Scramjet SSTO

"Alain Fournier" wrote in message
...
Jeff Findley wrote:

If you've got an aerospike engine anyway, just make your LOX tank a bit
bigger (stretching the LOX tank won't weigh much and will cost very
little)

I agree with most of your post, but in this particular point, I think it
isn't only the tank you are stretching, it is the truth. LOX tanks when
filled are heavy. This of course doesn't change the validity of your
argument.


Would this be practical? First stage is an air drop at some 50,000 feet
as with Scaled Composites, second stage is an aerospike, and
the third a conventional upper stage to get into orbit?




Alain Fournier

In article ,
says...

"Alain Fournier" wrote in message
...
Jeff Findley wrote:

If you've got an aerospike engine anyway, just make your LOX tank a bit
bigger (stretching the LOX tank won't weigh much and will cost very
little)

I agree with most of your post, but in this particular point, I think it
isn't only the tank you are stretching, it is the truth. LOX tanks when
filled are heavy. This of course doesn't change the validity of your
argument.


Would this be practical? First stage is an air drop at some 50,000 feet
as with Scaled Composites, second stage is an aerospike, and
the third a conventional upper stage to get into orbit?

The purpose of an aerospike is to optimize the expansion ratio
(performance) from sea level to vacuum. Adding air launch to such a
vehicle seems counter intuitive.

The size of the carrier aircraft needed for a sizable launch vehicle
would be quite large. If you look at any prior proposals for such a
vehicle using the biggest aircraft available at the time (C-5 or B-747),
you'll see that the orbital vehicle is quite small. Far smaller than
the space shuttle, that's for sure.

Jeff
--
The only decision you'll have to make is
Who goes in after the snake in the morning?

Jeff Findley wrote:

In article ,
says...

Would this be practical? First stage is an air drop at some 50,000 feet
as with Scaled Composites, second stage is an aerospike, and
the third a conventional upper stage to get into orbit?


The purpose of an aerospike is to optimize the expansion ratio
(performance) from sea level to vacuum. Adding air launch to such a
vehicle seems counter intuitive.

Indeed.


Alain Fournier

"Jeff Findley" wrote in message
...
In article ,
says...

"Alain Fournier" wrote in message
...
Jeff Findley wrote:

If you've got an aerospike engine anyway, just make your LOX tank a
bit
bigger (stretching the LOX tank won't weigh much and will cost very
little)

I agree with most of your post, but in this particular point, I think
it
isn't only the tank you are stretching, it is the truth. LOX tanks when
filled are heavy. This of course doesn't change the validity of your
argument.


Would this be practical? First stage is an air drop at some 50,000 feet
as with Scaled Composites, second stage is an aerospike, and
the third a conventional upper stage to get into orbit?

The purpose of an aerospike is to optimize the expansion ratio
(performance) from sea level to vacuum. Adding air launch to such a
vehicle seems counter intuitive.

The size of the carrier aircraft needed for a sizable launch vehicle
would be quite large. If you look at any prior proposals for such a
vehicle using the biggest aircraft available at the time (C-5 or B-747),
you'll see that the orbital vehicle is quite small. Far smaller than
the space shuttle, that's for sure.



I was reading some paper by the military, can't find it now, but it said
the military was assuming that the future for them to orbit needed
to work around a few assumptions. First is that to make space travel
for the military useful, that conventional airfields would have to
be used to fully take advantage of existing infrastructure. Another
is that to increase the scale and routineness of space flight, the
lower isp fuels would have to be used. Something closer to jet fuel, so
the military could use existing personnel and training levels.

The lower isp fuels could also allow the military to take advantage
of another valuable ability, mid-air refueling.Which they do very
routinely and at large scales.

So, given those assumptions, horizontal take-offs and lower
isp fuels, what kind of SSTO would take shape?

Maybe a hybrid, with conventional engines getting it to altitude?
Then taking on the fuel for the next stage, say an aerospike engine
after gaining altitude. It would only have to take off with the fuel
needed to get the conventional engine to altitude, and enough
oxidizer to get from altitude to orbit. Wouldn't that more than
make up for the lower isp fuels? While greatlly increasing the
versatility and scale of operations?



Jeff
--
The only decision you'll have to make is
Who goes in after the snake in the morning?

"Alain Fournier" wrote in message
...
Jeff Findley wrote:

In article ,
says...

Would this be practical? First stage is an air drop at some 50,000 feet
as with Scaled Composites, second stage is an aerospike, and
the third a conventional upper stage to get into orbit?


The purpose of an aerospike is to optimize the expansion ratio
(performance) from sea level to vacuum. Adding air launch to such a
vehicle seems counter intuitive.

Indeed.


I'm not so sure about that. What doesn't make sense is lifting all that
oxidizer from the ground to 50k feet, a jet engine has ten to fifteen times
the isp than a rocket in the lower atmosphere since it isn't carrying
oxidizer. It doesn't make sense to use a liquid rocket, even
an aerospike until at higher altitudes.

Scaled Composites seems to do pretty well with their small suborbital
essentially using a jet powered reusable first stage.





