Maraging Steel Thinsat Substrates

The current thinsat design presumes a pure aluminum substrate. However, maraging steel (68% iron, 18% nickel, 8% cobalt, 5% molybdenum, other elements) offers interesting advantages. We can probably get by with nonpurified asteroid/meteorite nickel-iron, stiffness is important, structural strength is not.

• Matweb.com Iron properties Added later - ordinary iron may be more usable!

• Matweb.com AISI Grade 18Ni (250) Maraging Steel, nominal annealed properties

The main advantages are launch stack density, thermal expansion, belt particle scattering, and magnetic properties. The main disadvantages are lower lateral thermal conduction and thin shell bending stiffness - the resistivity is higher, but not that important.

Thinsats will already "launch densely". Thinsats will be in multiple stacks, probably attached to the circumverence of the load bearing ring at the edge of the upper stage. India's PSLV has a 2.8 meter diameter second stage, 8.8 meters, so we can easily fit 50 stacks of thinsats onto an adapter around that ring. 15 meters of aluminum thinsats means 30 centimeter (1 foot high) stacks, 5 meters of thinsats means 10 centimeter stacks. A SpaceX Falcon 9 is 3.7 meters and 4 times the payload to LEO, 3x taller stacks.

Lateral thermal conduction helps cool chips, though they will be small and scattered and do not need to radiate over large areas.

Lower bending stiffness (2) makes area ripples in the curving surface slower and higher amplitude. However, slower is more easily corrected with the optical thrusters, and compensated by phasing of the emitters. Bending stiffness (1) is multiplied by thinsat shape factors, the same for both aluminum and maraging steel.

If the thinsats are magnetized on their north-south axis, then the earth's magnetic field will keep them aligned rotationally. Also, it will help the thinsats separate out of the launch stack. However, if a thinsat rotates 180 degrees in relation to a near neighbor, they may stick together inseparably. Shape tweaks to make them rotationally assymetric can reduce this effect.

Rutherford scattering is enhanced by higher nuclear weight and charge. Belt remediation will be faster, with less lattice displacement damage. Calculations should be scalable.

The mix of iron and nickel resembles meteoritic iron, however, meteoritic iron contains perhaps 5% of the cobalt. Still, far in the future, when space manufacturing becomes practical, meteoritic iron from asteroids or Late Heavy Bombardment impact sites on the moon might be suitable for thinsat substrates. Note that impact sites on the moon will be 60 MJ/kg less energetic than earth impact sites (like the Sudbury, Canada, nickel mining region), and they will not be weathered or oxidized. That does not make up for the current lack of infrastructure and capability and knowhow, but it might in half a century of server sky exponential expansion.

This requires more study.