Re: Multiple engines (was RE: Liquox)

At 08:29 AM 6/9/2004 -0600, you wrote:
>John,
>
>On the 24" engine costs, is this cost mostly in the catalysts?

About half of it is catalyst.

>   Is
>the cost of a nozzle machined out of solid bar stock becoming a
>major cost? At this size does the nozzle cost make other
>fabrication methods more attractive, such as spin forming or
>forging?

Our current fabricator (Entek) will max out at about 17" diameter 
billets.  We can still make the entrance profile, throat, and expansion 
cone for an 8" throat nozzle inside that, but we will have to weld it to an 
intermediate section of dished tank end to connect to a 24" diameter 
catalyst pack.

Spin forming doesn't seem like it is going to have a winning point over 
machining today.  The tooling cost is more expensive than machining several 
engines, and it still has to be made in two sections, so even mass produced 
it may be more expensive than billet machining.  None of the companies I 
spoke to would be able to spin form half inch thick 316 stainless into a 
24" engine, either.

For larger nozzles, it is going to have to be rolled and welded plate, 
either with a separately machined nozzle throat section, or possibly 
machining the rolled and welded joint.

We are considering an alternate nozzle strategy: lots of little 1" throat 
nozzles welded between two water jet cut plates.  This has cost and 
fabrication benefits, but it also has another really significant benefit: 
any flow separation from low chamber pressures would tend to be randomly 
distributed, rather than the entire engine thrust heading off at a 15 
degree vector, and we can position nozzles so the core jet is right over 
the jet vanes, even at very low chamber pressures.  Moving the jet vanes 
out to the diameter of the catalyst pack instead of the diameter of the 
nozzle exit would also give us 50% more roll authority.

>The engine temperatures look low enough that perhaps
>the last section of nozzle could be made with composite materials,
>perhaps saving some cost and weight.

Because of the relatively low chamber pressures, we don't have much 
expansion ratio, so the exhaust hasn't cooled off all that much by the end 
of the nozzle.  It is still around 1000 F.  Sometimes the bottoms of our 
nozzle look cool because of flow separation inside the nozzle.


>Now that you may not be so tight on time for development, have
>you considered doing more ground bench tests for the engines, to
>work out engine characteristics more?

Yes, but flight testing is more important.  If the engines are working 
"good enough", we want to concentrate on vehicles.  We could spend an 
arbitrary amount of time improving and testing the engines.


>What is your prospects for the flight waver?  How difficult is it to get
>and how much might it allow you to do?

It looks like we should have it fairly soon, but only for flights at the 
southwest regional spaceport in New Mexico, which is a long trip.  We are 
probably going to get a 120 second burn time waiver, which will cover us 
for everything we can do under the 200,000 lb-sec impulse limit.  AST isn't 
requiring a full environmental assesment for the waiver, but they are 
requiring some level of official environmental work, which is why we can't 
get one for our property in Texas.

>   With out the waver would
>you be allowed longer burn times as long as the vehicle is
>tethered?  Have you looked at using some of the new really strong
>but light and felxable cabling that could be spooled out to allow a
>long relatively high flight with minimal interference?

I don't think that would be looked on with favor, and we don't want to 
irritate AST.


>In many ways Bert beating everyone may be a good thing as I've
>been a bit concerned that the X-Prize cutoff date may have been
>pushing people a bit too hard and forcing people to take too much
>risk and jeopardize a future industry.

Really, I don't think there are any other teams in a position to fly.  I 
doubt any other vehicles will even be capable of flight this year, and even 
with statements to the contrary, I don't think anyone is dumb enough to 
actually get in a vehicle on its first flight.

John Carmack