Cheap Realistic Space Flight

(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 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.

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.

No, we are not. All materials and technologies that are available today
should be considered.

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?

With the suborbital/tether system mentioned below, one might be able to
reach 10$/pound in 50 years.

Note:**Please*avoid*the*use*of*wormholes*and*unobt anium.**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.

Consider the following system:

A ballistic space transport accelerates a payload to an altitude of 100km
and a velocity of, say 4000m/s or about half orbital velocity. At the
apogee of the suborbital trajectory the payload is picked up by a rotating
space tether (sometimes called rotovator) that is already in orbit. The
tether accelerates the payload to an orbital trajectory with a very high
apogee. At apogee the payload can use a small built-in rocket engine or
another tether to circularize the orbit. The ballistic space transport
lands vertically on a barge in the ocean and is ready for another flight in
less than 24h.

There are multiple advantages to this system compared to a traditional full
scale space elevator. The rotating tether only provides half the orbital
velocity and has a length of only about 200km, so it can be built with
materials that are available in ton quantities today such as Spectra 2000.
No unobtainium required. Another advantage of the rotating tether is that
you do not need climbers that travel the length of the tether, so you can
design the tether to be very spread out and survivable.

Of course there is no such thing as a free lunch. The tether system will
lose some angular momentum each time it throws a payload to a GTO
trajectory. But thanks to the earth magnetic field it can gain the lost
angular momentum back without using propellant. You just let some current
flow through a part of the tether so that the net lorenz force produced by
the interaction of the tether and the earth magnetic field is in the right
direction. You need a lot of energy, but this can be provided by solar
cells that also serve as a tether counterweight.

This system sounds very strange, but in fact all parts of this system could
be built today.

-A suborbital space transport with a total delta-V of 5000m/s is quite easy
to build, and in fact one is being built right now. I am talking about the
reusable first stage of the spacex falcon launcher www.spacex.com.

-The tether system itself does not require any advanced materials. It could
be built with many available materials such as glass fiber, carbon fiber or
Spectra 2000.

-The fact that interaction of a conducting tether with the earth magnetic
field can cause changes in angular momentum has been proved many times,
most notably by an experiment on the Space Shuttle.

-The rendezvous of the payload and the tether tip should be quite easy since
the relative velocity during capture is zero and both the tether tip and
the payload could be outfitted with GPS.

Some links to convince you that this is not just wishful thinking:

www.spacex.com : Are building a small two-stage launcher with a reusable
lower stage!

www.tethers.com : A lot of information about rotating space tethers,
including how to build a tether that survives space debris (Hoytether).

Here are some very interesting papers from the tethers.com site:
http://www.tethers.com/papers/MXERJPC2003Paper.pdf
http://www.tethers.com/papers/JPC00HASTOL.pdf
(replace the hypersonic scramjet aircraft with something more practical such
as a ballistic space transport or an air-launched HTHL craft to get a
workable system :-)

best regards,

***Rüdiger

p.s. I do not see why people are so excited about space elevators. I think a
rotating space tether combined with a suborbital craft would be much more
practical and flexible....

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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(Serg) writes:

"Charles Talleyrand" wrote in message
...

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.

If you are talking about cheap, but politically unrealistic
spaceflight, I don't think anything could beat Orion. More politically
plausible would be NTR , I think still cheaper then chemical (without
development cost).

As currently conceived, NTR doesn't fly --- literally. The reactor power
densities are so low that the thrust-to-weight ratio is less than unity;
hence, an NTR cannot even lift its _own_ weight in a 1 gee field, let alone
a spacecraft! One has to go to an "advanced" design like the DUMBO micro-
structured heat exchanger that can handle power-densities at least an order
of magnitude higher than current solid-core or "TRIGA pellet" designs.

