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April 23, 2012

Carnival of Space 246

Carnival of Space #246 is up at Links Through Space

The puzzle of dark matter has been perplexing astronomers for years, but a new study finds that the local region of space around the Sun seems to be completely devoid of it. What could this mean for astronomy...?

A group of Chilean astronomers made an extremely detailed effort to study the motions of around 400 stars in the part of the galaxy around the Sun... and they didn't find anything!

According to their study, all of the motions of stars in the local part of the Milky Way match perfectly with what they can see, and nothing more. As far as they can tell, there's no dark matter here. Nothing to detect in the Earth-based experiments, and no way for any of the current theories to explain the lack of dark matter in the local stellar neighbourhood. Needless to say, this comes as quite a shock. Actually, on mentioning this particular news story to a couple of friends of mine, their initial reaction was much the same as my own -- some pretty intense skepticism. The first thing pointed out is that the effect of dark matter isn't expected to be particularly high within the galaxy. Perhaps the study was simply on too small a scale. This does make sense. If it's uniformly distributed everywhere, then the overall effect would be expected to be negligible. But then, if it's affected by gravity (which is, after all, the whole point) then logically there should be some local variations caused by the gravity wells of stars and other objects. To assume otherwise defies logic, surely. Or perhaps it's an asymmetric effect, and light matter may be influenced by dark matter, but dark matter may not be influenced by light

The blog carnival Space Access was created after Henry Cate attended the 2007 Space Access. Henry recently attended the 2012 Space Access conference and summarizes the latest developments in New Space.






"Nextbigfuture - Can the properties of the quantum vacuum be used to propel a spacecraft? The near term focus of the laboratory work is on gathering performance data to support development of a Q-thruster engineering prototype targeting Reaction Control System (RCS) applications with force range of 0.1-1 N with corresponding input power range of 0.3-3 kW. Up first will be testing of a refurbished test article to duplicate historical performance on the high fidelity torsion pendulum (1-4 mN at 10 to 40 Watts). The team is maintaining a dialogue with the ISS national labs office for an on orbit DTO.

How would Q-thrusters revolutionize human exploration of the outer planets? Making minimal extrapolation of performance, assessments show that delivery of a 50 mT payload to Jovian orbit can be accomplished in 35 days with a 2 MW power source [specific force of thruster (N/kW) is based on potential measured thrust performance in lab, propulsion mass (Q-thrusters) would be additional 20 mT (10 kg/kW), and associate power system would be 20 mT (10 kg/kW)].
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Nextbigfuture - notes from the Nuclear and Emerging Technologies for Space conference - Session 462 Advanced Concepts: LENR, Anti-Matter, and New Physics. George H. Miley spoke on a Game-Changing Power Source Based on Low Energy Nuclear Reactions LENR. Dr. White said the team is developing an even larger Q-thruster, saying “We’ve had some experience in the 4000 micro-newton range with around 10 Watts of input power. But we’re trying to get more experience across a broader number of input parameters to help us understand if we have a good handle on the physics and engineering.” “A test article that we ran it at 2 MHz and 4 MHz, the predicted force was very close to the observed force. We’ll be building a much larger test article, we’re trying to get to the 0.1 million newton level of thrust, and we’ll be working on that over the next year.”

"Nextbigfuture - Last year, John Chapman of NASA proposed a pulsed laser system for megawatt class fusion propulsion. Here is a recent updated presentation. In Chapman’s aneutronic fusion reactor scheme, a commercially available benchtop laser starts the reaction. A beam with energy on the order of 2 x 10^18 watts per square centimeter, pulse frequencies up to 75 megahertz, and wavelengths between 1 and 10 micrometers is aimed at a two-layer, 20-centimeter-diameter target. The incremental thrust from a laser triggered p-11B target, assuming ~10^5 Alphas from a single laser pulse has been estimated to yield a few pico-Newton impulse per laser pulse from a 10 micron square target area. High pulse rate laser systems coupled with multiple square centimeters of active target area could effectively augment the effective thrust level towards Newton magnitude levels, particularly in conjunction with increased alpha yields from optimized target designs. Recent advances in laser technology indicate possibility of higher laser quantum efficiencies (over 25%) and higher femtosecond pulse train rates (~75MhZ). Bremstrahlung radiation and non-productive plasma also result in losses as well as particle collisions with the structure represent additional power losses from the propellant exhaust stream. Power is also lost in transverse momentum resulting in exhaust stream spreading.

Future development and the availability of high efficiency short pulse laser systems may result in overall gains that may make the A-LIFT (Aneutronic Laser Induced Fusion Thruster) offering ISP ~900,000 approach an attractive alternative to previous fusion ~1-10 kW/kg or ionic (ISP range from 2000 – 100,000 propulsion for In-Space thrust applications.
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