Here is a comparison between the DM1 and DM2 launch telemetry.1. The first difference is that the DM2 telemetry display only appeared at about T+00:14, so I've assumed that those 14 seconds were identical for both flights.2. The throttle bucket profile was identical.3. Both flights throttled back at the 140 second mark, but DM2 less so.4. DM2 staged a little lower and faster, leading to a less lofted S2 profile.5. DM2 maintained an essentially constant throttle for the entire S2 burn, unlike DM1, which throttled up at about 230 seconds, and then down at 458 and 524 seconds.
Quote from: OneSpeed on 05/31/2020 02:13 amHere is a comparison between the DM1 and DM2 launch telemetry.1. The first difference is that the DM2 telemetry display only appeared at about T+00:14, so I've assumed that those 14 seconds were identical for both flights.2. The throttle bucket profile was identical.3. Both flights throttled back at the 140 second mark, but DM2 less so.4. DM2 staged a little lower and faster, leading to a less lofted S2 profile.5. DM2 maintained an essentially constant throttle for the entire S2 burn, unlike DM1, which throttled up at about 230 seconds, and then down at 458 and 524 seconds.In the quoted post by Onespeed, the telemetry chart clearly shows that for the last 30-40 seconds of powered flight on Stage 2, the acceleration was greater than 3000 CM/S^2, which is roughly more than 3 Gs (which was the Shuttle limit).I'm really confused by the commentary here, and including that of the astronauts, regarding peak acceleration figures that are lower than what is plotted.Is there an error in the plotted data?
In the quoted post by Onespeed, the telemetry chart clearly shows that for the last 30-40 seconds of powered flight on Stage 2, the acceleration was greater than 3000 CM/S^2, which is roughly more than 3 Gs (which was the Shuttle limit).I'm really confused by the commentary here, and including that of the astronauts, regarding peak acceleration figures that are lower than what is plotted.Is there an error in the plotted data?
Quote from: Coastal Ron on 05/31/2020 11:57 pmThe crew reported that the ride was smooth. Falcon 9 uses liquid fueled engines, which don't have much vibration.The Ares I was essentially a Shuttle SRB, which is a solid rocket booster, and solid rocket engines are notorious for having a lot of vibration due to the uneven burning of the solid fuel, and as the SRB casing is emptied of fuel the casing oscillates. Here is an article about what they were trying to do to mitigate the vibrations on Ares I.But if you watch the capsule video you'll see that the ride inside the capsule is pretty smooth.During the PAO event when Bob and Doug were welcomed into ISS and answered questions from the ground, Bob did say they were a bit surprised at how smooth the first stage burn was, compared to Shuttle.But he went on to say that they had expected the stage 2 burn to get a lot smoother, but in fact the rocket was "huffing and puffing" all the way to orbit, and "we were definitely riding a dragon," that it was "not quite the same smooth ride as Shuttle" during the stage 2 burn.The "huffing and puffing" sounds like a reference to chugging or pogo oscillation, probably for reasons suggested upthread (much lower vehicle mass than Shuttle, one engine vs. multiple engines, etc.)So apparently stage 2 was an unexpectedly bumpy ride as compared to Shuttle (after SRB sep).
The crew reported that the ride was smooth. Falcon 9 uses liquid fueled engines, which don't have much vibration.The Ares I was essentially a Shuttle SRB, which is a solid rocket booster, and solid rocket engines are notorious for having a lot of vibration due to the uneven burning of the solid fuel, and as the SRB casing is emptied of fuel the casing oscillates. Here is an article about what they were trying to do to mitigate the vibrations on Ares I.But if you watch the capsule video you'll see that the ride inside the capsule is pretty smooth.
I haven't seen it mentioned yet, so I just want to point out something.The SpaceX youtube stream of this launch is listed at 56 million views, and the NASA is at 17 million. If you include the NASAspaceflight and everyday astronaut streams, it's probably above 75 million in total, and that's not including those who watched broadcast TV.Here in Norway at least two of the largest networks showed it live, and even my aunt (who has no real interest in spaceflight) watched it live.So this event has been a tremendous boost for interest in spaceflight!
It's certainly got attention and got people enthusiastic. Question is how long will this last. It's not my generation that needs to be grabbed but the teenagers and 20 year olds. We need to pitch it at their level, with something that interests them.
