It is customary for old folks (such as me) to fulminate loudly about change. The new is puzzling; loss of the old and the familiar is sad. What do I miss? The Bussard ramjet¹.
The Bussard ramjet purported to address two issues that would seem to prevent Nearly As Fast As Light (NAFAL) travel from becoming a reality: fuel and protection from the interstellar medium (ISM). As you know Bob, the ISM is the faint smear of hydrogen and other matter that is found in the near-vacuum of space. If you are going fast enough, the ISM will abrade and destroy your ship. But ISM can be your friend! Collect and compress the ISM, fuse some of the hydrogen, and use it as fuel. Any unused ISM can be ejected in the exhaust. So elegant!
The Bussard ramjet promised the stars, if one were willing to invest a little time. It took Magellan’s ships three years to sail around the world; one could reach Alpha Centauri in almost the same time. Without getting scurvy!
| Destination | Distance (Light Years) |
Time (Years) |
| Alpha Centauri | 4.3 | 3.6 |
| Tau Ceti | 11.9 | 5.1 |
| 40 Eridani | 16.3 | 5.7 |
| The Pleiades | 444 | 11.9 |
| Crab Nebula | 6,500 | 17.1 |
| Galactic Core | 28,000 | 19.9 |
| Andromeda Galaxy | 2,500,000 | 28.6 |
The near stars could be reached in only a few years, vast expanses of the Milky in about half a career. Even the nearer galaxies could be reached in less time than it took to go from Ferdinand de Lesseps’ initial vision to the actual Panama Canal. Not as convenient as any given episode of Star Trek, but nothing that would have daunted Zhang Qian.
Well…with one tiny catch: the times given above are those that would be measured by someone on the ship. Let’s add a column for how long the trips would take from the perspective of Earth.
| Destination | Distance (Light Years) | Ship Time (Years) | Earth Time (Years) |
| Alpha Centauri | 4.3 | 3.6 | 5.9 |
| Tau Ceti | 11.9 | 5.1 | 13.7 |
| 40 Eridani | 16.3 | 5.7 | 18.1 |
| The Pleiades | 444 | 11.9 | 446 |
| Crab Nebula | 6,500 | 17.1 | ~6,500 |
| Galactic Core | 28,000 | 19.9 | ~28,000 |
| Andromeda Galaxy | 2,500,000 | 28.6 | ~2,500,000 |
NAFAL trips mean crossing time as well as space. But that shouldn’t prevent exploration; anyone who would consider racing off that far into the future probably wouldn’t have friends and relatives about whom they deeply cared in any case.
Bussard ramjets seemed an ideal solution to the problem of sub-light interstellar travel. Science fiction authors soon noticed.
The classic Bussard ramjet novel is, of course, Poul Anderson’s Tau Zero. What was for other authors a convenient prop was one of the centerpieces of Anderson’s novel. The Leonora Christina sets out for Beta Virginis, a nearby star. A mid-trip mishap robs the ship of its ability to slow down. Repairs are impossible unless they shut down the ramjet, but if the crew did that, they would instantly be exposed to lethal radiation. There’s no choice but to keep accelerating and hope that the ship will eventually encounter a region in the intergalactic depths with a sufficiently hard vacuum so that the ramjet could be safely shut down. Even if they did find such a region, the crew is still committed to a journey of many millions of light years, one that will forever distance them from their own time.
Even before Tau Zero, Bussard ramjets were everywhere. Larry Niven’s A Gift From Earth feature an egregiously hierarchical society that is toppled thanks to a package delivered by robotic ramship. Jo Walton’s review of that novel is here.
One of the odder novels in which Bussard ramjets play a central role is Bob Shaw’s 1969 The Palace of Eternity. In that book, humans find themselves locked in merciless battle with the alien Pythsyccans. The Pythsyccans limit themselves to conventional fusion rockets, which gives humanity a considerable edge—or so the humans think. In fact, the aliens have a reason for making the choices they do. Former soldier Mack Tavenor will find out why, but the path that takes him to that destination is uncanny indeed.
