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ambicapter 2 hours ago

4 stages feels like a lot of added complexity for your first launch. I assume it gives you more performance margin to drop weight/stages more often?

MobiusHorizons 2 hours ago | parent | next [-]

4 stages is certainly a lot more than most rockets, but most rockets don’t use solid rocket stages. Solid rocket motors are generally much more reliable/ simpler than liquid fueled stages, but they can’t be throttled or turned off early which makes it hard to achieve precise orbits. My guess is the extra stages allow for better control by carefully choosing when to light the next stage. The scout family of rockets are also 4 stage solid rockets and probably a good comparison.

londons_explore 2 hours ago | parent [-]

Don't you need at least a little thrust ~40 mins later to circularize the orbit?

Obviously solid rockets can't be relit.

Could that be the use of the 4th stage?

numpad0 18 minutes ago | parent | next [-]

Rockets are usually two-staged + satellites. The booster take it to outside of the atmosphere, then the upper stage puts it into a ballistic trajectory, and the payload does the circularization burn 45 minutes or so after the liftoff at the peak of the parabola.

Above is the basic semantics, and it can be further optimized, such as by extending battery power for the second stage to use it for circularization, inserting a single purpose satellite-like pusher device above the responsibility boundary at the top of second stage and payload satellite and calling it the third stage, or just adding actual third stage above second stage, etc.

Adding more and more stages improve performance per Konstantin Tsiolkovsky's rocket equation, but it'll add risk factors and also obviously add more dead weights in electronics and engines and support equipment, so 2-3 stages is usually the good balance between performance and risk/costs. You can have as many stages as you want if you think you can handle it.

MobiusHorizons an hour ago | parent | prev [-]

Good point! The final stage being liquid would also give them more control to fix any errors with the orbit.

walrus01 2 hours ago | parent | prev | next [-]

It's three solid rocket boosters stacked on top of each other and a very tiny liquid fueled engine on the 4th stage. I would be interested in what the delta/v stats/capability of the 4th stage booster are with 350 kg payload.

wat10000 2 hours ago | parent | prev [-]

A partially empty stage wastes mass on propellant tanks sized for the full load. The mathematical ideal would be an infinite number of infinitesimally small stages.

londons_explore 2 hours ago | parent [-]

Except you pay the weight for the nozzles on each stage.

That makes there be a mathematically optimal number.