From: "Doug..." <dvandorn@uswest.net>
Newsgroups: sci.space.history
Subject: Re: crasher stages
Date: Sat, 11 Nov 2000 18:58:32 -0600

"doug holverson" <dholvrsn@netins.net> wrote in message
news:B6333ECF.364CE%dholvrsn@netins.net...
> What is the idea behind crasher stages and how do they work?
>
> DGH


What it is, is a braking rocket stage that removes all but a few hundred fps
of a descending spacecraft's speed, burning out fairly low to the ground (a
few thousand feet), so the lander can use relatively small thrusters, with a
relatively small fuel supply, to slow to a soft landing speed (5 fps or so)
when only a few feet above the surface.  The stage that does most of the
braking is still moving at several hundred feet per second, though, and when
it burns out and is dropped, it crashes into the surface.  If you're going
to use a crasher stage, you have to make sure you're not coming straight
down when you drop it, or you might end up landing on top of it...

Crasher stages were actually used on the Surveyor lunar landers.  Crasher
stages were planned for the Soviet lunar landers, as well as for the Apollo
direct ascent mode, had it been selected.  I believe that most, if not all,
of the American and Soviet unmanned landers used crasher stages.

Doug

Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: crasher stages
Date: Sun, 12 Nov 2000 03:56:36 GMT

In article <OZlP5.1300$hn2.373766@news.uswest.net>,
Doug... <dvandorn@uswest.net> wrote:
>What it is, is a braking rocket stage that removes all but a few hundred fps
>of a descending spacecraft's speed, burning out fairly low to the ground (a
>few thousand feet), so the lander can use relatively small thrusters, with a
>relatively small fuel supply, to slow to a soft landing speed...

The advantage of this, by the way, aside from not having to land the dry
mass of the crasher, is that the crasher and lander engines can be sized
for deceleration and touchdown respectively.  Normally you want a lot of
thrust for deceleration and rather less for touchdown, and combining those
two jobs in one engine requires deep throttling, which is technically a
bit awkward.
--
When failure is not an option, success  |  Henry Spencer   henry@spsystems.net
can get expensive.   -- Peter Stibrany  |      (aka henry@zoo.toronto.edu)