Randall Parker has the
details on a proposed method of getting a spacecraft to Mars (and back)
in 90 days using magnetic beam plasma propulsion. (Also see Stephen’s
post on the subject, below.) In the proposed design, the beam would be able
to push a spaceship along by means of a sail at a consistent rate of about 26,000
miles per hour. At that rate, it would take a little less than 80 days to get
to Mars. Not too shabby when you consider that, 125 years ago, 80 days was considered
a remarkable
speed just for doing a single lap around the Earth. However, designer Robert
Winglee thinks he can do better even than that, with the 90-day round-trip as
his goal.

Of course, the real advantage here isn’t the speed. We have rockets
that push payloads to that kind of speed all the time. The advantage is that
the magnetic beam would be able to push the spacecraft in a straight line from
point A to point B. When we send a probe to Mars, it doesn’t travel in a straight
line. It would take way to much rocket fuel to do that. So we put the probe
into an orbit around the sun that eventually intersects with Mars’ own orbit
of the sun, as shown below. From a rocket fuel standpoint, this is an extremely
efficient and economic way to go. But from a time standpoint, it is costly.
The inner circle, the orbit of Earth, takes one year to complete. (In fact,
each one of those orbits is what a year is. But of course, we all knew
that.) The outer circle, the orbit of Mars, takes almost two years to complete.
As you can see, the trajectory followed by a probe launched from Earth is somewhere
between the two in duration. Call it 18 months.

Granted, this is a vast oversimplification. Estimates on how long a manned
flight to Mars would take using the conventional approach range from a few months
to a couple of years. But you get the idea. And contrast that approach to Mars
with the approach that the proposed technology will allow:

Quite a bit shorter of a trip, isn’t it?

Of course, Mars isn’t the only place to go in the solar system. Closer to home,
a magnetic beam projector in low Earth orbit could push a spaceship to the moon
in about ten hours. Interestingly, at that rate, if you took the space
elevator up from Earth, the trip from Earth to orbit would take quite a
bit longer than the trip from Earth orbit to the moon. Over longer distances,
the advantages of the magnetic beam approach seem to dissipate. According to
my (admittedly highly suspect) calculations, the magnetic beam that gets us
to Mars in 80 days could get us to Neptune in about 12 years.

That is one big solar system we live in, folks.

Unless I’m mistaken, it also takes us about 12 years to get to Neptune using
the old orbital intersection approach. We will have to crank up the output of
the magnetic beam projector — which, as noted above, is exactly what Winglee
intends to do — before we see any real advantage over those kinds of distances.

In addition to making travel within the solar system much less expensive and
more practical, magnetic beam propulsion technology can serve as a precursor
to solar sail technology. Frank
Tipler has proposed the idea of focusing the energy of the sun into a laser
beam which we could then use to launch a very small (you could hold it in your
hand) interstellar probe. According to Tipler, such a probe could be accelerated
to about .9c (90% of the speed of light) within about a month and a half. That
means that we could have it to Alpha Centauri in less than five years, with
information coming back in less than 10. Contrast that with 12 years to get
to Neptune on a magnetic beam. Now we’re talking speed.

(Not that AC that would necessarily be our first target; I think Kathy
would agree that Epsilon
Eridani would make an excellent choice.)

But wait. How much interstellar exploration could we really get done using
such a tiny probe? Well, that’s where nanotechnology
comes in.

See how all this stuff fits together?

The concept of solar sails has been around awhile. But the idea of providing our own “wind” is newer. This morning Wired reported that a University of Washington team is working on magnetized-beam plasma propulsion. This group just received $75,000 in funding from NASA’s Institute for Advanced Concepts.

[What's the matter guys? Feel the private sector breathing down your neck? – ed.]

The idea is to push a spaceship equipped with a sail with a mag-beam shot from a space station. This would, in theory, be able to propel the ship to incredible velocities – 26,000 miles per hour. At that speed a trip to Mars and back again would take about three months.

Once shot off into space, onboard propulsion units would provide a spacecraft some power for minor flight corrections, but not enough to decelerate, which would be handled by a plasma station orbiting the destination.

Not having to carry the mass of the fuel required for acceleration and deceleration within the craft is a big advantage here. Going to Mars by traditional rocketry would be very slow, 2.6 years for a round trip, and prohibitively costly.

Obviously there are a lot of questions to answer. Presumably the plasma stations will have to deal with Newtonian physics, and this gun would have quite a kick. In order to keep from having to compensate, it might be best if it was located on a large and, relatively, unmovable object such as the Moon.

Also, does a mag-beam have the range to accelerate and decelerate a craft at a sufficient distance? Nobody knows yet.

And a commentor at FuturePundit thought of another problem:

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.

My guess is that engineers will address these issues in time. And I’m glad that NASA is thinking beyond the Shuttle.