The IIS Express

[halman]

mrmorris,<br /><br />I am a rather poorly educated layman, and I am inclined to use worst-case scenarios when talking about the applications of advanced technology. Thank you for pointing out the errors in my post! I had received the impression from another thread that iron was not very plentiful on the Moon's surface, so I thought that building flywheels of that material on the Moon might be prohibitively expensive. I had not considered the use of titanium in constructing flywheels because it is a fairly light metal, which means building bigger flywheels to store a given amount of energy versus a heavier material.<br /><br />As far as the initial acceleration of a load, I have always thought that a winch and a cable would work. Electric motors have very impressive amounts of torque, so starting a load is possible using electrical energy, provided by the same source which would power the rail launcher.<br /><br />I retract my suggestion regarding a nuclear powerplant in 'light' of the available solar energy! <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[marcel_leonard]

<font color="yellow">To make plans based around a concept such as your magnetic levitation isn't wise, discerning, or sensible. Instead it falls under a different latin root word: dementia - n. [L., fr. demens. See Dement.] Insanity; madness; esp. that form which consists in weakness or total loss of thought and reason; mental imbecility; idiocy.</font><br /><br />That doesn't change the fact that we don't know enough to make an intelligent decision either way. Romans had a name for people like you... [ignoro: to be ignorant of, not know; (rarely - neglect, overlook)] <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>

 

[fatjoe]

In oyur earlier post you mentioned; "<i>Because the Moon is an airless body, with a low gravity, it would be an excellent location to build a magnetic launcher. But someone took off on the tangent that magnetic launching is impossible on Earth, due to the atmospheric drag. So what seemed like a promising discussion regarding a major goal in the development of the Moon degenerated into a comedy routine about levitating a frog!</i>"<br /><br />Since air or better yet atmosphere seems to be the source of our problems in reaching orbital velocity, and the source of our ability to achieve flight in general. I would think that the solution key to this problem would to develope better scramjet technology. Perhaps looking at a better scheme for using our atmosphere as a propellant.

 

[fatjoe]

Great if you find the link could you post it please...

 

[halman]

FatJoe,<br /><br />The atmosphere can be either a help or a hinderance in launching spacecraft, depending on the method of launching. Any method which attempts to accelerate rapidly at lift-off is hindered, because of the thickness of the atmosphere. But the density of the atmosphere at low altitudes could be utilized to provide lift and oxidizer for a launch vehicle. This is the approach used for the White Knight in launching SpaceShip One.<br /><br />Wings which generate a lot of lift at low velocity are usually indicated for the first stage. Scramjets can be used on the second stage for the climb out of the atmosphere, but this adds complexity to the vehicle, and weight. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[fatjoe]

I believe someone in this thread mentioned the use of a ballon, or blimp launching stage. With the new advances in blimp technology, and a second stage scramjet vehical we could probably deliver about the same payload as the current shuttle design loads...

 

[mrmorris]

<font color="yellow">"With the new advances in blimp technology, and a second stage scramjet vehical we could probably deliver about the same payload as the current shuttle design loads... "</font><br /><br />Generally when making sweeping statement like that -- it's particularly useful if you provide some evidence behind your statement. There's several gotchas inherent in the system you describe.<br /><br /> Balloons/blimps (BB) -- conventional models top out at about 60-80k. Other problems with using them as a means of gaining initial altitude have already been discussed earlier in this thread (Page 6).<br /> Scramjets require supersonic velocities before they develop positive thrust. The BB launch gains altitude, but no velocity. So once your BB has reached max altiitude, the spacecraft must detach and ignite some form of engines (turbojets or rockets) which will then accelerate the ship to supersonic velocity. At this point the scramjets can kick in to take the plane to hypersonic velocities. At this point rockets must be used to take the craft to orbital velocities. It means the craft must have <b>at least</b> two types of engines (rocket-scramjet-rocket), or possibly three (turbojet-scramjet-rocket). Each of these systems adds weight, complexity, and failure points.<br /> Using scramjet technology also means that the craft will be a winged spaceplane. Let's think for a second on what this means at the time it detaches from tbe BB. Picture a 747 being launched by BB. It's lifted to 50,000 feet -- it then revs the engines to full throttle and detaches. I'm not an aeronautical engineer (nor do I play one on TV), but I'm pretty sure that the nil starting velocity means that the sucker is going to fly like a brick until its velocity increases to the point where the wings have some lift. Will there still be a net gain in energy from the BB launch? Yes -- but it won't be a significant fraction of the energy required to get to orbit, and it'll

