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 Post subject: The closest exoplanet has been discovered. PostPosted: 2012-10-16 08:08pm
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They just don't come any closer than this.

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Exoplanet found right next door in Alpha Centauri
May be roughly Earth-sized, but blazingly hot.

by John Timmer - Oct 16 2012, 4:16pm USMST

Today, planet hunters announced evidence there's a planet orbiting one of our closest stellar neighbors. One of the three stars of the α Centauri star system shows the sort of periodic changes in brightness that are a hallmark of the presence of an orbiting planet. And, even though the new world would be far too hot to support liquid water, the astronomers who discovered it point out small planets tend to form in groups. Odds are good that there are additional planets lurking further out from the host star.

Rapid advances in planet-hunting have led to an ever-increasing catalog of exoplanets, but most of these orbit distant stars. In contrast, the a Centauri system "is a household name," as Greg Laughlin of UC Santa Cruz put it. Just over four light years from Earth, the system includes two bright stars, Centauri A and B orbiting each other with an 80 year period, along with a red dwarf called Proxima Centauri. Centauri B has a Sun-like mass, but is quite a bit dimmer.

The planet was detected using the radial velocity method. As a massive body orbits its host star, it exerts a gravitational pull on it, pulling the star in slightly different directions as its position shifts. These create a small acceleration in the star itself, usually on the order of a few meters per second. That, in turn, shows up in the light emitted by the star as Doppler shifts in the light it emits, which vary with the orbital period of the planet.

Detecting these, however, can be a challenge, as a long catalog of factors can also cause periodic changes in the star's output. The authors of the paper describing the find list them as, "instrumental noise, stellar oscillation modes, granulation at the surface of the star, rotational activity, long-term activity induced by a magnetic cycle, the orbital motion of the binary composed of a Centauri A and B, light contamination from a Centauri A, and imprecise stellar coordinates."

To get around these, the authors relied on a massive catalog of observations, made using the HARPS instrument on a 3.6 meter telescope at the European Southern Observatory. Over a span of nearly four years, the authors made multiple observations of Centauri B, often several observations a night, spaced out two hours apart. This let them average out short-term variability on the span of hours, and reconstruct that star's equivalent of the solar cycle, in which its activity increased over the course of their observations.

One by one, they factored out all of the periodicities they could account for. What was left was a hint of a signal with a periodicity of 3.3 days. This was incredibly weak—in fact, the smallest yet detected—at only 0.8 meters/second acceleration. But, even though this signal was much smaller than some of the noise they filtered out, the authors calculated there was a "false alarm probability" of less than one percent. In other words, it's probably a planet. As scientist told a press conference earlier today, if it was any place other than Alpha Centauri, there would be nothing extraordinary about the claims.

But don't start building the colony ship just yet. With a 3.3 day orbit, the planet is only 0.04 Astronomical Units (1 AU is the typical distance from the Earth to the Sun). That makes this planet blazingly hot, at about 1,500 Kelvin. One of its discoverers indicated this would ensure the surface is "not solid, more like lava." The radial velocity method lets you estimate the lower bound on the mass of the planet. Assuming it's orbiting roughly in a plane that faces edge-on to Earth, it has a mass roughly equivalent to our home planet.

Even though the new planet is likely well outside the habitable zone, we shouldn't give up on a Centauri. The plane of the two large stars of a Centauri is oriented nearly face on to Earth, and forces that govern star formation would make it likely that any planetary disks would form in this same plane. That means the planet is more likely to be on the low end of the mass estimates—in other words, close to Earth-sized. As the discoverers noted, about 70 percent of the small planets we've discovered have been in systems with multiple planets. So, the chances of finding something else further out are much higher than you might otherwise expect.

The HARPS team (which was represented by Stéphane Udry and Xavier Dumusque of the Geneva Observatory) estimate that, based on Centauri B's habitable zone (which is roughly centered on distance that's equivalent to Venus' orbit) they should be able to spot a Super-Earth (having five to 10 times Earth's mass) in the habitable zone. And, given the probability that the system's plane is oriented towards Earth, we could also use an orbiting observatory to watch for planets transiting in front of Centauri B.

