Senior Contributing Editors:
Jesus Diaz
| AIM | Twitter
Mark Wilson, Reviews
| AIM | Twitter
Contributing Editors:
Matt Buchanan | AIM | Twitter
Adam Frucci | Twitter
Sean Fallon | Twitter
Jack Loftus | Twitter
John Herrman | Twitter
Dan Nosowitz
Chris Mascari
Danny Allen | Twitter
Rosa Golijan | Twitter
Chris Jacob
I don't understand how they determine Mach factor so high up in the atmosphere.
Mach is the speed of sound, but the speed of sound is progressively slower as you get higher in the atmosphere since it gets less and less dense, so Mach 21 in the upper atmosphere may not be all that impressive.
Is there a standard altitude or air density which determines Mach or is it variable? Is this Mach 21 as if it was at 30,000 feet?
First, this is awesome. Second, if I remember Physics 7B well enough, magnetic fields only interact with charged particles. Perhaps the upper atmosphere is mostly charged particles. Third, while this reduces friction of atmospheric gases on the ship's hull, it increases the overall drag coefficient. From the article "trajectory modification to compensate for the increased drag caused by the atmospheric gas deflection".
@The Lab: A reentry spacecraft heats the air around it enough to turn to plasma. Which is, of course, charged particles. :-)
So basically, the capsule hits the atmosphere and the compression heating of air forms a plasma. The field acts on the particles, which does a few things:
1. The plasma is directed away from and around the craft, cutting down on heat transfer and preventing the surface of the craft from superheating.
2. The magnetic field reacting with the plasma creates a drag force on the electromagnet, which slows down the capsule.
3. The plasma presses against the air, forming new plasma to replace that which has been pushed away.
@The Lab: Regular magnetic fields are way too weak to interact with anything that's not charged. Superconductor magnetic fields can interact with just about anything. Search YT for levitating frogs and mice to get the picture, or watch the attached video to upgrade your knowledge in physics. Some weird and amazing stuff is underway with superconductors.
@jepzilla: I had discounted the idea of plasma formation because I thought the plasma would only form upon being heated by the friction with the hull. However, if the vehicle is traveling fast enough, maybe the pressure front of the air it is pushing would create the plasma?
@zwer: There are a few inconsistencies in your post that make me question how much you really know about this subject. For instance, you make a distinction between "regular magnetic fields" and "superconductor magnetic fields". That makes no sense. There is no "regular magnetic field". Furthermore, you can create very weak or very strong magnetic fields using superconductors. Source of magnetic field =/= strength of field. It is important in scientific discussions to use language precisely.
@Duckspwn: Well, eliminating friction caused by air rubbing the skin of the ship. I don't think they mean all friction happening everywhere in the universe.
@Duckspwn: I was thinking that too, there might be some other uses for this technology. Of course I don't know how much energy it costs to create this magnetic field so that might outweigh the benefits of eliminating friction in the first place.
@Duckspwn: It's not eliminating the friction. It's preventing the superheated air molecules from making direct contact with the vehicle's surface during re-entry. A magnetic 'envelope' around the craft, sort of like the magnetic containment field used in Star Trek to keep matter and anti-matter separated.
Duckspwn promoted this comment
Edited by Jrsy Devil's Advocate® at 12/03/09 8:06 PM
Jrsy Devil's Advocate® was starred
Jrsy Devil's Advocate® was unstarred
@Duckspwn: My guess would be eliminating it from the hull itself. Somehow pushing the friction a few millimeters/inches/whatever off the the hull into the air itself? Only thing I can think of that makes any sense.
Either that, or they're using a buttload of Crisco.
@Jrsy Devil's Advocate®: So rather than saying it "eliminates friction", it could be said that it merely prevents friction from acting directly on the surface of the ship (therefore avoiding huge amounts of heat)?
@Duckspwn: I was being purposefully hyperbolic, but one would assume this would actually eliminate friction. I have no particular idea if this is true, but I always assumed that friction required two material substances to rub together, not a material substance and an energy field.
I mean... do mag lev trains generate friction along the field that supports them? or magnetic bearings along their track? I wouldn't think they do. There's nothing coming in contact with anything, so there are no molecules available to interact and cause friction.
In any case, even if this does not entirely eliminate friction, it must reduce it to close to zero. If nothing else because it's an active force pushing molecules away from the ship, instead of letting them hit the skin and slide along it.
@Pope John Peeps II: The friction is occurring between the particles of atmosphere being highly compressed against the magnetic field. The compression and friction creates heat.
I think the majority of re-entry heat is from compression anyway, but I'm not 100% sure. Either way, the vehicle isn't going any faster, or marginally so.
@KyleHuff: This is the SECOND time you've said this. It's not going to get any more correct. In fact, logically it's actually gotten 100 % MORE WRONG. Because you said it again.