The "Nuclear Light-Bulb" gaseous-core reactor design would be more
effective still --- if one could just figure out how to keep the "light bulb"
envelope from melting, while still efficiently transferring the radiative heat
to the propellant. (Sadly, Hydrogen tends to be rather more transparent than
most "light bulb" materials, so there is a slight technical problem in that
the "light bulb" wants to melt more than the propellant wants to get hot...
Also, I expect gas-core nuclear rockets to be at _least_ an order of magnitude
more Politically Incorrect than RTG-powered space probes --- which are already
routinely picketed by Greenpeace and the Union of Concerned "Scientists"...)


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

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. |

In article ,
John Schilling wrote:
$10/pound is close to the ultimate limit, barring miracle tech,
of three times the fuel/energy cost. That's where the airline
industry has stabilized after a hundred years of manned airline
flight, and the same economic logic seems to apply.

Yes and no. Max Hunter pointed out that we ought to be able to do better
than jet aircraft. Most of the operating costs do not scale with fuel
load -- "the multipliers are on the *empty* weight, and then add fuel" --
and we are so much more fuel-intensive that fuel ought to dominate our
ultimate-limit costs more.

However, this changes John's conclusion only by perhaps a factor of 2.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

Bernardz wrote:
In article , says...

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?



NASA was talking a few years ago of getting it to $1000/pound in the
future. No way will they achieve it soon.

But you need to specify more details.

Say it costs you $X to develop the rockets
Say you build a launch pad for $Y
Say each rocket costs $Z
Say each rocket carries P pounds

and use it to fire N rockets

Then your cost per rocket per pound = (x+y+z) * P / N

N at present is probably the most disappointing figure.

try
(X + Y + Z*N) / (P*N)
or
(X+Y+Z)/P for the first rocket
Z/P for each additional
X and Y will realistically far exceed Z.

In article ,
says...
Bernardz wrote:
In article , says...

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?



NASA was talking a few years ago of getting it to $1000/pound in the
future. No way will they achieve it soon.

But you need to specify more details.

Say it costs you $X to develop the rockets
Say you build a launch pad for $Y
Say each rocket costs $Z
Say each rocket carries P pounds

and use it to fire N rockets

Then your cost per rocket per pound = (x+y+z) * P / N

N at present is probably the most disappointing figure.

try
(X + Y + Z*N) / (P*N)

You are of course correct.

or
(X+Y+Z)/P for the first rocket
Z/P for each additional
X and Y will realistically far exceed Z.


Depends on whether you write off X and Y or whether you depreciate it.

In real terms I would expect that the cost of the rocket will be a minor
cost compared to the development costs.





--
I hope that God's behaviour improves in the future?

JRS: In article MPG.1a0bc43169ef91be989695@news, seen in
news:rec.arts.sf.science, Bernardz
posted at Fri, 31 Oct 2003 00:58:59 :-
In article , says...
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?


NASA was talking a few years ago of getting it to $1000/pound in the
future. No way will they achieve it soon.


NASA cannot do it, but the US Government might.

The Dollar is currently the least valuable unit of the major Western
countries, and, like almost all currencies, its value in real terms
(technological equipment apart) continues to fall.

There is very little in the UK that is normally bought as an individual
purchase for which the per-item cost is not a multiple of 5 pence
(except for cases such as £x.99); we hardly need our coppers now.
Presumably the cent is in a similar situation to the penny.

So it would be logical, in the foreseeable future, to redenominate the
Dollar; a new Dollar worth ten old Dollars, with the loss of present
coins under 10c, would be convenient (the change might be as popular as
changing to metric; but the situation needs to be faced. Granted, the
Italians managed with their lire).

That would, of course, at a stroke reduce NASA's Dollar costs tenfold.

FYI, the Soviets achieved a similar redenomination, probably by a factor
of 100, almost overnight, IIRC.


ISTM that there is too much stress on CATS, and more overt attention
should be paid to RATS. Where RATS lead(s), CATS follow(s).

R = Reliable.

--
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