Sound energy from liquid engines

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David Findlay - 27 Sep 2003 06:12 GMT

Is there a way to quantify the amount of noise created by an engine such as
an SSME? In a vehicle for use for manned long range exploration, would it
be possible to dampen the sound enough to allow engineers to work on a live
engine(well maybe the feed systems, control gear etc)? Thanks,

David

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Terrence Daniels - 27 Sep 2003 06:29 GMT

> Is there a way to quantify the amount of noise created by an engine such as
> an SSME? In a vehicle for use for manned long range exploration, would it
> be possible to dampen the sound enough to allow engineers to work on a live
> engine(well maybe the feed systems, control gear etc)?

If I remember right, the SSME's generate about 140db and the aft section of
the Shuttle is rated for ~170. I don't know how much of that is engine
machinery and how much is caused by the exhaust.

If you could hypothetically block off all sound created aft of the engine
core, what would it sound like? How loud would it be? I don't know the
answers to those questions... In any case, I don't think working on a live
running engine would be such a good idea. If something as complicated as an
engine was that badly broken that it would need human repairs, it wouldn't
be running anyway.

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David Findlay - 27 Sep 2003 06:56 GMT

> If you could hypothetically block off all sound created aft of the engine
> core, what would it sound like? How loud would it be? I don't know the
> answers to those questions... In any case, I don't think working on a live
> running engine would be such a good idea. If something as complicated as
> an engine was that badly broken that it would need human repairs, it
> wouldn't be running anyway.

Well I was actually thinking more from the aspect of maintinence of a second
engine while one was running. A mars spacecraft would really need the
ability to be maintained in flight, so having pressurised access to almost
everything would be useful. An ion or vasimr drive would be quite easy to
quieten enough for inflight monitoring and maintinence. Thanks,

David

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Ian Stirling - 27 Sep 2003 22:17 GMT

>> If you could hypothetically block off all sound created aft of the engine
>> core, what would it sound like? How loud would it be? I don't know the
[quoted text clipped - 8 lines]
> everything would be useful. An ion or vasimr drive would be quite easy to
> quieten enough for inflight monitoring and maintinence. Thanks,

The drive does not need to be maintained in action.
At any time other than takeoff you have at least days, possibly months
before getting the engine working again is critical.

And there is limited stuff you can do to an operating liquid fueled engine,
as it tends to be kind of hot and high-pressure.

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Brian Gaff - 27 Sep 2003 08:22 GMT

This thread reminds me of the tourist in Ireland who asked a passer by how
to get to Dublin, to which the response was...

If I were going there, I would not start from here.

What i mean is that you are unlikely to be continuously using a liquid
fuelled engine continuously on a deep space mission with men on board, they
are just not suited for that purpose. Far more likely is some form of Ion
engine.

If you have to service liquid fuelled engines in flight, you would do it
when they were not working.

Also, I'd think that it would be unlikely that any craft would pressurise
the engine pump area etc, it would be expensive and difficult to maintain
in itself, so as sound can, in the absence of air, only travel through
structure, there is no noise anyway!

Brian

--
Brian Gaff....
graphics are great, but the blind can't hear them
Email: briang1@blueyonder.co.uk
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David Findlay - 27 Sep 2003 10:00 GMT

> What i mean is that you are unlikely to be continuously using a liquid
> fuelled engine continuously on a deep space mission with men on board,
> they are just not suited for that purpose. Far more likely is some form of
> Ion engine.

Yes, but a liquid engine would still be useful for jumping out of orbits of
planets, or manuerving to miss something nasty.

> Also, I'd think that it would be unlikely that any craft would pressurise
> the engine pump area etc, it would be expensive and difficult to
> maintain
> in itself, so as sound can, in the absence of air, only travel through
> structure, there is no noise anyway!

How hard is it to pressurize an area? Is it considered a major engineering
challenge? It can't be as hard as going to the bottom of the sea. Thanks,

David

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Ian Stirling - 27 Sep 2003 22:07 GMT

>> What i mean is that you are unlikely to be continuously using a liquid
>> fuelled engine continuously on a deep space mission with men on board,
[quoted text clipped - 3 lines]
> Yes, but a liquid engine would still be useful for jumping out of orbits of
> planets, or manuerving to miss something nasty.

It's almost always best (for orbital mechanics reasons) to make all
manouevers at the maximum thrust you can.

Combine this with the low energy of chemical fuels and you'r looking at
burns of several minutes at most.
There is little point in trying to repair something when it's in use if
it's going to stop being in use before you can get the cover off.

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http://inquisitor.i.am/ | mailto:inquisitor@i.am | Ian Stirling.
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Space Forum / Shuttle / September 2003

Sound energy from liquid engines