Author Topic: Apollo Q&A  (Read 150649 times)

Offline brickmack

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Re: Apollo Q&A
« Reply #320 on: 12/25/2016 03:43 AM »
The Wikipedia article on Apollo 8 mentions that the SPS engine needed 'coating' (edit: with a short burn)
or it could explode in a long burn.
Is that right? I don't recall reading that anywhere else and variants of that engine (which may differ a lot, I've no idea) are used on various rockets and spacecraft.

Not been able to find any sources mentioning that (and the citation in the wiki article doesn't mention it either)

Offline the_other_Doug

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Re: Apollo Q&A
« Reply #321 on: 08/27/2017 03:17 AM »
The Wikipedia article on Apollo 8 mentions that the SPS engine needed 'coating' (edit: with a short burn)
or it could explode in a long burn.
Is that right? I don't recall reading that anywhere else and variants of that engine (which may differ a lot, I've no idea) are used on various rockets and spacecraft.

Sorry for the really late response.

This story is told in the excellent work "Apollo" by Murray and Bly-Cox.  As the story goes, on Apollo 8, it came out that the combustion chambers of a couple of test SPS engines had failed when they were started with both banks open prior to having been fired after assembly.

It was decided that a short burn on one bank (*) was needed to "wet" (not "coat") the SPS combustion chamber before it was safe to commit to a long two-bank burn, like the lunar orbit insertion.

Since you couldn't guarantee you would need a mid-course correction on the way out to the Moon, you couldn't guarantee you would have a chance to perform a "chamber wetting" burn.  So they had to plan in a combination S-IVB sep maneuver and a counter-maneuver (to undo the first one) to make certain they got the one-bank burn they needed to wet the chamber.

Borman was apparently quite irate about this, but it needed to be done.  On later flights, they got around the issue by starting the first two-bank burn on one bank for several seconds, letting the chamber pressures steady out, and then bringing in the second bank.  But as of the Apollo 8 timeframe, it wasn't clear that this was a safe alternative.  Additional flight experience with the engine proved it safe -- including that gained on Apollo 8.

(*) -- The SPS engine had redundant fuel and oxidizer flow plumbing, down to separate symmetrical sets of injection ports, called Banks A and B.  Each bank was configured to be connected to separate sets of fuel and oxidizer tanks, but the tank-to-bank plumbing was, ISTR, flexible and could be cross-connected.  Each bank had separate sets of valves.  The idea was, if you lost one bank, you could fly the mission completely nominally on the other bank.  Of course, if you were down to one bank, you might be no-go for LOI just on the basis of the one-more-failure rule...
-Doug  (With my shield, not yet upon it)

Offline the_other_Doug

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Re: Apollo Q&A
« Reply #322 on: 08/27/2017 03:30 PM »
A good example of the possibility of the "one more failure" rule making an Apollo mission no-go for LOI just occurred to me -- Apollo 15.

Right after they separated the CSM from the S-IVB and docked with the LM, the 15 crew noticed a light had come on that shouldn't have -- the SPS thrust light.  That light indicated that the SPS was burning, when it wasn't.  By manipulating the various switches and circuit breakers both upstream and downstream of the circuit that lit the SPS thrust light, they were able to determine that there was a short in the upstream leg of the thrust switch (a backup means of starting the engine -- they could, with the right configurations, have started the engine just by flicking that one switch).  The short only led into the Bank B wiring, through what was called the Entry Monitoring System (EMS), a secondary system of accelerometers that was primarily used during entry for a control mode called "riding down the G's", to be used if the primary (CMC) and secondary (SCS) systems went out.

The upshot of it was that, when the engine was completely armed (i.e., the pilot valves were opened), Bank B would open up and start the engine before the computer commanded it.  But the wiring into Bank A was fine.  So, they ended up doing all of their two-bank burns by disarming Bank B, starting the engine normally under computer command, then bringing Bank B on by opening its pilot valves.  And about 10 seconds before the commanded end of the burn, they would disable Bank B.

Had the short circuit been in a different spot and Bank B been completely disabled, they were indeed looking at a mission rule that would have made them no-go for LOI.  It was a huge sigh of relief when they discovered that the glitching bank was still usable, and just required a small change in procedures for near-nominal engine firings.  And had Bank A gone out, Bank B was still quite usable; it just required a manual start and stop, something the crew proved they could do when they tested Bank B with an "SPS test" that was actually a mid-course correction maneuver... hit it manually, operating just the pilot valves via their circuit breakers, to within a tenth of a foot per second.