 

[najab]

><i>we could probably deliver about the same payload as the current shuttle design loads..</i><p>Nope. Ain't gonna happen. Remember, air launch only gains you altitude, not speed. Scramjet technology will probably only get you to Mach 12-15, there's still a <b>lot</b> of acceleration required. You're gonna need a lot of propellant to get 60,000lbs of payload up to orbital velocity.<hr width="10%" align="left" />And, as mrmorris points out, you still need to get up to scramjet speed.</p>

 

[halman]

FatJoe,<br /><br />I am probably mistaken, but I doubt that scramjets will ever be used for anything except sub-orbital flights. They are not capable on their own of accelerating a vehicle to orbital velocities because orbital velocities inside the atmosphere are almost impossible. The air resistance heats the vehicle so quickly that it desintegrates.<br /><br />Also, using a scramjet without any other power source means diving toward the planet to gain enough speed to light the scramjet, then gradually pulling up after ignition. This means losing a lot of altitude after launch, and using a lot of propellant while the nose is lifted above the horizon.<br /><br />I really do not see any applications where a scamjet would be practical. Perhaps, someday, we will be able to build a turbine/scramjet/rocket hybrid, but there are some hairy problems involved. For right now, we are almost certainly better off to keep things simple. Getting payloads of the size the shuttle carries into orbit means using big rockets at some point. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[fatjoe]

My understanding of the scramjet technology is basically a jet/rocket engine that collects air and reuses said air as fuel. Once it collects air enough the way up it can ignite the fuel just as conventional boosters do. Except in this case the tanks didn't have to be heavy w/ fuel before the launch; thus reducing the weight requirement.

 

[nacnud]

I think that collecting and liquidising oxidiser from the atmosphere is very different from scram jet technology.<br /><br />A scram jet is a Supersonic Combustion JAM jet. Basically a complex tube where air is compressed fuel added and then burn, there are no moving parts but the engine only works at very high speed and within the atmosphere.<br /><br />What you are describing sound more like a Liquid Air Cycle Engine or LACE. A further refinement is the SABER engine. <br /><br />From Reaction Engines Limited<br /><br /><font color="yellow">The Sabre engine is essentially a closed cycle rocket engine with an additional precooled turbo-compressor to provide a high pressure air supply to the combustion chamber. This allows operation from zero forward speed on the runway and up to Mach 5.5 in air breathing mode during ascent. As the air density falls with altitude the engine eventually switches to a pure rocket propelling Skylon to orbital velocity (around Mach 25).</font>/safety_wrapper>

 

[nacnud]

Here is a schematic of a LACE/SABER engine cycle.

 

[mrmorris]

<font color="yellow">"My understanding of the scramjet technology is basically a jet/rocket engine that collects air and reuses said air as fuel."</font><br /><br />'Fuel' is not really a good term to use. Fuel is what makes engines run (like a car, boat, or prop plane). When talking about jets and rockets that use action-reaction to move, the terms to use are propellant (whatever gets 'thrown out the back' to create the 'action' that provides a forward impetus) and oxidizer. Rockets require an <b>on-board</b> source of both propellant and oxidizer. Jets, whether conventional (turbine), or ramjet/scramjet require only an on-board source of propellant -- the oxidizer is gathered from the Earth's atmosphere. Scramjets *still* require a propellant -- they don't provide forward motion with nothing more than the incoming air.<br /><br /><font color="yellow">"Once it collects air enough the way up it can ignite the fuel just as conventional boosters do. Except in this case the tanks didn't have to be heavy w/ fuel before the launch; thus reducing the weight requirement. "</font><br /><br />Scramjets do not *ignite* the incoming air. The incoming air (specifically the oxygen therin) allows the onboard propellant (generally Hydrogen) to be burned. Without a source of oxygen -- hydrogen won't burn. The scramjet must still carry sufficient hydrogen (or other propellant) in the tanks from the ground up. The weight savings come in the fact that it's not necessary to *also* carry oxygen for the scramjet. As I said earlier -- this weight savings is partially offset by the fact that there is additional weight of the scramjet engines themselves and supporting hardware. The scramjets <b>stop</b> being useful once the craft is high enough that there is insufficient oxygen coming in to the scramjet engine to allow the hydrogen to burn. At that point rockets must take over.<br /><br />Here's a r

