A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Space Science » History
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Apollo CM engine.



 
 
Thread Tools Display Modes
  #1  
Old October 8th 12, 06:18 PM posted to sci.space.history
Ken S. Tucker[_2_]
external usenet poster
 
Posts: 55
Default Apollo CM engine.

My 1st and lasting impression of the CM engine bell is it was to big.
I do know about the bell size as it relates to use in a vacuum, my
question is why the engine needed the thrust it had?
Seems to me, in all maneuvers, the same impulse would occur with say
1/2 the thrust and 2x the thrust time.
Which maneuver (engine firing) needed the supplied CM engine thrust?
Ken
  #2  
Old October 8th 12, 07:31 PM posted to sci.space.history
Jeff Findley[_2_]
external usenet poster
 
Posts: 1,388
Default Apollo CM engine.

In article , says...

My 1st and lasting impression of the CM engine bell is it was to big.
I do know about the bell size as it relates to use in a vacuum, my
question is why the engine needed the thrust it had?
Seems to me, in all maneuvers, the same impulse would occur with say
1/2 the thrust and 2x the thrust time.
Which maneuver (engine firing) needed the supplied CM engine thrust?


LOI burn?

LOI burn was the "big burn" which needed to be done by the SM. LOI burn
for Apollo 12 was already nearly 6 minutes long. Doubling that to 12
minutes would have done what?

It's been 20+ years since my orbital mechanics class, but my
recollection is that, with all other variables being equal, a burn like
this becomes *less* efficient (in terms of fuel burned) the longer the
burn takes. Since this burn took "33,500 pounds of propellant or about
60 percent - 61 percent of the propellant carried", making the burn less
efficient doesn't sound like a good idea. But I'll have to leave "the
math" to someone who has a better handle on orbital mechanics and has
the time to set this problem up in a proper simulator. I remember that
in 1991, we wrote our own simulation programs in Fortran 77 using a math
library to do the numerical integration. Gee, that was fun... :-P

Here is my source:

http://history.nasa.gov/ap12fj/10day4_loi.htm

The quote below comes right after 081:52:16

Public Affairs Office - "This is Apollo Control at 81 hours,
53 minutes. The spacecraft now traveling at a speed of 4,726
feet per second and about 4,000 nautical miles from the lunar
surface. We have the preliminary figures on the Lunar Orbit
Insertion maneuver, the first of two maneuvers to place the
spacecraft in a more or less circular orbit about the Moon.
The ignition for LOI-1 ignition time will be 83 hours, 25
minutes, 19 seconds. A burn duration will be 5 minutes, 58
seconds, and we'll subtract about 2,880 feet per second from
the spacecraft velocity with that maneuver. In performing
that 5 minute, 58 second burn, the Service Propulsion System
engine will consume about 33,500 pounds of propellant or
about 60 percent - 61 percent of the propellant carried.
The spacecraft currently weighs 96,076 pounds. We estimate
after the Lunar Orbit Insertion maneuver, the weight will
be about 62,491 pounds - the difference in weight, of
course, being accounted for in the propellant consumed
in the burn..."

Jeff
--
"the perennial claim that hypersonic airbreathing propulsion would
magically make space launch cheaper is nonsense -- LOX is much cheaper
than advanced airbreathing engines, and so are the tanks to put it in
and the extra thrust to carry it." - Henry Spencer
  #3  
Old October 8th 12, 07:34 PM posted to sci.space.history
Jim Davis
external usenet poster
 
Posts: 420
Default Apollo CM engine.

Ken S. Tucker wrote:

Which maneuver (engine firing) needed the supplied CM engine
thrust?


The one it was originally intended to fulfil - lifting off from the
surface of the moon.

When that requirement went away the higher thrust was still useful
for various aborts during launch after tower jettison.

Jim Davis
  #4  
Old October 9th 12, 03:44 AM posted to sci.space.history
Jan Philips
external usenet poster
 
Posts: 54
Default Apollo CM engine.

On Mon, 8 Oct 2012 18:34:22 +0000 (UTC), Jim Davis
wrote:

Ken S. Tucker wrote:

Which maneuver (engine firing) needed the supplied CM engine
thrust?


The one it was originally intended to fulfil - lifting off from the
surface of the moon.


That is what I read too. It was overengineered by about a factor of 2
when the direct ascent method was the plan.
  #5  
Old October 9th 12, 06:10 PM posted to sci.space.history
Ken S. Tucker[_2_]
external usenet poster
 
Posts: 55
Default Apollo CM engine.

Jeff Findley wrote:
In article , says...
My 1st and lasting impression of the CM engine bell is it was to big.
I do know about the bell size as it relates to use in a vacuum, my
question is why the engine needed the thrust it had?
Seems to me, in all maneuvers, the same impulse would occur with say
1/2 the thrust and 2x the thrust time.
Which maneuver (engine firing) needed the supplied CM engine thrust?


