Newsgroups: sci.space.history,sci.space.policy
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Rockets - Room for Improvement
Date: Mon, 17 May 1999 16:05:04 GMT

In article <7hbrd8$u05$1@nnrp1.deja.com>,  <knd6593@my-dejanews.com> wrote:
>Several times in this and related NG, Henry has stated that the
>current state or rocketry is still in its infancy and that the
>current state of the art is not optimial.
>How can rockets be improved upon?  I guess pressure rockets are
>one way, what other ways are there? Build them out of all composites
>materials?

Composites, for sure.  Altitude-compensating nozzles are another area
which could use some attention.  But above all, there ought to be an
ongoing effort to explore the technology and test-fly the most promising
ideas.  Far too many things in this field are still stuck using the first
method that worked well thirty or forty years ago... often accompanied by
baseless superstitions about why it's best.  Or something gets trashed
because it was tried *once* and didn't work well, often for completely
irrelevant reasons.

For an example of the former, consider regenerative cooling of chambers.
In fact, this is a particularly glaring example of an emperor with not
many clothes, because regenerative cooling *invariably* has to be
supplemented with something else, e.g. curtain cooling, to work well
enough.  Yet there has been little work on general-purpose alternatives,
even though regeneratively-cooled chambers are a pain to build and tend to
have short working lives.

For an example of the latter, consider staged combustion.  It got a bad
name in the US because of the SSME.  Turns out that the Russians use it
all the time and haven't had one tenth of the trouble.
--
The good old days                   |  Henry Spencer   henry@spsystems.net
weren't.                            |      (aka henry@zoo.toronto.edu)

From: greason@my-dejanews.com
Newsgroups: sci.space.history,sci.space.policy
Subject: Re: Rockets - Room for Improvement
Date: Wed, 19 May 1999 18:31:57 GMT

In article <FBvwoG.834@spsystems.net>,
  henry@spsystems.net (Henry Spencer) wrote:

> Composites, for sure.  Altitude-compensating nozzles are another area
> which could use some attention.

Yep.  There's a *LOT* of good ideas out there on altitude
compensation.  Aerospikes.  Dual Bells.  Dual Throat/Dual Expansion.
And some others which are a bit too sensitive to talk about.  All
out there for years -- never flown yet.

> For an example of the former, consider regenerative cooling of
> chambers.  In fact, this is a particularly glaring example of
> an emperor with not many clothes, because regenerative cooling
> *invariably* has to be supplemented with something else, e.g.
> curtain cooling, to work well enough.  Yet there has been little
> work on general-purpose alternatives, even though
> regeneratively-cooled chambers are a pain to build and tend to
> have short working lives.

Long-life chambers, regardless of mechanism, are a crying need
in rocket engines.  It's occupied a lot of my thinking for the
last 2 years.  I'm more bullish on regenerative cooling's
ability to provide long life than you seem to be -- but it's
another area with a huge collection of ideas floating around
very few experimental opportunities.  Rocket engine lives should
be measured in thousands of cycles and hundreds of hours, whereas
the best engines today are dozens of cycles and tens of hours.

Other areas:

* Engines have a *LOOONG* way to go in terms of cost.  A
  rocket engine is a much simpler artifact than a jet engine, but
  today they are *more* expensive, not less.

* Packaging flexibility: there's a lot you can do to improve
  overall vehicle performance by matching the packaging
  of the engine to the packaging requirements of the vehicle.
  Instead, today, most vehicle design efforts are handicapped by
  using one of the few viable existing engines, which grossly
  compromises the overall design.

* Reduced consumables -- most engines today use a lot more than
  fuel and oxidizer.  You've got start cartridges of some kind,
  probably two pressurant/purge gases, maybe some kind of
  hypergolic injectant, etc.  Wouldn't take a lot of development
  to come up with a "gas & go" rocket engine -- but it's never
  been a priority that I can think of.  Availability of good
  RCS thrusters which use common propellants with the main
  propulsion would also help here.

* Reduced inspections per flight.  Again, not something insuperable,
  but it takes work that hasn't happened yet.  Again, this is
  required for a "gas & go" vehicle.

Note that with the exception of altitude compensation, these areas
needing work aren't really performance-driven.  They're more
focused on cost and operability.  I don't see a lot of room for
improved vacuum performance of rocket engines with chemical fuel;
but then, they don't *need* much more performance.  I *do* think that
further increases in thrust/weight are attainable, but I'd be a lot
happer with today's thrust/weight but good altitude compensation and
operability!

Needless to say, this is a topic much on my mind, and I'm working
on tackling some of these areas.  Therefore, I'm not going to say
much about *how* I think they can be improved -- but they clearly
need improvement.
-----------------------------------------------------------------
Contact me at:                                Jeff Greason
   greason at ix dot netcom dot com           Propulsion Manager
All opinions expressed are solely my own.     Rotary Rocket Company