Back-up plan for Apollo

[Nowhere Man]

Just in case the Saturn V wasn't ready in time.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770078693_1977078693.pdf

Documents like these are really hard for Apollo-was-a-hoax believers to explain away except with "Obvious fake!" or "LA LA LA LA I CAN'T HEAR YOU!"

Fred

[Donnie B.]

Very cool document.  It took me a bit of reading to realize what was being proposed -- launching a complete CSM-LM stack unmanned on a non-man-rated Saturn V, and doing an earth-orbit rendezvous using a whole second manned "ferry" CSM launched on a Saturn 1B.  That CSM would be abandoned in orbit (or deorbited empty) after the crew transferred to the CSM-LM stack and headed for the Moon.  If anything went wrong with the rendezvous they would perform an alternate earth-orbit mission and return to Earth in the ferry CM.  Wowsers!

One little detail wasn't clear to me, and maybe hadn't been considered in this preliminary study.  A docking drogue would be used to dock the lunar and ferry CMs nose-to-nose for the crew transfer.  But which vehicle would carry the drogue?  The manned CSM would require an LES (escape rocket) so you couldn't have the drogue attached to that CM's nose.  The unmanned stack would be launched without an LES to increase the propellant load in the S-IVB (for longer duration in Earth orbit), so it could carry the drogue -- but that would cancel the advantage of eliminating the LES to some extent at least.  Besides, their drawings show the drogue on the ferry CM, not the lunar CM.

Maybe the drogue would have been carried on top of the S-IC, and the ferry CM would pick it up -- something like the way the lunar CMs picked up the LM after TLI.  Or were they actually considering launching the crew in a CM with a drogue and no LES?  Somehow I don't see that as being too popular with the astronaut corps.

[George Tirebiter]

Maybe the drogue would have been carried on top of the S-IC, and the ferry CM would pick it up

I would assume this to be the case, since that arrangement was eventually used for the ASTP docking adapter.

[Glom]

Maybe the drogue would have been carried on top of the S-IC, and the ferry CM would pick it up -- something like the way the lunar CMs picked up the LM after TLI.  Or were they actually considering launching the crew in a CM with a drogue and no LES?  Somehow I don't see that as being too popular with the astronaut corps.

Not likely since the S-IC would have been dropped long before reaching orbit and the Saturn IB didn't even have a S-IC stage.  I presume you meant S-IVB.

Combining the complication of Earth Orbit Rendezvous with the complication of Lunar Orbit Rendezvous is something we're pretty sure would be a mission mode now.  Seems like they were thinking of it in the most wasteful way though compared to pure EOR.

And of course CM on CM action would upset certain people.  Look at the trouble Gene Cernan got into for saying a naughty word.

[Donnie B.]

Maybe the drogue would have been carried on top of the S-IC, and the ferry CM would pick it up -- something like the way the lunar CMs picked up the LM after TLI.  Or were they actually considering launching the crew in a CM with a drogue and no LES?  Somehow I don't see that as being too popular with the astronaut corps.

Not likely since the S-IC would have been dropped long before reaching orbit and the Saturn IB didn't even have a S-IC stage.  I presume you meant S-IVB.

Yes, I did.  Must have been a glitch in the matrix there... 

And of course CM on CM action would upset certain people.  Look at the trouble Gene Cernan got into for saying a naughty word.

Hard core docking?

One thing this document underlines is the difficulty and criticality of achieving man-rating status.  The whole concept relies on the availability of the Saturn V, fully functional but not quite reliable enough for people to ride on.

[raven]

Not to mention, if I am reading it right, the SIVb would have to be man rated, even if the first two stages weren't.

[Glom]

Not to mention, if I am reading it right, the SIVb would have to be man rated, even if the first two stages weren't.

Easier to achieve. The Saturn IB was man rated for Apollo 1.

[ka9q]

I've heard the expression "man rated" many times but I still don't know what it really means.

Does it mean a probability of mission failure less than some threshold?

Or does it mean a probability of killing its crew that's less than some threshold?

[Donnie B.]

I've heard the expression "man rated" many times but I still don't know what it really means.

Does it mean a probability of mission failure less than some threshold?

Or does it mean a probability of killing its crew that's less than some threshold?

Well, there's this: http://nodis3.gsfc.nasa.gov/displayDir.cfm?Internal_ID=N_PR_8705_002B_

[ka9q]

Well, there's this: http://nodis3.gsfc.nasa.gov/displayDir.cfm?Internal_ID=N_PR_8705_002B_

Typical NASA bureaucratese - awfully verbose for what it actually says.

