Cheap Realistic Space Flight

I'm trying to imgaine cheap space flight. I'd also like to see it
sooner rather than later. Given this I believe we are limited to
chemical rockets.

What's the cheapest cost to orbit a chemical rocket is likely to
yield in the next fifty years? Will we see $100/pound to orbit?
How about $10/pound? And what underlying technology will
this rocket use?

Note: Please avoid the use of wormholes and unobtanium. Please
don't say "carbon nanotubes will solve everything" unless you also
believe that we will build 50,000 lbs structures in carbon nanotubes
sometime in the next 50 years. We're looking reasonably far into
the future (50 years or less) but trying to limit ourselves to chemical
rockets and things that can actually be built and used.

In article ,
Charles Talleyrand wrote:
I'm trying to imgaine cheap space flight. I'd also like to see it
sooner rather than later. Given this I believe we are limited to
chemical rockets.

There are actually a number of alternatives that would be realistic on
a timescale of a few decades, e.g. laser launchers. However, taking the
question as read...

What's the cheapest cost to orbit a chemical rocket is likely to
yield in the next fifty years?

That depends enormously on just how things evolve -- it is not primarily a
technological question. To the extent that it is technological, the
technical issues are things like heatshield maintenance requirements,
which are very difficult to predict.

Will we see $100/pound to orbit? How about $10/pound?

The former is very likely. The latter is conceivable but rather a
stretch: a cheap propellant combination like LOX/propane can in theory
put stuff in orbit for $1-2/lb of dry mass, but *payload* will be only a
modest fraction of the dry mass, and getting maintenance and overhead down
to the point where fuel cost is a large fraction of total operating cost
would be challenging.

And what underlying technology will this rocket use?

The best bets, in my opinion, are (a) carbon-fiber or *possibly* nanotube-
composite structures, (b) innovative engine designs with rather better
performance than conventional approaches, and (c) reentry concepts that
unfurl or inflate a large heatshield, much larger than the vehicle proper,
so as to reduce the demands on the heatshield materials. But there are
alternative approaches aplenty; again, much will turn on non-technical
issues.

don't say "carbon nanotubes will solve everything" unless you also
believe that we will build 50,000 lbs structures in carbon nanotubes
sometime in the next 50 years.

I think that's credible, but by no means certain. Making a good composite
structural material using nanotubes as the fiber is much harder than just
making nanotubes. Lots of people are working on it, but it's a difficult
problem and it might not *have* near-term solutions. (People have been
trying for nearly 20 years to make high-power wire using liquid-nitrogen
superconductors, with only the most limited results so far.)
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

"Henry Spencer" wrote in message ...
The best bets, in my opinion, are (a) carbon-fiber or *possibly* nanotube-
composite structures, (b) innovative engine designs with rather better
performance than conventional approaches, and ...

In what way will these engines be better than the current ones?

I understand that the current engines opperate at a very large fraction of
the theoretical performance. So I assume you're talking about either lower
weight or lower cost. Is that correct?

Is this also correct: you do not believe that concepts like ORTAG are
the way to go? Why? I have to admit the concept appeals to me.

-Curious
-Randy

Charles Talleyrand wrote:
Is this also correct: you do not believe that concepts like ORTAG are
the way to go? Why? I have to admit the concept appeals to me.

Big Dumb Boosters are a strongly viable short term
technology step; credible designs start at around a
thousand dollars a pound for multi-ton payloads and up,
and for high flight rates should drop below $500/lb.

The question is ultimately how cheap can they get.
The studies which have been done so far indicate
that the number is under $500/lb, possibly under $250/lb,
but almost certainly not less than $125/lb.

People are not going to be satisfied in the long
run with dropping costs only to a couple of hundred
dollars a pound or so. Barring magic materials or
fabrication technologies, BDB isn't going to get there.

Though, I have to say, the BDB implications of some of
the composite technologies which are now beginning to
see the light of day have not been openly fully evaluated
to date, and the possible implications for BDBs of cheap
carbon nanotube composites abound as well, so ruling out
magic is perhaps premature ;-)


-george william herbert

In sci.space.tech George William Herbert wrote:
Charles Talleyrand wrote:
Is this also correct: you do not believe that concepts like ORTAG are
the way to go? Why? I have to admit the concept appeals to me.
snip
Though, I have to say, the BDB implications of some of
the composite technologies which are now beginning to
see the light of day have not been openly fully evaluated
to date, and the possible implications for BDBs of cheap
carbon nanotube composites abound as well, so ruling out
magic is perhaps premature ;-)

If you take the question as stated, it kind of implies that if nanotube
composites are available cheaply, then they will be only a modest
amount stronger than conventional composites.
Once you start to get above 5-10* the state of the art, and hit 30-60Gpa
(200GPa is around the ultimate theoretical limit of nanotubes) space
elevators start looking almost easy.

