5 ms·

Who can sum it up with the least amount of words: Liquid smoother ride than solid rockets

sandworm101 6y ago
Don't forget aerodynamics. Shuttle suffered from all sorts of buffeting that a smooth cylindrical rocket would not. The complex shape also meant more unpredictable asymmetric vibrations. A liquid-fueled shuttle would still have been a rough ride. And shuttle took a much more aggressive path. SpaceX rockets aim very high for longer burn times (more up, less sideways on first stage). It is technically a less efficient approach but allows for the recovery trickery.
- nikofeyn 6y ago
  i'm not for sure what you're addressing. the astronauts described the falcon 9 as much more rough than the space shuttle.
  - dredmorbius 6y ago
    According to the briefing video above, smoother than the Shuttle off the pad (for Falcon), which is the lower-atmosphere phase with more aerodynamic interactions, rougher following Falcon MECO, under the single-engine second stage. During the equivalent flight phase the Shuttle has shed its solid rocket boosters and consists of the three space-shuttle main engines (SSME), and the external tank. Still not a vertical stack (so subject to greater structural dynamics), though the thought occurs that three engines might be smoother than one. There can be other effects as well --- the Saturn V had significant issues with "pogo oscillations", which are just what they sound like: strong periodic variations in vertical acceleration. Falcon 2nd stage issues might be similar. https://en.wikipedia.org/wiki/Pogo_oscillation https://en.wikipedia.org/wiki/Pogo_oscillation
deleted 6y ago
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manicdee 6y ago
Also more engines is smoother than fewer engines!
NikolaeVarius 6y ago
More liquids less brrrrrrrrrrr
- gpm 6y ago
  More liquids smoother
m463 6y ago
I wonder if rougher later was because of the engines more directly attached to ... well, posteriors.
- m4rtink 6y ago
  If rougher == more acceleration, it could be just due to the rocket (stage 2 & Crew Dragon) being lighter at the end of the burn due to all the fuel expended, resulting in rising acceleration at the end. Shuttle possibly being much to heavy for that & the final orbit insertion burns being done by the OMS, which was quite low acceleration given the mass of the shuttle.
  - godelski 6y ago
    They specifically mentioned less acceleration in upper stage than compared to the shuttle so we can conclude that "rougher != more acceleration" because g's == acceleration.
    - Cogito 6y ago
      Small correction, at least in the article they talked about the relative thrust of the upper stage engines, but don't discuss the acceleration profile of the two (noting that the shuttle is heavier so even with bigger engines not necessarily quicker to accelerate). Perhaps the best resource I know to compare the accelerations is flightclub.io, I ran two simulations for STS-129 [0] and DM-2 [1] so you can compare their profiles. These are in no way authoritative, but it does seem like Crew Dragon would have higher acceleration (as high as 3.7G) compared to shuttle (remaining under 3G the whole time). Note also that in the article says that Hurley described the ride on the Merlin Vacuum upper stage engine as "kind of like driving fast on a gravel road" which suggests that the proximity of the engines and vibrations may have been more important than raw acceleration. [0] https://flightclub.io/result/2d?id=bb67b508-71e1-4e4d-8cfc-ac43a68adf5c https://flightclub.io/result/2d?id=bb67b508-71e1-4e4d-8cfc-a... [1] https://flightclub.io/result/2d?id=4bd73964-9a16-4918-867c-c6cfa78b3f4e https://flightclub.io/result/2d?id=4bd73964-9a16-4918-867c-c...
miguelrochefort 6y ago
Which one is the Space Shuttle and which one is the Falcon 9?
- kinkrtyavimoodh 6y ago
  Space Shuttle Solid, Falcon 9 Liquid
- catalogia 6y ago
  The Space Shuttle had three liquid fuel rocket engines on the orbiter (pulling fuel from the big orange tank), but used two huge solid fuel boosters as well. The Falcon 9 does not use any solid fuel boosters.
  - dredmorbius 6y ago
    And for relative thrust, the SSRBs (solid boosters) developed a maximum of 14.7 MN (meganewtons) thrust each, or a total of 29.4 MN. The SSMEs (liquid fueled RS-25 engines) produced ~1.9 MN thrust each, or 5.7 MN for the three. Of the 35.1 MN of maximum total shuttle launch thrust, about 84% came from the solid boosters, only 16% from the somewhat misleadingly named "main" engines. https://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Booster https://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Boo... https://en.wikipedia.org/wiki/RS-25 https://en.wikipedia.org/wiki/RS-25
