Batteries
3.3 V Regulator
Gyros 5 V
Regulator 12 V Regulator Introduction
Subsystems
EM RWA Structure Avionics SW Comms Avionics HW Control Operations
05 December 2002 EMFFORCE - CDR EMFFORCE
<1 Amp required @ 3.3, 5, 12 Volts Use 12 batteries in series, voltage
Electronics
Comm. Board
Avionics, Sensors
Power Metrology
Systems
<TAS>
66
Test Results
•
•
• than expected
• in series Introduction
Subsystems
EM RWA Structure Avionics SW Comms Avionics HW Control Operations
05 December 2002 EMFFORCE - CDR EMFFORCE
Validate manufacturer’s lifetime specifications
0.8 Volts considered stopping point
Lifetime specs matches well, despite lower voltage levels Voltage data matches better when using multiple batteries
Power Metrology
Systems
<TAS>
This is a test of the maximum battery lifetime.
67
Test Results
•
•
recharging on “down” part of duty cycle
( )
1
0 5 10 15 20 25 30 35 40 45 50 55
( )
)
Introduction Subsystems
EM RWA Structure Avionics SW Comms Avionics HW Control Operations
05 December 2002 EMFFORCE - CDR EMFFORCE
Lifetime requirement far exceeded Extended lifetime due to due to battery
Voltage vs. Time 3 batteries, Current = 28A
0.8 0.9 1.1 1.2 1.3 1.4 1.5
Time min Normalized Voltage (Volts
Power Metrology
Systems
<TAS>
68
Power Subsystem Budgets
3.44 .1 .2 .3 .3 .33 2.21 Mass per vehicle (kg)
2500 -300
-Misc.
0.1 0.1 0.1 0.027 0.170 Unit Mass
(kg)
250 12
450 3
Controllers
200 2
Sensors
100 3
1200 13
D-cells
Total Cost ($) Item
Introduction Subsystems
EM RWA Structure Avionics SW Comms Avionics HW Control Operations
05 December 2002 EMFFORCE - CDR EMFFORCE
TOTAL SUBSYSTEM BUDGET:
TOTAL MASS PER VEHICLE:
AA-cells
Volt. Regs.
Qty.
Power Metrology
Systems
<TAS>
69
Power Concerns
sets of batteries on had (and charged)
Long charge time for D-cell batteries (~16 hours)
Use heat sinks wherever possible Buildup of heat in circuit
components, batteries
Use separate controllers for each battery cell if needed Difficulties with running
100 Amps through circuitry
Mitigation Concern
Introduction Subsystems
EM RWA Structure Avionics SW Comms Avionics HW Control Operations
05 December 2002 EMFFORCE - CDR EMFFORCE
Have extra complete
Power Metrology
Systems
<TAS>
70
Structure
Geeta Gupta
05 December 2002 EMFFORCE - CDR
71
Structure Overview
•
–
•
shielding
–
electronics and vice versa
•
cushion of gas for near frictionless translation over a flat floor
Introduction Subsystems
EM RWA
Avionics SW Comms Avionics HW Control Operations
05 December 2002 EMFFORCE - CDR EMFFORCE
Physical interfacing of subsystems
Provide structural “backbone” of vehicle
Subsystem packaging/magnetic
Prevent magnet from interfering with
Gas carriage provides pressurized
Power Structure Metrology
Systems
<GG, ALS>
The EMFFORCE packaging is meant to hold together the various
subsystems of the total system in a functional manner that allows for efficient use of volume and mass, as well as practical interfaces. The packaging must ensure that all subsystems have the necessary physical conditions to function correctly; the electromagnet must not interfere with the electronics, and the metrology subsystem must have a 360 degree unobstructed view of the vehicle’s surroundings.
