Black Zones – time out for Q&A

I have really appreciated all the questions and comments to my mini-series of blogs on Black Zones.  I am not done with the series yet, but I thought it was time to address some of the questions and comments.

First of all, not to be too grumpy, but I have to set a couple of new blog comment rules.  I have received a number of comments that are frankly undecipherable.  They are either written by non-English speakers or some type of computer program that strings together English words at random.  So my rule is if the comment is unintelligible and/or the grammar and spelling are so bad that most readers could not understand them — I won’t post them.  Clear enough?  My grammar and spelling aren’t perfect and I won’t hold you to perfection either, but it has got to make sense or it doesn’t get posted.  If your comment didn’t get posted, that is most likely why.

Second grumpy new rule:  I don’t do UFO comments.  I have no patience for these things, don’t even try to start here.  Go someplace else with your UFO comments.  I will not post them here.  This is my personal preference and should not reflect on the agency or anybody else. 

Thanks, I’m glad to get those off my chest.  On to serious comments.

No, there was no serious entry guidance anomaly on STS-1.  There was a significant lofting during ascent, but nothing to speak of during entry.  STS-2, 3, and 4 entries were flown automatically not manually with the exception of some short duration pilot test inputs to stimulate the entry flight control system to verify its robustness.  Some of these type of manual test inputs continued for a number of flights.  But there have been no manually flown entries of the space shuttle — its all been automatic until subsonic speeds.

At this date in the shuttle program, it is my belief that the bugs have been worked out of all the intact abort modes.  That is, for any single SSME premature shutdown, there is a very high confidence level that the vehicle and crew can successfully execute an RTLS, TAL, ATO.   The big assumption, though, is that nothing else goes wrong.  The shuttle requirement — which I believe it meets — is that any single premature SSME shutdown at any point in the trajectory will lead to an intact abort — safe landing by the orbiter on a runway and safety for the crew. 

I was pleased to see a post with the details of the Gemini ejection seats, but I would think that landing a mere 700 feet from an exploding Titan II rocket would not be a good thing.  Survivable if the wind was blowing the right way probably.  And I do agree that Schirra showed that he had the right stuff when he did not pull the ejection handle on Gemini 6A pad abort.

I probably should have started the series of posts with a definition of ‘black zone’ so here it is:  a portion of a manned rocket launch trajectory where the premature shutdown of any or all running booster engines will lead to loss of the re-entry vehicle and crew subsequently due to the over temperature or structural loads incurred from the resulting trajectory.  Is that too muddy?  Black zone does not mean what is going to happen in a normal case, only if an engine (or two or three) quits.  Black zone does not take into account the weather at the proposed abort landing site which is another way to kill a crew.

As to why EELVs were not chosen by the Exploration team early on — I don’t think black zones had a lot to do with it, but I really don’t know.  I should ask and I will ask and I will report to you at a later day.  However, the standard trajectory design for EELV launches would result in extensive black zones — which can be either greatly reduced or eliminated by adjusting the trajectory — which in turn leads to significant reductions in the mass which the EELV could place in orbit. 

The two early American suborbital flights — Shepard and Grissom — had carefully designed trajectories to keep the entry G level and heating relatively low.  If they had flown the type trajectory that the redstone rocket used as a weapon, that would not have been the case.  Similarly, the Soyuz T-10-1 high altitude abort had an extreme entry G level because the rocket staging went so poorly that the entry was steeper than it would have been for a clean abort — as if the 3rd stage engines had merely failed to light off. 

Well, that’s all for today folks.  The series resumes tomorrow.