Hi friends:

Nasa test its scramjet engine. The mark was Mach 10!!!!
The SSTO is approaching :)

tmpl=story&cid=570&ncid=753&e=1&u=/nm/20041117/sc_nm/space_scramjet_dc

I'm going to party now :) :)

Regards,

Omar Vega

> From: Omar E. Vega [mailto:oevega@...]
> Nasa test its scramjet engine. The mark was Mach 10!!!!
> The SSTO is approaching :)
>
117/sc_nm/space_scramjet_dc
> I'm going to party now :) :)

And on the other hand we have rockets which have worked for decades, are
easy to build and do not require optimisation of the rest of the vehicle in
order to merely function - let alone produce useful thrust. By all means
lets throw away the old and proven for the new and experimental.

If raw speed was an issue everyone wodl be using ground-based mass drivers.
I must confess I remain skeptical as to the utility of a airplane/spaceship
compromise.

John

how easy is it to build successful rockets? My impression was the weight to payload ratio made rockets unsatisfactory, as well as the one shot utility of many of them?

-----
And on the other hand we have rockets which have worked for decades, are
easy to build and do not require optimisation of the rest of the vehicle in
order to merely function - let alone produce useful thrust. By all means
lets throw away the old and proven for the new and experimental.

> If raw speed was an issue everyone wodl be using ground-based mass
drivers.
> I must confess I remain skeptical as to the utility of a
airplane/spaceship
> compromise.
>
> John

I don't believe so, John. I think that if the guys develop a motor
that is able to work as a jet engine, then the whole matter of
sending loads to the space will become more easy than today.

I see the following advantages:

(1) There is a large saving in fuel. In an important part of the path
the motor consumes oxygen from the atmosphere.

(2) In the future a 3-phases scramjet could start firing as a rocket,
switch to scramjet mode in the critical part of the path and back to
rocket again when it leaves the atmosphere. If that is done, the
savings in engine hardware and load will be very large indeed.

(3) If things goes well, that kind of motors could be used in regular
hypersonic planes for hurried executives. So, they could be mass
produced (the motors, not the executives :) ). Making the cost of
going up there a lot cheaper.

The point is. If going to the space became cheaper then, space
tourism, SPS, and finally space settlements, will be at reach.

That's what we are talking about. Aren't we? :)

Regards,

Omar Vega

"Omar E. Vega" wrote:
>
> > If raw speed was an issue everyone wodl be using ground-based mass
> drivers.
> > I must confess I remain skeptical as to the utility of a
> airplane/spaceship
> > compromise.
> >
> > John
>
> I don't believe so, John. I think that if the guys develop a motor
> that is able to work as a jet engine, then the whole matter of
> sending loads to the space will become more easy than today.
>
> I see the following advantages:
>
> (1) There is a large saving in fuel. In an important part of the path
> the motor consumes oxygen from the atmosphere.
>
> (2) In the future a 3-phases scramjet could start firing as a rocket,
> switch to scramjet mode in the critical part of the path and back to
> rocket again when it leaves the atmosphere. If that is done, the
> savings in engine hardware and load will be very large indeed.
>
> (3) If things goes well, that kind of motors could be used in regular
> hypersonic planes for hurried executives. So, they could be mass
> produced (the motors, not the executives :) ). Making the cost of
> going up there a lot cheaper.
>
> The point is. If going to the space became cheaper then, space
> tourism, SPS, and finally space settlements, will be at reach.
>

Omar, I'd agree with you ... except that (3) makes me remember the
Concorde, and the stink that was raised around the world against it when it
first started to fly. Even before the crash in France, it was losing
money, becoming pretty much only a fun thing to do for people who could
afford to pay $8k US to make the trip. Now video-conferencing solves most
of the "I need to see you tomorrow!" problems, and anything beyond tomorrow
or the day after can get by with ordinary, subsonic jet flight.

And it's a NASA project, which means that it will be over-engineered, but under-constructed.

Steve

From: ANTIcarrot [mailto:dante.feditech@...]

" And on the other hand we have rockets which have worked for
decades, are easy to build and do not require optimisation of the rest of
the vehicle in order to merely function - let alone produce useful thrust.
"

There *are* reasons to favour some of the newer approaches. The first is
that a Scramjet first stage -- or even a `normal' jet first stage, such as
Scaled Composites' `White Knight' lifter for `SpaceShipOne' -- can provide
Cheaper Access To Space (CATS), which has been a * very reasonable* goal
from the beginning. (Old-style rockets might be "easy to build", but that
doesn't mean they'll cost less than a new, better, more efficient system.
ELV vs. RLV) Second -- and much more important, I would think --we have to
talk about safety. The cryogenic fuels used in the rockets you favour --
and in the Shuttle -- are very expensive to store *and* to create, and very
dangerous. `Challenger' blew up during launch, because the cryogenic
fuel/oxidizer combination it used was extremely explosive. And `Columbia'
disintegrated in mid-air during an attempted landing, because the cryogenic
nature of it's fuel/oxidizer mix created massive pieces of ice, which came
off the ET during launch (possibly carrying pieces of insulation with
them?), that damaged the heat-shielding tiles. Neither of these tragedies
would have occurred using the Scramjet technology of the X-43, or the system
Scaled Composites demonstrated *can* reach space.

There's a line between using `what works' -- and switching to what's better.
I understand the more conservative viewpoint, but the old, cryo-fueled ELVs
need to go away, as quickly as possible, especially for manned launches.
Just IMO, of course...

Dave

> From: Omar E. Vega [mailto:oevega@...]

> I don't believe so, John. I think that if the guys develop a motor
> that is able to work as a jet engine, then the whole matter of
> sending loads to the space will become more easy than today.
>
> I see the following advantages:
>
> (1) There is a large saving in fuel. In an important part of the path
> the motor consumes oxygen from the atmosphere.
>
> (2) In the future a 3-phases scramjet could start firing as a rocket,
> switch to scramjet mode in the critical part of the path and back to
> rocket again when it leaves the atmosphere. If that is done, the
> savings in engine hardware and load will be very large indeed.
>
> (3) If things goes well, that kind of motors could be used in regular
> hypersonic planes for hurried executives. So, they could be mass
> produced (the motors, not the executives :) ). Making the cost of
> going up there a lot cheaper.

As I said, if it was purely a matter of speed then we'd all be using mass
drivers. But it isn't a matter of speed! It's a matter of going at that
speed _through_the_atmosphere_ for a prolonged period of time. The problems
of building a mach25 scram-jet pale in comparison with the problems of
building a ship that can withstand the heat long enough to get to those
speeds in the first place!

There are reasons rockets go up and then sideways, and not the other way
round as the spaceplane concept requires.

> From: Dave Logsdon [mailto:templar@...]
> There *are* reasons to favour some of the newer approaches.
> The first is that a Scramjet first stage can provide
> Cheaper Access To Space (CATS)

How? How can a technology that requires decades of expensive research before
it's up to the job and breakthroughs in material science before it's even
practical possibly be cheaper in the near term than a proven technology with
a wide technology base whose principles are widely understood?

> ELV vs. RLV

RLV has nothing to do with space planes. The X-43 is a spaceplane. It ain't
reusable though. The DC-X would not have been a spaceplane, but it would
have been reuseable.

> The cryogenic fuels used in the rockets you favour

And what will be powering your scram-jets if not highly explosive cryogenic
fuel? Fairy dust?

Challanger blew up because it was deliberately flown well outside of it's
operational envelope. You'd get exactly the same result if you tried to make
a 747 do a loop-the-loop. The only thing the hydrogen did was make the
fireworks a little prettier. The columbia broke up because of a string of
very stupid management decisions, going back to the basic design of the STS
shuttle. Please note that the shuttle is the ONLY rocket where the heat
shield, or any part of the payload, can be damaged by falling debris.

