Possible alternate propulsion methods?

[egnio98]

So I was roaming on wikipedia, with the free time I had after exams.

I then apparently found a few types of propulsion methods still under research, which I found to be quite interesting. Firstly,

http://en.wikipedia.org/wiki/Fission_fragment_rocket

The fission fragment rocket, if I understand correctly, is about exploiting the energy released from decaying molecules. On the wikipedia, it theoretically states that it can achieve 1 mil ISP, which is rather shocking, not to mention the new design was proposed by "Rodney L. Clark and Robert B. Sheldon" (Coincidence?!)

Secondly,

http://en.wikipedia.org/wiki/Antimatter_rocket

This sounds really weird, considering that we are using antimatter to propel our rockets through magical particles and whatnot. However, a lot of research has been done on it, where even formulas are existent! From what I understand, again it might be wrong, it is about converting mass into energy,(?) which also result in high efficiency.

Thus, I would like to hear your opinions on these new methods under research, and if they are viable. Please discuss!

Also, side-discussion: What if we are living in the antimatter world; its just relative to us that it's "matter" to us?!

Edited May 17, 2014 by egnio98
spelling?

[Yoha]

So I was roaming on wikipedia, with the free time I had after exams.

I then apparently found a few types of propulsion methods still under research, which I found to be quite interesting. Firstly,

http://en.wikipedia.org/wiki/Fission_fragment_rocket

The fission fragment rocket, if I understand correctly, is about exploiting the energy released from decaying molecules. On the wikipedia, it theoretically states that it can achieve 1 mil ISP, which is rather shocking, not to mention the new design was proposed by "Rodney L. Clark and Robert B. Sheldon" (Coincidence?!)

Keep in mind it is very theoretical. The Isp is directly proportional to the exhaust velocity (the factor is g; I still don't why we are using Isp instead of the exhaust velocity). According to the article you linked:

With exhaust velocities of 3% - 5% the speed of light and efficiencies up to 90%, the rocket should be able to achieve over 1,000,000 sec I_sp.

Indeed: 0.9 × 0.04 × c ∕ g = 1.10×10ⶠs. But the assumption is that the molecules on the edge of the disc are going at a tremendous speed. This is an engineering nightmare and we do not know materials resistant enough to survive this.

Secondly,

http://en.wikipedia.org/wiki/Antimatter_rocket

This sounds really weird, considering that we are using antimatter to propel our rockets through magical particles and whatnot. However, alot of research has been done on it, where even formulas are existent! From what I understand, again it might be wrong, it is about converting mass into energy,(?) which also result in high efficency.

Thus, I would like to hear your opinions on these new methods under research, and if they are viable. Please discuss!

*a lot

*efficiency

An antimatter rocket just says that its primary energy source is based on antimatter, but it does not say how the energy is extracted. Most likely, it would be by "fusionning" it with matter to release the equivalent energy (E=mc²). However, the problem now is that we need a way to:

• store antimatter
  
• know how to fusion matter and antimatter
  
• use the released energy
  

For the last point, the traditional way would be to simply use this energy for heating (the heat being then converted by known systems). This design would not be very efficient, since we cannot control where the energy goes very well. However, due to the considerable amount of energy stored in matter/antimatter, it would be handy for storing huge amount of energy. Again, keep in mind that we don't know much about antimatter.

Also, side-discussion: What if we are living in the antimatter world; its just relative to us that it's "matter" to us?!

It does not really make much sense. We just defined what we know as matter, and discovered that there could be an opposite to it, which we unimaginatively named antimatter. Now, we don't now much of this compound, or the forces it is subject to. Now, some think that the gravity in antimatter could be repulsive instead of attractive, meaning that stars and planets of antimatter could not appear (assuming there is antimatter out there).

[N_las]

The Isp is directly proportional to the exhaust velocity (the factor is g; I still don't why we are using Isp instead of the exhaust velocity).

The ISP has the unit 'seconds', which is the same in imperial and metric. Using the exhaust velocity could work as well, but it may introduce confusion (metric 'm/s' vs. imperial 'quarter-fiddlesticks per second'

[Yoha]

The ISP has the unit 'seconds', which is the same in imperial and metric. Using the exhaust velocity could work as well, but it may introduce confusion (metric 'm/s' vs. imperial 'quarter-fiddlesticks per second'

That's a fair point, but I guess that if engineers can't agree on using SI units, it just might go wrong with other values (say dimensions).

[phoenix_ca]

That's a fair point, but I guess that if engineers can't agree on using SI units, it just might go wrong with other values (say dimensions).

The Americans crashed one of their Mars probes because they couldn't handle metric-to-imperial conversions with diligence. Best to just make it easier for them.

