new topic

Ref:[Clements, Robert, Wed, 26/06/02 @ 10:05 +1000]
> > Why would this be that much better than a standard launch?
> The are some rocket efficiency advantages to this approach; & of course you
> significantly reduce the negative impact of friction by launching from
> 50+kms; this is why many amateur rocketeers aiming for height records use
> the approach; & some of the big agencies - including NASA & the DLR - are
> studying the concept. I doubt, thought, that our high altitude
> balloon/rocket technology has reached the point where it was really feasible
> to even consider using the approach at this stage, though.

And as someone else said, you avoid 28 miles of atmospheric
drag. Fair point, and I'm somewhat embarressed I didn't twig
to it, but are the savings enough to develop a whole new
launch method for conventional rockets? If you were slinging
a mass driver underneath, definitely. But for an ariane 5
class of launch platform? I'd want to see figures!

> > I'd personally prefer to see something like the DC-X project
> > restarted and funded as an X-project properly, and to see the
> > aerospike engine used "in anger". Or did I miss something
> > from the SR-71 test they ran with it? Even in 1965 the
> > numbers said that SSTO was the cheapest way to orbit with
> > chemical rockets.
>
> The SSTO numbers are theoretical based on technological capacity which even
> now doesn't really exist; & as i recall, never integrated developmental
> costs into the equation, giving a very distorted picture of the real numbers
> which advocates have been trying - & failing - to match in the real world
> ever since.

Hmmm. Other than the DC-X, how many SSTO projects have ever
gotten off the ground? Excuse the pun but I mean literally:
how many ever got to the stage of launching?
And as to the development costs, the SSTO figures were for
continous operation. Development is by nature harder to
budget for - I had to make out a budget before I built my
robot and I was out by a few hundred percent : but if I had
to do it again now, from scratch, I know how much and how
long it would take to do. That's just the way development
goes. So I wouldn't hold the development costs against the
SSTO concept, just it's operational costs.

> Frankly, though, the DC-X project was basically a technological joke with
> only one real value for space development (its low-cost mission
> administration; which may or may not have been scalable to a plausible
> flight vehicle). There are WWI biplanes still around with better flight
> characteristics than the DC-X; & the high-risk active descent mode is
> generally not considered a plausible way of bringing real craft down from
> orbit... for reasons the ultimate fate of the DC-X rather eloquently
> demonstrated.

Of course DC-X failed - that's what it was meant to do, it's
an X-project for pete's sake! And frankly I thought it was
quite a success. 8 flights in just under 2 years with a new
launcher, small crew working in a pretty unpleasant
environment, and half the launcher made from new materials.
Then DC-XA followed up with 4 flights in 3 months.
And last time I checked, *noone* has ever demonstrated
a 26-hour turn-around before. As to it's flight
characteristics, DC-X was a 1/3 model to demonstrate proof
of concept, not a full test flight model. So it's flight
characteristics were never under test. And the powered
descent is a mode of operation I'm somewhat biased towards
because I'm used to the idea that if the engine fails in
your plane that your landing just became an emergency one!

Mark Dennehy, Email : Mark.Dennehy@...
Computer Vision and Robotics Research Group,
Computer Science Dept., Trinity College Dublin