6 ms·

This comes from place of ignorance, so please be kind: why "speed record" is considered Mach 6.2 when ISS ground speed is like Mach 22? There are humans there,

by Svoka 7y ago

This comes from place of ignorance, so please be kind: why "speed record" is considered Mach 6.2 when ISS ground speed is like Mach 22? There are humans there, they got up to speed and regularly come back. How it is different than going to similar velocities in thin atmospheres over 50km?

dTal 7y ago
> the world record for speed by a piloted, powered aircraft It literally says it right there. The ISS is not a piloted, powered aircraft. Also it was Mach 6.7, not 6.2. Incidentally, the speed record for a crewed vehicle was set by Apollo 10 at 11.08 km/s - almost half as fast again as the ISS.
- hyperpallium 7y ago
  Fictional but germane scene from The Martian: > [after hearing he has to take the top off of the Mars Ascent Vehicle] I know what they're doing. I know exactly what they're doing. They just keep repeating "go faster than any man in the history of space travel", like that's a good thing. Like it'll distract me from how insane their plan is. Yeah, I get to go faster than any man in the history of space travel, because you're launching me in a convertible. Actually it's worse than that, because I won't even be able to control the thing. And by the way, physicists, when describing things like acceleration do not use the word "fast". So they're only doing that in the hopes that I won't raise any objections to this lunacy, because I like the way "fastest man in the history of space travel" sounds. I do like the way it sounds... I mean, I like it a lot.
- Aaargh20318 7y ago
  > It literally says it right there. The ISS is not a piloted, powered aircraft. Also it was Mach 6.7, not 6.2. But aren't the Soyuz capsules that dock with the ISS piloted and powered ?
  - masklinn 7y ago
    Soyuz can be manually piloted, but are normally automated (Progress can not be piloted and is essentially the same thing after all). They're also not aircrafts.
  - pjc50 7y ago
    Yes, but they're outside the atmosphere and therefore don't have a Mach number.
    - mumblemumble 7y ago
      A Soyuz capsule that never enters the atmosphere would have a very upset crew.
  - mumblemumble 7y ago
    I would assume that Soyuz capsules aren't considered aircraft. They don't really fly, per se, they get launched on a rocket and then fall like a rock back to earth. You could make a stronger argument for the Space Shuttle, which re-enters at about Mach 25, IIRC, and is gliding. But it's not doing so under power.
    - JshWright 7y ago
      > Soyuz capsules aren't considered aircraft While I suspect you're right, Soyuz capsules do use aerodynamic lift to control descent rate and steer to the landing site. In some ways they are very, very (very) inefficient gliders.
      - ansible 7y ago
        I'd expect the definition of a powered aircraft to include the ability to maintain some given flight altitude and speed for some appreciable amount of time. It is possible to do something sort of like this in a space capsule returning to Earth, where you muck up your entry vector and come in at too shallow an angle. You can then (depending on the circumstances) bounce off the atmosphere, and gain altitude briefly. And then you probably come back in the atmosphere on too steep an angle, and die due to g-load or overheating.
- pif 7y ago
  > was set by Apollo 10 at 11.08 km/s - almost half as fast again as the ISS. You mean twice as fast as the ISS, don't you? 11 km/s is escape velocity at ground level: no way ISS could stay in orbit going twice that fast!
  - maskros 7y ago
    "again" is the key word. It means 1.5x the speed of the ISS.
    - pif 7y ago
      I had never met that construction. Thanks a lot!
- michaelcampbell 7y ago
  > Also it was Mach 6.7, not 6.2. Hahah, when compared to Mach 22, is that pedantry relevant?
- vl 7y ago
  To be fair, calling X-15 “piloted, powered aircraft” is a stretch. While it’s piloted and powered, it’s definitely not conventional plane, i.e. aircraft. It’s a rocket that is launched from the carrier plane and has ability to land as (unpowered) glider after (unpowered) ballistic flight. In this sense it’s not different from the space shuttle: launched from the carrier vehicle, uses it’s rocket engine to go up, has orbital flight with ballistic descent, lands as a glider. Fair record category would be “takes off under own power, sets record, lands by itself with all the equipment”. X-15 definitely doesn’t qualify.
  - partialrecall 7y ago