Quote from: alexs on 05/31/2020 08:56 amQuote from: alexterrell on 05/31/2020 06:51 amThe obvious way to have a mic would be over a blue tooth link (or if NASA were doing this, some new standard they'd invent at great cost).Bluetooth is not the kind of technology I'd expect to see in a spacecraft. It's finicky even in regular consumer applications, the protocol is rather complex for reasons that make no sense in spaceflight applications, and if things go wrong, figuring out what went wrong and how to fix it is not easy. Take COTS components and pray it works is probably the only approach that favors Bluetooth.That said, Bluetooth is not the only wireless option. There are non-Bluetooth microphones easily available.Bluetooth works fine for simple things like headphones and microphone to computer. Once set up, it's reliable, and a lot better than a 12 foot cable.Of course there are other standards and wireless methods. The fact that none of them are used, would suggest wireless isn't allowed on Dragon. Is that correct?A quick Google says that there is WiFi on the ISS.
Quote from: alexterrell on 05/31/2020 06:51 amThe obvious way to have a mic would be over a blue tooth link (or if NASA were doing this, some new standard they'd invent at great cost).Bluetooth is not the kind of technology I'd expect to see in a spacecraft. It's finicky even in regular consumer applications, the protocol is rather complex for reasons that make no sense in spaceflight applications, and if things go wrong, figuring out what went wrong and how to fix it is not easy. Take COTS components and pray it works is probably the only approach that favors Bluetooth.That said, Bluetooth is not the only wireless option. There are non-Bluetooth microphones easily available.
The obvious way to have a mic would be over a blue tooth link (or if NASA were doing this, some new standard they'd invent at great cost).
Quote from: daveglo on 06/01/2020 02:34 am... I'm really confused by the commentary here, and including that of the astronauts, regarding peak acceleration figures that are lower than what is plotted. ...... Perhaps you could quote the contradictory commentary?
... I'm really confused by the commentary here, and including that of the astronauts, regarding peak acceleration figures that are lower than what is plotted. ...
Bob Behnken: As far as a comparison with the Space Shuttle, both Doug and I took a few minutes while we were accomplishing the approach and docking to, in our spare time, talk a little bit about it. We were surprised a little bit at how smooth things were off the pad. The Space Shuttle is a pretty rough ride heading into orbit with the Solid Rocket Boosters. And our expectation was, as we continued with the flight into Second Stage, that things would get a lot smoother than the Space Shuttle did. But Dragon was huffin' and puffin' all the was into orbit and we were definitely driving or riding a dragon all the way up. And so it was not quite the same ride, the smooth ride as the Space Shuttle was up to MECO. A little bit less G's, but a little bit more alive, is probably the best way I would describe it.
Quote from: OneSpeed on 06/01/2020 05:10 amQuote from: daveglo on 06/01/2020 02:34 am... I'm really confused by the commentary here, and including that of the astronauts, regarding peak acceleration figures that are lower than what is plotted. ...... Perhaps you could quote the contradictory commentary?ISS Welcome Ceremony @8:58:QuoteBob Behnken: As far as a comparison with the Space Shuttle, both Doug and I took a few minutes while we were accomplishing the approach and docking to, in our spare time, talk a little bit about it. We were surprised a little bit at how smooth things were off the pad. The Space Shuttle is a pretty rough ride heading into orbit with the Solid Rocket Boosters. And our expectation was, as we continued with the flight into Second Stage, that things would get a lot smoother than the Space Shuttle did. But Dragon was huffin' and puffin' all the was into orbit and we were definitely driving or riding a dragon all the way up. And so it was not quite the same ride, the smooth ride as the Space Shuttle was up to MECO. A little bit less G's, but a little bit more alive, is probably the best way I would describe it.Your graph (and thank you for them) shows DM-2 accelerating >3G for the final 45 seconds, where STS throttled SSME's for the last minute to keep acceleration <3G.Edit: Typos.