The Urashima effect of NAFAL travel—either through velocity time dilation or gravitational time dilation—can isolate human colonies from Earth and other advanced worlds. In Lee Killough’s 1979 A Voice Out of Ramah, the isolation of backwater world Marah ends when envoys bearing the means of interstellar teleportation arrive. It’s not until two crew members—one man, one woman—set down on Marah that they learn that Marah is home to a disease that kills the majority of boys at puberty. Bad news for the off-worlder man, who is not immune. Still, a reader might wonder why if 10% of the boys survive, their sons do not share their resistance. The answer to that question shapes the plot.
Similarly, the protagonists in Joan D. Vinge’s 1978 Outcasts of Heaven Belt set out to make contact with the nearby (in galactic terms) Heaven Belt, only to discover that in the centuries since their home system last got word from Heaven Belt, that asteroid-based constellation of cultures had discovered the hard way why war between artificial habitats is a very bad idea. The handful of survivors have lost even basic technologies like fusion; the visiting starship is therefore a treasure that people will kill to possess.
Perhaps the coolest aspect of NAFAL travel was something called the Starbow. Curious what the stars would look like to a traveller moving close to the speed of light, Ing E. Sänger’s calculations suggested that the ship would perceive itself to be preceded by a rainbow ring. Frederik Pohl borrowed the idea for the title of his 1972 Hugo- and Nebula-nominated and Locus Award-winning story “The Gold at the Starbow’s End,” in which elite travellers are granted an unusual voyage of discovery.
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Static Ruin
So, what happened, you ask? Why this lament? Well, people like T. A. Heppenheimer took a closer look at the physics of the Bussard ramjet. Alas, the ramjets seem to work better as brakes than as propulsion systems. There are workarounds for some of the issues with the tech, but the new designs aren’t those wonderful one-gravity-forever independent spacecraft that featured in so many stories I read in my teen years. The Bussard ramjet’s descendants will have much smaller accelerations, hence their peak velocities will be too low to generate significant relativistic effects. Some designs depend on active support from their home system while in flight.
In fact, it even turned out that Sänger made some erroneous simplifying assumptions and there is no Starbow. Bah.
A more detailed discussion of ramjets and their rise and fall can be found at the exemplary Atomic Rockets site.
There is an alternative to the Bussard ramjet that offers many of its advantages (at least as far the needs of science fiction authors go)—one that has inexplicably only been used by a single author to my knowledge. What that alternative is, however, will have to wait for another essay.
1: Not only ramjets. I miss proper hay bales. A hay bale should be just a bit too heavy for a kid to lift without hurting their back; it should be held together with two or three strands of twine that slice through youthful palms like garrote wire. Those hay bales built character! But I don’t think I can convince Tor.com to pay me to complain that modern bales are just plain wrong.
In the words of Wikipedia editor TexasAndroid, prolific book reviewer and perennial Darwin Award nominee James Davis Nicoll is of “questionable notability.” His work has appeared in Publishers Weekly and Romantic Times as well as on his own websites, James Nicoll Reviews and Young People Read Old SFF (where he is assisted by editor Karen Lofstrom and web person Adrienne L. Travis). He is surprisingly flammable.
My very first published story, appearing in the November 1998 Analog and finally back in print in my brand-new story collection Among the Wild Cybers (out in paperback this week), was a ramjet story called “Aggravated Vehicular Genocide.” It was inspired when I was thinking about the laser defenses a ramjet would need to deflect asteroids from its path… and wondered what would happen if one of those “asteroids” turned out to be an alien spacecraft or habitat instead. The revised version appearing in the collection addresses some of the technical problems with ramjets that I was unaware of when I wrote the original story.
Your link to the Wikipedia page for Urashima Tarō is missing an “o” from the end BTW.
2: Thank you. Fixed now.