The gas carriage portion of the structure will provide near frictionless translation over the test facility floor. It is important to minimize external forces on the vehicle so that the system’s force balance is undisturbed and also so that a space environment is simulated. The test facility floor may have a variety of surface finishes: very smooth, such as glass or Lockheed’s flat floor facility; or not as smooth, such as the floor of MIT’s Lobby 7. Lobby 7 could provide a valuable test surface for pre-Denver testing.
72
Requirements
•
– to within 1cm of center of EM field.
–
•
– interference from electromagnet generating field strength up to 0.03 Tesla.
•
– minutes of operation
Introduction Subsystems
EM RWA
Avionics SW Comms Avionics HW Control Operations
05 December 2002 EMFFORCE - CDR EMFFORCE
Feasible Packaging
Rotational symmetry; keep center of mass Center of mass kept low for stability
Shielding
Provide sufficient shielding to prevent
gas Carriage
Must provide gas supply sufficient for 20
Power Structure Metrology
Systems
<GG, ALS>
The requirements associated with the EMFFORCE packaging relate to the feasibility of the design. In order to maintain simplicity in maneuvering and handling, as well as to avoid control problems the packaging must be rotationally symmetric. The structures team must avoid a top-heavy design in order for stability, as well as take into consideration where the forces will act on the vehicles.
The packaging must include some sort of shielding (if necessary) to avoid magnetic interference between the magnet, electronics and other
subsystems on board.
The gas carriage must provide as long a test duration as possible. The minimum requirement is 20 minutes.
73
Design History
•
•
package subsystems
• –
–
• Rings on base
• – Introduction
Subsystems
EM RWA
Avionics SW Comms Avionics HW Control Operations
05 December 2002 EMFFORCE - CDR EMFFORCE
Symmetrical Design
Use volume inside rings to
Obstacles
Four attachment points on rings vs. three attachment points due to pucks
Mounting methods
Subsystems inside rings Keep mass MINIMAL
Power Structure Metrology
Systems
<GG>
In order to fulfill the requirements the preliminary conceptual design used a spherical volume formed by the two electromagnet rings to house the reaction wheel and other subsystems. The rings sat on a triangular plate attached to gas pucks.
Although the conceptual design maintained rotational symmetry and kept the reaction wheel in the center of the generated force field, mounting methods that kept the mass minimal needed to be developed. A geometrical location for the power subsystem batteries also needed developing.
74
Design History
•
•
• fi
with L-brackets
•
to rings and ri
ign Introduction
Subsystems
EM RWA
Avionics SW Comms Avionics HW Control Operations
05 December 2002 EMFFORCE - CDR EMFFORCE
Circular base used to decouple four-point to three point attachment.
Provides ample space for mounting batteries
Mount cross braces directly to ber-glassed foam containers
Use similar fiber-glassed brackets to mount gas tank ngs to base.
selected des rejected design
Power Structure Metrology
Systems
<GG>
To find four points at which to connect the rings and base plate and maintain as much rotational symmetry as possible we designed a circular ring base plate. In order to overcome attachment point obstacles and keep minimal mass, L brackets were specially designed to attach four connection points on the rings to a circular base. L brackets will be attached to the foam rings using cryogenic epoxy as well as fiber glass strips. These L brackets will also support braces suspended inside the rings to hold the avionics board, and reaction wheel assembly.
75
Packaging Design – Attach Points
s A
Introduction Subsystems
EM RWA
Avionics SW Comms Avionics HW Control Operations
05 December 2002 EMFFORCE - CDR EMFFORCE
Metrology attach point – flat eyelet bracket
Gas tank attach point – flat eyelet bracket
RWA attach point – L shaped eyelet bracket vionics attach point – L shaped eyelet brackets
PWR attach point – Velcro
EM / Gas Carriage Base attach pts.
– L shaped eyelet brackets Power
Structure Metrology
Systems
<GG>
All the attachment points are described above. Special brackets are designed and attached to the rings using the previously described method for the metrology system, gas tank, RWA, avionics, and base plate attach points. The power subsystem will be secured using Velcro to the base plate for easy replacement between tests.
76