How big would an SSTO be?

Sylvia Else wrote:

:Fred J. McCall wrote:
: Sylvia Else wrote:
:
: :
: :Well, the performance comes from using an engine that is air breathing
: :for part of the ascent. It all comes down to whether they can build that
: :engine, and that appears to be where they're spending what money they have.
: :
:
: It also comes down to one other thing. Once that engine is built,
: does it buy them what they're thinking it will or do realities make it
: less efficient than other methods.
:
: So far, it seems that rockets always wind up more efficient in the
: real world than air-breathers.
:
:What do you mean by "more efficient" ?
:

Better mass fractions once the real world effects are all taken into
account.

:
:A air breathing engine can have a much higher specific impulse than a
:rocket engine. The downside is that since you cannot use an airbreathing
:engine all the way to orbit, the engine has to be a hybrid, or there has
:to be a separate rocket engine. In both cases the result is increased
:engine mass. Then it comes down to whether having a higher specific
:impulse for part of the ascent gives a net benefit once the higher
:engine mass is taken into account.
:

There's more to it than that. There isn't just the parasitic weight
of an engine with more moving parts (the air breathing bits), but the
parasitic drag of having to accelerate the oxidizer regardless of
whether you carry it with you (a rocket) or grab it out of the
atmosphere (an air-breather). Rockets can be more streamlined because
they don't need inlets. They can weigh less because they don't need
inlets. Their engines are simpler and have more specific power with
fewer moving parts.

:
:The SABRE engine is a hybrid, and is predicted to have a significantly
:higher mass than a pure rocket engine of similar thrust. For all that,
:Reaction Engines have run the numbers and concluded that they work.
:

They frequently do ... on paper.

:
:Now, they may have overestimated the thrust in the air breathing mode,
r underestimated the mass, or the entire concept may be flawed, but I
:don't think you can write it off just by making vague allegations about
:the real world.
:

It's the most specific of allegations - if it's such a great idea and
so many people have tried it (and they have), why hasn't anyone ever
built one that works?


--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw

On 30 Jun, 18:45, (Rand Simberg) wrote:
On Sat, 30 Jun 2007 07:40:33 -0700, in a place far, far away, Ian
Parker made the phosphor on my monitor glow in
such a way as to indicate that:

One last remark about Concorde and supersonic aviation. The money is
now on an executive NOT an airliner. We could have one hypersonic
variant which was an LEO launcher and another that was a long range
executive. One imperative - a small launcher must operate WITHOUT a
pilot.

There's nothing at all imperative about that.

It is you know. All aircraft and spacecraft would benefit from not
having pilots. In an airliner (short haul) you could make 2 extra
seats available. If an airliner seats 400 or so this is not a large
penalty. As soon as you get to executive aviation, pilots atart
getting to be a major cost components. If you could run the mini jet
the Eclipse with no pilots 2 seats would make one hell of a
difference.

A spacecraft has similar economics. Any space launcher has to have a
cargo capability. A large launcher does not have a high penalty. The
Shuttle would have been a lot more competitive without crew. A small
launcher has to have a cargo only capability.

I don't know whether rockets 100% of the way really are better. I
think we should have an open mind on this. What I am saying however
is :-

1) Public money should not be involved either with rockets or
hypersonic aircraft.
2) All launches should be made by the cheapest method regardless of
flag. I understand from previous discussions that Ariane has less
bureaucracy than its competitors. Shouldn't a customer friendly
approach be adopted here as elsewhere. Under capitalism there is a
dictum that the customer is king.
3) Building a small hypersonic aircraft is less risky than building
something much bigger. If Richard Branson wants to do it - let him.
You might be able to get private finance for a small plane. If private
finance is unavailable public money should NOT be spent.


- Ian Parker

On 1 Jul, 10:21, Fred J. McCall wrote:
: :
: :Well, the performance comes from using an engine that is air breathing
: :for part of the ascent. It all comes down to whether they can build that
: :engine, and that appears to be where they're spending what money they have.
: :
:
: It also comes down to one other thing. Once that engine is built,
: does it buy them what they're thinking it will or do realities make it
: less efficient than other methods.
:
: So far, it seems that rockets always wind up more efficient in the
: real world than air-breathers.
:
:What do you mean by "more efficient" ?
:

Better mass fractions once the real world effects are all taken into
account.