    - catalogia 6y ago
      Percentage of total maximum thrust is one way to look at it. Another is to consider that the SRBs get dropped when the shuttle is going about 4,000 km/h, after which the SSMEs bring the shuttle up to 28,000 km/h.
hoorayimhelping 6y ago
I don't think it's that simple. William Anders on the Saturn V's first stage: (which was RP-1 and oxygen, same as the falcon 9) >The sideways shaking was unbelievable. The vibration was so intense, you couldn't see the instrument panel. I thought we'd had it... https://youtu.be/kqAzLyFS_pk?t=41 https://youtu.be/kqAzLyFS_pk?t=41 They said that the Titan II, which launched the Gemini missions was incredibly smooth, just very powerful and loud. https://en.wikipedia.org/wiki/Titan_II_GLV#Flights https://en.wikipedia.org/wiki/Titan_II_GLV#Flights
txcwpalpha 6y ago
That's such a reduction that it completely misses the crucial point that the Falcon 9 is overall not smoother than the shuttle. The first stage was smoother, because as you said "liquid smoother than solid rockets", but the second stage was noticeably rougher than the shuttle (specifically the stage separation/transition, which the shuttle did not suffer from due to the SSMEs continously firing even during SRB separation). The article is quoting comments from a press event, but I remember on the livestream one of Bob/Doug specifically commented on how rough the ride was as one of the first things they said after SECO/docking (can't remember exactly which). I'm thinking it must have been pretty dang rough if it was the first thing on their mind. It's unsourced, but I've seen other comments on the internet remark that certain satellite payloads actually can't use the Falcon 9 due to its vibration profile being too rough compared to others rockets.
- ringshall 6y ago
  Correct about the comment in the livestream, see here: https://youtu.be/zNklfC6jgBs?t=14653 https://youtu.be/zNklfC6jgBs?t=14653 It was Bob. Rough transcript: "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 SRBs, and our expectation was as we continued with the flight into second stage that things would basically get a lot smoother than the space shuttle did, but Dragon was huffing and puffing all the way into orbit and we were definitely driving and 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 Gs, but a little bit more alive is probably the best way I would describe it." Edit: Just noticed that that description is in the original article, too, fwiw
  - txcwpalpha 6y ago
    Thanks for finding the timestamp/quote! That is what I was talking about, I specifically remembered the "riding a dragon" part. I do see it included in the article now too.
  - Melting_Harps 6y ago
    > but Dragon was huffing and puffing all the way into orbit and we were definitely driving and riding a dragon all the way up... How can this be interpreted as a negative thing, if anything if I were a school boy watching that it that would make me want to get involved and want to experience it myself! An astronaut talking about taking a Capsule (dragon) all the way to Space, and describing it that way... what could be cooler than that? Also worth noting that no one in involved in Space is expected to do a comfy job, much less being an Astronaut as it requires decades of rigorous physical and mental conditioning, training and exercise and psychological evaluation to just be a candidate in order to prepare you to live in an environment where even going to the bathroom, sneezing, or coughing could all kill you and potentially everyone in your crew in Space. Yi So-yeon did an interview at MIT earlier this year with Mar's Society [1] describing this exact situation, and even when having almost died upon re-entry due to a faulty heat-shield malfunction that messed up the trajectory of the landing that almost killer her and her whole crew she was the first to sign up for another mission! That's what an Astronaut is, they're cut from the same clothe as protype Fighter Jet pilots, where death was the most likely outcome; they're not 'normal' People and this doesn't phase them when confronted to do it again for a bigger purpose. Its why they're such exceptional Human beings and why they should be treated as such. 1: https://www.youtube.com/watch?v=jvXAy6YKWOU https://www.youtube.com/watch?v=jvXAy6YKWOU

