Spacecraft control ignoring dM/dt

Kirk's _Optimal Control Theory_ (amazon.com/dp/0136380980) includes some pr=
actice examples involving spacecraft control, "neglecting the change in mas=
s resulting from fuel consumption" for simplicity. (To be fair, in a later=
section -- after introducing inequality constraints on state & control -- =
he does treat the full lunar soft-landing problem, including the changing s=
ystem mass.)
My question: Is the simplification *ever* reasonable? Are there classes o=
f rocket engines where the consumed fuel comprises so small a fraction of v=
ehicle mass that it can be (to low order) ignored? Nuclear-thermal rockets=
? Ion drives?
--Joel
Reply to
Joel C. Salomon
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resulting
treat the full
of vehicle
Ion drives?
Steering thrusters, perhaps.
If the mission is long enough that the changing mass happens slowly with respect to the required vehicle dynamics (i.e., a trip to Mars on chemical rockets), then the control problem is eased to one of gain scheduling, rather than having to treat the thing as a full-blown time-varying problem.
Reply to
Tim Wescott

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