MP 3

Question 1

Describe the Central Processing Unit

Answer 1

16 bit microprocessor. is the working component of the ACE. performs addition and multiplication and shifting of data. there are 2 fully redundant CPUs that can be switched by discrete command

Question 2

Describe Read only Memory

Answer 2

Firmware (software routines burned into ROM boards)
2 redundant 8k (8192 word) 16 bits long read only. Information cannot be erased or written over and will remain stored without power.

Question 3

What is the inner loop?

Answer 3

Part of the ROM, calculations are done every cpu cycle (1.024 seconds)

Question 4

What is the outer loop?

Answer 4

Part of the ROM, 2 modes.
2 sec update cycle (maneuvers) performs calculations every 2.048 seconds
16 sec update cycle (nominal) performs calculations every 16.384 seconds

Question 5

Describe Random Access Memory

Answer 5

Used to store calculations, contains BLRP, 2 8k boards, hardened and have read/write capability
low ram = scratch pad = 40,000 to 57,776
high ram = RAM patch = 60,000 to 77,776
b10/12 only have 1 board active at a time

Question 6

Describe Digital Data Bus

Answer 6

50 lines, ensures all components talk

Question 7

What is embedded software?

Answer 7

software stored in ROM, the original launch config that runs every 1.024 s.

Question 8

what are the 5 modules for embedded software?

Answer 8

Executive Controller, Trap Services, Circumvention, Discrete, DSCS Controller

Question 9

Describe Executive Controller Module

Answer 9

The main Operating System, the overall supervisor, keeps DSCS healthy

Question 10

Describe Trap Services Module

Answer 10

Responds to errors on ACE Processing, displayed on TW 5
illegal instruction trap-CPU does not understand direction given, NR, 02
Odd Address trap-CPU only processes even addresses, NR, 04
software trap - computational error, normal ops since BLRP causes this, R, 08
time out trap - CPU sends master sync and does not receive slave sync, R, 09

Question 11

Describe circumvention module

Answer 11

responds to NUDET and ACE P/U, displayed in Power-Up Event Timer
NUDET - PET counter 300-1, 5 cpu cycles for ES to return to normal, 10
ACE P/U - PET counter 120-0, RAM Patch disabled, 00

Question 12

Describe discrete module

Answer 12

Used to generate DW and TW’s
DW - configuration of ACE, left to right, binary
TW - what the ACE is doing, right to left, hexidecimal
DW 1-4 (hard) DW 5-6 (Soft)

Question 13

Describe DSCS Controller

Answer 13

flight software, runs every 1 CPU cycle, drives RW/thrusters, Runs auto functions, used for Earth/Sun acquisition
Performa attitude and housekeeping functions
State vector determination, calcs state vector which drives RW

Question 14

Describe Thruster Control Laws

Answer 14

rate check (1st) - momentum greater than deadband, fire thrusters
rate plus position check (2nd) - more sensitive

Question 15

Describe all 4 Thruster Torque Modes

Answer 15

Auto Unload - Normal Ops, rate, 16 Sec, 1 PW, every 4th U/D cycle
Manual Unload - commanded Aunl, same as above, not used if sapos>425
Auto Torque - Earth Acq, Rate/RPSN, 1 & 1/4 PW, 2 Sec, every U/D cycle
Low Torque - MUNL for SAPOS>425, Rate/RPSN, 1/4 PW, 2/16 Sec, every U/D cycle
RPSN - RPSN, 1/4 PW, 2 sec, bypass rate clock

Question 16

Describe the Attitude Control Electronics

Answer 16

The brain of the ACS. It is a microcomputer that controls many peripherals. the hardware accepts sensor inputs which calculate attitude and angular velocity of satellite. Consists of CPU, ROM, RAM, peripherals.