Xilman (aka Paul) what are your thoughts on this?
[url]https://www.centauri-dreams.org/2020/03/27/introducing-the-q-drive-a-concept-that-offers-the-possibility-of-interstellar-flight/[/url]

[QUOTE=Uncwilly;541382]Xilman (aka Paul) what are your thoughts on this?[/QUOTE]

I would also be very interested in hearing any thoughts on this by people who understand these kinds of spaces (no joke intended) better than I do.

[QUOTE=Uncwilly;541382]Xilman (aka Paul) what are your thoughts on this?
[url]https://www.centauri-dreams.org/2020/03/27/introducing-the-q-drive-a-concept-that-offers-the-possibility-of-interstellar-flight/[/url][/QUOTE]I took a quick look but haven't studied it in enough detail to say how likely it is to be built.

The Newtonian mechanics is straightforward but the engineering is anything but. Ensuring that the exhaust velocity is the same (or near enough within acceptable efficiency) as the wind velocity is likely to be much harder. Even if the mean exhaust velocity can be matched precisely, which is far from obvious to me, it is not clear to me how the inevitable velocity dispersion will affect the efficiency of the drive.

I see how the Mercury orbiter mission works; I do not yet see how to do anything but a fly-by of anything further out from the sun. The latter are valuable, of course, but it would be nice to have a Neptune orbiter for instance.

OTOH, a flight along the solar gravitational focal line could be [I]very[/I] interesting.

I should think about how to implement fuel-efficient brakes...

[QUOTE=xilman;541908]I should think about how to implement fuel-efficient brakes...[/QUOTE]

Could a bounced laser beam be of any use?

Have a huge light-sail which is used to accelerate towards the target. Then when you get near your destination, a smaller sub-section of the sail from the center separates. This then continues to get the (now lesser) impulse from the light-source, and the (greater) bounced (and, importantly, focused) photos off of the (expendable) larger section.

I assume the idea has been discussed before (both "hard" sci-fi, and real-world feasibility analysis). Should work, but you'd need /many/ *very* powerful lasers in Earth (or some) orbit -- would make a nice weapon in the wrong hands...

[QUOTE=chalsall;542547]Could a bounced laser beam be of any use?

Have a huge light-sail which is used to accelerate towards the target. Then when you get near your destination, a smaller sub-section of the sail from the center separates. This then continues to get the (now lesser) impulse from the light-source, and the (greater) bounced (and, importantly, focused) photos off of the (expendable) larger section.

I assume the idea has been discussed before (both "hard" sci-fi, and real-world feasibility analysis). Should work, but you'd need /many/ *very* powerful lasers in Earth (or some) orbit -- would make a nice weapon in the wrong hands...[/QUOTE]This approach is well known in the specialist literature but, perhaps, not more widely. I could try to dig up references for those interested.

However, my response was within the context of the drive in question as opposed to, say, sails.

Weapons: such devices would be very fragile because of their power requirements. Either they have on-board fusion sources, in which case earth-bound counterparts could take them out with ease as tight beamwidths are not needed, or they would rely on the pitifully feeble ~1kW/m^2 solar power density in these parts and an asat would be sufficient. Even in Mercury orbit the power density is only ten times greater. Even today the likes of India could fly an effective asat.

[QUOTE=xilman;542557]Either they have on-board fusion sources, in which case earth-bound counterparts could take them out with ease as tight beamwidths are not needed...[/QUOTE]

I don't entirely understand this statement. (Love the conversation though -- I learn something every time! :smile:)

Are you saying an adversary could overwhelm the thermal radiation that such a power-plant would require? Wouldn't that "kit" need to be in a higher orbit, since presumably the radiators would be pointed away from Earth?

Or am I missing something obvious?

[QUOTE=chalsall;542558]Or am I missing something obvious?[/QUOTE]I suspect so.

The power density for a feasible interstellar sail would be high enough to fry any unprotected installation. A tiny probe can be made very reflective and is tiny. A multi-square kilometre collecting array (1 km^2 collects around 1GW and an interstellar probe will likely need more than that to get anywhere in a reasonable time) is likely to be much more difficult to protect.

An earth-bound TW laser need only have an beamwidth of a few arcsec (assuming it is atmosphere limited) and can easily deliver GW/m2 to earth orbit. Enough to vaporize anything, protected or not.

[URL]https://www.bbc.com/news/science-environment-52264743[/URL]

:mike:

[QUOTE=xilman;542560]I suspect so.

The power density for a feasible interstellar sail would be high enough to fry any unprotected installation. A tiny probe can be made very reflective and is tiny. A multi-square kilometre collecting array (1 km^2 collects around 1GW and an interstellar probe will likely need more than that to get anywhere in a reasonable time) is likely to be much more difficult to protect.

An earth-bound TW laser need only have an beamwidth of a few arcsec (assuming it is atmosphere limited) and can easily deliver GW/m2 to earth orbit. Enough to vaporize anything, protected or not.[/QUOTE]
A GW is a large generating plant. A TW is a little more than twice the US mean stationary electrical generation. TW laser output implies multi-TW input. [URL]https://www.eia.gov/energyexplained/electricity/electricity-in-the-us-generation-capacity-and-sales.php[/URL]
And the oft advocated method of increasing or replacing grid capacity has its down sides. [URL]https://foreignpolicy.com/2019/09/06/the-path-to-clean-energy-will-be-very-dirty-climate-change-renewables/[/URL]
Energy storage challenges are even greater. [url]http://css.umich.edu/factsheets/us-grid-energy-storage-factsheet[/url]

Could be a fun project, if you had the financial support of Bill Gates, Elon Musk, Jeff Bezos, George Soros, Michael Bloomberg, etc. or a large portion of the US defense budget, and no concern about global warming from the multiple TW increase in waste heat. [URL]https://www.quora.com/What-would-happen-if-I-had-a-1-terawatt-laser-outputting-constantly-How-big-would-it-be-and-how-powerful-would-it-be-What-about-a-petawatt-laser-And-a-yottawatt-laser?share=1[/URL]
Or go maser. [URL]https://en.wikipedia.org/wiki/Astrophysical_maser[/URL]

[QUOTE=kriesel;543054]A GW is a large generating plant. A TW is a little more than twice the US mean stationary electrical generation. TW laser output implies multi-TW input.[/QUOTE]You are quite correct but...

Generating peak powers in the TW range is much easier for a pulsed laser than for one operating in CW mode.

Petawatt lasers have been in operation for over thirty years. [url]https://en.wikipedia.org/wiki/Vulcan_laser[/url] is an example. [url]https://www.extremetech.com/extreme/290863-massive-10-petawatt-laser-can-vaporize-matter[/url] is a 10PW laser.

How Space Tries to Kill You and Make You Ugly

Oh also, it makes you blind and stupid, too.

[url]https://www.wired.com/story/how-space-tries-kill-you-make-you-ugly/[/url] [quote]Outer space is the most noxious of substances: devoid of air and filled with a soup of deadly particles in the form of high-energy photons and energetic bits of atomic nuclei. The lack of gravity there affects every element of your being, as even the proteins in your body can’t figure out which way is up.[/quote]