Engineering Newsletter

[T.L.G.vanderLinden@student.utwente.nl (Timothy van der Linden)]

ReplyTo   : Kelly
ReplyFrom : Timothy

>>> Externally fueled did that mean scooping? I'm not sure 
>>> anymore, please tell me if my assumption is right.
>
>Not quite.  In my Exporer ship design I assumed the fusion fuel was launched
>ahead of the ship with a linear accelerator.  As the ship accelerates it
>contiually scoops up pre launched fuel going at nearly its speed.  So the
>ship looses very little momentum scooping up the fuel packets.  That would
>allow you to get up to light speed with "only" 200 times the ships mas in
>fusion fuel.  However like Kevins system.  We have a serious problem stoping.
> I though using a ramscope to produce a lot of drag might do it, but never
>found a good woorkup of the numbers.

This method of prelaunching fuel packets will cost the same amount of energy
that is needed if you take those same packets with you from the start.
Why? Because all packets have the same speed as the Asimov after it has
accelerated. Accelerating a lot of small packets or just one big packet does
not save energy.

>By the way.  Did anyone calculate the drag on the sail structure from
>interstelar debre?  If you can maintain enough of an electric charge to use
>the microwave sail as a parachute that might help with stoping.

The problem is that there are no accurate numbers of the density of
interstellar debris. So any number is almost a guess.

===============================================================================

ReplyTo   : Steve
ReplyFrom : Timothy

>In a frame where the ship is in motion, the photon changes energy
>when it bounces off the ship; its reflected energy is less than
>the incident energy if the ship receding, greater if the ship is
>approaching.  You actually were right to compare this to doppler
>radar, because it's this effect that doppler radar measures to
>determine velocity.

Huh, are you saying I was right the first time?

Am I right saying the following:

Photons loose energy because they accelerate the car. Only because of that
acceleration their frequency is lowered.
Because it takes more energy to transfer the same amount of momentum to a
faster moving car (E=v^2 versus p=v) the frequency is lowered even more.

>Mass is a more subtle concept than energy; while energies add
>linearly, masses as magnitudes of momenergy vectors do not.

Agreed.

> > I would conclude from this that moving bodies excert greater gravitation
> > either because of gain of mass or gain of energy. I feel both can be used,
> > its a bit like the wave-particle duality.
>
>What I really want to see is the general relativistic formula
>that says whether spacetime curvature is the result of an
>object's mass or its energy.

It's hard to find such a formula, all books about general relativistics use
tensor calculus. I have a hard time understanding them, so I don't know much
about formulas in general relativistics. But don't think we need this
formula any more:

In Taylor & Wheelers terminology I think curvature would be the result of
energy. In "more" general terms it would be either the result of its
relativistic mass or the result of its rest mass AND its kinetic energy (ie.
together the total energy).

> > >> Is it this translation of energy to mass that gives the trouble?
> > >
> > >It is that my studies of relativistic kinematics do not allow for
> > >the treatment of energy and mass as identical quantities.
> > 
> > They are indeed not identical but equivalent, meaning they can be be
> > interchanged.
>
>Not in Taylor and Wheeler's terminology.  The only time they
>allow mass and energy to be spoken of as equivalent is when you
>are dealing with an object in its rest frame.  In any other frame
>the object's energy is not equivalent to its mass.

No indeed not equivalent to its rest mass but equivalent to its relativistic
mass.

>>>> I say that "relativistic mass increase" is a misnomer and that
>>>> you are better off treating mass as invariant.

I guess that is what I always did, only I was not that much aware of the
problems others might have with the duality in the terminology.

After all this, can we conclude a charged battery is heavier than an
uncharged battery?

================================================================================

ReplyTo   : Kelly
ReplyFrom : Timothy

>Question.
>Diverted beams of photons converge on a forward pointing cone.  This (not
>considering the beam cancelation due to interfearence, reflection loses, and
>other such nonsence) is the origional beam moving forward in a much more
>concentrated form than its pre sail moments.  Net thrust to the ship near zip
>(give or take).  In frount of this stream we put an ionized reaction mass.
> Beam slams into it and throws it forward.
>
>A) A lot of the beam (most?) would reflect back off the ionized reaction mass
>(micro-waves do that off ionized matter)  Would this act as Forward's
>sacrificial outer-sail in "Dragons egg (?)"?  I.E. could we use the forwardly
>reflected beam for drive power?  Efectivly the reaction mass (now renamed
>plasma reflection mass) has gotten boosted forward at a hellish speed, but
>bounced the beam back down our throats.  (Just like Forwards outer drop
>sail.)  We would have to continuously replenish this "reflection mass", but
>on the bright side we could be very sure it will clean all the interstellar
>mass out from in frount of the ship.  ;)

Replenishing the "mirror" will probably take lots of ions or in other words
mass that has to be taken with us. Also using such a light (non heavy) sail
will mean that the "mirror" is accelerated a lot and lot of energy is lost
due to the Doppler effect.
Also I have doubts how well the "mirror" reflects, ionized particles attract
or repell each other so, it won't take long befor the "mirror" has destroyed
itself.

>B)
>Instead of just dumping this superheated reflect mass forward.  How about
>using it as a rocket stream also.  At the least we can ride the expanding
>shock wave from the stuff.

Shock wave? I don't understand, please explain again.

>Anyway, between A & B we have used part of the beam to create a high temp
>plasma thurst, and reflected the rest off said plasma onto a rearwardly
>reflective part of the ship. Momentum/kinetic energy interactions between
>the beam and the ship are pretty much canceled out until it hits the
>reaction/reflection mass.  The ship needs NO POWER CONVERTERS!  We never
>convert it to electricity to drive an accelerator.  (Ok, ok, we convert a
>little to run the ship and power the magnetic feilds that keep the plasma off
>the back of the ship.) But other than that, we just reflect it around and
>feed it mass.

==============================================================================

Steve writes:
>The reality that static stress does not continue to dissipate
>energy over time is not intuitive, because our muscles aren't
>static structures like boards or rods or wires; they must
>dissipate energy even to hold a weight motionless above your
>head, while a table holding the same weight does not dissipate
>energy.

Yes, in fact is does not take any energy to keep floating a few metres above
Earth's surface.

Timothy