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Comments on LLW draft on "Advanced Space Transportation"

Question for Jerry:  To what extent is it important to reduce the amount
of technical knowledge and familiarity with space technology required
to understand the proposals?

1. I think a paragraph should be devoted to the importance of specific
impulse by giving its relation to mass ratio.  This will make clear its
relation to costs.

2. We should soft-pedal the tower till the paper is published.  We can
mention it, but perhaps make a soft-pedalling comment, such as that
the idea is new and hasn't received critical comment yet.

3. We should somehow mention that the political problems of NERVA are
less than those of ORION, since ORION was scuttled for frankly political
reasons and its revival will be opposed by the science establishment,
while NERVA is nominally ok with them.

4. We should mention that fusion torch propulsion is a follow-on to
laser fusion for energy.

5. The value of separating the problem of transporting materials to
orbit by a cheaper system than is used for transporting people should
be made explicit.

6. Question: Can we afford to recommend pursuing the development of
alternative space technologies in parallel possibly with the help
of allies?

	If you agree with some of these proposed changes and you want
me to, I can prepare some paragraphs.  Some prose follows:

	The cost of getting material into orbit by rocket depends
critically on the specific impulse of the rockets.  Present specific
impulses (450 seconds for the Shuttle engines which are almost the
best possible for chemically fueled rockets) require that
the mass leaving the Earth be at least 20 times that which reaches
low earth orbit.  For various reasons, the mass ratio of the Shuttle
is actually about 100.  The NERVA rocket would permit a mass ratio
of xxx, and the ORION a mass ratio of xxx.  The numbers for longer
journeys are even more spectacular.  The Apollo system takeoff mass
was 1000 times the mass delivered to te moon, whereas the mass ratio
for a NERVA system would be xxx and an ORION system xxx.

	The large mass-ratios are the main reason for the high cost
of space transportation.  The only way to reduce these costs is
to use high specific impulse rockets or to avoid rockets as much
as possible.

	Until we can use resources from the moon or the asteroids,
space travel is a pyramid with its base the step from the Earth
to low earth orbit.  Even when these resources become available,
moving people and material to Earth orbit will still be a major
cost.  Therefore, it makes sense to consider every possible way
of reducing the costs of transportation to low earth orbit.

	While people and delicate equipment must be transported
into Earth orbit, the bulk of what has to be transported is material,
and the single most important material is rocket fuel.  What material
is used for rocket fuel depends on the kind of rocket, but all
materials can stand much higher accelerations than people can.
This is fortunate, because many of the possible systems for economical
transportation involve high accelerations.  Thus we may envisage
using rockets to transport people and delicate equipment and
other systems for bulk material and less delicate equipment.

	Many ideas for inexpensive space transportation are old
and have been laid aside by NASA's concentration on the project
of the moment.  However, in spite of the lack of encouragement,
the last few years have seen the proposal of several promising
new ideas.

	Many of the ideas mentioned above are in mutual competition,
and it will eventually be necessary to make choices.  Also they are
available on different time scales.  Nevertheless, it is prudent
to develop several technologies in parallel to be sure of having
the best choice available in the end.  Perhaps the best way to
do this is to enlist our allies and divide the work of pursuing
promising possibilities.  Today both the Europeans and the Japanese
have the technology to develop major systems.