Propellant/Reaction mass

[Macross Junky]

Something I've always wondered about...

We know that the powerplant for the VF-1 Valkyrie is the fusion turbine, and that's all well and good for generation of electrical power for the mecha. My question is what is the fuel that allows the engine to produce thrust?

Theoretically in atmosphere air sucked into the intake at the front end of the turbine could be superheated by the ongoing fusion reaction and expelled from the thruster as plasma. However, transferring thermal energy to air is inefficient, and such a process would work better with a liquid--in theory even water could be used.

The question of propellant is even more critical in space. Obviously some sort of mass has to be expelled to produce thrust... I guess something like liquid hydrogen or nitrogen could be used as fuel. However, this brings up the question of fuel supplies on the SDF-1. How could the SDF-1 undergo an extended journey in space without running out of reaction mass for the Valkyries to burn? Are the fuels used for air vs. space the same, or different?

This leads me to another question... The SDF-1's power plant is the heat pile system, but... what does the SDF-1 use as fuel? I would think that there would have to be a significant quantity of fuel burned for the SDF-1 to undertake any kind of orbit, and this doesn't even take into question reserves for course changes etc.

Anyone care to shed any insight into these mysteries?

[ewilen]

The SDF-1 is big. It may or may not be credible, but I think the basic argument regarding propellant for the Valkyries is going to be that there was enough onboard the SDF-1 at launch, plus whatever was scavenged from Macross City and stored on the Prometheus and Daedalus (or ARMD platforms, in DYRL), to supply the Valks.

Also regarding the Valks, I doubt they they would have intakes similar to a conventional jet if they didn't use air for thrust in an atmosphere. In space, DYRL has them always using the Super/Strike FAST packs, which may imply that the FAST packs are where the space propellant is kept. However, the Compendium sticks with the TV show development chronology, with FAST packs being deployed 11 months after the beginning of Space War I.

I also think we have to accept that the SDF-1 carries enough reaction mass for its own maneuvering. Perhaps we could hypothesize that some reaction mass was taken from the gas giant planets on the way back to Earth, but I don't recall that ever being shown or discussed.

[JB0]

I also think we have to accept that the SDF-1 carries enough reaction mass for its own maneuvering. Perhaps we could hypothesize that some reaction mass was taken from the gas giant planets on the way back to Earth, but I don't recall that ever being shown or discussed.

Well, they DID skip large amounts of the trip.

Everything between Pluto and Saturn, and Saturn and Mars was ignored.

Though it was stated that they'd been under pretty regular attack between Saturn and Mars, which may have prvented a stopover at Jupiter. And they were likely too busy setting up a counter-offensive at Saturn to refuel.

Unless they were scooping particles out of the rings, but I'd think the scoop would've been on the bow of the ship, which was pointing upwards during the Saturn operation, if I'm not mistaken. And as the Macross wasn't originally designed to be a long-range vessel, I have doubts as to whether a bussard scoop was there to begin with.

But Uranus and Neptune were untouched. If they were capable of refueling from gas giants, that's where they'd've done it.

[Prime]

There are two issues really. The first is what powers the thermonuclear engines? There needs to be "ingredients" for the fusion reaction. Presumably the engine creates an enviroment where fusion can occur. This reaction creates a pile of energy, which is great, but the engine has to utilize that energy somehow. This is where the mass being fired out the back comes in. My physics days are long behind me though

[JB0]

There are two issues really. The first is what powers the thermonuclear engines? There needs to be "ingredients" for the fusion reaction. Presumably the engine creates an enviroment where fusion can occur. This reaction creates a pile of energy, which is great, but the engine has to utilize that energy somehow. This is where the mass being fired out the back comes in. My physics days are long behind me though

Presumably hydrogen.

It's cheap, easy to find(especially in space), and easily fusible.

On the downside, it's not very massive. And spraying beactor byproducts out the back is a really bad idea in an atmosphere(if you thought anti-nuke protestors were bad now...). Hence the need for a seperate propellant that can be heated by the reactor and expelled out the back.

[ewilen]

Hm. We can calculate where the planets will be at the time of SDF Macross. I'd be surprised if it turns out that they'll be lined up in such a way as to make efficient "way stations" on the road home to earth.

This is useful:

http://www.fourmilab.ch/cgi-bin/uncgi/Solar

We don't know exactly where the SDF-1 folds to at the beginning of its journey--somewhere around the orbit of Pluto, I believe, but not necessarily near Pluto's current position at the time.