You can't fairly use the shuittle as a rocket case study because it is so
unique, and because it so uniquely badly designed. Though the same can't be
said when comapiring it to the space planes you seem to favour. For
instance, how you you incorporate an escape system into the design? What
happens when you try and take off from a French airport and one of your
wheels throws a piece of jagged metal up against the TPS? Or the tire
explodes and you're hurtling down the runway at hundreds of miles per hour?
What happens when one of your beyond bleeding edge engines goes wrong and
the fuel catches fire just before rotation?

I also agree that ELVs should be replaced. I'm just more inclined to the
TSTO VTOL RLV, instead of the SSTO HTOL RLV, as simplier, cheaper and more
likely to succeed. Space planes are potentially very useful, but they are
not the universal solution to a simple problem - as people sometimes claim
they are.

John

ANTIcarrot wrote:

>There are reasons rockets go up and then sideways, and not the other
way
round as the spaceplane concept requires.

With respect, that's a deeply biased argument. Rockets go up for two
reasons:

1/ to get out of the bulk of the atmosphere as efficiently as possible
since it's nothing but drag for them.

2/ to reduce gravity costs on a non-lifting body.

Scramjets will fundamentally take a different approach ("flying into
space") since:

1/ flying your scramjet up and through Mach10 to Mach20ish requires an
atmosphere. ...Preferably a very thin high altitude one. ;-)

2/ the airframe will provide lift to offset gravity.

Thinking further on that thin atmosphere issue (and how the recent test
was /hot/ on the vehicle)...Drag is proportional to the density times
velocity-squared. So it must be possible to develop a scramjet airframe
for which the drag (and hence the heating) is comparable to modern jet
aircraft, by simply flying it high enough.

Here's an example: the SR-71 flew at (a sustained) Mach-3 over forty
years ago, at an altitude of 85000' (~22mb) and it reached skin
temperatures of 430C. If I want to fly my scramjet to Mach-20 before
lighting the rockets for orbit, I'd want to do it where the pressure's
about 1mb for a similar level of skin heating. Say at 48km or so.
(There's a handy pressure/altitude calculator here:
http://www.digitaldutch.com/atmoscalc/). Hmmm...Are there any online
studies of scramjet launch profiles I could be pointed to that have
previously looked into this? Or does the additional need for a TPS on
the vehicle for re-entry generally mean that high speed flight
conditions are automatically covered?

Andy Goddard

Scram jets on their own are a complete non-starter. They need to be
accelerated to supersonics speeds before they can even be started, so
any launcher based on the scram-jet idea would need to be boosted to
high speed by a rocket, which would probably mean a complex muti-
stage vehicle which kind of defeats the object of a cheap launcher.

A British company called Reaction Engines limited have been working
on a better solution for around 10 years already, called Skylon.
Unfortunately Britain being Britain, they have received no government
support whatsoever and so funding for research has been very limited.

Before you say - "Oh nice slick website with nice graphics but I
can't see that working", bear in mind that the Designer of the Sabre
Engine for Skylon is Alan Bond, once the head of engine design at
Rolls Royce, a brilliant and innovative Engineer. Alan had already
designed and produced a prototype air breathing rocket (LACE) engine
for a previous rocket plane idea called HOTOL.

If only Alan had American government backing, a cheap launcher would
already be available to NASA and their current exploration plans
would appear far more realistic.

Take a look at the Reaction Engines website:-

http://www.reactionengines.co.uk/

Mark

--- In spacesettlers@yahoogroups.com, "Andrew Goddard"
wrote:
> ANTIcarrot wrote:
>
> >There are reasons rockets go up and then sideways, and not the
other
> way
> round as the spaceplane concept requires.
>
> With respect, that's a deeply biased argument. Rockets go up for two
> reasons:
>
> 1/ to get out of the bulk of the atmosphere as efficiently as
possible
> since it's nothing but drag for them.
>
> 2/ to reduce gravity costs on a non-lifting body.
>
> Scramjets will fundamentally take a different approach ("flying into
> space") since:
>
> 1/ flying your scramjet up and through Mach10 to Mach20ish requires
an
> atmosphere. ...Preferably a very thin high altitude one. ;-)
>
> 2/ the airframe will provide lift to offset gravity.
>
> Thinking further on that thin atmosphere issue (and how the recent
test
> was /hot/ on the vehicle)...Drag is proportional to the density
times
> velocity-squared. So it must be possible to develop a scramjet
airframe
> for which the drag (and hence the heating) is comparable to modern
jet
> aircraft, by simply flying it high enough.
>
> Here's an example: the SR-71 flew at (a sustained) Mach-3 over forty
> years ago, at an altitude of 85000' (~22mb) and it reached skin
> temperatures of 430C. If I want to fly my scramjet to Mach-20 before
> lighting the rockets for orbit, I'd want to do it where the
pressure's
> about 1mb for a similar level of skin heating. Say at 48km or so.
> (There's a handy pressure/altitude calculator here:
> http://www.digitaldutch.com/atmoscalc/). Hmmm...Are there any online
> studies of scramjet launch profiles I could be pointed to that have
> previously looked into this? Or does the additional need for a TPS
on

> From: Andrew Goddard [mailto:a.goddard@...]
> With respect, that's a deeply biased argument. Rockets go up for two
> reasons:
>
> 1/ to get out of the bulk of the atmosphere as efficiently as possible
> since it's nothing but drag for them.

True.

> 2/ to reduce gravity costs on a non-lifting body.

Not true. Rockets 'reduce their weight' through orbital speed, not height.
You have to thousands of km up before such a reduction is even noticable.

> 1/ flying your scramjet up and through Mach10 to Mach20ish requires an
> atmosphere. ...Preferably a very thin high altitude one. ;-)

Ugh. Okay, let's assume you're right and they *fly* into space. Flying is
when the wings provide a substantially larger thrust vector than the engines
do. (On a 747 they produce 3x more. On a F-15 they can produce 10x more.) By
nature they have poor acceleration when compaired to rockets. This means
that it will take you much longer to get into orbit that a rocket. Because
you're trying to shove through the atmosphere, a huge chunk of your
potential acceleration is going to dissapear. So it's going to take you much
much much longer to get into orbit.

An hour or more (instead of 6 minutes) is probably not unreasonable when you
compare the 0-Mach3.0 times of any rocket based missile and any jet capable
of that speed. I'll come back to this in a minute.

> So it must be possible to develop a scramjet airframe
> for which the drag (and hence the heating) is comparable to modern jet
> aircraft, by simply flying it high enough.

Yes it would be. But you'd have lots of problems getting the same aiframe
generating any lift at landing speeds. It's be the same problem of the
dog-fight wing VS the landing-wing that have plagued jet fighters for
decades. Except much worse of course.

> Here's an example: the SR-71 flew at (a sustained) Mach-3 over forty
> years ago, at an altitude of 85000' (~22mb) and it reached skin
> temperatures of 430C.

Which sounds impressive, until you are told that the SR-71 was intended to
go half a mach number higher, but that they could never get it to work that
way. Flying very fast through an atmosphere is terribly difficult. In all
those decades the best a jet-aircraft has managed is Mach 9.9 - and only
within the past week. The X-15 was IIRC flying before the SR-71, and beat
its never exceeded speed by a good 100%.

But lets say you can build a scam-jet that can throttle between mach 3 and
mach 25 (and throttable for the associated thrust levels!) and that you can
find some way to fly it up through the air without exceeding a skin
tempreature of 430C. You've got to insulate your passengers, your payload,
your RCS/OMS fuel, and your cryogenic scamjet fuel from that tempreatures
for the length of your flight to orbit. This is also terribly difficult.
Then come the horrid part. Getting back down again.