    "Aircraft" doesn't make assumptions about the power source. Piston engine, turboprob, turbojet and turbofan aircraft are all called aircraft despite all having different sorts of propulsion. All of those still breath air of course, but we don't hesitate to apply the term to experimental/prototype electric aircraft either. So an aircraft needn't breath air, and therefore having a rocket engine shouldn't be a disqualifier. "Takes off under it's own power" is a qualification you're not the first in proposing, but it's controversial because it would disqualify many famous aircraft, such as the Bell X-1 and according to some (mostly Brazilians) the Wright Flyer. There is also the matter of carrier-launched aircraft that take off when the carrier is running flat out into the wind, let alone with a catapult; it's easy to say they are not taking off entirely under their own power. You could make a similar argument for rocket-assist JATO configurations, if the plane drops the JATOs after takeoff.
    - vl 7y ago
      This is exactly my point, records should be apples-to-apples. This particular record should go to Shuttle or similar “aircraft”. In particular Shuttle is hard to distinguish from X-15. Same thing, but more of it. “Takes off under it’s own power and brings all equipment back” is good limitation - otherwise you can trivially design a system that drops multi-stage booster and lands tiny glider after setting a record.
- Svoka 7y ago
  I don't get how you missed "There are humans there, they got up to speed and regularly come back"
pjc50 7y ago
In-atmosphere flight is completely different, and the line is normally considered to be somewhere between 70 and 100km. Re-entry is faster, but not powered. Other vehicles (missiles etc) achieve high speeds but are unmanned. Also, mach number is dependent on altitude if I remember correctly.
- KineticLensman 7y ago
  The speed of sound is not a constant; in a gas, it increases as the absolute temperature increases, and since atmospheric temperature generally decreases with increasing altitude between sea level and 11,000 meters (36,089 ft), the speed of sound also decreases. For example, the standard atmosphere model lapses temperature to −56.5 °C (−69.7 °F) at 11,000 meters (36,089 ft) altitude, with a corresponding speed of sound (Mach 1) of 295.0 meters per second (967.8 ft/s), 86.7% of the sea level value. [0] [0] https://en.wikipedia.org/wiki/Mach_number https://en.wikipedia.org/wiki/Mach_number
cyberferret 7y ago
I think the differentiator is "powered flight". The ISS relies on momentum and gravitational pull to sustain that speed. Similar with the Apollo 13 CM which reached something like 36,000 MPH on the return leg, giving the astronauts on board the moniker as the fastest that humans have ever travelled in a man made vessel - not considered a speed record per se because it wasn't using an internal power source to propel (to a major extent). The X-15 still had to deal with the other aspects of atmospheric flight like weight (carrying its own fuel source), drag and heating due to friction etc.
- Svoka 7y ago
  ISS does not relies on anything to sustain its speed, this is not how speed works. But again, I wrote rather short comment, and part of it was: > There are humans there, they got up to speed and regularly come back To put it in other words, to get to ISS, crew has to accelerate to it's speed, and to get back, to lose it.
OscarCunningham 7y ago
Does that mean that when you're flying an X15 you lose 6.2/22 = 28% of your bodyweight to the Coriolis force? That's pretty neat.
- jacquesm 7y ago
  That depends on your orientation.
  - deleted 7y ago
    [deleted]
- pdonis 7y ago
  > Does that mean that when you're flying an X15 you lose 6.2/22 = 28% of your bodyweight to the Coriolis force? I think you mean centrifugal force. Unfortunately, no, you don't feel quite that much less weight, because centrifugal force goes like the square of the velocity, so the ratio is the square of 6.2/22, or about 0.08, i.e., only 8%.
  - bzbarsky 7y ago
    There is a Coriolis force here too; it's just much smaller than the centrifugal force. Consider a plane flying at ground level along the equator at groundspeed velocity v in the direction of the Earth's rotation. In the Earth's (rotating) reference frame there is a centrifugal acceleration based on the Earth's angular velocity and a Coriolis acceleration given by -2 W x v, where W is the Earth's angular velocity and v is the plane's velocity. This ends up pointing straight up in this configuration. So in the plane's reference frame there is a straight-up centrifugal acceleration, given by (W + v/R)^2 * R = W^2 * R + 2W x v + v^2/R which is balanced by the aerodynamic and gravitational forces on the plane (which in this frame is non-accelerating), while in the Earth's reference frame there is a straight-up centrifugal acceleration given by W^2 * R and a straight-up Coriolis acceleration of 2W x v, and the plane is accelerating radially down at v^2/R due to gravity and lift combined. Now to put numbers to this, the speed record for an X15 is about 2000 m/s, R is 6.4 * 10^6 m, and W is 1 revolution per 24 hours, or 1/86400 s^1. So the three force components look like this, if I am doing my numbers right: W^2 * R is .00086 m/s^2 2W x v is 0.04 m/s^2 v^2/R is 0.63 m/s^2. So the v^2/R "centrifugal force due to the plane's motion" term is by far the biggest contributor here.

