19 January 2013

FWS Topics: Sub-Light Starship Propulsion


Since the 1972 Apollo 17 lunar mission, humanity has not ventured more than 400 miles away from Terra...all of the promise made to my generation about Martian colonies have been broken and the human species lingers in the shallow end of deep space. When (or if) we spread out to the stars, armed conflicts will break out over resources or just ownership of the planets themselves, and thus soldiers will need to be transported to these very distant shores to protect their government's interstellar interests.The far-future armed forces, like today's military organizations, will regard getting to the battlefield has half the battle. The primary mission of Future War Stories is to be a resource for military science fiction authors and creators, and here is the best list I could assembly on the various sub-light hard science starship propulsion. This is not meant to be an exhaustive scientific article, but more a highlight list. The genesis of this blogpost, which has been in the draft pile since day one of FWS, came when I read this month's National Geographic, and I thought it was high time to dive into starship propulsion. FWS will be writing the second part of this, FTL propulsion systems, in the next few months. That one will be fun...I think. One thing to consider before reading this list, acceleration must be matched at the end of the journey in de-acceleration, adding to the amount of propellant carried onboard. Also, acceleration needs to be at around 1G for the crew NOT to be transformed into chucky salsa, causing the acceleration time-table to be greater than an umanned interstellar probe, which could travel at 12G.

Magnetoplasmadynamic (MPD) Thruster
What is it?
MPD thrusters are, according to NASA, the most powerful form of electromagnetic propulsion that uses charged particles from ionized gas fuel, such as xenon, neon, and lithium, are pumped into an acceleration chamber, and expelled as thrust via a nozzle. NASA's official work on the top speed of MPD thrusters is about 200,000 MPH.
PRO:
MPD thrusters actually seem to work, and are being researched by NASA for use in future probe and manned missions. Tests have demonstrated that MPD thrusters can delivery up to 200,000 MPH worth of thrust, similar to a chemical rocket, but more fuel-efficient. This could be a real possibility for future space crafts. Several of my MSF novels along with the USS Sulaco from ALIENS feature MPD thrusters for sub-light propulsion.

CON:
The power needed to generate the field need for acceleration is on the order of hundreds of kilowatts, which the current RTGs cannot generate. That means using a space-based nuclear power plant for the required power, and current Terran thinking is hinky on putting nukes into space.


The Woodward Effect Particle Recycle Drive
What is it?
This highly experimental theory on particle behavior could led to a sub-light starship engines that has an 'endless' supply of fuel by 'looping' or 'recycling' the needed particles. According to the theory, a Woodward Effect Particle Recycle Driver starship would loop the needed particles to change their mass based on push and pull, depending on their mass. When light mass, we pull, when heavy, we push...like Aikido. Since the Woodward Effect Particle Recycle Drive is so experimental, I could find much on the possible velocity.


PRO:
If it works...no more fuel!

CON:
Some believe that this 'Woodward Effect' does not exist. One of those nonbelievers was Einstein.

Mustafa's Space Drive

What is it?
19 year old Egyptian physics student, Aisha Mustafa, developed a new type of spaceship propulsion based on a new theory on quantum physic concerning the nature of how empty space really is. According the theory which Ms. Mustafa used is that the universe is not a vacuum, but vast gulfs of empty space with rolling 'seas' of particles and anti-particles. These twin forces destroy each other so quickly, that we cannot detect it. As near as I can tell, the Mustafa Drive uses movable shaped silicon plates that adjust based on the flow of this particle sea, and this 'push-and-pull' effect leads to thrust, similar to the Woodward Effect Particle Recycle Drive. There are a few sites that have worked out that Mustafa's space drive would only produce about 3% of C, others say that it build up to faster speeds.

PRO:
No fuel is needed to propel the vessel, and the propulsion system is quiet simple, making it as complex as a solar sail.

CON:
The theory on which the drive system based would need to be proven, and it would still need RCS thrusters. What if the starships runs into a region of space where the particle sea is less dense?

Nuclear Pulse Propulsion 
What is it?
First suggested in 1947, and undertaken in 1958 as a study project under the name 'Orion'. The idea was to eject a nuclear fission charge out of the rear of our spacecraft then set off the charge, having the energy of the explosion use for propulsion via pusher plates on the space vehicle. Sounds simple enough. To test the theory, a 230lbs test vehicle of the basic shape was constructs, called 'Hot Rod', then launched via gunpowder explosion then and propelled upwards for 105 meters via a series of C4 explosion in 1959. Excitement ran high for the Orion Project, causing speculation that by the 1970's, NPP equipped craft would be visiting Saturn in just seven-month trip. While since Virgin Galactic is not selling cruises to see the rings of Saturn, the Orion Projection was halted due to concerns over using nukes in space along wit the space test-ban treat. Some sites content that there was conspiracy regarding the cancellation.One of the only visual examples of NPP in sci-fi media is the starship Phaeton from the 2009 TV pilot Virtuality. 

PRO:
Unlike a great of the propulsion technology mentioned here, the NPP has be tested and would work. Most of the technology is already here, and Terra has plenty of nuclear weapons for propellant. It was believed that the Project Orion NPP ship would generate 12 to 19 miles per second worth of thrust or even up to 10% of C or 2.9 million meters per second.