:
:A air breathing engine can have a much higher specific impulse than a
:rocket engine. The downside is that since you cannot use an airbreathing
:engine all the way to orbit, the engine has to be a hybrid, or there has
:to be a separate rocket engine. In both cases the result is increased
:engine mass. Then it comes down to whether having a higher specific
:impulse for part of the ascent gives a net benefit once the higher
:engine mass is taken into account.
:

There's more to it than that. There isn't just the parasitic weight
of an engine with more moving parts (the air breathing bits), but the
parasitic drag of having to accelerate the oxidizer regardless of
whether you carry it with you (a rocket) or grab it out of the
atmosphere (an air-breather). Rockets can be more streamlined because
they don't need inlets. They can weigh less because they don't need
inlets. Their engines are simpler and have more specific power with
fewer moving parts.

In fact carrying liquid oxygen is not parasitic. It is always carried
in a rocket. The energy it has in fact contributes to the final energy
of the spacecraft. If you are travelling at 4.5 km/s the exhaust gases
(LOH/LOX) are stationary. This is where a rocket is 100% effecient and
the energy acquired in hypersonic air breathing is in fact being
conserved.


- Ian Parker

Fred J. McCall wrote:
Sylvia Else wrote:

:Fred J. McCall wrote:
: Sylvia Else wrote:
:
: :
: :Well, the performance comes from using an engine that is air breathing
: :for part of the ascent. It all comes down to whether they can build that
: :engine, and that appears to be where they're spending what money they have.
: :
:
: It also comes down to one other thing. Once that engine is built,
: does it buy them what they're thinking it will or do realities make it
: less efficient than other methods.
:
: So far, it seems that rockets always wind up more efficient in the
: real world than air-breathers.
:
:What do you mean by "more efficient" ?
:

Better mass fractions once the real world effects are all taken into
account.

What are these real world effects?


:
:A air breathing engine can have a much higher specific impulse than a
:rocket engine. The downside is that since you cannot use an airbreathing
:engine all the way to orbit, the engine has to be a hybrid, or there has
:to be a separate rocket engine. In both cases the result is increased
:engine mass. Then it comes down to whether having a higher specific
:impulse for part of the ascent gives a net benefit once the higher
:engine mass is taken into account.
:

There's more to it than that. There isn't just the parasitic weight
of an engine with more moving parts (the air breathing bits), but the
parasitic drag of having to accelerate the oxidizer regardless of
whether you carry it with you (a rocket) or grab it out of the
atmosphere (an air-breather). Rockets can be more streamlined because
they don't need inlets. They can weigh less because they don't need
inlets. Their engines are simpler and have more specific power with
fewer moving parts.

And the hybrid engine is using the same energy to accelerate a large
mass of gas to lower velocities. Since the kinetic energy of the gas is
proportional to the square of the velocity, but the momentum is
proportional to the velocity, you get a greater delta-v per unit fuel
consumption.

I've already said that hybrids weigh more. There's no doubt about that.
I've also observed that the question then is whether the extra weight is
worth it.

The increased complexity and moving part count is not relevant to a
discussion about performance.


:
:The SABRE engine is a hybrid, and is predicted to have a significantly
:higher mass than a pure rocket engine of similar thrust. For all that,
:Reaction Engines have run the numbers and concluded that they work.
:

They frequently do ... on paper.

Can you point to any LACE or similar engine that has reached a point in
its development where it could be seen that the numbers are wrong?

:
:Now, they may have overestimated the thrust in the air breathing mode,
r underestimated the mass, or the entire concept may be flawed, but I
:don't think you can write it off just by making vague allegations about
:the real world.
:

It's the most specific of allegations - if it's such a great idea and
so many people have tried it (and they have), why hasn't anyone ever
built one that works?

How many people have tried building LACE engines?

http://en.wikipedia.org/wiki/Liquid_air_cycle_engine

claims that a working LACE engine testbed was working as early as 1960.

Sylvia.

On Sun, 01 Jul 2007 03:25:54 -0700, in a place far, far away, Ian
Parker made the phosphor on my monitor glow in
such a way as to indicate that:

On 30 Jun, 18:45, (Rand Simberg) wrote:
On Sat, 30 Jun 2007 07:40:33 -0700, in a place far, far away, Ian
Parker made the phosphor on my monitor glow in
such a way as to indicate that:

One last remark about Concorde and supersonic aviation. The money is
now on an executive NOT an airliner. We could have one hypersonic
variant which was an LEO launcher and another that was a long range
executive. One imperative - a small launcher must operate WITHOUT a
pilot.

