"Stephen" <mcavoys_AT_aolDOT.com> wrote:
> "Cousin Ricky" <ric### [at] yahoocom> wrote:
> > "Jon S. Berndt" <jsb### [at] hal-pcorg> wrote:
> > > "Cousin Ricky" <ric### [at] yahoocom> wrote in message
> > > news:web.458015c7ff75702c85de7b680@news.povray.org...
> > > >
> > > > Does this estimate take relativistics effects into account?  (I've long
> > > > forgotten how to do the math.)  A vehicle that gets to Alpha cen in 4.5
> > > > years has to go pretty close to the speed of light.  The relativistic mass
> > > > gain would surely affect the thruster's ability to maintain acceleration.
> > >
> > > You're thinking about this way too hard! ;-)
> >
> > Well, he *did* say "realistic."  It's details like this that cause
> > expensive, taxpayer-funded space probes to vanish without a trace.
>

> taxpayer-funded space probes to vanish without a trace.

don't forget to put povray units in the mix too and get strange results for
things really far too big and far away... thankfully, no tax paying... ;)

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> Does this estimate take relativistics effects into account?  (I've long
> forgotten how to do the math.)  A vehicle that gets to Alpha cen in 4.5
> years has to go pretty close to the speed of light.  The relativistic mass
> gain would surely affect the thruster's ability to maintain acceleration.

I think 9 years is more likely to be the one-way trip, assuming you
accelerate at 1g to halfway and then turn round and decelerate ass-first
the rest of the way. A round trip would be more like 16-18 years. The crew
would only see it as 7-8 years, of course.

This is based on this page:
http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html

I haven't checked the maths but it looks right!

The mass gain is irrelevant, really. From the ship's point of view,
acceleration is constant and the universe deforms. :-)

Bill

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"Stephen" <mcavoys_AT_aolDOT.com> wrote:
> "Cousin Ricky" <ric### [at] yahoocom> wrote:
> >
> > Well, he *did* say "realistic."  It's details like this that cause
> > expensive, taxpayer-funded space probes to vanish without a trace.
>
> No it’s getting Imperial and Metric units mixed up that costs
> taxpayer-funded space probes to vanish without a trace.
> Ok there was a trace :-)

Or relying on the atmospheric pressure for altimeter readings for when to
cut the landing thrusters (a possible fate of Beagle).

Or forgetting to take the Doppler effect into account in radio
communications.  This almost happened to Cassini-Huygens; luckily (or
prudently), the error was discovered during the dry run when Cassini
returned to Earth for a gravitational assist.

Or sending your lander into the kitchen without building it to stand the 740
kelvin and show grace under 9100 kilopascals (all of the early Veneris
missions).  (Kudos to the former Soviets as the only country to
successfully land on Venus, and the only country other than the USA to land
*anywhere* successfully.)

Or typing a period in a computer program where there should have been a
comma.  Er... OK, so it *could* have happened if NASA hadn't caught the bug
in time.  Unfortunately, they didn't catch the missing hyphen in Mariner 1's
backup guidance software...

And the most grievous error of all:  Sending your space ship to Mars!  After
Spirit and Opportunity successfully docked with the Angry Red Planet, NASA
convened a study to find out what went *right*. :-O

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"Stephen" <mcavoys_AT_aolDOT.com> wrote:
> "Pun (n.): the lowest form of humour" —Samuel Johnson, lexicographer
> "Hanging is too good for a man who makes puns; he should be drawn and
> quoted." —Fred Allen
> "The pun is mightier than the sword." — James Joyce
> "Puns are the last refuge of the witless."
> "Immanuel doesn't pun; he Kant."

punish (v) to tell a pun.
punishment (n) the telling of a pun.
--unknown

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"Bill Pragnell" <bil### [at] hotmailcom> wrote in message 
news:web.458138e3ff75702c731f01d10@news.povray.org...
>> Does this estimate take relativistics effects into account?  (I've long
>> forgotten how to do the math.)  A vehicle that gets to Alpha cen in 4.5
>> years has to go pretty close to the speed of light.  The relativistic 
>> mass
>> gain would surely affect the thruster's ability to maintain acceleration.
>
> I think 9 years is more likely to be the one-way trip, assuming you
> accelerate at 1g to halfway and then turn round and decelerate ass-first
> the rest of the way. A round trip would be more like 16-18 years. The crew
> would only see it as 7-8 years, of course.

I omitted relativity, the 9 years would be shipboard time, including
some fudge factor for midpoint turn around time and time for the
actual mission...
We don't really know what would happen at those speeds, we
only know that we have observed relativity at the slow end of
the curve IRL.