All that said, I imagine Dave Scott would have argued strenuously for a relaxation of the rules, so he and his crew could be allowed to proceed with the mission.  After all, it was Dave who, during Apollo 16, was in the MOCR arguing strenuously with Jim McDivitt that 16's degraded SPS secondary control mode was good enough to serve as backup, to allow that mission to move forward to a landing.  And he had a lot more skin in the game on 15 than he did sitting on the ground nine months later... ;)
« Last Edit: 08/29/2017 03:57 PM by the_other_Doug »
-Doug  (With my shield, not yet upon it)

Online envy887

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Re: Apollo Q&A
« Reply #323 on: 09/19/2017 05:51 PM »
I would like to know about the micrometeoroid impact probability and the dangerous physical phenomenons the astronauts where exposed to (cosmic rays, radiation, etc).

Lots of people argue that we never went to the moon because of these things... I have no doubt we went to the moon, but would really like to know more about this since I know nothing...

The quick and dirty summary:

Van Allen belts - occurred soon after TLI and soon before entry, so velocity was still relatively high (passed through belts quickly); during outbound leg crew was confined to the (relatively) better shielded CM to minimize exposure.

Solar flares - just plain lucky that one didn't occur during an Apollo mission. There was one observed flare (between 16 and 17, I believe) that would likely have killed a crew had there been one up at the time.

Cosmic rays - crew undoubtedly took doses; effects minimized due to short missions.

Micrometeoroids - odds of impact very low over mission duration.

Bottom line is that future missions will still need to get crews through the Van Allen belts quickly (rules out low-thrust propulsion for crew) and will need better shielding for long-duration surface stays.

Re. the Van Allen belts: the Apollo TLI trajectory was quite inclined, and passed over the highest radiation parts of the belt which are more equatorial.

http://www.braeunig.us/apollo/apollo11-TLI.htm
« Last Edit: 09/19/2017 05:52 PM by envy887 »

Offline Ronpur50

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Re: Apollo Q&A
« Reply #324 on: 01/01/2018 10:31 PM »
From Apollo 17:  Does anyone know what type of material was used to protect the CSM as shown in this photo?

Offline Darren_Hensley

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Re: Apollo Q&A
« Reply #325 on: 01/02/2018 05:29 PM »
Looks like the prototype for fiber reinforced vulcanized silicone rubber based canvas. We used the newer stuff on Frame Supported Tensioned Fabric Shelters (FSTFS) in the 90' USAF Harvest Falcon assets, The Army used it for Clamshell shelters of various sizes. Can be sewn like heavy canvas, Bonded like roof membranes or fluid bladders, and seems to last for many decades. It can be vacuum molded over simple shapes to give better protection on smaller objects. It remains flexible in cold weathers, and wont loose its shape in hot weather, fairly chemical resistant and repels water like a Ducks back. Great stuff.
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Offline damnyankee36

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Re: Apollo Q&A
« Reply #326 on: 01/03/2018 06:54 PM »
I found it interesting when I discovered a while back that this cover was left installed throughout the trip to the pad.  What was the reason for this?

I suppose it was removed after the MMS was in place?

Offline Jim

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Re: Apollo Q&A
« Reply #327 on: 01/09/2018 12:29 AM »
I found it interesting when I discovered a while back that this cover was left installed throughout the trip to the pad.  What was the reason for this?

I suppose it was removed after the MMS was in place?

No, not really

Offline the_other_Doug

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Re: Apollo Q&A
« Reply #328 on: 01/09/2018 06:15 PM »
The Apollo SM and BPC were really not designed for extended exposure to the elements.  Since the stack would be rolled out to the pad a month or more prior to launch, and the MSS was not a perfect weather covering, putting a big canvas wrap over the whole thing was a cheap outside-layer weatherproofing system that was easily removed a day or two prior to launch, and partially removed and replaced at need during launch prep on the pad.

Especially after Apollo 6 had problems with rainwater incursion into the honeycomb SLA panels, it became obvious that any panels designed to be opened up (even while only on the ground) or separated, either on the rocket or the spacecraft, could only be designed to be weatherproof to a given point.  For example, the BPC had to have pieces that could be removed and replaced -- not just the BPC hatch, but also fuel/drain ports for the CM RCS system and other interfaces that you needed to access underneath the BPC, while the stack was on the pad.  The BPC leaked *buckets* in the rain for the first five or six manned launches.  In the worst case, the Apollo 12 crew recalled seeing water running down the outsides of all the windows during the final count, and Conrad during the debrief described sheets of water coming down along the windows, and freezing in place, at BPS/LES jettison.

