Part 1: Book Review - Prospects for Interstellar Travel

Last week I received a copy in the mail of Prospects for Interstellar Travel by John H. Mauldin, 1992. So far I've finished reading the first four chapters and I'm impressed by the amount of thought that went into this book and I'm studying it in detail so decided to write up a comprehensive book review as it seems there aren't that many copies around these days available and helps me digest this book anyway. Although somewhat dated, most of the material is still relevant and covers the prospects and problems of interstellar travel and is highly readable with next to no maths in the main text, for those who like to see what the numbers have to say, there's a comprehensive Appendix as well.

This book is a good read for those who have wondered if it is feasible one day in the not so distant future for us to venture to nearby star systems and their exoplanets. John has done his homework in writing this book with many references along the way from earlier work by Forward, Johnson, Matloff to name a few. According to the short blurb about the author, John has worked at NASA in electronic power engineering for the Voyager missions among other things and has an engineering physics background. Let's get into it. Wherever I put in [CI: this means these are my own thoughts not the author's from the book.]

The book starts off with an introduction to general concepts dealing with interstellar travel explaining what destinations we might want to goto and within what Earth timeframe. This determines mission parameters in the first place (acceleration, speed, time, force, mass etc). Although Proxima Centauri at 4.2 Ly is our closest star, the author points out that "planning for a 10 Ly mission is more realistic" p6, as there are a dozen stars within this distance that could have habitable planets. It would be difficult to justify a mission to the Alpha Centauri system if we are just going to observe and do some scientific sightseeing because of the expected high cost of such a mission. [CI: I read a US magazine article that there's some chance NASA's funding to goto the moon might be scrapped. If the astronomers get lucky and confirm an Earth like planet in another star system within 10 Ly this would be one of the good reasons to justify the cost of such a mission]. There's a table where the author outlines 4 model missions on p9 which shows some of the problems especially the timeframes involved. Note that it makes sense to talk about mission timeframes in Earth years and not the relativistic dilated time for the travellers because we are (presumably) interested in science or material return to Earth.


Moving on to the first chapter, the author explores the basics of space travel explaining such concepts as force, thrust, acceleration, gees etc and newtonian orbital mechanics, the concepts of kinetic and potential energy with rocket propulsion as the focus. The author points out the inefficiencies of using chemical rockets but notes that "chemical rockets handle the most mass per unit of energy making high thrust good for liftoff (and not much else)" [CI: unfortunetly so far we have no other option that will provide this high thrust required to escape Earth's gravity well, more on this later]. I like rockets myself, there're big, they make lots of noise and they go fast ;-) however as the author points they are out of the question for interstellar travel due to the distances involved and the fuel/mass problem required by chemical rockets that they need to carry. It's pointed out that if a starship was 1000 tonnes, it would require at least 50 shuttle missions for the construction parts alone, in other words starships will not be built deep inside Earth's gravity well but in orbit or elsewhere in our solar system, unfortunetly this means having in place an extensive space infrastructure.

An outline is given on planetary gravitational sling shot mechanics and how this can be used to boost a starship's escape velocity to leave the solar system and also dicusses starship course corrections using stars: "If the speed is 1000Km/s (0.0033c), a starship aimed a close 10 million Km from the center of the star would be deflected about 2° from its original course" p32, and also mentions the interesting case of binary star flyby for speed reduction.

In the second chapter the author looks at advanced propulsion methods which carry more energy per kilogram than chemical fuels can or those that leave the fuel behind such as solar powered missions, nuclear fission/fusion, electric ion propulsion and solar sails. Past Jupiter's orbit the intensity of sunlight becomes too low to produce useful power for propulsion. Nuclear fission rockets have more than a million times more energy per kilogram that can be extracted from nuclear fuels such as uranium than from chemical fuels however for interstellar missions this still appears inadequate but looks useful for planetary missions in our solar system. Launching nuclear powered rockets from Earth's surface is not a good idea because of the problems dealing with radioactive waste and potential pollution hazards.