CON:
The real bitch with the NPP is not the acceleration, but slowing towards your designation, causing the NPP ship to use more nuclear charges to slow them down. Once the mission is complete, you have to build up speed, and slow back down again. This all adds up to a massive amount of nuclear charges being needed for a trip to Alpha Centauri. Some sites suggest that the Orion equipped spacecraft would achieve 5% of C, which would take 85 years to reach Alpha Centauri, others say 10%. Either way, it's going to be a real long trip...better pack the Xbox 360 and some snacks and beer.

Anti-Matter Catalyzed Nuclear Pulse Propulsion (AMCNPP)
What is it?
This works in a very similar manner to the traditional nuclear fission pulse propulsion, but uses anti-matter changes instead, which could, in theory, propel a vessel at 16% of C.

PRO:
Bigger explosion=Greater Speed.

CON:
Bigger explosion=more mass for the structure of the spaceship to survive the shockwave, not to mention the cost of producing that much anti-matter for a four lightyear trip. Much like the NPP, the AMCNPP would need fuel for several accelerations and de-accelerations, and to watch the acceleration for the health of the crew. Lastly, there is the issue of long-term containment of anti-matter...a single unit's containment failure could led to the expensive space voyage coming to a sudden, but bright, end.

NERV Rocket
What is it?
Nuclear Engine for Rocket Vehicle Application or NERVA works via super-heating liquid hydrogen and forced out of a nozzle for thrust. According to my research, the hydrogen would generate thrust propelling the space vehicle at 20,000m MPH. NERVA was thought to be the next step in manned American space exploration. So much so, that between 1965 and 1973, the US Atomic Engery Commission and NASA attempt to construct NERAs for a 1978 return to the Moon and a 1981 target date for construction of a lunar base. Once these were completed, a NERV would send humans to Mars. Sadly, the project was cancelled in 1973 by the Nixon Administration  It was a victim of the times, the American public interest in space decreased after we beat the Soviets to the Moon, there was the expense of the Vietnam War, which ended that year, and there were environmental worries over launching a nuclear reactor into space.  

PRO:
Twice has a effective has a conventional chemical rocket, with greater range and speed. Plus, the technology is close, if not, already here. The supply of hydrogen for the rocket could be supplied by a Bussard ramscoop.

CON:
Having a nuclear reactor, which can be tricky, has your primary source of thrust and close to your space vehicle. There also worries about the greater temperature that a NERVA systems would be under while burning towards the red planet. Then, of course, the NERVA needs a supply of hydrogen.

VASIMR

What is it?
Vaccum-to-Antimatter Rocket Interstellar Explorer System or VASMIR would be a proposed starship that used solar arrays to power a highly intensity laser that would through, advanced physics, create anti-matter while near a star. This newly minted anti-matter would be stored for fuel. The thrust for our VASIMR ship would come from an anti-matter rocket.
PRO:
Being about to collect anti-matter from nearby stars could allow our starship to travel into deep space. The design, if correct, could able to travel at 125 miles per second (or 6% of C...if my calculator is right)

CON:
For anti-matter generation to occur, the starship must be near a star that can power the laser and given the stated speed of 6%, reaching another star before you exhaust your supply of expensive anti-matter could be a risky.

Chemical Rockets
What is it?
These are the good old rockets that are feed by liquid, solid fuels, or both. Since the first space launch in 1957, these have propelled us beyond our world into space...well...to the Moon. These types rockets are very useful at allowing spacecraft and satellites to achieve orbit, propelling at above Mach 24. During the Apollo mission, the last stage of the Saturn V rocket, S-IVB, gave the final push towards trans-lunar injection, and were ejected outside



PRO:
Current on-the-shelve technology and they are a proven technology.

CON:
Chemical rockets are useful for getting the space vehicle into orbit and for possibly getting the space craft up to speed...but for interplanetary missions, chemical rockets are just too thirst and require too much fuel to effective in crossing the gulf of interstellar space.

Pulsed Plasma Thruster
What is it?
Plasma, while unrealistic for future DEWs, does seem a likely source for future starship propulsion...even Star Trek uses plasma for their 'impulse drive'. Pulsed plasma thruster, (AKA plasma jet engine), use a solid block of propellant. Teflon was used in the real-world test and an arch of electric current to general thrust. Pulsed plasma thrusters have been used on space probe reaction control system (RCS) since the 1960's.
PRO:
Could be a low-cost solution for smaller space vehicle propulsion, and we know it works with current technology.

CON:
One of the more inefficient starship propulsion system, but could used for RCS or smaller craft, just not for primary sub-light propulsion.


Fusion-Plasma Rocket

What is it?
Deuterium pellets are injected into fusion generation at an amazing rate of 250 times a second. Electron guns would rise the temperature inside the pellets to cause an explosion at around the same rate, and a magnetic field would channel the blast has thrust. This could reach up 13% of C, allowing our fusion-plasma rocketship to reach Pandora in a few decades.



PRO:
The exhaust velocity would be around 250 miles per second, or around 13% of light speed or even as high as 20% of C, and it is possible for Jupiter to be a refueling station due to it's high levels of Deuterium.

CON:
The reason I'm still paying electric bills is because a fusion generators are still experimental  but the Europeans are close, and the other main element for the engine is deuterium. Heavy water is not common on Terra, but Jupiter has a great supply. That being said, some research work on a proposed fusion rocket ship called Discovery II that could get to Jupiter in 118 days, but had to carry 11 tons of those pellets...just imagine the load for a trip to Alpha Centauri or Sirius AB.

