brody@eos.arc.nasa.gov (Adam R. Brody) (11/08/90)
Anybody know in what vehicles hydrazine is used as a monopropellant?
dil@mace.cc.purdue.edu (Perry G Ramsey) (11/08/90)
In article <7565@eos.arc.nasa.gov>, brody@eos.arc.nasa.gov (Adam R. Brody) writes: > Anybody know in what vehicles hydrazine is used as a monopropellant? Just about every US unmanned spacecraft these days uses monopropellant for maneuvering fuel. GOES, Hughes spin stabilized comm satellites, ERBS, come to mind immediately. Monopropellant is much simpler and cleaner than bipropellant. Cleanliness is important for spacecraft that have to last a long time. The only advantage of bipropellant is that it has a little higher Isp. -- Perry G. Ramsey Department of Earth and Atmospheric Sciences perryr@vm.cc.purdue.edu Purdue University, W. Lafayette, IN USA dil@mace.cc.purdue.edu Congress thinks that if you have nine women pregnant simultaneously, you can get one baby in one month.
henry@zoo.toronto.edu (Henry Spencer) (11/08/90)
In article <5987@mace.cc.purdue.edu> dil@mace.cc.purdue.edu (Perry G Ramsey) writes: >> Anybody know in what vehicles hydrazine is used as a monopropellant? > >Just about every US unmanned spacecraft these days uses monopropellant for >maneuvering fuel. GOES, Hughes spin stabilized comm satellites, ERBS, come >to mind immediately. Also the Voyagers, and probably most of the other planetary missions other than Galileo (which is bipropellant, I believe). Note that it's usually monomethylhydrazine, not plain hydrazine. I believe the primary difference is better behavior at temperature extremes. -- "I don't *want* to be normal!" | Henry Spencer at U of Toronto Zoology "Not to worry." | henry@zoo.toronto.edu utzoo!henry
stanb@hpnmdla.HP.COM (Stan Bischof) (11/09/90)
Would someone explain as concisely as possible just what hydrazine is, how it acts as a propellant, and why it seems to be so popular? Thanks Stan Bischof HP-NMD
dil@mace.cc.purdue.edu (Perry G Ramsey) (11/10/90)
In article <3250005@hpnmdla.HP.COM>, stanb@hpnmdla.HP.COM (Stan Bischof) writes: > Would someone explain as concisely as possible just what hydrazine > is, how it acts as a propellant, and why it seems to be so popular? Hydrazine is N2H4. H HH H \/ \/ N = N Under the right conditions (1) heating in the presence of a catalyst, or (2) in the presence of a strong oxizizer and a catalyst, it decomposes into it's components, releasing a lot of hot gas. Typically, monomethyl hydrazine (MMH), which is formed by replacing one of the H above with a CH3, is used in the first mode. This is very useful for control thrusters because it is simple, reliable, and reasonably clean. A combination of MMH and unsymetrical dimethyl hydrazine (replace two of the hydrogens on the same side with CH3's), along with nitrogen tetroxide is used in the second mode. This is very useful for higher thrust applications, like the Titan core or the Shuttle OMS. These types of systems are popular because 1) The propellants can be stored for a long time at room temperature 2) They aren't explosive per se like hydrogen is 3) You don't need an ignition system to get the engine going. Just add propellant and maybe some heat. On the flip side, 1) They are less efficient than hydrogen 2) They are awfully toxic. -- Perry G. Ramsey Department of Earth and Atmospheric Sciences perryr@vm.cc.purdue.edu Purdue University, W. Lafayette, IN USA dil@mace.cc.purdue.edu Congress thinks that if you have nine women pregnant simultaneously, you can get one baby in one month.
ehopper@ehpcb.WLK.COM (Ed Hopper) (11/10/90)
There has been some discussion here regarding hydrazine. A friend of mine, who works for a NASA contractor, once told me that hydrazine is a major concern when working on a satellite during EVA. Hydrazine is highly toxic. Contact with the skin can be fatal. Additionally, hydrazine molecules are small enough to penetrate the fabric of the current EVA spacesuit. If hydrazine leaked from a satellite during any repair or refueling, it could be very dangerous for the astronaut in the immediate vicinity. Ed Hopper Ed Hopper's BBS 713-997-7575 - Houston - Free Access to AT&T Employees USENET - ILink - Smartnet PC Board - Markmail Offline Reader System "I've fallen and I can't get up!"