 

[najab]

><i>...the terms to use are propellant (whatever gets 'thrown out the back' to create the 'action' that provides a forward impetus) and oxidizer....Rockets require an on-board source of both propellant and oxidizer.</i><p>As you say, propellant is what gets thrown out the back. For both jets and rockets the 'thing' that gets thrown out the back is hot gas. A jet creates the hot gas by combusting its fuel supply with oxygen. A rocket does it by combining its fuel supply and oxidizer supply. Okay, now to the point of this post (it helps if your post has one): for a jet propellant and fuel are the same thing. For a rocket the propellant is the fuel and oxidizer.</p>

 

[radarredux]

> <i><font color="yellow">For both jets and rockets the 'thing' that gets thrown out the back is hot gas.</font>/i><br /><br />Or ions. In which case I guess the "fuel" is electricity to create an electrostatic force and the ionized molecules are the propellant.</i>

 

[najab]

><i>A jet creates the hot gas by combusting its fuel supply with oxygen. </i><p>Of course, what I forgot to say was that the source of the oxygen is the atmosphere.</p>

 

[halman]

FatJoe,<br /><br />As far as I know, air cannot be used as fuel. It can act as an oxidizer, which is the substance that the fuel reacts with to produce energy. Hydrogen, either alone, or in combination with another element, (frequently carbon) is the usual fuel of most engines.<br /><br />A scram jet is a variation on the ramjet, which is an engine which uses the velocity of air entering the engine to compress the air, which raises the temperature of the air high enough that the fuel will ignite on contact with the hot air.<br /> <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[marcel_leonard]

I beleive FatJoe was referring to LACE/SABER engine technology. Since air consists of mostly hydrogen, oxygen, and nitrogen all three make good candidates for a propellant; thus it will only be a matter of a few more graduating physics classes before we may some day see air itself used as a rocket fuel into orbit. <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>

 

[najab]

><i>Since air consists of mostly hydrogen, oxygen....</i><p>Oh my God! Please, for the sake of all that's good: <b>NOBODY LIGHT A MATCH!!!</b>.<p>Oh, wait....there's actually less than 0.005% Hydrogen in the atmosphere. *Phew* We're safe.</p></p>

 

[nacnud]

So thats why smoking is bad for your health...<br /><br />

 

[najab]

On a planet with a hydrogen/oxygen atmosphere, smoking would be bad for <b>everyone's</b> health!!!

 

[nacnud]

At least you won't have time to get addicted.

 

[marcel_leonard]

<font color="yellow">Oh my God! Please, for the sake of all that's good: NOBODY LIGHT A MATCH!!!.</font><br /><br />Well another thing to look at is that if we didn't have carbon minoxide, nitogen, water mixture of atmosphere nobody would be here to light a match let alone invent matches!!!<br /><br />The solution to the propellant problems is to simply study muons, neutrinos, and deutirium until we discover anti-matter drives so we can beat Z. Cocrain to Alpha Centuri<img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>

 

[craigmac]

I always thought muons, neutrinos, and deutirium were byproducts of electrons, protons, and nuetrons when heated to 10^6 Kelvins within the heart of a star.

 

[marcel_leonard]

It's still all just theory? At last count there were about 32 sub-atomic partical in high energy physics... <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>