Bussard Interstellar Ramjet
What is it?
In 1960, Dr. Robert W. Bussard developed a interstellar propulsion system that drew its fuel from space itself. A cylinder shaped space vehicle uses powerful EM field to collect interstellar hydrogen that is compressed then expelled has propellant for a fusion rocket. The speed is relative when using the ramscoop, much would depend on the density of the hydrogen, drag via the collection of the medium, the thrust vs. mass, and if or when the collection system breaks from use. If the name seems familiar, the Enterprise-D has two 'Bussard Collectors' on the front of the warp nacelles (the red cap on the front) and were used to be emergency fuel sources for the warp drive or just for a nice show.

PRO:
There is no issue with mass, if the flow of the fuel is correct. Some sources estimate, if the conditions are correct, that a ramscoop ship could move at 77% of C, which is greater than a anti-matter rocket ship. That, coupled with the lean fuel needs (once under way), make the interstellar ramscoop a good choice.

CON:
According to some research, the Bussard Ramjet could achieve mean range 12% of C, and others say that greatly depends on the density of interstellar hydrogen, higher or lower. That could led the inability to maintain a constant speed.  To make matters worse, the collector array would have to be massive...like kilometers in size to scoop and the space craft would need to be moving at 6% of C in order to gather the needed hydrogen particles for thrust. That means our Ramjet-equipped Enterprise would need another type of propulsion until the desired speed is met...which adds mass to our ship. Having an object that large in space that is moving at a high rate of speed will certainly attach more than just hydrogen. Any crew of a Bussard Ramjet vessel would have to worry about micro-meteors and other types of collision on their ramscoop array.

Ion Thruster

What is it?
Ion propulsion has been proposed since the early part of the 20th century, and is in current use. This is a form of electric propulsion that uses an electrostatic field to excite particles to generate thrust via inert gas, like xenon. This system is being looked has a low-cost, low-mass propulsion system. In 1998, the NASA Deep Space 1 probe's NSTAR successfully used ion propulsion to intercept asteroid 9969 Braille. Currently, the NASA space probe, Dawn, is on its way to Ceres and Vesta with the help of three ion thrusters. This type of propulsion is  famous in science fiction for their usage  in the Star Wars Imperial TIE fighters.

PRO:
Scientifically proven current technology that has deployed on space probes, and given the efficiency, less fuel is needed. The ESA has a working prototype of a dual four-stage grid ion drive (DS4G) that produced 130 miles-per-second thrust, and NASA has kept their xenon-based ion engine running continually for five years. Powering this little seven kilo-watt wonder was either a nuclear or solar power source and this hallmarks the ability of an ion-based propulsion system to be efficient, reliability, and space-worthy.
CON:
Ion thrusters are by nature, low thrust, speed is builts up over time...one example reached 60 kilometer-per-second in four days and could take 80,000 years for travel between the stars. Bugatti Veyron it is not. This low-burn makes for ion thrusters being better for lower mass robotic missions.

Solar Sail and Beamed Solar Sail
What is it?
Are two ways to sail our way into the solar system and possible beyond, the solar sail that uses solar photons to push a hair-thin reflective carbon-fiber fabric at speeds relative to the size of the sail and distance from the sun. This is already proven technology, with an 3,400 foot version was tested at NASA vacuum labs, and in 2010, a small solar sail was deployed in low-Terran orbit. The Japanese IKAROS solar sail traveled toward Venus in 2010, and became the first interplanetary solar sail, demonstrating the technology could work for intrasolar missions. The second way is for faster space sails, the beam solar sail that uses a lens and light source, normally a laser to feed the sail. Much like using a electric fan on a model sail ship.

PRO:
Scientifically proven with current technology via real outer space tests, and NASA is moving forward with their use on the Sunjammer probe that explore our Sun in 2014. One big positive is that Solar Sail do not need fuel...if they pushed via solar pressure, that is.

CON:
Solar Sails must build up to speed, taking years, and the size of the sail determines the speed. NASA's Sunjammer will be 1,500 and generate 100,000 MPH of velocity after several years of being deployed, and at is going towards the sun. An interstellar solar sail wouldn't work that well. Solar pressure for good velocity depends on proximity to a star, and would be difficult in the wastes being the stars. To solve this issue, a laser could be used to generate pressure on the sails creating thrust. According to the January 2013 issue of National Geographic, for a beamed solar sail to reach Proxima Centauri in a few decades of travel time, the sail would be the size of Alabama and Mississippi combine and the laser would require the combined power output of Terra. And that is just to move a probe the size of a desk. Making matter worse for the beam interstellar solar sail is that the laser would have to be powered, creating more mass, and expanding the solar sail, which would mean that the laser and lens would have to be bigger, which means more sail....and so on.

Anti-Matter Rocket
What is it?
Protons and anti-protons are feed into a special chamber, were they crash into one another, creating a burst of charged particles that move at near the speed of light. A powerful magnetic field directs this flow of rapidly moving charged particles to become thrust for out Venture Star. According to the RDA ship from AVATAR, injection of hydrogen atoms into the charged plasma stream for more thrust.

PRO:
Some believe, including James Cameron, that AM rockets could achieve up to 70% of C (or 130,000 KPS) and be one of the more effective and efficient interstellar propulsion system available in the realm of hard science.

