Prospects for Interstellar Travel
Be aware of Paul Titze’s continuing exegesis of John Mauldin’s book Prospects for Interstellar Travel (Univelt, 1992). I used Mauldin again and again as I developed my Centauri Dreams book, finding the dense and lengthy volume covered every conceivable aspect of interstellar flight as understood by current physics. But the book was published in a small press run and is hard to track down, although Amazon usually has a few copies from independent resellers available. Paul is doing the community a service by going through Mauldin chapter by chapter, highlighting the salient points with commentary.
A quote from an early chapter:
Relativity makes energy a serious problem through the limits imposed to prevent speeds greater than light. Relativity also offers tantalizing solutions: the slowing of time and Total Conversion of mass to energy. How closely propulsion might approach TC is explored in Chapter 4. One could hope to find a way to travel without the action-reaction rocket method–no exhaust, no acceleration, little travel time, no deadly beams, no titanic low-mass energy source–but these are still mostly dreams from sf. Thus far it is not surprising that “visitors” from other stars have not appeared recently nor left their garbage laying about. They also must contend with what their Einsteins discover about interstellar travel. If visitors were to arrive, one of the first facts we would want to know is “how did they do it?”
All of which, as Paul notes, impinges on the three goals once defined by the Breakthrough Propulsion Physics project:
- Mass: Discover new propulsion methods that eliminate (or dramatically reduce) the need for propellant.
- Speed: Discover how to circumvent existing limits (light-speed) to dramatically reduce transit times.
- Energy: Discover new energy methods to power these propulsion devices.
Mauldin’s treatment of other propulsion options, from solar sails and beamed propulsion to nuclear fusion and antimatter, is exhaustive even if dated, but there is much to engage the interest in later chapters on interstellar navigation, the building of colony ships, shielding options, starship subsystems, and the advantages of self-replicating probes. Science fiction writers will find enough fodder in Mauldin’s pages to justify the price, as will anyone serious about making the case for venturing beyond the Solar System. Paul Titze is doing us all a service by going through these pages sequentially and with thoughtful annotations.
SPESIF 2010 Approaches
The Space, Propulsion & Energy Sciences International Forum 2010 will be held beginning February 23 at the Kossiakoff Center, Applied Physics Lab, Johns Hopkins University. Aerospace engineer Glen Robertson moderates the sessions, which include NASA’s Les Johnson presenting “From Research to Flight: Surviving the TRL ‘Valley of Death’ for Robotic and Human Space Exploration,” and a panel on the first fifty years of the space age and prospects going forward moderated by Roger Launius, curator of the National Air and Space Museum. Robert Zimmerman, author of The Universe in a Mirror and other books, will speak at the conference’s banquet. More information available at the IASSPES site.
Looking Back at Life Elsewhere
In a lively new article, the Daily Mail takes a retrospective look at two events that tantalized us with the possibilities of finding extraterrestrial life. In fact, author Michael Brooks simply declares Gilbert Levin ‘the man who found life on Mars.’ Well, we thought so for a few days back in 1976, when an experiment on board the Viking Mars lander got a positive result, prompting Champagne, a party, and a jubilant phone call from Carl Sagan. But later experiments found no carbon in the Martian soil, the Champagne lost its bubbles and Sagan retracted his congratulations. These days Levin would like to see the mission results revisited, especially the possible malfunctioning of the carbon-detecting instrument, but we may have to wait for future probes to really understand what Viking did or didn’t find.
Which takes us back to August 15, 1977, when Jerry Ehman found a puzzling signal in data from a radio telescope in Ohio. The signal’s frequency looked promising — it came in at the 1420 MHz hydrogen line — and to this day Ehman says ‘I am still waiting for a definitive explanation that makes sense.’ From the Daily Mail‘s article:
Ehman and his colleagues have explored every possibility: military transmissions, reflections of Earth signals off asteroids or satellites, natural emissions from stars, but nothing fits.
The strangest thing of all is that it came from a blank patch of sky. When Ehman and his colleagues looked at the exact location of the source, it turned out to be devoid of stars. Ehman’s only thought is that it could have been beamed from a spaceship travelling through the universe in search of some sign of life.
Not that he is totally convinced it really was aliens but he has never come up with a better explanation.