https://twitter.com/astrokarenn/status/1267455962459377666Quote When nerves and apprehension turn into exhilarating pride. #crewdragon #endeavour #falcon9
When nerves and apprehension turn into exhilarating pride. #crewdragon #endeavour #falcon9
Quote from: Kabloona on 06/01/2020 12:36 amQuote from: Coastal Ron on 05/31/2020 11:57 pmThe crew reported that the ride was smooth. Falcon 9 uses liquid fueled engines, which don't have much vibration.The Ares I was essentially a Shuttle SRB, which is a solid rocket booster, and solid rocket engines are notorious for having a lot of vibration due to the uneven burning of the solid fuel, and as the SRB casing is emptied of fuel the casing oscillates. Here is an article about what they were trying to do to mitigate the vibrations on Ares I.But if you watch the capsule video you'll see that the ride inside the capsule is pretty smooth.During the PAO event when Bob and Doug were welcomed into ISS and answered questions from the ground, Bob did say they were a bit surprised at how smooth the first stage burn was, compared to Shuttle.But he went on to say that they had expected the stage 2 burn to get a lot smoother, but in fact the rocket was "huffing and puffing" all the way to orbit, and "we were definitely riding a dragon," that it was "not quite the same smooth ride as Shuttle" during the stage 2 burn.The "huffing and puffing" sounds like a reference to chugging or pogo oscillation, probably for reasons suggested upthread (much lower vehicle mass than Shuttle, one engine vs. multiple engines, etc.)So apparently stage 2 was an unexpectedly bumpy ride as compared to Shuttle (after SRB sep).Interesting to compare this to astronauts describing Saturn V S-II and S-IVB stages. Exact same engines, S-II was described as smooth, but the S-IVB was described as "ratty".I don't recall any accounts on how a Saturn Ib felt, that seems like a better direct comparison to a Falcon 9.For F9, I would expect at least part of the ride "quality" be down to the flexible niobium nozzle extension.
Saturn's second stage has some known, and very scary vibration problems. Google POGO to read more about it. Fascinating stories about almost losing a couple of Saturn launches.These days, I think that computational structural models would be able to identify vibrational issues and help fix the design.
Quote from: freddo411 on 06/01/2020 05:17 pmSaturn's second stage has some known, and very scary vibration problems. Google POGO to read more about it. Fascinating stories about almost losing a couple of Saturn launches.These days, I think that computational structural models would be able to identify vibrational issues and help fix the design.I'm not talking about pogo.
Quote from: Coastal Ron on 05/31/2020 11:57 pmQuote from: averow45 on 05/31/2020 10:31 pmFor what it is worth there was discussion during the ARES-1 program in modelling that the ride could be potentially so filled with vibrations and low frequency noise that the astronauts might have trouble with seeing screens and pressing keys and/or screens. I wonder if the test pilots were alluding to this kind of noise and/or vibration with yesterdays ascent ?The crew reported that the ride was smooth. Falcon 9 uses liquid fueled engines, which don't have much vibration.The Ares I was essentially a Shuttle SRB, which is a solid rocket booster, and solid rocket engines are notorious for having a lot of vibration due to the uneven burning of the solid fuel, and as the SRB casing is emptied of fuel the casing oscillates. Here is an article about what they were trying to do to mitigate the vibrations on Ares I.But if you watch the capsule video you'll see that the ride inside the capsule is pretty smooth.During the PAO event when Bob and Doug were welcomed into ISS and answered questions from the ground, Bob did say they were a bit surprised at how smooth the first stage burn was, compared to Shuttle.But he went on to say that they had expected the stage 2 burn to get a lot smoother, but in fact the rocket was "huffing and puffing" all the way to orbit, and "we were definitely riding a dragon," that it was "not quite the same smooth ride as Shuttle" during the stage 2 burn.The "huffing and puffing" sounds like a reference to chugging or pogo oscillation, probably for reasons suggested upthread (much lower vehicle mass than Shuttle, one engine vs. multiple engines, etc.)So apparently stage 2 was an unexpectedly bumpy ride as compared to Shuttle (after SRB sep).
Quote from: averow45 on 05/31/2020 10:31 pmFor what it is worth there was discussion during the ARES-1 program in modelling that the ride could be potentially so filled with vibrations and low frequency noise that the astronauts might have trouble with seeing screens and pressing keys and/or screens. I wonder if the test pilots were alluding to this kind of noise and/or vibration with yesterdays ascent ?The crew reported that the ride was smooth. Falcon 9 uses liquid fueled engines, which don't have much vibration.The Ares I was essentially a Shuttle SRB, which is a solid rocket booster, and solid rocket engines are notorious for having a lot of vibration due to the uneven burning of the solid fuel, and as the SRB casing is emptied of fuel the casing oscillates. Here is an article about what they were trying to do to mitigate the vibrations on Ares I.But if you watch the capsule video you'll see that the ride inside the capsule is pretty smooth.
For what it is worth there was discussion during the ARES-1 program in modelling that the ride could be potentially so filled with vibrations and low frequency noise that the astronauts might have trouble with seeing screens and pressing keys and/or screens. I wonder if the test pilots were alluding to this kind of noise and/or vibration with yesterdays ascent ?
