From: henry@spsystems.net
In article ,
Josh Gigantino wrote:
>...use ballutes for deorbit...
Doing deorbit with a drag device has serious problems.
For one thing, if you started from a reasonably long-lived orbit, the drag
device has to be huge to suddenly turn it into a very short-lived orbit.
(And if you used maneuvering rockets to take you into a low orbit first,
why not just do the whole job with the rockets?)
For another, it's very imprecise, especially since the density of Earth's
outer atmosphere is quite variable and not very predictable. Unless
you're willing to deflate and re-inflate it repeatedly for control, you
could come down almost anywhere with latitude<=inclination. That means,
by the way, a high probability of coming down in open ocean.
For a third, if it's an inflatable drag device, what if it gets punctured?
You're going to need maneuvering rockets for rendezvous operations anyway.
You might as well use them for retrofire too.
Using a drag device for *reentry* -- to increase drag and do your
decelerating higher up, in thinner air -- is a different story. But
ordinary ballutes in particular suffer from being pure drag devices, with
no lift. This gives a purely ballistic reentry, and quite high G-loads,
7-8G, like Mercury. A shaped drag device that can supply some lift is
better, permitting a Gemini/Apollo-style lifting reentry at 3G or so.
>They would have an exterior shell of carbon fiber or Al...
You're going to need some sort of outer thermal protection with either of
those materials. The trailing part of the body (trailing during reentry,
that is) doesn't get nearly as much heat as the leading part, but it does
get some. And neither carbon composite nor aluminum is very tolerant
of heat.
>The base of the craft would be a micro-printed structure (think
>inkjet/3d printer) on a titanium outer shield. The ceramic prints have
>thousands of microchannels twisting through it, above that is several
>sandwiches of material forming a fuel cell. During deorbit, water from
>the fuel cell is forced through the microchannels, forming a
>transparational-cooled vapor barrier - aided by the ballute.
I don't see the point of trying to integrate the fuel cell. Reentry is
not generally a time of particularly high power demand, but it does
require quite a bit of cooling, if you're using active cooling. Stored
water is preferable. (Whether it ultimately comes from fuel cells is a
separate question... but solar arrays are normally preferred nowadays.
And remember that you have to be able to make an emergency reentry
immediately after, or even during, ascent.)
>The capsules are generally recovered from freshwater ponds, would use
>a paraglider and GPS for accuracy.
This works, although some would argue that the pond is unnecessary -- if
you have glide capability already, you can do a flare maneuver to touch
down on a hard surface with essentially zero descent rate.
Note, though, that another problem with ballistic reentries is that they
are inaccurate. Coming down within glide range of your pond is likely
to require a lifting reentry, because it's more controllable.
>The main issues I'd like to discuss are: materials esp CF vs Al,
>docking adapters, the "printed" heat shield. What would be the ideal
>material to build a new capsule from?
Depends a little on your priorities. Aluminum is easier to work with and
hence cheaper. Carbon composites are generally lighter. If cost was not
a priority, or ample up-front investment was available to reduce overhead
mass, you'd probably go with carbon composites for almost all "cold"
structure.
>Is a larger diameter APAS useful and appropriate?
If you do *not* have historical constraints, what you probably want to do
is forget about docking (in the strict sense of the word) and use
berthing. That is, instead of banging into the station :-) hard enough to
trip latches in the docking mechanism, you *stop* just clear of it, and an
arm reaches out and grabs you and positions you on the berthing adapter,
with the latches triggered electronically when the position is just right.
This is gentler and simpler, puts less stress on the station, and makes it
easier to accommodate a large pressurized passageway.
Berthing is how the non-Russian parts of ISS (including the logistics
modules that the shuttle takes up and down) are joined together, and in
the pre-Russian days, there was to be no docking at all on the station --
even the shuttle would berth instead. The CBM adapter is lighter than
APAS, and will pass an ISS experiment rack, which APAS won't.
>...Is a 6m hammerhead fairing
>on Proton launching from Texas [too] ridiculous to read about?
6m is quite a sizable hammerhead, but not ridiculous.
Proton launching from the US is not an impossible strain, Sea Launch
having paved the way there... although there will be difficulties with
environmental review, especially for a large rocket with toxic fuels.
(Probably the single hardest part of the FAA launch-licensing process is
environmental approval. Aviation has categorical exemptions from most of
it; rocketry does not.)
A big expendable rocket had better be launching from the Texas *coast*.
And that's going to severely limit launch directions, since it is probably
unacceptable to overfly Florida or the Gulf Coast, and overflying Cuba or
Mexico is iffy.
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since Oct; first surprises seen; papers pending. | henry@spsystems.net
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