The IIS Express

[marcel_leonard]

We are currently stuck on 2000 year old conventional liquid/solid fuel rocket boosters to presently launch materials into space. But when we begin mining the Moon, Mars, and the asteroids, where we will not have a source of fuel for conventional rockets, we shall need a more effective way. Electromagnetic lauchers may be the answer. A small prototype of Maglev, and the electromagnetic rail gun, can presently accelerate a projectile from rest to a speed of 10 km/s (2000 mi/h).<br /><br />When I calculate the mass of the Earth (5.98e24), the radius @ (6.37e6); I get [v=(2GM/r)^1/2], or 1.37e8 m/s=ans.<br /><br />But most books will tell you that Escape Velocity for the Earth is 40200 km/s, or about 1.11e4 m/s; which equal to about 25000 mi/h. So, an object which has this velocity at the surface of the earth, will totally escape the earth's gravitational field (ignoring the losses due to the atmosphere.) It is all there is to it.<br /><br />I believe we can achieve these speed if we combine a few existing technologies [ie. ScramJat/ AeroSpike/ Maglev launch rail.] <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>

 

[craigmac]

At Fermilab we’ve done some very promising test with Muon acceleration. Theoretically once we’ve figured out the mechanics anti-gravity (dark energy) there is no limit to the amount of mass that we could accelerate. My guess is late in this century we will reach orbit using photonic energies…

 

[najab]

marcel, 10 km/sec = 22000+ mph

 

[marcel_leonard]

Sorry converting from SI to foot, pound system always throws me off. Makes you kind of wonder why in the world this country still uses the old british system; when even the British as well as the rest of the planet Earth uses SI....<img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>

 

[marslauncher]

As a Brit (in Austin Texas) The metric system which we use in England for weights is really easy to use, however we still use miles/ft for measurements (long distance) (short distance we use metric metre's and centimenters)<br /><br />Confusing isnt it. No wonder then that the MPL (Mars Polar Lander missed) (maybe as well as Beagle)

 

[craigmac]

Not to stray away from the subject of alternative energies for launching spacecraft, but there must be a lot of loss revenue, and economic deficit created by hanging to the old British system. Imagine the trillions of dollars we would free up if you all used SI units.<br />We probably could wipe out world poverty. <br /><br />Nah I guess not someone would find away to screw up!!!<br />

 

[fatjoe]

Most would agree that escape velocity is about 25000 mi/h; although since there are no actual test flights at that speed no one knows for sure...

 

[najab]

I was wondering when you'd show up. Your friends have been here for a while without you.

 

[marcel_leonard]

It never fails; SDC always finds a way to change the subject. can anybody here show me links to electromagnetic launch technologies under developement? <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>

 

[mrmorris]

<font color="yellow">"...can anybody here show me links to electromagnetic launch technologies under developement? "</font><br /><br />Well there's ESA's Phoenix/Hopper. Hopper is supposed to be launched from a rail. None of the URLs I checked right quick gave details on whether the rail was an EM-based system or not. I have always assumed so.

 

[mrmorris]

Figures -- should have checked one more link. This one says the Hopper will be 'accelerated by either magnetic fields or steam'.<br />

 

[fatjoe]

The ESA have the right idea but I believe marcel_leonard had the idea of using an EM conductive rail were a shuttle like craft could be accelerated to speeds of up to 25000 mph; thus achieving escape velocity.<br /><br />Lets be realistic if we are going to pioneer outer space we are going to have to do a lot better than conventional rockets boosters…<br />

 

[marcel_leonard]

Can anyone explain escape velocity? <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>

 

[mrmorris]

<font color="yellow">"... a shuttle like craft could be accelerated to speeds of up to 25000 mph; thus achieving escape velocity."</font><br /><br />Um... no. There's a teensy-tiny problem of frictional heating due to the atmosphere. Marcel asked about rail-launched systems so I provided the Hopper link. However -- while the Hopper concept will be used to provide a significant initial velocity to the craft without using on-board propellants it will be nowhere close to escape velocity. In fact I think Hopper is only supposed to be sub-orbital. The cargo will have a kick-stage that takes it to orbit.<br /><br />Frictional heating limits long-term travel through the air to about 1,500 mph without special measures to keep the vehichle cool. The SR-71 flew at 2,000 mph, had to be painted black, and was constructed largely of titanium. It was also flying at high altitudes where frictional heating was considerably reduced. We're talking about speeds ten times what it flew at and altitudes much closer to sea level. That's going to be one toasty spacecraft.<br /><br />Also -- the length of a railgun required for speeds in the range being discussed is considerable. from the following site -- it's projected that a railgun length required to reach 11000 m/s (24,606 mph) accelerating at 10g would need to be 605 kilometers long (376 miles).

