Most likely candidate for future spaceship propulsion

[Roadam]

A while back I come upon an article in wikipedia about the launch loop. …

 

Moderation note: This and three related post have been moved to the thread 16574, because it’s a separate subject, deserving of its own thread.

[JoeRoccoCassara]

As the ieee.org article Gardamorg links emphasizes, despite decades of research, nobody’s really confident that self-sustaining fusion power will be possible anytime in the near future, or even if it can be accomplished, how much net power it will produce.

 

Also, as the wikipedia article “energy density” describes, the theoretical maximum energy/fuel mass ratio for fusion is only from 3 to 20 time that of fission, and about 1/140 to 1/300 times that to the absolutely greatest fuel, matter-antimatter.

 

OK, I take it back, it seem pretty safe to name the greatest potential energy source, so long as it’s antimatter.

 

But unlike Antimatter, after a certain point in time, a large enough self sustaining fusion reactor doesn't require any fuel, and it's energy production will eventually achieve greater energy than Antimatter Annihilation, and it will continue to achieve even greater amounts of energy after that.

[CraigD]

But unlike Antimatter, after a certain point in time, a large enough self sustaining fusion reactor doesn't require any fuel, and it's energy production will eventually achieve greater energy than Antimatter Annihilation, and it will continue to achieve even greater amounts of energy after that.

Wherever did you get these idea, Gardamorg?!

 

Nuclear fusion produces energy by transforming elements with low atomic numbers (eg: hydrogen, atomic number 1) into ones with higher atomic numbers (eg: helium, atomic number 2) The slight difference in mass between the beginning and end product (eg: [ce]H2 \to He[/ce]) results in energy, according to the famous old equation [math]E=mc^2[/math], where [math]m[/math] in this case is the difference in mass between the beginning and end products.

 

A fusion reactor needs fuel, in the form of low atomic number elements. What’s meant by “self sustaining” is not that the reactor doesn’t need fuel, but that it doesn’t need an outside source of energy to run, either more energy than it produces (an “under unity” reactor) or less (an “over unity” reactor, the goal of fusion power research). So far, all man-made fusion reactions have either been under unity (various experimental “controlled fusion” reactors, or fusion bombs, which produce much more energy than that of the explosives and fission bombs used to cause the fusion reaction, but are very destructive and difficult to harness for such things as electric power generation or spacecraft propulsion.

 

An ideal fusion reactor could use the end product of one fusion reaction (eg: [ce]H2 \rightarrow He[/ce]) as fuel for another (eg: [ce]He3 \rightarrow C[/ce]). Once a fusion reaction has produced nickel (atomic number 56), it’s impossible to use the end product to generate more energy, as the next fusion reaction produces end products that mass slightly more than their beginning. Such reactions are seen only in stars, which are in a sense ideal fusion reactors.

[Roadam]

Antimatter would be great if we would know how to produce it efficiently. At the moment I think the number stands at about a few percent.

 

So if efficient conversion would be possible, one could build large power plant of some sort(solar, fusion, fission,... whatever). And use the energy to produce and store antimatter. Containers could then be loaded onto a starship and there you go, fast space travel.

[CraigD]

Antimatter would be great if we would know how to produce it efficiently. At the moment I think the number stands at about a few percent.

According to Robert Forward’s 1995 IMHO classic popular science book “Indistinguishable from Magic”, antimatter factories are about 0.000003% (1 in 60 million) efficient. Including the cost of the factory and its operation, the present cost of antimatter at about ten trillion dollars per milligram. The present production rate of antimatter is about [math]10^{-12} \,\mbox{g/day}[/math] (one trillionth of a gram per day).

So if efficient conversion would be possible, one could build large power plant of some sort(solar, fusion, fission,... whatever). And use the energy to produce and store antimatter. Containers could then be loaded onto a starship and there you go, fast space travel.

In the same chapter/essay (chapter 1), he cites a study he did for the US Air Force concluding that, if a factory were designed carefully to maximize production (present day factories are based on accelerator/collectors designed to provide the maximize useful scientific data), the efficiency for on-grid, Earth-based factories could be improved to about 0.01% (1 in 10 thousand). The resulting cost is about ten million dollars per milligram, though production rate would still be too low to meet present day spaceflight demand. Still, assuming a first-generation antimatter powered water steam rocket, such a cost would be about 1/10th the cost of current chemical rockets for routine tasks such as orbiting satellites and sending spacecraft to other planets.