Don't forget aerodynamics. Shuttle suffered from all sorts of buffeting that a smooth cylindrical rocket would not. The complex shape also meant more unpredictable asymmetric vibrations. A liquid-fueled shuttle would still have been a rough ride. And shuttle took a much more aggressive path. SpaceX rockets aim very high for longer burn times (more up, less sideways on first stage). It is technically a less efficient approach but allows for the recovery trickery.

nikofeyn 6y ago
i'm not for sure what you're addressing. the astronauts described the falcon 9 as much more rough than the space shuttle.
- dredmorbius 6y ago
  According to the briefing video above, smoother than the Shuttle off the pad (for Falcon), which is the lower-atmosphere phase with more aerodynamic interactions, rougher following Falcon MECO, under the single-engine second stage. During the equivalent flight phase the Shuttle has shed its solid rocket boosters and consists of the three space-shuttle main engines (SSME), and the external tank. Still not a vertical stack (so subject to greater structural dynamics), though the thought occurs that three engines might be smoother than one. There can be other effects as well --- the Saturn V had significant issues with "pogo oscillations", which are just what they sound like: strong periodic variations in vertical acceleration. Falcon 2nd stage issues might be similar. https://en.wikipedia.org/wiki/Pogo_oscillation https://en.wikipedia.org/wiki/Pogo_oscillation

deleted 6y ago

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manicdee 6y ago

Also more engines is smoother than fewer engines!

NikolaeVarius 6y ago

More liquids less brrrrrrrrrrr

gpm 6y ago
More liquids smoother

m463 6y ago

I wonder if rougher later was because of the engines more directly attached to ... well, posteriors.

m4rtink 6y ago
If rougher == more acceleration, it could be just due to the rocket (stage 2 & Crew Dragon) being lighter at the end of the burn due to all the fuel expended, resulting in rising acceleration at the end. Shuttle possibly being much to heavy for that & the final orbit insertion burns being done by the OMS, which was quite low acceleration given the mass of the shuttle.
- godelski 6y ago
  They specifically mentioned less acceleration in upper stage than compared to the shuttle so we can conclude that "rougher != more acceleration" because g's == acceleration.
  - Cogito 6y ago
    Small correction, at least in the article they talked about the relative thrust of the upper stage engines, but don't discuss the acceleration profile of the two (noting that the shuttle is heavier so even with bigger engines not necessarily quicker to accelerate). Perhaps the best resource I know to compare the accelerations is flightclub.io, I ran two simulations for STS-129 [0] and DM-2 [1] so you can compare their profiles. These are in no way authoritative, but it does seem like Crew Dragon would have higher acceleration (as high as 3.7G) compared to shuttle (remaining under 3G the whole time). Note also that in the article says that Hurley described the ride on the Merlin Vacuum upper stage engine as "kind of like driving fast on a gravel road" which suggests that the proximity of the engines and vibrations may have been more important than raw acceleration. [0] https://flightclub.io/result/2d?id=bb67b508-71e1-4e4d-8cfc-ac43a68adf5c https://flightclub.io/result/2d?id=bb67b508-71e1-4e4d-8cfc-a... [1] https://flightclub.io/result/2d?id=4bd73964-9a16-4918-867c-c6cfa78b3f4e https://flightclub.io/result/2d?id=4bd73964-9a16-4918-867c-c...

miguelrochefort 6y ago

Which one is the Space Shuttle and which one is the Falcon 9?