There's nothing at all imperative about that.

It is you know.

No, I don't know that. Only ignorant loons know that.

All aircraft and spacecraft would benefit from not
having pilots.

Yes, those stupid airlines, what are they thinking?

rest of ignorance snipped

Len wrote:
On Jun 30, 6:03 am, Alex Terrell wrote:
On 30 Jun, 04:38, Sylvia Else wrote:



Len wrote:
On Jun 29, 6:55 pm, Sylvia Else wrote:
David Cornell wrote:
If someone were to build an SSTO using realistic assumptions about mass
ratios and available power systems, how big a vehicle would be needed to
send (say) three people and a modest amount of cargo into LEO? I have
seen Apollo capsules in museums, so I am using them as my baseline.
Would such a thing be the size of a regular jetliner? Or the new Airbus
super jumbo jet? Or are we talking about a Zeppelin on steroids?
Also, how would these things scale? If we wanted to increase the crew
from three to four, would the vehicle size go up by a third? Or more?
Thanks
David Cornell
You didn't say so, but I'm assuming you mean a reusable craft.
Disposable SSTO's seem a waste of effort.

The most developed design I've seen for a reusable SSTO is

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

It has a payload of 12 tonnes, and a maximum takeoff weight around 280
tonnes, similar to that of a 777-300. It uses a new engine design with
some technological challenges, but they seem to have made some progress
with it. They're obviously financially constrained, so if you have a
spare $billion, I'm sure they be interested in talking.

Skylon is an automated system, and as such is not designed to have a
crew, but could carry people as payload. This document

http://www.reactionengines.co.uk/dow...56_118-126.pdf

discusses that application using a module carrying 40 people, though
that's obviously in a transport application (to a space hotel, perhaps).
If you have space tourism in mind, with passengers not leaving the craft
and floating around the cabin, then presumably they'd need more space
per passenger.

It's hard to say how this scales for a smaller payload, but at a guess,
I'd say you could get a craft to carry four people that was the size of
a small airliner in the 50 seat range.

Sylvia.

I have probably looked at as many launch vehicle concepts
--rocket powered and airbreathers--as anybody in the world.
The devil is in the details. I would not consider Skylon
anywhere close to realistic. As for purely rocket-powered
approaches, I have never been able to convince myself
that any SSTO having a gross mass of
less than about 800 tonnes was very realistic. And for
HTOL, some type of ground cart to support the vehicle
at gross mass is probably necessary--thus making it
really an assisted SSTO, rather than a pure SSTO.

Staging--even subsonically at altitude or at low supersonic
speeds greatly relieves the challenge. IMO, staging
can sometimes be beneficial from the operations point
of view--as wsll as the performance point of view. SSTOs
are undoubtedly appealing from the psychological point
of view. However, they may not be a good way to run
an airline.

At some combination of size and yet-to-be-discovered
technology, SSTOs will make technical, economic and
marketing sense; but I don't see this happening soon.

Len

Would you care to expand on your concerns. At the moment, you've
basically said that you're an expert and that we should believe your
claim that Skylon is not realistic.

Sylvia.

I believe Len is an expert and would take his word for it.
Nevertheless, an expansion on the concerns would be of interest.

However, I don't see the benefit in SSTO when concepts like Quickreach
2 (http://www.astronautix.com/lvs/quieach2.htm) could reach orbit for
relatively low cost.

Len - how does Quickreach 2 compare to the latest space van proposals?

I have been out of town. I'll respond in more detail
tomorrow.

As a quick answer, Quickreach should be able
to launch a nearly twice as large payload a
couple of years earlier than the Space Van 2011.

We expect to carry 2000-kg--or eight passengers
--to an ISS-type orbit (not our main mission) for
a price (including ROI) of $2,000,000 per flight
in 2007 dollars. This compares to a Quickreach
cost (price?) of $20,000,000 in 2005 dollars.
The Space Van should be able to achieve much
more frequent flights, since there are no expendable
parts or reusable parts that require extensive
refurbishment between flights.

The Space Van should have good abort options
throughtout its flight regime--starting with
engine-out abort capablility just after liftoff
with derated engines. The engines are
derated for much improved time between
overhaul.

