The official audio Record of Apollo 11

[Tedward]

I might add in that sticking around, you read some of the previous topics. I have ingested so much information reading the replies here my brain implodes (what there is of it). Someone challenges and the replies are so informative it is most enlightening to human kinds abilities.

[scooter]

I just watched the "Moon Machines" series on YouTube, another great piece highlighting not only the amazing technical leaps but also the folks directly involved in the challenges of developing the hardware and processes. Five stars for sure!

[Kiwi]

...I  also read that the heat shield on the command module was designed to melt away during reentry this seems odd since today heat shields are not designed to melt but just the opposite...

Dakdak, have you considered the faster Earth entry speeds of the manned lunar missions, compared with earth orbital missions of Apollo and the Space Shuttles, and thought about whether the faster speeds might require a different heat shield?  You might find that the Shuttle and it's protective tiles would have burnt up if it re-entered at the slowest Apollo lunar mission's speed, that of Apollo 17.

I don't have entry speeds of the Shuttles and leave it to you to find them, but the following link in the Apollo By the Numbers series gives figures for the Apollo missions:
http://history.nasa.gov/SP-4029/Apollo_18-40_Entry_Splashdown_and_Recovery.htm
and I show the mph conversion for the slowest and fastest figures.

Earth Orbit Mission -- Earth entry velocity
Apollo 7 -- 25,846.4 ft/sec -- 17,622 mph
Apollo 9 -- 25,894 ft/sec

Lunar Mission -- Earth entry velocity
Apollo 8 -- 36,221.1 ft/sec
Apollo 10 -- 36,314 ft/sec -- 24,759 mph -- over 7,000 mph faster than Apollo 7
Apollo 11 -- 36,194.4 ft/sec
Apollo 12 -- 36,116.618 ft/sec
Apollo 13 -- 36,210.6 ft/sec
Apollo 14 -- 36,170.2 ft/sec
Apollo 15 -- 36,096.4 ft/sec
Apollo 16 -- 36,196.1 ft/sec
Apollo 17 -- 36,090.3 ft/sec

[Not Myself]

I don't have entry speeds of the Shuttles and leave it to you to find them

I would guess that it is pretty similar to the Apollo 7 and 9 missions - the braking power applied to de-orbit is pretty minimal, isn't it?

[Valis]

17,500 mph is given as a "typical" figure for Shuttle here: http://www.grc.nasa.gov/WWW/BGH/hihyper.html

[Not Myself]

17,500 mph is given as a "typical" figure for Shuttle here: http://www.grc.nasa.gov/WWW/BGH/hihyper.html

OK, and the Wikipedia page claims that the braking applied to de-orbit slowed the shuttle down by about 200 mph.  Then given the loss of altitude, it may be possible that the re-entry speed was actually higher than the orbital speed, I haven't run the numbers.

ETA - specifically, this Wikipedia page. http://en.wikipedia.org/wiki/Space_Shuttle

[scooter]

The shuttle would accellerate at a very slowly increasing rate as it descends after the deorbit burn, but entry interface at it's high (and banked) AOA puts a stop to that. Orbital mechanics say that the maximum orbital speed would be at periapsis, where vertical speed and horizontal Delta_v has dropped back to zero. (edit...this is only in a vaccuum, descending into the atmosphere changes everything)

I recollect seeing a report in the shuttle reentry profile, it talked about the tradeoffs between shorter reentry profiles, where high dynamic surface heating is the problem, vs longer profiles, where heat soak into the structure becomes an issue.  The operational reentry profile was a very carefully designed compromise.

[Not Myself]

I recollect seeing a report in the shuttle reentry profile, it talked about the tradeoffs between shorter reentry profiles, where high dynamic surface heating is the problem, vs longer profiles, where heat soak into the structure becomes an issue.  The operational reentry profile was a very carefully designed compromise.

OK, this is interesting stuff.

Purely speculative here, I haven't studied these things, but I would guess you would want to use all the fuel you've got for the re-entry burn, to get your velocity down as low as possible?  (After all, what are you going to do with it, if you don't burn it.)  So you need to come in at the right angle, and you also need to time it so that your landing spot has rotated to be approximately underneath you when you reach the ground (and you also need to be at the right latitude).  So I am wondering, if you are in a moderately eccentric orbit, there may be reasons to do your re-entry burn at a time other than immediately before you take the plunge.  Might you even want to do it while your altitude is increasing?

Just thinking out loud here, some of these thoughts may be rubbish.

[scooter]

The Shuttle did it's deorbit butn over the Indian Ocean, roughly half an orbit before landing. The capsules of the earlier programs did them significantly later, and much closer to their desired ocean landing points. They had solid motors of fixed total impulse which have them a more significant, but still precise, decelleration (when burned in a precise vector). The shuttle, with it's significant lift, could make a longer, and less rigouous, decelleration through the atmosphere. It also had less g tolerances, so couldn't withstand the higher decelleration (g) forces experienced by the earlier capsules. Apollo was something of a "lifting body", so it could do a "double dip" reentry coming back from the Moon, with some ability to control it's descent rate through the upper atmosphere. It was actually a gentler (and longer) reentry than experienced in Mercury and Gemini.
The shuttle did it's deorbit burn to get it's periapsis to a certain level at a certain point, and burned just enough to get it to that orbital configuration . After that, there was an "OMS fuel dump" to discard some excess OMS fuel and adjust it's weight and balance for reentry.

It's still magic to me how it's done so precisely, but that's what makes spaceflight so interesting.

[Bob B.]

