Scramjet, Pulse Detonation Engines

I read that the X-43 scramjet is being tested today, and I hope all
goes well. But what I also read was that this technology is not
considered optimal for the new agenda on missions to the Moon and
Mars.

It seems that part of the rationale against them, is that they would
likely be SSTO vehicles, whereas Earth-to-Moon and Earth-to-Mars would
favor multi-stage vehicles.

On the other hand, practical scramjet transportation would open up
much greater economies of scale, due to their use in the rapid
intercontinental transit market. This could then significantly reduce
costs for building/operating SSTO scramjet vehicles. Such SSTO
scramjets could be used to dock with and resupply vehicles
specifically designed to travel from earth's orbit to the moon's
surface (ie. non-aerobody)

But what's happening with Pulse Detonation Engines right now? These
would be versatile way to get around, if they prove to work. I've
read that a weakness of Pulse Detonation Engine technology is that it
requires significant ambient backpressure (ie. atmospheric pressure)
in order to work efficiently.

I'd imagine then that in a TSTO, PDEs could be used for the lower
stage, which could return back to earth unpiloted and under its own
power. Then the upper stage could be a regular rocket.

Here's a recent picture of one:
http://www.space.com/imageoftheday/i...ay_030804.html

Looks like something off a suped-up hot rod.

So which technology looks like a more promising mass-market candidate
-- PDEs or scramjets? Both seem designed for mass-market use, but PDEs
seem more versatile, since they could even be used for vertical
liftoff.

In article ,
sanman wrote:
...But what I also read was that this technology is not
considered optimal for the new agenda on missions to the Moon and Mars.

It's not optimal for anything to do with spaceflight. It's a technology
for high-speed cruising flight within the atmosphere, which is a
completely different application.

But what's happening with Pulse Detonation Engines right now?

They're the technology of the future, just like they have been for half
a century now... and probably will be for the next half-century too.

So which technology looks like a more promising mass-market candidate
-- PDEs or scramjets?

Neither. At present, both are of interest only for specialized military
applications.

And neither has much to do with spaceflight. Rockets are the technology
of choice for that.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

(Henry Spencer) wrote in message ...
It's not optimal for anything to do with spaceflight. It's a technology
for high-speed cruising flight within the atmosphere, which is a
completely different application.

But what's happening with Pulse Detonation Engines right now?

They're the technology of the future, just like they have been for half
a century now... and probably will be for the next half-century too.

Well, that's why I posted the AFRL site link, which claims more
demonstrable progress in this technology. Please check out the videos,
which I found to be very interesting.

Neither. At present, both are of interest only for specialized military
applications.

Well, perhaps the desire for rapid intercontinental travel will
generate more interest in commercial development.

And neither has much to do with spaceflight. Rockets are the technology
of choice for that.

I thought that scramjets can help to achieve a good part of escape
velocity, with some supplementary rocket thrust required to achieve
orbit. I've read that PDEs can also be adapted for rocket propulsion,
perhaps as part of combined-cycle engines, as might scramjets.

sanman wrote:
Well, perhaps the desire for rapid intercontinental travel will
generate more interest in commercial development.

IIRC, at the moment, the time to get from SFO to LHR is something like
11 hours. One leaves at say 1900 one day and arrives at something
like 1400 the next. (I may have things off by an hour or two, I'm
recollecting from a trip back in 1999)

Am I really better-off jet-lag wise if I get there in two hours?

If I still leave at 1900 SFO time, arrive at 0500 LHR time, probably
not having slept at all where the previous flight time had some chance
(well, as likely as one can on a commercial airliner today) of having
slept.

I suppose perhaps I'm now better-off leaving SFO at 0900 and arriving
at LRH at 1900, but I'm not sure yet.

Are things better going the other direction?

rick jones
--
oxymoron n, commuter in a gas-guzzling luxury SUV with an American flag
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to raj in cup.hp.com but NOT BOTH...

In article ,
sanman wrote:
...At present, both are of interest only for specialized military
applications.

Well, perhaps the desire for rapid intercontinental travel will
generate more interest in commercial development.

Not likely. Engines are not the bottleneck in the development of rapid
intercontinental travel. In the past, studies of this have generally
concluded that the point of diminishing returns sets in around Mach 5 or
so: beyond there, the shortening of travel time no longer buys you as
much, the technology becomes more and more problematic, and the necessary
changes in infrastructure (e.g. facilities for new fuels) start to become
very costly. Turboramjets should be adequate to go that fast.