As for Sylvia's request, I am not sure
exactly what cycle Skylon plans to use,
but I suspect that it is some type of
combined-cycle engine. The poor-man's
approach to analyzing combined cycle
performance (except for potential benefits
from saving installation space through
integration) is to imagine separate rocket
and airbreathing engines. The resulting
thrust and specific impulse usually equals
the goals for the combined cycle engine.
This anaylis trick allows a quick
assessment of how much airbtreathing
and how much rocket the designer would
like to have. If one then goes through some
tradeoffs of different ratios and allows for
real-trajectory estimates of drag losses and
real-structure mass estimates allowing for
realistic inlets and the impact of flying the
whole vehicle at relatively high dynamic
pressures and velocities, I have always
found that the best ratio is 100 percent
rocket. Many others--including highly
knowledgeable people like Henry Spencer
--have noted that the airbreathing appeal
is rather superficial and vanishes under
realistic analyses.

Having been out argued on this in my younger days, the only mid term
hope I can see for air breathing would be to attach military derived
ramjets or scram jets onto the outside of the rocket, and have these
drop off at Mach whatever. These could drop off with the wings, which
starts to move towards a 2 stage model.

The investment would only make sense if there are suitable missiles
that can be adapted. Some countries are experimenting with supersonic
ramjet missiles, IIRC for cruise at about Mach 3.

On 1 Jul, 14:12, (Rand Simberg) wrote:

It is you know.

No, I don't know that. Only ignorant loons know that.

All aircraft and spacecraft would benefit from not
having pilots.

Yes, those stupid airlines, what are they thinking?

You obviously think there is something about pilots that cannot be
reproduced by a machine. In the 19th century people used to think of
some "vital force" for organic compounds.

In fact there is very little a pilot does as it is. I do NOT think
airlines should get rid of their pilots immediately. There are a lot
of safely issuues to be sorted out. Fundamentally though pilots are
increasingly there simply to provide reassurance.

I did say that if you have a small aircraft the pilots constitute a
higher percentage of capacity than with airliners. In the case of the
Eclipse one pilot is 25% of capacity and two pilots 50%. In the case
of a small hypersonic aircraft pilots would again be 50%.

We can if you like discuss the safely issues. The relative loss rates
of the Predator verus manned aircraft is not really relevant. In
manned aircraft there are better redundant systems built in and there
is also mission profile.

Also it would in fact cost far less in terms of bandwidth for ATC
information to be transmitted digitally. This today is very much old
hat technology. All that a pilot seems to do is interperate oral
infomation which should have been sent digitally anyway.

Only a small hypersonic plane will ever get built, not unless a
socialist inclined government decide to spend large tranches of public
money.

Proceeding the way you seem to want would be sheer lunacy. It could
only be done under Socialism - that is to say where pressure groups
dictate the spending of public money. All the best scientific work has
been done with unmanned vehicles. Unmanned exploration has become more
and more sophisticated as the years have gone by. Automatic equipment
has dug on Mars and navigated in space to a fantastic precision.

To explore space with astronauts is going to be incredibly expensive
and slow. Far, far better to simply send something that does not need
to return.

I find you right wingers hard to understand. During the Cold War
belief in Free Enterprise was what typified the "right". Now it
appears to be a negation of Free Enterprise. You want an American
solution, not a solution based on high quality and low price. This is
siege economics.


- Ian Parker

On Sun, 01 Jul 2007 08:34:57 -0700, in a place far, far away, Ian
Parker made the phosphor on my monitor glow in
such a way as to indicate that:

On 1 Jul, 14:12, (Rand Simberg) wrote:

It is you know.

No, I don't know that. Only ignorant loons know that.

All aircraft and spacecraft would benefit from not
having pilots.

Yes, those stupid airlines, what are they thinking?

You obviously think there is something about pilots that cannot be
reproduced by a machine.

As does the Federal Aviation Administration. It's going to continue
to be much easier to get an experimental permit and launch license for
a piloted spacecraft than an unpiloted one, particularly for inland
launches, for a long time.

AI fantasies snipped

To explore space with astronauts is going to be incredibly expensive
and slow.

I've little interest in "exploring" space. I want to go. I can't do
that with a robot.

I find you right wingers hard to understand.

That's at least partly because I'm not a "right winger."