Finally, more than one astronaut became concerned about the minus-X SM RCS thruster bells getting filled with rainwater during final count rain showers.  Their concern was that such water could turn to ice in orbit and block the combustion chambers long enough to deform or degrade them.  Conrad was certainly concerned about it on Apollo 12, after their wet (and eventful) launch.

While the engine bells were stainless steel, IIRC, I doubt it was good for the operational lifetime of those thrusters to sit on the pad, filled with rainwater with salt sea breezes blowing past...  ???

edit -- corrected my butchered acronym.  Thanks, Jim!
« Last Edit: 01/09/2018 07:35 PM by the_other_Doug »
-Doug  (With my shield, not yet upon it)

Offline Jim

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Re: Apollo Q&A
« Reply #329 on: 01/09/2018 06:56 PM »
It is MSS

Offline S.Paulissen

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Re: Apollo Q&A
« Reply #330 on: 01/11/2018 11:47 PM »
Because computational power isn't really what makes spaceflight (and moon landings) hard.
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Re: Apollo Q&A
« Reply #331 on: 01/11/2018 11:47 PM »
Human in Circuit

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Re: Apollo Q&A
« Reply #332 on: 01/11/2018 11:52 PM »
More tolerance for risk in the 60's since it was literally a race with the Soviet Union. The moon landings had a much higher chance for loss of life than what would be tolerated today.

Offline edkyle99

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Re: Apollo Q&A
« Reply #333 on: 01/11/2018 11:55 PM »
Funding.  It was essentially unlimited for a time during the early to mid 1960s.   Apollo was a national priority, like the Manhattan project and the ICBM and SLBM development efforts.  Guidance and flight control was important back then, of course, but propulsion was the real key to the program.  They spent tons of money on F-1 and J-2 and the Apollo and Lunar Module propulsion systems.  Elon Musk recognized the importance of propulsion too, which is why his company devoted so much effort to Merlin engine development from the day it opened for business.

 - Ed Kyle
« Last Edit: 01/12/2018 12:02 AM by edkyle99 »

Online MATTBLAK

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Re: Apollo Q&A
« Reply #334 on: 01/12/2018 12:05 AM »
Supersonic retro propulsion in a thick atmosphere hadn't really been tried before SpaceX had a go. There were concepts in the 1950s and 60s for reusable rockets, but you would have had to sacrifice a fair bit of payload to do it, and 1960s era computing couldn't really keep up with the dynamics of it. 1950s, 60s and 70s rockets were all about maximizing the payload, not the reusability. Piloted vehicles like the X-15 used 'the human computer' to control a high speed reentry and landing. And in the Shuttle era, multiple redundant computers, fly-by-wire and humans controlled a very high speed atmospheric reentry and landing sequence.

And as for Apollo; there was no 'supposedly' about it. Check out several good books on the Apollo computing systems, including:

https://www.amazon.com/Apollo-Guidance-Computer-Architecture-Operation/dp/1441908765

and:   https://www.amazon.com/Apollo-Flew-Springer-Praxis-Books/dp/1441971785/ref=pd_sim_14_1?_encoding=UTF8&pd_rd_i=1441971785&pd_rd_r=N3GMQV91VEZZHTYDXYS0&pd_rd_w=FZqsX&pd_rd_wg=6nbzF&psc=1&efRID=N3GMQV91VEZZHTYDXYS0

Once out of the Earth's atmosphere and most of it's gravitational influence, it was really all about rates, changing those rates and 'delta-v', and careful and timely application of rocket thrust and propellants. Most of the math was done on the ground ahead of time - courses and trajectories, velocities etc. People like Kraft Ehricke, Von Braun, John Houbolt, Katherine Johnson and a whole host of others building on work started by Konstantin Tsiolkovsky - these guys worked out the overall math long ago.

The onboard computers for Apollo worked as live updaters for state vectors and navigational inputs from the Astronauts and mission control. The CSM essentially navigated by way of stellar coordinates with updates manually input by Astronauts to align with as needed those parameters already programmed aboard. The Apollo computers had very little erasable memory by modern standard and the related systems had to be realigned frequently. And all figures, changes and movements were checked by the ground constantly. The LM computer was tied closely to it's landing and rendezvous radar, updating expectations all the time. A glorified 'number cruncher'? Partly. Apollo LM crews flew the final descents themselves.