by Svoka 7y ago

dTal 7y ago

> the world record for speed by a piloted, powered aircraft It literally says it right there. The ISS is not a piloted, powered aircraft. Also it was Mach 6.7, not 6.2. Incidentally, the speed record for a crewed vehicle was set by Apollo 10 at 11.08 km/s - almost half as fast again as the ISS.

hyperpallium 7y ago
Fictional but germane scene from The Martian: > [after hearing he has to take the top off of the Mars Ascent Vehicle] I know what they're doing. I know exactly what they're doing. They just keep repeating "go faster than any man in the history of space travel", like that's a good thing. Like it'll distract me from how insane their plan is. Yeah, I get to go faster than any man in the history of space travel, because you're launching me in a convertible. Actually it's worse than that, because I won't even be able to control the thing. And by the way, physicists, when describing things like acceleration do not use the word "fast". So they're only doing that in the hopes that I won't raise any objections to this lunacy, because I like the way "fastest man in the history of space travel" sounds. I do like the way it sounds... I mean, I like it a lot.
Aaargh20318 7y ago
> It literally says it right there. The ISS is not a piloted, powered aircraft. Also it was Mach 6.7, not 6.2. But aren't the Soyuz capsules that dock with the ISS piloted and powered ?
- masklinn 7y ago
  Soyuz can be manually piloted, but are normally automated (Progress can not be piloted and is essentially the same thing after all). They're also not aircrafts.
- pjc50 7y ago
  Yes, but they're outside the atmosphere and therefore don't have a Mach number.
  - mumblemumble 7y ago
    A Soyuz capsule that never enters the atmosphere would have a very upset crew.
- mumblemumble 7y ago
  I would assume that Soyuz capsules aren't considered aircraft. They don't really fly, per se, they get launched on a rocket and then fall like a rock back to earth. You could make a stronger argument for the Space Shuttle, which re-enters at about Mach 25, IIRC, and is gliding. But it's not doing so under power.
  - JshWright 7y ago
    > Soyuz capsules aren't considered aircraft While I suspect you're right, Soyuz capsules do use aerodynamic lift to control descent rate and steer to the landing site. In some ways they are very, very (very) inefficient gliders.
    - ansible 7y ago
      I'd expect the definition of a powered aircraft to include the ability to maintain some given flight altitude and speed for some appreciable amount of time. It is possible to do something sort of like this in a space capsule returning to Earth, where you muck up your entry vector and come in at too shallow an angle. You can then (depending on the circumstances) bounce off the atmosphere, and gain altitude briefly. And then you probably come back in the atmosphere on too steep an angle, and die due to g-load or overheating.
pif 7y ago
> was set by Apollo 10 at 11.08 km/s - almost half as fast again as the ISS. You mean twice as fast as the ISS, don't you? 11 km/s is escape velocity at ground level: no way ISS could stay in orbit going twice that fast!
- maskros 7y ago
  "again" is the key word. It means 1.5x the speed of the ISS.
  - pif 7y ago
    I had never met that construction. Thanks a lot!
michaelcampbell 7y ago
> Also it was Mach 6.7, not 6.2. Hahah, when compared to Mach 22, is that pedantry relevant?
vl 7y ago
To be fair, calling X-15 “piloted, powered aircraft” is a stretch. While it’s piloted and powered, it’s definitely not conventional plane, i.e. aircraft. It’s a rocket that is launched from the carrier plane and has ability to land as (unpowered) glider after (unpowered) ballistic flight. In this sense it’s not different from the space shuttle: launched from the carrier vehicle, uses it’s rocket engine to go up, has orbital flight with ballistic descent, lands as a glider. Fair record category would be “takes off under own power, sets record, lands by itself with all the equipment”. X-15 definitely doesn’t qualify.
- partialrecall 7y ago
  "Aircraft" doesn't make assumptions about the power source. Piston engine, turboprob, turbojet and turbofan aircraft are all called aircraft despite all having different sorts of propulsion. All of those still breath air of course, but we don't hesitate to apply the term to experimental/prototype electric aircraft either. So an aircraft needn't breath air, and therefore having a rocket engine shouldn't be a disqualifier. "Takes off under it's own power" is a qualification you're not the first in proposing, but it's controversial because it would disqualify many famous aircraft, such as the Bell X-1 and according to some (mostly Brazilians) the Wright Flyer. There is also the matter of carrier-launched aircraft that take off when the carrier is running flat out into the wind, let alone with a catapult; it's easy to say they are not taking off entirely under their own power. You could make a similar argument for rocket-assist JATO configurations, if the plane drops the JATOs after takeoff.
  - vl 7y ago
    This is exactly my point, records should be apples-to-apples. This particular record should go to Shuttle or similar “aircraft”. In particular Shuttle is hard to distinguish from X-15. Same thing, but more of it. “Takes off under it’s own power and brings all equipment back” is good limitation - otherwise you can trivially design a system that drops multi-stage booster and lands tiny glider after setting a record.
Svoka 7y ago
I don't get how you missed "There are humans there, they got up to speed and regularly come back"