CLB@1
The Mote In God’s Eye goes into ramjet defenses shooting at non-threatening ships a bit.
Well, if we can’t have Bussard’s interstellar ramjet, perhaps we’ll still have his polywell reactor…
That is a very early 1970s cover for Tau Zero. Still, better than the one Tales of the Flying Mountains got from its publisher.
If it makes you feel any better, I have 120 hay bales that are just as you describe (they’re about 20kg per bale) in my barn right now. They have not yet died out, at least not in the UK.
Yay!
“ A hay bale should be just a bit too heavy for a kid to lift without hurting their back; it should be held together with two or three strands of twine that slice through youthful palms like garrote wire. “
That takes me back to the 1970s, and my summers on my uncle’s farm.
Rock picking was worse than bailing, I think. For all you urbanites, during the winter, frost heave brings a new crop of rocks up to the surface. Rather than break valuable farm equipment, kids got to walk through the fields, removing the new rocks.
@4/wiredog: I don’t think I ever read The Mote in God’s Eye, even though I used to read a lot of Niven.
Mote did not have a Bussard ramjet, as I recall. I remember a moon-sized solar sail, whose boost phase was powered by a vast battery of laser cannons. The Moties being the sort of beings they were, when the MacArthur came to investigate the object falling into the system at several percent of the speed of light, they used the sail to focus a lot of sunlight onto the MacArthur.
10: Wait, so the rock farm that Pinkie Pie’s family owns could have been for real?
(Mindblown)
I have not read that. Perhaps the author also had the wonderful experience of prying rocks out of the ground barehanded.
If you could find the Mother Rock that was spawning all the infants annually and dynamite it then the field would be blessedly free of new crops of rocks from then on. Well, after the short sharp rain of rock fragments from above dies down…
CLB@11,
Mote is one of the better First Contact novels. Aliens that are alien, but explicable, and not bad guys even if they are potential enemies.
I’m one of the few who also likes the sequel, The Gripping Hand, so make of that what you will. Hand retcons the Muslim from Mote into a more multi-dimensional character and makes him a hero.
Of course, the most familiar form of the Bussard Ranjet is its descendant, the Bussard Collector, better-known as those glowing “caps” on the front of a warp nacelle.
Though for me, “Ramjet” still conjures up images of the idiotic conehead.
Not Roger Ramjet?
https://en.wikipedia.org/wiki/Roger_Ramjet
@16/wiredog I also enjoyed The Gripping Hand. The changes made in the Bury character were very welcome.
Assuming they are feasible – How do Ramjets figure in future trips? With the jets scooping up all usable material within wide swaths of space on each journey, won’t subsequent trips be required to move further and further away from the original path? Even if new fuel is expelled into the path by cosmic events, you will still encounter very large doldrums created by previous ship travel.
You would have to set up an extensive array of communication nodes to broadcast all flight plans to avoid ships encountering the dead space left in another ship’s wake. You could even have Piracy take advantage of this. They would know the projected path and speed of a Cruise liner ramjet, then use their own ramjet to scoop up all of the fuel in a section of its projected path. The cruise liner will be required to coast or even stall in the section and be vulnerable to attack.
Yes, space is absolutely gigantic. But it is safe to assume that ships will still take the absolute minimum path to any future colony. That would mean lots of ships traveling a near identical course.
Stars move so no two trips would take the same course.
twine bales, hah! Real men (of the 1960’s) baled with wire; 80-100 pound bales and you had to use a baling hook (looked like a meat hook) to grab them; we’d stack ’em 10 high on the wagon, and even higher in the barn.
Dan @@@@@ 20:
The wake of a ramjet would be filled in very quickly. Just because the gas in the interstellar medium (ISM) is thin does not mean it stops behaving like gas: create a local vacuum, and neighboring gas will move in to fill it. (You don’t leave a long-lasting trail of vacuum in the air behind you when you go walking, do you?)