kinkrtyavimoodh 6y ago
Space Shuttle Solid, Falcon 9 Liquid
catalogia 6y ago
The Space Shuttle had three liquid fuel rocket engines on the orbiter (pulling fuel from the big orange tank), but used two huge solid fuel boosters as well. The Falcon 9 does not use any solid fuel boosters.
- dredmorbius 6y ago
  And for relative thrust, the SSRBs (solid boosters) developed a maximum of 14.7 MN (meganewtons) thrust each, or a total of 29.4 MN. The SSMEs (liquid fueled RS-25 engines) produced ~1.9 MN thrust each, or 5.7 MN for the three. Of the 35.1 MN of maximum total shuttle launch thrust, about 84% came from the solid boosters, only 16% from the somewhat misleadingly named "main" engines. https://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Booster https://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Boo... https://en.wikipedia.org/wiki/RS-25 https://en.wikipedia.org/wiki/RS-25
  - catalogia 6y ago
    Percentage of total maximum thrust is one way to look at it. Another is to consider that the SRBs get dropped when the shuttle is going about 4,000 km/h, after which the SSMEs bring the shuttle up to 28,000 km/h.

hoorayimhelping 6y ago

I don't think it's that simple. William Anders on the Saturn V's first stage: (which was RP-1 and oxygen, same as the falcon 9) >The sideways shaking was unbelievable. The vibration was so intense, you couldn't see the instrument panel. I thought we'd had it... https://youtu.be/kqAzLyFS_pk?t=41 https://youtu.be/kqAzLyFS_pk?t=41 They said that the Titan II, which launched the Gemini missions was incredibly smooth, just very powerful and loud. https://en.wikipedia.org/wiki/Titan_II_GLV#Flights https://en.wikipedia.org/wiki/Titan_II_GLV#Flights

txcwpalpha 6y ago

That's such a reduction that it completely misses the crucial point that the Falcon 9 is overall not smoother than the shuttle. The first stage was smoother, because as you said "liquid smoother than solid rockets", but the second stage was noticeably rougher than the shuttle (specifically the stage separation/transition, which the shuttle did not suffer from due to the SSMEs continously firing even during SRB separation). The article is quoting comments from a press event, but I remember on the livestream one of Bob/Doug specifically commented on how rough the ride was as one of the first things they said after SECO/docking (can't remember exactly which). I'm thinking it must have been pretty dang rough if it was the first thing on their mind. It's unsourced, but I've seen other comments on the internet remark that certain satellite payloads actually can't use the Falcon 9 due to its vibration profile being too rough compared to others rockets.

ringshall 6y ago
Correct about the comment in the livestream, see here: https://youtu.be/zNklfC6jgBs?t=14653 https://youtu.be/zNklfC6jgBs?t=14653 It was Bob. Rough transcript: "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 SRBs, and our expectation was as we continued with the flight into second stage that things would basically get a lot smoother than the space shuttle did, but Dragon was huffing and puffing all the way into orbit and we were definitely driving and 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 Gs, but a little bit more alive is probably the best way I would describe it." Edit: Just noticed that that description is in the original article, too, fwiw
- txcwpalpha 6y ago
  Thanks for finding the timestamp/quote! That is what I was talking about, I specifically remembered the "riding a dragon" part. I do see it included in the article now too.
- Melting_Harps 6y ago
  > but Dragon was huffing and puffing all the way into orbit and we were definitely driving and riding a dragon all the way up... How can this be interpreted as a negative thing, if anything if I were a school boy watching that it that would make me want to get involved and want to experience it myself! An astronaut talking about taking a Capsule (dragon) all the way to Space, and describing it that way... what could be cooler than that? Also worth noting that no one in involved in Space is expected to do a comfy job, much less being an Astronaut as it requires decades of rigorous physical and mental conditioning, training and exercise and psychological evaluation to just be a candidate in order to prepare you to live in an environment where even going to the bathroom, sneezing, or coughing could all kill you and potentially everyone in your crew in Space. Yi So-yeon did an interview at MIT earlier this year with Mar's Society [1] describing this exact situation, and even when having almost died upon re-entry due to a faulty heat-shield malfunction that messed up the trajectory of the landing that almost killer her and her whole crew she was the first to sign up for another mission! That's what an Astronaut is, they're cut from the same clothe as protype Fighter Jet pilots, where death was the most likely outcome; they're not 'normal' People and this doesn't phase them when confronted to do it again for a bigger purpose. Its why they're such exceptional Human beings and why they should be treated as such. 1: https://www.youtube.com/watch?v=jvXAy6YKWOU https://www.youtube.com/watch?v=jvXAy6YKWOU