Superman Returns and Zero-G

[four elevener]

I was going to put this in Entertainment, but it probably belongs here. I have $25 riding on this. Warning: some spoilers below.

During the shuttle sequence in Superman Returns, right after Superman separates the two vessels, the 777 it was piggybacked on gets pulled into space and everything inside the plane starts to float. Seconds later, it's falling back to Earth. A buddy of mine says that it was right at the fringes of space, enough to where Earth's gravity was able to pull it back. I say the plane should have continued onward and out into orbit since that's where the shuttle's trajectory was taking it and it had already reached zero gravity. Who's right?

PS: I checked Phil Plait's article on this film but didn't find any informaton on this particular anomally. And please, let's ignore all other implausibilities associated with a film about a flying man in tights.

 

[wollery]

Haven't seen the film but I doubt a 777 could remain intact for long in such a low pressure environment as space, planes aren't designed for it, so they almost certainly wouldn't have got out of Earth's gravitational field (particularly considering that you have to get well out of the atmosphere to do that). In which case, sorry, but the people are floating because they're in free fall. I.e. the plane and the people in it are falling at the same rate, so they appear weightless wrt the plane, but are still in Earth's gravitational field. This is actually the reason astonauts on the Shuttle float around, not because they're out of Earth's gravitational field (if they were they wouldn't be in orbit), but because they're in free fall.

 

[Squishua]

During the shuttle sequence in Superman Returns, right after Superman separates the two vessels, the 777 it was piggybacked on gets pulled into space and everything inside the plane starts to float. Seconds later, it's falling back to Earth. A buddy of mine says that it was right at the fringes of space, enough to where Earth's gravity was able to pull it back. I say the plane should have continued onward and out into orbit since that's where the shuttle's trajectory was taking it and it had already reached zero gravity. Who's right?

I think your friend may be right. Just because everything is floating, certainly doesn't mean the shuttle had escape velocity, let alone was outside the earth's gravitational pull.

Everything floats because it is in free fall. In fact, that's how they produce a lot of those "weightless" sequences in movies nowadays. They fly the actors and crew up in one of those "vomit comets" and then let the plane free fall while they get twenty or thirty seconds of filming in.

-Squish
PS - sorry about the $25.

ETA - Damn! Woolery beat me to it!

 

[switchtech]

Floating in space...

The point where people float isn't specifically anywhere near space, or even way out in space. People float when the trajectory of their vehicle follows a ballistic arc (the vomit comet purposely enters a free fall trajectory to train people in a weightless environment). The difference about an orbit in space is that the falling object misses the Earth (like Arthur Dent).

So, for a spiffy Hollywood special effect they showed the people weightless. While the aircraft was high enough to fall with little air resistance the people inside would indeed experience weightlessness as they free fall with their aircraft. Once the acceleration toward the Earth met with significant resistance from the air (and the aircraft ceased free falling), the people inside the plane would have fallen to the earthward side of the craft and felt the return of weight.

If we were able to set a platform in space that didn't actually orbit but could essentially hover, then the occupants would experience a portion of their earthbound weight (depending on distance from the center of mass).

As an example, when the solid rocket boosters and later the fuel tank separate from the shuttle they fall back to Earth. If you were riding inside the fuel tank (somehow still alive) you could experience weightlessness for a while and still fall back to Earth. Of course the SRB are still burning at separation and that changes their dynamic somewhat but the fuel tank enters free fall immediately.

jbs

 

[Aerik]

"The point where people float isn't specifically anywhere near space"

But everything is already in space, all the time, silly!

 

[Ziggurat]

The point where people float isn't specifically anywhere near space, or even way out in space. People float when the trajectory of their vehicle follows a ballistic arc (the vomit comet purposely enters a free fall trajectory to train people in a weightless environment). The difference about an orbit in space is that the falling object misses the Earth (like Arthur Dent).

NASA uses a commercial airline plane to do precisely this: fly in a parabolic arc which maintains zero G inside the plane for short periods of time. It's nick-named the "vomit commet" for the nausea it induces.

