Dual-mode SCRAM/conventional jet possible?

(Derek Lyons) wrote:

The real question is... Why add a *second* propulsion system in the
first place? If you need a rocket to get from to the scramjet range,
and then a rocket to get from scramjet range to orbital range... What
is the scramjet adding?

D.

What if you don't want to get to orbit? Let's drop the bias, ok? If a
scramjet isn't useful for putting something in orbit, that doesn't mean it
ain't useful at all.

There are clearly potential uses for scramjets that do not involve
spaceflight at all, and others that involve it only indirectly -- say, as a
reuseable air-launch carrier. Those need to be considered.

As best I can determine, there is no better forum that this one for such
discussion. Let's drop the blinders and consider other possibilities. To
quote Henry's sig, "the box isn't our friend".

/kenw
Ken Wallewein
K&M Systems Integration
Phone (403)274-7848
Fax (403)275-4535

www.kmsi.net

wrote:

(Derek Lyons) wrote:

The real question is... Why add a *second* propulsion system in the
first place? If you need a rocket to get from to the scramjet range,
and then a rocket to get from scramjet range to orbital range... What
is the scramjet adding?

D.

What if you don't want to get to orbit? Let's drop the bias, ok? If a
scramjet isn't useful for putting something in orbit, that doesn't mean it
ain't useful at all.

No, I'm not going to drop the bias. Note that the name of this group
is sci.SPACE.tech, and thus that is context of our discussions here.

There are clearly potential uses for scramjets that do not involve
spaceflight at all, and others that involve it only indirectly -- say, as a
reuseable air-launch carrier. Those need to be considered.

A reuseable air-launcher is *directly* involved in spaceflight...
Period. Thus my objection stands. Any other usage is irrelevant to
the purposes of this forum.

As best I can determine, there is no better forum that this one for such
discussion. Let's drop the blinders and consider other possibilities. To
quote Henry's sig, "the box isn't our friend".

Until you've earned your chops around here, your attitude won't win
friends or influence people. At any rate, your primary question has
already been adressed, and as is the way of Usenet, the thread is
drifting a wee bit.

D.
--
Touch-twice life. Eat. Drink. Laugh.

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

On Thu, 20 Jan 2005 02:10:16 GMT, wrote:

[...]
What if you don't want to get to orbit? Let's drop the bias, ok?

Why? This is a space group, not rec.aviation.hypersonic

If a scramjet isn't useful for putting something in orbit, that doesn't
mean it ain't useful at all.

We'll give you that.

There are clearly potential uses for scramjets that do not involve
spaceflight at all, and others that involve it only indirectly -- say,
as a reuseable air-launch carrier. Those need to be considered.

As best I can determine, there is no better forum that this one for such
discussion. Let's drop the blinders and consider other possibilities.

Actually, you can google for X-43A on sci.space.* and find that we've
discussed it before. The prevailing opinion is that scramjets are a neato
solution still looking for a problem. The most viable problems that
scrams might address seem to be cruise missiles, but for commuter traffic
US to Australia (for example), it sin't clear that they beat suborbital
rockets.

To quote Henry's sig, "the box isn't our friend".

No, but it is nice to have someplace solid to stand when you're thinking
outside the box. And Henry himself doesn't have a problem he wants to
solve with scrams.

/dps

--
Using Opera's revolutionary e-mail client: http://www.opera.com/m2/

writes:

(John Schilling) wrote:
writes:

SCRAMjets would seem to have limited value if they can only be launched
via rocket.

Why? If the only purpose of the rocket is to accelerate the scramjet
to scramjet operating speeds, well, rockets are the absolute best choice
there is for accelerating quickly to hypersonic speeds. Turbojets can

Rockets, as you point out, kinda suck for aircraft because they burn so
much fuel. For craft that may need to cycle multiple times between
supersonic and hypersonic (if you'll accept that terminology) operation
during a single flight, rockets are at a serious disadvantage.