We may have to wait a bit, though. The team told the press conference the orbit of the system's two large stars could be problematic; they were coming very close to each other over the next four years. This would make observations extremely challenging. It'll be eight years or more before we'll have good conditions for observations again. But, on the plus side, telescope tech is advancing dramatically these days, and a decade's worth of progress will put us in a much better position to learn something about our neighbors.

What about visiting? Laughlin estimates that, given our current technologies, any probe we sent wouldn't arrive for about 40,000 years. So that's probably a no-go, "given our propensity for instant gratification." But there are some unproven propulsion ideas that could get us there much more quickly, and Laughlin said that, should this find ignite enough interest, we may look into those more seriously.


While this putative exoplanet is far too hot to land safely on, let alone have any life on it . . . where there's one terrestrial planet, there are usually more. Assuming the observations are repeatable, the whole Alpha Centauri system suddenly just got a lot more desirable to visit.




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 Post subject: Re: The closest exoplanet has been discovered. PostPosted: 2012-10-16 11:40pm
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I wonder if anyone would consider naming this Polyphemus.

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 Post subject: Re: The closest exoplanet has been discovered. PostPosted: 2012-10-17 02:19am
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We need to send an enormous cee-fraction probe there like right now. Seriously - an R&D project like this would bring technological advances greater than Apollo, energize and motivate humanity and frankly be extremely freakin' cool.

Also, it has the possibility to return data within one human lifetime, which is always cool.



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 Post subject: Re: The closest exoplanet has been discovered. PostPosted: 2012-10-17 06:19am
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By now, is there any doubt left that practically all stars have planets?



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 Post subject: Re: The closest exoplanet has been discovered. PostPosted: 2012-10-17 08:59am
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PeZook wrote:
We need to send an enormous cee-fraction probe there like right now. Seriously - an R&D project like this would bring technological advances greater than Apollo, energize and motivate humanity and frankly be extremely freakin' cool.

Also, it has the possibility to return data within one human lifetime, which is always cool.

Question: given our current technology, what is the quickest we could expect such a probe to reach the system?

Also, how big/sophisticated a transmitter would you need to send back data? Can we build one capable of sending data over four lightyears?

In which case - how long it takes to get there + 4 years and some change and we have images and data from our nearest solar system(s).



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 Post subject: Re: The closest exoplanet has been discovered. PostPosted: 2012-10-17 09:12am
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Well, the best current tech (NERVA) would still require a prohibitive amount of fuel to get up to any appreciable fraction of C ; But at least AC being only 4 LY away means it's at least physically possible to get something there in a single human lifetime, unlike for most other exoplanets we've detected so far :)



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JULY 20TH 1969 - The day the entire world was looking up

It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn't feel like a giant. I felt very, very small.
- NEIL ARMSTRONG, MISSION COMMANDER, APOLLO 11

Signature dedicated to the greatest achievement of mankind.

MILDLY DERANGED PHYSICIST does not mind BREAKING the SOUND BARRIER, because it is INSURED. - Simon_Jester considering the problems of hypersonic flight for Team L.A.M.E.

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 Post subject: Re: The closest exoplanet has been discovered. PostPosted: 2012-10-17 11:22am
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In human lifetime is impossible.

Even Voyager is making a 'meager' 3.3xx AU/year which is about 26 light minutes per year. Let's be generous and assume 30 light minutes/year, and it still would take roughly 70000 years to go there. So anything you propose would need to go at least 1000x faster than the fastest man man-made object to leave the solar system. Or ~300x times faster than the fastest spacecrafts ever made. (Helios probes, 150000miles/hour at the fastest point of their sun orbit)



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 Post subject: Re: The closest exoplanet has been discovered. PostPosted: 2012-10-17 11:55am
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LaCroix wrote:
In human lifetime is impossible.