pjc50 7y ago

In-atmosphere flight is completely different, and the line is normally considered to be somewhere between 70 and 100km. Re-entry is faster, but not powered. Other vehicles (missiles etc) achieve high speeds but are unmanned. Also, mach number is dependent on altitude if I remember correctly.

KineticLensman 7y ago
The speed of sound is not a constant; in a gas, it increases as the absolute temperature increases, and since atmospheric temperature generally decreases with increasing altitude between sea level and 11,000 meters (36,089 ft), the speed of sound also decreases. For example, the standard atmosphere model lapses temperature to −56.5 °C (−69.7 °F) at 11,000 meters (36,089 ft) altitude, with a corresponding speed of sound (Mach 1) of 295.0 meters per second (967.8 ft/s), 86.7% of the sea level value. [0] [0] https://en.wikipedia.org/wiki/Mach_number https://en.wikipedia.org/wiki/Mach_number

cyberferret 7y ago

I think the differentiator is "powered flight". The ISS relies on momentum and gravitational pull to sustain that speed. Similar with the Apollo 13 CM which reached something like 36,000 MPH on the return leg, giving the astronauts on board the moniker as the fastest that humans have ever travelled in a man made vessel - not considered a speed record per se because it wasn't using an internal power source to propel (to a major extent). The X-15 still had to deal with the other aspects of atmospheric flight like weight (carrying its own fuel source), drag and heating due to friction etc.

Svoka 7y ago
ISS does not relies on anything to sustain its speed, this is not how speed works. But again, I wrote rather short comment, and part of it was: > There are humans there, they got up to speed and regularly come back To put it in other words, to get to ISS, crew has to accelerate to it's speed, and to get back, to lose it.

OscarCunningham 7y ago

Does that mean that when you're flying an X15 you lose 6.2/22 = 28% of your bodyweight to the Coriolis force? That's pretty neat.

jacquesm 7y ago
That depends on your orientation.
- deleted 7y ago
  [deleted]
pdonis 7y ago
> Does that mean that when you're flying an X15 you lose 6.2/22 = 28% of your bodyweight to the Coriolis force? I think you mean centrifugal force. Unfortunately, no, you don't feel quite that much less weight, because centrifugal force goes like the square of the velocity, so the ratio is the square of 6.2/22, or about 0.08, i.e., only 8%.
- bzbarsky 7y ago
  There is a Coriolis force here too; it's just much smaller than the centrifugal force. Consider a plane flying at ground level along the equator at groundspeed velocity v in the direction of the Earth's rotation. In the Earth's (rotating) reference frame there is a centrifugal acceleration based on the Earth's angular velocity and a Coriolis acceleration given by -2 W x v, where W is the Earth's angular velocity and v is the plane's velocity. This ends up pointing straight up in this configuration. So in the plane's reference frame there is a straight-up centrifugal acceleration, given by (W + v/R)^2 * R = W^2 * R + 2W x v + v^2/R which is balanced by the aerodynamic and gravitational forces on the plane (which in this frame is non-accelerating), while in the Earth's reference frame there is a straight-up centrifugal acceleration given by W^2 * R and a straight-up Coriolis acceleration of 2W x v, and the plane is accelerating radially down at v^2/R due to gravity and lift combined. Now to put numbers to this, the speed record for an X15 is about 2000 m/s, R is 6.4 * 10^6 m, and W is 1 revolution per 24 hours, or 1/86400 s^1. So the three force components look like this, if I am doing my numbers right: W^2 * R is .00086 m/s^2 2W x v is 0.04 m/s^2 v^2/R is 0.63 m/s^2. So the v^2/R "centrifugal force due to the plane's motion" term is by far the biggest contributor here.