How fast this happens depends on how large a wake your ramjet carves out and the speed of sound in the gas (this is the typical speed of atoms or ions in the gas, which lets you figure out approximately how long it takes for atoms or ions to cross from one side of the wake to the other). If there are supersonic turbulent motions in the gas — which is true for at least some of the ISM — then the tunnel can be filled in even faster.
Typical sound speeds in the ISM are 1 to 10 km/s. If we assume a ramscoop throat width of 1000 km, then the wake will be filled in within a matter of minutes. Even if the ramscoop throat is 100,000 km wide, you’ll still get the wake filled in within a few hours.
Why does everyone focus on time? This is the part of relativity that makes no sense. When have we had any evidence that time moves at a different speed for someone moving then someone standing still? Never! It was a theory! What happens if distance is not looked at as a constant, but time is? If time is the constant and distance is variable, then any speed is possible because distance is what seems to decrease to those on the ship and time stays the same, if they are gone 20 years then 20 years have gone by everywhere in the universe. I wish scientists would explore that possibility, that Einstein was wrong, time does not and CANNOT change, but distance is variable. Maybe everyone here just accepts that travel at light speed = time disruption, but I find it foolish, he might have got the math wrong people, he was just a human.
23: fascinating. So are you saying that there would actually be an advantage to streamlining your starship?
Quite a few times. Try googling “proof of time dilation”. Experiments involving highly accurate clocks and jet aircraft. For example https://en.m.wikipedia.org/wiki/Hafele–Keating_experiment
That Atomic Rockets link was terrific, even if it ate my entire morning. I didn’t even get to the FTL page due to exhaustion. I’ll save that for another day when I’m rested! Thanks!
@24/Joshua: Relativistic time dilation is an everyday reality. The clocks in our GPS/satellite navigation systems are so precise that the software needs to correct for relativistic effects in order for GPS to function at all:
http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html
It can also be observed in particle accelerators when particles accelerated to near the speed of light decay more slowly, and in numerous other ways. Indeed, there’s a much simpler proof: magnets. Magnetism is a relativistic side effect of electricity, a result of the way the movement of electric charges alters the way they perceive each other’s speed and distance. Relativistic effects are also the reason for the color of gold.
http://www.iflscience.com/physics/4-examples-relativity-everyday-life/
“It was a theory!”
It’s a myth that “theory” means something less than “fact.” It’s actually the other way around. A fact is merely a data point, an observation. A theory, as the term is used in science, is a model that explains the underlying reasons for multiple observed facts and offers predictions that can be tested by gathering further facts. For instance, it is a fact that we see color, and color theory is the model that explains why we see the colors we do and what the underlying processes are. A theory is something much more powerful than a fact, because it points the way to finding new facts. So a theory remains a theory no matter how thoroughly it’s been proven. And relativity is one of the most extensively verified theories in physics.
“What happens if distance is not looked at as a constant, but time is?”
Neither one is a constant. That’s why it’s called relativity — because it shows that all our measurements of distance, time, mass, energy, etc. are relative to a particular observer’s reference frame rather than being universal. The only constant is the speed of light itself, which has to be a constant because it’s a factor in many laws of physics and the laws themselves must be universal. So since different observers are going to be moving at different speeds and directions relative to a beam of light, their perceptions of time and distance need to change in order to ensure that they all see that beam of light traveling at the same speed, even if they disagree on every other measurement.
“I find it foolish, he might have got the math wrong people, he was just a human.”
Science takes nothing on faith. Everything is tested. Einstein’s equations are accepted because they work, because they’ve passed all the thousands of tests they’ve been subjected to, including the test you perform every time you use your GPS to navigate somewhere.
Unsurprisingly, there is at least one example of an author just tossing relativity overboard that also has Bussard ramjets: Bob Shaw’s Orbitsville books. They also feature a Dyson sphere to which the shell theorem inexplicably does not apply.