Now in theory, you can fly down BUT ONLY if you have enough cryogenic
scram-jet fuel to power you for another hour; since flight at such safe
speeds requires your scram-jets to be working. Otherwise you generate more
drag than lift, fall into the lower atmosphere and melt. With an established
refueling station in orbit this would be easy, but otherwise you have to
carry that fuel up from the ground, keep it in orbit, and then keep it
protected from the same one hour long oven tempreatures of 430C until you
land again. Of course that will also be rather fun considdering the problems
of lift.

Of course you could carry a 5000C rated heatshild like the shuttle does and
reenter the hard way, but that has *major* problems of its own, and whatever
super-light super-strong TPS you can come up with can just as easily be
applied to capsule designs. Which will be simplier and cheaper for the next
few decades at least.

John

Hi there!

I wrote:
>> 2/ to reduce gravity costs on a non-lifting body.

ANTIcarrot replied:
>Not true. Rockets 'reduce their weight' through orbital speed, not
height.
You have to thousands of km up before such a reduction is even
noticable.

I think I wasn't clear enough. You could rocket into orbit at 1/10g,
taking your time (and your granny), /if/ fuel wasn't an issue. That
rockets do it as fast as possible is to reduce the fuel requirements
imposed on them by the presence of a gravity well. These are the gravity
costs I was referring to.

>Ugh. Okay, let's assume you're right and they *fly* into space.

You're perhaps being a little disingenuous. They will fly (as in
generate lift in an atmosphere) for as long as possible, before a final
rocket kick gets them into true orbit. This last part will be ballistic,
as the atmospheric density will be virtually nil.

>Flying is
when the wings provide a substantially larger thrust vector than the
engines
do. (On a 747 they produce 3x more. On a F-15 they can produce 10x
more.)

The scramjet, at Mach 15 - possibly the upper limit to air-breathing
engines - will have gained 2/3rds of its orbital velocity. At these
speeds that old centripetal acceleration actively /reduces/ the lift
required from the wings. In a near-horizontal flight at Mach-15 the
gravity component is - what? - down to about 6m/s2.

>By
nature they have poor acceleration when compaired to rockets. This means
that it will take you much longer to get into orbit that a rocket.

That's fine: after all, it doesn't need to carry the oxidiser to achieve
a whole 2/3rds of its orbital velocity, nor does it need to carry the
fuel and oxidiser to propel that oxidiser. It's win-win.

Look at any LOX/LH mix: the SSME has a listed mixture ratio of 6.03:1.
The oxidiser is the "6" part. Imagine saving 60%-80% of the
fuel/oxidiser currently burned per kilo to reach orbit. The vehicle
would be smaller, presumably more durable, and able to commit a larger
fraction of its flying weight to payloads.

>> So it must be possible to develop a scramjet airframe
>> for which the drag (and hence the heating) is comparable to modern
jet
>> aircraft, by simply flying it high enough.

>Yes it would be. But you'd have lots of problems getting the same
aiframe
generating any lift at landing speeds. It's be the same problem of the
dog-fight wing VS the landing-wing that have plagued jet fighters for
decades. Except much worse of course.

No. The designed lift required for flight in the hypersonic envelope
will mean more lift when the vehicle returns unpowered (as it'll have
less mass). Why assume a powered fly back? The shuttle is more than a
little lacking in lift during its landing approach, but it's energy-rich
(has lots of PE to shed) and has had no landing accidents to date. Why
assume a scramjet needs to fly back under power to its launch site, or
need to do better than a shuttle glide-in?

>But lets say you can build a scam-jet that can throttle between mach 3
and
mach 25 (and throttable for the associated thrust levels!) and that you
can
find some way to fly it up through the air without exceeding a skin
tempreature of 430C. You've got to insulate your passengers, your
payload,
your RCS/OMS fuel, and your cryogenic scamjet fuel from that
tempreatures
for the length of your flight to orbit. This is also terribly difficult.

Well, you'll have to insulate those items that reach 430C (leading
edges). Is that difficult? Not if you're rich in a large mass of LH to
start with. So cryogenic cooling would be one answer - and it'd help by
warming the LH for subsequent combustion, too.

>Of course you could carry a 5000C rated heatshild like the shuttle does
and
reenter the hard way, but that has *major* problems of its own, and
whatever
super-light super-strong TPS you can come up with can just as easily be
applied to capsule designs. Which will be simplier and cheaper for the
next
few decades at least.

I agree with you there. Don't get me wrong - I'm all for the
man-inna-can option that's worked well for decades, but I wouldn't rule
out a potentially safer and more efficient route to space for the masses
in a 20-30 year timeframe.

Andy Goddard

> From: Andrew Goddard [mailto:a.goddard@...]
> Don't get me wrong - I'm all for the
> man-inna-can option that's worked well for decades, but I
> wouldn't rule out a potentially safer and more efficient
> route to space for the masses in a 20-30 year timeframe.

Ah - sorry. ;) Thought you were one of the people that insisted that a
spacecraft must look like a plane in order to operate like a plane, and that
an RLV capsule based design could never do this. Similarly, don't get me
wrong. A scramjet-spaceplane would have tremendous advantages over a capsule
in terms of safety, utility, and comfort.

However I agree with the 20-30 year estimate as a minimum, and can't hlep
but wonder if a space-elevator could be possible by then. Which would beat
both other options hands down. ^.^

In answer to your other points...

> I think I wasn't clear enough. You could rocket into orbit at 1/10g,
> taking your time (and your granny), /if/ fuel wasn't an issue. That
> rockets do it as fast as possible is to reduce the fuel requirements
> imposed on them by the presence of a gravity well. These are
> the gravity
> costs I was referring to.

Ah, my mistake. That would mean though that you're carrying more fuel than a
rocket would for an equivolent payload. A good 2/3s of the shuttle's
external tank is liquid hydrogen. You'll always need a lot of volume if
you're using that. Methane would be a good substitute, but it's not quite as
light.

> The scramjet, at Mach 15 - possibly the upper limit to air-breathing
> engines - will have gained 2/3rds of its orbital velocity. At these
> speeds that old centripetal acceleration actively /reduces/ the lift
> required from the wings. In a near-horizontal flight at Mach-15 the
> gravity component is - what? - down to about 6m/s2.

Yes, but it's at low speeds that lift becomes a problem. This was the part
of the 'it'll take ages so you'll need to carry a hell load of fuel'
arguement.

> The vehicle
> would be smaller, presumably more durable, and able to commit a larger
> fraction of its flying weight to payloads.

Probably not. Hydrogen takes up ~3x the volume of oxygen. Beyond a certian
point the increased size and weight of the hydrogen take outweighs the
savings in oxygen.

> No. The designed lift required for flight in the hypersonic envelope
> will mean more lift when the vehicle returns unpowered (as it'll have
> less mass).

Lift is directly proportional to speed. Reasonable lift at M15 means
negligable lift at M0, and reasonable lift at M0 means control difficulties
at M15 without a complex or variable geometry wing. It's a solvable problem,
but not an easy one.

> Why assume a powered fly back?

Otherwise you'll need a very fragile or very heavy heatshield - or wait a
couple of decades for the material science to catch up. It'd also be far
more comfortable for passengers and crew. But I agree this isn't an
essential requirement if you're willing to wait for a light weight
heatshield.

> Why
> assume a scramjet needs to fly back under power to its launch site, or
> need to do better than a shuttle glide-in?

Because waiting for the weather to be reasonable enough for the shuttle to
land has caused a lot of problems for the programme over the years. Notably
a mis-forecast forced a delay on Challanger which made the controllers make
a haisty decision on whether to launch after a frosty night. I'd also
strongly recomend some kind of engine for a second chance at landing, or to
allow diversion to a second landing strip.