We do know the SDF-1 flies by Saturn on April 3, 2009, lands on Mars at beginning of October, 2009, and reaches Earth around mid-November. (All this from http://macross.anime.net/story/chronology/...2009/index.html )

Here are the planets' positions at those times, based on the web-based calculator above. First, April 3, 2009:

[ewilen]

(Ignore this post, I screwed up.)

Edited September 16, 2003 by ewilen

[ewilen]

Next, October 5, 2009:

[ewilen]

October 5, 2009 (just the inner planets):

[ewilen]

November 15, 2009 (just the inner planets):

[ewilen]

Since Saturn is the only giant planet on the "left" side of the solar system at the time, it seems likely to me that the SDF-1's trajectory would start somewhere to the left of Saturn, curve around that planet, and then head more or less straight/clockwise toward Mars's October 5 position. After taking off from Mars, SDF-1 would continue clockwise to Earth.

In order to meet the other gas giants as well as Saturn, SDF-1 would have to follow a very long, spiralling, counterclockwise trajectory.

[Opus]

On the downside, it's not very massive. And spraying beactor byproducts out the back is a really bad idea in an atmosphere(if you thought anti-nuke protestors were bad now...). Hence the need for a seperate propellant that can be heated by the reactor and expelled out the back.

I think your thinking of fission reactors. Fusion engines would produce no radioactive waste. That's why every one wants them so badly.

[ewilen]

Another possibility would be to follow a counterclockwise trajectory from Saturn past Jupiter to Mars. This would give them one more gas giant to suck up some reaction mass, and I'm guessing it would be easier to enter into Mars orbit if you're approaching the planet from "behind".

Edit: but if they took this route, they might as well have gone straight to Earth from Jupiter.

Edited September 16, 2003 by ewilen

[JB0]

On the downside, it's not very massive. And spraying beactor byproducts out the back is a really bad idea in an atmosphere(if you thought anti-nuke protestors were bad now...). Hence the need for a seperate propellant that can be heated by the reactor and expelled out the back.

I think your thinking of fission reactors. Fusion engines would produce no radioactive waste. That's why every one wants them so badly.

Depends on the fusables.

Fusion CAN create radioactive byproducts, though not as many.

The main advantages to fusion reactors are

A. You get FAR more power for a given fuel mass, because fusion releases far more energy than fission.

and

B. Hydrogen, the most easy fuel to fuse, is cheap. It's present in some 70% of the Earth's surface, and seperating it from the oxygen atoms it's bound too is a very simple process.

Indeed, most fusable materials are cheap. Unlike the very large atoms needed for fission, the small atoms used for fusion are quite stable and very common.

[JB0]

Another possibility would be to follow a counterclockwise trajectory from Saturn past Jupiter to Mars. This would give them one more gas giant to suck up some reaction mass, and I'm guessing it would be easier to enter into Mars orbit if you're approaching the planet from "behind".

Edit: but if they took this route, they might as well have gone straight to Earth from Jupiter.

Regarding your edit note:

You forgot they were FORCED to Mars. They intended to go straight to Earth and the Zentradi attacks forced them off-track.

...

Ah, forget it. I wasn't following things right.

Edited September 16, 2003 by JB0

[Nied]

Something else to think about. Most of the materials suggested emit radio waves while cooling from a plasma state, not something you want in any military spacecraft. I've always liked the MAT theory of using kerosene for fuel. SInce it's two main components are hydrogen and carbon it could easily be used as a simple fuel/reaction mass combo. Just seperate the Hydrogen from the carbon for the reactors (a simple catylist could do that), and use to carbon as reaction mass (carbon doesn't emit radio waves while cooling).

[Nied]

Another thought on using air as reaction mass in an atmosphere. Yeah gas isn't quite as efficient as a liquid, but so what? That's exactly how modern jet engines do it and they don't seem to have much trouble.

[Yohsho]

Always remember that when talking about nuclear reactions that we have to deal with the half-lives of the fuels.

[JB0]

Always remember that when talking about nuclear reactions that we have to deal with the half-lives of the fuels.

Only for fission.

Fusion cares not for half-lives. It doesn't even need radioactive substances.

[Batou]

Always remember that when talking about nuclear reactions that we have to deal with the half-lives of the fuels.

Not in the case of fuel for a fusion engine, which is the case of the VF-1. Nuclear fission requires (well, really doesn't require, but it makes it a lot easier) radioactive materials to bombard with neutrons and cause the fission reaction. Fusion works like the sun, and can use pretty much anything - probably hydrogen into helium or another light element for efficiency's sake.

[Arrowyn]

Whoa there, let's not forget about the catch-all back door, Overtechnology. They have stuff we can only dream about (and do..).

