What "weed need" is a space mission! - Page 50

Dubslow · 2016-09-01, 21:19

The SpaceX explosion is a massive setback -- at least as massive as the CRS-7 setback, and they came out on the relatively bright side of that (6 month turnaround is a lot less than I would have guessed going into that).

In this case, 6 months is again absolute best case scenario I imagine. Depends of course on what the initial analysis is -- not to mention rebuilding the pad, which they didn't need to do last time.

(Regarding the other conversation in this thread, perhaps it would be wise to split that off to a separate thread? Possibly titled "What "wee need" is a space mission -- to Proxima Centauri!")

chalsall · 2016-09-01, 21:23

Quote:

Originally Posted by kladner

Ah Shoot! Dang! etc.

Woke up this morning at 0623 local time with electrical power having just been cut off (island wide power outage; still to be explained by BL&P).

Woke up again this morning at 0803 with no mains water (Barbados pumps water up hills using electricity into large tanks to provide gravity feed to water consumers).

Finally(!) get Power, Cellular and terrestrial Internet back at about 1135.

Immediately check my news feeds... Trump has lied again, and SpaceX's rocket blew up during fuelling for a preflight test firing.

A bit of a bummer of a day....

kladner · 2016-09-01, 21:26

@Paul: My thanks, as well. I've already fired off the links to a friend who should really appreciate them. I have started on the PDF: Roadmap to Interstellar Flight. Some of the math is a bit dense for me, but I get the idea, at least in proportions. 0.26 C is a stunning possibility.

chalsall · 2016-09-01, 23:52

Quote:

Originally Posted by LaurV

Well... not, not here. We do not agree now... Laser diodes which are bloody cheap have also a very short life time. Like 4000 hours or so. That is because they suffer a phenomenon called COD (Catastrophic Optical Damage). A powerful COD-free laser diode costs millions.

I hope you don't mind me discussing this with you a little bit on this topic...

Assuming most of the energy for interplanetary, or interstellar, investigations was sender sent, would this not be possible within ten years or so?

One would assume that upgrades to the sent craft would not be possible.

On the other hand, upgrades to the orbitals lasers powering said crafts is simply a question of money, rather than physics.

Please correct me if I am wrong.

LaurV · 2016-09-02, 03:49

What do you mean "sender sent"? Oh, do you propose to have the lasers here, and only have some "mirrors" or whatever, on the spaceships? I was assuming the other way around, for I don't know which reason, I was thinking that the lasers have to be on board

But you may also need lasers for propulsion?

Actually, hm.. the lasers for communication (if they are separate) will only need to work from time to time, and the lasers for propulsion (if they are separate) can work until they are exhausted, to bring the ship to speed (well, keep a little for steering). So, somehow, you can not mix them (make an "all in one" laser), as they have different working habits. And you need lasers for propulsion on board if you are talking about speeds comparable to c. But the idea of having the communication lasers here, that may work.

Or the proposal is to have all the lasers here and create a "laser wind" (by analogy with the solar wind) to push the ships all the way? Is that feasible? (I honestly have no idea!)

xilman · 2016-09-02, 06:22

Quote:

Originally Posted by LaurV

Or the proposal is to have all the lasers here and create a "laser wind" (by analogy with the solar wind) to push the ships all the way? Is that feasible? (I honestly have no idea!)

That is the idea, though the push lasts for only a short time. For the lightest craft around 10 minutes of thrust gives a final velocity of 0.2c or more. Thereafter it coasts for the other 99.999% or so of the journey.

Lasers on the space craft are used for two things: attitude control and communication back to the solar system. The latter is short term, the former very intermittent.

Much more detail in the links already posted.

Spherical Cow · 2016-09-02, 13:52

Quote:

Originally Posted by xilman

For the lightest craft around 10 minutes of thrust gives a final velocity of 0.2c or more. Thereafter it coasts for the other 99.999% or so of the journey.

That is one of the most fascinating aspects- the acceleration to 0.2c is so quick. When I first read about this is in the "normal" news, I assumed the lasers would need to be pushing for years to get the craft up to speed.

Norm

chalsall · 2016-09-02, 20:20

A complete tangent, if I may...