@@@@@Joshua: “…any evidence …”
Simple — We know the lifetime of a free neutron. We can measure the lifetime of neutrons moving at high velocity. They live longer at the rate calculated by Special Relativity.
A side issue in settings with NAFAL travel is governance. Which is to say realistically speaking lag times of decades or centuries would seem likely to be an insurmountable opportunity as far as coordinating policy goes. But there are setting that I can think of with slower than light travel combined with interstellar governments (Viagens, for example, although it doesn’t use Bussard ramjets.). How are they doing that?
@31/James: Karl Schroeder’s Lockstep came up with a rather imaginative solution to the travel-lag problem — entire colony worlds go into periodic hibernation for the entire length of time it takes sublight ships to travel between them on a regular, set schedule, so that the inhabitants and travelers remain in sync with each other’s lives. This also has the advantage of conserving resources and energy reserves on the rogue interstellar planetoids they inhabit.
But a lot of SF, like Poul Anderson’s, just assumes that the individual worlds are mostly autonomous and govern themselves, and that being subject to a larger empire or the like is just a matter of paying taxes and tribute — not so unlike widespread empires of antiquity.
@31/James Davis Nicoll: I was thinking of Ursula K. Le Guin’s Ekumen, but that’s probably more an interstellar United Nations than an interstellar government. And it only really gets going after the invention of instantaneous communication.
I forgot which one, but one of the books in Nivens Ringworld series has Ramjets playing an integral part of the plot (…actually now that I think about it, it may even be the titular book).
34: a big part of the Known Space universe is that Bussard ramjets work but the magnetic field required is lethal to humans; humanity’s exploration of space started with unmanned “ram-robot” probes, and when the probes found a habitable planet they were followed up with manned “slowboats” carrying settlers in cryogenic sleep. The Ringworld natives, the City Builders, had explored the space nearby with manned ramships, using the Ringworld’s spin to their advantage; all you need to do to hit the minimum working speed for a ramship is to drop it off the Ringworld through a hole in the floor.
Unsurprisingly, there is at least one example of an author just tossing relativity overboard that also has Bussard ramjets: Bob Shaw’s Orbitsville books
You have to admire the boldness of an author who sidesteps all that tedious mucking around with time dilation, Lorenz contractions, red shifts, the lightspeed limit and so on by simply saying in passing “oh, yeah, relativity. When we tested it we found it was rubbish.”
#28, it’s also worth pointing out that Einstein did get several things wrong, notably his initial refusal to accept the Uncertainty Principle. Scientists don’t worship Einstein as some sort of infallible prophet. They keep the ideas that worked and discard the ones that turned out not to.
To be pedantic, the clock in a GPS satellite runs faster than one on the ground, not because the difference in velocity (which actually makes it run slower from our point of view), but because it’s further away from any large masses (ie the Earth).
That said, both effects were predicted by the Theory of Relativity*, and when the first GPS satellites were launched, the predictions were correct.
* Well, theories plural, Special and General Relativity, where ‘special’ means ‘in certain circumstances, such as might be experienced by hairless apes on the surface of a ball of rock’ (ie the easy version), and General Relativity which includes things like gravity, and is consequently much more complicated to work out.
@36/ajay: “You have to admire the boldness of an author who sidesteps all that tedious mucking around with time dilation, Lorenz contractions, red shifts, the lightspeed limit and so on by simply saying in passing “oh, yeah, relativity. When we tested it we found it was rubbish.””
So… what color is gold in that universe? And do magnets not exist there?
@39/CLB: “So… what color is gold in that universe? And do magnets not exist there?”
These are not the questions you should be asking. [Jedi wave]
@25,
Surprisingly, yes. This starts getting into a rather specialized area of fluid mechanics, rarefied gas dynamics, but an analogy could be ricocheting bullet: streamlining means that the particle impacts are glancing, and less energy and momentum are transferred to the ship.