CON:
Anti-matter is the most expensive man-made item in existence, and could trillions of today's dollars to gas up the damned thing! Storage of anti-matter is also very difficult, because it reacts, violently, with matter. Storage is normally accomplished with a magnetic Penning Trap or could be done via cooling and a high vacuum environment. Also, due to the heat generated by an AM rocket, the radiator would need to be massive, think Florida, and may the Lords of Kobol protect you over you if a micro-meteor strikes them, because it would be much bigger than the habitat portions of the AM rocket ship.     

24 comments:

  1. Great post William.

    I always learn stuff here -and always have a good laugh too. Keep it coming !

    ReplyDelete
  2. This is one of those blogposts that I am simply out of my element on. Physics was never my strongest subject, and reading some of the professional research papers drove me to drink. But, I felt like it was important to list the major hard-science sub-light propulsion systems, and the high points of them. I'm just glad you enjoyed it.
    Thanks for reading and commenting!

    ReplyDelete
  3. Christopher PhoenixJanuary 22, 2013 at 5:41 PM

    Hi, William!! I enjoyed this blogpost- spacecraft propulsion has always been one of my favorite subjects. I would like to make a few corrections to your list, though- I spotted a few errors, possibly from your sources, and the list on the whole seems a bit haphazard. "Crackpot physics" space drives that rely on vacuum energy don't really fit right next to plasma engines that are already running in laboratories, and said plasma engines don't really classify as starship drives unless you intend to wait for well over 10,000 years to reach Proxima Centauri.

    A number of the propulsion systems you mention are rockets, which work by expelling propellent out the back in order to be pushed by the reaction force. Whether a rocket expels the products of chemical combustion or a gentle stream of ions, all rockets have two main limitations- the amount of force they get in respect to propellent used per unit time, which is called specific impulse (ISP), and the amount of thrust the engine can generate. Rockets are limited by the amount of propellent they can carry and how much total thrust they can get by expelling all this propellent. Basically, ISP is kind of like the MPG of a car. A low ISP means that you get less total amount of force per unit mass of your propellent, and must carry a lot of propellent to get where you want to go. The thrust of engine is important if you want to take off against the gravitational field of a planet or get up to speed quickly.

    Chemical rockets can have very high thrust, but guzzle the gas. Ion rockets are very low thrust (and could never take off of a planet), but can keep running for months and eventually hit very high velocities. The ISP is related to the exhaust velocity of the rocket, that is, how fast the propellent is going when it is spewed out. The exhaust from a chemical rocket is relatively slow compared to the speeds we wish to reach (about 3km/s from what I've heard), while an ion engine expels neutral plasma at a much higher velocity, thus getting a much higher ISP.

    Our basic problem is respect to interstellar travel, is that the distances are very, very large (tens of trillions of miles!!) and even getting there in sometime closer to a century requires very high delta-Vs (term for change in velocity, the proper term for evaluating the total amount of go you can get from a rocket). But, all are current rockets- even more efficient ones like NERVA nuke thermal or super-duper ion engines- require such huge masses of propellent for even slow interstellar flights it is just absurd, and at feasible mass ratios (the ratio of how much of the rocket is structure and payload to how much consists of propellent for the every-hungry rockets) you just take too long. I don't know exactly how long it takes to turn into a skeleton, but 10,000 years is undoubtedly more than enough time for your skeleton to crumble into dust before you even approach Alpha C.

    So, in addition to the speed problem, we have the propellent mass problem. The obvious solution is to try to build even better and more powerful rockets with ever greater fuel-mass to energy conversion ratios and ever higher exhaust velocities- thus ever higher ISPs. This was the insight of the German rocket engineer Eugene Sanger, who imagined jet propulsion systems based on nuclear energy in which the exhaust stream is a beam of light, and the radiation pressure pushes the ship. If we want to travel at significant fractions of the speed of light, our exhaust velocities must be close to the speed of light- high energy jets of energetic particles or photons powered by fusion or antimatter annihilation. At the very least, our exhaust velocities must be much greater than those we play with today. This is why we look into antimatter rockets and so on- with a exhaust velocity as high as antimatter might allow, we can achieve missions impossible with todays chemical or even nuclear rockets.

    ReplyDelete
  4. Christopher PhoenixJanuary 22, 2013 at 6:09 PM

    You discussed several types of rockets. However, antimatter rockets are the only ones that show potential for fast interstellar flight- you list two, the VARIES system and the one shown in AVATAR. Fusion rockets might be able to allow us to launch something at 10% of C, possibly, but require very large amounts of fuel- just look at the size of that rocket!!

    The kind of antimatter rockets that might be used for interstellar travel are the plasma core and beam-core antimatter rockets. Plasma core engines would heat a large mass of propellent by injecting antiparticles, and exhaust the resulting high-temperature plasma with magnetic fields. In a beam-core engine, and equal amount of particles and antiparticles would annihilate and the resulting pion explosion be directed out the back.

    VARIES includes a bank of solar panels and an antimatter maker to allow the rocket ship to refuel itself at the destination star. If the ship can refuel itself without relying on antimatter from home, the astronauts will have fuel for the return journey, and they won't have to drag it all the way from home.

    VARIES is not the VASIMR system, which is a plasma rocket that is currently being tested. VARIES's maximum velocity will be well over 125 miles per second, which is only .067% of C according to my calculator- 6% of C would be over 11,000 miles per second. 125 mi/s is the quoted speed of the Solar Probe Plus, which would take 6,450 years to reach a nearby star. VARIES would take a crew to another star and return to Earth within their lifetime, so it must travel much faster.