Even Voyager is making a 'meager' 3.3xx AU/year which is about 26 light minutes per year. Let's be generous and assume 30 light minutes/year, and it still would take roughly 70000 years to go there. So anything you propose would need to go at least 1000x faster than the fastest man man-made object to leave the solar system. Or ~300x times faster than the fastest spacecrafts ever made. (Helios probes, 150000miles/hour at the fastest point of their sun orbit)


Uh...so Voyager can't do it, big deal? It doesn't mean it's an at all impossible task. Alpha Centauri being 4 LY away means that at least we don't have to break physics to do it.



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JULY 20TH 1969 - The day the entire world was looking up

It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn't feel like a giant. I felt very, very small.
- NEIL ARMSTRONG, MISSION COMMANDER, APOLLO 11

Signature dedicated to the greatest achievement of mankind.

MILDLY DERANGED PHYSICIST does not mind BREAKING the SOUND BARRIER, because it is INSURED. - Simon_Jester considering the problems of hypersonic flight for Team L.A.M.E.

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 Post subject: Re: The closest exoplanet has been discovered. PostPosted: 2012-10-17 02:30pm
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Getting it up to speed to get there in a human lifetime is probably the "easier" part of this, since we could front-load much of the work at home. Slowing it down there would be the bigger problem, along with designing a probe that's more or less completely autonomous for its entire operation (you could broadcast signals from home that it could pick up, but getting them back would take too long to really control it much during its operational life-time).



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 Post subject: Re: The closest exoplanet has been discovered. PostPosted: 2012-10-17 03:44pm
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Well I'd say it'd take a massive beefing-up of existing technologies, but it could be done. Think a massive automated probe with the biggest ion drive we can plausibly construct. It'd have to be nuclear powered with a huge number of redundant systems. Something like that could accelerate constantly, then flip around and decelerate constantly until it reached the Centauri system. I figure that if it can accelerate at only 1/2 G, it would be approaching lightspeed by the time it gets halfway there. If it can accelerate at one full G, it would take less than a year to accelerate to near lightspeed, another 2 and a half years transit, then a year to decelerate. Even if you bring that speed down to 1/4 G, it's still only a decade-long trip...as long as the New Horizons probe took just to get to Pluto. The key would be constant acceleration which only an ion drive could provide.

Once it arrives, it would run all the tests we could program into it, launch micro-probes to investigate individual planets (think Hyugens probe), and either hang around until the reactor goes dead, or possibly collect samples and return to Earth?

I am curious about communication, however. Over a distance of 4 lightyears, any communication with enough bandwidth to handle the sheer amount of data that would be generated would have to be very tight-beam and consume a lot of power.



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 Post subject: Re: The closest exoplanet has been discovered. PostPosted: 2012-10-17 06:16pm
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C'mon guys, someone finds an earth like planet in a binary system, and we're ten posts in and no one makes the obvious joke!

Fine, I'll do it;

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 Post subject: Re: The closest exoplanet has been discovered. PostPosted: 2012-10-17 07:04pm
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Because it's the wrong kind of system for that. The planet only orbits B, rather than both, so most of the time the stars are on opposite sides of the sky.

What you want is a circumbinary planet like Kepler 16b. Which is already nicknamed Tattooine. :p



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 Post subject: Re: The closest exoplanet has been discovered. PostPosted: 2012-10-17 07:44pm
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I was going to say Vulcan, just to be different. :P

On topic though...quite an interesting discovery. I was always holding out hope that AC would have some planets, since it is the closest star to Earth. Now to figure out a way to get there before I've turned to dust in my grave. :P



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 Post subject: Closest Exo-planet found. How do we get there? PostPosted: 2012-10-18 12:28am
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So...as the name suggests and a new topic since it's a different question to the previous "Yippee, we found a planet really close to home!" thread.

So, ideas? Suggestions?

How about a multi stage system? An Orion to get a lot of mass up to speed and then a NERVA for cruising/long duration acceleration?

I noted in another thread the question of 'How de we slow it down?'

My question is 'Why slow down?'. Why not simply make any probes have enough braking re-mass to do that job and have the main rocket just sling-shot around something and come home?