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Attachments:
Download 'space_thruster.jpg' (33 KB)

Preview of image 'space_thruster.jpg'

"Cousin Ricky" <ric### [at] yahoocom> wrote in message

> Or typing a period in a computer program where there should have been a
> comma.  Er... OK, so it *could* have happened if NASA hadn't caught the 
> bug
> in time.  Unfortunately, they didn't catch the missing hyphen in Mariner 
> 1's
> backup guidance software...
>
> And the most grievous error of all:  Sending your space ship to Mars! 
> After
> Spirit and Opportunity successfully docked with the Angry Red Planet, NASA
> convened a study to find out what went *right*. :-O

Actually, it's good to keep in mind that NASA has landed 5 spacecraft 
successfully on Mars out of 6 attempts (the accidental attempt to land an 
*orbiter* doesn't count! ;-) -  I'm referring to MCO; I'm also not counting 
penetrators).

Mars has "eaten" a lot of spacecraft. The former USSR tried several times 
and was unsuccessful. Beagle was a high-risk attempt that failed. It's too 
bad these probes were not heard from again, because I'm sure they would have 
produced fascinating results. To provide some balance, the former USSR was 
successful twice at returning images from the surface of Venus - an 
admirable accomplishment when you consider the conditions on the surface of 
that hellish place.

Recently, the images returned by the Soviet Venera craft have been 
reprocessed using modern techniques. The newly revitalized images are very 
nice and worth a long look:

http://tinyurl.com/yn7dtf

Space exploration, planets, etc. are all a great field to take inspiration 
for POV art!

Jon

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"Tim Attwood" <tim### [at] comcastnet> wrote

Hey, I kind of like this (I think I've seen something like this in my 
kitchen, too!)

A couple of notes:

1) There should be no over-expansion of the nozzle, I think. All of the flow 
would be almost all directed aft.

2) I'm sure this is a WIP, but thought I'd mention that there would be more 
to the engine (a lot of equipment creating magnetic fields - coils and 
stuff, supply lines for fuel, etc.)

3) The structural elements would include more bracing, similar to the 
trusses you see on the space station. Maybe some antennas, too (a large-ish 
dish?)

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Jon S. Berndt nous apporta ses lumieres en ce 14-12-2006 22:07:
> "Tim Attwood" <tim### [at] comcastnet> wrote

> Hey, I kind of like this (I think I've seen something like this in my 
> kitchen, too!)

> A couple of notes:

> 1) There should be no over-expansion of the nozzle, I think. All of the flow 
> would be almost all directed aft.
The over-expansion is unavoidable. All you can do, is try to minimise it.

> 2) I'm sure this is a WIP, but thought I'd mention that there would be more 
> to the engine (a lot of equipment creating magnetic fields - coils and 
> stuff, supply lines for fuel, etc.)
Depending on the scale, that can be all contained within the nozle.

> 3) The structural elements would include more bracing, similar to the 
> trusses you see on the space station. Maybe some antennas, too (a large-ish 
> dish?) 




-- 
Alain
-------------------------------------------------
Do not bite at the bait of pleasure, till you know there is no hook beneath
it.
Thomas Jefferson

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"EagleSun" <nomail@nomail> wrote in message news:457f2619

> Hi Jon!
>
> It's really exciting to see someone from Houston on this forum AND 
> publishing magazines.  Looks like Tek has a very good ship for you.... 
> would you need background to go with it?  I've been rendering planets, 
> including a few to show in a movie...
>
> Let me know if you need something...

If a ship does come out of this, a planet might be a nice background. Not 
sure if the image would portray braking into orbit or leaving ... hmmm.

Jon

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"Alain" <ele### [at] netscapenet> wrote in message 
news:45828032@news.povray.org...
> Jon S. Berndt nous apporta ses lumieres en ce 14-12-2006 22:07:
>> "Tim Attwood" <tim### [at] comcastnet> wrote
>
>> Hey, I kind of like this (I think I've seen something like this in my 
>> kitchen, too!)
>
>> A couple of notes:
>
>> 1) There should be no over-expansion of the nozzle, I think. All of the 
>> flow would be almost all directed aft.

> The over-expansion is unavoidable. All you can do, is try to minimise it.

>> 2) I'm sure this is a WIP, but thought I'd mention that there would be 
>> more to the engine (a lot of equipment creating magnetic fields - coils 
>> and stuff, supply lines for fuel, etc.)

> Depending on the scale, that can be all contained within the nozle.

Visually, what I would like to see is probably best illustrated by looking 
at a Hall thruster:

http://fluid.ippt.gov.pl/sbarral/hall.html

(see Pratt and Whitney thruster at bottom of this page)
http://www.engin.umich.edu/dept/aero/spacelab/thrusters/thrusters.html

http://www.adastrarocket.com/Plasma.html

There is little, if any, overexpansion of exhaust in these images. The image 
by Tek was very good in this respect.

Jon

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