Ships for Space Travel

I lay watching Mars the other night, and I thought about how we might
build a ship to take people there. In a lot of ways, we are like
ancient man right after he has built his first boat, yet we are trying
to cross oceans in our flimsy craft.

It seems to me that we need something with a lot of volume for long
distances. It doesn't need a lot of mass, maybe something like a big
bubble.

The pressure hull need not be terribly strong, but it should be
protected from impacts inside or outside the vehicle. Of course, the
docking ports would need to be stronger, and so there would probably
be some sort of skeleton that is much stronger than the pressure hull.

I like the plan to have a perpetually cycling ferry running between
Earth and Mars. It could be a simple craft. Maybe we could beam power
to it, perhaps by laser to solar panels? Then, we would could have
simpler, lighter and safer power for the astronauts (the only
realistic alternative would be nuclear reactor, which is fine for
unmanned craft, but not so great for manned). The engines could be ion
engines, using an inert gas, so there would be less risk of explosion
or poisoning by the fuel.

What other sorts of things might differ between this interplanetary
ship and the vehicles we currently have?

(Richard Alexander) writes:

I like the plan to have a perpetually cycling ferry running between
Earth and Mars. It could be a simple craft.

I like the idea of a cycler, too.

http://www.spacer.com/news/tourism-02b.html

http://clowder.net/hop/railroad/railroad.html

Maybe we could beam power
to it, perhaps by laser to solar panels? Then, we would could have
simpler, lighter and safer power for the astronauts (the only
realistic alternative would be nuclear reactor, which is fine for
unmanned craft, but not so great for manned).

Beaming wouldn't be practical: once an orbit or so it would be behind
the Sun. There would also have to be multiple beaming stations on the
Moon since the Moon revolves. In addition, I don't think you could
focus a beam at interplanetary distances (without a REALLY big lens).

I'm in favor of one or more nuclear reactors, perhaps with solar
panels as alternates.

It seems to me that we need something with a lot of volume for long
distances. It doesn't need a lot of mass, maybe something like a big
bubble.

ASSUMING the human body needs some "gravity" to stay healthy in the
long run, we need some rotation. I favor a central core, with
storage, landers, main engines, etc., and two habitat modules on long
cables or "towers" (masts for rigidity).

At 2 rpm and .5 g, the cables or towers would be 450 m each. In
comparison, the Eiffel Tower is 300 m, the Petronas Towers are 452 m,
and the CN Tower is 553 m.

To accelerate, the cycler could reel in the habitats, if they were on
cables, or have strong enough masts or towers (or have independent and
coordinated rockets on each section).

-paul-
--
Paul E. Black

Paul B:
Richard A:

I like the plan to have a perpetually cycling ferry running between
Earth and Mars. It could be a simple craft.

I like the idea of a cycler, too.

-----
Like the idea, but would go unmanned at first and bootstrap using scrap.
No space rock required with over 180 tons of aluminum in orbit. Russia
has a small number of reactors up and station-keeping ion engines will
be more plentiful. Add large antennas and new programmable control systems
to be combined with the excellent but less than state of the art sensors
in orbit and a few new sensors as required.

The building site would be a telerobotic platform in geostationary
orbit, itself partially built from available materials using a solar
furnace to extrude tubing and die cast joints.

The thinking is along the lines of a long spaceframe with an array of
attachment points for container freight. At first this would go out
with exploration craft and generic supplies including survival gear.
Early returns would be mostly samples. Later trips could include
landing craft, fuel, and bulk supplies for early flag-planting events.
Space station modules....

I always wanted to do this, but I'll cheer on anyone who creates the
hardware or any related system.
--
Anvil*

(Paul E. Black) wrote in message ...
(Richard Alexander) writes:

[snip]

Maybe we could beam power
to it, perhaps by laser to solar panels? Then, we would could have
simpler, lighter and safer power for the astronauts (the only
realistic alternative would be nuclear reactor, which is fine for
unmanned craft, but not so great for manned).