Fusion makes energy production 10 times better than nuclear fission making it a possible candidate for a starship powerplant and propulsion with less problems with radioactive byproducts. Fusion reactor fuel such as hydrogen, deuterium and helium-3 are available in low density in interstellar space and for any long interstellar mission living off the land makes sense. The author describes a fusion drive and how it could work and describes the Daedalus [CI: see Project Icarus] and Orion projects as case studies. A description is given for electric ion propulsion and mass ejector systems however these don't look promising for interstellar missions.

Photos: Right photo, bottom right is Daedalus.

Next we have the solar sail concept described in detail together with several references made to Gregory Matloff's earlier 80's work in this area. With solar sails the big advantage is that one doesn't have to carry fuel and we use sunlight's momentum for propulsion. Some of the problems outlined include the mass problem of the sail (Kg/m^2), the need to bring the solar sail very close to the Sun (to get the boost required to make interstellar trips viable) and issues with the structural fragility of the sail and connecting the sail to the starship. The mentioned designs so far are big (100Km diameter sail). As mentioned earlier past Jupiter's orbit the sunlight's intensity starts to become weak so everything needs to go just right when grazing the Sun's furnace. Towards the end of the chapter on p65, one sentence stood out which I'd like to quote:

"Like other missions involving long-term Earth support of a starship,

they require an extraordinary amount of social commitment."

In Part 2 of this book review, we'll look at Chapters 3 and 4 on relativity and more advanced propulsion systems described by the author.

Australia Day 2010

It was another great day to be on the water on Australia Day with just about anything that floats on Sydney Harbour out for the day. Several flying machines turned up as well. Some shots from my camera (click on photos for bigger version):

The Known Universe

Nuts and bolts (15/12/09)

Some interesting items I came across recently worth a look at:

Interstellar Propulsion Research: Realistic Possibilities and Idealistic Dreams by Les Johnson gives an introductory rundown on the current status of possible interstellar missions and propulsion options. Apart from the mentioned warp drive (update: read this and this), all of the options are based on sound physics however all of them have severe technical and engineering difficulties to overcome if they are going to happen one day. Ironically getting the hardware required into orbit for these big spacecraft could be the biggest hurdle to overcome as using chemical rockets is expensive. The above options are based on our current understanding of Physics and we still have a lot to learn how nature really works.

The Final Frontier: The Science of Star Trek, interview with Lawrence Krauss. I read the first version of his book years ago and found it quite stimulating reading should interest all you Star Trek fans out there. I saw the world premiere opening of the movie at the Sydney Opera House and got a few autographs myself from the (new) Spock, Sulu and JJ Abrams,  I liked the movie.

A Blueprint for a Quantum Propulsion Machine, here's also a review from Paul Gilster on this paper by Alexander Feigel. It remains to be seen if these so called "magneto-electric particles" do change the momentum of the quantum vacuum and thereby provide a means to change the orientation of a spacecraft without using propellant although many do this already using gyroscopes for eg however the physics if sound would be very interesting as this would provide another avenue to study the Quantum Vacuum. Another paper on this worth reading is here.

Been busy working on Sydney Harbour most days day and night as it is the busy season here. Some recent photos: Nice sailing boat in Farm Cove and checkout this sailing boat skipper going under the Anzac bridge, got his air draft right! Big tow job Bradley's Head outbound (click on photos for larger version).

Poem mystery author

Although I can't say I'm a big fan of poetry, I do like a very few which deal with the stars, our Universe and (big surprise here) Man's quest to venture to the stars. When I was a small boy and pointed my telescope to Saturn for the first time, this was one of those moments you never forget for the rest of your life. After countless nights behind the eyepiece (it's quite addictive!), one eventually starts to ponder on thoughts on interstellar travel and watching StarTrek makes it worse ;-) There is one poem which I can't seem to find out who wrote it. I've posted the question to poem newsgroups and contacted various knowledgeable people but to no avail. It's engraved on the back on one of my brass compasses (Dollond London) which I got from a flea market a while ago next the Maritime Museum. Do you know who wrote this poem so I can give this mystery author proper credit?