On Jun 29, 7:38 pm, Len wrote:
On Jun 29, 6:55 pm, Sylvia Else wrote:





David Cornell wrote:
If someone were to build an SSTO using realistic assumptions about mass
ratios and available power systems, how big a vehicle would be needed to
send (say) three people and a modest amount of cargo into LEO? I have
seen Apollo capsules in museums, so I am using them as my baseline.
Would such a thing be the size of a regular jetliner? Or the new Airbus
super jumbo jet? Or are we talking about a Zeppelin on steroids?

Also, how would these things scale? If we wanted to increase the crew
from three to four, would the vehicle size go up by a third? Or more?

Thanks

David Cornell

You didn't say so, but I'm assuming you mean a reusable craft.
Disposable SSTO's seem a waste of effort.

The most developed design I've seen for a reusable SSTO is

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

It has a payload of 12 tonnes, and a maximum takeoff weight around 280
tonnes, similar to that of a 777-300. It uses a new engine design with
some technological challenges, but they seem to have made some progress
with it. They're obviously financially constrained, so if you have a
spare $billion, I'm sure they be interested in talking.

Skylon is an automated system, and as such is not designed to have a
crew, but could carry people as payload. This document

http://www.reactionengines.co.uk/dow...56_118-126.pdf

discusses that application using a module carrying 40 people, though
that's obviously in a transport application (to a space hotel, perhaps).
If you have space tourism in mind, with passengers not leaving the craft
and floating around the cabin, then presumably they'd need more space
per passenger.

It's hard to say how this scales for a smaller payload, but at a guess,
I'd say you could get a craft to carry four people that was the size of
a small airliner in the 50 seat range.

Sylvia.

I have probably looked at as many launch vehicle concepts
--rocket powered and airbreathers--as anybody in the world.
The devil is in the details. I would not consider Skylon
anywhere close to realistic. As for purely rocket-powered
approaches, I have never been able to convince myself
that any SSTO having a gross mass of
less than about 800 tonnes was very realistic. And for
HTOL, some type of ground cart to support the vehicle
at gross mass is probably necessary--thus making it
really an assisted SSTO, rather than a pure SSTO.

Staging--even subsonically at altitude or at low supersonic
speeds greatly relieves the challenge. IMO, staging
can sometimes be beneficial from the operations point
of view--as wsll as the performance point of view. SSTOs
are undoubtedly appealing from the psychological point
of view. However, they may not be a good way to run
an airline.

At some combination of size and yet-to-be-discovered
technology, SSTOs will make technical, economic and
marketing sense; but I don't see this happening soon.

Len- Hide quoted text -

- Show quoted text -

The likes of h2o2/c3h4o should do the reusable LRB (fly-by-rocket)
trick of SSTO.

Keeping the primary craft inert mass to a minimum is obviously key to
any SSTO craft, and having energy packed density is key to
accomplishing the least possible inert mass.

This being a hybrid SSTO; meaning that a pair of reusable and fully
robotic flown LRBs of h2o2/c3h4o should make for the primary reusable
craft having the least possible inert mass.
-
Brad Guth

On Jun 29, 9:25 am, David Cornell wrote:
If someone were to build an SSTO using realistic assumptions about mass
ratios and available power systems, how big a vehicle would be needed to
send (say) three people and a modest amount of cargo into LEO? I have
seen Apollo capsules in museums, so I am using them as my baseline.
Would such a thing be the size of a regular jetliner? Or the new Airbus
super jumbo jet? Or are we talking about a Zeppelin on steroids?

Also, how would these things scale? If we wanted to increase the crew
from three to four, would the vehicle size go up by a third? Or more?

Thanks

David Cornell

I tend to agree with Len's 800 tonnes worth of initial mass, whereas
Skylon is simply offering too much hybrid fly-by-rocket pie in the
sky, especially at a mere 23.3:1 ratio of rocker/payload.

However, the likes of h2o2/c3h4o should do the reusable LRB (fly-by-
rocket) trick of SSTO.

Keeping the primary craft inert mass to a minimum is obviously key to
any SSTO configuration, and having as much energy packed density as
possible is key to accomplishing the least possible inert mass.

This being a hybrid SSTO; meaning that a pair of reusable and fully
robotic flown LRBs of h2o2/c3h4o should make for the primary reusable
craft as having the least possible inert mass.

You simply can't be hauling the likes of dead engines and empty
tankage of whatever fuels fully into orbit, such as within any SSTO
mono-hull craft, that which also has the added mass and drag of
aerodynamic considerations along with viable options of safly getting
those paying passengers away from a potentially flaming and/or
exploding fiasco.
-
Brad Guth