So, for a spiffy Hollywood special effect they showed the people weightless. While the aircraft was high enough to fall with little air resistance the people inside would indeed experience weightlessness as they free fall with their aircraft.

There's always going to be significant air resistance, but the engines can compensate for that. The key thing is the falling: the aircraft has to be decending, and at an accelerating rate. For an aircraft that just had its tail section burnt to a crisp (which controls the up-down motion of the plane), going from a level flight trajectory to something falling fast isn't hard to believe. After a while, though, they'll hit terminal velocity even with engines pushing forwards.

 

[TjW]

NASA uses a commercial airline plane to do precisely this: fly in a parabolic arc which maintains zero G inside the plane for short periods of time. It's nick-named the "vomit commet" for the nausea it induces.



There's always going to be significant air resistance, but the engines can compensate for that. The key thing is the falling: the aircraft has to be decending, and at an accelerating rate. For an aircraft that just had its tail section burnt to a crisp (which controls the up-down motion of the plane), going from a level flight trajectory to something falling fast isn't hard to believe. After a while, though, they'll hit terminal velocity even with engines pushing forwards.

The aircraft doesn't even have to be descending: you do a 2 gee or so positive pullup to get the plane and everything in it going upward at a fair clip, then pitch negative to just match the climb rate of the contents of the aircraft. About half the zero gee time is while you're going up.

 

[Art Vandelay]

If "zero gravity" means "the thrusters have finished thier burn", then unless the aerodynamic profile of the plane dramatically changed, it should continue on the intended trajectory.

Certainly doesn't sound as bad as SW III. A ship presumably in orbit falls apart, so for some reason it falls towards the planet. Smoke billows out of it, rising upwards.

 

[Schneibster]

GAH!

Look, there are several serious problems.

1. Being in space doesn't necessarily mean you're weightless.
2. Being weightless doesn't necessarily mean you're in space.
But those are only the obvious ones.
3. A 777 is powered by fanjets, which are basically turbojets that have a big fan on the front to provide a laminar airflow around the nacelle to keep the engine quieter. The fan also provides a bit of extra compression, but not enough to allow the jet to operate above the usual ceiling for such an engine. In addition, the wings' lift is limited by the combination of falling air pressure and maximum airspeed, the first of which is a feature of increasing altitude, and the second of which is a combination of thrust-vs-drag from the thrust of the engines, and top speed imposed by the ability of the airframe's covering to dissipate the friction heat from the air. That ceiling is on the close order of 40,000 feet- about eight miles. The atmosphere is 100 miles high, more or less- and the stratosphere goes up to about 15 miles. So, basically, no commercial aircraft is capable of leaving the stratosphere, with the exception of the SST.
4. Orbital velocity at about 100 miles' altitude (called Low Earth Orbit, or LEO) is 7.8km/s, which is about 17,500mi/hr. That's about Mach 25. There are no aircraft that go Mach 25; in fact, it is likely that it is impossible for a material object to go Mach 25 in the stratosphere because there is no object capable of withstanding the frictional heat. Anything that tries to move at orbital velocity below about 90 miles' altitude is going to get very hot very fast, and will lose a great deal of velocity very quickly.
5. And a passenger jet (again, with the exception of the SST) can't even go Mach 1.
6. A very special trajectory is required for occupants of an aircraft to experience zero-G. This trajectory is a parabola, of a very particular shape, depending on the altitude and the speed of the plane. Just a little bit off, the slightest miscalculation or misguidance of the aircraft, and significant acceleration effects will "pull" the occupants toward the outside of the plane, up, or down, or to one side or the other.
7. A plane's jets don't just "stop pushing." They take a while to spool down. They're spinning at thousands of RPMs and weigh thousands of pounds. You can't stop something like that instantly without it coming apart in a very good imitation of an explosion. I have seen fragments of disks from inside old disk drives made in the 70s and 80s penetrate the thick, cast aluminum casing that surrounds the spindle and head assemblies when the disks shattered while spinning at a few thousand RPM. I was very happy that the casings were made of thick hard metal. The results otherwise would have been uncomfortably similar to a hand grenade.