    You also mention ramjets. Ramjets are an effort to get around the mass-ratio problem by scooping up the very thin interstellar medium for use as fuel in a fusion the rocket. The problem is that the ion scoop would likely create more drag than thrust, and what we can scoop up is not good fuel for fusion reactors. One variant would only use the scooped up mass as propellent, in what is called a Ram Augmented Interstellar Rocket (RAIR). The idea of gather up our own propellent as we go along is a valuable one, though, since with an unlimited supply of fuel the ship could accelerate continuously to near light speed.

    Various proposals involving very large lightweight sails can make closes approaches to the sun, or be pushed by various beamed energy sources (laser, pellet stream, etc.) to reach high speeds. However, these have their own limitations, including the high energy requirements and the attenuation of the beam with distance. They do not have to carry any fuel or engine, however, which makes them quite valuable.

    ReplyDelete
  5. Christopher PhoenixJanuary 22, 2013 at 6:46 PM

    Nuclear pulse propulsion seems to be pretty slow- Freeman Dyson's nuclear pulse starship would take several hundred years to reach the nearby stars, and perhaps longer.

    I haven't seen any discussion of using pure antimatter bombs for propulsion, perhaps because it easier to extract energy from M/AM propellent in a steady burn rather than a messy explosion. Antimatter-catalyzed pulse propulsion uses small amounts of antimatter to trigger subcritical fissionable fuel, or to trigger pellets of fusion fuel. So, they are really just a sanitized version of the original concept. So, too, is the Daedalus rocket- triggering fusion pellets with electron beams is not quite as controversial as actually using bombs, but we can use bombs today.

    I have not heard of Mustafa's drive, but Woodward's Mach effect drive has been knocking around for a while. Efforts to find "breakthrough" space drives have been around for a while- google the Dean Drive and you will see what I mean. Quite a few cranks have been involved, too, so be careful what you reference. Marc Millis's discussion of what would be required is pretty good, you should google the Breakthrough Propulsion Physics project. They have a good website that discusses WHY interstellar travel is so tough, and what we are trying to do to crack the problem. The problem with all these "breakthrough" ideas is that they require currently unproven physics concepts, so they aren't even at the point where we know if they are possible, let alone at the point of building one.

    http://www.nasa.gov/centers/glenn/technology/warp/warp.html

    In terms of breakthrough sublight drives, I would have mentioned the idea of an idealized "space drive" that converts onboard energy totally into thrust without expelling exhaust. This would seem to fly in the face of conservation of momentum, so it would have to involve new physics that would describe "something" in the vacuum of space that we could push against. Maybe, if we changed space behind the spaceship, space would then push on the craft and move it- a bit like those soap boats being driven along by a drop of detergent. All this is purely hypothetical at this point. We don't even know if physical law will allow for such craft.

    Some other exotic drives, featured in some SF stories, are those that use the quantum vacuum. We now know that the seemingly "empty" space around us roils with activity in the quantum realm- particles pop in and out of existence all the time, and it may be that a cupful of vacuum contains enough energy to boil away all the oceans of Earth, according to some calculations. This is all very, very complex physics and some scientists question if our calculations reflect physical reality, but quantum vacuum is real and does in fact cause forces, as seen in the Casimr experiment.

    Some people have proposed starship drives based on tapping the quantum vacuum, sometimes termed "quantum ramjets". If we could tap almost infinite energy from empty space, we could accelerate to very high speeds without using any fuel- and the whole universe would be open to us. Such drives are sometimes called "quantum drives", "zero point energy drives", or "GUT drives" in fiction. Unfortunately, we don't know if the quantum vacuum can in fact be tapped, and it sounds a lot like something for nothing to me- so this is just speculation for now.

    It has also been suggested that the quantum vacuum might be responsible for inertia, so if we could somehow manipulate the vacuum, maybe we could make "inertia drives". This is also still only speculation, so no inertialess starship for you yet. I would be worried about the possible effects of lowering inertia on living organisms- would we die when our blood lost all inertia and raced through our bloodstream at hundreds of miles per hour?

    ReplyDelete
  6. Christopher PhoenixJanuary 22, 2013 at 6:56 PM

    Man, I seem to have made a longer comment than the blogpost!! D: But, I cannot help it.

    In regards to acceleration- you are right that it is unhealthy for astronauts to be under accelerations much than 1g for prolonged periods of time, but 12g is not quite chunky salsa territory if you are safely strapped in. Modern day fighter pilots withstand 10-12g during acrobatic maneuvers. By 25g and over, though, you are quite likely to be injured. The highest acceleration ever reached by a human was about 46.2 g during a rocket sled experiment, and the subject suffered some damage to his vision.

    The Stansilaw Lem book "Return From the Stars" gives some unpleasant details as to the woes of high acceleration as experienced by the interstellar crews. During training, the astronauts are made to endure accelerations so high blood squeezes through the pores in their backs!! After returning from their flight, they find that their muscles have built up to a point that they look like Hector out of the Trojan War because they hibernated at 2g for prolonged periods of time. In Buzz Aldrin's "Encounter With Tiber", the alien Nisuans immerse themselves in fluid and fill every body cavity with supporting gel in order to withstand tremendous, deadly accelerations in the early phases of their interstellar flights.

    Ironically, one paper I have read on interstellar probes indicates that accelerations over 1g do not cut down the timespans of flights to nearby stars by much, so maybe our crews won't have to endure the crushing accelerations faced by those fictional astronauts.