You could do an analogous experiment at your local firing range with some steel plates, a load cell, and a machine gun.
@31: In some of the Man-Kzin Wars stories, the way that the huge but non-FTL Kzin empire is run is discussed. Turtledove’s “World War” books also have an interstellar, but non-FTL empire. In both cases, the societies are pretty conservative, with strong devotion to the ancient central authority.
41: thanks. I’ll maybe just take your word for it.
ajay @25:
The short answer is: Yes, for a couple of reasons.
Traditional drag from the interstellar medium won’t matter for short journeys (e.g., if you want to go from here to Alpha Centauri), but starts to matter for distances of several hundred light years or more.
Also, impacts with atoms at even modest fractions of c are energetic radiation events, and impacts with dust grains will be small explosions, so it makes sense to reduce reduce the cross-sectional area of your starship for that reason as well.
(I had a longer answer going into the numbers, but tor.com isn’t letting me post it for some mysterious reason.)
39: Shaw is also the person whose method of indicating a novel was set in a universe where the physical laws were different was revealing that the value of pi was exactly three.
I could swear I remember a 1970s Star Trek novel where the Bussard ramjet got namechecked, which is where I first came across the concept. In any case, the glowing domes on the front of Trek starships’ warp nacelles are supposed to be Bussard collectors.
@47/Shem: You’re probably thinking of the Bantam Star Trek novel The Galactic Whirlpool by David Gerrold, which actually came out in 1980. It was a story about a lost generation ship from Earth, based on an unsold 2-parter outline that Gerrold had pitched to the original show and gotten rejected because it was too ambitious to make on a TV budget. Though I suppose it might also have been World Without End by Joe Haldeman, which came out in 1979 and involved the Enterprise encountering an alien generation ship. I don’t recall whether that ship used ramjets. I don’t think it did, but I can’t be certain.
The forward nacelle structures were first identified as “space energy/matter acquisition sinks” in the Star Trek: The Motion Picture Blueprints by David Kimble, but the concept may have come from TMP illustrator Rick Sternbach, who had previously worked with Dr. Bussard on a ramjet-related project and would later establish the term “Bussard collectors” in his capacity as a technical advisor on Star Trek: The Next Generation. (Rick also did the illustrations of the Bussard ramjet and Orion and Daedalus starship concepts that appeared in Carl Sagan’s Cosmos.) The domes were never given a name in TOS per se, although apparently they were called “ball power nodules” among the show’s design and visual effects staff.
The issue of the Bussard Collectors slowing down the ship is something that I (as a self-publishing Sci-Fi author) see as a boon and used in my novel “All The Stars Are Suns”… though I didn’t call them that. Instead, they are magnitohydrodynamic brakes used to slow a low C fractional ship, originally boosted by microwave sail in the Solar System, as the ship passes the local heliopause of the destination star, encountering the local ‘solar’ wind enough such that fusion powered ion engines fired during perihelion converts the hyperbolic orbit to a highly eccentric elliptical one. Subsequently, the magnitohydrodymic interaction is used to bring the elliptical orbits eccentricity down to one where the ion engines can be used for planetary orbital insertion after a millenia pretending to be a comet.
Someone commented above on streamlining. Yes, an interstellar ship should be very needlelike to reduce its cross-section to the path of the ship. As I see it, even at low C fractional velocity, any encounter with a gas molecule will NOT be simply glancing no matter the shape of the nose. It will enter the material. Thus, the material should be very low density so as to slow the molecule down through multiple collisions to reduce ablation. A highly cross-linked polymer would probably be best. The dust strikes will be explosive, as was already pointed out… so the nose should be very thick (long)… so that it may be ablated and still survive the voyage with sufficient thickness. Thus, the nose may be blunt ended as the thickness at the begining of the voyage should be uniform in cross-section. Thus, the look of the ship is a long wire with a blunt leading edge.