 

To produce antimatter at sufficient rates for routine space travel, production would need to be on the order of 1 g/day. According to Forward, this would require space-based factories with the equivalent of a present-day photovoltaic panel 100 km by 100 km at 1 Earth’s orbit (AU) distant from the Sun (which would equate to about 1/7th the area at a distance of about 0.38 AUs, just inside the orbit of Mercury.

 

My views on the subject are pretty close to Forward’s.

[JoeRoccoCassara]

According to Robert Forward’s 1995 IMHO classic popular science book “Indistinguishable from Magic”, antimatter factories are about 0.000003% (1 in 60 million) efficient. Including the cost of the factory and its operation, the present cost of antimatter at about ten trillion dollars per milligram. The present production rate of antimatter is about [math]10^{-12} \,\mbox{g/day}[/math] (one trillionth of a gram per day). In the same chapter/essay (chapter 1), he cites a study he did for the US Air Force concluding that, if a factory were designed carefully to maximize production (present day factories are based on accelerator/collectors designed to provide the maximize useful scientific data), the efficiency for on-grid, Earth-based factories could be improved to about 0.01% (1 in 10 thousand). The resulting cost is about ten million dollars per milligram, though production rate would still be too low to meet present day spaceflight demand. Still, assuming a first-generation antimatter powered water steam rocket, such a cost would be about 1/10th the cost of current chemical rockets for routine tasks such as orbiting satellites and sending spacecraft to other planets.

 

To produce antimatter at sufficient rates for routine space travel, production would need to be on the order of 1 g/day. According to Forward, this would require space-based factories with the equivalent of a present-day photovoltaic panel 100 km by 100 km at 1 Earth’s orbit (AU) distant from the Sun (which would equate to about 1/7th the area at a distance of about 0.38 AUs, just inside the orbit of Mercury.

 

My views on the subject are pretty close to Forward’s.

 

The stations would be destroyed by mass coronal ejections, you don't put something that close to the sun and expect it to survive, unless you could build it really strong, and if it weren't made of photovoltaic material, than it wouldn't work.

[CraigD]

The [solar-powered antimatter factory] stations would be destroyed by mass coronal ejections, you don't put something that close to the sun and expect it to survive, unless you could build it really strong, and if it weren't made of photovoltaic material, than it wouldn't work.

What’s your source of this prediction, Gardamorg? :( :D

 

We orbited Mariner 10 within the orbit of Mercury in 1974. CMEs occur from about 0.5 to 6 times a day, and Mariner 10 didn’t fail due to them, but rather when it ran out of propellant in 1975.

 

There are certainly challenges to operating spacecraft near the Sun. As with all spacecraft, preventing and managing damage to delicate electronics is critical. Heat dissipation, always a problem with spacecraft that generate a lot of heat, is a problem even for those that don’t. Mariner 10 managed heat in part by angling its solar panels to control how much it absorbed. MESSENGER, which is currently making a series of Mercury flybys to adjust it trajectory to begin orbiting Mercury in 2011, uses both solar panel angling, and a reflective and insulating heat shield that keeps most of the spacecraft in shadow.

 

The same team that designed and built MESSENGER, JHU/APL, is planning a dedicated solar probe spacecraft, named rather unimaginatively Solar Probe, planned launch in 2015, that will have an orbit that brings it within 10 solar radii (about 6.6e6 km) of the Sun, about 10 times closer than Mercury.

 

A close orbiting solar-powered factory like I describe would need a more effective heat dissipation system than spacecraft that have or are planned to closely orbit the Sun. Radiators are the obvious and traditional approach. I’ve read about a few more novel ones.

[Cyberia]

Bussard Ramjet is the fastest, therefore it has my unconditional, unchangeable vote.

 

I tried the Ramjet link and the original blog has gone.

 

The problem with the ramjet is that it needs to get up to a high initial speed to work, maybe a few percent of light speed to collect enough atomic hydrogen to use so it can go even faster. Another problem is that you are building up your own friction in space like running into an endless dense cloud of comparatively very slow moving particles, which will try and slow you down.

 

If you had said to someone living 200 years ago that people would be able to travel from England to America in just a few hours (Concorde) and asked them how they thought it would be done, even the brightest people of the time might have thought of super-galleons with lots and lots of sails. Maybe a year, maybe a decade, maybe a century from now we might discover some new method of travel which will bring the planets of our solar system within easy reach and the nearby stars several years or even just months away.

 

Scientists have been working for some time on human hibernation where voyages lasting years may be possible, where astronauts are in some kind of suspended animation and don't need huge quantities of air, food and water for such a long journey. There is even talk of hollowing out an asteroid so people can live in that for years, even decades on a voyage to the stars.