Digest Number 531

>
>Message: 3
> Date: Sun, 01 Sep 2002 12:44:23 -0000
> From: "spider_boris"
>Subject: Re: Asteroid Belt First
>
[Carl Mullen message, which Boris replied to snipped]

>
>Hi Carl
>
>I was thinking that any robots capable of such surveying, assaying
>and doing microgravity mining would be capable of many more
>missions. The robots I have in mind (and for which I am currently
>developing the control systems) are serpentine robots, with grippers
>at each end that would allow each robot to use a range of tools.
>Robots could also connect end-to-end to form longer robots.
>
>This type of robot could operate in semiautonomous teleoperated mode
>(to be used as remote manipulator arms for delicate tasks), in
>independent autonomous mode (ruled by "instinct" as exploratory
>rovers on planetary surfaces) and in cooperative mode (several robots
>working together through radio communication to perform larger tasks,
>some teleoperated, some autonomous). Such robots could operate on
>planetary surfaces such as the moon or mars through various
>locomotive techniques, in microgravity or zero-gee by climbing along
>trusses like snakes in trees, or even swimming for use in deep-sea
>missions.
>
>The first task that I want these robots to perform is orbital salvage
>of space shuttle external tanks. They would be mounted along with
>their tools and equipment in the ring frame assembly inside the ET
>intertank, and would go into action after the ET was released from
>the shuttle. With the shuttle carrying the ET for just a few seconds
>more, the tank could be salvaged by the robots while still in orbit.
>
It sounds like you have some pretty ambitious plans for your robots;
I hope your current prototypes holds up well - space is notoriously hard
on moving parts. The only serpentine robot I have had the pleasure to
see (in my admittedly limited experience) was in a US TV program -
"Battlebots". Its performance did not inspire confidence; but this is a
young technology - and I hope to see it develop well. My own musings
have centered on some pretty young (and unproven) technologies as well,
but I have limited my robots to simpler approaches.

>
>(( NASA is required by law (signed by President Reagan in one of his
>more lucid moments) to give away for free these external tanks if the
>following conditions are met: 1) either cover or remove safely the
>spray-on foam insulation; my robots would unroll a Mylar sheet (or
>inflate it with helium if it is equipped with "veins")
>
Like you, I had envisioned a robotic "Salvage Module" between
the liquid fuel tanks on a kind of standardized "Inter-Tank Pallet"
(ITP), but weight and the complex demands placed on the system have made
me wonder recently if the solution might not involve a separate launch
(on something cheap - a non-human rated, possibly old Soviet booster or
something) but that introduces all sorts of docking intricacies (again,
something that old Soviet technology has conquered in the form of the
'Progress' resupply ships) that I am unsure how to handle.
Going with just the ITP for now, your idea of aluminized Mylar
seems like a great idea, and I also like the 'inflatable veins'
approach, but why helium? Heck, you have a whole tank (or at least the
dregs of a whole tank) of liquid H2 and a separate tank of O2. Adding
another whole tank - especially of something as exotic as helium seems
odd. Why not go with CO2 (can be had cheaply) or Nitrogen (I have an
ulterior motive for suggesting N2)?
Also, the 'inflatable veins' idea seems far superior to
'unrolling' the Mylar - far fewer moving parts. And as long as we are
on the subject, why have your ITP robots go outside at all? It seems
like you could attack the various modules to go outside onto the Mylar,
and have valves in the veins control how they unfurl; since the Mylar
will be tailored to cover the tank anything attached to it will end up
in a pre-defined place on the outside of the tank. Run control and
power circuits along sleeves in the Mylar and you can have these "Mylar
Deployed Modules" (MDMs) attach themselves to the outside of the tank -
this will hold your Mylar in place once the gas leaks out of the veins
(inevitable - just a matter of time) - and heck, each MDM could be at
the intersection of two veins, and control the valves which run the
inflation.