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 Post subject: Re: Closest Exo-planet found. How do we get there? PostPosted: 2012-10-18 12:49am
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With current knowledge, it is my understanding we need a really big nuclear rocket. As in one powered by direct nuclear fission with the fission products making a nice radioactive trail of debris.

As for slowing down, that more than doubles the mass to get there, and to solar-break (aerobreaking won't work - there is too much energy and the probe would be so hot to have any effect that it would end up being a fourth sun as it went through the atmosphere). Also, momentum is why you can't slingshot something moving at even low fractional C velocities.



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 Post subject: Re: Closest Exo-planet found. How do we get there? PostPosted: 2012-10-18 08:05am
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Ion drive. They've already proven to be very reliable and fuel-efficient in smaller tests (Deep Space 1), so a much bigger version would be the way to go. You'd need constant acceleration in the range of 1/4g to 1g to get there within a reasonable timeframe (less than a decade)...and even a nuclear rocket can't do that. Only an ion drive can provide steady acceleration for years on end.



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 Post subject: Re: Closest Exo-planet found. How do we get there? PostPosted: 2012-10-18 09:03am
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Yeah, NERVA would need an absolutely prohibitive amount of fuel. It gets stupendous ISP, but stupendous is still not enough. Ion drives seem like the only way, but we'd have to crack the thrust problem first.

Somebody needs to throw 300 billion dollars at the problem.



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JULY 20TH 1969 - The day the entire world was looking up

It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn't feel like a giant. I felt very, very small.
- NEIL ARMSTRONG, MISSION COMMANDER, APOLLO 11

Signature dedicated to the greatest achievement of mankind.

MILDLY DERANGED PHYSICIST does not mind BREAKING the SOUND BARRIER, because it is INSURED. - Simon_Jester considering the problems of hypersonic flight for Team L.A.M.E.

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 Post subject: Re: Closest Exo-planet found. How do we get there? PostPosted: 2012-10-18 09:11am
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PeZook wrote:
Yeah, NERVA would need an absolutely prohibitive amount of fuel. It gets stupendous ISP, but stupendous is still not enough. Ion drives seem like the only way, but we'd have to crack the thrust problem first.

Somebody needs to throw 300 billion dollars at the problem.


Yeah sure let me get my chequebook...

Yeah, ion drive is the only real choice. I found one example of a test burn where it fired continuosly for 35,000 hours at full power with no faults or defects. That's pretty awesome.



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 Post subject: Re: Closest Exo-planet found. How do we get there? PostPosted: 2012-10-18 10:10am
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Ion drives are nice, and there are types that have been running 2 years continuously without problems, the only problem is that they only achieve this by generating thrusts in the 0.00x g range. You'd need to make the average drive 50+ times more powerful to get them to 1/4 g, at which point, you loose the ISP edge it has over others.

Or you need a hilariously huge helium tank and strip a couple of dozen ion drives onto it in order to propel a smallish drone.



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 Post subject: Re: Closest Exo-planet found. How do we get there? PostPosted: 2012-10-18 10:26am
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If we can figure out some means of fusion propulsion, can get to a few percent of c.

Dropping a ridiculous quantity of conventional fuel in a bottom burn slingshotting around the Sun can also get to a few percent of c. Probably the only thing we'd have a hope of doing at the moment.

Light-sails can get to the speed limit imposed by the ISM, but that requires political commitment. And a massive infrastructure.



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 Post subject: Re: Closest Exo-planet found. How do we get there? PostPosted: 2012-10-18 10:50am
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If we decide on a longer time limit, a lot can be done with relatively little money, at least compared to some things ; Of course it wouldn't be an infrastructural project in the common sense, but the technology and orbital infrastructure we'd get from it would continue to provide benefits for decades after the money's spent.



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JULY 20TH 1969 - The day the entire world was looking up

It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn't feel like a giant. I felt very, very small.
- NEIL ARMSTRONG, MISSION COMMANDER, APOLLO 11

Signature dedicated to the greatest achievement of mankind.

