Re: Ares vs DIRECT

John Schilling <schillin@xxxxxxxxxxxxx> wrote:

On Tue, 27 Nov 2007 01:31:14 GMT, fairwater@xxxxxxxxx (Derek Lyons) wrote:

John Schilling <schillin@xxxxxxxxxxxxx> wrote:

On Thu, 22 Nov 2007 12:36:27 -0500, Michael Gallagher
<mikejoe7g@xxxxxxxxx> wrote:

I'm sure you could arrange to fly Orion to ISS on top of an Ares V,
if you were really wedded to the one-launcher idea. Massive overkill,
but doable.

Henry proposed it a looong time ago as a cost saving measure.

And surprisingly similar to what the DIRECT people are proposing...

It just occurs to me... Has anyone compared DIRECT to "Brown Bess"?

Interesting thought; I don't think everyone has ever done that, so I
might as well tackle it now.

Interesting analysis - but I'd like to toss out a few
comments/questions.

The general architectures are similar; a heavy-lift expendable launcher
built around Shuttle components, carrying ~100 tons to LEO in their
nominal configuration, with an option for deleting the upper stage
for lesser payloads.

That last is a bigger hassle than it might seem; it is particularly not
a matter of, "Hey, we don't need the upper stage, let's just leave it
behind this time and save money!". There's a whole lot of structures
and dynamics work that needs to be redone for the new configuration,
plus the upper stage is usually where all the smarts go. So you really
don't get to include that option in your architecture and still say
"We're better because we're doing everything with one vehicle!".

But both DIRECT and Brown Bess did that, so they're tied there.

Sure, the structures and dynamics have to be redone - but what does
that actually do to the cost of the program? I'm assuming that the
costs aren't down in the noise - but also that we aren't talking a
huge fraction of the basic costs.

For my part, I reagrd the comment about not being 'one vehicle' as
verging on semantic nitpicking. A tightly done family is better (from
a costs and operations viewpoint) than a semi-random collection. It's
not really any different from the Delta IV family frex.

The 'smarts' issue is largely a red herring - we aren't talking a
Saturn class IU here, but rather a couple of footlockers with no
particular preference as to which tank dome they are nestled next to.
(Especially if one returns to the Saturn V concept of each stage being
an individual vehicle.)

DIRECT probably wins on vehicle integration. Parallel-staging with the
solids is troublesome, but it's a brand of trouble we have plenty of
experience with, and it's otherwise a pretty well-balanced design. The
Brown Bess's oversized upper stage is troublesome for assembly, and for
dealing with lateral loads. It also leads to performance penalties for
off-nominal missions, e.g. only twenty tons to LEO for the short-stack
version, rather than forty-five tons for DIRECT.

The solids also increase the costs and greatly increase handling
difficulties.

Major difference is, Henry understands that building shuttle-derived HLVs
is a fundamentally bad idea, suitable only for armchair engineering,
whereas the DIRECT proponents seem to thing NASA ought to actually go
out and build the damn thing.

The assumptions behind Bess were pretty much (IIRC) "If we _have_ to
build a Shuttle derived launcher, lets build the technically sweetest
one rather than most politically acceptable one". The DIRECT team
seems, to me, to have adhered to the latter philosophy as does Ares
itself. That's probably the wisest course if one is stumping to
replace Ares.

Folks here all too often forget the political equation is every bit as
real as the rocket equation.
D.
--
Touch-twice life. Eat. Drink. Laugh.

http://derekl1963.livejournal.com/

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL
.

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