> 2)
>circularize the orbit; my robots would attach small engines to the
>tank and drain the fuel and LOX necessary from the remnants left in
>the 4 inch and 17 inch lines)
>
I really hate to use up and throw away this resource, to which
end I have been playing with the notion of "Electro Dynamic Tethers"
(EDTs). Not my idea, but the concept is simple enough - a conductive
cable / wire / tether / whatever passing through the Earths magnetic
field generates a current in exactly the same way a conventional
generator produces current. If, instead of collecting this current
(consuming this energy), you instead expend energy in the form of a
current passed through the cable then you will be using the Earths own
magnetic field as the armature in an electric motor. The current you
expend produces a tiny amount of thrust.
Needless to say, the thrust is small and must be provided over
the long term, and the energy to run the EDTs has to come from
somewhere. Where? From the fuel cell on your ITP - you already have
plenty of pure H2 and O2 on hand, and electrolyzing H2O back down into
its constituent parts is well understood. Once the Mylar and MDMs (I
envision at least eight EDTs arranged on the points of two interlocking
tetrahedrons) are deployed, the next thing to go through the service
hatch would be a solar collector (possibly with your communication array
on the tip). The fuel cell would exhaust the available fuel turning it
into water (stored in a small tank on the ITP) whenever the EDTs are
needed to boost the ET to a higher orbit, and the solar collector would
either augment the fuel cells output (when thrust is urgently needed) or
run an electrolysis unit which separates the water and pumps the
resulting gases back into the appropriate tanks.

> 3) control the temperature of the
>residual propellants; the Mylar (being reflective) will do much of
>this, and heat dissapators will do the rest... temperature
>differences from one end of each tank to the other end will drive
>propellant through the lines to the engines, so most of it will be
>used up
>
Alright, I hadn't really thought about this; and with the fuel
cell producing prodigous amounts of heat it is something which has to be
addressed. My first impulse is to have a black parabolic IR emitter on
the 'back' side of the solar array... probably no good, but maybe
someone else will jump in with a few interesting comments. I also
hadn't thought of how to get the fuel to flow, in my naivete I had
assumed that being under pressure in the tanks would be enough - but
perhaps fuel heaters and pumps will be needed. Heck, that's extra
weight - and a few more moving parts that have to function routinely.

> 4) establish power, communications, and maneuvering for the
>ET, in short making it a controllable sattelite; my robots will erect
>solar panels and communications antennae for this purpose.
>
I certainly understand the need to control the salvaged ETs; and
I believe that what I have suggested satisfies most of these
requirements... though I cannot deny that having a reliable, versatile,
autonomous, and mobile general purpose robot would be a plus, I don't
really think one is absolutely necessary.

>
>All of the Mylar, engines, helium tank, heat dissapators, and so on
>would be stored in the intertank ring frame along with the
>snakebots. Once four or five external tanks are salvaged, they may
>rendezvous to form a cluster, each with its own set of salvage
>equipment.
>
Always a great idea - maybe I should throw in an MDM or two for
docking up several tanks once they are close to each other - but I do
have some reservations about the precision of control acheivable with
EDTs - on the up side, they can be such low thrust srives as to render
any docking accident a very low energy event. And eventually of course
(and this is where the nitrogen comes in handy) you will want to pump
all of the fuel into just one ET, and use the (now empty) tanks in the
others for habitation (you mix the nitrogen with the O2, and maybe a
little water) and/or industry.

> These would dismantle the system for parts no longer
>needed (such as the helium tanks and most of the engines, solar
>panels, and communications arrays) to create orbital maneuvering
>vehicles. These would be entirely recycled from the orbital salvage
>system, their tanks filled with residual fuel and oxygen; they may
>even convert some of the Mylar sheets into solar sails. They would
>be used for further salvage operations such as retrieving expended
>Apollo and Soyuz stages, some of which have been orbiting for thirty
>years. These stages would be brought back to the ET cluster and
>drained of residual propellants. Other OMVs could be used for the
>asteroid-hopping missions described above.
>
This is further than I had previously thought as well; but Iam
unsure whether it is wise to try salvaging the fuels from discarded
Apollo and Soyuz stages - I certainly would not build a business model
around doing so. First, anything left in space with volatiles on board
might well be empty by now; second, a lot of those old fuels wern't the
friendliest of substances when they were fresh and age may have rendered
them (especially the monopropellants) extremely unstable; and third, the
fuels may (someone help me out here) be radically different from each
other. If memory serves, the Saturn V used kerosene and a non-O2
oxidizer, the lunar lander was fueled by Hydrazine, and I have no idea
what the Soviets used (or if they even used a particular fuel mixture
consistently). On the other hand, such fuel remnants (if they still
exist) do represent a ready source of much needed volatiles.

>
>The system I have described will make extensive use of recycling,
>using one tool for many different purposes, particularly the
>snakebots. It only makes sense to use as much as possible the stuff
>that has already been loaunched, for as many different tasks as
>possible.
>
>:) ed
>
It seems as though everyone has a different vision for
exploiting space; and each brings a fresh approach and potentially
valuable ideas and concepts with them. I hope what I have said might
spark off a few insights and inspirations, and I wish you luck in your
robotic endeavor. Anybody else care to throw their two cents in on this?

Joe.