Elon Musk and his team are to be applauded for raising the state of the art and what is possible.
« Last Edit: 02/11/2018 03:51 AM by MATTBLAK »
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Offline AS-503

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Re: Apollo Q&A
« Reply #335 on: 01/12/2018 12:10 AM »
The 1960s landings are all that more impressive when done with a digital calculator's computing power! Don't you want a seat?  8)

With regard to Elon and his "super computers" only being able to launch and land recently, I have a feeling you have no idea what this feat actually represents.

Your post seems less like a real question and more like an un-informed statement from your incredulous position of not understanding the bigger picture.
« Last Edit: 01/12/2018 02:40 AM by Chris Bergin »

Offline jeffreycornish

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Re: Apollo Q&A
« Reply #336 on: 01/12/2018 12:11 AM »
But I can sum up the marvel that was the Apollo program in two phrases:  National Will, Large Budget.

At it's peak NASA's budget was 5% of the US Government's expenditures.. https://en.wikipedia.org/wiki/Budget_of_NASA
In 1966 NASA's total budget was $5.9 Billion dollars. That is $42 billion dollars in  2017 dollars.
Today NASA's budget is only $19 Billion (.5% of the US Government budget) , with Manned Spaceflight (mainly the Space Station and the Space Launch System) taking up a lot of that.

National Will.  If you would love to go to the Moon, you might ask your friends, coworkers, and family if they would be interested, and they might say yes.  Then ask them if they would be willing to pay more in taxes, and you will find that a lot of people just aren't interested.  Apollo came out of JFK's 'We choose to go to the Moon by the end of the decade' speech.

If he hadn't been assassinated there would have been no focus, and plenty of reasons to put those billions of dollars towards other things.

Going to the Moon is exactly like driving across town--hear me out.

Okay, I ask you if you'd like to drive across town, or to another city. and you say "Sure! I've never been there before!"

Here's the catch.  We don't have a car.  We will have to build one, and there are no car dealers, or even car parts stores.  So, could you build a car? 

sure you could!  First you need are wheels, and we want to make them out of rubber, and steel.  So you have to go make rubber, and steel.  And you need an engine that you are going to have to build yourself.  And Gasoline, so you are going to have to make that.

Pretty big task.  That's what the Army/Navy/Airforce rocket programs started out doing (with a V2 and some scientists from Germany post WWII).  Look at the history of rocketry, and the engines and the fuels.  there were competing programs (Vanguard was perferred over the German lead Explorer/Redstone rocket team, but Vangard blew up on the pad, so the Explorer team launched the first US Orbital rocket)

Next NASA was formed and worked out a plan to address all of the unknowns.  Mercury proved a man could be launched into space.  Gemini worked on navigation and longer duration flight.  Apollo was the culmination of all of that work

in  1958 NASA was formed and the programs that the military had been working on were put under it's control.  (in the car analogy we had some wheels, and some engines that would get us a block away, but nothing that could go across town)

So NASA worked out what needed to be developed.  strong lightweight metals, high energy fuels, reliable control systems

after a decade of work and billions of dollars invested (spent is the wrong word here, there was nothing to 'spend' anything on) Apollo 11 landed on the moon.

But is was already over.  Apollo 18, 19 and 20 had already been cancelled.  After Apollo 17 the of remaining Saturn V rockets one was used to launch Skylab and the rest became museum pieces, rotting away.

So, what is going to the Moon worth to you.  How much would you be willing to invest/spend?

« Last Edit: 01/12/2018 02:40 AM by Chris Bergin »

Offline su27k

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Re: Apollo Q&A
« Reply #337 on: 01/12/2018 01:10 AM »
Also SpaceX is not the first to launch and land a rocket, DC-X did it in 1993, using a F-15 flight computer.

Offline Rocket Science

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Re: Apollo Q&A
« Reply #338 on: 01/12/2018 02:00 AM »
It was not the first attempt, it was incremental with 7, 8, 9, the dry run on Apollo 10 and landing on Apollo 11...
« Last Edit: 01/12/2018 02:39 AM by Chris Bergin »
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Offline Chris Bergin

Re: Apollo Q&A
« Reply #339 on: 01/12/2018 02:46 AM »
I had to get rid of the OP of the Moon Landing thread as he was given a chance, but his second post made me totally suspect he was a hoaxer. Not having any of those types on here. Saved the responses, removed quotes of his posts and merged them into here :)

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