Re: LA-4541-MS

How does one land and take off with a large nuclear pulse rocket?

One approach would be to use a conventional rocket stage to lift the
spacecraft to an appropriate altitude, and detonate the first nuclear
pulse. This requires building chemical rockets, or jets, or nuclear
thermal rockets, of unprecedented size.

Another approach is to develop a launching/landing structure that
allows the use of pulse units close to the ground. One of the major
problems of pulse unit rockets near a planetary surface is that the
pulse gets reflected by the surface, causing a secondary pressure
pulse. A surface that absorbs, disappates, or channels the reflected
pulse would allow a landing.

While it may seem difficult to arrange for a landing that lets a
vehicle fall 300 m or more without thrust, it should be remembered
that the momentum conditioning surface is built for precisely this
type of operation - to absorb this level of momentum change. Even so,
timing is a critical issue. Also, there is no need to have every
pulse unit exactly the same size. There is clearly an optimal change
in timing and size as one approaches a landing - so the momentum
absorber is spared during the final pulse, with the final pulse being
far smaller than the typical pulse.

A pusher plate attached to a payload through a large spring should be
able to execute a powered landing ON the pusher plate with an
appropriate series of pulse units, timed so that the plate makes
contact in the fully extended position, and the pulse of the plate
hitting the ground cancels all motion. Upon take off, 'stand-off'
legs lift the entire vehicle to an appropriate height for the smallest
charge, and the charges are detonated in the reverse order as the
vehicle gains altitude. Chemical rockets are used to provide small
corrective thrusts to fine tune the landing.

In built up areas one can imagine structures forming a 'spaceport'
These consist of slightly tapered conical wells larger than the
vehicle at the opening, narrowing down to nearly the pusher plate
diameter. The wells evacuate to a flame bucket type arrangement.
The wells are deep enough so that when contact it made at the base,
the payload is level with the ground surface. Upon take off, the
vehicle is lifted to the stand off distance of the smallest unit, and
the vehicle departs in a manner reverse of the landing. Here, the
built up area is not harmed by vehicle operation - as would happen in
an un-prepared field.

Modular payload units equipped with self-propelled tracks,can be used
to operate the vehicles some distance from unprepared fields. The
modules, which may take days or weeks to load and unload, can in this
way be prepared at a facility some distance away from the landing and
take off points, and the propulsive units can be kept in more or less
constant use. For example, 8 vehicles operating on 40 day flight
cycles each way between Mars and Earth - would provide an arrival
every 10 days. A vehicle would land, and a self propelled payload bay
some 1.95 million tons, would motor to a service point a few
kilometers removed from the touchdown point. Meanwhile a preveiously
prepared payload module is ready for its return to Earth - it motors
back to the propulsion unit.. The newly arrived payload unit is
unloaded and stocked with materials to return to Earth, by the time
the next unit arrives in 10 days. Meanwhile, the second payload unit
motors up to the propulsion unit, docks in place, inserts its pulse
units, and takes off when the field is clear. In this way 54 million
tons may be shipped to Mars from Earth, and 54 million tons may be
shipped form Earth to Mars.

Without water, present technology requires 1 ton of material to
support one person per year. With water,and power, present technology
requires 200 lbs of material to support one person per year. Mars has
free water, so 8 ships of the type just described, operating every 80
days round trip between Earth and Mars, could support 540 milion
people on Mars. Since a colony would likely be self-sufficient well
before this number is reached,its easy to see that the development of
this vehicle class opens the solar system to human industry
development and habitation.

To maintain people at a reasonably high standard of living requires
power and about 4 tons of material per year per person. This means
that if half the materials come from Earth, the eight vehicles could
sustain 27 million people on Mars, and allow the importation of 54
million tons of goods and materials from Mars.

If the $2,600 per ton of vehicle structure can be maintained - and
this is 4 times larger than typical freighter tanker construction -
but 1/500th the cost of typcal aerospace construction - the cost of
lithium-deuteride and its energy content is such that the cost of $10
per ton shipped across the solar system in 40 days - is easily
achieved.
.

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