How big would an SSTO be?

Len wrote:

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

Len,

Thank you for the informative and realistic reply. I tend to agree that
a
TSTO would likely be a better first step than an SSTO, but I am just an
interested
bystander with no experience in the field, so what do I know. I have
been trying to get a picture in my mind of what a realistic near-term
space craft might look like,
how big it would be, how much noise it would make, what kind of
maintenance and support it would require, etc. Too much of my
imagination is cluttered with images of the fantasy spacecraft of sci-fi
movies, in which the heroes flit around the galaxy with no regards to
cost or logistics.

Has anyone done any studies of the likely operational costs of
recovering and reassembling the stages of a TSTO versus the savings in
developmental (and perhaps operational) costs that a TSTO would have
over an SSTO of similar capacity?
Obviously, if going with a TSTO saved you billions in development cost
and many years in development time, the fact that getting the stages
back together might be an operational PIA might be a moot point.

Thanks again for your insights.

David Cornell

Sylvia Else wrote:

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.

Yes, I was assuming a reusable craft. I guess I took that for granted.

Thank you for the information on Skylon. I had heard the name but
didn't know much about it. I wish I had either money or talent to
contribute to the cause, but all I have is an interest in the subject
and a little bit of imagination. In any case,
Skylon's proposed performance sounds too good to be true, but I would be
delighted to be proved wrong.

David Cornell

Alex Terrell wrote:

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?

Alex,

Thanks for the pointer to Quickreach 2. I had never heard of it
before. It is
interesting that they boast of the complex technology that they have
managed to avoid using (complex on-the-pad abort tower system, complex
pressurization and regulation system, etc.) rather than the usual
boasting on how they are on the bleeding edge of technology. This gives
me some hope that they might be on the right track.

David Cornell

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.

On 30 Jun, 17:56, David Cornell wrote:
Alex Terrell wrote:
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?

Alex,

Thanks for the pointer to Quickreach 2. I had never heard of it
before. It is
interesting that they boast of the complex technology that they have
managed to avoid using (complex on-the-pad abort tower system, complex
pressurization and regulation system, etc.) rather than the usual
boasting on how they are on the bleeding edge of technology. This gives
me some hope that they might be on the right track.

David Cornell

Quickreach 2 was part of the t-space proposal to NASA for VSE. NASA
asked private companies to come up with alternative architectures and
there were a lot of really good ideas. T-Space even threw a prototype
rocket out the back of a plane. Unfortunately, NASA decided to go for
a slower, more expensive and arguably riskier route.

Someone at Astronautix puts it nicely:
"t/Space's partners demonstrated the technology that would ensure that
it could deliver a launch system that would deliver a crew of four to
orbit at a cost of $20 million per launch within three years of go-
ahead. This was less than 10% the cost and half the time that NASA
planned to spend on its own CEV approach. Naturally this was of no
interest to NASA and further contracts were not forthcoming."

http://www.astronautix.com/craft/cxv.htm

David Cornell wrote:
Sylvia Else wrote:

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.

Yes, I was assuming a reusable craft. I guess I took that for granted.

Thank you for the information on Skylon. I had heard the name but
didn't know much about it. I wish I had either money or talent to
contribute to the cause, but all I have is an interest in the subject
and a little bit of imagination. In any case,
Skylon's proposed performance sounds too good to be true, but I would be
delighted to be proved wrong.

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.

Sylvia.

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.

Len

On Jun 30, 9:15 pm, 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.

Len

Oops. Our price goal in 2007 dollars is
$2,200,000 or less per flight, depending
upon flight level, with a minimum flight
level of 200 flights per year. I had said
ealier the price was $2,000,000 per flight.

Len

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.


--
"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

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" ?

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.

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.

Now, they may have overestimated the thrust in the air breathing mode,
or 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.

Sylvia.