Author Topic: How much slam can you put in a hoverslam.  (Read 3000 times)

Offline speedevil

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How much slam can you put in a hoverslam.
« on: 02/07/2015 03:51 AM »
Current F9 lands at 1.4-2G or so.

(well, for various values of lands so far).

In some ways the harder you slam, the better.

Less time for the grid-fins to become aerodynamically ineffective, significantly higher vertical velocity than windspeed meaning better targeting.

Clearly there are issues - if you're doing it at 5 or 10G - FOD may be slightly bigger concern, and the stage being slow to spool up would be really, really bad.

What does spinup variance of current engines look like?

And yes - I was wondering about people commenting on F9R with raptor and how it couldn't be reusable.

Offline guckyfan

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Re: How much slam can you put in a hoverslam.
« Reply #1 on: 02/07/2015 07:24 AM »
What does spinup variance of current engines look like?

I second that question.

Offline cscott

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Re: How much slam can you put in a hoverslam.
« Reply #2 on: 02/09/2015 06:25 PM »
It's not just spinup variance -- that can be compensated for by throttle settings, to some degree.

It's really the sum total of all sources of variance, and the tightness of the control loop.  That gives you a standard deviation on your touchdown: zero velocity +/- X m/s, with Y sigma confidence.   You pick your confidence, then design your legs to withstand/buffer the X m/s landing.  Obviously you would like X to be as small as possible, so your legs can be as flimsy/lightweight as possible.  That sets your hoverslam limits.

Offline SoulWager

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Re: How much slam can you put in a hoverslam.
« Reply #3 on: 02/09/2015 09:19 PM »
More slam means less gravity losses, but tighter timing margins for both ignition and cutoff, It also means less time with gimbaled engines, and complications if you need more than one engine to get the higher TWR.

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