Black Zones – Part 3

The basic assumption for the shuttle design is that the shuttle would be like an airliner: no ejection seats, no parachutes (except for the first test flights) — crew safety consisted in total vehicle safety and the crew riding the vehicle down to a runway.

In retrospect that was a very poor assumption.

Adding crew escape to the space shuttle has received tremendous attention over the years and there are actually some methods that might work.  Not to put too short a discussion on it, the problem with all of the best methods is the additional weight.  After adding the crew escape system (capsules, rockets, whatever) and ballast to get the center of gravity right, there is no payload capacity left.  The shuttle would become a huge crew transportation device with no capability to carry much of anything else up or down. Not to mention  the pricetag to develop some of these devices!  Wow.  So, in the final analysis, the best way to make the shuttle safer is to retire her as soon as possible and go to a different type of vehicle.  Sorry but there it is.

Actually, the shuttle does have a minimal crew escape capability.  If the shuttle gets to a straight and level glide (actually not very level since the shuttle glides mostly like a rock), then down at 30,000 feet or less the the crew can jettison the side hatch and bail out with parachutes like some WWII bomber crew.  This is better than ditching in the ocean or rough terrain.  All studies show touchdown “off-runway” would not be survivable.  So the subsonic, aircraft-in-control, bailout is all there is.  And in most cases the crew probably winds up sitting in a tiny inflatable rubber raft in the middle of the North Atlantic waiting for somebody to pick them up.  Not a lot of fun.

But the shuttle does have a remarkable capability that most other rockets do not.  In virtually all expendable rockets, if any one of the booster engines shut down prematurely — even if that shutdown is benign — the mission is over, the payload is going into the ocean somewhere, and the Flight Control Officer is going to “send functions”.  On the other hand, the shuttle is designed — required — to be able to safely return the orbiter, crew, and payload to a runway landing following the benign shutdown of any one of the three SSMEs.

A word about “benign”.  High performance liquid rocket engines have a tendency to come apart in a hurry if something goes wrong.  The SSMEs have been extensively instrumented and tested.  Their computer control brain has a number of ways to detect an impending failure and turn the engine off before it comes apart.  The system is not completely foolproof, but should prevent an explosive catastrophe in most cases.  The only SSME premature shutdown in flight history occurred in 1985 on STS-51F when faulty temperature sensors erroneously indicated a problem with the engine and the computer shut that engine down.  This occurred late enough during the boost phase that the mission continued to a completely successful conclusion.  After that flight we spent a lot of time building more reliable temperature sensors.

So if any single SSME shuts down prematurely at any point in the launch phase, a safe return of the shuttle and crew will result.  All the various options have been examined, simulated, and verified by computer analysis, wind tunnel testing, etc., etc., etc. 

From launch to about 4 minutes into flight the shuttle can perform the scariest type of abort – a Return to Launch Site abort (RTLS).  Prior to the first shuttle flight, somebody proposed that we do an RTLS on purpose as a test — they called it the “Sub-Orbital Flight Test (SOFT).  Capt. John Young, the chief of the astronaut office and the commander of STS-1 was noted for his colorful memos that he would regularly send on topics of the day.  The SOFT proposal drew a classic response:  “RTLS requires continuous miracles interspersed by Acts of God to be successful” John wrote in 1980.  And in fact, on STS-1, a trajectory bug lofted the shuttle trajectory higher than expected and an RTLS probably would not have been successful. 

Since those days, RTLS has been significantly improved and would most likely work — but I’d just as soon not find out.  In particular the separation from the External Tank is very tricky.  ‘Nuff said on that subject.

From about 2 1/2 minutes into flight until almost orbital insertion loss of an SSME could result in a Trans-Atlantic Landing abort (TAL).  The shuttle keeps going forward but aims for Europe rather than orbit.  The entry is very similar to a normal end-of-mission entry and the landing would occur at a prepared runway in Spain or France (in the early days we also had landing sites in west Africa).

Later in flight, from about 4 1/2 minutes on, loss of an SSME would result in an Abort To Orbit (ATO) where the shuttle presses forward and we try to scavenge out all the propellant in the External Tank to go on to orbit.  Sometimes a dump of propellant from the Orbital Maneuvering System is required, sometimes other adjustments to the trajectory are required, but ATOs can range from landing after a few orbits on launch day to having a fully successful mission depending on many variables.  The longer the main engines run, the closer to normal the shuttle can get.

The Abort Once Around (AOA) mission – which is exactly what it sounds like – is basically not used these days except for problems like a big air leak from the crew cabin.

Now all of that is fine as long as two of the three SSMEs continue to operate and the shuttle remains under control.  If control is lost, then all is lost since the shuttle does not fly sideways very well.  A capsule might right itself, but the shuttle will break up.