Most of it is circular and therefore rather meaningless: "human-rating is making a system safe for humans". The one specific requirement I do read into it is for features to protect and recover the crew even after serious failures that otherwise prevent mission completion.

For the Saturn/Apollo system, these would include a) the launch escape tower and b) the Emergency Detection System (EDS) active during first stage flight. It would also include the related operational considerations of flying a trajectory such that survivable abort options always exist were one or more engines to fail or go "hard over" (experience a steering actuator failure).

By this definition, I'd say the Shuttle never achieved a human rating, mainly because it was never designed to have one. Neither would the Aries I have been human-rated, because certain credible failures (notably a SRB breach during first stage flight) would have been unsurvivable even with an escape tower; the parachutes would have been burned up by flaming chunks of propellant.

The Saturn V also had considerably wider operating margins than most launchers. It could (and actually did) lose engines at certain points in flight and still achieve its mission. Few unmanned launchers even come close.

[ka9q]

Let's see...the partial failures I'm aware of during Saturn launches include:

Apollo 6 - premature shutdown of two J-2s during S-II flight, failure of S-IVB J-2 to re-ignite. Mission was still a partial success, and had it flown with a crew they would likely have been recovered.

Apollo 13 - premature shutdown of center J-2 during S-II flight. Still reached nominal cutoff targets and performed TLI.

Skylab I - second-plane separation failure (the interstage ring between the S-IC and S-II failed to jettison 30 seconds after staging). Payload still achieved nominal orbit. (Problems with micrometeroid shield and solar array were unrelated to Saturn V performance.)

I can't think of any Saturn IB failures, manned or unmanned - were there any?

[raven]

Not to mention, if I am reading it right, the SIVb would have to be man rated, even if the first two stages weren't.

Easier to achieve. The Saturn IB was man rated for Apollo 1.

Still must have been a process in itself considering it not only had to work, it had to work twice with perfect reliability or there would be no mission.

[ka9q]

The mission itself would have been quite a challenge. If the Saturn V were launched first, its S-IVB would have to wait some time for the the Saturn IB to bring the crew.

The S-IVB in an Apollo parking orbit had a very short life; the altitude was kept extremely low so as to avoid wasting propellant that would be better used for TLI, and the cryogenic propellants boiled off so quickly that the hydrogen had to be continually vented. In fact, the hydrogen vents were used to provide a little thrust to help compensate for the drag of the low parking orbit. Obviously it couldn't endure that for very long and still make it to the moon. Each operational lunar mission had only two opportunities for TLI, otherwise the S-IVB wouldn't have enough propellant left.

[raven]

Fascinating. This what I love about these forums, I always learn something. 

[ka9q]

To illustrate why first going into a parking orbit costs energy over a direct escape trajectory, consider the following thought experiment.

Imagine that the earth, instead of being a solid/liquid sphere, consists of a thin hollow shell with the earth's diameter plus a infinitesmal black hole at the center containing the earth's entire mass. The space between the shell and the black hole is a vacuum.

Imagine strapping a rocket on your back, opening a trap door in the earth, and jumping in. You do this from the equator so you start with the earth's eastward equatorial velocity of 465.1 m/s.

About 15 minutes later you would reach periapsis with the black hole at a radius distance of a little over 11 km, moving tangentially at a little over 268 km/sec.

Now you fire the rocket on your back in a prograde direction (to boost your velocity). It's a really puny one, with a delta-V of only 233 m/sec.

As you climb away from the black hole on your return to the surface, you will of course slow down again.  Assuming you have planned ahead and made arrangements for someone to open a trap door for you in the proper location, you will fly through it with a velocity of 11,186 m/sec - the earth's surface escape velocity.

You will then fly off into space, never to return.

Imagine -- escaping from the earth entirely with a delta V of only 233 m/sec. If you wanted to remain in orbit, you'd need even less.

What this really says is that the most energy-efficient way to escape the earth is on a hyperbolic trajectory with a perigee as close to the earth's center as possible. Since, sadly, the real earth is unreasonably dense even if not completely solid, you will have to fly a less energy-efficient trajectory from your surface launch site to your departure hyperbola, joining it at the first post-perigee point above the amosphere. Your subterranean perigee is then of no consequence since you won't be coming back to fly through it. But if you are required to complete one or more parking orbits before departure, then a subterranean perigee is a definite problem. You'll have to spend some of your launcher capability on raising it to a safe level -- capability you would have preferred to spend on raising your apogee.