    Damn, I just never shut up when we get on this topic. I should sign these comments, "A Starfleet Cadet". XD I guess you could guess where I would end up if I lived during the 23rd century...

    ReplyDelete
  7. What kills me about this subject is that the American education does a shit job on educating kids about the real nature of space and how we could get to point b from a...too many people, me included, had science fiction to teach them. I think you avoided that Mr. Phoenix, which is good for this blogpost!
    Some of the propulsion systems were hard to get firm number on % of C, math and I just do not get along! I plugged some numbers in and then were was debate on different sites about % of C...ugh.
    Thanks for clearing those points up! Another point that confused the hell out of me was how many sub-types of different engines. There were lists of plasma fusion type engines and I couldn't bring myself to list all of them. Seriously, it would have Jack and Cokes until I passed out!
    Some of the more exotic drive systems took me quite a bit of reading and I threw some out, like the zero-point systems...sounded too Black Mesa for my tastes. I've read of vacuum based systems, but it seems so odd to me.
    When deep space exploration does happen, it could be like early automobiles, where different engines and fuel types were tested or we could even have the VHS/BetaMax wars all over again!
    Gee Force in terms of space travel is one of those elements I'm still getting used to. Dude! You totally mentioned Encounter with Tiber! Haven't thought about that book in a decade!
    Chief Engineer Phoenix has a nice ring to it...
    Thanks for reading and commenting!

    ReplyDelete
  8. Oh...I wanted to make another point on the blogpost but did not. Given my belief in UFOs...I know, very Fox Mulder of me, but there is someway that they or them are coming here. Even if, some of the crackpots online believe, that the aliens have a lunar base, they still came from some other star system. If they can do it...why can't we? Travel between stars is possible if they have been coming here since the dawn of human civilization.

    ReplyDelete
  9. Christopher PhoenixJanuary 23, 2013 at 4:29 PM

    Yeah, American education does not seem to do a good job teaching kids about space and space travel. I think that self-education is more important than accepting what you are spoon fed. With the number of books, lecture courses on DVDs, and even streamed science courses from places like MIT, it is easy to learn nowadays. I remember reading the novel version of "2001" and envying the astronauts their electronic teaching consoles, but nowadays that sort of tech is real- I've found science and math courses streamed from places like MIT on youtube!!

    For reference, C is approximately 300,000 km/s or 186,000 miles/sec., so you can convert to and from % of C pretty quickly by converting a speed into the appropriate units and dividing by the speed of light to get the decimal form. For instance- 13,110 km/s would be 13,110/300,000=0.0437, or 4.37% C. Fast enough to reach Alpha C in 100 years. Obviously, I chose those numbers because of that. Heh. It can be surprising how fast even "slow" speeds are in space- at those speeds, a starship would reach the Moon in thirty seconds!! That is a distance the Apollo astronauts took three days to cross, and this thing would do the same in thirty seconds but still takes a century to reach the nearest stars.

    Well, the one thing I wanted to make clear was that no matter how many different sub-types of plasma engines you might see, they are all just rockets. The things to keep in mind are how much thrust a rocket can get from its fuel, and how long that fuel will last.

    Propulsion schemes based on the quantum vacuum are oddly popular both in speculation on starflight and in a number of SF stories. I think the reason why is that pushing a payload to very high speeds necessarily requires a LOT of energy, as kinetic energy increases by the square of the speed. So, even when you accept the difficulties of having no warp drive, you face the problem of how to get your massive relativistic starship up to speed. A virtually limitless source of energy found in every cubic centimeter of space would obviously be very helpful, if we could tap it. The "quantum ramjet" would convert energy from the quantum vacuum into radiant energy, and use radiation pressure to push the ship.

    Additionally, these systems have something of an air of plausibility because of the Casimir effect. When two metal plates are brought close together, about a few atomic diameters apart, they exclude some wavelengths of the virtual photons popping in and out of existence between them, and create a force that either pulls them together or repulses them apart. This force supposedly has to do with the zero-point field. This is very complex physics and not for the uninitiated, but it is odd to know that "empty" space does create forces we can detect.

    Here is an interesting discussion of various fictional plausible starships, including the Wahkopem Zomos and the Venture Star from AVATAR. http://www.icarusinterstellar.org/blueprints-for-a-starship/

    ReplyDelete
  10. Christopher PhoenixJanuary 23, 2013 at 4:50 PM

    On UFOs- what is funny is that I have read about flying saucers and our purported alien visitors for years, in everything from books on UFOs to "Chariots of the Gods".

    I even got my first exposure to the idea of finding ways to achieve starflight with the physics that we have from a book titled "Flying Saucers and Science" by Stanton Friedman, who dismisses pronouncements that interstellar flight is impossible in the second chapter of the book. He suggests that the flying saucers are Earth Excursion Modules (EEMs) coming from giant interstellar motherships which are not suited to landing on planets.

    However, I have never seen any really conclusive evidence to back the "they-are-here-and-watching-us" school of thought, even though I think that interstellar travel is possible and that the kind of chance communication advocated by SETI is the last way an alien civilization would go about finding and communicating with their neighbors. I do wonder if aliens could have visited Earth a long time ago, perhaps even before human civilization arose, and we have simply never found any traces of this contact. Maybe they are here- but no one has conclusively gone through all the sightings to find conclusive evidence of this, or answered who "they" are.