And neither has much to do with spaceflight. Rockets are the technology
of choice for that.

I thought that scramjets can help to achieve a good part of escape
velocity, with some supplementary rocket thrust required to achieve
orbit.

The question, always, is not whether it can be done, but whether it's
actually *better* than just making a rocket's tanks bigger. Replacing
simple tanks of liquid oxygen with heavy, complex high-tech machinery
which requires flight in extremely hostile aerothermal conditions is most
unlikely to be a net win.

"Throwing away the LOX tanks on a launch vehicle is very nearly the
stupidest possible design decision ever." -- Christopher M. Jones

--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

In article ,
Rick Jones wrote:
Well, perhaps the desire for rapid intercontinental travel...

IIRC, at the moment, the time to get from SFO to LHR is something like
11 hours...
Am I really better-off jet-lag wise if I get there in two hours?

Yes and no.

To jet lag, per se, it makes no difference at all. That's driven by the
difference in time zones between the two ends, not by the trip time. If
you sat in your living room for the specified trip time, and were then
instantaneously teleported to the destination, you'd still have jet lag
when you tried to switch to the destination's sleep/wake schedule.

However, reducing the fatigue produced by the trip itself, and the
disruption of sleep schedules caused if the trip occurs during normal
sleep times, might make the transition a bit less unpleasant.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

"sanman" wrote in message
om...
(Henry Spencer) wrote in message
...

Neither. At present, both are of interest only for specialized military
applications.

Well, perhaps the desire for rapid intercontinental travel will
generate more interest in commercial development.

And neither has much to do with spaceflight. Rockets are the technology
of choice for that.

I thought that scramjets can help to achieve a good part of escape
velocity, with some supplementary rocket thrust required to achieve
orbit. I've read that PDEs can also be adapted for rocket propulsion,
perhaps as part of combined-cycle engines, as might scramjets.

I'm no expert, but I think you might have got caught up in the emotion of
all this and overlooked a couple of minor points:

1. Supersonic Combustion (SC) Ramjets only work at *supersonic* speeds...
and aren't much good either side of that speed (around Mach 7 it seems)
either. Cruising at Mach 7 for a bit, is certainly no way to get to orbit.

2. You have to *get* to the right speed first, before you can use it. This
makes scramjets great for ICBM's (hell, at that speed you wouldn't even need
a warhead! ;-) and lousy for passenger transport ("hang onto your hats
folks!" ;-).

As for PDE's? Well...

Cameron:-)

In article ,
says...
sanman wrote:
Well, perhaps the desire for rapid intercontinental travel will
generate more interest in commercial development.

IIRC, at the moment, the time to get from SFO to LHR is something like
11 hours. One leaves at say 1900 one day and arrives at something
like 1400 the next. (I may have things off by an hour or two, I'm
recollecting from a trip back in 1999)

Am I really better-off jet-lag wise if I get there in two hours?

You are. If you're going there to attend a meeting or pick something of
high value up, you're going to be back in your own bed before bed-time.
At worst you're looking at having a meeting after missing most of a
night's sleep.

If you're going there to stay, the long slow trip on a conventional jet
liner doen't give you enough time to shift your bio-clock anyway, so you
might as well take the rapid transport and waste less time in the air.

If what you're trying to accomplish is of enough value, the faster
transport will always win out. Jet lag really isn't a consideration.

Marc

http://www.pr.afrl.af.mil/divisions/...Q/pde_faq.html

PDE's can take off under their own power and attain mach four with great
efficiency. They are light and simple to make.
As airbreathing flyback launchers with very good Isp, what's not to like,
unless you're a misanthrope wishing us all the worst luck?
^
//^\\
~~~ near space elevator ~~~~
~~~members.aol.com/beanstalkr/~~~

In article ,
Allen Meece wrote:
http://www.pr.afrl.af.mil/divisions/...Q/pde_faq.html
PDE's can take off under their own power and attain mach four with great
efficiency. They are light and simple to make.

And not one has ever flown. All those nice properties are "projected" or
"predicted" or "estimated"... and the impact of nasty little problems like
noise and vibration is still uncertain. (Notice that the pretty graph on
that web page also shows scramjets, another largely-vaporware technology.)

As airbreathing flyback launchers with very good Isp, what's not to like...

Noise, vibration, uncertain lifetime, unverified performance, poorly
developed technology, lack of commercial availability.

And of course, the fact that not everybody thinks an airbreathing flyback
launcher is worth the trouble.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |