Re: Venusian orbital carbon industry?


Bryan Derksen wrote:
>On 9 Nov 2005 07:43:46 -0800, "IsaacKuo" <mechdan@xxxxxxxxx> wrote:

>>Gigantic balloons are pretty difficult technology to deal
>>with even here on Earth. I can't think of any reason to
>>think they'd be easier to deal with on Venus.

>We have a heck of a lot more experience with balloon
>technology than we do with "skimmer" spacecraft that dip
>in and out of the atmosphere repeatedly.
[...]
>Hanging a mass driver from a string of these seems like
>a relatively straightforward extrapolation of existing
>technology. Just put up more of them. What's the
>show-stopper?

The weight of the support string puts an upper limit on
the lifting capability, and you're vulnerable to sheer
winds. Clustering the balloons helps a LOT, but it's
still heavier and more vulnerable to winds than a single
balloon. Also, maintaining the gas for multiple gas bags
is more complex and expensive than for a single gas bag.
Really, the factors in favor of a single large gas bag
over multiple ones are overwhelming. Even if you have
no choice but to use multiple gas bags, you want to at
least enclose them within a more aerodynamic outer shell.

Here on Earth, balloons may potentially have an advantage over
satellites because of the far lower launch cost. Even so, the
advantages of satellites cause them to still be dominant for
long term missions. For a Venus mission, balloons would not
have a lower launch cost--in fact, the costs would be higher
since much/most of the mass inserted into Venus orbit would
be for the balloon rather than the operating equipment.
(I assume that there's essentially no cost to going from
Venus orbit into Venus's atmosphere; the reentry heatshield
could be reused for other purposes.)

We have had good success with repeated aerobraking maneuvers.
We have had expensive failures with gigantic balloons.
We have difficulty with repeated use of high velocity
electromagnetic mass launchers, and even those can't
reach orbital velocities.

The showstopper, as I see it, is that even if you are
confident of developing an orbital velocity mass launcher,
it's going to be big and heavy. That implies a stupendous
balloon and support structure--far larger than anything
we've succeeded with even here on Earth. Even if we can
hammer out the problems with (expensive) research balloons
here on Earth, Venus's atmosphere is different and not
understood well enough to reasonably predict balloon
performance. We have some data about what it's like to
barrel through the atmosphere at high speed with a HTA
craft. That's just not good enough to figure out what
it's like for a LTA craft buffeted by gusts and wind
sheer.

Like I said, we don't even know whether there's lightning
on Venus and we suspect that there's lightning on Venus
but it may be different from the sort we're used to seeing.
We simply have no idea where best to go to avoid lightning
risk. The upper atmosphere where an orbital airscoop would
dip into should be safe, and even if it isn't the metal
body of the satellite could protect it. But a balloon
with such a heavy payload needs relatively thick air to
operate in.

Also, there's the question of what you fill the balloons
with. If you use hydrogen or helium brought from Earth,
then you have a limited supply before it's gone forever.
If you use locally available oxygen, then your balloon is
not going to have very strong lift.

>Besides which, if you've only got near-term doable
>technology, what are you needing literally astronomical
>quantities of carbon dioxide for? We don't have the
>capacity for a space industry that can use that
>much stuff yet.

Maybe a global warming sunshield; that's the only near
term application I can think of which requires huge
quantities.

For a less radical near term goal, I was thinking of
building space station hulls and rocket hulls out of
the stuff. These could ship themselves to Earth orbit.
Why do this from Venus instead of Earth? Not much
carbon dioxide in Earth's atmosphere. An Earth airscoop
could supply other niceties, like water, hydrogen
propellant, and nitrogen. For a thriving growing
space colony, you need carbon also.

Once you get some Earth orbital colonies going, and
work out the kinks, you can ship stuff from Earth
airscoops to Venus orbit for Venus orbital colonies.
You might want to do this for the extra solar power, and
because it's easier to ship stuff from Earth to Venus
than the other way around. Shipping from Venus to
Earth depends upon inefficient carbon/oxygen fuel.
Shipping from Earth to Venus could use more efficient
hydrogen/oxygen fuel.

>>>Alternately, if your heart is set on using a spacecraft
>>>of some sort, how about a rotating tether?

>>This seems to me a better concept than atmospheric mass drivers.
>>Still, space tether technology is even less mature than big balloon
>>and mass driver technology.

>You're sending mixed messages here. :)

My message is simply that while I agree that it's a
better concept, it also depends upon immature technology.

Isaac Kuo

.

Relevant Pages

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