    I do think that interstellar flight is possible. Fusion and antimatter annihilation, or even more exotic energy sources, can provide the energy required for interstellar travel. The ship could have a multigenerational crew, or the astronauts could hibernate to sleep through years or decades. Alternatively, if the ship can travel at near-light speeds, the astronauts could take advantage of time dilation to cover vast distances in under a human lifetime. There are just too many different ways to explore the stars at sublight speeds to dismiss interstellar fight out of hand. Probably, there are civilizations out there for whom the invention of interstellar flight is ancient history.

    Oh, and on "Encounter With Tiber"- I enjoyed the parts about the journey of the Wahkopem Zomos, and Nisuan disaster on Earth. I rather liked the Nisuan landers, especially how they could pump air out of their interior in order to become an aerostat. I never thought of combining a vacuum airship and a rocket.

    I like the idea of a steam rifle, too, perhaps one could work by rapidly injecting something like sulfuric acid into the water in order to boil it and propel a bullet with the steam explosion. Gives us something different from a standard gunpowder combustion hand weapon.

    ReplyDelete
  11. Alas, your blogpost does contain a few errors, which others have remarked on.
    If you are interested, I have a list of rocket propulsion systems. Google "Atomic Rockets engine list" (most comment systems do not allow including URLs)

    You did miss one entertaining propulsion system. Google "Zubrin nuclear salt water rocket". Remember the nuclear pulse propulsion from your blogpost? Where the rocket is driven by a series of discrete nuclear detonations?

    Well, imagine CONTINUOUSLY detonating nuclear rocket.
    Most propulsion systems are either high-thrust/low-specific-impulse (like chemical rockets) or low-thrust/high-specific-impulse (like ion drive). Zubrin's NSWR is the only one I've ever seen that was both high thrust and high specific impulse.

    It is a pity that when you ask Zubrin how you keep a continuously detonating nuclear explosion from annihilating your spaceship he gets sort of vague and says "...and then a miracle happens..."

    ReplyDelete
  12. Hi, I've read your series and find it fun and interesting; but now I'm planning to write a short story, but need to know just what would be an ideal propulsion system for my heroes. I'm thinking back to "Outland", so in your opinion, what kind of propulsion system would make it feasible to go to "IO" to mine whatever they were mining?

    ReplyDelete
  13. Time is one way to think about how to select a sub-light drive system. How fast do your characters need to get to Io and back. Then think about level of technology of your fictional world. If they can create Anti-Matter readily, than things are much simpler. Given that Io is very near Jupiter, a prime source for He3, allowing for use of a Fusion Rocket to be a good choice. If you want something different, than Nuclear Pulse Propulsion is a rare drive in scifi.

    ReplyDelete
  14. must mention VASIMR is actually VaRiable Specific Impulse Magnetoplasma Rocket, it is a more powerful equivalent of an ion engine. personally my money would be on the bussrad ramjet, it would be a hell of an engineering challenge but if(when might be a better word here) one works it will make interstellar exploration a possibility as opposed to a fantasy.

    ReplyDelete
  15. After working on the FTL travel blogpost, I think it is interesting how much sub-light is glanced over and the real work is devoted to FTL technology, while in reality, FTL is a pipe dream, and sub-light is the real challenge.

    ReplyDelete
  16. even for a mars voyage, let alone an interstellar one, chemical rockets become prohibitively expensive so nuclear power WILL be required. Tree-hugging types must get over the fears and realise that as long as your launch vehicle is reliable then nuclear power in space is a very safe thing to develop and use. the bussard ramjet is another excellent idea and would be ideal for an interstellar flight if certain problems with constructing the massive scoop and the issue of extreme drag due to the hydrogen being collected having to be accelerated to the ship's speed can be solved, if the scoop can be built but the drag issue cannot be beaten there is always RAIR (ram augmented interstellar rocket) which uses onboard power supplies (from fusion, or if we can't dvelop that then fission) fuels but get's it's reaction mass from the scoop. as the reaction mass doesn't need to be accelerated up to the speed of the rocket before it can be used (where hydrogen collected to feed a reactor would need such an acceleration) the drag problem is rather reduced. if a true bussard ramjet, or a RAIR rocket can't be developed then there are options for a fusion powered rocket or a fission powered one. the fusion rocket might use fusion to heat a separate reaction mass or it may use the helium product from the reactions as it's propellant. the fission rocket usually has a fluid pumped past a hot reactor, this heating expands the reaction mass and shoots it from the rear at a nice high exhaust velocity. specifically NERVA was an investigation into using a fission rocket with a hot reactor and propellant being pumped past, your image in the nerva section of this post actually shows the JIMO (jupiter icy moons) probe concept which although it would have carried a fission rector would use it for power generation not propulsion, in the case of JIMO the reactor would supply electrical power to ion or vasimr(vasimr is usually used to mean VARiable Specific Impulse Magnetoplasma Rocket as it is in the case of JIMO) engines where on a nerva craft the reactor directly heats a fluid giving better thrust but possibly slightly lower delta V. also your mention that the technology of nerva would help with a bussard ramjet is somewhat incorrect, a bussard ramjet would use fusion where the nerva program was only ever concerned with developing a particular type of fission rocket(the solid core nuclear thermal rocket to be precise). although the act of developing nerva might give us a better understanding for when the time comes for the generation of rockets after that. the most shocking fact in the end is that we could build nerva rockets TODAY and they would work BETTER than the best chemical propulsion systems in use, it's a real shame that nerva research stopped (largely due to a UN treaty). we could also build orion drives TODAY but they could be a bit messy, their greatest danger to us coming from the EMP they could produce because if launched from some places on earth's surface there would be no-one within the potential fallout danger radius.another propulsion system you might want to consider is a nuclear lightbulb, this is another type of nuclear thermal rocket but this time it is a gas core with the fissioning gas kept safely separate from the exhaust stream it heats by use of quartz walls (hence the name lightbulb). once again the lightbulb is a technology that although it couldn't be built with today's technology it could be built with the tech we WOULD have today IF nerva had been fully developed. in the end the key things for a propulsion system are delta V and thrust, current chemical rockets have plenty of thrust, so can accelerate fast but absolutely rubbish delta V, so burn out before reaching the speeds you need for manned interplanetary travel. ion rockets have great delta V but very poor thrust so are useful for unmanned probes to planets in our system but would be too slowly accelerating to reach another star easily, they could never lift a craft from earth to orbit.

