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Unformatted text preview: f (t) is obtained from a single rocket engine on the spacecraft, with a given
maximum thrust; an attitude control system rotates the spacecraft to achieve any desired direction
of thrust. The thrust force is therefore characterized by the constraint f (t) 2 ≤ F max . The fuel
use rate is proportional to the thrust force magnitude, so the total fuel use is
T td γ f ( t)
0 2 dt, where γ > 0 is the fuel consumption coeﬃcient. The thrust force is discretized in time, i.e., it is
constant over consecutive time periods of length h > 0, with f (t) = fk for t ∈ [(k − 1)h, kh), for
k = 1, . . . , K , where T td = Kh. Therefore we have
vk+1 = vk + (1/m)fk − ge3 , pk+1 = pk + (1/2)(vk + vk+1 ), where pk denotes p((k −1)h), and vk denotes p((k −1)h). We will work with this discrete-time model.
For simplicity, we will impose the glide slope constraint only at the times t = 0, h, 2h, . . . , Kh.
123 (a) Minimum fuel descent. Explain how to ﬁnd the thrust proﬁle f1 , . . . , fK that minimizes fuel
consumption, given the touchdown time T td = Kh and discretization time h.
(b) Minimum time desce...
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- Fall '13
- The Aeneid