[egnio98]

Indeed: 0.9 × 0.04 × c ∕ g = 1.10×10ⶠs. But the assumption is that the molecules on the edge of the disc are going at a tremendous speed. This is an engineering nightmare and we do not know materials resistant enough to survive this.

So, a ISP of ~ 1 million s is theoretical limit; we can essentially use the strongest material known to mankind, and limit the speed accordingly, and yield the highest ISP possible? With carbon, ISP reaches about 100,000 s [also in the link, under "Research"] Thus, I find Fission-fragment rockets highly viable in the near future.

It does also seem that anti-matter rockets are currently very theoretical, many questions cannot be answered yet. However, if E=mc², wouldn't it mean that even 1g from an object possess a huge amount of energy? Plus, the rocket literally burns its mass, thus making it extra efficient. ( < mass, > acceleration, F=ma). However, would the force be all exerted at once? If so, the g-force might be abit too strong for humans to handle, wouldn't this limit the use of anti-matter rockets?

Please bear with me and my understanding of this, I just happen to be a teenager with a strong interest for the cosmos. Physics classes aren't that... advanced yet.

[egnio98]

The Americans crashed one of their Mars probes because they couldn't handle metric-to-imperial conversions with diligence. Best to just make it easier for them.

Don't forget the aircraft that had the same problem but wasn't as disastrous as the probe. If only we could standardize units.

[N_las]

It does also seem that anti-matter rockets are currently very theoretical, many questions cannot be answered yet. However, if E=mc², wouldn't it mean that even 1g from an object possess a huge amount of energy?

Yes. 1 g antimatter would be an incredible amount of energy. But even that is far from currently possible: "Assuming a 100% conversion of antiprotons to antihydrogen, it would take 100 billion years to produce 1 gram antihydrogen"

Plus, the rocket literally burns its mass, thus making it extra efficient. ( < mass, > acceleration, F=ma).

Every rocket gets lighter while burning its propellant. Nothing special there about antimatter rockets.

However, would the force be all exerted at once? If so, the g-force might be abit too strong for humans to handle, wouldn't this limit the use of anti-matter rockets?

There is no reason why all antimatter should be used at once. It should be possible to us it at a slow rate, to produce small g-forces.

If only we could standardize units.

We can, and we did in 1799.

Edited May 17, 2014 by N_las

[Sirrobert]

Don't forget the aircraft that had the same problem but wasn't as disastrous as the probe. If only we could standardize units.

We already have. America is simply a little slow on playing catchup with the rest of the world.

That said, good scientists in america already use SI units. It's usually the engineers that can't handle it

[christok]

You may be interested in Rubia's engine, which (confusingly) is also known as a fissile fragment engine.

The idea is somewhat similar to that of the fission fragment engine egnio98 linked to. In Rubia's engine, a reactor still heats a propellant (hydrogen). Unlike a conventional reactor/NERVA, the fuel is in thin tubes and so the fissile fragments are flung out into the propellant, dumping most of the heat there instead of heating first the fuel rods and then the propellant indirectly. This change allows the propellant to be heated to a temperature higher than the melting point of the fuel.

Unfortunately, it isn't doable with cheap uranium. One needs a fuel with a very low critical mass, which is likely to restrict it to americium-242m. To make matters worse, there isn't enough data on these sorts of fuels in the non-classified literature.

It's likely to be impractically expensive but I must admit I just like the idea.

Edited May 19, 2014 by christok
Clarification

[phoenix_ca]

Don't forget the aircraft that had the same problem but wasn't as disastrous as the probe. If only we could standardize units.

Touché!

Though I would point-out that at least that was caused by a bit of confusion as we smartened-up and converted to metric. The probe was caused by being anachronistic and holding on to the imperial system.

[Idobox]

Keep in mind it is very theoretical. The Isp is directly proportional to the exhaust velocity (the factor is g; I still don't why we are using Isp instead of the exhaust velocity). According to the article you linked:

Indeed: 0.9 × 0.04 × c ∕ g = 1.10×10ⶠs. But the assumption is that the molecules on the edge of the disc are going at a tremendous speed. This is an engineering nightmare and we do not know materials resistant enough to survive this.

You don't need anything special, really. You just let the fission products exit your engine on one side, and put something to slow them/stop them of the other side. Nothing in the system will get anywhere close to the temperature of the particles.

[Yoha]

You don't need anything special, really. You just let the fission products exit your engine on one side, and put something to slow them/stop them of the other side. Nothing in the system will get anywhere close to the temperature of the particles.

Sorry, I don't get which point of my remark you are addressing. Could you develop?