Perhaps, but I don't see how there would ever *be* any "craft that need to
cycle multiple times between supersonic and hypersonic operation during
a single flight".

What mission did you have in mind? And no, ultra-fast jet fighters
dogfighting all over a flight envelope that extends into the hypersonic,
aren't going to happen. The hypersonic missions the military is actually
interested in, only require accelerating once.


--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
* for success" *
*661-718-0955 or 661-275-6795 * -58th Rule of Acquisition *

On Thu, 20 Jan 2005 21:44:33 -0800, in sci.space.tech
(John Schilling) wrote:

Perhaps, but I don't see how there would ever *be* any "craft that need to
cycle multiple times between supersonic and hypersonic operation during
a single flight".

What mission did you have in mind? And no, ultra-fast jet fighters
dogfighting all over a flight envelope that extends into the hypersonic,
aren't going to happen. The hypersonic missions the military is actually
interested in, only require accelerating once.

Accelerating once,yes. But that doesn't then mean you don't need the "low
speed" system to return home for Global Recon or Strike missions. DoD is
definitely interested in this in all our talks with them.
----------
Ed Ruf Lifetime AMA# 344007 )
http://EdwardGRuf.com

Ed Ruf writes:

On Thu, 20 Jan 2005 21:44:33 -0800, in sci.space.tech
(John Schilling) wrote:

Perhaps, but I don't see how there would ever *be* any "craft that need to
cycle multiple times between supersonic and hypersonic operation during
a single flight".

What mission did you have in mind? And no, ultra-fast jet fighters
dogfighting all over a flight envelope that extends into the hypersonic,
aren't going to happen. The hypersonic missions the military is actually
interested in, only require accelerating once.

Accelerating once,yes. But that doesn't then mean you don't need the "low
speed" system to return home for Global Recon or Strike missions. DoD is
definitely interested in this in all our talks with them.


Well, they're certainly going to be interested in getting their vehicle
back. But I rather suspect the best way to do that, is hypersonic. That
is after all what the vehicle is designed for, and the choice is between
the fuel economy of a hypersonic aircraft in its element or the fuel economy
of a hypersonic aircraft wallowing around in the subsonic. The efficiency
of the purpose-built subsonic cruiser was never on the table.

But either way, you still only get one acceleration to the hypersonic.


--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
* for success" *
*661-718-0955 or 661-275-6795 * -58th Rule of Acquisition *

Derek Lyons wrote:

The real question is... Why add a *second* propulsion system in the
first place? If you need a rocket to get from to the scramjet range,
and then a rocket to get from scramjet range to orbital range... What
is the scramjet adding?

Potential weight savings from not having to carry oxidiser along means
smaller booster stage and/or larger payload for given booster stage size.

But will that outweigh the greater weight of the scramjet engine?

No-one knows for sure yet. The University of Queensland scramjet research
program is quite explicitly looking at using them as the second stage for
launchers as its primary mission.

--
Malcolm Street
Canberra, Australia
The nation's capital

In article ,
Malcolm Street wrote:
Potential weight savings from not having to carry oxidiser along means
smaller booster stage and/or larger payload for given booster stage size.

Note, stage costs are largely insensitive to stage size. Actual stage
costs (as opposed to those claimed by simplistic cost models) are driven
strongly by complexity, closeness to leading edge of technology, and
thinness of margins, and only very weakly by size. The big payoff is not
reducing the size of a stage -- especially the first stage, which is
usually a cheap one -- but eliminating a stage.

But will that outweigh the greater weight of the scramjet engine?
No-one knows for sure yet. The University of Queensland scramjet research
program is quite explicitly looking at using them as the second stage for
launchers as its primary mission.

Trouble is, using a scramjet as a second stage means you need a first
stage and a third stage, presumably both rockets.

But... you can get into orbit on two rocket stages alone. In fact, an
Atlas III or V or Delta IV can get you to GTO on two rocket stages alone.

Unless the scramjet weighs nothing and costs nothing, it's quite likely to
raise the total cost, not lower it.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |