Engineering limits to speed

[SLD]

We all know that relativity forbids us going to light speed or beyond. But from an engineering perspective, what is the practical speed limit? Is there any reason to think we will be able to achieve 0.99c? Or is that just a engineering impossibility?

SLD

 

[Bronzeage]

The ultimate limit of any engineering pursuit is the strength of materials. Right now, it's very likely that the maximum speed of a traction vehicle on the earth's surface has been reached. To drive a vehicle at the speed of sound, the tread of the wheels has to turn slightly faster than the speed of sound. This becomes a problem because a sonic boom at ground level is very violent.

It's possible to turn a fighter jet upside down and just let the wheels roll, but the sonic boom is still a problem, because even if the wheels are just rolling, they are still covering the ground at the speed of sound. Despite this, it has been done, but 763.035 mph was the best they could manage. This is slower than the text book speed of sound, but SoS depends on air density. This might not be such a problem on a planet with very little atmosphere.

It's possible some similar natural phenomena could occur at speeds approaching the speed of light.

The real question is how to generate the energy. The first practical rocket was powered by black powder, and explosive with so little thrust, it can barely lift the unburned fuel. A couple thousand years of intense research has led us to rockets which go very fast and move enormous loads.

Current rocket technology is focused on escaping Earth gravity. Once free of gravity, very little force is needed and most of that is used for direction control. The obvious problem of propelling an object to near the speed of light is that whatever is pushing it has to be going faster than the object. That maybe the key. All we have to do is find a way to push something to the speed of light, in the opposite direction of where we want to go.

 

[Jimmy Higgins]

I think the larger issue is dealing with deflecting any mass that would be in the way of the ship going anywhere near 0.001 times the speed of limit.

 

[skepticalbip]

The term, speed, really has no meaning unless it is followed by "with respect to...". Here on Earth the last part is generally omitted because it is assumed to be with respect to the surface of the Earth. But since you are asking about approaching c, it may be important to understand why c is so special. The speed of light is special because it is the same regardless of what is taken as the reference point. A space ship traveling toward a star at millions of MPH with respect to the star will measure the speed of that star's light (with respect to that rocket) at c, the same as a rocket traveling away from that star at millions of MPH will measure it at c (with respect to itself).

So to travel at 0.99 the speed of light is no problem. We are already doing it if the reference is taken as a quasar or galaxy we say is receding at that speed away from us. The problem of us accelerating a ship to 0.99c with respect to the Earth or Sun is however most likely what you are asking about. The first problem is sufficient energy which we don't and can't have with chemical rockets - we need to convince Scottie to tell us how he gets energy from dilithum crystals and where we can find them.

 

[barbos]

You can't use distant quasar as a frame of reference here. In general relativity there are no global reference frames.
And you can't say they are moving, correct way is to say space-time is expanding along with everything in it.
Also while it's incorrect to quote velocity without reference frame, when we are talking about velocities close to speed of light one usually assume reference frame of CMB.

 

[Valjean]

If you've got plenty of time on your hands a light sail might be practicable, but accelerating mass with conventional rockets becomes cost prohibitive at high speeds

 

[SLD]

If you've got plenty of time on your hands a light sail might be practicable, but accelerating mass with conventional rockets becomes cost prohibitive at high speeds

Would a light sail continue to generate much thrust once you're far away from the main star, say at a Neptune orbit? Seems to me that a light sail might be useful to get on around the inner solar system but not really much further.

SLD

 

[skepticalbip]

You can't use distant quasar as a frame of reference here. In general relativity there are no global reference frames.
And you can't say they are moving, correct way is to say space-time is expanding along with everything in it.
Also while it's incorrect to quote velocity without reference frame, when we are talking about velocities close to speed of light one usually assume reference frame of CMB.

We usually assume the reference frame as the measurement instrument's frame when discussing such velocities, for example the accelerated particles in the LHC or high energy particles striking the upper atmosphere. Although in some cases such as high energy particles emitted by the Sun, the Sun (the source) will be used as a reference frame to describe their energy or velocity.

 

[barbos]

You can't use distant quasar as a frame of reference here. In general relativity there are no global reference frames.
And you can't say they are moving, correct way is to say space-time is expanding along with everything in it.
Also while it's incorrect to quote velocity without reference frame, when we are talking about velocities close to speed of light one usually assume reference frame of CMB.

I don't understand how the CMB can be a reference frame for measuring velocity. The CMB is everywhere and, since it is EM radiation, would always have a velocity of c with respect to anything. Alternately, if it is used as the reference then everything has a velocity of c.

We usually assume the reference frame as the measurement instrument's frame when discussing such velocities, for example the accelerated particles in the LHC or high energy particles striking the upper atmosphere.

CMB is moreless isotropic, but if you somehow get on on spaceship moving with velocity 0.99c then it will no longer be isotropic.
There is a CMB reference frame, it's where CMB is isotropic.