At the upper end of that range, the ratio of tether to maximum payload
is getting towards single digits, and you can bootstrap in a year or so
(assuming adequate composite) from 1 ton to a million ton payloads.

In article ,
Charles Talleyrand wrote:
The best bets, in my opinion, are (a) carbon-fiber or *possibly* nanotube-
composite structures, (b) innovative engine designs with rather better
performance than conventional approaches, and ...

In what way will these engines be better than the current ones?
I understand that the current engines opperate at a very large fraction of
the theoretical performance. So I assume you're talking about either lower
weight or lower cost. Is that correct?

"Performance" has a number of dimensions.

Current engines are not too far from the limits on Isp, although
incremental improvements remain possible and can make a substantial
difference to vehicle performance (because the relationship between
the two is very nonlinear).

Current engines are (in my opinion) *nowhere* *near* fundamental limits on
thrust/weight, even without magic materials like nanotube composites.
Improving that means lighter engines for the same thrust, or more thrust
in the same package. This matters both directly -- engine mass is a
significant part of the orbited dry mass -- and indirectly -- many RLV
concepts have center-of-gravity problems for reentry because of all that
engine mass in the tail.

The ability to operate efficiently over a wide range of altitudes (i.e.,
ambient pressures) would be very useful for a first-stage or SSTO engine.

Even such a small, mundane thing as being able to operate with very low
pump-inlet pressures -- that is, a reduced requirement for tank
pressurization -- could significantly ease vehicle design.

Manufacturing cost, maintenance workload, and working lifetime are all
important.

Reliability and robustness are important for costly, long-lived vehicles.
This insane business of safety factors of 1.25 or less has got to stop.

Is this also correct: you do not believe that concepts like ORTAG are
the way to go? Why? I have to admit the concept appeals to me.

There are limits to how far you can reduce costs with expendable rockets,
even mass-produced ones with cheap components. More subtly, there are
limits to how reliable they can be, since it is impossible to test-fly one
before entrusting a valuable payload to it. (Today's expendables have
failure rates that any other branch of transportation engineering would
class as criminal negligence, and the situation does not seem to be
improving significantly.)

As George has pointed out, they remain of some interest in the short term,
but they're not what people want in the long term.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

(Henry Spencer) wrote in message ...
...
And what underlying technology will this rocket use?

The best bets, in my opinion, are (a) carbon-fiber or *possibly* nanotube-
composite structures, (b) innovative engine designs with rather better
performance than conventional approaches,

For what definition of "performance"? Energy efficiency is already
fantastic in today's rockets. Thrust/Weight? Performance in the
atmosphere?

Oren

In article ,
Oren Tirosh wrote:
...(b) innovative engine designs with rather better
performance than conventional approaches,

For what definition of "performance"? Energy efficiency is already
fantastic in today's rockets.

Well, no, it's not all that terrific... but it is probably about as good
as it is going to get, aside from the question of altitude compensation.

Thrust/Weight? Performance in the atmosphere?

Yes, and some other things -- see previous posting.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

Charles Talleyrand wrote:

What's the cheapest cost to orbit a chemical rocket is likely to
yield in the next fifty years? Will we see $100/pound to orbit?

Sure.

How about $10/pound?

Probably not.

And what underlying technology will
this rocket use?

High flight rates. No reason we couldn't achieve $100/lb using 1960's
tech. Just need to build in numbers and fly a lot.


--
Scott Lowther, Engineer
Remove the obvious (capitalized) anti-spam
gibberish from the reply-to e-mail address

Scott Lowther writes:

Charles Talleyrand wrote:

What's the cheapest cost to orbit a chemical rocket is likely to
yield in the next fifty years? Will we see $100/pound to orbit?

Sure.

How about $10/pound?

Probably not.

And what underlying technology will this rocket use?

High flight rates. No reason we couldn't achieve $100/lb using 1960's
tech. Just need to build in numbers and fly a lot.

....Kind of like the Russions do with their "Proton" booster...


-- Gordon D. Pusch

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