October 18, 2004
90 Day Mars Trip With Magnetic Sail Plasma Beam Propulsion?
90 days to Mars? I want to go! (same article here)
A new means of propelling spacecraft being developed at the University of Washington could dramatically cut the time needed for astronauts to travel to and from Mars and could make humans a permanent fixture in space.
In fact, with magnetized-beam plasma propulsion, or mag-beam, quick trips to distant parts of the solar system could become routine, said Robert Winglee, a UW Earth and space sciences professor who is leading the project.
Currently, using conventional technology and adjusting for the orbits of both the Earth and Mars around the sun, it would take astronauts about 2.5 years to travel to Mars, conduct their scientific mission and return.
"We're trying to get to Mars and back in 90 days," Winglee said. "Our philosophy is that, if it's going to take two-and-a-half years, the chances of a successful mission are pretty low."
Mag-beam is one of 12 proposals that this month began receiving support from the National Aeronautics and Space Administration's Institute for Advanced Concepts. Each gets $75,000 for a six-month study to validate the concept and identify challenges in developing it. Projects that make it through that phase are eligible for as much as $400,000 more over two years.
Note that NASA's funding level for this concept is miniscule. Meanwhile billions per year are spent on the obsolete and flawed Space Shuttle. For a complete list of the 12 funded projects see here.
A space station beam generator would shoot ions at the spacecraft and the spacecraft would use a magnetic sail to capture the momentum of the particles blowing at it from what would essentially be an ion wind blown at the spacecraft.
Under the mag-beam concept, a space-based station would generate a stream of magnetized ions that would interact with a magnetic sail on a spacecraft and propel it through the solar system at high speeds that increase with the size of the plasma beam. Winglee estimates that a control nozzle 32 meters wide would generate a plasma beam capable of propelling a spacecraft at 11.7 kilometers per second. That translates to more than 26,000 miles an hour or more than 625,000 miles a day.
Mars is an average of 48 million miles from Earth, though the distance can vary greatly depending on where the two planets are in their orbits around the sun. At that distance, a spacecraft traveling 625,000 miles a day would take more than 76 days to get to the red planet. But Winglee is working on ways to devise even greater speeds so the round trip could be accomplished in three months.
But to make such high speeds practical, another plasma unit must be stationed on a platform at the other end of the trip to apply brakes to the spacecraft.
"Rather than a spacecraft having to carry these big powerful propulsion units, you can have much smaller payloads," he said.
Winglee envisions units being placed around the solar system by missions already planned by NASA. One could be used as an integral part of a research mission to Jupiter, for instance, and then left in orbit there when the mission is completed. Units placed farther out in the solar system would use nuclear power to create the ionized plasma; those closer to the sun would be able to use electricity generated by solar panels.
The mag-beam concept grew out of an earlier effort Winglee led to develop a system called mini-magnetospheric plasma propulsion. In that system, a plasma bubble would be created around a spacecraft and sail on the solar wind. The mag-beam concept removes reliance on the solar wind, replacing it with a plasma beam that can be controlled for strength and direction.
A mag-beam test mission could be possible within five years if financial support remains consistent, he said. The project will be among the topics during the sixth annual NASA Advanced Concepts Institute meeting Tuesday and Wednesday at the Grand Hyatt Hotel in Seattle. The meeting is free and open to the public.
Winglee acknowledges that it would take an initial investment of billions of dollars to place stations around the solar system. But once they are in place, their power sources should allow them to generate plasma indefinitely. The system ultimately would reduce spacecraft costs, since individual craft would no longer have to carry their own propulsion systems. They would get up to speed quickly with a strong push from a plasma station, then coast at high speed until they reach their destination, where they would be slowed by another plasma station.
"This would facilitate a permanent human presence in space," Winglee said. "That's what we are trying to get to."
I've seen claims that the Space Shuttle has had as much as $100 billion spent on it and we have little to show for all that money. For a much smaller amount of money we could have a set of space highways running around the solar system moving spacecraft at faster speeds than any conventional propulsion system could achieve.
A test flight could be made within 5 years with proper funding.
“If we are solidly funded we could at least mount a test flight in five years,” says Winglee. A test flight alone would cost $1 million, while a trip to Mars would cost billions because it would require building a space station there.