LOI burn?

LOI burn was the "big burn" which needed to be done by the SM. LOI burn
for Apollo 12 was already nearly 6 minutes long. Doubling that to 12
minutes would have done what?

It's been 20+ years since my orbital mechanics class, but my
recollection is that, with all other variables being equal, a burn like
this becomes *less* efficient (in terms of fuel burned) the longer the
burn takes. Since this burn took "33,500 pounds of propellant or about
60 percent - 61 percent of the propellant carried", making the burn less
efficient doesn't sound like a good idea. But I'll have to leave "the
math" to someone who has a better handle on orbital mechanics and has
the time to set this problem up in a proper simulator. I remember that
in 1991, we wrote our own simulation programs in Fortran 77 using a math
library to do the numerical integration. Gee, that was fun... :-P

Here is my source:

http://history.nasa.gov/ap12fj/10day4_loi.htm

The quote below comes right after 081:52:16

Public Affairs Office - "This is Apollo Control at 81 hours,
53 minutes. The spacecraft now traveling at a speed of 4,726
feet per second and about 4,000 nautical miles from the lunar
surface. We have the preliminary figures on the Lunar Orbit
Insertion maneuver, the first of two maneuvers to place the
spacecraft in a more or less circular orbit about the Moon.
The ignition for LOI-1 ignition time will be 83 hours, 25
minutes, 19 seconds. A burn duration will be 5 minutes, 58
seconds, and we'll subtract about 2,880 feet per second from
the spacecraft velocity with that maneuver. In performing
that 5 minute, 58 second burn, the Service Propulsion System
engine will consume about 33,500 pounds of propellant or
about 60 percent - 61 percent of the propellant carried.
The spacecraft currently weighs 96,076 pounds. We estimate
after the Lunar Orbit Insertion maneuver, the weight will
be about 62,491 pounds - the difference in weight, of
course, being accounted for in the propellant consumed
in the burn..."
Jeff


Interesting Jeff, Wiki on the CSM agrees with Jim Davis,
but I think you're also right, in that, the LOI would need
a longer burning and a bit more propellant using a smaller
engine that wouldn't make the hassle of changing motors
worth it.
Wonder if you're same argument is better justified by the
A13 trans Earth burn with the LM attached.
Thanks all.
Ken


  #6  
Old October 9th 12, 07:00 PM posted to sci.space.history
Chris Jones
external usenet poster
 
Posts: 120
Default Apollo SM engine [was Apollo CM engine.]

Note subject correction.

"Ken S. Tucker" writes:

[...]

Interesting Jeff, Wiki on the CSM agrees with Jim Davis,
but I think you're also right, in that, the LOI would need
a longer burning and a bit more propellant using a smaller
engine that wouldn't make the hassle of changing motors
worth it.
Wonder if you're same argument is better justified by the
A13 trans Earth burn with the LM attached.


That burn was performed by the LM descent engine, since the SM engine
(the entire SM actually) was not available.
  #7  
Old October 9th 12, 10:12 PM posted to sci.space.history
Jeff Findley[_2_]
external usenet poster
 
Posts: 1,388
Default Apollo CM engine.

In article , says...

Jeff Findley wrote:
In article ,
says...
My 1st and lasting impression of the CM engine bell is it was to big.
I do know about the bell size as it relates to use in a vacuum, my
question is why the engine needed the thrust it had?
Seems to me, in all maneuvers, the same impulse would occur with say
1/2 the thrust and 2x the thrust time.
Which maneuver (engine firing) needed the supplied CM engine thrust?


LOI burn?

LOI burn was the "big burn" which needed to be done by the SM. LOI burn
for Apollo 12 was already nearly 6 minutes long. Doubling that to 12
minutes would have done what?

It's been 20+ years since my orbital mechanics class, but my
recollection is that, with all other variables being equal, a burn like
this becomes *less* efficient (in terms of fuel burned) the longer the
burn takes. Since this burn took "33,500 pounds of propellant or about
60 percent - 61 percent of the propellant carried", making the burn less
efficient doesn't sound like a good idea. But I'll have to leave "the
math" to someone who has a better handle on orbital mechanics and has
the time to set this problem up in a proper simulator. I remember that
in 1991, we wrote our own simulation programs in Fortran 77 using a math
library to do the numerical integration. Gee, that was fun... :-P

