Unit 1 Flashcards
What is attitude control?
Orientation of the spacecraft
What is orbit adjust?
Position and velocity of the spacecraft in its orbit
Describe the blow down system type
Hydrazine is forced from propellant tanks using helium bladder blow down system. The pressure is non regulated and the thruster efficiency decreases over time
Describe the Propellant Tanks
4 spherical tanks, oriented w/ fuel towards center, 2 parts (pressurant and propellant) both filled prior to mating, 152 lbs of hydrazine (150 usable) per tank. 350 PSI of helium at BOL (drops to around 80 by EOL)
Describe Fill/Vent and Fill/Drain
4 each located on each tank. Located on the exterior of the spacecraft.
Vent is for pressurant. Drain is for Propellant
Describe the Pressure Transducers
4 located downstream of the fliter. registers the pressure of the tank using a bellows and potentiometer
Describe the Filters
4 located downstream of the four tanks and filter any unwanted particles in the propellant so LV, thruster valves, and injectors downstream aren’t damaged.
series of titanium case surrounding a series of stacked etched discs.
Describe Latch Valves
6 LV’s that control the flow of fuel from tanks to thrusters
nominally 001001
opened and close w/ electromagnetic switch
stay in last commanded position in power failure
LV will contain leaks by isolating a tank or bank.
Should not be opened if it connects two tanks w/ pressure difference greater than 200 psi
Describe the Thrusters
16 total
A bank has +- N ; B bank has +- S
Consists of two sections (Propellant valve assemblies and thruster assembly)
Thrusters are named for torque they apply on satellite
Roll(-z and not used for maneuvers), P/Y (+-x, delta v’s), N/S (delta i’s)
Describe Propellant valve Assemblies
ACE sends thruster port command to thruster port
Electronic switch forces a plunger to open which allows fuel to flow
Describe the thruster assembly
Capillary tube carries fuel from valves to thrust chamber
Injector sprays fuel into catalyst bed
nozzle 1:135 expansion ratio
Describe the catalyst bed heaters
32 CBH but only one per thruster is used during maneuvers
Cause hydrazine to decompose to gas
CBH must be heated to 140 deg celsius before firing
ACE controls catbed => CBHCTL=OVDS (nominal)
MCT controls catbeds => CBHCTL=OVEN (maneuver)
Describe Hydrazine
Freezes at 1.7 deg celsius and constricts when freezes.
All components must therefore be above 10 deg celsius at all times
After freezing, the hydrazine can heat back up and expands (the fuel line is still frozen) it can cause a line rupture causing a tank leak
Thruster Bank Swap
DR0415
switches PRY thrusters and CBH heaters from one bank to another
Ensures amount of fuel used from both tanks are equal
Ensures center of mass for satellite remains stable
Run before/after a maneuver/OA direction
Cannot be performed during AUNL- new thruster fire over cold catbed which reduces thruster efficiency
Good Cal Ready
Used for COLA also,
What is the purpose of the propulsion subsystem?
Maintain the orbit within orbit tolerances as well as acting as an actuator for the ACS
