Starship Radiators
icarusinterstellar.org
icarusinterstellar.org
http://static3.wikia.nocookie.net/__cb20100127043621/jamesca...
This comes with an interesting model that has far-reaching implications, such as "should we have detected these a long time ago?" Of course the method comes with all the usual Fermi caveats, namely that space is big and the statistical likelihood of the effect happening nearby enough for us to see it.
The primary difference would be the lack of spectral bands. That would be pretty easy to pick out, and so I don't think there's an advantage to having a SETI search with this as the primary goal.
> That would be pretty easy to pick out, and so I don't think there's an advantage to having a SETI search
So, because you say it's an easy search that's an argument why we shouldn't do it? It's not at all clear that we should have discovered this already by accident, if that's your point. I say it's incredibly hard, and also that it's worthwhile.
Our current telescopes probably aren't good enough to catch a small hot object by now, but there is nothing to gain from explicitly including that as a goal.
Any search which can pick out a small hot interstellar spaceship will be very effective at searching for brown dwarfs and other low temperature objects in space. ("Low" means "not a fusing star".)
I doubt there's anything you can do to optimize a SETI search which makes the identification of brown/red dwarfs more difficult. In fact, since you don't know what the background low-temperature IR sources are, you would need the brown dwarf survey to help characterize what's normal vs. a possible spaceship.
There's already funding for dwarf studies, and it's an area of astronomy which is relatively new and unexplored. (The first brown dwarf was not discovered until 1995, for example.) So we know that's a proposal that many can get behind.
Identification of possible non-stellar objects falls out necessarily and almost trivially (compared to the survey itself) from the data.
Position and velocity data is also important for brown dwarf observations, so you'll get that anyway.
So you can tell me - why should we prioritize a very low probability SETI search when there's a high probability that a brown dwarf survey will be scientifically useful, and end up with useful SETI information?
For something the size of a plausible ship, the surface area is astronomically smaller, while the temperature of most of its surface would likely be kept at or lower than the range which is compatible with macro-scale organisms and biochemical processes. A ship would also be trying to manage its heat, probably using an insulating exterior.
Meanwhile it would be pointing its thruster - the only part meaningfully above 300K - away from you for at least half the trip if directly oncoming, with angular efficiency coefficients if heading somewhere else. Recall that the ship itself is insulated & temperature-regulated, and therefore shields the emissions of the thruster. The thruster would also likely be focused as much as possible, so we could expect thermal radiation at steeper angles to drop off sharply.
Even something like a nuclear pulse rocket would be hard to spot until it was within a very small neighborhood, and then it would be up to whether you're actually observing that part of the sky during the time when it might be visible.
Ships are very hard to detect until they're almost on top of you.
Thermal insulation isn't necessary or helpful, except as it separates crew spaces from hot spaces and gives the radiators time to reject heat.
Also, the exhaust plume will be very hot and very bright. Even if the ship doesn't radiate, the exhaust will
Q: Why did you choose fusion based propulsion for Project Icarus?
A: Well, we thought about it and we realized that the only appropriate power source for an imaginary starship was a likewise imaginary one. And while there are certainly many options in the field of imaginary power generation, we rejected some of the main contenders for a variety of reasons.
"Maxwell's Demons" would have alienated both the new-agey spiritual sci-fi crowd and also the fundamentalists because it sounds medieval and just evil at the same time.
"Dilithium crystals" was taken. The zero-point people are bunch of wack jobs and we certainly didn't want to be tarred with that brush. "Fairy wings" just sounds too wussy for our tastes.
So, you see, there aren't all that many choices of power left for an imaginary starship. Fusion sounds just about right, especially if you say is slowly, with gravitas, like "fuuuuuuusion".
ETA: Yup, I was considering the Ramjet design. Scale of the scoop overwhelmed itself trying to acquire enough to function. I was just startled at how little interstellar hydrogen there is; I knew it wouldn't be much, but 0.01g in ten million cubic kilometers was even less than I'd assumed.