Alain Fournier

On 6/19/2010 4:21 AM, John M wrote:

So, given those assumptions, horizontal take-offs and lower
isp fuels, what kind of SSTO would take shape?

I would think it would be a two-stage-to-orbit vehicle, with a winged,
jet-powered craft carrying a rocket powered aircraft or lifting body
style spacecraft up to around Mach 3 and 80,000 feet (jets alone) or
Mach 5 and 150,000 feet (jets plus rockets) for release.
The carrier aircraft might employ the SR-71 concept of talking off
lightly loaded and then getting fuel added from a tanker once airborne,
but that might not be necessary if the acceleration and climb is high
enough after takeoff as total flight time could be fairly short for the
carrier.
Even if aerial refueling is used, like on the laughable Black Horse
concept - whose math regarding mass fraction and isp makes no sense -
you would have a very hard time getting SSTO to work without resorting
to LOX/LH2 or some sort of exotic propellant combos. LOX/kerosene just
isn't going to cut it from a isp viewpoint, plug nozzle or not.
One thing you don't want to do is drag the jet engines you use for
takeoff with you all the way to orbit, as that will really eat into your
payload capability and they aren't necessary for the flight back down,
as the Shuttle showed.

Maybe a hybrid, with conventional engines getting it to altitude?
Then taking on the fuel for the next stage, say an aerospike engine
after gaining altitude. It would only have to take off with the fuel
needed to get the conventional engine to altitude, and enough
oxidizer to get from altitude to orbit. Wouldn't that more than
make up for the lower isp fuels? While greatlly increasing the
versatility and scale of operations?

You also have to weigh the cost of building the system against how many
flights a year you expect it to make.
You do get a quicker response time if you can tank it up, roll it out on
the runway and send it one its way, but this is supposed to be a
reusable system, and just like the Shuttle that means that you need
acceptable weather for both takeoff _and return_, and that could screw
things up.
The Shuttle is constrained at launch not only by weather at the Cape,
but also at the emergency abort sites, and countries that would find it
perfectly acceptable to have a civilian spacecraft make a emergency
landing there might look at things entirely differently if a military
one might be arriving some day.
You could get around that problem to some extent by launching things
into low-inclination orbits over the continental US from the West Coast
or Hawaii, but the polar orbiting ones (vital for the reconsats) are
going to be a tough nut to crack, as even North Dakota to Texas might
not be a long enough distance if a abort is required.
I imagine you could use Alaska to Hawaii, but the weather in Alaska can
get pretty severe, as indeed it can here in North Dakota.
One thing you don't want to do is launch it northward over the Pole, as
that will make the Russians very nervous indeed.

Pat

"Pat Flannery" wrote in message
dakotatelephone...
On 6/19/2010 4:21 AM, John M wrote:

So, given those assumptions, horizontal take-offs and lower
isp fuels, what kind of SSTO would take shape?

I would think it would be a two-stage-to-orbit vehicle, with a winged,
jet-powered craft carrying a rocket powered aircraft or lifting body style
spacecraft up to around Mach 3 and 80,000 feet (jets alone) or Mach 5 and
150,000 feet (jets plus rockets) for release.


So a reusable jet powered first stage appears to be a good starting
point for lower cost to orbit, But lofting what? Something like
the X-51?


The carrier aircraft might employ the SR-71 concept of talking off lightly
loaded and then getting fuel added from a tanker once airborne, but that
might not be necessary if the acceleration and climb is high enough after
takeoff as total flight time could be fairly short for the carrier.
Even if aerial refueling is used, like on the laughable Black Horse
concept - whose math regarding mass fraction and isp makes no sense - you
would have a very hard time getting SSTO to work without resorting to
LOX/LH2 or some sort of exotic propellant combos. LOX/kerosene just isn't
going to cut it from a isp viewpoint, plug nozzle or not.


It seems to me that having to lug around the oxidizer is the big problem.
Once a rocket engine starts, you're limited by the amount that can be
carried all the way from take off. to orbit. An aerospike just extends
the range of rockets to lower altitudes, but isn't extending the amount
of flight that's dependent on cryogenics the wrong way to go?
Shouldn't a reusable craft try to reduce the use of cryogenics
by having the hypersonic portion handled by air breathing engines
instead of a rocket engine?

And I would also think that anything that uses cryogenics really
can't be considered reusable, or routine. An air breathing second
stage could be reusable.


One thing you don't want to do is drag the jet engines you use for takeoff
with you all the way to orbit, as that will really eat into your payload
capability and they aren't necessary for the flight back down, as the
Shuttle showed.

Maybe a hybrid, with conventional engines getting it to altitude?
Then taking on the fuel for the next stage, say an aerospike engine
after gaining altitude. It would only have to take off with the fuel
needed to get the conventional engine to altitude, and enough
oxidizer to get from altitude to orbit. Wouldn't that more than
make up for the lower isp fuels? While greatly increasing the
versatility and scale of operations?

