Recycling the ET

Since the approval of a derived shuttle heavy lifter is a done deal, let's continue the study of using the external tank beyond its initial role of holding fuel for liftoff.  I did some looking into this possibility many posts ago.  It turns out that there was a NASA generated pdf for anyone interested enough to see what studies have already been done on this idea.  I downloaded it and am now in the process of reading it.  I think the point here is that the idea of doing this is not at all far fetched.  It has been considered.  Evidently, somebody in policy making circles decided not to pursue this avenue when this was produced in the early eighties.  But since the external tank is still going to be available for this as a possible use, perhaps these ideas should be revisited.

In the actual shuttle configuration that this pdf studied, there was significant amount of fuel left at Main Engine Cutoff (MECO).  There were ideas on what to do with this of course.  One conclusion is that the external tank could be put into Earth orbit indefinitely.  As for what could be done with it while it is up there, several options were considered.  Here are a few ideas in line with what I have written about before:

a) use of ET for tethering techniques
b) use of ET mass as shielding
c) use of the ET as a "strong-back" to support a space station concept

The report points out that the ET will have to be modified somewhat to made more useful in space.  These modifications are to be kept to a minimum.  Among these modifications are:

1. an attitude control system
2. access ports to the interior of the tanks in the ET must be made accessible
3. handling attachments to facilitate movement and various connections for devices
4. a way of altering the geometry of the ET  (proposed study)
5. better tools, equipment, facilities to exploit the potential of the ET


Update:

Here are some applications of tethers to enhance space station (ET) capabilities
1. De-orbiting the ET and booster the orbiter ( with shuttle this is obsolete)
2. Lowering orbiter and boosting ET or payloads  ( also obsolete )
3. Controlling ET drag and prolonging orbital life ( now this is interesting, can quadruple ET orbit life)
4. Adjusting reentry zone of a decaying ET  ( safety measure )
5. Lowering orbiter, raising space station and payloads, and generating power (power?)
6. Rendezvous with satellites and debris collection ( question: could these be launched, then captured?)
7. Orbiter rendezvous with space station ( same question as in 6)
8. Applications with advance materials tethers ( since this report is 30 years old, this is relevant)

In the last application (#8), much longer tethers may be possible with materials available today.
here is a list of applications using longer tethers
a)  apparent gravity of .1 g or more for personnel throughout a mission
b) single state to tether vehicles ( answer to #6, 7)
c) reentry velocities low enough for hot-structure reentry vehicles ( huh?)
d) release of payloads from LEO into GEO transfer orbits without rockets ( a great deal if possible)
e) tether base transportation between lunar surface, orbit, and escape ( ditto)

Update: of course, the above is not all that can be done with the ET.  Significant amount of use can be made of the materials and structures that make up the ET itself.  Here is a schematic of a solar furnace that uses that liquid hydrogen tank of the ET.

The amount of heat that this furnace could generate could melt all the aluminum in the tank.  The aluminum could then be reused for other purposes, even rocket fuel!

Update:
Very interesting quote from p. 107
       "...They can provide the means by which we learn to develop growing manufacturing capability off-Earth in the immediate future and do so economically.  The ET's can be an inexpensive, readily available resource base (350-1100 tons/yr) for use in Earth orbit rather than being wasted."

Keep in mind when reading the above quote that this was written nearly thirty years ago.  If it was true then, it is even more true today.

Update:
The thought occurred to me that, before in situ resources recovery from the moon or asteroids is even considered, this plan should be executed first.  The reason that the external tanks themselves are an excellent site for in situ resource extraction.  It would be a great place to try out the techniques.  A good knowledge base could be built on this alone, not to mention the other uses for which external tanks could be used.

In addition to the above updates and comments by me, there was even more to this report that is of interest that I haven't even gotten to yet.  For example, an external tank would be a good place for space habitat, or in one recommendation, it could be used as refuge in case of a disaster in space.