John

> > 2/ to reduce gravity costs on a non-lifting body.
>
> Not true. Rockets 'reduce their weight' through orbital speed, not height.
> You have to thousands of km up before such a reduction is even noticable.
>

I think the gravity equation uses r-squared as the divisor, so that if you
assume that Earth's surface is 6400 km from the "center of gravity" then at
about 1440 km (900 miles) altitude you've lost half of your "weight", which
I think would be pretty noticeable.

Or have I screwed up my math? ... 30 years of writing computer
programs that summarize invoices have rotted my brain. :-)

Steve

On Thu, 18 Nov 2004 11:08:03 -0500, Steve Long wrote:
(...)
> I think the gravity equation uses r-squared as the divisor, so that if you
> assume that Earth's surface is 6400 km from the "center of gravity" then at
> about 1440 km (900 miles) altitude you've lost half of your "weight", which
> I think would be pretty noticeable.
>
> Or have I screwed up my math? ... 30 years of writing computer
> programs that summarize invoices have rotted my brain. :-)
(...)

Uh... To get half of your weight, you would have to be
6400*sqrt(2)50 Km far from the center of Earth - that is,
9050-6400&50 Km altitude.

Lucio de Souza Coelho wrote:
>
> On Thu, 18 Nov 2004 11:08:03 -0500, Steve Long
> wrote:
> (...)
> > I think the gravity equation uses r-squared as the divisor, so that if
> you
> > assume that Earth's surface is 6400 km from the "center of gravity"
> then at
> > about 1440 km (900 miles) altitude you've lost half of your "weight",
> which
> > I think would be pretty noticeable.
> >
> > Or have I screwed up my math? ... 30 years of writing computer
> > programs that summarize invoices have rotted my brain. :-)
> (...)
>
> Uh... To get half of your weight, you would have to be
> 6400*sqrt(2)50 Km far from the center of Earth - that is,
> 9050-6400&50 Km altitude.
>

See! Stay away from business programming applications, they'll rot your
mind!! You're right, of course. I think I was looking at the 1/3 point,
not the 1/2 point.

Steve <-- enrolling in Remedial Math for First Graders tomorrow ...

From: ANTIcarrot [mailto:dante.feditech@...]

"RLV has nothing to do with space planes. The X-43 is a spaceplane. It ain't
reusable though. The DC-X would not have been a spaceplane, but it would
have been reuseable."

I never said "spaceplanes" were the only form of RLV. The DC-X and Roton
designs are a couple of alternatives; there are probably some others out
there. As far as the X-43 is concerned, it's a test bed, not a final design.

"And what will be powering your scram-jets if not highly explosive cryogenic
fuel?"

Until you asked, I admit I was under the impression that
scramjets used jet fuel. My mistake. As you noted, I'm not fond of cryo-fuel
systems, if there are alternatives. The jet-fueled White Knight and hybrid
propulsion SpaceShipOne add up to a two stage RLV design that doesn't need
cryo-fuels. SpaceDev has other hybrid designs, besides the one they built
for Scaled Composites. There was a time that the dangers and expenses of
LH/LOX were justified, because that was the only game in town. But with
cheaper, safer hybrid systems available, and WK/SS1 demonstrating that
conventional jet engines can drive a reusable `first stage', I think it
might be time to retire the cryo-fuels, especially for manned missions.

"Challanger blew up because it was deliberately flown well outside of
it's operational envelope ... The columbia broke up because of a string of
very stupid management decisions, going back to the basic design of the STS
shuttle. Please note that the shuttle is the ONLY rocket where the heat
shield, or any part of the payload, can be damaged by falling debris."

Your points are all valid. However, the "operational envelope" issue with
Challenger involved it's fuel system. The cause of the "falling debris" that
damaged the Columbia's heat shield was the fuel system. That was the point I
was trying to make. Also, the Challenger is a long way from being the only
time a launch turned into a "catastrophic disassembly" -- don't you just
love NASA-speak? Even if all the safety issues could be addressed, the cost
savings alone of hybrid systems make them worth considering.

"For instance, how you you incorporate an escape system into the design?
Or the tire explodes and you're hurtling down the runway at hundreds of
miles per hour?"

Commercial jets seem to get by without an escape systems, military jets only
have them because of the possibility of combat damage. Why would any such
system be needed in a HTO/HL TSTO, based on the WK/SS1 design? As to the
tire blowout scenario, I refer you again to common aviation practices, and
their safety record.

"What happens when you try and take off from a French airport and one of
your wheels throws a piece of jagged metal up against the TPS?"

Now, you're reaching. Do you really think there's an aircraft designer out
there who doesn't take what was learned with the Concorde crash, and
consider it in their work?

"I also agree that ELVs should be replaced. I'm just more inclined to the
TSTO VTOL RLV, instead of the SSTO HTOL RLV"

I'm no fan of the SSTO concept; TSTO seems more reasonable, at least at this
time. But HTOL offers the advantage of letting virtually any airport become
a spaceport. That might not be important for a gov't space agency, but it
widens the options for the private sector. And the safety record of HTOL in
aviation beats any VTOL system designed so far. The only thing I can think
of that might be considered a disadvantage to HTOL is that it seems to be
harder to get all those tricky, expensive, high-maintenance valves and pumps
needed for cryo-fuels to work than on VTOL systems. ;) Someone else posted
here recently that Marshall won't even look at HTOL designs that use cryo. I
suppose you and I will disagree as to that being a point against HTOL, or
against cryo-fuels... So, what do you see as the advantages of VTOL?
And cryo-fuels?

Dave

Dave wrote:

>So, what do you see as the advantages of VTOL? And cryo-fuels?

I don't see any advantages of the VL part of the equation, if the
suggestion is a powered vertical landing. It's a nonsense to go down the
DC-X route (essentially flying your landing fuel to orbit and back) when
there's plenty of air around the planet to use in a fuel-saving
parachute or in an unpowered fly-back airframe.

As to cryo-fuels, it's partly an Isp issue...not much comes close to
H2/O2 in terms of power, though granted the refrigeration costs can add
to the mass and/or limit their use to lift-offs only. It's also /much/
cleaner than any other fuels which approach that Isp. Burning thousands
of tonnes of OF2/B2H6, for example, is not going to make anyone many
friends when we accept that the need is to launch multi-hundred tonne
loads to orbit, in order to achieve much at all.

Regards,

Andy Goddard

> From: Dave Logsdon [mailto:templar@...]

> The jet-fueled White Knight and hybrid
> propulsion SpaceShipOne add up to a two stage
> RLV design that doesn't need cryo-fuels.

But not an orbital RLV though. I've also yet to see a design for a launch
vehicle with a hybrid engine. Not that I'm saying that it's impossible, but
because of its low impulse, such systems will always face substantial
performance penelties in comparison to liquid or solid fuels.

> I think it might be time to retire the
> cryo-fuels, especially for manned missions.

For sub-orbital flights, maybe. Then again an engine like the RL10 has a
excillent reliability record - which at present is unmatched by any hybrid.

> Your points are all valid. However, the
> "operational envelope" issue with
> Challenger involved it's fuel system.

Er - no. The operational envelope had to do with the O-Ring seal on the
multi-section strap on booster. The cold weather meant it couldn't expand
properly, and the solid rocket exhaust began to leak out. It had nothing to
do with cryogenics until the the SRB ripped loose and smashed the tank's
super-structure. I put it to you that if your biggest engine rips loose and
damages the super-structure at high speed, you're screwed no matter what
design you use. ;)

> The cause of the "falling debris" that
> damaged the Columbia's heat shield was
> the fuel system.

Again that is I'm afraid very much incorrect. The only reason the tank has
insulation in the first place is because if it didn't, ice might form and
fall off during launch, damaging the shuttle's heatshield. Spot the irony.
Watch a saturn-v l;aunch sometime. You can see it's covered with ice that
falls off during launch. This was never a serious issue before the shuttle.

