http://www.dsti.net/News/56469.htm
美國測試更安全、更簡單的火箭燃料：鋁冰
[據美國defensenews網站2009年9月21日報導] 美國空軍正在資助一項新型火箭燃料的研發，這種燃料產生的推力有望達到現有推進劑的水準，並且更加安全簡便。使用這種推進劑可能成本更低並且對環境有利，它由冰凍的細鋁粉和水的混合物製成。
美國空軍、NASA和來自普渡大學以及賓夕法尼亞州立大學的科學家于8月將一個2.7米（9英尺）的火箭發射到約400米（1300英尺）的高空。這是對裝有ALICE推進劑（根據其組份：鋁和冰來命名）的火箭進行的初始試驗飛行。
來自普渡大學的航空學教授蒂摩西•波波因特（Timothee Pourpoint）稱，此火箭在0.8秒內加速到320千米/小時（200英里/小時）。
他說：“這次試驗飛行帶來了新的希望，但是並不優於現有的推進劑。”ALICE的研發人員有信心可以做得更好，波波因特說：“對於改進這種推進劑我們有很多想法”。
如果鋁冰推進劑的性能大幅提高，它將會為美國空軍做出許多貢獻。
科學研究中心空軍辦公室的宇航推進專案負責人米塔塔•柏坎（Mitat Birkan）說：“這種推進劑比其他推進劑更安全，意外點火的幾率較小。這種推進劑掉在地上也不會發生爆炸，靜電放電帶來的危險也可以忽略不計。”
柏坎還認為，這種推進劑和當今使用的其他推進劑相比對環境更有利。他說：“比如NASA就必須在風吹離海岸方向時才能進行發射，因為發射航天器會產生成噸的對人體有害的鹽酸。”
使用ALICE推進劑的火箭發動機排出的是氫和鋁的氧化物，柏坎認為毒性相對較低。
波波因特說：“排出鋁的氧化物也並非十分理想，但是這相對氫氯酸來說好一些。”
也許ALICE推進劑最吸引人的地方就在於它可以“現場”製造，十分簡單，也就是說幾乎可以在任何地方進行生產。柏坎說：“只需要有水源、一些鋁粉和一台混合機就可以了，這可以極大簡化空軍的後勤管理。”
對NASA來說，“現場製造”就意味著有可能在月球上、火星上或者其他地方進行ALICE推進劑的生產。這樣探索宇宙的飛行器也許就不用返回地球來重新補充燃料了。”
波波因特說：“我們知道月球上存在鋁，火星上也有一些，而且火星上還存在水。如果月球上沒有水的話，我們可以將水運送過去。”
使用鋁和水製造推進劑的想法並不是最新提出的。
8月，賓夕法尼亞州立大學的格蘭特•日沙（Grant Risha）教授在其關於ALICE推進劑的論文中寫到：從20世紀60年代就開始對作為可行推進劑的鋁-水燃燒進行了研究。
柏坎說：“先前是在鋁粒子的規格上製造鋁水推進劑的。最新研究使用了“納米鋁粒子”，和之前的鋁粒子是完全不同的。”
之前使用的鋁粉是微米級粒子。1微米大概比人類的頭髮細100倍。但這些粒子還是太大了，必須加熱到2400 開氏度（3860華氏度 ）才能點燃。納米鋁粒子比微米級粒子小1000倍，用低一半的溫度就可以點燃。
波波因特說：“問題的關鍵就在於納米鋁粒子，如果我們還使用微米級鋁粒子，那還是不能起作用。”
將納米鋁和水混合製成一種稠度類似於黏土的藥漿。然後將此混合物裝進鑄模冷卻到零下20華氏度。
波波因特說：“冷凍藥漿的目的在於防止鋁粒子和水發生反應。”
為了點燃冰凍的推進劑，將熱氣沿其空心通道注入，直到鋁被加熱到燃點。燃燒需要的氧來自水，水以冰的形式存在於冷凍藥漿中。
加入像過氧化氫一樣的富氧源可能會提升ALICE推進劑的性能，其含氧量是水的兩倍。
波波因特說：“雖然ALICE推進劑是冷凍的，但是和一些火箭燃料相比溫度算暖和的。比如液氫就必須在零下423華氏度保存。這使得ALICE成為一種有吸引力的衛星燃料。”
波波因特說：“即使是在太空，太陽的熱量也很難使氫保持液態。但使鋁冰保持冷凍狀態卻很容易。這樣，使用 ALICE推進劑的衛星使用壽命就更長。”
除用於衛星外，鋁-水燃燒可用在火箭和導彈的推進中。
柏坎說：“這個反應生成氫，事實上，這是產生氫的最有效的方法之一。這種方法還可用在氫氣站，為氫能源汽車提供燃料。” （航太科工六院602所 程根旺 王寧）
http://www.defensenews.com/story.php?i=4286114
A Safer, Simpler Rocket Fuel
USAF, Experts Explore Use of Aluminum-Ice Propellant
By william matthews
Published: 21 September 2009
The U.S. Air Force is funding the development of a new rocket fuel that promises to be as powerful as current propellants, but safer and simpler to handle, possibly cheaper and environmentally benign. It's made from a frozen mixture of finely powdered aluminum and water.
