sevenperforce Posted August 16, 2017 Share Posted August 16, 2017 4 hours ago, Elthy said: Maybe he is counting in the rotation of earth. But afaik the speeds shown in the stream are relative to ground, since they start from zero. Speed shown in the stream start relative to the ground, but the speed tracking algorithm changes to orbital speed gradually during ascent, because there is a smooth transition from zero to orbital speeds. This can be seen in cases where the speed of stage 2 is tracked; the final velocity is correct for the orbit rather than being reduced by 409 m/s. Quote Link to comment Share on other sites More sharing options...
cubinator Posted August 16, 2017 Share Posted August 16, 2017 23 minutes ago, sevenperforce said: Speed shown in the stream start relative to the ground, but the speed tracking algorithm changes to orbital speed gradually during ascent, because there is a smooth transition from zero to orbital speeds. This can be seen in cases where the speed of stage 2 is tracked; the final velocity is correct for the orbit rather than being reduced by 409 m/s. Besides, the speed of the ground changes with latitude. Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted August 16, 2017 Share Posted August 16, 2017 30 minutes ago, cubinator said: Besides, the speed of the ground changes with latitude. Already factored that in. At the equator the ground's speed is 464 m/s due east; at 28 degrees N latitude (Cape Canaveral) it is 409 m/s due east. Quote Link to comment Share on other sites More sharing options...
cubinator Posted August 16, 2017 Share Posted August 16, 2017 Just now, sevenperforce said: Already factored that in. At the equator the ground's speed is 464 m/s due east; at 28 degrees N latitude (Cape Canaveral) it is 409 m/s due east. Right, but then the rocket flies northeast to get closer to the same plane as the ISS, so the ground's velocity directly under the rocket actually changes during flight. Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted August 16, 2017 Share Posted August 16, 2017 13 minutes ago, cubinator said: Right, but then the rocket flies northeast to get closer to the same plane as the ISS, so the ground's velocity directly under the rocket actually changes during flight. It's a RTLS, though, so it all balances out. Quote Link to comment Share on other sites More sharing options...
CatastrophicFailure Posted August 16, 2017 Share Posted August 16, 2017 I'll just leave this here... Quote Link to comment Share on other sites More sharing options...
Codraroll Posted August 16, 2017 Share Posted August 16, 2017 (edited) 6 hours ago, tater said: There are times when I wonder how complex certain tasks in space really can be, and if the (probably perfectly valid!) reasons why they are so complex can ever be trivialized. When something as conceptually simple as opening a hatch becomes an operation that has to be scheduled and set aside for later, things either seem too complex or too daring to shake my faith in the whole "space future" thing. EDIT: Initially misread as "the hatch will be opened tomorrow". Point still stands, though. I'm either wondering why they can't just reach a hand out and open the damn thing already, or if the reasons they have to wait are so challenging and dangerous that space travel can never be made practical or convenient. Edited August 16, 2017 by Codraroll Quote Link to comment Share on other sites More sharing options...
Spaceception Posted August 16, 2017 Share Posted August 16, 2017 (edited) @Codraroll Well, like what Mark Watney said (paraphrasing) NASA is full of worrywarts. I'm sure that they could've opened it after confirming the dock. At least most of the time anyway, not counting when something is actually wrong. Edited August 16, 2017 by Spaceception Some errors Quote Link to comment Share on other sites More sharing options...
Ten Key Posted August 16, 2017 Share Posted August 16, 2017 57 minutes ago, Codraroll said: Point still stands, though. I'm either wondering why they can't just reach a hand out and open the damn thing already. . . They likely could. But if you have the time to spare, why not take it? Quote Link to comment Share on other sites More sharing options...
Xemina Posted August 16, 2017 Share Posted August 16, 2017 On 14/08/2017 at 7:03 PM, kerbinorbiter said: just tuned into the stream right at landing WHAT LUCK Me too (12) Quote Link to comment Share on other sites More sharing options...