FWIW this is an old sci-fi idea / plot device called a Bussard ramjet:
http://en.wikipedia.org/wiki/Bussard_ramjet
But this isn't meant to dispute your calculations. The linked article comes to the same conclusion: it's not feasible, too little interstellar hydrogen.
Naturally, a very large force field ramjet will deplete interstellar hydrogen along the main routes between stars, leading to a situation known as "peak hydrogen", and possibly prompting the invasion of developing hydrogen-rich planets on some sort of flimsy pretext.
Most scientists working on imaginary spacecraft projects therefore eschew the Bussard, correctly anticipating the moment when, shortly after the leader gives a speech on the deck of a starship in front of a huge "Hydrogen Accomplished" banner, the price of hydrogen rises to over $5 a gallon and starships are all left to rust in the front yard.
... and yet that 0.01g of stuff would produce lots of friction and heat if spaceship flies with 10%+ of light speed...
That reminds me on a project I worked on where we were getting the operations of the Hunterston B AGR explained to us and I asked an incredibly stupid question - given the 1,500 MW thermal output of each reactor and ~700 MW electrical output, where does the rest go. The answer is, of course, "to heat the Clyde".
15,000 GW is a lot of waste power!
[Edit - the power figures are per reactor - with each AGR station having two].
If there's a lot of it and you're not making it go elsewhere, assume that the system and it its environs are going to get a bit toasty.
Sometimes you also get things like radiation and vibration. These mostly show up in meaningful quantities in predictable places - nuclear systems, mechanical systems, high-power A/C or RF systems, high-power transducers.
You'll usually do okay if you guess that the system uses energy at around ~60% efficiency, which is enough to give you some idea of the heat to expect if you know the input power.
Or more generally, assume all input power goes to heat and plan to handle operation at that limit - while being aware that your expectations of power consumed by the system may well be low.
Edit: Or maybe one of these bad boys? http://physicsworld.com/cws/article/news/2013/dec/09/new-gen...
But they tend to have low efficiency, thermally-dependent efficiency, and the need for a temperature differential. They operate in response to a temperature gradient, not just heat.
Using Wikipedia for a quick-and-dirty figure, you can expect efficiencies to peak around 5-8%. And you can't just stack infinite thermocouples until system efficiency reaches 99.99% because of the thermal gradient issue.
You can even make several layers of that, with thermal machines between the layers. As the number of layers increase, the efficiency of each one reduces, but the total work goes always approaching a constant assintote.
Ultimately, you don't even need thermocouples, you just need more heat engines with ever decreasing working fluid temperatures, and then it all comes down to your capital costs.
() fission produces waste subproducts, have to be shutdown for maintenance and cool down, fusion requires an electrical generator to sustain the fusion (also fuel, have to centrifuge deuterium etc) and of course antimatter have to be collected and stored in magnetic containment devices which require power to maintain. etc.
The main problem with Icarus is that it aims to create a ship that can do the trip on the scale of a human lifetime. With space travel, the amount of energy required, and therefore the difficulty of the project, is related almost exclusively to how fast you want to get there, the delta-v, if you will.
Therefore, it is unreasonable for Icarus to set a timetable.
If you really want to set a timetable, there is an easier way: stop worrying about how long it takes. Concentrate all of your effort into curing death, and then build a starship with a solar-sail, or some other sort of environmentally-friendly, but slow, technology.
The advantages to this approach are many: easier to get funding, direct economic payoff, no difficulty convincing people that your effort is worthwhile, and, oh yes, you get to cure death.
Then, while you are aboard your starship, you can spend the hundreds of years (say) that it takes you to get to Alpha Centauri further advancing science. If you are adequately equipped, as a nuclear-pulse propulsion vessel would likely be, you can invent better propulsion technology as you go along.
In a sense, the problem of human senescence and its attendant illnesses and the problem of interstellar travel are one and the same. If someone asked me to solve the latter as quickly as possible, I would begin by solving the former.
The Shuttle used a combination of heat pipes and circulating freon (and dumped the waste heat during ascent into the cargo bay, poor cargo!), but also did not have a nuclear reactor on board.
In other words, you could use the main engines to get to Alpha Centauri, then use the radiant heat for the precision maneuvers around the system.
:)