> Even if all the safety issues could be
> addressed, the cost savings alone of
> hybrid systems make them worth considering.

That's like saying, 'Cars crash and are unreliable. We should all start
using bicycles.' lanes fall out of the sky. Ships sink. Cars crash. And yes,
rockets do blow up sometimes. It's more often the case that they're blown up
by ground control after they go off course rather than an accident. And
that's basically a philosophy of 'make everything as light weight as
possible and hope for the best'. An RLV probably wouldn't be built like
that.

> Commercial jets seem to get by without
> an escape systems, military jets only
> have them because of the possibility of
> combat damage. Why would any such
> system be needed in a HTO/HL TSTO,
> based on the WK/SS1 design?

In case of systems failure. Would you really like to tell your astronauts,
"We're pretty sure it's safe, but on the off chance we're wrong you're
completely screwed?" Combat jets sometimes fail for no apparent reason
because they're flying at the endge of material science. You're going to be
flapping your wings on the other side of that edge in any kind an RLV. And
escape route is a really good idea.

> Now, you're reaching. Do you really
> think there's an aircraft designer
> out there who doesn't take what was
> learned with the Concorde crash, and
> consider it in their work?

I thik you'll find the solution was, don't make your aircraft go faster than
M0.9. ;)

> But HTOL offers the advantage of
> letting virtually any airport
> become a spaceport.

Where as VTOL has the advantage of making any patch of concrete anywhere
into a space-port. Consider the Harrier and the A-10. Which needs more
concrete? Which has greater flexibility?

No HTOl designfor space has ever been tested. None of the engines even exist
on paper, let alone in real life with a reliable record.

> So, what do you see as the
> advantages of VTOL?
> And cryo-fuels?

Vertical take off is the way every rocket has ever worked.
It's a proven method.
The design shapes are very simple. Hence easy to build and maintain.
Though it would be a higher G reentry, this would translate to less heat
absorbed by the spacecraft.
Heatshields can be kept small (with only the base being armored) which
allows heavier but more reliable technology.
Small VTOLs can operate from almost anywhere.
They can be sold commercially, because the design doesn't lend itself to
weapons deployment.
No useless weight in orbit.
With very slight modifacations and refueling in orbit, the VTO can go to
Luna, Mars or GEO.
Multiple landing options, including parasail or powered landing.
Greater flexibility in positioning the base of operations.
Able to land and take off in bad weather.
Fewer enviromental (sound) problems.

Example design for a small TSTO VTOL:
http://www.hobbyspace.com/AAdmin/archive/SpecialTopics/RocketCom/titlePage.h
tml

ANTIcarrot.

On Mon, 22 Nov 2004 15:25:59 -0000, ANTIcarrot
wrote:
>
> > From: Dave Logsdon [mailto:templar@...]
>
> > The jet-fueled White Knight and hybrid
> > propulsion SpaceShipOne add up to a two stage
> > RLV design that doesn't need cryo-fuels.
>
> But not an orbital RLV though. I've also yet to see a design for a launch
> vehicle with a hybrid engine.

Check out the Skylon design. Orbital RLV with a hybrid engine.

> None of the engines even exist
> on paper, let alone in real life with a reliable record.

Actually, Skylon's Sabre engines can do SSTO HTHL, on paper.

The evidence from the experiments done so far seem to back up that
this can work.

> ANTIcarrot.

--
-Ian Woollard

"In theory there is no difference between theory and practice, but in
practice there is."
"a society in which people can do and say what they want will also
tend to be one in which the most efficient solutions win" - Paul
Graham

--- In spacesettlers, "ANTIcarrot" wrote:

>> From: Dave Logsdon

>> Now, you're reaching. Do you really think there's an aircraft
>> designer out there who doesn't take what was learned with the
>> Concorde crash, and consider it in their work?

> I thik you'll find the solution was, don't make your aircraft go
> faster than M0.9. ;)

That sounds rather defeatist. However, I note the winking smiley, so
perhaps you don't really mean it. Boeing now expects me to get all
excited about their so-called "Sonic Cruiser," which will travel at
just *under* Mach 1. Gee, so it will go *almost half* as fast as a
plane built nearly forty years ago? Color me not impressed.

Xenophile (who won't comment on VTOL v HTOL, as he has no dog in the
fight)

> From: Ian Woollard [mailto:ian.woollard@...]
> > > The [...] hybrid propulsion SpaceShipOne [...]

> Check out the Skylon design. Orbital RLV with a hybrid engine.

Sorry, should have used a more specific term than hybrid. ;) Skylon does not
use a misture of liquid oxidiser and solid fuel, like SS1 does. Other forms
of hybrid (ram/scram engines, dual-fuel rocket engines) could reach orbit,
but I've yet to see one that uses SS1's method of propulsion. ^.^

> From: Xenophile [mailto:xenophile2002@...]

> That sounds rather defeatist. However, I note
> the winking smiley, so perhaps you don't
> really mean it.

High speed in the air means high speed on the ground during take off and
landings, because with thin supersonic wings an aircraft cannot control
itself well or generate a safe level of lift at low speeds. This puts more
strain on the wheels and is just another reason why no one wants to build
another concorde. Let alone something that goes faster! ;)

It might be worth noting that the orrigonal HOTOL design used a rocket
trolly for launch, because making the landing gear large enough for take off
killed the cargo capacity. I think this was a function of the unusual intake
more than anything else, as Skylon doesn't have this probem - but it still
shows how ground problems can make or break a project.

John

--- In spacesettlers, "ANTIcarrot" wrote:

>> From: Xenophile

>> That sounds rather defeatist. However, I note the winking smiley,
>> so perhaps you don't really mean it.

> High speed in the air means high speed on the ground during take
> off and landings, because with thin supersonic wings an aircraft
> cannot control itself well or generate a safe level of lift at low
> speeds.

So don't use thin supersonic wings when taking off or landing. Use
an oblique wing, which has the added advantage of being boomless up
to Mach 2.something-or-other (Concorde speeds).

> This puts more strain on the wheels and is just another reason why
> no one wants to build another concorde. Let alone something that
> goes faster! ;)

Hmph. That may be one reason, but we both know that the main reason
is the same as the reason that we are not on the Moon, Mars and the
asteroids: lack of testicular fortitude.

> It might be worth noting that the orrigonal HOTOL design used a
> rocket trolly for launch, because making the landing gear large
> enough for take off killed the cargo capacity. I think this was a
> function of the unusual intake more than anything else, as Skylon
> doesn't have this probem - but it still shows how ground problems
> can make or break a project.

Again, if you keep takeoff speed to 200 Kmph or so, this ceases to be
a problem. Heck, even 300 Kmph can probably be made safe today
(Concorde's was 360, and landing was 300... but hey, that was nearly
40 years ago).

Xenophile (googling on "oblique wing" and "sonic boom")

On Mon, 22 Nov 2004 22:15:23 -0000, ANTIcarrot
wrote:
> It might be worth noting that the orrigonal HOTOL design used a rocket
> trolly for launch, because making the landing gear large enough for take off
> killed the cargo capacity. I think this was a function of the unusual intake
> more than anything else, as Skylon doesn't have this probem - but it still
> shows how ground problems can make or break a project.

No, they've just done a tonne of work on it:

a) make the brakes smaller by using water/steam cooling rather than
air cooling (jettison water after successful takeoff- water is only
needed if you change your mind during takeoff)
b) use high pressure tyres
c) use a reinforced runway

> John

--
-Ian Woollard

"In theory there is no difference between theory and practice, but in
practice there is."
"a society in which people can do and say what they want will also
tend to be one in which the most efficient solutions win" - Paul
Graham

Hi Xenophile!

