Re: Multiple engines (was RE: Liquox)

John,

On the 24" engine costs, is this cost mostly in the catalysts?  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?  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.

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?

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

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.

Looking forward to seeing the medium sized vehicle flying soon!

 - Edward Rupp

John Carmack wrote:
> 
> At 12:01 AM 6/9/2004 +1200, you wrote:
> >Not that I claim to know anything, but:
> >I'm wondering if John is walking (or flying) the inevitable path to
> >gimballing?
> >Starting with multiple engines seemed really marvellous (and it 
was) but he
> >found that jet vanes were immensely more satisfactory in 
practice.
> >The first successful mass produced liquid fuelled rocket used 
jet vanes, but
> >they have pretty much vanished from the medium to large 
sector and been
> >replaced either by vectoring using fluid injection or by 
gimballing. What
> >are the advantages of jet vanes over gimballing?
> >
> >Perhaps:
> >- Less actuator force?
> >- Quicker response?
> >- Includes roll control?
> >- Engine rigidly fixed to frame.
> >- ???
> 
> All of those are indeed benefits of jet vanes.
> 
> The bottom line is that the half dozen times we fired the big 
vehicle with
> four engines, we had noteworthy problems every single time 
getting the
> engines to all warm up at the same time, perform identically, and 
have
> sufficient responsiveness and authority.  In contrast, we have 
done over 30
> jet vane flights with excellent results.
> 
> We have reason to believe that our current build method of heavier
> retaining plates and welding the top hot pack plate in under 
significant
> hydraulic pressure does help the startup procedures, so we 
would probably
> have less trouble with multiple engines than we did a couple 
months
> ago.  It will be an interesting test to see how the new vehicle 
works out,
> because it is using one of the older engines from the big vehicle's
> differential incarnation.
> 
> We have considered making a cluster of four 12" engines with 
interconnect
> pipes between them underneath both the hot pack and cold pack 
to provide
> some level of balancing, but I would still expect some problems 
with that
> arrangement over a single 24" engine.  We don't see any 
particular problem
> in fabricating a 24" engine, it will just cost about $30,000 and 
take a
> month and a half.
> 
> At this point, since it looks likely that Burt is going to win the X-
Prize,
> we are going to stay focused on the 12" engines and waivered 
flights
> without a launch license until one of the commercial spaceports 
actually
> gets their environmental work done so we can bypass paying 
WSMR $1 mil+ for
> doing our flight tests there.  If Burt crashes or otherwise fails in 
his
> attempt this month, we may consider racing at it, but there 
probably isn't
> enough time in any case.
> 
> John Carmack
> 
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