The problems of transit time vs. human lifetime are dealt with in a novel fashion that you will just have to read the book <evil grin>
Thanks for this article! Much enjoyed reading it(and the majority of the very knowledgeable comments!). I cannot for the life of me remember this book, but when I was 11 or 12, I remember encountering a book at the local library that talked about the many possible ways of traveling interstellar distances. Wish I could remember more about the book, but I do remember the ramjet being discussed. I was endlessly fascinated and I date the origin of my love for sci-fi to somewhere around that time in my life. Space travel is supremely interesting and I’m grateful to both the scientists and authors who have contributed to my love for this subject!
@49
IIRC, in “The Songs of Distant Earth” Arthur Clarke used water ice on the front of the starship to absorb impacts from interstellar dust.
Regarding Bussard ramjets: They always seemed a bit “perpetual motion machine”-ish to me; an intriguing idea that ignored things like friction that always get in the way of nifty devices.
Regarding rocks: The picturesque stone walls of New England were not built for show, nor to hold animals in the fields; they are simply the edges of the fields, where all the new rocks were carried each spring. This I know from personal, and back-breaking, experience.
Regarding the Atomic Rockets website: An awesome must-see for anyone who ever dreamed of writing SF.
Those picturesque New England stone walls were made from the year’s crop of stones grown in the fields.
Has no one read “A Deepness in the Sky”, part of the Zones of Thought series, by Vernor Vinge. Such a well done book, and covers Bussard Ramjets very, very well, along with trip times, trade, and governance.
@54 Good catch, Doug. Another great novel with NAFAL travel at its heart.
Shaw is also the person whose method of indicating a novel was set in a universe where the physical laws were different was revealing that the value of pi was exactly three.
In the words of Charlie Brown: AAAUUGHH.
Ever since reading Joan Vinge’s “Tin Soldier” I have thought of ramscoops etc as being AAFAL rather than NAFAL:
“…this area here is for the AAFAL drive, first devised by Ursula, an early spacer who—”
“What’s awful about it?”
“What?”
“Every spacer I know calls the ship’s drive ‘awful.’”
“Oh— Not ‘awful,’ AAFAL: Almost As Fast As Light.”
I never came across the “NAFAL” acronym until fairly recently, I don’t think. I always thought of it as “STL” or “sublight,” or “relativistic” if you wanted to talk specifically about velocities close to lightspeed.
@58: Ursula LeGuin often used NAFAL (as I recall), which is probably why Joan Vinge (quoted in @57) mentions “Ursula” in the discussion of AAFUL.
@54: Deepness in the Sky was terrific. I’m eagerly awaiting the next book in the series.
@59/AndyLove: The third “Zones of Thought” book, The Children of the Sky (a sequel to A Fire Upon the Deep), came out in 2011. It definitely left things open for a sequel, but as far as I can tell, no fourth book has been announced.
@60: Darn. I liked “Children of the Sky” and am hoping for that fourth book (or a direct sequel to Deepness).
@34 — Protector was the Known Space book that had a lengthy chase/space combat sequence between a couple of ramjets. Ramjets were also part of Ringworld Engineers, at least; I don’t remember if they were mentioned in Ringworld. And there was at least one short story in Neutron Star that was very ramjet-dependent: “The Ethics of Madness”.
Currently, my own favorite NAFAL book is probably Alastair Reynolds’ House of Suns, although I don’t remember the exact mechanism the ships use.
my own favorite NAFAL book is probably Alastair Reynolds’ House of Suns, although I don’t remember the exact mechanism the ships use.
It’s never mentioned, as far as I remember, or at least never gone into detail.
hoopmanjh @@@@@ 63:
my own favorite NAFAL book is probably Alastair Reynolds’ House of Suns, although I don’t remember the exact mechanism the ships use.
As I recall, the mechanism (or mechanisms) went by vague names like “parametric engine”, which doesn’t actually mean anything but sound kind of cool and physics-y. I had the impression they were tantamount to something like Niven’s “inertialess drive”. (Weren’t the ships able to accelerate at pretty extreme rates without turning their human passengers into a fine paste?)