That's what comes to mind off the top of my head. To critique it any better, I'd have to see it- and I am singularly uninterested in watching a movie that the producers, writers, and directors didn't think enough of to hire someone who knows enough physics to steer such things correctly- or else to listen to them after they had hired them. It's difficult enough for me to suspend disbelief enough to watch Superman in the first place- to have someone blatantly screw up something as easy to get right as this situation is would have me out of my seat and up at the box office demanding a refund.

 

[rjh01]

Do you want to experience zero G? You can!
Method 1. Jump up so high you leave the ground. You will experience zero G until you land.
Method 2. Go to a great height (no higher than four feet) and jump.
Method 3. Jump out of an aircraft. Please ensure you know how to use and are carrying a parachute. For the first few seconds after jumping you will have zero-G. After that air resistance kicks in.

 

[Roboramma]

I just watched the DVD of superman the other day. It was a pretty mediocre movie... but anyway I thought I'd let it be known what actually happens. (I've just put the DVD on to make sure I get it right).

GAH!

Look, there are several serious problems.

1. Being in space doesn't necessarily mean you're weightless.
2. Being weightless doesn't necessarily mean you're in space.

The people in the plane don't experience zero-g when they go into space. The plane is attached to a space shuttle that has accidentally caried them along for the ride. Superman detaches them from it while the shuttle's rockets are still burning. The moment the airplane detaches, it begins falling back to earth, and the people on it experience zero-g. This seems to make sense to me...

But those are only the obvious ones.
3. A 777 is powered by fanjets, ...<SNIP>... no commercial aircraft is capable of leaving the stratosphere, with the exception of the SST.

This is covered above - it didn't get out of the atmosphere under it's own power - it was carried along by the space shuttle.
Of course the question of whether the shuttle would have enough fuel and thrust to carry a 777 along with it...

4. Orbital velocity at about 100 miles' altitude (called Low Earth Orbit, or LEO) is 7.8km/s, which is about 17,500mi/hr. That's about Mach 25. There are no aircraft that go Mach 25; in fact, it is likely that it is impossible for a material object to go Mach 25 in the stratosphere because there is no object capable of withstanding the frictional heat. Anything that tries to move at orbital velocity below about 90 miles' altitude is going to get very hot very fast, and will lose a great deal of velocity very quickly.

I don't know if this applies or not.

6. A very special trajectory is required for occupants of an aircraft to experience zero-G. This trajectory is a parabola, of a very particular shape, depending on the altitude and the speed of the plane. Just a little bit off, the slightest miscalculation or misguidance of the aircraft, and significant acceleration effects will "pull" the occupants toward the outside of the plane, up, or down, or to one side or the other.

Again, they were out of the atmosphere, and began to experience zero-g only when detached from the shuttle and it's rockets. Shortly after this they seem to hit the earth's atmosphere hard and experience crazy erratic g-forces (lois lane goes bouncing around the inside of the cabin the moment they hit atmosphere).
I have no idea if this is realistic or not.

7. A plane's jets don't just "stop pushing." They take a while to spool down. They're spinning at thousands of RPMs and weigh thousands of pounds. You can't stop something like that instantly without it coming apart in a very good imitation of an explosion. I have seen fragments of disks from inside old disk drives made in the 70s and 80s penetrate the thick, cast aluminum casing that surrounds the spindle and head assemblies when the disks shattered while spinning at a few thousand RPM. I was very happy that the casings were made of thick hard metal. The results otherwise would have been uncomfortably similar to a hand grenade.

I'm not quite sure what your point is here.