One of the reasons why I bought this compass was because I liked this poem very much, if I didn't know better my first thoughts were either a Physicist wrote it or an author with deep thoughts on Nature. It talks about time, "a continuum moves and swirls..." (the vacuum?), the celestial sphere and life. Talk about big topics! The vacuum is central to Physics and today is still "beyond my inner sight and imagination" ie Physicists still don't understand it at the quantum level although they are getting better. Actually understanding the vacuum has been central to Physics most of our history, see this very interesting painting.

Some of you who work on Sydney Harbour may have noticed that Thor Gitta was docked in White Bay for quite a while (over a month), the mystery why she was there for all this time has been solved: she was waiting for this barge to unload her big load of cable:

Cosmology, The Big Bang and Entropy

I went to Sean Carroll's talk yesterday at Sydney University. As many of you are aware, Sean is one of the bloggers on Cosmic Variance and is touring Australia for his talks. He also has an upcoming book titled From Here to Eternity: The Quest for the Ultimate Theory of Time.

Sean talked about all the big ideas that face Cosmologists these days and in particular Entropy and its relation to the evolution of our Universe starting from a state of low entropy / high order progressing towards a state of high entropy / low order. I didn't like his interpretation of time (particularly the "arrow of time") as mentioned in my previous post and as for the state of the Universe, this is ambiguous because we cannot observe the Universe from the outside hence there is no entropy for the Universe either.

Cosmologists have a fairly good idea what the state of the Universe was 1 second after the Big Bang however at "t = 0" (time cannot be defined here as there is no matter at this stage hence no clocks), no one knows as General Relativity breaks down however before the Big Bang? Sean speculated on an idea that our Universe may have begun from a single quantum fluctuation from the inherent energy of the vacuum, ie we live in a baby Universe an offshoot from another Universe. There was quite a good turnup and the lecture theatre was pretty full, all in all enjoyed the talk.

Still experimenting with $\LaTeX$ in Blogger using this script. Testing...

\[\tan(2\theta) = {2\tan\theta \over 1-\tan^2\theta}\]

\[\int \csc^2x\, dx = -\cot x+ C.\]

\[\ P_{r-j}=\begin{cases} 0& \text{if $r-j$ is odd},\\ r!\,(-1)^{(r-j)/2}& \text{if $r-j$ is even}. \end{cases}\]

\[\qquad \lim_{\alpha\to \infty} {\sin\alpha \over \alpha} = 0\]

\[\root n \of {\prod_{i=1}^n X_i} \leq {1 \over n} \sum_{i=1}^n\]

\[\ \cfrac{1}{\sqrt{2}+\cfrac{1}{\sqrt{2}+\cfrac{1}{\sqrt{2}+\dotsb }}}\]

\[\ \nabla \cdot \mathbf{D} = \rho_f \]
\[\ \nabla \cdot \mathbf{B} = 0 \]
\[\ \nabla \times \mathbf{E} = -\frac{\partial \mathbf{B}} {\partial t} \]
\[\ \nabla \times \mathbf{H} = \mathbf{J}_f + \frac{\partial \mathbf{D}} {\partial t } \]

\[\ \boxed{m &= \frac{m_0}{\sqrt{1-\frac{v^2}{c^2}}}}\]

Review: LyX and viXra

Been busy the last few days between work learning about LaTeX. Widely used by the academic and research community to write up high quality documents, scientific papers, books etc and especially useful for writting out mathematical formulae with their many special formatting requirements. The text it produces is beautiful.