DerekL1963 Posted August 16, 2017 Share Posted August 16, 2017 2 hours ago, Codraroll said: When something as conceptually simple as opening a hatch becomes an operation that has to be scheduled and set aside for later, things either seem too complex or too daring to shake my faith in the whole "space future" thing. "Conceptually simple" != "is actually simple in reality". Closing a submarine's hatch is "conceptually simple". (And procedurally simple too.) However, simple isn't the same as unimportant or without risk. To close a hatch for patrol, if nothing went wrong, involved at least four people and sometimes as much as fifteen to twenty minutes. (One person cleaning and inspecting and closing, two people (one at each end) on the comms circuit, a fourth to inspect and verify. Then the rig for dive team (two more people) would layer check it again when we verified the ship was ready to dive.) If something went wrong*, it could take more people and more time. Why? Because that hatch absolutely had to be properly secured, as our lives absolutely depended on it for the next three months. Once we dove, and it took sea pressure, there was no second chance. We could close it faster if we had to, but if we didn't have to, there was no point in assuming the risk. The station crew is in the same position, there's no hurry, so why hurry? In risky environments, hurrying gets people killed. * On our AMR1 hatch, it went wrong practically every time... The "hatch closed" sensor on either the upper or lower hatch (or both) would get knocked and misaligned by the sheer amount of traffic through the hatch. But the hatch isn't closed until the monitoring panel in the control room said it was closed, so the sensor had to be repaired before the hatch could be declared closed. (Nine time out of ten, I was the guy on the AMR1 end of the comm circuit...) Quote Link to comment Share on other sites More sharing options...
CatastrophicFailure Posted August 16, 2017 Share Posted August 16, 2017 47 minutes ago, DerekL1963 said: Closing a submarine's hatch is "conceptually simple". Grimlock: Me Grimlock love @DerekL1963's war stories. Grimlock: Tell Grimlock about petro-rabbits submarine hatches again. no doubt belongs in its own thread but I could listen to that kinda stuff for days... Quote Link to comment Share on other sites More sharing options...
Grand Ship Builder Posted August 17, 2017 Share Posted August 17, 2017 The cancellation of the propulsive landing for Dragon 2 and Red Dragon kind of makes me sad, mad, and disappointed all at the same time. It's like waiting so long for something you really want just to have it sold out and production stopped. I was really hoping for the Red Dragon animation, which was the missing piece of the puzzle. Quote Link to comment Share on other sites More sharing options...
cubinator Posted August 17, 2017 Share Posted August 17, 2017 4 hours ago, DerekL1963 said: The station crew is in the same position, there's no hurry, so why hurry? In risky environments, hurrying gets people killed. But I heard there is ice cream on that Dragon! All joking aside, I watched the most recent Soyuz docking, and (I assume the procedure for Dragon is not so different) basically they do a ton of leak checks and very slowly equalize the pressure between station and visiting vehicle, because if the station were to depressurize it would probably have to be evacuated (anyone that survives, at any rate), even with the emergency closing hatches, and it would be really bad even if the whole thing doesn't have to be scrapped. So that's a situation they will take their time with, making sure every part of the seal is absolutely safe before going in and getting their ice cream. Quote Link to comment Share on other sites More sharing options...
Racescort666 Posted August 17, 2017 Share Posted August 17, 2017 6 minutes ago, cubinator said: But I heard there is ice cream on that Dragon! I seem to remember something about a refrigerated payload... Quote Link to comment Share on other sites More sharing options...
CatastrophicFailure Posted August 17, 2017 Share Posted August 17, 2017 Irony of a Dragon bearing ice cream... Quote Link to comment Share on other sites More sharing options...
Jaelommiss Posted August 17, 2017 Share Posted August 17, 2017 11 minutes ago, CatastrophicFailure said: Irony of a Dragon bearing ice cream... Only the most fortunate members of humanity are permitted to gaze down upon the blue marble as they glide silently above its surface, delicately snacking on ice cream borne by falcon's wings and plumes of dragonfire. Quote Link to comment Share on other sites More sharing options...
kerbiloid Posted August 17, 2017 Share Posted August 17, 2017 Spoiler A Song of Ice and Fire Quote Link to comment Share on other sites More sharing options...
