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A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

nytimes.com

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Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#241

Post by hughes »

jondiggsit wrote: post #240

Here's my big question: How do you slow down? 4.37 light years does not take into account all the time required to slow the hell down. Am I missing something? Isn't this the biggest fundamental issue with long range space travel?

You don't. You get a few hours (tops) to look around at anything interesting in Alpha Centauri before zooming out of the target system and off into really deep space.

Kind of like the New Horizons mission, which never stopped at Pluto. It just flew right on by, but still got a ton of useful scientific data.

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#242

Post by NZGumboot »

jerryhuang100 wrote: post #223
grecy wrote: post #179

Earlier quoted context omitted.

You're right to be skeptical, because this is going to be very difficult and has many challenges that need to be overcome. But that doesn't mean we should sit here and say "nope, can't be done". People were skeptical when planes first flew, when it was attempted to put people on the moon, and so on. Jeez, people were skeptical when SpaceX said they could land a first stage on a barge at sea, and posted endlessly abou…

Skepticism could be constructive. Most of time people just want to improve some novel idea in question format. If someone really do not care about it they would not even bother to raise a question. I do want to raise my hand about how the sails is going to avoid space objects (meteoroid, space dusts... visible, non-visible, or even dark matters) given its large surface.

Outside of Earth orbit, space objects become incredibly rare, and outside the solar system they are rarer still. There are much bigger problems to worry about, believe me.

By the way, dark matter is likely passing through your body right now. It's effects can only be seen on the scale of galaxies.

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#243

Post by ryao »

If this works, it would probably be more useful for probing objects in our solar system. You could send a probe to Jupiter and hear back in ~4 hours. Waiting ~25 years for results from Alpha Centauri would be rather painful in comparison. Getting anything interesting back would be a long shot as the instruments would be rather limited and solar systems tend to be rather large.

I imagine/hope that they would probably do tests in the solar system before trying to send them to Allha Centauri.

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#245

Post by IndianAstronaut »

rayiner wrote: post #228
grecy wrote: post #179

Earlier quoted context omitted.

You're right to be skeptical, because this is going to be very difficult and has many challenges that need to be overcome. But that doesn't mean we should sit here and say "nope, can't be done". People were skeptical when planes first flew, when it was attempted to put people on the moon, and so on. Jeez, people were skeptical when SpaceX said they could land a first stage on a barge at sea, and posted endlessly abou…

People were also skeptical of all the people before the Wright brothers who jumped off cliffs and killed themselves. Skepticism is the natural worldview of an engineer, because the universe is incredibly hostile to our ideas.

>Skepticism is the natural worldview of an engineer

This is in a nutshell why me and my (MBA)boss get into arguments.

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#247

Post by simonh »

ryao wrote: post #190
jerf wrote: post #36

Earlier quoted context omitted.

Their speed isn't particularly relevant, what matters more is their energy. As big as that number is to us, it's still pretty insignificant; there's a lot of objects already traveling around with us in our own solar system with 70kT (per PaulHoule in other comments) of energy. A looooooot of objects. In the grand scheme of things, this is a rounding error on a rounding error. We are small .

It would be rather anticlimatic if it hit one of them before reaching Alpha Centauri and no one noticed.

That's one of the reasons they want to send thousands of them.

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#249

Post by DavidSJ »

ridgeguy wrote: post #238
DavidSJ wrote: post #189

Earlier quoted context omitted.

> about 3.9e4m^3 every second, which contains about 3.9e11 hydrogen atoms I think this step is off by 1e5. It contains 3.9e16 hydrogen atoms at 1e6/cm^3. So that 631 MJ becomes 63.1 TJ.

I assumed an interstellar medium density of 10 H atoms/cm^3, which is 1e7 atoms/m^3, given 1e6 cm^3 per m^3. I think the volume swept out by the spacecraft is about right: (3e8m/sec) (.2) 6.45e-4m^2 is about 3.9e4m^3/sec. Then, 1e7 H atoms/m^3 * 3.9e4m^3/sec gives about 3.9e11 atoms/sec hitting the (1 inch square) spacecraft.

I see, I missed the part where you assume 10 atoms per cm^3.
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