 

[skepticalbip]

I don't understand how the CMB can be a reference frame for measuring velocity. The CMB is everywhere and, since it is EM radiation, would always have a velocity of c with respect to anything. Alternately, if it is used as the reference then everything has a velocity of c.

We usually assume the reference frame as the measurement instrument's frame when discussing such velocities, for example the accelerated particles in the LHC or high energy particles striking the upper atmosphere.

CMB is moreless isotropic, but if you somehow get on on spaceship moving with velocity 0.99c then it will no longer be isotropic.
There is a CMB reference frame, it's where CMB is isotropic.

You are right. I thought of that after I posted and deleted it while you were writing your response.... (damned cross posting )

But then, assuming we had intergalactic (relativistic speed) ships and were making a trip to the Andromeda galaxy, the only reasonable speed measurement would seem to me to be with respect to Andromeda. Using the closing speed to describe the ship's speed would seem to be the most useful or even most reasonable measurement.

 

[Malintent]

The ultimate limit of any engineering pursuit is the strength of materials. Right now, it's very likely that the maximum speed of a traction vehicle on the earth's surface has been reached. To drive a vehicle at the speed of sound, the tread of the wheels has to turn slightly faster than the speed of sound. This becomes a problem because a sonic boom at ground level is very violent.

It's possible to turn a fighter jet upside down and just let the wheels roll, but the sonic boom is still a problem, because even if the wheels are just rolling, they are still covering the ground at the speed of sound. Despite this, it has been done, but 763.035 mph was the best they could manage. This is slower than the text book speed of sound, but SoS depends on air density. This might not be such a problem on a planet with very little atmosphere.

It's possible some similar natural phenomena could occur at speeds approaching the speed of light.

The real question is how to generate the energy. The first practical rocket was powered by black powder, and explosive with so little thrust, it can barely lift the unburned fuel. A couple thousand years of intense research has led us to rockets which go very fast and move enormous loads.

Current rocket technology is focused on escaping Earth gravity. Once free of gravity, very little force is needed and most of that is used for direction control. The obvious problem of propelling an object to near the speed of light is that whatever is pushing it has to be going faster than the object. That maybe the key. All we have to do is find a way to push something to the speed of light, in the opposite direction of where we want to go.

Materials Science is definitely the key to the next (possibly every 'next') giant leap in technology... and will be the next multi-billion dollar industry.

As for the sonic boom issue... I completely disagree that any physical limit exists, much less be reached, by the issue of managing (or failing to manage) a sonic boom. Test pilots said that it was impossible to fly faster than the speed of sound due to unmanageable flight characteristics at the trans-sonic level. Fly-by-wire technology and redesign of the control surfaces solved the problem.

perhaps the solution may be in the elimination of 'the wheel', but perhaps not. But, BA, you sound like Bill Gates when he said that no one will ever need more than 640K of addressable memory in a computer.

 

[T.G.G. Moogly]

Light speed always struck me as a misnomer because as stated, it has no reference point. As such it cannot be categorized with speed.

 

[repoman]

The solar system orbits the galactic center about 200 km/sec. Is this enough to be able to see a very slight red/blue shift to the CMB?

 

[barbos]

Aircrafts measure their speeds with respect to air, it's pretty meaningful.
Same is true for measuring speed with respect to CMB. According to wiki Local group moves 627±22 km/sec with respect to CMB

 

[barbos]

The solar system orbits the galactic center about 200 km/sec. Is this enough to be able to see a very slight red/blue shift to the CMB?

more than enough.

 

[Bronzeage]

The ultimate limit of any engineering pursuit is the strength of materials. Right now, it's very likely that the maximum speed of a traction vehicle on the earth's surface has been reached. To drive a vehicle at the speed of sound, the tread of the wheels has to turn slightly faster than the speed of sound. This becomes a problem because a sonic boom at ground level is very violent.

It's possible to turn a fighter jet upside down and just let the wheels roll, but the sonic boom is still a problem, because even if the wheels are just rolling, they are still covering the ground at the speed of sound. Despite this, it has been done, but 763.035 mph was the best they could manage. This is slower than the text book speed of sound, but SoS depends on air density. This might not be such a problem on a planet with very little atmosphere.

It's possible some similar natural phenomena could occur at speeds approaching the speed of light.

The real question is how to generate the energy. The first practical rocket was powered by black powder, and explosive with so little thrust, it can barely lift the unburned fuel. A couple thousand years of intense research has led us to rockets which go very fast and move enormous loads.

Current rocket technology is focused on escaping Earth gravity. Once free of gravity, very little force is needed and most of that is used for direction control. The obvious problem of propelling an object to near the speed of light is that whatever is pushing it has to be going faster than the object. That maybe the key. All we have to do is find a way to push something to the speed of light, in the opposite direction of where we want to go.