Leonard David of Space.com has an article discussing other advanced propulsion concepts NASA is funding. But keep in mind that the funding level for most of these projects is still pretty low. If the Space Shuttle was retired and that money put into advanced propulsion concepts we could greatly accelerate the rate of development of much more advanced approaches to space travel.
Great idea. Where do I sign up?
Reminds me of the way the Moties propelled their ship in The Mote in God's Eye.
Some random thoughts:
1. Permanent deployment of transmitters of this type would probably require an orbit 90' perpendicular to the plane of the ecliptic to prevent accidental crossing of beams in high traffic situations. Of course an initial station in near earth orbit should be able to power future stations to their permanent locations...
2. What prevents the transmitter from moving in the exact opposite direction from the beam it is transmitting? If the beam itself provides momentum would it not be practical to use it as an engine in a spacecraft itself rather than as an external system?
3. What are the implications of such devices for orbit modification of comets/asteroids.
4. What is the potential of such a device for use as a weapon against planetary targets or other space based vehicles?
When I first saw this story on Google News I thought "That's stupid." Not that the science was stupid (I'm sure it's quite creative), but my thinking was along the line of "NASA should be investing in propulsion technologies that can get us to Mars in the first place." The need for a decelerator at the other end suggests a level of infrastructure buildout on another frickin' planet that we are decades away from at least. We haven't even sent the Nina, Pinta or Santa Maria yet, and they're wasting money on inter-sytem light rail?
But then the 'big picture' hit me. NASA, which like most government agencies, always seems to be about 20-30 years behind the private sector in non-military innovation, has finally grokked the angel investing/ venture capital model which rewrote the start-up book back in the 80's and 90's. Even is this particular investment is a flop, the fact that they're finally using financial incentives to nurture and encourage quasi-private sector research is a huge step in the right direction.
I sure hope a couple of these technologies take off for at least two reasons. One, I want to go to Mars myself. Two though, I don't want NASA to fund these twelve, get little result, and get discouraged. They might retreat back to their old ways at that point and once again we'd lose billions to subsidizing poorly designed rockets.
PS - It didn't occur to me until I reread the story a second time that the Magneto-Slingshot thingy doesn't absolutely have to have a decelerator at the other end if you're willing to sacrifice speed. This would be a cool way to toss probes at the outer planets and the Oort cloud. Like the man said, taking the inter-sytem grade engine off the probe gives you a lot more flexibility.
PPS - How accurate does the incoming craft's trajectory have to be to balance perfectly on the decelerating beam? Think about it. You're essentially pushing against a huge amount of inertia with a magnet - which is damn slippery. Unlesss I'm misunderstanding something it seems like the decelerator would have to be absolutely perfectly over the craft's center of gravity to not push it off course. It would be like decelerating a bullet without deflecting the bullet.
PPPS - I would hate to see one of these things be used to through kinetic weapons from the Moon to the Earth. Considering the gravity difference it would be like throughing rocks down a well.
Uh...no. We already have the "advanced technology" for a 90 trip to Mars. The prototype VASMIR engine provides constant plasma thrust to a space vehicle and can theoretically cut the transit from 270 days to less than 90. The engine will be space-tested on a satellite in a couple of years and should be ready for use by the time we're ready to go to Mars.
The real holdup right now, aside from building and boosting the components into space, is radiation shielding. Out beyond the Van Allen Belts you can get your lifetime maximum exposure to radiation *right quick*. Mars has virtually no protection on the surface from radiation so explorers will have to build bermed shelters quickly and limit their exposure time on the surface. NASA is working on that.
#2 - Good question. What's the range on these suckers? It might be better to have the actual accelerator and decelerator on something big - you know, like the moon.
#3 - Not much if the asteroid isn't magnetic.
#4 - I thought about that too, but two things came to me. For firing an armed warhead, not much. I think there's nothing it could do that an ICBM couldn't, and the ICBM can be fired anywhere on earth. As for kinetic weapons think lots of damage, neatly contained. During the Iraqi invasion we dropped bombs that were essentially big rocks. We could destroy one building and leave the rest of the buildings untouched. A kinetic weapon would need a very high rate of fire to be an effective weapon of mass-war.
