(Session Tues 2 July 1991), Missions to NEA's and Utilization, International Conference on Near-Earth
Asteroids, , San Juan Capistrano Research Institute, San Juan Capistrano, California, USA

Zuppero, Anthony C & Michael G. Jacox(28 August thru 5 sept, 1992) "Nerar Earth Object Fuels (neo-fuels):
Discovery, Prospecting and Use," 43rd Congress of the International Astronautical Federation, Washington DC,
paper # IAA-92-0159

APPENDIX 1
"Slow Orbit Decay of Ice Packetsin Heat Shield containers"

This short analysis suggests that ice objects in the mass range of 100 to 2000 tons can withstand the compressive
stresses associated with significant orbital decay processes. The breakup acceleration for objects entering the
atmosphere even to as low as 60 km and with velocities associated with HEEO orbits of 120 earth radii (Re) apogee,
do not break up. There appears to be two orders of magnitude margin between the forces and the compressive and
shear strength of ice.

TABLE A-1 shows this. It shows the acceleration required to breakup ice with 100 psi (70 KPa) compressive
strength, and it shows the decelerations produced by skimming the atmosphere for a range of altitudes from 60 km
thru 100 km. If breakup does occur, a 2000 ton payload becomes a cloud. A typical 1% humidity cloud of one cubic
mile diameter contains ~50,000 tons of water.

The orbital decay can be completed within one year so long as the vehicle descends to less than 90 km in the
atmosphere. Table A-2 shows this. It shows the apgee height, measured in Earth Radii, after 1 year for various
skimming altitudes. The question of heat shield cooling has not been addressed. The availability of active cooling
material should make this easy to accomplish.

TABLE A-1. Decellerations, measured in "milli G's," for payloads of mass ranging from 1 to 2000 tons and
penetrating into the atmosphere at depths ranging from 60 to 100 km. One "G" is 9.8 m/s/s, the acceleration of
gravity at Earth surface. Note that all are much less than the breakupacceleration. But breakup is guaranteed if the
payload descends to aircraft altitudes. Then the payload becomes a small cloud and may emit as much noise as a
very loud thunder.

TABLE A-2. Apogee after one year for the same objects as in TABLE A-1. An apogee of less than 1.5
Earth Radii is desired. Note that after 1 year even the heavy payload descends to a low earth orbit.