> Boeing now expects me to get all
excited about their so-called "Sonic Cruiser," which will travel at
just *under* Mach 1. Gee, so it will go *almost half* as fast as a
plane built nearly forty years ago? Color me not impressed.

Well, Boeing /don't'/ expect you to get excited any more...it was
shelved back in December 2002. Put the champagne away!

My personal thoughts were the project was (at least in part) out to try
and bankrupt/mislead Airbus Industries, who took the bigger=more
economical route with their A380, announced more or less at the same
time.

Andy (conspiracy-theory) Goddard

John wrote:

>High speed in the air means high speed on the ground during take off
and
landings, because with thin supersonic wings an aircraft cannot control
itself well or generate a safe level of lift at low speeds...

Yes, but that in itself helps promote the case for a TSTO vehicle, the
carrier aircraft being designed for the slower/lower part of the flight
envelope, and launching an optimised vehicle at high altitudes for
orbital insertion.

Given current Isps and materials the maths alone makes TSTO a more
practical goal for RLVs.

Andy Goddard

> From: Xenophile [mailto:xenophile2002@...]
> So don't use thin supersonic wings when taking off or landing. Use
> an oblique wing, which has the added advantage of being boomless up
> to Mach 2.something-or-other (Concorde speeds).

The problem with all the no-boom designs so far is that they have higher
(and in some cases *much* higher drag) then conventional designs. This
equates to larger engines and noise problems at take off and landing unless
you shrink the size of the aircraft.

> Hmph. That may be one reason, but we both know that the main reason
> is the same as the reason that we are not on the Moon, Mars and the
> asteroids: lack of testicular fortitude.

Plus there's that little problem of global warming which you may have heard
off. The Jet industry is the second largest contributor after the car
industry and current research is centered around fixing that problem rather
than going faster.

> Again, if you keep takeoff speed to 200 Kmph or so,

If you use magic fairy dust it also ceases to become a problem too. Both are
easier said than done.

> From: Ian Woollard [mailto:ian.woollard@...]
> a) make the brakes smaller by using water/steam cooling rather than
> air cooling (jettison water after successful takeoff- water is only
> needed if you change your mind during takeoff)
> b) use high pressure tyres
> c) use a reinforced runway

A) That would work but it won't stop the tire exploding, nor will it stop it
throwing up chips of dirt, stone, concrete, and metal to chip/gouge away at
Skylon's ceramic heatshield.
B&C) What do you think they designed HOTOL to work on? Rough dirt? ;)
Besides, increases in tire pressure means a decrease in Mean Time Between
Blowouts. ^.^

> From: Andrew Goddard [mailto:a.goddard@...]
> Yes, but that in itself helps promote the case for a TSTO vehicle, the
> carrier aircraft being designed for the slower/lower part of
> the flight envelope, and launching an optimised vehicle at high altitudes
for
> orbital insertion.

Very true. However the second stage still has to land again. So it either
needs low speed wings, or a paracute/parasail.

John

On Tue, 23 Nov 2004 13:46:49 -0000, ANTIcarrot
wrote:
> Plus there's that little problem of global warming which you may have heard
> off. The Jet industry is the second largest contributor after the car
> industry and current research is centered around fixing that problem rather
> than going faster.

Irrelevant to launch vehicles for the foreseeable future. Launches
aren't common enough for them to be significant. Skylon of course uses
hydrogen, which doesn't necessarily contribute to global warming at
all (depending on the source of energy used, say, hydroelectric or
nuclear.)

> > Again, if you keep takeoff speed to 200 Kmph or so,
>
> If you use magic fairy dust it also ceases to become a problem too. Both are
> easier said than done.

Great. Where can I get magic fairy dust?

> > From: Ian Woollard [mailto:ian.woollard@...]
> > a) make the brakes smaller by using water/steam cooling rather than
> > air cooling (jettison water after successful takeoff- water is only
> > needed if you change your mind during takeoff)
> > b) use high pressure tyres
> > c) use a reinforced runway
>
> A) That would work but it won't stop the tire exploding, nor will it stop it
> throwing up chips of dirt, stone, concrete, and metal to chip/gouge away at
> Skylon's ceramic heatshield.

So don't leave chips of dirt, stone, concrete and metal on the runway.

> B&C) What do you think they designed HOTOL to work on? Rough dirt? ;)

HOTOL used a rocket assisted sled. The Skylon runway is described as
'heavily reinforced' and the tyres run at extremely high pressure.

> Besides, increases in tire pressure means a decrease in Mean Time Between
> Blowouts. ^.^

No.

> John

--
-Ian Woollard

"In theory there is no difference between theory and practice, but in
practice there is."
"a society in which people can do and say what they want will also
tend to be one in which the most efficient solutions win" - Paul
Graham

From: ANTIcarrot [mailto:dante.feditech@...]

"But not an orbital RLV though. I've also yet to see a design for a launch
vehicle with a hybrid engine. Not that I'm saying that it's impossible ..."

That's my point. Not yet, but not impossible. That's why I believe hybrid
fuel systems should be used now, for anything they are currently capable of.
First, because they're cheaper to build, cheaper to operate, and safer.
Second, because using what they're able to do now supports the R&D to create
better, possibly orbit-capable hybrid fuel systems.

RE: Challenger: "I put it to you that if your biggest engine rips loose and
damages the super-structure at high speed, you're screwed no matter what
design you use. ;) "

Well, maybe it's the way you described it. Or maybe, the SRB failure
detonated the *explosive* fuel in the ET, but if the fuel for the SSMEs
hadn't been explosive, the pilot *might* have had a few extra seconds to
initiate SRB separation, and try for an emergency landing. Might have.
Maybe. Hey, I've had enough close calls in my life that I'll always take a
slim chance over none at all.

"The only reason the tank has insulation in the first place is because if it
didn't, ice might form and fall off during launch, damaging the shuttle's
heatshield. Spot the irony. "

Yeah, I spot the irony. Now, would you please spot the point I've been
making? So, why was the insulation there? Because ice might form. And, why
might the ice form? Because of the *cryogenic* fuels! *IF* we can get rid of
cryo-fuels, we eliminate this problem.

"Watch a saturn-v launch sometime. You can see it's covered with ice that
falls off during launch. This was never a serious issue before the shuttle."

Reverting to an old-fashioned, straight-up, single-stack VTOL is, indeed,
*one* way of dealing with the problem. But, is it the *only* way? NO. If
not, is it the *best* way? Well, that's our current discussion.

I posted:
Even if all the safety issues could be addressed, the cost savings alone of
hybrid systems make them worth considering.

"That's like saying, 'Cars crash and are unreliable. We should all start
using bicycles.'"

I don't see how you're relating cost savings to this. If your point was
actually in reference to the safety issue, then I'd say the comparison is
between your fondness for an earlier model, and my preference for a later
model that's less expensive to make, requires much less maintenance, and is
safer to `drive'. No matter if it's cars or spacecraft, anything that's
cheaper *and* safer is an improvement.

I really don't understand what your problem is with the idea of using an
alternate rocket system that costs less, *and* is safer, on the occasions
it's up to the job. Or with promoting this alternate system, in the hope
that it can be developed into something that *might* be able to replace our
current fuel systems for all applications.

"In case of systems failure. Would you really like to tell your astronauts,
"We're pretty sure it's safe, but on the off chance we're wrong you're
completely screwed?"

My analogy was to current, commercial aircraft, that fly *thousands* of
times a day without any need for any escape mechanism. But, if you want to
insist on an evacuation system, then the ejection systems used in some
military aircraft could easily be added to the jet-powered lifter/first
stage, and the orbiter/second stage could be equipped with an ejectable
`survival module', similar to the one in the FB-111.

"Where as VTOL has the advantage of making any patch of concrete anywhere
into a space-port."