Different tools for different jobs. The VASMIR engine is the craft that gets us to Mars, and perhaps builds the decelerator. The Magneto-Slingshots would be for the inter-system commuter.
Total non-techie question here. How will travelling at 26,000 miles per hour affect the human cargo? Does no "g" mean no significant forces exerted on the human body at these speeds? Just curious.
Yaarh, me space hearties! Five AU's before the mast...
It's an interesting idea. Doing something like that would be a lot easier on the wallet and power source than making a thousand engines and adding their weight to each intrasystem voyage. Just the lift-off cost would be worth a couple billion per trip. Not to mention that one engine is a lot easier to maintain.
There's some interesting questions, though. A kinetic weapon is much more serious than just the energy it would pick up from gravity, although that alone would be quite a problem. 11.7 kilometers per second. If you took a large chunk of ceramic coated steel and aimed it at the Earth, you'd be able to do some damage, saying you aimed it right so that it didn't get too many loses from friction, I'd think you'd have the makings of a bad sci-fi movie. Although the rock responsible for the K-T extinction, which nothing larger than a chicken managed to survive, was huge, it was moving slower than this possible system could move things. That chunk of metal could knock a nice big whole in a city or two. Now imagine a random, large, and metal-rich asteroid passing nearby... and some moron hiting the wrong buttons.
That said, it's no more dangerous than having tons upon tons of rocketfuel near a major city, and it's much easier on the wallet.
Speed doesn't effect us, unless we run into something. What causes blackouts & such is the acceleration. This sort of system has a very slow acceleration, but isn't limited by fuel. As long as you're in range of a beam transmitter, you've got an unlimited total acceleration or delta-V. (delta-V is change of velocity)The difficulty, of course, is that your ship has no engines of its own. If something should happen to the transmitter, you're FUBARed.
A few points on the practicability of a decelerator on the Mars end:
1) Imagine a spaceship with a magnetic sail but with the rocketry needed to decelerate. Well, it could carry only deceleration fuel, not acceleration fuel. That would be a big savings right there. It could carry a lot more payload.
2) Manning a decelerator would be difficult. One big problem is radiation. Away from Earth there is no Van Allen Belt. If the decelerator was in Mars orbit it would need enormous shielding for its operators. How big would the shielding need to be?
3) An operational decelerator could get replacement staff shipped to it at regular intervals once it was operational.
4) An automated deceleator might not be as reliable as a manned accelerator. However, an automated accelerator could be used to send supplies. Humans weigh only a small fraction of their supplies.
5) Multiple decelerators (automated or manned) could be sent to Mars to provide redundancy.
Mars, Mars, Mars. There's nothing on Mars. It's too far away. It's too hard to get to.
Why can't we just start with something practical like a moon colony? We've been there. We know how to do it. There's stuff to be done up there. And, it's a perfect way station to Mars if and when we decide to go there.
The shuttle is merely a symptom. NASA's problem is a lack of focus. Let's resolve to go back to the moon and then do it.
so take 1000kg going at 11.7 km/s you get 136.89 GJ or about 68 tons TNT equivalent...
now since you don't need to decelerate... you can probably amp up the speed... at least doubling it (and thus getting 270 tons TNT equivalent per 1000kg of mass)
so for a space shuttle equivalent (104 000 kg at landing) you get 28 kilotons.. fairly respectable as a weapon...
amp up the weight a bit, to say a 100m diameter ball of iron (1.16 billion kg) and its 280 MT
thats one hell of a weapon... and we're ignoring gravity, which would impart a fair kick for an aerodynamic object...
When the initial investment is paid off, will they take down the tollbooths?
Odd. All that mention of velocity, and absolutely not a scrap of reference to acceleration time. The beam only needs to be on while acceleration is taking place, and I'm confident the issue of how long it actually takes to accelerate to 11.7 km/s using a sail system isn't one that's lost on the NASA crowd. Also missing is how, at distances of millions of kilometers, one can keep a beam of particles from diverging to the point where most of the energy doesn't fall on the sail. Especially when they're ions, and tend to want to get the hell away from each other.
Maybe it's the magnetic part. Still, I'd want to see some evidence that one can keep the beam collimated over these distances. Not to mention, point it stable. Not to mention, keep the beam generator in place in the presence of the substantial reaction force. Not to mention, what the solar wind and other externals are going to do to the beam. But I guess that's why we fund this sort of thing.
