1) A ground penetrator that uses a spacecraft's momentum for a hard landing could eliminate the need to slow down or stop the spacecraft, reducing fuel needs. Material would flow through the penetrator during impact and the sample return container would be returned to the surface via a high strength tether. 2) Testing showed that honeycombed aluminum provides protection for the sample return container during impact, and its strength can be increased through additives like Kevlar. However, pressure decreases rapidly during penetration, limiting sample yield to a few grams instead of the desired kilograms. 3) Equipping a spacecraft with multiple penetrators could enable collecting samples from more locations on a single body or different objects

1. Sample Return Systems for Extreme Environments
R. M. Winglee1, C. Truitt1, and R. Hoyt2
1Department of Earth and Space Sciences, University of Washington; 2Tethers Unlimited
Minimizing Delta V
Surviving the Impact
0
50000
100000
150000
200000
250000
0 2 4 6 8 10 12 14
CompressionForce(kN)
Distance Compressed (mm)
Compression Testing: Initial Sample Size 70 X 70 X 16 mm
Hexcel (20 gm)
Hexcel + Foam Epoxy
(34gm)
with Kevlar 1.0 in spacing
(45 gm)
with Kevlar 0.5 in spacing
(50 gm)
with Kelvar 0.25 in
spacing (65 gm)
NIAC Phase ISample Return
Sample return missions provide detailed information about the
evolution of our solar system, but current approaches make them an
expensive affair. The present soft landing method requires that fuel
takes up a significant amount of mass of the spacecraft due to large
changes in the spacecraft’s velocity. By reducing the spacecraft’s
Delta V, sample return missions become more affordable and offer
the potential to collect kilograms of material from multiple targets
instead of grams from a single location.
Sample Return
Container
Crumple Zone
Penetrating
Nose Cone
Multiple Samples
NIAC Phase II
Sample Return Penetrator (Gravedigger)
Flow Stagnation
Increasing Sample Yield
Acknowledgments
A ground penetrator can use a spacecraft’s
momentum for a hard landing, eliminating
the need to slow or stop the spacecraft.
Material flows through the penetrator
during impact, and the sample return
container is returned from the surface via a
high strength tether.
Honeycombed aluminum provides protection for the
sample return container during impact. The
honeycomb’s strength can be dramatically increased
through the use of various additives.
Equipping a spacecraft with multiple penetrators opens the
possibility of either collecting samples from more than one location
on a single body, or collecting samples from a number of different
objects.
Multiple penetrators
with independent
tethers envisioned on
a concept spacecraft.
Phase I field testing was conducted in March 2013, in the Black Rock desert in Nevada.
The two impacts created very different impact shafts: the subsonic impact produced well
defined slickensides (1d); the supersonic impact shaft walls experienced an oscillating
diameter, but was badly charred from remaining propellant in the solid motor (2c).
1a
1b 1c
1d
2a 2b
2c
Phase II field testing was conducted on a private ranch in California
during late December 2014, and consisted of three separate flights.
Gravedigger 3 Preliminary Results:
• Low Velocity impact (subsonic)
• Impact angle ~10˚ from normal
• Penetration depth ~ 1 meter
• Sample was collected, but stagnation resulted in low
yield
Gravedigger 4 Preliminary Results:
• High velocity impact (~340 m/s)
• Impact angle ~80˚ from normal due
to issue with ignition timing
• Penetration depth ~1.8 meters
• Sample was collected, but stagnation
resulted in low yield
Gravedigger 5 Preliminary Results:
• High velocity impact (~400 m/s)
• Impact angle ~5˚ from normal
• Penetration depth ~1 meter
• No sample collected due to feed
chimney structural failure
• Sample return container intact and at
surface of impact
Pressure gradients during impact
rapidly decrease, and while fine
ejecta is captured in the sample
return container, the bulk of the
material is clogging the feed
chimney at about one third of the
penetration depth. This is
limiting the sample yield from the
desired kilograms to a few grams.
The stagnation point can be seen
on the right.
Sample Return Container
Fine ejecta
captured in a
backflow baffle
inside Sample
Return Container
Stagnation Point
Gravedigger 1 Results (1a-c):
• Demonstrated survivability of the system
• Impact velocity <200 m/s
• Impact angle ~30˚ from normal
• Penetrating depth of ~1.5 meters
• No sample, feed ports did not open
Gravedigger 2 Results (2a-b):
• Impact velocity ~400 m/s
• Impact angle ~10˚ from normal
• Penetration depth of ~ 2 meters
• Potential seismic mapping capability
• Sample collected, but badly charred
In the next design evolution, the two current nose cone
designs will be combined to increase the flow rate of
material through the system. Relative flow velocity
modeling suggests that by tapering the center bore and
combining both feed port configurations, higher flow
velocities can be reached than the current geometry allows.
We would like to thank NIAC for providing the funding that has
allowed this research to be conducted, Thomas Swett and Laurie
Lord for providing us with proving grounds, and the students and
volunteers with the UW ESS High Power Rocketry class for all
their efforts and support. In addition we
thank Robert Hoyt and his crew at
Tethers Unlimited for helping us with the
tether dynamics that make recovering
our samples possible.