Beaming wouldn't be practical: once an orbit or so it would be behind
the Sun.

That depends on where one places the transmitter. We could also have
more than one transmitter.

We could have a transmitter on Mars and Moon. We could have
transmitters out of the ecliptic plane. We could have orbiters out of
the ecliptic plane. Indeed, we could have orbiters that are massive,
unmanned power plants, beaming power to spacecraft thousands of
kilometers away.

There would also have to be multiple beaming stations on the
Moon since the Moon revolves. In addition, I don't think you could
focus a beam at interplanetary distances (without a REALLY big lens).

My rough estimate shows me that a 10 meter telescope could focus a
beam from Earth to Mars down to less-than a one-meter spot at 400 nm
wavelength. This exceeds our requirements, but is not too technically
difficult.

http://www.de.afrl.af.mil/News/2003/03-36.html
http://www.coseti.org/radobs14.htm

I'm in favor of one or more nuclear reactors, perhaps with solar
panels as alternates.

I believe that any serious deep space exploration will require some
type of nuclear energy, at least in our lifetimes. But, I don't
believe that nuclear reactors on vessels containing humans are a good
match, due to radiation hazards. Shielding is expensive and heavy, and
placing the reactor on a long boom complicates the design. If we can
simply beam power to the ship, we could shrink the size of the
shipboard power plant down to a small closet.

It seems to me that we need something with a lot of volume for long
distances. It doesn't need a lot of mass, maybe something like a big
bubble.

ASSUMING the human body needs some "gravity" to stay healthy in the
long run, we need some rotation.

That is one of my main concerns. I believe we need gravity to remain
healthy. I believe that a big, rotating vessel (or segment of a
vessel) is better with less mass and simplier mechanics. Thus, beam
the power to the ship, rather than carrying a full-scale power plant
aboard ship. They could still have back-up generators, that would
provide emergency power.

Unfortunately, we have never launched a spacecraft that was intended
to provide artificial gravity. I understand the design is too
complicated.

In article ,
Richard Alexander wrote:
...In addition, I don't think you could
focus a beam at interplanetary distances (without a REALLY big lens).

My rough estimate shows me that a 10 meter telescope could focus a
beam from Earth to Mars down to less-than a one-meter spot at 400 nm
wavelength...

I fear you've dropped a decimal point somewhere. Spot size is very
approximately distance*wavelength/diameter. Mars's distance varies
depending on where it is in its orbit, but let's take a couple of
hundred million kilometers as typical. 200e9 * 400e-9 / 10 = 8000.
A spot size of 8km is just not practical.

A factor of 100 improvement would bring it down within reach of reason,
but a 1km mirror is beyond what's reasonably practical in the near future.
Eventually, yes.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

(Henry Spencer) wrote:

A factor of 100 improvement would bring it down within reach of reason,
but a 1km mirror is beyond what's reasonably practical in the near future.
Eventually, yes.


Is there any indication of how big a bubble could be blown in
microgravity to create an Al or Au sphere, that could be sectioned to
provide several spherical mirrors (yes, I know, there's another conic
section that is better for focussing; ignore the man behind the
curtain for the moment) ?

Surface tension vs expansion rates and cooling issues are the obvious
factors; using a chemical rocket for the blowing (and maybe for
heating the melt) might give some ability to sustain an elastic
temperature, though, by filling the bubble with hot exhaust.

/dps

(dave schneider) writes:

(Henry Spencer) wrote:

A factor of 100 improvement would bring it down within reach of reason,
but a 1km mirror is beyond what's reasonably practical in the near future.
Eventually, yes.

Is there any indication of how big a bubble could be blown in
microgravity to create an Al or Au sphere, that could be sectioned to
provide several spherical mirrors (yes, I know, there's another conic
section that is better for focussing; ignore the man behind the
curtain for the moment) ?