#2 - Solution: 2 mag-beams, pointing in opposite directions and firing simultaneously. The rear-facing beam should be unfocused, so as to not accdentally accelerate something else.
As others have pointed out, this sort of technology has been proposed before -- light-sails etc. (The Mote In God's Eye, Niven's The Fourth Profession). But it's encouraging to see it brought to engineering practicality.
Personally, I'd be nervous about leaving your engine behind. (It's not quite analogous to wind-powered ocean-going vessels; the winds were unreliable, yes, but there was never the danger of human factors SHUTTING OFF the wind.)
If the plasma beam got cut off, for whatever reason, the vessel would be coasting... and thus get off course right quick, presumably with no way to get back home under its own power. (And no, I'm not talking terrorism or its equivalent. But suppose a particular orbital station, or Moonbase, has the task of putting out the plasma beams and keeping them focused. What happens when the crew goes on strike?)
I'm not concerned with the engineering details; those get solved, sooner or later. But the potential political factors frighten me, just a little.
Perhaps it's just as well that, if this gets off the ground, it'll get thoroughly tested with cargo first!
Daniel in Brookline
What ever became of jaunting?
I despise the Space Shuttle just as much as the next guy. But it needs to be pointed out that none of these plasma beams and magnetic sails are going to solve the fundemental problem: getting off of Earth and into orbit!
NASA's #1 priority should be replacing the space shuttle with a better launch vehicle, or else focusing on the space elevator. And once you have the space elevator, the mars mission becomes a cinch.
Not that I'm any sort of expert on space flight... but when I saw this story on Slashdot a few days ago, I wrote up on my blog why I didn't think it would pan out as a solution for manned space flight. Here's what I said.
During the Cold War I, both the Soviet and American military scientists were thinking
of designing directed energy weapons by using proton or electron beams, but this turned
out to be useless because such charged particle beams tend to defocus and spread themselves
since the electron (or proton) beam particles push each other due to the fact that they have
the same charge, and as a result, the beam disappears over long distances.
Apparently, if I understood Randall Parker's article (and the links) correctly, the plasma
beam probably compensates for the charged particle pushing each other, but making the total
charge zero, since the plasma would be a mixture of electrons and protons, cancelling the total
charge. But I STILL worry that the beam might defocus itself, since the free electrons or protons
might manage to push each other to spread the beam a little bit.
Can anyone enlighten me about this issue? Is this a problem or not? I don't have the exact
figures here. Of course, another possibility that the plasma beam is made to combine back to
normal atoms and molecules as soon as the beam leaves the plasma gun, but how is this possible?
I'm still not sure what a "magnetized plasma beam" is supposed to mean. Is this supposed to be proof against the bending and diffracting effects of the various magnetic fields in the Solar System? Has anything even remotely similar been demonstrated in the lab?
The idea of "leaving your engine behind" has been around for a while; one of the less-publicized ideas is the microwave sail (gets thrust from a beam of microwaves instead of light). The plasma beam idea would give a great deal more thrust per unit of power in the beam, and is superior in that regard for in-system travel. But I wonder if there isn't an even better method, say by throwing dust-sized solid particles (similar to the "crashportation" concept for getting things into Earth orbit using matter on an elliptical trajectory from the Moon). Advantage of the dust would be that you would have much smaller influences from ambient magnetic fields; disadvantage is that you couldn't catch it with an artificial magnetosphere unless you found a way to vaporize each particle as it got close (perhaps not difficult if you made each one a little retroreflector and scanned for blue-shifted echoes coming at you).
As for the site for the Mars-side momentum gun: If you're on-target for the planet anyway, you could try to use aerobraking as a backup. If you need radiation shielding or a momentum sink, put it on Phobos (and boost only when the resulting thrust would be pro-grade).
"Personally, I'd be nervous about leaving your engine behind."
Bingo. I'm no engineer, but I would be very reluctanct to sign on to any proposal that does not allow for some maneuverability in case something goes wrong. And something WILL go wrong, for sure.
If I understand Hey's mass/energy explanation above, the force needed to decelerate the ship can be reduced substantially if the ship is made lighter...say, without engines. Is that one reason they're proposing this?