    ReplyDelete
  17. continued, this site doesn't seem to like posts over 4000 characters.

    nuclear systems have thrust somewhere on a scale from "decent" to "brilliant" depending which one you choose and delta V on a scale from "nice" to "perfect", the key thing is you trade one for the other. vasimr is not as good as a nuclear system in either respect but it is a pointer of how the perfect nuclear rocket could function with different gears, one for high thrust, one for high delta V, and some inbetween. this gear change is done by getting the engine to put unit amounts of energy into large amounts of reaction mass for high thrust(but low exhaust velocity, which is linearly related to delta V) or the same amount of energy into a far smaller mass of propellant to give it a higher exhaust velocity hence a better delta V. if you can find an engine type that gives high thrust and high delta V you have a "torchship", whether this is possible is currently uncertain but it is clear from the equations that one of the key requirements is a huge amount of power (as in joules per second) going into the reaction mass. one can calculate that to get high thrust and delta V from a fusion motor at the same time might need power requirements similar to earth's overall consumption, it's tough but even a few grams of hydrogen fusing per second could do it.

    ReplyDelete
  18. Hi William
    About the beam sails concept – I believe you didn’t understand it, the power generator & beam emitter aren’t locate on the vessel but stays at home solar system while the sail propelled by the beam. The mass of the power generator & beam emitter aren’t relevant to the sail acceleration at all.
    Instead of mass problem there's a deceleration and return home problems:
    Deceleration – every interstellar vessel must spent a large portion of the journey & fuel on deceleration before enter to destination solar system, since the beam sail don’t have onboard propulsion and the beam at home can only repulse not attract then the sail might served as unmanned probe that just pass thru the target solar system/s, taking pictures and transmitting back home. Like the Voyager probes were.
    If you want to decelerate the sail then you have to use two stage sail, before deceleration the first stage sail will detached from the second, the beam will be aimed to the first stage that will reflect the beam back to the second stage, the result- first stage continue to accelerate while the second decelerate.
    Return home – the crew/A.I. onboard will have to construct beam emitter in the target solar system that could push them/it back home.

    Yoel
    P.S. congratulation for your new job!

    ReplyDelete
  19. war in the future?. No thanks. WAR NEVER MORE.

    ReplyDelete
  20. This comment has been removed by the author.

    ReplyDelete
  21. Great article! There are a few issues with the science, such as engines being described as having a "top speed." Not only does that not usefully describe the capabilities of an engine, the whole notion of speed is especially ambiguous in space travel and completely dependent on one's frame of reference. For instance, when departing Earth orbit and entering Solar orbit, one's orbital speed suddenly jumps from between 3 and 7 km/s up to 30 km/s, even though no acceleration has occurred. The frame of reference has simply changed. A more accurate description of an engine's performance is maximum delta-v, or total change in velocity. Even this is ambiguous, though, because it is strongly affected by the propellant-to-payload ratio of the rocket. If you have more fuel, you can always go faster--regardless of what engine is being used.

    The Woodward effect and Mustafa drive deserve to be thrown in the trash. They are perpetual motion machines--just like the Dean drive--but with more current pseudoscience thrown around to confuse people. The problem with quantum fluctuations in mass is that they are fundamentally random. There is absolutely no way to change the probability of whether a particle will briefly increase or decrease in mass. When the probability is 50%, there ends up being no net motion. The Woodward drive wiggles its particles back and forth in futility. Even when one invokes spooky quantum physics, the universe always balances its books and conserves momentum at the macro-scale. Always.

    Also, I'd like to point out that the acronym VASIMR stands for something else. It's another type of plasma rocket, and it deserves to be on this list as well. It's really quite interesting! The main advantage is that it can "shift gears," trading exhaust velocity for greater thrust. This means that it can start out with the oomph and power of a chemical rocket to accelerate hard and break orbit quickly, then it can switch over to "cruise mode" once in deep space, giving the spacecraft the huge exhaust velocity and fuel efficiency of something like an ion engine. It's also very near to being ready for flight.
    https://en.wikipedia.org/wiki/Variable_Specific_Impulse_Magnetoplasma_Rocket

    ReplyDelete
  22. better: Future Peace stories. Around the World everybody must to say: No more Wars...No more Nations...No more Frontiers

    ReplyDelete
  23. These are the examples of human intelligence and brain. This theory of matter and anti-matter is actually very interesting to know as I always read that universe is composed of matter and vacuum.
    Regards:
    MA Gun License

    ReplyDelete