Anyway, I just thought it was worth clearing up what actually happened in the movie. To reiterate: the space shuttle is attached to an airplane that carries it up into the sky (which seems a little ridiculous), the shuttle malfunctions and isn't able to detach from the airplane or abort it's launch, so when the engines go off, it carries the plane along for a ride. Superman comes along and detaches them, but after they've exited the atmosphere, at which point the people on the plane experience zero-g. A few seconds later, the plane hits atmosphere and experiences crazy g-forces. Superman lands it in the middle of a baseball stadium and everyone cheers. He gets a stupid look on his face, then flies off.

 

[Roboramma]

Do you want to experience zero G? You can!
Method 1. Jump up so high you leave the ground. You will experience zero G until you land.
Method 2. Go to a great height (no higher than four feet) and jump.
Method 3. Jump out of an aircraft. Please ensure you know how to use and are carrying a parachute. For the first few seconds after jumping you will have zero-G. After that air resistance kicks in.

Method 4. Bungee jumping!
Method 5. Learn to rock climb. Now go out and climb a mountain beyond your ability without a rope.

 

[Capsid]

3....and the second of which is a combination of thrust-vs-drag from the thrust of the engines, and top speed imposed by the ability of the airframe's covering to dissipate the friction heat from the air.

My understanding is that it's mostly ram pressure and not frictional heat.

 

[Overman]

In random celebration of new emoticons.

 

[Art Vandelay]

The people in the plane don't experience zero-g when they go into space. The plane is attached to a space shuttle that has accidentally caried them along for the ride. Superman detaches them from it while the shuttle's rockets are still burning. The moment the airplane detaches, it begins falling back to earth, and the people on it experience zero-g. This seems to make sense to me...

That doesn't seem to be the same thing as what's described in the OP: "I say the plane should have continued onward and out into orbit since that's where the shuttle's trajectory was taking it and it had already reached zero gravity."

If the rockets are firing, then it hasn't reached "zero gravity".

 

[Schneibster]

My understanding is that it's mostly ram pressure and not frictional heat.

Depends on how fast you're moving, I guess...

The SR-71 Wikipedia article's section on the skin of the aircraft refers to frictional heating. OTOH, ram pressure is cited as the reason for meteoroids vaporizing in the atmosphere. I suspect that you have to be moving pretty fast for ram pressure heating to significantly override frictional heating.

 

[tracer]

Of course the question of whether the shuttle would have enough fuel and thrust to carry a 777 along with it...

The space shuttle as shown in that movie didn't even have its external fuel tank attached. The real-life Space Shuttle's main engines are fed exclusively off the external tank. If there is no external tank attached, the main engines cannot fire.

The two little orbital engines above and to the sides of the main engines run off of an internally-stored fuel supply (a hypergolic, I believe?), but they don't even have enough fuel to boost an empty space shuttle out of the atmosphere, let alone one that's dragging a jet airliner along with it.

 

[Roboramma]

That doesn't seem to be the same thing as what's described in the OP: "I say the plane should have continued onward and out into orbit since that's where the shuttle's trajectory was taking it and it had already reached zero gravity."

If the rockets are firing, then it hasn't reached "zero gravity".

The OP may be misremembering the movie - not only were the shuttle's engines still firing when the plane was detachted from it, superman gives it an extra push (I assumed because it wouldn't achieve it's orbit otherwise).

To tracer - yeah, that part seemed very silly to me too.

 

[davefoc]

A slight digression:
It is interesting to me that one can't detect how strong a gravitational field one is in if one is just falling and one doesn't use external clues to determine that he is accelerating. I am assuming that the gravitational field is constant for the individual being accelerated.

 

[Zygar]

A slight digression:
It is interesting to me that one can't detect how strong a gravitational field one is in if one is just falling and one doesn't use external clues to determine that he is accelerating. I am assuming that the gravitational field is constant for the individual being accelerated.

I hope I understand the question. As long as the body is in equilibrium, the gravitational field will be undetectable. We "feel" gravity as us pushing against something when we stand, or sit, or whatever. If we were falling through the air, we wouldn't "feel" it because we wouldn't be pushing against it.