Perhaps I'm too locked into mental pictures of ships maneuvering at will throughout the solar system, a la Star Trek. But isn't that what we want, ultimately?
The idea is to save Huge on weight. It's the FUEL that is heavy in conventional rockets. Unless your going with some exotic form of fussion/linear-accelerator/Antimater engine, a normal rocket is a fraction of the wieght of the fuel needed to accelerate it. The big problem with conventional engines is that the faster you wish to go the more fuel you need, the more fuel you have the more power you need to accerate, the more power you need the more fuel you need... start spiral here. Very quickly you get to the point where all you can move is the fuel. I think your fear is not unfounded but for the wrong reason. There really isn't any reason to "manuver" as they do in StarTrek because there is only a few things of intrest in the solarsystem. I mean why would you want to go to a point 134 degrees out of phase of Mars... there isn't anything there. Small manuvering jets and a small in orbit engine are all you need to move your orbit within a planet system.
As for the Radiation, Why not create a allen belt to shield ourselves from the harmful radiation on Mars. We know that we can reflect radiation.
A Van Allen belt requires a magnetic field, which Mars doesn't have. Further, the magnetic field only protects against low-energy charged particles like solar protons; uncharged particles like X-rays and high-energy cosmic rays zip right through. To stop those, you need lots of mass. Earth's ton of atmosphere per square foot does the job, but on Mars you'll need help.
Getting back to off-board propulsion sources for a minute: a quick BOTE calculation indicates that a stream of matter moving at 20 km/sec relative could impart a force of roughly a metric ton at a mass-flow rate of 500 g/sec. A metric ton of force could accelerate a 10-ton craft to a speed of 86 km/sec in 1 day. Creating a 500 g/sec stream of matter at 20 km/sec relative would require about 100 MW of power; at 100 km/sec relative, about 500 MW. These power levels are within reach.
For the 100MW or 500MW couldn't we use big arrays of satellite photovoltaic solar power collectors? The effort to develop the collector system could also be used to run collectors to beam power back to Earth.
Collectors would be highly scalable too. Just keep adding more satellites to get small incremental increaes in power. Earlier and smaller solar power satellites could be used to boost small probes toward the outer planets. With time larger collector systems could be built up to boost larger objects and collectors could be sent to Mars orbit for setting up there.
Great idea, but the comparison to the Shuttle is unwarranted. Even if (when) this scheme, or a similar one, is in place, we'll still need a way to get into and out of Earth orbit. We need is a similarly innovative solution to that problem. Perhaps Burt Rutan will provide it.
For power levels this low it would probably be cheaper to build an orbital rectenna and beam power up from the ground; you wouldn't have to establish much in the way of manufacturing plants just to get your transport system operational. The one thing you would need is something to make lots of little mass-particles to be thrown at your spacecraft, preferably ones which can be easily vaporized into plasma (or will self-vaporize at the appropriate time).
I don't have any solid ideas for those yet, but I've got a couple concepts. One is to make milligram-scale piece of aerogel, shaped as corner cubes with a gossamer reflector coating. I don't know how to vaporize them easily but they should be easily fended off with meteor bumpers. The other is to make little circles or spheres of iron wire mesh and launch them electrostatically; if you had a strong enough magnetic field at your spacecraft the rapidly-moving conductive particle would hit the plasma in the "artificial magnetosphere", take a large current from the VxB and vaporize in the resulting electric arc. I have no idea what the conductivity of the plasma in such a magnetosphere would be so I don't know if this is a slam-dunk, completely ridiculous or somewhere between.
"Unless your going with some exotic form of fussion/linear-accelerator/Antimater engine,[...]"
Why, as a matter of fact, I've been working on just such a design...I have the plans around here somewhere...
But seriously, thanks for your thoughtful response to my question. I knew that fuel would be a problem, I just didn't realize that it was THAT MUCH of a problem! It's much more complicated than I had assumed. And I hadn't really considered that there are only a relatively few points of interest in the solar system, so we don't need the USS Enterprise...at least, not right now.
I agree with some here who feel that we should concentrate on the more immediate problem of finding a repeatable, cost-effective method of getting off Earth. My problem is that I want us to do it all...astro-bus, moon base, commuter system to Mars, etc. Alas, it's 2004, and I'm still waiting for my rocket pack.
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