Materials Science is definitely the key to the next (possibly every 'next') giant leap in technology... and will be the next multi-billion dollar industry.

As for the sonic boom issue... I completely disagree that any physical limit exists, much less be reached, by the issue of managing (or failing to manage) a sonic boom. Test pilots said that it was impossible to fly faster than the speed of sound due to unmanageable flight characteristics at the trans-sonic level. Fly-by-wire technology and redesign of the control surfaces solved the problem.

perhaps the solution may be in the elimination of 'the wheel', but perhaps not. But, BA, you sound like Bill Gates when he said that no one will ever need more than 640K of addressable memory in a computer.

There is a world of difference between a sonic boom at high altitude and on at ground level. Perhaps a roadway of super smooth high strength concrete would make this a gentler experience, but the whole project is pretty expensive and that's just for the car.

This is a question about engineering, which means current technology must be examined to see if it can overcome current obstacles. In this case, we don't actually know what the obstacles are when near the SoL. We still haven't solved the Unified Field Theory, which would be very helpful in pursuit of the speed of sound. But then again, maybe there is no such thing as a unified field.

 

[Malintent]

Materials Science is definitely the key to the next (possibly every 'next') giant leap in technology... and will be the next multi-billion dollar industry.

As for the sonic boom issue... I completely disagree that any physical limit exists, much less be reached, by the issue of managing (or failing to manage) a sonic boom. Test pilots said that it was impossible to fly faster than the speed of sound due to unmanageable flight characteristics at the trans-sonic level. Fly-by-wire technology and redesign of the control surfaces solved the problem.

perhaps the solution may be in the elimination of 'the wheel', but perhaps not. But, BA, you sound like Bill Gates when he said that no one will ever need more than 640K of addressable memory in a computer.

There is a world of difference between a sonic boom at high altitude and on at ground level. Perhaps a roadway of super smooth high strength concrete would make this a gentler experience, but the whole project is pretty expensive and that's just for the car.

This is a question about engineering, which means current technology must be examined to see if it can overcome current obstacles. In this case, we don't actually know what the obstacles are when near the SoL. We still haven't solved the Unified Field Theory, which would be very helpful in pursuit of the speed of sound. But then again, maybe there is no such thing as a unified field.

I agree... but when you say "can overcome current obstacles", I encourage the thought to be "can overcome current obstacles [with new tools]".
Before fly-by-wire, it was 'impossible' to keep an aircraft stable at trans-sonic speed with the [at the time] current tools of steel wire actuators. With the current state of technology, it may be 'impossible' to overcome the violence of an as-yet unmitigated sonic boom using concrete and rubber... but concrete and rubber are not the constants.

 

[Bronzeage]

There is a world of difference between a sonic boom at high altitude and on at ground level. Perhaps a roadway of super smooth high strength concrete would make this a gentler experience, but the whole project is pretty expensive and that's just for the car.

This is a question about engineering, which means current technology must be examined to see if it can overcome current obstacles. In this case, we don't actually know what the obstacles are when near the SoL. We still haven't solved the Unified Field Theory, which would be very helpful in pursuit of the speed of sound. But then again, maybe there is no such thing as a unified field.

I agree... but when you say "can overcome current obstacles", I encourage the thought to be "can overcome current obstacles [with new tools]".
Before fly-by-wire, it was 'impossible' to keep an aircraft stable at trans-sonic speed with the [at the time] current tools of steel wire actuators. With the current state of technology, it may be 'impossible' to overcome the violence of an as-yet unmitigated sonic boom using concrete and rubber... but concrete and rubber are not the constants.

While we are pushing the envelope of technology, why not a submarine that operates in magma, so we can travel to the center of the Earth?

 

[Malintent]

I agree... but when you say "can overcome current obstacles", I encourage the thought to be "can overcome current obstacles [with new tools]".
Before fly-by-wire, it was 'impossible' to keep an aircraft stable at trans-sonic speed with the [at the time] current tools of steel wire actuators. With the current state of technology, it may be 'impossible' to overcome the violence of an as-yet unmitigated sonic boom using concrete and rubber... but concrete and rubber are not the constants.

While we are pushing the envelope of technology, why not a submarine that operates in magma, so we can travel to the center of the Earth?

that's impossible
why not indeed ... need to invent / discover unobtainium.

 

[fromderinside]

Speaking of going to the center of the earth why don't we build tunnels, evacuate them making them more or less like dirty space and then use MAGLEV to propel our speed needing folks along at about, SAY 30,000 KPH. Don't need to think about sonic booms unless someone's figured out the rate earth bleeds into vacuum that provides sufficient air like capacity to cause problems. Hell. We might seal the tunnel well enough to generate a launch capacity before the missile leaves the tunnel and it might be long enough so G forces tolerable to humans can be maintained.

IOW fuck the air and fuck limits to G forces. What was that mining species back in the day of Star Trek?