ESA Document - Emits - ESA

s
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 227 of 422
The multi-shock shield was chosen because a Nextel/Kevlar shield provides better protection
than double-aluminium bumper shields of equal weight by stopping 50% to 300% more passive
projectiles, [RD56]. The objective of the bumpers is to break up debris on impact and distribute
the particle energy and momentum over a large area. Due to the reduction in particle size and
velocity, the resulting debris cloud does not penetrate the monolithic pressure wall behind them.
Nextel improves shield performance, compared to aluminium because it is better at shocking
projectile fragments, while Kevlar improves shield performance because it is better at slowing
debris expansion, having a greater strength to weight ratio than aluminium. When using a
Nextel/Kevlar intermediate shield, the particle size of bumper materials within the debris cloud
is smaller than for aluminium intermediate shields. Figure 3-69 shows the differences between
the debris cloud resultant from the impact of a particle in an aluminium bumper and a Nextel
bumper.
Figure 3-69: Debris cloud contact between aluminium and Nextel MOD, [RD56].
The Nextel Meteorite and Orbital Debris shield (MOD) selected consists of two walls. The front
wall consists of three Nextel AF-10 bumpers, each one separated by a 10 cm standoff of lowweight
open-cell foam, which serves as the support material. The rear wall consists of five layers
of Kevlar fabric and provides final barrier to high penetration. This shield offers the advantage of
being initially transported compressed to a thickness of 5 cm. Once in place, outside the
settlement, the foam inside the shield is inflated to its full thickness of 30 cm. For this mission
due to the thermal protection, it is decided to launch it at its maximum thickness. This
configuration is capable of resisting impacts of incidents objects with a diameter of 6.35 mm and
a velocity of 6.82 km/s.
Figure 3-70 – MOD Shielding Configuration