Air Liquification TSTO

[PurduesUSAFguy]

Hello all, I recall reading about a start-up that was shopping around a concept for an air launched TSTO that would take off without oxidizer and would collect and enrich LOX in flight and feed it into it's upper stage. For the life of me I can not remember what they were called and couldn't find them on google for some reason. Does anyone know what I am talking about or am I insane and imagine their website, lol. Any help would be appreciated. Actually for that matter pointing me in the direction of any research done on air liquifcation cycle engines would be much appreciated, thanks.  

[lmike]

(Other than BAE not being a start-up) Hotol was supposed to be like that.  Maybe these guys:  http://www.reactionengines.co.uk/main.php?content=sabre ?

[yinzer]

I think you're talking about the Alchemist system, proposed by Andrews Space.  It is supposed to work about as you described, takes off and then liquefies LOX from the air.  Two papers on the topic can be found here and here.

[PurduesUSAFguy]

Thanks, it was Andrews Aerospace I was thinking of.

[publiusr]

The LACE concept. All very Rube Goldberg.

[coach]

What is the status of the Alchemist program at Andrews?  This appears to be an innovative alternative to traditional rocket launches.  How much (somebody run a few rough numbers please!) of an advantage would this offer?  The idea is to take off from a runway using jet engines and as the jet fuel is expended, LOX is made from the air and used in kerosene/LOX rockets to propel a vehicle to suborbital heights where a second stage separates and goes to LEO.  

Animation here...  http://www.andrews-space.com/content-main.php?subsection=MTA4

Does anyone know of a timetable of testing of the system?  It's hard to get up to date info from private aerospace websites.  What is the rate of LOX production necessary for the system to be feasible?  How close are they to this value?  Suborbital tourism is the first thing pops into my mind for a rival to Virgin that could provide bigger vehicles with more passengers and longer rides than Spaceship 2.  Cheaper too!

Coach

[lmike]

lmike - 28/9/2006  7:23 PM

(Other than BAE not being a start-up) Hotol was supposed to be like that.  Maybe these guys:  http://www.reactionengines.co.uk/main.php?content=sabre ?

Sorry, just noticed they've moved their web-pages around so the link above doesn't work.  The current address is http://www.reactionengines.co.uk/sabre.html

[lmike]

"On the fly" oxygen liquefaction via condensation requires additional energy which has to be carried along (in the form of the jet fuel to power the compressor)  There could be 2 schemes: it could slowly "collect" enough LOX into a tank for a subsequent rocket engine boost to the orbit, or it could attempt it in real time.  In the latter case it would need to maintain the needed mass flows to keep up the thrust.  Partial vaporization rather than full LOX conversion prior to combustion could be more realistic, although the reaction would contain less "energy" than that with standard LOX.  

I think these are theoretically "interesting" schemes, but personally, I'm not a fan of either on practical grounds.  Liquifying the oxidizer prior to the flight (i.e. applying work to condense the energy) and then using it as a pre-made propellant is sensible enough (as it's currently done in ELVs)

[wannamoonbase]

Sadly, I think having LOx drop tanks will be cheaper and more efficient for a long time.

[tom nackid]

If i remember correctly Andrew's approach does not use a compressor and in fact has no moving parts at all except for the plane itself. It uses an obscure venturi-type effect to cool and compress the air. Its an effect that has been known for over a hundred years but has never found a practical application yet.

[kevin-rf]

In industial applications (such as oil refineries, chemical plants) that have compressed air available it is not all that uncommon to cool electronic cabinets with them...

Though I've never delt with one, I did have have an end user use one to cool an electronics box ... http://www.exair.com/cabinetcooler/cc_page.htm

The great thing about them is they have no moving parts (and produce no sparks) and cool as long as you have a supply of compressed air (or dry nitrogen).

Edit (Adding): In refference to "an obscure venturi-type" in the previous post, I think andrews was using a variant of vortex tubes.

[yinzer]

Vortex tubes are certainly reliable and lack moving parts, but I think their efficiency is somewhat poor.  Not a problem if you are cooling a relay box in a chemical plant, but possibly an issue if you are trying to do bulk liquefaction of air onboard an airplane.

[BarryKirk]

They also are incapable of generating the extreme cold temperatures required to liquify oxygen.

A standard condensation system is going to need a radiator to reject waste heat.  This radiator is both heavy and bulky.

Remember how much trouble Elon Musk had in getting another shipment of LOX out to his launch island.  LOX manufactoring facilities
are heavy and bulky.  In other words, not something you want to put in the air.

[kevin-rf]

Off of Andrew's webpsite.

http://www.andrews-space.com/content-main.php?subsection=MTAz

It is a vortex tube. The upper atmosphere must be cold enough for this work.

[lmike]

You still need the compressor (and the fuel to power it) to produce the (air-stage) thrust (a.k.a jet engine) to propel those tubes for collection.