Newsgroups: sci.space.shuttle
From: henry@spsystems.net (Henry Spencer)
Subject: Re: One part Oxygen, two parts Hydrogen and BOOM!
Date: Fri, 13 Oct 2000 14:05:09 GMT

In article <B60C0D3F.48AD%Danny@Skarka.com>,
Danny Skarka  <Danny@Skarka.com> wrote:
>So what "ignites" the SSMEs? I know about the fuel flow and how pressure is
>kept in the ET...all those fun details, but what is the ignition source?

The SSMEs use "torch" igniters, little oxygen/hydrogen burners firing into
the preburners and chambers.  The igniters themselves are ignited by,
essentially, high-tech spark plugs.
--
Microsoft shouldn't be broken up.       |  Henry Spencer   henry@spsystems.net
It should be shut down.  -- Phil Agre   |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.shuttle
From: henry@spsystems.net (Henry Spencer)
Subject: Re: One part Oxygen, two parts Hydrogen and BOOM!
Date: Sat, 14 Oct 2000 03:37:23 GMT

In article <slrn8ue2f1.bv2.zaitcev@js006.noname.ru>,
Pete Zaitcev <zaitcev@yahoo.com> wrote:
>> The SSMEs use "torch" igniters, little oxygen/hydrogen burners firing into
>> the preburners and chambers.  The igniters themselves are ignited by,
>> essentially, high-tech spark plugs.
>
>I see... obviously there cannot be a spark in a vacuum.

Not entirely true, but irrelevant -- when the igniter fires up, there's an
oxygen/hydrogen gas mixture there for the spark to travel through.

>Is the plug the reason engines cannot be restarted in orbit or
>there is more to the story?

There's nothing *fundamental* in the SSME which makes an in-space restart
impossible -- no one-shot parts or anything like that -- but it's a
complicated engine which has to be set up exactly right for a successful
start, and ground equipment (and gravity!) helps out with that.  It would
not be difficult to develop a variant which could start itself in space,
but there has been no reason to do that.
--
Microsoft shouldn't be broken up.       |  Henry Spencer   henry@spsystems.net
It should be shut down.  -- Phil Agre   |      (aka henry@zoo.toronto.edu)