Question

Figure 5.21: "Bang- bang" attitude control. 5.12 Problems 1. Attitude control thrusters are rated according to their "min bit" p (N s), the minimum amount of linear momentum tha can provide in one pulse. Four thrusters are mounted on a satellite moment of inertia I, a distance R from the Figure 5.21. The thrusters fire whenever the satellite strays from an angular window (the "deadband") of width θ, a technique referred to as "bang-bang" control. Argue that the satellite usually has angular momentum the thruster with center of mass, as shown in within 5.91) and an average angular velocity 2pR (5.92) This causes the time interval between thruster firings to be about At so the satellite eats through its fuel supply at a rate proportional o 16 (5.93) 2pR 5.94 16 Why are small minimum impulse bit (MIB) thrusters desirable?

Answer 1

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ANS:

AS PER QUESTION GIVEN

Here, Impulse(p) = change in the linear momentum(L)

angular momentum = linear momentum x R

since the linear momentum(L) = 2p

subs. it in the Ang. Mom. , we get H = 2pR

As we know, ang.mom =Inertia x ang. vel.

we get $w\approx 2pr/I$

Why are small minimum bit thrust desirable?

The accuracy of a satellite is very important. When the larger impulse bit is applied, the operating frequency becomes too low. This affects the angular velocity which needs to be corrected. Hence this impulse bit should always be maintained low.

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