You *know* it takes more than a "patch of concrete" to create a spaceport!
On the physical side, you'll need a gantry, a complete cryogenic system to
process your fuel and oxidizer, possibly a VAB, maybe a `crawler' to carry
the assembled ship into position... whatever. As I've mentioned before, HTOL
systems will be able to use the infrastructure already in place for
aircraft. This would save millions for any company starting a private launch
business. Plus you'll have to convince the FAA, the owners of the airport,
and the community gov't, that you should be certified to do what you want.
If you can't get legal certification, you ain't gonna fly. HTOL looks and
sounds like just another aircraft taking off. This isn't a real issue for a
nat'l gov't space program, but for a private company?

"Consider the Harrier and the A-10. Which needs more
concrete? Which has greater flexibility?"

You know as well as anyone reading this that the Harrier uses the same
resources and infrastructure as any other aircraft. The more desperately you
try to dance around the point, the more you prove my side of this.

"Vertical take off is the way every rocket has ever worked."

And your point is?

"The design shapes are very simple. Hence easy to build and maintain."

Hybrid-fueled systems are simpler and cheaper than cryo-fueled systems. HTOL
systems -- aka aircraft -- have been built and maintained longer, and at
lower costs, than any VTOL system.

"Heatshields can be kept small (with only the base being armored) which
allows heavier but more reliable technology... Multiple landing options,
including parasail or powered landing."

This brings up something I've been concerned about re: VTOL systems, but you
might have just addressed it. Just how accurately can your preferred system
park itself where it's needed? Gov'ts can afford to chase all over the place
to recover their space capsules, but private companies can't. An HTOL craft
landing at an airport/spaceport has access to any facilities needed to deal
with it's passengers and cargo. Are VTOL craft able to do this? Roton and
the DC-X were intended to be controllable-descent designs, but the
parachutes all the *successful* VTOL designs have used just drop the capsule
somewhere in the general vicinity of a awfully big `landing site'. Maybe
current VTOL systems can deal with this? How accurately can a parasail land
a capsule?

"Small VTOLs can operate from almost anywhere."

*After* you build the infrastructure to operate from, which can cost
millions per location. HTOL can operate from existing airports, saving
millions in creating said infrastructure. In addition, VTOL can operate
"almost anywhere" only *IF* they're certified and permitted to operate. NASA
and the U.S. military -- and their equivalents in other countries -- do what
they want, wherever they want. But private companies have to answer to the
FAA, OSHA, other Federal agencies, and a host of local bureaucrats and
agencies. Spacecraft that launch like an airplane, and land like an
airplane, are more likely to be thought of as airplanes. This second point
*might not* be an issue, but it strikes me as something that needs to be
looked at.

"They can be sold commercially, because the design doesn't lend itself to
weapons deployment."

Oh, you *GOTTA* be kidding me! What do you call a VTOL suborbital? I call it
an ICBM! The creation of boosters capable of reaching space was originally
created as almost an afterthought to ballistic missile development; the
Redstone, Atlas, and Titan boosters were all originally designed as weapons.

"With very slight modifacations and refueling in orbit, the VTO can go to
Luna, Mars or GEO."

Assuming there would ever be a reason to use the *same* craft for those
missions -- and I make no such assumption. Why would we ever want to try to
create a craft that's supposed to climb in and out of Earth's atmosphere
into the edge of space, and then expect that *same* craft to go voyaging off
somewhere else? Isn't this something like expecting Columbus to slap wheels
onto the side of the Santa Maria, and then hitch up some oxen, to do
somewhat the equivalent of the Lewis and Clark expedition?

"Greater flexibility in positioning the base of operations."

See my infrastructure points above. The `bases of operation' for HTOL
already exist, all over the world.

"Able to land and take off in bad weather."

Aircraft regularly take off and land in weather that grounds rocket
launches.

"Fewer enviromental (sound) problems."

Interesting point. I've never been around for a major rocket launch, so I
can't compare it to the countless aircraft launches I have been near. The
impression I've always had was that rockets were much louder, but if they
do, in fact, require a smaller `sound abatement zone', then this would be a
legitimate point in your favour, *if* you're building a completely new
spaceport. So, *once again*, we're back to my point that HTOL systems will
be able to utilize the infrastructure of *existing* airports, avoiding the
need to build a new, separate, very expensive spaceport.

Dave

On Tue, 30 Nov 2004 17:40:22 -0600, Dave Logsdon wrote:
>
> From: ANTIcarrot [mailto:dante.feditech@...]
>
> "But not an orbital RLV though. I've also yet to see a design for a launch
> vehicle with a hybrid engine. Not that I'm saying that it's impossible ..."
>
> That's my point. Not yet, but not impossible. That's why I believe hybrid
> fuel systems should be used now, for anything they are currently capable of.
> First, because they're cheaper to build, cheaper to operate, and safer.

So far as I know, the cheaper to operate has not yet been show. They are
not necessarily safer either- a hybrid is a pressure vessel, and
hybrids *have* failed (pressure vessel failure- booom!)

> RE: Challenger: "I put it to you that if your biggest engine rips loose and
> damages the super-structure at high speed, you're screwed no matter what
> design you use. ;) "
>
> Well, maybe it's the way you described it. Or maybe, the SRB failure
> detonated the *explosive* fuel in the ET, but if the fuel for the SSMEs
> hadn't been explosive, the pilot *might* have had a few extra seconds to
> initiate SRB separation, and try for an emergency landing.

Nope. The studies say that the vehicle comes apart like wet tissue paper
if you do that. In fact, the ET didn't exactly explode. The real
damage was done by the loss of attitude- then the supersonic airflow
ripped off the tail and one of the wings of the orbiter. The loss of
attitude was caused by the SRB burning through on the of the struts
and then the SRB went sideways through the main tank. That's always
going to be a bad day, whatever kind of propulsion you use.

> "The only reason the tank has insulation in the first place is because if it
> didn't, ice might form and fall off during launch, damaging the shuttle's
> heatshield. Spot the irony. "
>
> Yeah, I spot the irony. Now, would you please spot the point I've been
> making? So, why was the insulation there? Because ice might form. And, why
> might the ice form? Because of the *cryogenic* fuels! *IF* we can get rid of
> cryo-fuels, we eliminate this problem.

Um. Hybrids would almost certainly use LOX if you want orbit. Nitrous
doesn't really have the ISP.

> "Watch a saturn-v launch sometime. You can see it's covered with ice that
> falls off during launch. This was never a serious issue before the shuttle."
>
> Reverting to an old-fashioned, straight-up, single-stack VTOL is, indeed,
> *one* way of dealing with the problem. But, is it the *only* way? NO. If
> not, is it the *best* way? Well, that's our current discussion.

No, he's saying that the problem is a feature of the unusual layout of
the Shuttle. It was realised quite late on in the day that this was an
issue. The fix- the foam- has turned out to be quite problematic.

> I posted:
> Even if all the safety issues could be addressed, the cost savings alone of
> hybrid systems make them worth considering.
>
> "That's like saying, 'Cars crash and are unreliable. We should all start
> using bicycles.'"
>
> I don't see how you're relating cost savings to this. If your point was
> actually in reference to the safety issue, then I'd say the comparison is
> between your fondness for an earlier model, and my preference for a later
> model that's less expensive to make, requires much less maintenance, and is
> safer to `drive'. No matter if it's cars or spacecraft, anything that's
> cheaper *and* safer is an improvement.

The performance of current hybrids are lower than the performance of
liquids, and IRC solids. That usually means that your payload ends up
costing more per kg, even if the rocket is cheaper.

