded an abort from that laptop? I don't know, but it wouldn't surprise me if they could command a hold or even an abort. The SpaceX commentary to the docking video makes it quite clear that the ISS crew can and did command Crew Dragon. At least the following commands were described as being given from the ISS to Crew Dragon, during this approach and docking: - command to turn on the blinking white nav light - command to retreat from the 150 m waypoint to 180 m - command to turn on the continuous (non-blinking) white docking light - command to set the approach speed, when Crew Dragon was again approaching. In addition, the ISS crew's ability to command abort was clearly stated. However, when Crew Dragon is docking and very close (one or two meters, if I remember correctly) there seems to be a "crew hand-off point" at which ISS crew commanding stops and Crew Dragon is left to dock autonomously. But it was not clear to me if this is just a procedural rule, or technically prevented in some way. -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ . |
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Dragon2 test flight
Niklas Holsti wrote on Sun, 3 Mar 2019
21:32:59 +0200: However, when Crew Dragon is docking and very close (one or two meters, if I remember correctly) there seems to be a "crew hand-off point" at which ISS crew commanding stops and Crew Dragon is left to dock autonomously. But it was not clear to me if this is just a procedural rule, or technically prevented in some way. It wouldn't surprise me greatly if there is a lockout. We do the same thing with Man-In-The-Loop missiles based on early experience with remote operators pulling the missile off target using the manual controls because the remote display can make it look like the missile is going to miss when it is right on track to the target. So we insert a 'MITL Lockout Point' beyond which MITL is disabled. Same thing with the F/A-18 during carrier launches. It's difficult for aircrew to not pull back too far on the stick when the cat fires. There's no mechanized lockout to prevent it, but if you watch a launch you'll see the pilot reach up and hold a grab handle on the side of the cockpit. This is so they don't subconsciously pull back on the controls so that the jet will fly its programmed pattern on launch. -- "Insisting on perfect safety is for people who don't have the balls to live in the real world." -- Mary Shafer, NASA Dryden |
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Dragon2 test flight
"Rocket Man" wrote on Sat, 2 Mar 2019
10:17:49 +0100: "Jeff Findley" wrote in message ... In article , says... "JF Mezei" wrote in message ... Saw an animation of the upcoming Fragon 2 test flight and it included docking to the station. Has NASA changed its policy that the first test flight nears the station but doesn't get t touch it? Or have they agreed to let it do the "no touch" test flight and if that works, then allow it to dock? Since this is first Dragon flight docking at the modified PMA2 with totally new guidance/navigation to it, what special steps would be taken? Being crewless, will this be totally automated, or will the ISS crew use the SpaceX equivalent to the Toru manual remote control ? I read that the Russians are pretty nervous about Dragon2 since it doesn't have an independent backup computer system. If it fails the Dragon2 capsule may beome uncontrollable and collide with the station. NASA has brushed aside these concerns, I sure hope they know what they're doing. From what I understand, Dragon 2 has a triply redundant computer system so any computer hardware problem shouldn't be an issue. I'd bet the updated computer hardware on Dragon 2 is at least somewhat based on what was done with Dragon, which has been successful in terms of its software used to approach and station keep near ISS so that the SSRMS can grab it. The difference is that Cargo Dragon is docked via a robotic arm, whilst Crew Dragon docks via the airlock. That's a significant difference. Yeah, I screwed that up a while back and asserted that Dragon 1 did the auto-docking thing. Also, the astronauts don't have any control over Crew Dragon, it's completely autonomous. If something goes wrong, there's nothing they can do to prevent a catastrophe. Which astronauts? The ones on ISS have only limited control (I think), but I'm sure they can tell it to open away from the station because they tested that. If it was actually manned rather than a test the astronauts on board could fly it completely manually. -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw |
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JF Mezei wrote on Wed, 6 Mar 2019
03:41:16 -0500: On 2019-03-04 02:41, Fred J. McCall wrote: Yeah, I screwed that up a while back and asserted that Dragon 1 did the auto-docking thing. Because your goal was to insult me after I said Dragon 2 used new untested computers/software for the first time to get to station. (context was Russians nervous about this single docking computer). And you're a liar. I don't need a reason to insult you. You beg for it. -- "Ordinarily he is insane. But he has lucid moments when he is only stupid." -- Heinrich Heine |
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