‘It had all the earmarks of being a signal from an intelligent civilisation,’ Ehman told me on the phone. ‘There it was, like it was saying, “Here I am – can you see me?”‘ But, he concedes, we may never have proof one way or the other.
Proof, of course, is what we need, but the WOW! signal still stands as perhaps our most interesting single SETI reception, one that could not be confirmed but impels many in the field to renewed commitment to the search. Brooks wonders whether we have been both extraordinarily lucky in possibly receiving a genuine signal of extraterrestrial life and amazingly careless in that we couldn’t follow it up or, for that matter, the elusive evidence of what happened on Mars. Good stories both, but the only practical thing is to go forward with new life detection methods for planetary surfaces as well as the depths of interstellar space.
The Shape of ETI
What would any alien we heard from via SETI actually look like? New Scientist took a crack at this question in its January 23 issue (thanks to Gary Bennett for the tip), noting factors like its probably predatory instincts, or the fact that an extraterrestrial must be able to send and receive radio waves, laser beams or some other forms of communication. That seems to presuppose a basic technology and a social structure. From the article, quoting astrobiologist Dirk Schulze-Makuch :
So message-sending aliens will probably have some form of society. It need not be anything like human societies, however. “There are meta-intelligences in the societies of bees and termites. I can imagine something like a termite or ant colony that gets really intelligent,” says Schulze-Makuch. This does not tell us, however, whether they will be furry, scaly or slimy. Even on Earth, clever brains come in a wide variety of packages: dolphins and primates, parrots and crows, sea otters, honey badgers, octopuses and squid.
Yes, and what about convergent evolution? Do hearts and eyes and other features develop independently in different branches of life’s tree? We might then find aliens with recognizable eyes, and probably some kind of manipulating organs to work with their technology:
Putting it all together, the daring astrobiologist might be prepared to make a very small bet that SETI-type aliens will be social multicellular predators with eyes, sexes, and sticky-out bits of some sort. Unless, of course, the aliens were usurped by smart machines or decided to modify themselves using biotechnology. In that case, we might find tentacled monsters, pale skinny humanoids, shimmery beings of pure energy…
I see that Hauser (Heim theory), Woodward (Mach-Lorentz thrusters), and Tajmer are presenting at this conference. It should be an interesting conference.
Eyes and wings have developed independently several times in terrestrial lifeforms. Hearts, no. And even if they look very similar to us, their motivations and thought processes might still be, well, alien. Think of elephants, dolphins, chimpanzees, bonobos. All mammals, all intelligent. How much insight do we have into their mindsets?
In connection with another portion of this entry, Dirk Schulze-Makuch also made the interesting suggestion that the Viking probes may have inadvertently destroyed Martian bacteria. He theorized that if their optima differ significantly from “median” terrestrial bacteria, the tests of the probes – heating, adding water – would be lethal. His speculations, if correct, could explain and reconcile the contradictory results from the biological experiments conducted by the Viking landers.
I wrote about his theory when it first appeared here:
You Only Find What You’re Looking For
http://www.starshipnivan.com/blog/?p=5
Nice point Athena. “Viking” tested for a very narrow definition of ‘life’ and – aside from Levin’s question mark – found something that didn’t fit our expectations… well ‘duh!’
Levin thinks there’s a better Life test – turning a growth medium cloudy or some such – but how do we know what ‘Mars bugs’ will like in advance?
What happens to the fuel in a ship travelling at relativistic velocities? Presumably it would gain mass, and thus energy – how would this impact the crafts maximum velocity?
Traveling at significant percentages of c is enough to go on voyages to nearby stars. As far as moving around the galaxy quickly, one of the main concepts I heard about for that would be foldspace – warping or bending space-time in such a way that you could “jump” over great distances. This seems like the most realistic bet to me, although the engineering of this is way out of reach. I’m not personally optimistic about breaking the c barrier in direct speed.
As far as extraterrestrial life, who knows? We shouldn’t assume that all life has to be like us, or that life needs an earthlike planet to survive. Life on earth is extremely adaptable – especially extremophiles (like tardigrades and others) which can survive in the most extreme conditions. Naturally, some worlds will be more conductive to life than others, but I’m sure that life could adapt to different gravity, atmosphere, radiation, temperature, and so on. Life could possibly exist in the clouds of gas giants. It is true that the rest of the universe is bound to the same laws of physics as us, so we do have some idea of what to look for, but an open mind is thoroughly necessary when looking at the universe.