Also, you can't use the reaction itself to propel the Valkyrie (or SDF). The reaction only gives you neutrons, but if you use those to propel you, you won't have enough neutrons to keep the reaction going for many more cycles.

The secret's in the sauce...er...superdimensional fortress. Watch your heads, now. That baby's long overdue for her fall.

Oh, here's a thought- The engines of the larger ships are Music Powered!. Yeah, each "furnace" is really a rehearsal space for Rock and Roll bands!

Rock On!!

[JB0]

Also, you can't use the reaction itself to propel the Valkyrie (or SDF). The reaction only gives you neutrons, but if you use those to propel you, you won't have enough neutrons to keep the reaction going for many more cycles.

And again we confuse fission with fusion.

Fusion's output depends on the input, but can be as simple as helium gas.

In the real world, Helium3 fusion(yes, the Gundam reaction) is rather promising because it releases a lot of energy and puts off NO neutrons. At all.

He3 combines with He3 to generate 2 protons, an He4(which is a more stable helium isotope), a heck of a lot of energy, and if you happen to live in the Gundam universe you get some minovsky particles.

On the downside, it's a royal pain to get the reaction started.

Not that I think helium gas is a great propellant, but it's there for the usage.

[Macross Junky]

Right, the nuclear reaction itself does not produce thrust. It merely generates energy to power generation of electricity and waste heat. What I figure is that that the waste heat is somehow harnessed and used to superheat propellant, which is fed into a chamber and superheated, then expelled out of the exhausts to produce thrust.

I was thinking "air" being used as the reaction mass in atmosphere for the Valkyries, as the intakes for the engines seem to be open/uncovered in F and G modes, when the engines are providing thrust. The advantage being, that as long as the fusion turbines are generating heat, there is an unlimited amount of propellant available, within the confines of the atmospheric service ceiling. When I think about it, the air that's being drawn in is probably getting compressed in the process--possibly to a state that is dense enough for superheating to work efficiently... In B mode, the fusion turbines are functioning primarily to generate electricity, and the intakes get covered--unless the foot thrusters are being used.

In space, there must be some sort of material that is injected into the chamber for superheating and expulsion to generate thrust... That would be the reaction mass carried in the FAST packs.

I guess that the Valkyrie has an internal "fuel" supply, but that is fuel for the fusion reaction only. The FAST packs may contain their own fusion reactors and fusion fuel supplies as well (IIRC there were radiation symbols on the FAST packs during the launch scene at the start of DYRL?)...

Does this make sense, or am I thinking too much about it?

[Prime]

Right, the nuclear reaction itself does not produce thrust. It merely generates energy to power generation of electricity and waste heat. What I figure is that that the waste heat is somehow harnessed and used to superheat propellant, which is fed into a chamber and superheated, then expelled out of the exhausts to produce thrust.

This is what I was saying earlier. The thermonuclear engine needs fuel for the fusion reaction, but also fuel for the mass to push out the back to create thrust. Fusion just provides the energy to drive the mechanism. It is like nuclear reactors now. It creates energy, which is use to drive turbines or whatever to create electricity. This is the same as using coal or hydro damns to make the turbines go (efficiencies aside).

I was thinking "air" being used as the reaction mass in atmosphere for the Valkyries, as the intakes for the engines seem to be open/uncovered in F and G modes, when the engines are providing thrust.  The advantage being, that as long as the fusion turbines are generating heat, there is an unlimited amount of propellant available, within the confines of the atmospheric service ceiling.  When I think about it, the air that's being drawn in is probably getting compressed in the process--possibly to a state that is dense enough for superheating to work efficiently...  In B mode, the fusion turbines are functioning primarily to generate electricity, and the intakes get covered--unless the foot thrusters are being used.

Air is used in an atmosphere as the reaction mass, but this option isn't avaiable in space. One thing that is in the Valkyries (or any spacecraft's) favor is that much less thrust is needed in space than in an atmoshpere. In an atmoshpere, constant thrust is needed to counter drag and maintain enough speed so that its wings can provide lift. This requires a lot of mass to fire out the back, but the air provides that. In space, drag is not an issue, so the mass is only needed to increase/decrease speed, and change course. This requires much less fuel. So the Valkyrie only needs to store enough mass for those types of manouvers.

There are also some good points here on the differences between fusion and fission.

[David Hingtgen]

Just a quick note from me:

The basic, basic idea of jet propulsion (not necessarily kerosene-fueled aircraft jets, merely the concept--waterjets, etc too) is to accelerate mass for thrust.

To increase the thrust, you can either move more mass, or move the mass faster. (or both).

