Propellantless propulsion

Tom James @ 25-08-2009

Tether-satellite-NASAFollowing on from solar sails we have a discussion of that other science fictional bastion of propellantless propulsion – the space elevator – it turns out that space elevators and space tethers can be used for more than just getting into orbit:

A series of bolo tethers, each tether passing a spacecraft onto the next, could be used to achieve even larger orbit changes than a single system. For example, one tether system could catch a spacecraft from a very low orbit and swing it into a somewhat higher orbit. Another bolo picks it up from there and puts the satellite into a geosynchronous transfer orbit (GTO). A third tether catches the load again and imparts sufficient velocity to it so that it reaches escape velocity. A satellite initially orbiting just above the atmosphere could thus be slung all the way into an interplanetary orbit around the Sun, and all this without using any rocket propulsion and propellant

This is in the context of a review by Centauri Dreams of Space Tethers and Space Elevators by Michel van Pelt, which explores tethers and space elevator concepts in some detail.

[from Centauri Dreams][image from Wikimedia and NASA]

Thrown off course by relativity

Tom James @ 24-08-2009

Cosmos1-2006-2A preview of space-flight issues of the future: how do you account for the effects of relativity when travelling long distances? A solar sail launched from close to the Sun would have to account for relativistic effects when navigating to the edges of the solar system:

And even though those effects are relatively minor to start with, they have a significant effect over long distances.

The calculations carried out by Kezerashvili and Vazquez-Poritz show that the effects of general relativity could push a solar sail off course by as much as a million kilometers by the time it reaches the Oort Cloud

The promise of solar sails as a propulsion mechanism is impressive:

By one calculation, a solar sail with a radius of about a kilometer and a mass of 300 kg (including 150 kg of payload) would have a peak acceleration of about 0.6 g if released on a parabolic trajectory about 0.1 astronomical unit (AU) from the sun (where the radiation pressure is higher).

That kind of acceleration would take it beyond the Kuiper belt to the heliopause, the boundary between the solar system and interstellar space (and a distance of 200 AU), in only 2.5 years.

In 30 years, a solar sail could travel 2,500 AU, far enough to explore the Oort Cloud.

Of course we need to actually build one of these things first.

[from Technology Review, via Technovelgy][image from Wikimedia]

Over to Mars in 39 days

Tom James @ 23-07-2009

marsA fascinating article at New Scientist on a new nuclear powered ion drive called VASIMR that could transport astronauts to Mars in as little as 39 days:

VASIMR works something like a steam engine, with the first stage performing a duty analogous to boiling water to create steam. The radio frequency generator heats a gas of argon atoms until electrons “boil” off, creating plasma. This stage was tested for the first time on 2 July at Ad Astra’s headquarters in Webster, Texas

Thanks to the radio frequency generator, VASIMR can reach power levels a hundred times as high as other engines, which simply accelerate their plasma by sending it through a series of metal grids with different voltages. In that setup, ions colliding with the grid tend to erode it, limiting the power and lifetime of the rocket. VASIMR’s radio frequency generator gets around that problem by never coming into contact with the ions.

Hitherto most plans to get to Mars involve lengthy journey times, during which exposure to cosmic rays and extended periods of weightlessness (ameliorated somewhat by centrifugal artificial gravity) could have a debilitating effect on the adventurers.

The creation of these powerful ion drives is an exciting and interesting development. Certainly I hope to see someone get to Mars within my lifetime. I wonder what technique will be used?

[from New Scientist][image from chipdatajeffb on flickr]

Bussard ramjet revisited

Tom James @ 10-06-2009

star_and_barsAn interesting discussion of Bussard ramjet interesteller propulsion technology here at Centauri Dreams and Adam Crowl:

Robert Bussard put the interstellar ramjet into the public eye back in 1960 in a paper proposing that a starship moving fast enough would be able to use the hydrogen between the stars as a source of fuel, enabling a constant acceleration at one g.

One of the key problems with Bussard ramjets is the speed of the fusion reactions:

Physicist Daniel Whitmire tackled this problem in a 1975 paper that proposed using hydrogen for fuel but exploiting a catalytic nuclear reaction chain instead of straight proton burning.

It’s all interesting stuff, but even if the Bussard ramjet is unfeasible as a propulsion system it may be feasible as a brake for interstellar spacecraft.

[image from kevindooley on flickr]

Help re-imagine Project Orion – nuclear space propulsion in the noughties

Paul Raven @ 24-06-2008

NASA\'s Project Orion - concept artIf you’re in need of something to bring a bit of excitement to your Tuesday (and let’s face it, who isn’t?), maybe you’d like to get involved with re-thinking the idea of launching space missions using the Project Orion model – in other words, the sixties concept space vehicle propelled by small nuclear explosions. [image courtesy NASA via Wikimedia Commons]

No, that’s a genuine NASA concept. And this is a genuine request; the following email turned up in the Futurismic contact inbox over the weekend from one Peter Queckenstedt:

“My name is Peter, I’m a Canadian designer, currently studying for my master’s in transportation design at the Umea Institute in Sweden.

I’m doing some advance work on my upcoming final degree project, and thought Futurismic might be able to aid me. My plan is to revive the idea of Project Orion, the atomic bomb-propelled ship designed in the 60s. My focus is not so much on the engineering side, but more on the ‘blue-sky’ ideas side. I want to explore what kind of changes 50 years of technology would make to this craft. My main intent is to get people excited about the idea of sending people into space in a serious manner.

If you know of anyone that might be interested in collaborating, sponsoring, or providing inspiration and input please let me know. Engineers, fiction writers, artists, mad scientists, bloggers … I’m open to anything as long as it’s interesting.”

There you have it, folks – if you fancy getting your crowdsource on and thinking about nuclear-powered rockets, now’s your chance! I think the best way to do this would be for you to leave a comment below if you’re interested in helping out, making sure to use a valid email address which I can then forward on to Peter.

But feel free to share ideas at the same time – for example, is Project Orion any more or less reasonable a suggestion now we’ve had five more decades of experience with nuclear power and weapons, not to mention the economic cost of space exploration?

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