> "In case of systems failure. Would you really like to tell your astronauts,
> "We're pretty sure it's safe, but on the off chance we're wrong you're
> completely screwed?"
>
> My analogy was to current, commercial aircraft, that fly *thousands* of
> times a day without any need for any escape mechanism. But, if you want to
> insist on an evacuation system, then the ejection systems used in some
> military aircraft could easily be added to the jet-powered lifter/first
> stage, and the orbiter/second stage could be equipped with an ejectable
> `survival module', similar to the one in the FB-111.

As I understand it, these modules are not very successful. The
designers of the ill-fated European manned vehicle fought long and
hard to avoid these modules being used. Even the designers of the
capsules were unhappy with them.

> "Where as VTOL has the advantage of making any patch of concrete anywhere
> into a space-port."
>
> You *know* it takes more than a "patch of concrete" to create a spaceport!
> On the physical side, you'll need a gantry, a complete cryogenic system to
> process your fuel and oxidizer, possibly a VAB, maybe a `crawler' to carry
> the assembled ship into position... whatever.

As you say, whatever that particular vehicle needs, you need.

> As I've mentioned before, HTOL
> systems will be able to use the infrastructure already in place for
> aircraft.

Apart from different fuels, different airports, different runways, a
different regulatory position, a different safety, a different
passengers and a few more things, yes, exactly the same!

> HTOL looks and
> sounds like just another aircraft taking off.

No.

> This isn't a real issue for a
> nat'l gov't space program, but for a private company?
>
> "Consider the Harrier and the A-10. Which needs more
> concrete? Which has greater flexibility?"
>
> You know as well as anyone reading this that the Harrier uses the same
> resources and infrastructure as any other aircraft.

No, he's right, Harrier can take off from a very small area, even
grass at a push (although it tends to blow soil away). You only really need
a tanker of kerosene.

> "Vertical take off is the way every rocket has ever worked."

Actually, no. Pegasus is horizontal takeoff. And either X1 or X15 took
off horizontally atleast once.

> And your point is?
>
> "The design shapes are very simple. Hence easy to build and maintain."
>
> Hybrid-fueled systems are simpler and cheaper than cryo-fueled systems. HTOL
> systems -- aka aircraft -- have been built and maintained longer, and at
> lower costs, than any VTOL system.

They haven't been orbit capable though. You might be able to use it as
a booster though.

> "Heatshields can be kept small (with only the base being armored) which
> allows heavier but more reliable technology... Multiple landing options,
> including parasail or powered landing."
>
> This brings up something I've been concerned about re: VTOL systems, but you
> might have just addressed it. Just how accurately can your preferred system
> park itself where it's needed? Gov'ts can afford to chase all over the place
> to recover their space capsules, but private companies can't.

Well, the Roton could have landed with pinpoint accuracy.

> An HTOL craft
> landing at an airport/spaceport has access to any facilities needed to deal
> with it's passengers and cargo. Are VTOL craft able to do this? Roton and
> the DC-X were intended to be controllable-descent designs, but the
> parachutes all the *successful* VTOL designs have used just drop the capsule
> somewhere in the general vicinity of a awfully big `landing site'. Maybe
> current VTOL systems can deal with this? How accurately can a parasail land
> a capsule?

As accurately, in principle, as the Shuttle.

> "Small VTOLs can operate from almost anywhere."
>
> *After* you build the infrastructure to operate from, which can cost
> millions per location.

AFAIK all orbital HTOLs would use specially built runways anyway. It's not
like you are going to get these things landing at JFK. Suborbitals can
probably use normal runways.

> HTOL can operate from existing airports,

Suborbitals yes, orbital no. These vehicle take off carrying *large*
quantities of LOX.

The technique for extinguishing a fire from a vehicle containing fuel
and LOX involves running shoes- you run the other way very fast, and
wait for it to burn itself out. There's no way you can put it out, and
there's no way that large LOX vehicles can mix it with 777s. Ain't gonna
happen in a million years. Or, it might, until the first accident. It
makes that crashed Concorde look like a camp fire.

The problem with LOX is that it tends to expand more than a 1000x in a
fire (density goes from 1 tonne per m^3 to less than 1kg per m^3),
whilst adding oxygen to the fire, and carrying the fire with it,
starting secondary fires. LOX and cold oxygen gas itself are also
heavier than air, so hug the ground, as does the fuel. *Really* nasty.
AFAIK nitrous is similar, but not quite as bad.

I saw some footage of somebody putting a bucket full of LOX onto a
barbeque. A camera 20-30 feet away rapidly caught fire. The barbeque
itself was flattened, the sausages on it vanished; the coals were just
gone.

> saving
> millions in creating said infrastructure. In addition, VTOL can operate
> "almost anywhere" only *IF* they're certified and permitted to operate. NASA
> and the U.S. military -- and their equivalents in other countries -- do what
> they want, wherever they want. But private companies have to answer to the
> FAA, OSHA, other Federal agencies, and a host of local bureaucrats and
> agencies. Spacecraft that launch like an airplane, and land like an
> airplane, are more likely to be thought of as airplanes. This second point
> *might not* be an issue, but it strikes me as something that needs to be
> looked at.

No, that is pretty much how it has gone for the last few years. New
regulations are coming in now. I think that aeroplanes that
essentially can stand on their tail for most of their powered flight are
treated as launch vehicles now.

> "They can be sold commercially, because the design doesn't lend itself to
> weapons deployment."
>
> Oh, you *GOTTA* be kidding me! What do you call a VTOL suborbital? I call it
> an ICBM!

Nope!

ICBMs (*Intercontinental* Ballistic Missiles) are usually orbital
capable with about 30% less payload, given modifications to the
guidance system of course. Suborbitals typically have a range of ~50
miles or so; if it is capable of 100 miles vertically. Surprising,
huh? It's because they leave the atmosphere and go ballistic.
Attempting to go sideways scrubs off too much speed, and so range is
low.

> "With very slight modifacations and refueling in orbit, the VTO can go to
> Luna, Mars or GEO."
>
> Assuming there would ever be a reason to use the *same* craft for those
> missions -- and I make no such assumption. Why would we ever want to try to
> create a craft that's supposed to climb in and out of Earth's atmosphere
> into the edge of space, and then expect that *same* craft to go voyaging off
> somewhere else?

Correct! You'd be carrying a lot of unnecessary weight around, that
costs fuel. On-orbit fuel is very expensive.

> "Greater flexibility in positioning the base of operations."
>
> See my infrastructure points above. The `bases of operation' for HTOL
> already exist, all over the world.

I suppose you might be able to use a military base, but there aren't
many that are
suitable. These vehicles are much, much more unreliable than
conventional aeroplanes, so very few airports will allow takeoff.

> "Able to land and take off in bad weather."
>
> Aircraft regularly take off and land in weather that grounds rocket
> launches.

Correct. It's got a lot to do with the low speeds at takeoff- they
usually worry about it striking a tower if there is one; there can
also be problems with windshear.

> "Fewer enviromental (sound) problems."
>
> Interesting point. I've never been around for a major rocket launch, so I
> can't compare it to the countless aircraft launches I have been near. The
> impression I've always had was that rockets were much louder, but if they
> do, in fact, require a smaller `sound abatement zone', then this would be a
> legitimate point in your favour, *if* you're building a completely new
> spaceport. So, *once again*, we're back to my point that HTOL systems will
> be able to utilize the infrastructure of *existing* airports, avoiding the
> need to build a new, separate, very expensive spaceport.

Depends on the exhaust velocity. If you assume that the rocket is far
noisier than an equivalent thrust jet engine you won't go far wrong at
all. Most orbital rockets are atleast 160 dBA.

The noise is actually caused by the wake. Decent rockets have
incredibly fast exhaust, much, much faster than an equivalent jet, so
they are much, much noisier.

> Dave

--
-Ian Woollard

"In theory there is no difference between theory and practice, but in
practice there is."
"a society in which people can do and say what they want will also
tend to be one in which the most efficient solutions win" - Paul
Graham