In August, the Air Force, NASA and scientists from Purdue and Pennsylvania State universities launched a 9-foot rocket 1,300 feet into the air during an initial test flight of the propellant ALICE - so named for its ingredients, aluminum and ice.
The rocket accelerated to 200 miles per hour in 0.8 seconds, said Timothee Pourpoint, an aeronautics and astronautics professor at Purdue.
That's a promising start, but not better than current propellants, he said. ALICE developers are convinced they can do better. "We have a lot of ideas on how to improve performance," Pourpoint said.
If performance can be boosted, aluminum-ice propellant offers a number of attractive attributes to the Air Force.
It's safer than other propellants, said Mitat Birkan, program manager for space power and propulsion at the Air Force Office of Scientific Research. It's less prone to ignite accidentally, "you can drop it and it won't explode, and the danger from electrostatic discharge is negligible."
And it's environmentally benign compared with some of the rocket fuels in use today, Birkan said.
NASA, for example, "can't launch the space shuttle until the wind is blowing off shore" because the shuttle's engines "produce tons and tons" of hydrochloric acid, which is harmful to humans, Birkan said.
An engine fueled with ALICE emits hydrogen and aluminum oxide, which Birkan said is relatively innocuous.
"Aluminum oxide is not something we want to be coating everything with, but not as bad" as hydrochloric acid, Pourpoint said.
Perhaps the most intriguing ALICE attribute is that the propellant is simple enough to be produced "in situ" - meaning just about anywhere. All that's needed is a source for water, powdered aluminum and a mixer, Birkan said. Together, those attributes could greatly simplify logistics for the Air Force, he said.
To NASA, in-situ manufacturing suggests that it might be possible to produce ALICE propellant on the moon, Mars or elsewhere. Space exploration may require being able to refuel without returning home.
"We know there is aluminum on the moon and some on Mars, and we know there is water on Mars," Pourpoint said. Water could be delivered to the moon if none is found there, he said.
The idea of using aluminum and water as a propellant isn't new.
"Aluminum-water combustion has been studied since the 1960s as a viable propellant," Grant Risha, a Penn State professor, wrote in a paper on ALICE propellant in August.
But previous attempts to make aluminum and water fuels foundered on the size of the aluminum particles that were used, Birkan said.
What's new here is "nano aluminum particles. That's completely different from anything that has been done before," he said.
Earlier efforts with aluminum powder used micron-size particles. A micron is about 100 times smaller than the width of a human hair. But those particles were much too big. They must be heated to 2,400 degrees Kelvin - about 3,860 degrees Fahrenheit - to ignite. Nano particles are 1,000 times smaller and will ignite at half that temperature.
"The key in here is nano aluminum," Pourpoint said. "If you do the same thing with micron-size aluminum, it will not work."
Nano aluminum is mixed with water to make a slurry that assumes the consistency of clay. The mixture is then packed into molds and cooled to about minus 20 degrees Fahrenheit.
Freezing the slurry prevents the aluminum particles from reacting with the water, Pourpoint said.
To light the frozen propellant, hot gas is forced down its hollow core until the aluminum reaches its ignition point. To burn, the aluminum needs oxygen, and it gets that from the water - manifested as ice - in the frozen slurry.
One way to improve ALICE propellant performance might be to add a richer oxygen source, possibly hydrogen peroxide, which has twice as much oxygen as water.
Even though it is frozen, ALICE propellant is warm compared with some rocket fuels, such as liquid hydrogen, which must be kept at minus 423 degrees Fahrenheit. That makes ALICE attractive as a fuel for satellites, Pourpoint said.
Heat from the sun makes it difficult to keep hydrogen liquid, even in space, he said. It would be much easier to keep aluminum ice frozen. That would give it a longer useful life as a propellant for satellites, he said.
Aluminum and water combustion may be used to power other vehicles besides satellites, rockets and missiles.
"This reaction produces hydrogen," Birkan said. "In fact, it's one of the most efficient ways to produce hydrogen." It could be used at hydrogen stations to make fuel for a generation of hydrogen-powered automobiles, he said.
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