New Space Survey

By | March 26, 2006
3 Comments

Here’s a greatly expanded version of our recent survey on humanity’s future in space. This one doesn’t provide instant results, but we’ll be publishing them after we get some responses.

10 Questions About the Future in Space

UPDATE: The big winner for question 10 so far has been Other. Here are some of the comments. (Note the two write-ins for warp drive!):

- We’re just beginning to discover the connection betwenn the EM spectrum and gravity. I think within a hundred years we’ll have a practical “gravity drive” of some sort, and that will take us to the stars.

- Good question

- generation ship

- Very low thrust, high specific impulse plasma or ion drive.

- Fusion, perhaps assisted in the collection of fuel with some varient of the Bussard Ramscoop

- Laser Sail/Fusion with Magsail to brake at destination star system.

- wormhole

- fusion/antimatter or new physics

- a propulsion technology not develloped yet (but not like warp or someting exotic like that, just something we haven’t thought of seriously yet)

- Question is poorly formed; not amenable to an exclusive multiple-choice format; STL generation ship will use multiple means including all the above, while FTL ship’s propulsion is probably post-Singularity and therefore unpredictable.

- When rich full sensory virtual reality becomes possible (2020-2030 according to Kurzweil) Telepresence in very accurate virtual environments may be very satisfying and more acceptable than long seperation from a humanity entering a technological singularity.

- Heim space drive!

- Ion Thruster

- nuclear

- Undiscovered Technology

- Warp Drive (albequere) Not the Star Trek one

- New technology will be needed to make flights to another solar system feasible. The new technology need not necessarily be propulsion. Radical life extension could increase the probability for Ark-like missions to colonize a new world. (Mostly likely, that kind of commitment would require finding an Earthlike world in a relatively near area.)

- Warp engines.

  • Paul F. Dietz

    I have a couple of dark horse candidates for interstellar propulsion:

    (1) Momentum transfer scoops. This is in the same family as Bussard Ramscoops, but with a significant difference. In this scheme, the relative motion of the vehicle with respect to the interstellar medium is exploited to generate power (causing some drag). The power is used to accelerate on-board reaction mass. Done properly, thrust will exceed drag, and the vehicle will accelerate. In effect, some of the initial kinetic energy of the vehicle is being concentrated in the vehicle and remaining unused reaction mass.

    In practice, I imagine this being done by having a very thin sail that excites a plasma wave in the passing ionized component of the ISM. This wave would have an electric field in which reaction mass ions would be injected. This avoids entirely the need to significantly compress the ISM, as Bussard ramscoops must (and of course no nuclear fusion of ordinary hydrogen is necessary).

    (2) Laser ions sails. This variant of laser propulsion uses the pressure of laser light scattered off ions trapped in a magnetic field. Some ions, particularly singly ionized alkali earth elements like magnesium or calcium, have very strong absorption/emission lines. The cross section of the ions at these lines can be enormous, leading to very high thrust/mass. Moreover, by tuning the laser, it can preferentially scatter off ions whose thermal motion in the plasma is toward or away from the source, effectively cooling or heating the plasma. This means very high laser intensities should be possible without the thermal limits of conventional light sails. The laser must also be tunable to compensate for doppler shifts, of course.

  • Karl Hallowell

    Paul, sorry but I have to dis your ideas. Where’s the power source for the momentum transfer scoops. Otherwise, you’re stuck with the momentum transfer going the wrong way. Frankly, I doubt the problem is that solvable since you’d need to have a power source on board or beamed in that effectively accelerates the incoming matter from practically standing still to moving substantially faster on average than the vehicle (otherwise you don’t get a useful thrust). In comparison, you can get a momentum boost even from throwing stuff (off the vehicle) in the right direction.

    Second, not only are reflective materials easier to make than absorptive ones, but they give twice the momentum transfer! With the former, you bounce a photon so that it heads back in the direction that it came from. That’s twice the momentum transfer of capturing a photon. Further, you don’t have to worry so much about heating effects since most of the energy that isn’t retained by the reflected photon goes into acceleration rather than being absorbed into the sail.

  • Paul F. Dietz

    Karl: I explained what the power source for the momentum transfer scoop is — it’s the relative motion of the ship and the interstellar medium.

    But wait, you might be thinking — this produces drag, and therefore this can’t be used to accelerate the ship, right? Wrong! Imagine the vehicle has a rocket powered by the energy from this generator. What is the thrust of that rocket, per unit of power input? The answer is: as high as you want it to be, since the thrust per power is inversely proportional to its exhaust velocity. Pick the exhaust velocity low enough, and thrust will exceed drag.

    This scheme does not violate any conservation laws. Think about it.

    Now, about the ion sails: you are right that a perfectly reflective sail will have higher efficiency. But it might also be considerably heavier, and therefore require more laser power for a given acceleration. Ions on resonance have truly enormous scattering cross sections, so the mass of the plasma sail can be very low. Note that this is not a pure absorbing sail, since the excited ions will re-emit the incident light in about 100 ns (depends on linewidth). If the plasma is optically thick at the resonant wavelength (and it probably would be) then photons emitted forward will tend to be absorbed again, eventually doing a random walk and coming out the illuminated side of the plasma. So, it will act like a diffusely reflecting surface, delivering about 3/4 of the force/incident power that a perfectly reflecting sail would.

    I want to point out that sail researchers have been moving in the direction of carbon foam sails over reflective metallized sails — the carbon sails can operate at much higher temperature, and therefore much higher laser intensity. Plasma sails could operate at even higher temperature.