MILDLY DERANGED PHYSICIST does not mind BREAKING the SOUND BARRIER, because it is INSURED. - Simon_Jester considering the problems of hypersonic flight for Team L.A.M.E.

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 Post subject: Re: Closest Exo-planet found. How do we get there? PostPosted: 2012-10-18 01:20pm
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LaCroix wrote:
Ion drives are nice, and there are types that have been running 2 years continuously without problems, the only problem is that they only achieve this by generating thrusts in the 0.00x g range. You'd need to make the average drive 50+ times more powerful to get them to 1/4 g, at which point, you loose the ISP edge it has over others.

Or you need a hilariously huge helium tank and strip a couple of dozen ion drives onto it in order to propel a smallish drone.


Oh well certainly it'd have to be huge...we're talking several times bigger than a Saturn V at least just for the fuel, and yeah the drives would have to be vastly more powerful than current models. That kinda goes without saying, given the distance. A probe would have to arrive in no more than I'm guessing 15 - 20 years, else it could degrade simply due to age. So to arrive within that time frame you're looking at maybe 1/8g acceleration for a 20 year trip, 1/4g for a 10 year trip, etc...

To arrive within the lifespan of the hardware on the probe, as well as the people who worked on the program, it'd need to accelerate to a good percentage of lightspeed.



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 Post subject: Re: The closest exoplanet has been discovered. PostPosted: 2012-10-18 01:54pm
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Merged the two topics about this.

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 Post subject: Re: The closest exoplanet has been discovered. PostPosted: 2012-10-18 01:56pm
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Ion drives just don't have the ISP to do an interstellar mission. You're pretty much restricted to some variety of nuclear or antimatter drive if you're going with a self-contained rocket, since nothing else has the requisite energy density. You could alternatively go with a laser-propelled optical sail, but that requires some intense infrastructure. Slowing down is a lot easier, fortunately; you can use a magnetic sail to brake against the ISM.

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 Post subject: Re: The closest exoplanet has been discovered. PostPosted: 2012-10-18 02:11pm
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What? Ion drives can have an ISP on the order of 10 000 seconds, which beats VASIMIR by 100% and NERVA by 1000%.

NASA thinks that there might be a possibility to use antimatter or some sort of uber ion drive to achieve ISP of 50 000 seconds, but that seems to the physical upper limit of reaction drives.

In fact, there's a short overview/article dealing with the problem on NASA's website:

NASA Geeks wrote:
Just how limited are rockets for interstellar travel? Although rockets are reasonable for journeys into orbit or to the moon, they become unreasonable for interstellar travel. If you want to deliver a modest size payload, say a full Shuttle cargo (20,000 kg), and you are patient enough to wait 900 years for it to just fly by the nearest star, here's how much propellant you'll need: If you use a rocket like on the Shuttle (Isp~ 500s), there isn't enough mass in the universe to get you there. If you use a nuclear fission rocket (Isp~ 5,000s) you need about a billion super-tankers of propellant. If you use a nuclear fusion rocket (Isp~ 10,000s) you only need about a thousand super-tankers. And if you assume that you'll have a super-duper Ion or Antimatter rocket (Isp~ 50,000s), well now you only need about ten railway tankers. It gets even worse if you want to get there sooner. (Based on mass fractions from ref 1, p. 52)


So, a thousand super-tankers (assuming 500 thousand tons per ship) is 500 MILLION tonnes of fuel to get to Alpha Centauri using a theoretical nuclear fusion rocket.

I might've been a little too optimistic about our capability of getting to Alpha Centauri :D



Image
JULY 20TH 1969 - The day the entire world was looking up

It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn't feel like a giant. I felt very, very small.
- NEIL ARMSTRONG, MISSION COMMANDER, APOLLO 11

Signature dedicated to the greatest achievement of mankind.

MILDLY DERANGED PHYSICIST does not mind BREAKING the SOUND BARRIER, because it is INSURED. - Simon_Jester considering the problems of hypersonic flight for Team L.A.M.E.

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