No matter how hot air might get from compression, if it does not touch the skin of the ship there is no possibility of heat transfer from convection. Haven't you ever had a vacuum thermos? it's the same principle! They've been around for like... a hundred years.
@Pope John Peeps II:
Guy, I don't even know what to say to you. This system most certainly does not work like a vacuum thermos, and it does not work by reducing friction.
At the velocities they are talking about, radiative heating may be a bigger problem than convection anyway.
Would you like me to explain why vacuum thermoses are silvered?
Why don't you just explain it to me Kyle "XY" Huff? Why don't you explain why a vacuum does not insulate, and how delfecting air does not reduce friction.
Why don't I just make myself a tea, settle in to an armchair, and Kyle XY here is going to give me a goddamn lesson in how to read an article. So, Kylie. Let's go. Here's your chance. Dazzle us. Do it.
@Pope John Peeps II: You need to chill out, maybe attach one of these devices.
Vacuum insulates, but heat can still be transferred through radiation. Thus why things will eventually freeze in space and heat-sinks do work (though they need to be larger).
Deflecting the air certainly changes the friction since air molecules aren't getting caught on the molecular ridges of the vehicle's surface, however air molecules are still slamming into each other creating plenty of heat and the magnetic field may not be perfectly smooth either.
A perfectly frictionless vehicle will still be slowed down and heated up when travelling through a medium unless it was perfectly aerodynamic (both "perfects" are impossible).
OMG! Baseon the the name alone we can surmise that this will come about sometime in the next 91 years! This is truly a disaster from the standpoint US competitiveness and technological leadership!
12/04/09
12/04/09
12/04/09
12/03/09
12/04/09
12/03/09
12/04/09
12/04/09
12/04/09
12/03/09
Mach is the speed of sound, but the speed of sound is progressively slower as you get higher in the atmosphere since it gets less and less dense, so Mach 21 in the upper atmosphere may not be all that impressive.
Is there a standard altitude or air density which determines Mach or is it variable? Is this Mach 21 as if it was at 30,000 feet?
12/03/09
12/03/09
12/03/09
12/03/09
12/03/09
So basically, the capsule hits the atmosphere and the compression heating of air forms a plasma. The field acts on the particles, which does a few things:
1. The plasma is directed away from and around the craft, cutting down on heat transfer and preventing the surface of the craft from superheating.
2. The magnetic field reacting with the plasma creates a drag force on the electromagnet, which slows down the capsule.
3. The plasma presses against the air, forming new plasma to replace that which has been pushed away.
12/03/09
12/03/09
12/03/09
12/03/09
12/03/09
12/03/09
12/03/09
12/03/09
12/03/09
12/03/09
12/03/09
12/03/09
12/03/09
Either that, or they're using a buttload of Crisco.
12/03/09
12/03/09
12/03/09
12/03/09
12/03/09
I mean... do mag lev trains generate friction along the field that supports them? or magnetic bearings along their track? I wouldn't think they do. There's nothing coming in contact with anything, so there are no molecules available to interact and cause friction.
In any case, even if this does not entirely eliminate friction, it must reduce it to close to zero. If nothing else because it's an active force pushing molecules away from the ship, instead of letting them hit the skin and slide along it.
12/03/09
I think the majority of re-entry heat is from compression anyway, but I'm not 100% sure. Either way, the vehicle isn't going any faster, or marginally so.
12/03/09
All the re-entry heat is from compression. Friction is a red herring.
12/03/09
12/03/09
No matter how hot air might get from compression, if it does not touch the skin of the ship there is no possibility of heat transfer from convection. Haven't you ever had a vacuum thermos? it's the same principle! They've been around for like... a hundred years.
12/03/09
Guy, I don't even know what to say to you. This system most certainly does not work like a vacuum thermos, and it does not work by reducing friction.
At the velocities they are talking about, radiative heating may be a bigger problem than convection anyway.
Would you like me to explain why vacuum thermoses are silvered?
12/04/09
Why don't you just explain it to me Kyle "XY" Huff? Why don't you explain why a vacuum does not insulate, and how delfecting air does not reduce friction.
Why don't I just make myself a tea, settle in to an armchair, and Kyle XY here is going to give me a goddamn lesson in how to read an article. So, Kylie. Let's go. Here's your chance. Dazzle us. Do it.
12/05/09
Vacuum insulates, but heat can still be transferred through radiation. Thus why things will eventually freeze in space and heat-sinks do work (though they need to be larger).
Deflecting the air certainly changes the friction since air molecules aren't getting caught on the molecular ridges of the vehicle's surface, however air molecules are still slamming into each other creating plenty of heat and the magnetic field may not be perfectly smooth either.
A perfectly frictionless vehicle will still be slowed down and heated up when travelling through a medium unless it was perfectly aerodynamic (both "perfects" are impossible).
02/02/09