Unit 2

Question 1

What is the semi-major axis?

Answer 1

The size of the orbit

Question 2

What is eccentricity?

Answer 2

It is the shape of the orbit

Question 3

What is Inclination?

Answer 3

The displacement of the orbital patch from the equator

Question 4

What is the Right Ascension of Ascending Node?

Answer 4

The longitudinal measurement of the ascending nodes position (from the first point of Aries to the ascending node)

Question 5

What is the Argument of Perigee?

Answer 5

The orientation of the orbit within the orbital plane (measured from the ascending node to perigee)

Question 6

What is True Anomaly?

Answer 6

The position of the spacecraft within the orbit as a specified time (from perigee to the satellite)

Question 7

What are maneuvers used for?

Answer 7

COLA and station change/keeping

Question 8

How many tanks are nominally connected to each bank performing a maneuver and why?

Answer 8

2 tanks to equalize fuel pressure and keep the center of mass stable.

Question 9

Describe a Delta-V Maneuver

Answer 9

Used for East/West maneuver, starts 75 mins before TIG, ends 75 after TCO, burn duration is usually about 30s, total time is about 150-151 mins, CBH greater than 140 deg celsius, 3 Phases

Question 10

Describe Phase 1 of the maneuver

Answer 10

It is the set up for the burn, thruster bank swap if req’d, latch valves opened, manual unload so wheels do not saturate during maneuver.

Question 11

Describe Phase 2

Answer 11

It’s the actual burn.
One command is sent to ignite thruster (within 5 minutes of TIG)
Verify burn is good with TW9, PDSV, RDSV, YDSV
Terminate burn at correct time (reset pulse width command must be sent on time)

Question 12

Describe Phase 3

Answer 12

The post burn clean-up.
Undo everything from phase 1.
Restore satellite back to normal operating mode (TBS if req’d and putting the sat in 16 sec mode)
30 secs to send PW reset command after TCO

Question 13

What is thruster deadband?

Answer 13

(xDB)
the parameter used to limit the amount of momentum stored in the satellite during unloads.
it represents the attitude limit within the sat. does not need to fire thrusters in order to correct deviations.
nominal 2,4,8 (.08deg/s, .04, .08)

Question 14

What is Thruster Deadband Offset Commanded?

Answer 14

(xDBOC)

values that bias the thruster deadbands during maneuvers in order to improve pointing performance. calculated in the SOC

Question 15

What is Delta-v Correction?

Answer 15

(xDVCOR)
what the satellite actually calculated and used to correct the thruster inefficiencies and mismatch during the maneuver to ensure that the maneuver
Become DCOBs for next maneuver w/ same config

Question 16

What is Thruster Pulse Width?

Answer 16

(xPW)
the number of counts of data that will be sent to the thruster port when a firing is called for
nominal (Pitch32,Roll32,Yaw64)

Question 17

What is Thruster Rate Increment?

Answer 17

(xRTINC)

momentum equivalent rate imparted, wheels would be driven without taking into account firings

Question 18

What is Delta-V Duration?

Answer 18

(DVDURC)
the duration of an orbit adjust maneuver
the number of CPU cycles during which a pair of thrusters will be turned on full
(CPU cycle)

Question 19

what is on/off pulsing

Answer 19

on pulsing - firing 1 thruster

off pulsing - shutting off 1 thruster for duration of PW

Question 20

Describe the planning process for maneuvers

Answer 20

OA determines need to perform maneuver
Plan bank, tank, thruster, TIG, TCO, date, duration, LV config
Create study (rough guess)
Create Gen (actual document SVO will use to write a maneuver, more accurate and official)
MP creates Maneuver Planning Worksheet (what crew is responsible for what actions and when they are to be accomplished) and DEO verifies all info
MPs the schedule the support and subsequent numbered healths
2 SVOs use Gen and MPW to create two copies of maneuvers
SVO 1 will generate specific reports and use these reports to write one copy of maneuver
SVO 2 will do the same and then compare the maneuvers.
SVO 1’s copy is used to run maneuver, 2’s goes to DEO’s desk

Question 21

Delta V Maneuvers

Answer 21

Once every 6 weeks using P/Y thrusters

Question 22

What is positive delta-V?

Answer 22

pushes the spacecraft in the direction of travel(east)
Performed at Apogee to raise perigee
West thrusters (-x face)

Question 23

What is negative delta-V maneuver?

Answer 23

Against the direction of travel
Performed near perigee to lower the apogee altitude
east thruster (+x face)

Question 24

What are our station keeping limits?

Answer 24

Maintain earth footprint, .1 deg latitude, .2 deg longitude