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Fraser
2007-Nov-15, 07:15 PM
With the shuttle and station in the news these days, it's easy to forget there's a whole other space program in the works: Constellation. Over the next decade, we'll go back to the Moon - this time to stay. ...

Read the full blog entry (http://www.universetoday.com/2007/11/15/radical-new-steering-thruster-tested/)

danscope
2007-Nov-16, 01:56 AM
Hi, That was interesting. Keep it simple, and less toxic . Seems to beat Hydrazine.
Best regards, Dan

IsaacKuo
2007-Nov-19, 04:44 PM
Compressed methane/compressed oxygen for low thrust? Sounds brilliant. With low thrust, you only need low chamber pressure, so the tanks may be pressurized without heavy tanks. So you only need a couple propellant valves and a spark plug ignition system. Brilliant!

Jerry
2007-Nov-19, 05:19 PM
Hi, That was interesting. Keep it simple, and less toxic . Seems to beat Hydrazine.
Best regards, Dan
Hydrazine systems are very simple and as you noted very toxic, but it is the stability and danger during laboratory testing issues that drive the choice away from hydrazine.

George
2007-Nov-19, 06:04 PM
Using my handy 1941 Marks' Handbook, the heat value for methane is second only to hydrogen.

Methane HHV = 23,910 Btu/lb
Hydrogen HHV = 61,045 Btu/lb

All the other "anes" are around 21,000 Btu/lb.

Jerry
2007-Nov-21, 04:00 AM
Using my handy 1941 Marks' Handbook, the heat value for methane is second only to hydrogen.

Methane HHV = 23,910 Btu/lb
Hydrogen HHV = 61,045 Btu/lb

All the other "anes" are around 21,000 Btu/lb.

What's this BTU thingy?

Yes, Methane is the most energetic hydrated carbon compound. Nitrates and nitramines are another story...

George
2007-Nov-21, 04:41 AM
What's this BTU thingy? Sorry, I tend to be nostalgic, usually not by choice. :) What do you want, kJ/kg?

JustAFriend
2007-Nov-21, 03:31 PM
..not to mention the fact that most of the outer solar system contains vast amounts of methane. Always helps to be able to re-fuel along the way rather than carry every drop you need!

Jerry
2007-Nov-25, 06:07 AM
Sorry, I tend to be nostalgic, usually not by choice. :) What do you want, kJ/kg?
how about horse power years per stone? It bothers me to no end that so many different competing unit of measure persist in the US while the rest of the world has more-or-less standardized. It increase the bean counting in science and adds zero value. In fact it increases the probability of errors. Very unreasonable.

Noclevername
2007-Nov-25, 12:42 PM
So you don't want to know how many cubits the it could push a hundredweight in one breath? :D

George
2007-Nov-25, 08:35 PM
how about horse power years per stone? It bothers me to no end that so many different competing unit of measure persist in the US while the rest of the world has more-or-less standardized. It increase the bean counting in science and adds zero value. In fact it increases the probability of errors. Very unreasonable. From what I've seen, it looks like college science and engineering have evolved to embrace the mks system. It was tried when I was in college in the early 70's to go metric, but it flopped, probably due to re-tooling costs. This meant we had to learn to use both, though the metric was the obvious choice. I never did get comfortable with the use of lbm in some forumula since there were times you had to divide by 32.2 to convert properly.

Of course, in the case above, I am using the BTU, British Thermal Unit. :)

filrabat
2007-Nov-25, 09:45 PM
http://en.wikipedia.org/wiki/Conversion_of_units

1 BTU (British Thermal Unit) = 1,054.350 Kj

or 1.054,350 Kj in European notation

Tuckerfan
2007-Nov-25, 10:02 PM
how about horse power years per stone? It bothers me to no end that so many different competing unit of measure persist in the US while the rest of the world has more-or-less standardized. It increase the bean counting in science and adds zero value. In fact it increases the probability of errors. Very unreasonable.
I've seen recent pieces on the Beeb which give weights in stone, and IIRC, British merchants were upset that the EU was requiring them to list weights in metric units rather than pounds.

In the US, most scientific organizations, the military, and the auto industry have gone metric.

Oh, yeah, it seems folks are having trouble figuring out exactly how much a kilogram weighs. (http://news.bbc.co.uk/2/hi/science/nature/7084099.stm)
But around 30 years ago scientists discovered a problem.

The international prototype was no longer the same mass as the other cylinders. And, since then, the drift has continued.

"Relative to the average of all the sister copies made over the last 100 years you could say it is losing [mass], but by definition it can't," explained Dr Richard Steiner of the National Institute of Standards and technology (NIST) in the US. "So the others are really gaining mass."

The fluctuation is about 50 parts in a billion, less than a single grain in a bag of sugar. But whilst it is tiny, the change can have important consequences, particularly for scientists who require precise definitions of the kilogram for other measurements such as voltage.

Jerry
2007-Nov-25, 10:25 PM
This puzzles me to no end - The handling of weighing standards is tightly controlled, and this should not be happening. One almost has to assume poor handling, but are there other unexpected variables? Corrosion? Gas absorption? Were there trapped nuclear isotopes in the original standards? Are microbes eating precious metals? Proton decay? Is the mass of an object the function of its history as well as space and time?

Tuckerfan
2007-Nov-25, 10:33 PM
My understanding is that it's simply what happens when atoms bang into the standard and knock a couple of them off. As of yet, we do not have the technology to be able to make a perfect vacuum. Of course, we don't really know how accurately the standards were originally made, as the technology back then was rather primitive compared to what we have today.

Jerry
2007-Nov-26, 05:09 AM
Oh, yeah, it seems folks are having trouble figuring out exactly how much a kilogram weighs. (http://news.bbc.co.uk/2/hi/science/nature/7084099.stm)


Dr Steiner at NIST has so far managed to measure the Planck constant with uncertainties of 36 parts in a billion.

But their value is different from that measured at NPL, leaving scientists on both sides of the Atlantic scratching their heads.

Gravity as always, behaving badly.