dietz@cs.rochester.edu (Paul Dietz) (11/10/90)
>Under the right conditions (1) heating in the presence of a catalyst, or >(2) in the presence of a strong oxizizer and a catalyst, it decomposes into >it's components, releasing a lot of hot gas. > >Typically, monomethyl >hydrazine (MMH), which is formed by replacing one of the H above with a CH3, >is used in the first mode. This is very useful for control thrusters >because it is simple, reliable, and reasonably clean. I believe hydrazine is mostly used as a monopropellant, I believe. MMH is used with in bipropellants. MMH and UDMH can poison the catalyst in hydrazine monopropellant engines. >A combination of MMH and unsymetrical dimethyl >hydrazine (replace two of the hydrogens on the same side with CH3's), >along with nitrogen tetroxide is used in the second mode. >This is very useful for higher thrust applications, like the Titan core >or the Shuttle OMS. Shuttle OMS and RCS rockets use MMH, not a MMH/UDMH mixture. >These types of systems are popular because ... >2) They aren't explosive per se like hydrogen is Not really. Not only are they flammable at a wide range of concentrations (MMH's flammability range is 2.5% to 98% by volume in sea level air), but they can spontaneously ignite when spilled on surfaces or on cloth. They also can explode all by themselves, as they have positive heats of formation (as you would expect of monopropellants). Hydrazine decomposes explosively when subjected to shocks at temperatures as low as 367 K. MMH is less sensitive, but more toxic. Paul F. Dietz dietz@cs.rochester.edu
spgreg@earth.lerc.nasa.gov (Greg Macrae) (11/13/90)
In article <kNuDs2w163w@ehpcb.WLK.COM>, ehopper@ehpcb.WLK.COM (Ed Hopper) writes... >There has been some discussion here regarding hydrazine. A friend of >mine, who works for a NASA contractor, once told me that hydrazine is a >major concern when working on a satellite during EVA. Hydrazine is highly >toxic. Contact with the skin can be fatal. Additionally, hydrazine >molecules are small enough to penetrate the fabric of the current EVA >spacesuit. If hydrazine leaked from a satellite during any repair or >refueling, it could be very dangerous for the astronaut in the immediate >vicinity. > >Ed Hopper > The current space suit leaks like a seive. It outgasses at a rate that is unacceptable for use near the space station. There is a benefit to this, however. Because there is a flow of gas out of the suit, nasty chemicals like hydrazine are extremely unlikely to find their way back into the suit during an EVA. The first place an astronaut is likely to contact the hydrazine is in the airlock when hydrazine adsorbed or even frozen to the outside of the suit and EVA equipment can evaporate or sublime. The astronaut is endangered when he unseals his suit. It is a real and serious concern and not just when satellites in the vicinity use hydrazine--the shuttle itself does. -------------------------------------------------------------------- MacRae | Too curious flower | Watching us pass, met death... spgreg@csd.lerc.nasa.gov | Our hungry donkey. | -Basho --------------------------------------------------------------------
dietz@cs.rochester.edu (Paul Dietz) (11/14/90)
In article <1990Nov13.142644.27781@eagle.lerc.nasa.gov> spgreg@earth.lerc.nasa.gov writes: >and EVA equipment can evaporate or sublime. The astronaut is endangered >when he unseals his suit. It is a real and serious concern and not just >when satellites in the vicinity use hydrazine--the shuttle itself does. More accurately, the shuttle uses monomethylhydrazine. MMH is more toxic than hydrazine when inhaled. MMH is used because its melting point, 220.7 K, is lower than that of hydrazine, 274.5 K, and because it has better shock resistance and heat-transfer properties. Paul F. Dietz dietz@cs.rochester.edu
Patrick.Hayes@cediag.bull.fr (Patrick Hayes) (11/15/90)
In article <kNuDs2w163w@ehpcb.WLK.COM> ehopper@ehpcb.WLK.COM (Ed Hopper) writes: >Additionally, hydrazine >molecules are small enough to penetrate the fabric of the current EVA >spacesuit. If hydrazine leaked from a satellite during any repair or >refueling, it could be very dangerous for the astronaut in the immediate >vicinity. Excuse me? If the suits were permeable enough to let Hydrazine in they'd leak O2 like a kitchen sieve. Additionally, how exactly would the hydrazine diffuse into a positive pressure suit??? As long as He's got the suit on I don't imagine astronaut being in any danger, however, If he gets coated with hydrazine, He might have problems taking it off back in the shuttle. Pat -- +-------------------------------+-----------------------------------------+ | Patrick Hayes | EMail : Patrick.Hayes@cediag.bull.fr | | BULL CEDIAG | or hayes@bull.fr | | 68, Route de Versailles | or ...!mcvax!inria!bullfr!hayes | | F-78430 Louveciennes FRANCE | Tel : (33 1) 39 02 49 55 | +-------------------------------+-----------------------------------------+
gwh@monsoon.Berkeley.EDU (George William Herbert) (11/16/90)
In article <PATRICK.HAYES.90Nov14181711@troy.cediag.bull.fr> Patrick.Hayes@cediag.bull.fr (Patrick Hayes) writes: >Excuse me? If the suits were permeable enough to let Hydrazine in they'd leak >O2 like a kitchen sieve. Additionally, how exactly would the hydrazine diffuse >into a positive pressure suit??? > >As long as He's got the suit on I don't imagine astronaut being in any danger, >however, If he gets coated with hydrazine, He might have problems taking it >off back in the shuttle. Having the unique position of being in a NASA-sponsored Spacesuit Design class here at UC bBerkeley, I feel the need to point out that the current Shuttle suit leaks aroudn 50CC/minute of atmosphere to the outside environment. Now, what it's made out of isn't particularly permeable to Hydrazine, but I would consider getting it on or near the current suit a very, very bad idea. As would most of the astronauts who will be using it. == George William Herbert == **There are only two truly infinite things,** == JOAT for Hire: Anything, == * the universe and stupidity. And I am * =======Anywhere, My Price======= * unsure about the universe. -A.Einstein * == gwh@ocf.berkeley.edu == ********************************************* == ucbvax!ocf!gwh == The OCF Gang: Making Tomorrow's Mistakes Today