The current trend in jet engines is to move more mass (actually slower as well, but the increase in mass is so great it more than counteracts the decrease in speed).

[ewilen]

If I'm not mistaken, the basic idea of rocket propulsion is also accelerating mass for thrust. It's just that the mass is carried with you instead of grabbed from your environment.

So to carry your point a bit further, one way the Valkyries (and Macross) can achieve high efficiencies in use of reaction mass is to shoot it out the back really, really fast--provided they have enough energy at their disposal. At a certain point you may run into weird relativistic effects (like if you try to accelerate a 300,000 ton space battleship 10 mph by shooting a single hydrogen atom) and/or the jet of reaction mass coming out the back may be a better weapon than your lasers/cannons/railguns. So there may be practical limits on the force achievable by accelerating a given mass out the back of your spacecraft, regardless of how much energy you have available.

[JB0]

... and/or the jet of reaction mass coming out the back may be a better weapon than your lasers/cannons/railguns.

MAN-MZIN WARS!

[Angel's Fury]

Just a quick note from me:

The basic, basic idea of jet propulsion (not necessarily kerosene-fueled aircraft jets, merely the concept--waterjets, etc too) is to accelerate mass for thrust.

To increase the thrust, you can either move more mass, or move the mass faster. (or both).

The current trend in jet engines is to move more mass (actually slower as well, but the increase in mass is so great it more than counteracts the decrease in speed).

So, if they want to manufacture such an engine, they have to start from scratch? Would nuclear power in miniturized form work in this case?

[ewilen]

While quite different from the Valkyrie's fusion-powered jet engines, there was a project to develop a jet that used either a fission reactor or heat from radiactive isotopes to power its engines. See these links (I'm pretty sure this isn't a put-on):

Nuclear Energy for the Propulsion of Aircraft

NEPA Polonium-Powered Aircraft

The general idea was to use either nuclear fission or radioactive isotopes to heat air, causing it to expand and exit the engine at high speed.

For comparison, here's a good site explaining how jet engines work:

http://www.geae.com/education/engines101/

Anyway, to answer your question, yes, a fusion-powered jet engine would have to be designed from scratch, since the method of transferring heat to air would necessarily be different from a conventional jet, which uses combustion.

Edited September 19, 2003 by ewilen

[Angel's Fury]

Thanks ewilen!

[Gammera]

We kinda had this discussion not to long ago this is ruffly what we came up with plus/minus an exit turbine. (Sorry for any typo’s in the PDF)

As for the Macross having enough fuel for it's self. It only has to fire the engines twice, once to leave Pluto’s orbit (if I remember correctly they we not ACTUALLY at Pluto just somewhere around its orbital ring.) and once to enter Mars orbit, and possibly once to help with a sling shot around Saturn. It's just simple celestial mechanics after that Sir Ike Newton will do the rest of the driving.

engine.pdf

[ewilen]

That PDF's actually pretty good. Do you know to what extent it's based on info from the books (such as the blueprint included in the Gold Book)? Is the original discussion that produced the document somewhere on line?

The only thing I find dubious is the idea of gathering hydrogen from water vapor in the atmosphere and using plasma from the reactors for afterburner and space propellant. I suspect instead that the propellant (whatever it is--could indeed be water) is stored in the wings and that there's no afterburner pe se .But the basic compression/heat exchange/bypass looks good.

It's true that the Macross wouldn't need to fire its engines very much to make the trip, but would mean either a very long trip or the acceleration during the 2-3 burns would be enormous (implies requiring a lot of propellant) in order for it to go from the outer Solar System to Saturn to Earth in nine months.

I forget to mention earlier, though, that if the Macross is capable of generating artificial gravity, it could possibly use the same technology for maneuver (although the show doesn't seem to portray things that way).

[Nied]

We kinda had this discussion not to long ago this is ruffly what we came up with plus/minus an exit turbine. (Sorry for any typo’s in the PDF)

A couple of things regarding this. First the chest "intakes" are actually used for aerodynamic control (the compedium lists them as being used in lieu of glvoe vanes) so the couldn't be collecting water vapor. Secondly I don't see how collecting water vapor could work, under the best conditions there's hardly enough in the atmosphere to create a sustainable fusion reaction, and under the worst conditions (such as in desert climes) there's none at all. Finnally I don't think the space explanation is workable either. Simply squirting reactor plasma out the back wouldn't provide enough thrust, you'd need a reaction mass to really be effective (which again is why I like MAT's solution of kerosene it gives you reactor fuel and reaction mass all in one easily storeable liquid).