The fact that the story takes place several million years in the future allows for a certain amount of handwaving…
I don’t think I ever saw the acronym NAFAL before this column, but it is a useful little acronym.
I am not going to try to embed the ngram I did for NAFAL but there’s definitely a non-zero incidence. I cannot say how much of it is for the acronym and how much for the name, though.
I cannot express how upset I was to reach for my new DM11L to realize I’d forgotten how to do the relevant equations for this.
@64,
Inertialess drive was from EE “Doc” Smith, although it was probably “borrowed” by many others.
___________________________________
There is probably as much hand waving about nearly-as-fast-as-light starships as about FTL. The amount of energy required to accelerate something to 99.99% of light speed is mind-bogglingly huge.
@68/swampyankee: But that’s exactly the advantage of ramjets as a concept — you can replenish your fuel from the very space around you, so you theoretically have an effectively limitless supply of energy. Although making it work in practice is another matter.
“What that alternative is, however, will have to wait for another essay.”
Please write that essay soon. I’m very curious about this.
Every time I read one of your essays, my list of books to read gets longer. This is by far one of my favorites of yours. As it turns out, I had sketched out a version of the ramjet featured on the original cover of Niven’s “A Gift from Earth” in my notebook under the heading of “What happened to starships?”
Another use for Bussard Ramjets I’ve thought of is to explain the Fermi Paradox.
The Fermi Paradox is the question of why we have never been visited by interstellar beings. It turns out that Earth is in a region of space called the Local Bubble. This is a ~300 light-year region of space where the interstellar gas density is a factor of 10 lower than average. Any Bussard Ramjet venturing into the local bubble will soon find itself sucking hot thin gas unlike the thick cool soup (0.5 atoms/cm^3! why do you even need a pressure suit?) it was built for.
Nobody visits this region of space. Not if they ever want to leave.
It’s as if we are sitting in the middle of a desert, never seeing any visitors, while the lusher regions of the Galaxy teem with vast trading networks of interstellar civilizations.
I think whenever a ramjet is discussed, we shoudl also remember Larry Niven’s short story “Rammer”, as well as it’s expansion (or incorporation) into the novel “A World Out of Time”. Both revolve nicely around the concept.
https://en.wikipedia.org/wiki/A_World_Out_of_Time
Niven also had a nice ramship chase story “The Ethics of Madness”
@15,
Blowing up the mother rock would have all the positive effects of ending rainstorms by trying to blow up a cloud. Rocks are what happens when the particles of dirt grows up.
@74,
I thought that was one of his better stories.
Except, of course, for the incredibly inaccurate portrayal of insanity.
@76: As I recall, Niven was dissatisfied with the story and wrote “Madness has its Place” in response to his earlier work (though I could be misremembering).
Huh! You’ll be telling us next that there are no seas on Venus, and Pluto isn’t a planet! ;-)
Or that Mercury isn’t tidally locked!
So, Bussard ramjets don’t work as a propulsion method…
… but the scoop part would still clear atoms and small particles out of one’s path, which at NAFAL is a good idea.
Then you don’t need a hundreds-of-kilometers-wide scoop. Just big enough to get your ship through before the interstellar dust/gas fills in the gap you create… so the faster you’re going, the smaller a scoop you need.
My Uncle raises horse. I was helping pick up hay in the field and move to the barn. We had 4 people in the barn loft. I was 2nd or 3rd in line from the conveyor belt. The bales would get thrown from person to person. I was not used to that work and dealing with hay bales. The bales would bounce on the floor and bang into my knees and legs. So I figured that if I backed up about 4 feet the bales would bounce to a stop right in front of me.
Nope. The man in front of my just threw them that much harder. :)
I did try to take the # 1 spot after one of our breaks. But I couldn’t keep up with the bales coming off the conveyor belt.
Good times.