Isn’t it all relative? Fuel would have more mass but so would the rest of the ship…
OK, you convinced me. I dropped some big bucks on a copy of Prospects for Interstellar Travel. But the tid-bits Paul Titze gives us tell me that it will be money well spent.
Winchell, it’s money well spent indeed. Mauldin should be on your shelf because it’s a wide-ranging, comprehensive text. You’ll find plenty to work with there. Let me know what you think of it.
TH, mass is a scalar and is velocity independent. Momentum and energy are quantities that are relative to the velocity between the observer and the observed. For those on the ship, the momentum of the fuel is the same as it would be for the chair you’re sitting on: zero, since you and the fuel/chair are co-moving. Momentum and kinetic energy are only non-zero for those outside the ship who are in relative motion to the ship.
“Speed: Discover how to circumvent existing limits (light-speed) to dramatically reduce transit times.”
Ya know, this theme comes up again and again and again, and it is just one huge, overweight red herring. I’ll say it again: relativity puts no limit on how quickly you can travel between points A and B. None!
There is no need to “circumvent existing limits (light speed)” since it is not a limit in the conventional sense that seems intuitive to our minds. There is no such thing as exceeding light speed, since all you’re doing is time travel — and probably messing up causality in the process. That is, it doesn’t get you to point B any sooner according to the traveler’s clock.
Often this obsession is simply misleading shorthand for utilizing (as yet unproven) non-simply connected paths through spacetime, such as worm holes. They’re unproven since their physicality is uncertain even though the mathematics of general relativity doesn’t exclude the possibility. That is, like tachyons and singularities, they may merely be unphysical mathematical artifacts.
Interstellar travel is about energy; conventional propulsion requires too much of it. We should concern ourselves with propulsion energy, not light speed, which is addressed in the point below the one I quoted at the start of this comment. Then there’s the matter bashing through the ISM at high relative velocity, which is a safety concern to be dealt with.
I’ve always wondered if the 1977 WOW! signal was meant for someone (or something) past Earth. We might have just been in the path of the signal and picked it up by sheer luck; nothing says it was meant for us. Maybe (and it’s a tenuous maybe) there was an intended target we haven’t looked for or considered.
Could be, though I’ve always wondered if some alien former starship officer isn’t sitting (or whatever) in its equivalent of a bar, lamenting how its career ended when it accidently activated the emergency beacon near that lousy planet. “No way they coulda heard anything.”
The Wow Signal is intriguing, to say the least. It was very strong, and it was observed for 72 seconds – the maximum amount of time the Big Ear focused on one point in the sky. I wonder if anyone knows how many lightyears away the source of it was? In any case, if it wasn’t ETI, it’s hard to say what it was. Could it have been an artifact of advanced space travel, or a beacon? Who knows…
Well, since it is a hydrogen line, and hydrogen is commonplace, could it have been some sort of a natural maser, driven by a neutron star or black hole somewhere and hitting the Earth by chance at that time?
Or perhaps a chance beam generated by gravitational lensing between a star and a glowing hydrogen cloud?
re athenas comment above and adams excellent reply…yes my friends alien life will be… well errr ahhhh – alien! thank you george
Hi Eniac
One of Carl Sagan’s last papers discussed scintillation of any radio signal by diffuse plasma in the ISM. A good discussion of the implications can be found here… http://patriot.net/~jlazio/mercury.html
Perhaps ETI is out there, but just too far away to do more than tantalise us.
et is out there,but too far for any practical contact etc. ? yes sir that DOES remain a tragic possibility! space is huge to say the least. respectfully your friend george
Adam, I am disturbed a little by this bit:
No mention of natural extraterrestrial sources. That seems like a rather huge omission, unless I am missing something.
E said, “…unless I am missing something.”
Read the first four words of point 1 again.
Yeah, perhaps with a very inclusive definition of noise. Still, there are a lot of extraterrestrial things in the sky (stars, for example), and you could be forgiven to think that not all that is natural is noise.
I take a very strict definition of signal, one that defines everything else as noise. That seemed the appropriate choice to make in answering E’s specific question: ET is signal, all else is noise. A radio astronomer might reverse these!