You also have to weigh the cost of building the system against how many
flights a year you expect it to make.
You do get a quicker response time if you can tank it up, roll it out on
the runway and send it one its way, but this is supposed to be a reusable
system, and just like the Shuttle that means that you need acceptable
weather for both takeoff _and return_, and that could screw things up.
The Shuttle is constrained at launch not only by weather at the Cape, but
also at the emergency abort sites, and countries that would find it
perfectly acceptable to have a civilian spacecraft make a emergency
landing there might look at things entirely differently if a military one
might be arriving some day.
You could get around that problem to some extent by launching things into
low-inclination orbits over the continental US from the West Coast or
Hawaii, but the polar orbiting ones (vital for the reconsats) are going to
be a tough nut to crack, as even North Dakota to Texas might not be a long
enough distance if a abort is required.
I imagine you could use Alaska to Hawaii, but the weather in Alaska can
get pretty severe, as indeed it can here in North Dakota.
One thing you don't want to do is launch it northward over the Pole, as
that will make the Russians very nervous indeed.


From what I've read about our military ambitions in space, they'll have
plenty of reasons to be nervous before long. Reading through their
websites, two themes are heard over and over. "Full spectrum warfare".
And "At the speed of need". They appear to be pushing ahead for
missile defense and combat capability in all three flight realms, subsonic,
hypersonic and orbital. While trying to develop the ability to strike
quickly.
Which means lasers.

It looks like they plan on getting around the problem of putting
expensive weapons in orbit, making them vulnerable, by putting
mirrors in orbit instead.

Mirrors aren't weapons, can be small, cheap and quickly replaced.
While the laser can then be ground based and protected. And just one
laser for the world is needed, so to speak.

Boeing Demonstrates Aerospace
Relay Mirror System-- Presentation

http://www.dtic.mil/cgi-bin/GetTRDoc...f&AD=ADA495239




Pat

John M wrote:

"Alain Fournier" wrote in message
...

Jeff Findley wrote:

In article ,
says...

Would this be practical? First stage is an air drop at some 50,000 feet
as with Scaled Composites, second stage is an aerospike, and
the third a conventional upper stage to get into orbit?

The purpose of an aerospike is to optimize the expansion ratio
(performance) from sea level to vacuum. Adding air launch to such a
vehicle seems counter intuitive.

Indeed.

I'm not so sure about that. What doesn't make sense is lifting all that
oxidizer from the ground to 50k feet, a jet engine has ten to fifteen times
the isp than a rocket in the lower atmosphere since it isn't carrying
oxidizer. It doesn't make sense to use a liquid rocket, even
an aerospike until at higher altitudes.

Scaled Composites seems to do pretty well with their small suborbital
essentially using a jet powered reusable first stage.

I'm not saying that air launch never makes sense. But if you are doing
air launch, why should the rocket be an aerospike. The purpose of
the aerospike is to have a rocket engine which performs well at sea
level and in vacuum. If you are going to use it only in near vacuum
might as well use a normal rocket engine optimized for vacuum.


Alain Fournier

Pat Flannery wrote:

On 6/20/2010 9:56 AM, Alain Fournier wrote:

I'm not saying that air launch never makes sense. But if you are doing
air launch, why should the rocket be an aerospike. The purpose of
the aerospike is to have a rocket engine which performs well at sea
level and in vacuum. If you are going to use it only in near vacuum
might as well use a normal rocket engine optimized for vacuum.

The FDL-5 design AF minishuttle was going to be air-launched at high
altitude, and it was going to use a AMPS-1 aerospike engine, which they
actually got to the ground test firing phase - liquid fluorine
propellant and all:
http://www.picturetrail.com/sfx/album/view/8379229
http://www.picturetrail.com/sfx/albu...9229/322567580
http://www.picturetrail.com/sfx/albu...9229/230887461

I think that the AF minishuttle was a classified project. If so, those
that have first hand information about the project wouldn't be talking.
And the information that does come out is just as likely to be
disinformation as to be real information. Anyway, even if someone
has proposed to build such a thing, before considering that sane
I would need to have some explanation.

Do you think that my understanding of the purpose of an aerospike
(having good efficiency at a wide range of atmospheric pressure)
is wrong? Or do you think that the atmospheric pressure at an
altitude of 13 km is high enough that a normal rocket engine optimized
for near vacuum wouldn't be efficient there.


Alain Fournier

On 6/20/2010 9:56 AM, Alain Fournier wrote:

I'm not saying that air launch never makes sense. But if you are doing
air launch, why should the rocket be an aerospike. The purpose of
the aerospike is to have a rocket engine which performs well at sea
level and in vacuum. If you are going to use it only in near vacuum
might as well use a normal rocket engine optimized for vacuum.

The FDL-5 design AF minishuttle was going to be air-launched at high
altitude, and it was going to use a AMPS-1 aerospike engine, which they
actually got to the ground test firing phase - liquid fluorine
propellant and all:
http://www.picturetrail.com/sfx/album/view/8379229
http://www.picturetrail.com/sfx/albu...9229/322567580
http://www.picturetrail.com/sfx/albu...9229/230887461

Pat