MP 2

Question 1

What are sensors?

Answer 1

They are the “eyes” of the vehicle and are used to detect the true attitude of the vehicle in relation to a fixed point.

Question 2

Describe the Sun Sensor

Answer 2

Used to detect angular displacement between sun and solar arrays
4 on each array yoke at 40deg (2roll 2pitch)
North Sun Sensor (-RSS,+PSS)
South Sun Sensor (+RSS,-PSS)

Question 3

What is the pitch sun sensor used for?

Answer 3

Solar Array Alignment

Question 4

What are the Roll Sun Sensors used for?

Answer 4

Only for detecting yaw

Question 5

When are the roll sun sensors perfect yaw sensors?

Answer 5

6am/6pm

Question 6

When are the roll sun sensors perfect roll sensors?

Answer 6

Noon/Midnight

Question 7

What is individual eye mode?

Answer 7

Where sun sensor signals are converted to be processed by ace. 2 roll signals are subtracted and form the error signal AFTER digitized and sent to ACE memory

Question 8

What is Roll Differential Sun Sensor Processing?

Answer 8

the pair of analog signals are subtracted BEFORE digitization, more accurate than individual eye mode, and nominal.

Question 9

Describe the Earth Sensor

Answer 9

Used to detect Pitch and Roll errors
Measures displacement from z-axis and Earth’s IR field
Takes readings from Earth Presence Detectors, IR detectors, Sun Detector

Question 10

Describe the Earth Sensor Infrared Detector Ring

Answer 10

8 paired IR sensors in a ring, image of earth focused on center of IR ring
Field of view of array is 21.5deg conical

Question 11

Describe the Sun Detector Ring

Answer 11

8 paired in a ring, sense visible light, used to keep IR rings from misinterpreting the sun for the Earth

Question 12

What is sun mode?

Answer 12

When a pair of IR detectors are switched off due to the Sun Detector Rings

Question 13

Describe the Earth Presence Detector

Answer 13

2 Point to the center of the IR ring, indicates whether Earth is in the center. EPRES
A detector is hardwired to A ES electronics, B to B
Both are powered but the ACE may only select 1
If earth is center, EPRES shows both

Question 14

Describe the rate gyro

Answer 14

1 non-redundant that senses yaw rate, tested during LEO and QRP, attached to the RWA

Question 15

Describe the Inertial Reference Unit

Answer 15

1 on MYP/SLEP, used w/ DYSE for enhanced yaw pointing.
Made up of 2 gyros that sense pitch, roll, yaw (only used for YAW)
High rate = 8deg/min
Low rate = 3deg/min
full or half speed
Nominal FULL/HIGH

Question 16

What are Actuators?

Answer 16

They are controlled by the ACE and used to correct attitude errors.
They include 4 reaction wheels and 16 thrusters

Question 17

Describe the Reaction Wheels

Answer 17

They are inclined at 45deg, and counteract the satellite’s movement
They all counteract pitch, 2yaw/2roll, maintains pointing control
Each wheel has a port, driver, momentum processor.
Port- allows ACE to communicate w/RWA
Driver-replaces drive info from ACE converted to digital pulse
Processor - 683 deg tach counts over 1 cpu cycle=2500rpm

Question 18

Describe the Thrusters

Answer 18

16 thrusters that maintain station keeping, dump reaction wheel momentum, not used for AC
Each bank contains 8 +-pitch,roll,yaw
A bank +-north thrusters
B bank +-south thrusters
ACE determines thrusters need to be fired
2 catbed heaters per thruster