Nibb31 Posted August 17, 2017 Share Posted August 17, 2017 (edited) 10 hours ago, Codraroll said: There are times when I wonder how complex certain tasks in space really can be, and if the (probably perfectly valid!) reasons why they are so complex can ever be trivialized. When something as conceptually simple as opening a hatch becomes an operation that has to be scheduled and set aside for later, things either seem too complex or too daring to shake my faith in the whole "space future" thing. Ignorance is bliss. Extreme environments are hard and dangerous, and they always will be. Sorry to burst your bubble. Quote EDIT: Initially misread as "the hatch will be opened tomorrow". Point still stands, though. I'm either wondering why they can't just reach a hand out and open the damn thing already, or if the reasons they have to wait are so challenging and dangerous that space travel can never be made practical or convenient. Even for something as simple as opening a hatch, there are many things that can go wrong. Sure, you could do it quicker, but what if there is a pressure differential and the hatch slams into someone's nose? What if there has been a hydrazine leak inside the Dragon? What if the seal between the two vehicles leaks? The ISS has cost a significant percentage of several countries' GDP. The cost of astronaut man-hours is high and that time is best spent on producing science. However, time spent on dealing with unplanned contingencies, especially when the risk is life-threatening, is much more expensive and disruptive than time spent dealing with planned procedures. Cutting corners often costs much more than following procedures. Edited August 17, 2017 by Nibb31 Quote Link to comment Share on other sites More sharing options...
Grand Ship Builder Posted August 17, 2017 Share Posted August 17, 2017 1 hour ago, kerbiloid said: Reveal hidden contents A Song of Ice and Fire Spoiler Dragon Breath Ice Cream, made with liquid nitrogen straight from the Falcon! Quote Link to comment Share on other sites More sharing options...
Skylon Posted August 17, 2017 Author Share Posted August 17, 2017 (edited) 18 hours ago, CatastrophicFailure said: I'll just leave this here... At 5:26 I noticed a moving smaller nozzle pictured on 1 and 2. Did/does the Merlin Vac have a vernier nozzle for roll control? And I didn't realise that CRS-8 landed on a barge Edited August 17, 2017 by Skylon Quote Link to comment Share on other sites More sharing options...
Steel Posted August 17, 2017 Share Posted August 17, 2017 (edited) 1 hour ago, Skylon said: At 5:26 I noticed a moving smaller nozzle pictured on 1 and 2. Did/does the Merlin Vac have a vernier nozzle for roll control? ... I suspect that's the exhaust from the pre-burner that they're using as a vernier. Edited August 17, 2017 by Steel Quote Link to comment Share on other sites More sharing options...
KamenRiderzero1 Posted August 18, 2017 Share Posted August 18, 2017 22 hours ago, Skylon said: At 5:26 I noticed a moving smaller nozzle pictured on 1 and 2. Did/does the Merlin Vac have a vernier nozzle for roll control? And I didn't realise that CRS-8 landed on a barge CRS-8 was the first barge landing. It was also the first to fly again. Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted August 18, 2017 Share Posted August 18, 2017 23 hours ago, Steel said: I suspect that's the exhaust from the pre-burner that they're using as a vernier. I doubt it. The Falcon 1 used a gimballed preburner exhaust nozzle for roll control on its single first-stage engine, but per the Falcon 9 User's Guide, second-stage roll control is provided only by cold-gas thrusters. The Merlin 1D Vacuum vents preburner exhaust into the nozzle extension for extra thrust and specific impulse (this takes advantage of the fact that the static pressure in the nozzle is very low even though the axial dynamic pressure is rather high). Quote Link to comment Share on other sites More sharing options...
Codraroll Posted August 18, 2017 Share Posted August 18, 2017 On 17.8.2017 at 8:10 AM, Nibb31 said: Ignorance is bliss. Extreme environments are hard and dangerous, and they always will be. Sorry to burst your bubble. Thanks for the replies, everybody (very interesting story, @DerekL1963!). I guess that the takeaway is that the future is here, and we have a precense in space and do interesting things there, but space is still so dangerous that even with the best technology and the smartest people available, it is still necessary to take half a day to open a hatch. Opening hatches is an inherently dangerous activity in space. Thinking about that fact is a bit of an ice bucket in the face of the optimistic sci-fi enthusiast in me, but I guess I should be really excited about the fact that we have found a way to open hatches in space at all, given how much can go wrong with it. Here's hoping that plenty of hatches will be opened safely in the future too! Quote Link to comment Share on other sites More sharing options...
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