For a sufficiently large focal length, you don't even need spherical sections;
the individual sections can be optically _flat_, and still not deviate from
the ideal figure by more than a fraction of a wavelength. (IIRC, a 10 km
focal length is sufficient for this to be true.) The primarily problem
then becomes one of _aligning_ the array of mirrors --- not machining.


-- Gordon D. Pusch

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

Gordon D. Pusch wrote:
(dave schneider) writes:
(Henry Spencer) wrote:
A factor of 100 improvement would bring it down within reach of reason,
but a 1km mirror is beyond what's reasonably practical in the near future.
Eventually, yes.

Is there any indication of how big a bubble could be blown in
microgravity to create an Al or Au sphere, that could be sectioned to
provide several spherical mirrors (yes, I know, there's another conic
section that is better for focussing; ignore the man behind the
curtain for the moment) ?

For a sufficiently large focal length, you don't even need spherical sections;
the individual sections can be optically _flat_, and still not deviate from
the ideal figure by more than a fraction of a wavelength. (IIRC, a 10 km
focal length is sufficient for this to be true.) The primarily problem
then becomes one of _aligning_ the array of mirrors --- not machining.

There was a story in Analog science-fiction magazine some time
ago about exactly such a project.

Subplots abounded, but the major technical problem was the
structure's vibrational modes...


-george william herbert

(George William Herbert) commented:
Gordon D. Pusch wrote:
(dave schneider) writes:
(Henry Spencer) wrote:
A factor of 100 improvement would bring it down within reach of reason,
but a 1km mirror is beyond what's reasonably practical in the near future.
Eventually, yes.

Is there any indication of how big a bubble could be blown in
microgravity to create an Al or Au sphere, that could be sectioned to
provide several spherical mirrors (yes, I know, there's another conic
section that is better for focussing; ignore the man behind the
curtain for the moment) ?

For a sufficiently large focal length, you don't even need spherical sections;
the individual sections can be optically _flat_, and still not deviate from
the ideal figure by more than a fraction of a wavelength. (IIRC, a 10 km
focal length is sufficient for this to be true.) The primarily problem
then becomes one of _aligning_ the array of mirrors --- not machining.

There was a story in Analog science-fiction magazine some time
ago about exactly such a project.

Subplots abounded, but the major technical problem was the
structure's vibrational modes...


Well, the idea I had about the bubble was that it would a) take care
of the aligning of sections and b) reduce or eliminate the need for
truss sections.

/dps

Dave S:
Henry S:

A factor of 100 improvement would bring it down within reach of reason,
but a 1km mirror is beyond what's reasonably practical in the near future.
Eventually, yes.

Is there any indication of how big a bubble could be blown in
microgravity to create an Al or Au sphere, that could be sectioned to
provide several spherical mirrors (yes, I know, there's another conic
section that is better for focusing; ignore the man behind the
curtain for the moment) ?

Surface tension vs expansion rates and cooling issues are the obvious
factors; using a chemical rocket for the blowing (and maybe for
heating the melt) might give some ability to sustain an elastic
temperature, though, by filling the bubble with hot exhaust.


Personally I don't see a problem manufacturing a 1 or 2km conic section
using an inflatable structure. Accuracy is less a problem for focusing
power. A ten-meter spot size seems about right. Using a more accurate
semi-ridged mirror to focus down to a 20 cm spot. Rather a nozzle-bell
shape with a spherical clear end, much like a flashlight reflector.

One-half mill Kapton with a sputtered silver/gold reflector layer and
the end with a UV stabilized PET with a selective filter coating under
an anti-reflective coating. After the main area is inflated a grid of
tubes would be inflated on the mirror section and then the whole mirror
section plasma-sprayed with aluminum. Once completed the structure
should have the pressure reduced to a minimum to avoid the risk of
overpressure.

Current Vacuum sputter coating technology limit the width of gores to a
two-meter width and length to ~8km. Dupont's large width for Kapton is
54" but 2 meters should be negotiable with a very large order.
Fabrication would have to be planet side.
--
Anvil*

Personally I'd rather see such a structure used as a solar furnace to
scrap space junk into useable forms.