Here is my source:

http://history.nasa.gov/ap12fj/10day4_loi.htm

The quote below comes right after 081:52:16

Public Affairs Office - "This is Apollo Control at 81 hours,
53 minutes. The spacecraft now traveling at a speed of 4,726
feet per second and about 4,000 nautical miles from the lunar
surface. We have the preliminary figures on the Lunar Orbit
Insertion maneuver, the first of two maneuvers to place the
spacecraft in a more or less circular orbit about the Moon.
The ignition for LOI-1 ignition time will be 83 hours, 25
minutes, 19 seconds. A burn duration will be 5 minutes, 58
seconds, and we'll subtract about 2,880 feet per second from
the spacecraft velocity with that maneuver. In performing
that 5 minute, 58 second burn, the Service Propulsion System
engine will consume about 33,500 pounds of propellant or
about 60 percent - 61 percent of the propellant carried.
The spacecraft currently weighs 96,076 pounds. We estimate
after the Lunar Orbit Insertion maneuver, the weight will
be about 62,491 pounds - the difference in weight, of
course, being accounted for in the propellant consumed
in the burn..."


Interesting Jeff, Wiki on the CSM agrees with Jim Davis,
but I think you're also right, in that, the LOI would need
a longer burning and a bit more propellant using a smaller
engine that wouldn't make the hassle of changing motors
worth it.
Wonder if you're same argument is better justified by the
A13 trans Earth burn with the LM attached.


Jim Davis has the history correct. I was just pondering what maneuver
might benefit from the (possibly) over-sized engine that was originally
spec'd. The one that stands out is the LOI-1 burn because of the large
delta-V, large burn time, and large amount of fuel and oxidizer
consumed.

My guess is that since performance was so tight that any change which
made that burn less efficient would have had ripple effects elsewhere.
The performance problems that the program was having was mostly
squeezing the S-II stage and the LEM, since the design of the rest of
the system was (mostly) fixed earlier in the program.

Jeff
--
"the perennial claim that hypersonic airbreathing propulsion would
magically make space launch cheaper is nonsense -- LOX is much cheaper
than advanced airbreathing engines, and so are the tanks to put it in
and the extra thrust to carry it." - Henry Spencer
  #8  
Old October 13th 12, 06:33 PM posted to sci.space.history
Ken S. Tucker[_2_]
external usenet poster
 
Posts: 55
Default Apollo SM engine [was Apollo CM engine.]

Chris Jones wrote:
Note subject correction.

"Ken S. Tucker" writes:

[...]

Interesting Jeff, Wiki on the CSM agrees with Jim Davis,
but I think you're also right, in that, the LOI would need
a longer burning and a bit more propellant using a smaller
engine that wouldn't make the hassle of changing motors
worth it.
Wonder if you're same argument is better justified by the
A13 trans Earth burn with the LM attached.


That burn was performed by the LM descent engine, since the SM engine
(the entire SM actually) was not available.


Yes, the LM descent engine, thrust ~10K#, compared to the ~20K#
the CSM had.
Ken
  #9  
Old November 12th 12, 09:01 AM posted to sci.space.history
[email protected]
external usenet poster
 
Posts: 30
Default Apollo CM engine.

On Monday, October 8, 2012 1:34:27 PM UTC-5, Jim Davis wrote:
Ken S. Tucker wrote:

Which maneuver (engine firing) needed the supplied CM engine
thrust?


The one it was originally intended to fulfil - lifting off from the
surface of the moon.


....Correct. By the time LOR had won out, the SM part of the CSM stack had been pretty much locked into place. To have redesigned it as extensively as switching to, say, a set of smaller engines would have required significantly more $$$ than NASA could afford even with the "Go Fever" funding at the time.

....One thing I can't recall seeing any posts on over the years is whether or not anyone's taken a good draftsman's look at the final design of the SM to see if any hardpoints for mounting the landing gear. With regards as to whether they retained once DA and EOR were dropped, and/or where they were situated and intended to be mounted on the SM. Another little space history mystery that needs to be resolved one day.

[thinks]

....Hmm. "Space History Mysteries". Wonder if I can sell that to the Inbred...er, I mean Hitler...oh, no wait, that's the *History* Channel, right?

OM
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
NASA Administrator Supports Apollo Engine Recovery Doug Freyburger Policy 1 April 1st 12 10:40 PM
Seo , Search Engine Optimizer , Seo Search engine Optimization , search engine optimization services, SEO Consulting Se0 Guy Amateur Astronomy 0 December 25th 07 09:33 PM
Conversations with Apollo Podcast Episode 4 - Apollo Team Support, David A. Ballard [email protected] Policy 0 September 5th 07 08:29 PM
Nexus Rocket Engine Test Successful; 10 Times More Thrust Than Deep Space 1 Engine and Lasts 3 Times Longer (10 years) [email protected] Technology 5 December 30th 03 08:44 PM
Apollo 13 - Midcourse Corrective Burn with LM Engine Richard Brideau History 5 September 7th 03 10:17 PM


All times are GMT +1. The time now is 12:30 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.