The Shuttle deorbited from a variety of orbits depending on the mission it performed, thus there is no single answer regarding the magnitude of the deorbit burn, the velocity at entry interface, etc.  However, I can provide an example to give an idea of the velocities we're dealing with.  According to the STS-1 pre-flight mission plan, the Shuttle was to deorbit from a 150 nautical mile circular orbit.  The planned delta-V of the deorbit burn was 299 m/s.  After the burn the Shuttle's orbit would be 149 n.mi. X 2 n.mi.  This orbit has an apogee velocity of 25,121 ft/s (17,128 mph) and a perigee velocity of 26,200 ft/s (17,864 mph).  The velocity at entry interface (400,000 feet altitude) is 25,729 ft/s (17,542 mph), and the entry angle is -1.19 degrees.  The velocity would continue to increase for a time after interface until drag started to slow the Shuttle down.  I don't have the data to tell me what the maximum velocity was, though I would guess it wasn't more than about 100 m/s higher than the interface velocity.  The actual flight data varied somewhat from the pre-flight plan, though not by much.

[Not Myself]

OK, interesting stuff.

My first thought was, "use all the fuel to slow down as much as possible", but if the change in velocity is 300 m/s relative to an orbital velocity of roughly 26,000 fps, we're talking about a whopping 0.15% decrease in kinetic energy.  So more effective than pissing out the window to slow down, but not by too much - sounds like it is the atmosphere doing almost all of the work.

[Bob B.]

The Shuttle did it's deorbit butn over the Indian Ocean, roughly half an orbit before landing.

My previous calculations appear to agree with this.  Based on the example, entry interface is crossed at a true anomaly of 276.7 degrees, i.e. 96.7 degrees past apogee and 83.3 degrees before perigee.  If the deorbit burn is performed over the Indian Ocean, entry interface would then be crossed somewhere over the middle of the Pacific Ocean.  Of course, entry interface is just the beginning of the atmosphere.  The Shuttle would travel considerably further before maximum deceleration occurs.

[Bob B.]

My first thought was, "use all the fuel to slow down as much as possible"

The deorbit burn is used to lower the perigee to a point deep inside the atmosphere so that drag can then be used to slow the spacecraft.  As you correctly figured out for yourself, the deorbit burn contributes almost nothing to decreasing the spacecraft's kinetic energy.  The burn is designed more to get the entry angle right for an optimal reentry.

[VincentMcConnell]

When Apollo 11 blasted off from Kennedy space center Neil Armstrong was clearly heard saying Houston we have a roll program. And that has been standard ever since. Of course if you watch the extremely edited versions of  any Apollo  liftoffs now the massive Saturn V rockets are silent. How is this possible?

The microphones used by the Apollo astronauts were designed to only pick up immediately close sound. You'd be lucky to hear much engine noise and Neil was pulling only a few G's. The average human can easily withstand 3G's for quite a bit of time. The Saturn didn't give them much more than that. Besides, Neil was one of the best astronauts in the whole program. Hell, look at his work on Gemini 8. That guy was a BOSS. A few G's is nothing for the astronauts and most of the vibration on the Saturn was attributed to its "gimballing" engines. That means that you'd feel a lot of movement, but not necessarily notice it being carried over to your voice.

I  also read that the heat shield on the command module was designed to melt away during reentry this seems odd since today heat shields are not designed to melt but just the opposite.

Yes, the heatshields were actually designed to melt away. This allowed the heat to be absorbed, save weight for the chutes and work as a more efficient method of keeping the 3000 degree flames safely confined. I'm sure the exact technicalities could be researched. Hey, that's a good word. You should try it!

Finally,Were the large inflatable balls and the orange float on the bottom of the command modules already on the command module?

Yes, they were on the CM already. When the CM hit the water, they pulled a breaker to detach the parachutes and then another to deploy those inflatable bags. Actually, those bags were the reason Apollo 11 got righted from "stable II" to "stable I". Would you have guessed it? NASA actually thought ahead to give them inflatable bags. LOL. What's your point here?

[ka9q]

I've seen Apollo deniers seriously arguing that the Apollo missions were fake because they didn't hear enough stress and noise in the commander's voices to suit their expectations. For "proof" they show a cockpit video of a shuttle launch -- a totally different beast than a Saturn V with totally different acceleration-vs-time, noise-vs-time and vibration-vs-time curves.

Both vehicles were pretty rough from liftoff to tower clear because of ground reflections and tower strike avoidance maneuvers (e.g., the Saturn's yaw maneuver), but the parallel-staged Shuttle had a very different acceleration profile than the serially staged Saturn V. The Saturn V lifted off the pad very slowly - barely more than 1 g, but peaked (twice) at 4g during S-IC flight: first at inboard shutdown and again at outboard shutdown. The S-II and S-IVB stages were considerably smoother and gentler, their H2/O2 engines optimized for high Isp rather than the high thrust (but low Isp) of the S-IC's F1's.

In fact, with full propellant loads the S-II and S-IVB upper stages gave initial accelerations of less than 1 g -- the astronauts weighed less than they had while waiting for launch!

So if you listen to an Apollo launch, you will note that the air-to-ground channel is pretty quiet throughout first stage flight, with just the commander's brief acknowledgements of abort mode changes. If they do say anything near the end of S-IC flight, you will hear it in their voices. They all become far more talkative after staging when things settle down to a far easier ride. Their abort options also become far less critical once they're out of the atmosphere.

The Shuttle, on the other hand, is especially loud and violent during early SRB burn and MaxQ (solids are very turbulent), tapering to near silence as the stack reaches vacuum even before the SRBs burn out. But unlike the Saturn where the peak loads were at the end of first stage flight, the highest Shuttle g-loads come toward MECO as the external tank steadily empties; the engines are actually throttled back to limit those loads to 3g's. But even though the acceleration late in a Shuttle launch is considerably than that of the Saturn V late in its boost, both rides are pretty smooth and quiet.