As a young person, I read Larry Niven and Jerry Pournelle's /The Mote in God's Eye/. The aliens were detected approaching us because their laser propulsion system was noticed

A reasonably good read.

xilman · 2016-09-02, 20:32

Quote:

Originally Posted by chalsall

A complete tangent, if I may...

As a young person, I read Larry Niven and Jerry Pournelle's /The Mote in God's Eye/. The aliens were detected approaching us because their laser propulsion system was noticed

A reasonably good read.

Not a complete tangent, IMAO. The information transferred by the lasers in that story was only a few bits. The roadmap paper linked previously points out that two 10-km laser launch sites could communicate at ethernet speeds over a distance of more than gigaparsec. Ping times would be rather lengthy.

Interstellar communication within our galaxy at bandwidths of megabytes per second is already well within present-day capabilities. A 10-metre telescope and a 100kW laser at each end will do it. The current problem is arranging for the two ends to have the equipment and to know where to point it.

chalsall · 2016-09-02, 21:07

Quote:

Originally Posted by xilman

Ping times would be rather lengthy.

Yeah. Welcome to Earth.

Quote:

Originally Posted by xilman;441417I

The current problem is arranging for the two ends to have the equipment and to know where to point it.

I understand this is currently being worked.

kladner · 2016-09-02, 21:55

Quote:

Originally Posted by chalsall

A complete tangent, if I may...

As a young person, I read Larry Niven and Jerry Pournelle's /The Mote in God's Eye/. The aliens were detected approaching us because their laser propulsion system was noticed

A reasonably good read.

I think of Mote as an ultimate Malthusian warning. It would be well for humankind to pay attention. In this household, we blame Pournelle for all the royalty/nobility stuffed into a good story. I guess you gotta have some social framework, though.

2016-09-01, 21:19	#540
Dubslow Basketry That Evening! "Bunslow the Bold" Jun 2011 40<A<43 -89<O<-88 3·29·83 Posts	The SpaceX explosion is a massive setback -- at least as massive as the CRS-7 setback, and they came out on the relatively bright side of that (6 month turnaround is a lot less than I would have guessed going into that). In this case, 6 months is again absolute best case scenario I imagine. Depends of course on what the initial analysis is -- not to mention rebuilding the pad, which they didn't need to do last time. (Regarding the other conversation in this thread, perhaps it would be wise to split that off to a separate thread? Possibly titled "What "wee need" is a space mission -- to Proxima Centauri!") Last fiddled with by Dubslow on 2016-09-01 at 21:20

2016-09-01, 21:26	#542
kladner "Kieren" Jul 2011 In My Own Galaxy! 2×3×1,693 Posts	@Paul: My thanks, as well. I've already fired off the links to a friend who should really appreciate them. I have started on the PDF: Roadmap to Interstellar Flight. Some of the math is a bit dense for me, but I get the idea, at least in proportions. 0.26 C is a stunning possibility. Last fiddled with by kladner on 2016-09-01 at 21:27

2016-09-02, 03:49	#544
LaurV Romulan Interpreter Jun 2011 Thailand 3×3,221 Posts	What do you mean "sender sent"? Oh, do you propose to have the lasers here, and only have some "mirrors" or whatever, on the spaceships? I was assuming the other way around, for I don't know which reason, I was thinking that the lasers have to be on board But you may also need lasers for propulsion? Actually, hm.. the lasers for communication (if they are separate) will only need to work from time to time, and the lasers for propulsion (if they are separate) can work until they are exhausted, to bring the ship to speed (well, keep a little for steering). So, somehow, you can not mix them (make an "all in one" laser), as they have different working habits. And you need lasers for propulsion on board if you are talking about speeds comparable to c. But the idea of having the communication lasers here, that may work. Or the proposal is to have all the lasers here and create a "laser wind" (by analogy with the solar wind) to push the ships all the way? Is that feasible? (I honestly have no idea!) Last fiddled with by LaurV on 2016-09-02 at 03:52

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2016-09-02, 20:20	#547
chalsall If I May "Chris Halsall" Sep 2002 Barbados 2×67×73 Posts	A complete tangent, if I may... As a young person, I read Larry Niven and Jerry Pournelle's /The Mote in God's Eye/. The aliens were detected approaching us because their laser propulsion system was noticed A reasonably good read.