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Asteroid Sample Return
Progress as of 3/12/2008
GN&C
Sensor Data
Star Tracker
• Galileo Avionica A-STR Autonomous Star Tracker
• FOV: 16.4 X 16.4˚• Power Consumption: 8.9 W at 20˚C
13.5 W at 60˚C• Size: 195 (L) X 175 (W) X 288 (H) mm• Mass: 3 kg
IMU
• Honeywell Miniture IMU• Mass: 5 kg• Size: Unknown• Power Consumption: Unknown• This device has very little information
available to us.
Altimeter
• Yet to be decided upon discussion with Steve
High Level Control System
Control Inputs – Reaction Jets Vehicle Dynamics
Sensors-Star Tracker
-IMU-Altimeter
Planned Trajectory
Telecomm
• Waiting for answers to questions
Approach of Asteroid
• GN&C has developed a code that gives the required delta v based on the point where the free fall begins.
• This will be finalized once the structures group determines what impact loads are acceptible.
Propulsion• Propulsion has developed a code to determine fuel
needs based on the delta v requirements and thrust for attachment.
• Code provides suggestions for tanks and thrusters required for mission based on data retrieved through web research of thrusters and tanks.
• Final fuel requirements are based on thrust requirements for attachment, which depends on final structure design
Structures Work so Far
Force needed to hold Spacecraft
NNnFF
NsmkgNgmFF
n
NF
smg
kgm
needreq
astscdrineed
dri
ast
sc
25.8)5.1(5.5
5.5))/006.0(750(10
5.1
10
/006.0
750
2
2
Finding Needed Torque offset due to drill
mmN
F
nR
nRF
Nfeet
FF
NNNnF
n
mN
NFN
foot
sc
scfootfoot
fricfoot
sfric
s
sc
need
055.0)6875.0(4
)1.0(5.1
4
4
6875.04
75.2
4
75.2)5.5(5.0
5.1
5.0
1.0
5.5
Initial Sketch of Spike and Holding MethodSpike 3 inches in length and ¼ inch in diameter
Spike exits through hole in foot and head of spike clamps down on foot
Barbs on spike increase surface area and holding power in ground
Attachment Method• Use Mechanical fastening system based on Hilti Gun
model DX E72.• Assume built weight for guns to be same as hilti gun. • Use F=m(v/t) to determine force from anchor
deployment.• t is assumed to be .01 s• Determine required Thrust and Fuel based on Force.• Deploy one anchor at a time to reduce thruster
requirements.• Assume 30s to deploy all 4 anchors• Use _____ Anchor based on research.
Hilti Gun DX E72
• .22 caliber powder actuated fastening tool
• Drives up to 2.8” nails into concrete or steel
• 2 kg each • Modify Design using
space worthy materials
http://www.us.hilti.com/holus/modules/prcat/prca_navigation.jsp?OID=-16951
Reaction Force
Ballistics information found at: http://www.korabrno.cz/bal-22.htmlUsed: Remington .22 Short CB Cap
• Bullet Weight = 1.87 g• Velocity = 213.36 m/s• Force from Attachment =
(213.36/.01)*(1.87/1000)=39.898N per anchor
Thrust and Fuel Requirements
• Using Moments = 0 and forces = 0 • T1=40(L/L=a) + (40-M)• T2=40(L/L=a) - (40-M)• T1 – thrusters on same side as anchor• T2 – thrusters on opposite side as anchor• M – Mass*g • g=.006
Anchor Specifications Ideas
Trade Study
• (Final trade study between mech. And thruster methods will go here)
• At this point estimated fuel usage for 24 hr bun is ~ 300kg
Initial Trade StudyIdea How works Pros Cons
Spikes on Impact Drive stakes in when land from legs
Don’t need separate propulsion system (less weight)Highest probability for successLeaves nothing behind
Harpoon Shoot something out and reel ourselves in
Compensation torquesProbably use more fuelWay more mechanisms involvedProbably get tangled to roll back up.
ThrustersPropulsion Only
Use thrusters to hold in place
Extra fuelTorque when drillingNeed momentum wheel, “spikey feet”
Cork Screw
Spikes Post-Impact Two arms with small explosion that would rotate and come back while nailing into the ground
Would work…kindaAble to retry
Even more complicated than harpoon
Initial Trade Study Cont.Thrusters Harpoon Spikes on Impact Spikes Post-
ImpactCorkscrew
Weight bad bad goodish okay Bad
MechanicalComplexity
Good (best)
BAD good okay BAD
FuelConsumption
BAD good good okay good
Power Requirements
good bad good good Bad
Dependability good bad okay good Bad
Applied Loads good good bad okay good
Reusability good bad bad okay okay
Methods in bold font further researched to come to final decision.
Mass Budget
• Mass budget is under construction.