GRENDEHL

GRENDEHL – works by mechanical acceleration of payloads irrespective of mass
Physics / engineering well understood
Stealth signatures – no EMP, no propellant gas blast, limited to supersonic shocks –
weak N-waves & high-speed machinery acoustics
Low angular dispersion of launched projectiles
No excessive barrel heating due to hot propellant gases or Ohmic heating
Efficiency ∼50%, and better (half of energy or more goes into projectile)
Pulse power demands relaxed by length of acceleration distances
High launch rates – proportional to gyration frequencies (typically 30 – 90 gps, limited only by prime power)
Safe – no explosives or propellants, no high currents/voltages involved in acceleration process
Scalable from validated designs to high payload masses / velocities
No special materials required in manufacturing
Potential utility for routine delivery of matériel, fuels, structural materials to Low Earth Orbit (LEO)
and above with Earth surface launches (“Space Train”)
Routine mining ore transfer to Earth from moon-based accelerator using free-return orbits (“Moon Train”)
Asteroid deflection using Moon facility to launch multi-ton impactors at tens of kilometers per second
Routine supply train to Mars (“Mars Train”)

Swing arm – length L, density ρ, Young’s Modulus Y, yield stress σ_y
Root radius (swing arm axle attachment): y(L)
Root must be thick enough to support g-loaded (n_g) projectile and swing arm
Support must be provided throughout acceleration process → static yield stress governs structural integrity

Plot of swing-arm mass (yellow) and swing-arm length (green – for selected g-loadings) as functions of launch velocity
Assigned projectile mass: 100 kg. Results scalable to other payload masses
Material stress everywhere in swing arm set to yield stress (no safety margin) (σ_y = 240 MPa for titanium)
Note: extreme swing-arm mass requirements for launch speeds greater than about 1km/s rule out centrifuge launchers for suborbital and above applications

Abandons swing-arm design
Provides projectile inertial acceleration field by means of gyrating – not rotating raceway
Projectile rides on gas bearing to achieve extreme efficiencies
Projectile reaching launch velocity resides at any point of raceway for only extremely short times
→ dynamic stress hardening ensures raceway viability
Experimental results and rigorous modeling indicate improving gas bearing efficiency with increasing projectile mass and launch velocity
→ projectiles from tens of kilograms to tens of metric tons and launch speeds in tens of kilometers per second are feasible

Swirling the liquid and ice contents in a tumbler by moving it in a circle without rotation – fixed orientation (tumbler doesn’t slip in the hand).

Outer radius = 19.1 m
Gyration radius = 1.59 m
Number of turns = 5
Gyration rate = 30 gps
Gyration period = 33 ms
Gyration velocity = 300 m/s
V_launch = 3.6 km/s
Time to launch (launch period) = 165 ms
Note: both the gyration rate & g-loading can be decreased by scaling up the outer & gyration radii while holding V_launch & v_gyration fixed