I tested out LyX, which is a free Windows based Graphical User Interface (GUI) document processor for LaTeX and automatically will download MiKTeX during installation which is also required for your computer. Seems to work very well on my small laptop. Once you write up your document, you can preview it with Lyx's DVI previewer. Once you're happy with it, export the document in Adobe PDF format and you're done. LaTeX has many formatting tags if you look at the source code and although Lyx has also many GUI buttons, it's useful to sometimes type in the code by hand. There's also an excellent beginer's guide to LaTeX which I found handy called A Gentle Introduction to TEX. Great thing is, MiKTeX and LyX are both free for download! Google Documents also have the ability to insert equations and their online chart rendering feature has LaTeX command options (see links for the following):

 A few days ago I also found out about the new viXra.org e-print archive. Unlike arXiv.org, this is open to anyone who wants to publish a paper and you don't need a "sponsor" (which is required by arXiv). This is great for people who aren't affililated with a research institution, university etc or can't find someone to endorse their paper. There are many Physics papers out there that are highly speculative and many academics aren't willing to be affiliated with a paper that at first appearances could be junk. The only problem is this doesn't help scientific progress. Their Why page explains all this in more detail. Because this is open to anyone, many junk papers will be found there however there are some interesting ones as well worth a read, all in all think viXra is a great idea. Worth keeping an eye on.

Attached photos: Students practicing survival at sea skills, liferaft deployment etc at the Qantas training pool, Sydney Airport.

What exactly is time?

I came across today the following paper reviewed on the arXiv Blog and also on arXiv: Can the Arrow of Time be understood from Quantum Cosmology?

The question itself used as the title is flawed. There is no such thing as the "Arrow of Time" in Nature and after reading the paper suspect this will lead to another Not Even Wrong theory. This is a common misunderstanding in Physics so what exactly is time? It's about time we have a look. There's a wiki article however I prefer the explanation on p40 of the first volume of Motion Mountain:

"Time is what we read from a clock."

That's it! Your first intuition is correct ie you check your clock to find out what time it is. Note that clocks can be the Moon, the Sun, sundials, atomic clocks, Harrison's H1 clock etc.

Schiller goes on:

"Time is a concept introduced specially to describe the flow of events around us; it does not itself flow, it describes flow. Time does not advance. Time is neither linear nor cyclic. The idea that time flows is as hindering to understanding nature as is the idea that mirrors Page 71 exchange right and left. The misleading use of the expression ‘flow of time’, propagated first by some flawed Ref. 36 Greek thinkers and then again by Newton, continues. Aristotle (384/3–322 bce), careful to think logically, pointed out its misconception, and many did so after him. Nevertheless, expressions such as ‘time reversal’, the ‘irreversibility of time’, and the much-abused ‘time’s arrow’ are still common. Just read a popular science magazine chosen at random.

The fact is: time cannot be reversed, only motion can, or more precisely, only velocities of objects; time has no arrow, only motion has; it is not the flow of time that humans are unable to stop, but the motion of all the objects in nature. Incredibly, there are even books written by respected physicists that study different types of ‘time’s arrows’ and compare them with each other. Predictably, no tangible or new result is extracted. Time does not flow."

There you have it, if you were thinking of becoming a time traveller with exotic machinery don't waste your time. However time machines are available for purchase if you want one ;-), they only allow you to see back in time though and we are constrained to seeing the observable Universe.
 
Because light from the Sun for eg takes just over 8 minutes to reach us here on Earth, astronomical objects you see in the sky are essentially as they were when the light left them and because of the vastness of space and the speed of light, it takes time for the light from these objects to reach us. For eg light from our neighbour the Andromeda Galaxy takes 2.5 million years to reach us so if you look at it with a telescope (or with binoculars), you are seeing the galaxy as it was 2.5 million years ago. The bigger the telescope, the further you can see back:
 

At time t = 0, current Physics cannot explain what happened as the Physics cube mentioned in the previous post isn't complete. And before that? Roger Penrose gave a good talk in 2007 at Darling Harbour titled: What happened before the Big Bang?

Photos: Claudia I coming into Blackwattle Bay the other day delivering more concrete supplies.