On Tue, 8 Jun 2004, David Weinshenker wrote:
> > Systems with small numbers of engines require either close matching
> > of engine startup characteristics, or a pad hold-down system to
> > absorb transient startup torques.
>
> I suppose that with sufficient throttling capability, it might be possible
> to start each engine at reduced thrust, such that the total thrust stayed
> below the vehicle's liftoff weight - then when they're all running at partial
> power, bring them up to full thrust together.
It's possible in principle. Essentially this divides startup into two
phases, confining any poorly-controlled transients to the first low-thrust
phase, and then throttling up after things are (presumably) under tight
control.
DC-X fired up that way, starting the engines at 30% and then throttling up
to lift off -- it had no hold-downs (although it did have well-understood
engines with fairly predictable startup behavior).
Depending on the configuration and the initial T/W ratio, it may require
fairly deep throttling (and a capacity to start deeply throttled) to make
this work.
Henry Spencer
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