 

[spacester]

Escape velocity is an abstract concept that has little practical use in space flight computations. In has its uses, but as an imaginary mathematical concept only.<br /><br />Escape velocity is dependent not only on the mass of the body you are escaping from, but also the distance from the center of that body. Typically, one uses the radius of the planet in question, so "Earth escape velocity" is the value you get from the surface of the earth.<br /><br />Escape velocity defined: the instantaneous velocity an object must have relative to the center of a body, at a given distance from that center, in order to coast to a dead stop at an infinite distance away, the slowing down being due solely to the effect of the body's gravity field. (When I researched this on the web almost 4 years ago, this definition was not found, so I won't be surprised if you cannot verify it explicitly. But it is the shortest mathematically correct definition I know of.)<br /><br />In reality, there is no such thing as escape velocity from the Earth's surface because 1) you need infinite acceleration to go from zero to escape velocity in zero seconds, and 2) atmospheric drag and other factors will help slow down the object.<br /><br />Also, in the real solar system, when you "escape" the gravity of a Planet, you are still in the Sun's gravity field. This is why real trajectories are calculated using the "patched conic" method and the Sphere of Influence distance.<br /> <div class="Discussion_UserSignature"> </div>

 

[marcel_leonard]

Know your talking! Don't you just love that raw brain power...<img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>

 

[craigmac]

I agree that escape velocity is a vague concept, but it does help layman understand the factors involved in reach orbit. What would you suggest would be a better way to explain reaching the speed need to launch a craft into space?

 

[spacester]

Orbital velocity is much more useful than escape velocity.<br /><br />But to really understand what's going on, my recommendation is to think in terms of orbital energy. It's not nearly as simple as escape velocity; if you do not have a grounding in high school physics, you're going to have a rough time of it. You need to understand Kinetic Energy and Potential Energy.<br /><br />Possibly the best place to start is to google "vis-viva equation". If you have the basic physics down and you spend some time with the subject, it's really not that hard. Me, I love space math. YMMV, but all it really takes is some perseverance.<br /><br />As far as getting to orbit, I can dig up old posts to show how to account for everything. You have zero orbital energy on the surface, you need to add energy to get the orbital energy you want (in the right direction). You need to correct for latitude, elevation, atmospheric drag and gravity losses. The first two are simple formulas, drag and gravity losses are in principle simple but in practice very hard to calculate exactly. <div class="Discussion_UserSignature"> </div>

 

[spacester]

If you're really interested in the math . . . <div class="Discussion_UserSignature"> </div>

 

[craigmac]

No matter whether you choose to call the speed escape velocity, or orbital velocity; the question remains how do we feasibly achieve such speeds economically and safely?

 

[marcel_leonard]

Composite metals that can hold up to extreme heat. <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>

 

[mrmorris]

<font color="yellow">"Composite metals that can hold up to extreme heat. "</font><br /><br />Excellent example. I'd forgotten about the heat shield of the Shuttle. It makes for an excellent example of the corrolary of the atmospheric heating that I didn't mention in my post. The reason the heat shield of the shuttle gets so hot is because of atmospheric <b>braking</b>. Every bit of the heat created is accompanied by a reduction in the velocity of the spacecraft. The shuttle begins this braking process in the very upper wisps of atmosphere, and has shed much of its velocity by the time it gets into thicker air. A rail-launched spacecraft has its <b>highest</b> velocity in the thickest part of the atmosphere. Also -- since it's going to lose a huge amount of speed as heat during the light up through the atmosphere, the initial velocity must be well in excess of the actual velocity needed for the intended orbit.<br /><br />Per a quick Google search, the shuttle's orbital velocity is ~17,532 miles/hour (obviously this changes depending on the orbit). I believe it lands at something on the order of 200 miles/hour. So its flight through the atmosphere scrubs off more than 98% of the orbital velocity. Granted the shuttle takes a flight path and insertion angle intended to use frictional braking but even a configuration designed to minimize frictional effects is still going to lose a <b>significant</b> percentage of its initial velocity -- especially given the atmospheric density issue detailed above. <br /><br />Oh -- and while the shuttle tiles are pretty good, they *still* aren't good enough to withstand heat at the levels needed for a ground level launch that can reach the speeds you're proposing. That's not to say something won't be developed which <b>can</b> -- but it still doesn't resolve the larger issues

 

[marcel_leonard]

Maybe the thing to do here is to look at the problem another way. A classic text experiment demonstrates a frog being levitated in a magnetic field produced by current in a vertical solenoid right below said frog. The solenoid’s upward magnetic force on the frog balances the downward gravitational force on the animal. <br /><br />In theory if I had a large enough magnetic I could cancel out any load acting on an object, and literally levitate into orbit...<br /> <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>

 

[najab]

><i>In theory if I had a large enough magnetic I could cancel out any load acting on an object, and literally levitate into orbit...</i><p>First off, you would be levitating into space, not orbit. Turn off the magnetic field and the frog would drop 100 miles, straight down (can anyone say "splat"?) Secondly, magnetic fields obey the power law - the field strength drops off as the square of the distance. A field powerful enough to support an object at 100 miles would be insanely powerful on the ground - you'd be collecting ferrous objects from miles around!</p>

 

[marcel_leonard]

The fact of the matter is we still don't really know that much about (B) fields or (E) fields for that matter. Just as light spreads out in all directions; once we discoverd how to focus photons in one direction we discovered lasers.<br /><br />The same thing could be true for electromagnetic propulsion.... <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>