If two of the SSMEs quit but one remains running, there are some options to steer toward the east coast of the United States and land at an emergency airfield somewhere on the Atlantic Coast of North America.  However, many of these trajectories result in entry conditions that exceed the capability of the shuttle orbiter either thermally or structurally:  black zones.  The possibility of executing a successful East Coast Abort Landing (ECAL) is far from guaranteed, but in that situation it is worth a try.  What is the other choice?  If the shuttle doesn’t break up or burn up on the steep ballistic trajectory for an ECAL there is every reason to believe that a safe landing will occur.  That is sort of a big “if”, however.

If three SSMEs quit all at once, there is real trouble.  There is little to no way to control trajectory and the black zones get immense.  In some lucky cases a successful ECAL might result but then you are not really having a lucky day if all three engines quit, are you?

My least favorite abort is a low alpha (low angle of attack) stretch to try to cross the Atlantic and make it to Ireland or someplace.  These multiple-engine-out aborts result in extreme heating on the wing leading edge and the RCC panels are likely to fail.  Another thing to try if there are no other options.

And of course, if the whole stack comes apart, its game over. Don’t even talk about a failure of a Solid Rocket Booster, either. 

So the shuttle has a lot of capability compared with other rockets — and a lot less capability than any capsules.

More black zone discussions tomorrow.


13 thoughts on “Black Zones – Part 3”

  1. great launch watch it as i was watching the launch i starting about about would the orion class would hand and emergecy and if the spacecraft was in the blackzone

  2. John Young is also credited with the quote of “you don’t have to practice bleeding” while expressing his severe lack of enthusiasm to fly a SOFT in order to verify RTLS capability.

    Wayne, this probably doesn’t belong here, and it’s certainly not critical to much of anything, but by all means, *please* nudge someone at PAO or elsewhere to finally replace the big world map display used in the MCC rooms in Houston with a contemporary and up-to-date one. The one currently in use there is of Cold War vintage, for crying out loud. You have a divided Germany on it, Yugoslavia intact, and a Soviet Union. And you fly that thing daily on NASA-TV. Makes me slightly cringe every time I see it. (Really just slightly, but I mean, come on…)

  3. The airliner concept is right out of Clarke’s 2001 Space Odyssey. In truth I think it has to be accepted that until the idea of the DC3 truck type vehicle gets re-established, space habitation won’t ever be routine. As I see it now we are going back to the special purpose vehicles for the sole purpose of going back to the moon and then later onto Mars. Problem is, as you pointed out in a couple of blogs ago, the advance comes from not going once but from going over and over with a purpose. The model Clarke came up with pro ably will be the model needed to go over and over. Having just looked at the mineral composition of Mars (admittedly in old and maybe out of date documents) and seeing that the most abundant mineral is iron ore (not too useful in space according to the literature) the big question becomes the purpose. Until people and corporations want to go to Mars for an economic advantage (analogous to the lure of gold to the Spaniards) I can’t see the over and over part of the equation. I can see the over and over part of the equation for near earth orbit though. Why, because the first thing the Chinese did with their ICBMs after sticking the bomb on it was to convert it to manned space flight in near earth orbit. There is a whole host of things that can be done in near earth orbit right now that requires a truck. I wonder if the Air Force X-37B (or something else also secret) was supposed to be that truck. Given that its initial flight was supposed to be on the Shuttle it looks like its more like a pickup than a semi though.

  4. Thanks for a very interesting blog! I have a question regarding the different abort scenarios you have talked about. Are they all the same regardless of a launch from KSC or from Vandenberg AFB? The shuttle has never been launched at Vandenberg, but as I understand things that was the idea at the beginning of the shuttle development. On a side note, I think I have read somewhere about one usages of such a polar orbit, and that would be to do a once around to capture a foreign satellite. Since the Earth rotates, that scenario would also require the shuttle to glide to a landing a long distance from the launch site – hence to large wings. But I don’t know if that story is true… 🙂

  5. as regarding to the Ares I-X Test Flight Video and Explanation.
    Does anybody care about all the trash ans debris sinking into the depths of the atlantic ocean that no one will recover?

    Is that part of climate and environmental care? nope!
    That’s just besides the stuff that tests and flights pumping into the atmosphere.
    However, seems that there is no escape from earth anyway…


  6. Hi. This is a very interesting subject, thank you.

    In the future, please consider discussing the manual reentries of STS-2 through 4, where S-turns were performed by pilot rather then by computer due to reentry trajectory miscalculations during STS-1.
    This is a very interesting, but largely uncovered shuttle topic.

    Thanks again, Dmitry

  7. @Claes:
    Not so much capture a satellite from polar orbit when launching from Vandenberg, but also rather release one into polar orbit (more than just a bit likely a military satellite).

    You’re right about the necessity of having to glide a requisite range to land again in such a “once around” polar orbit launched from Vandenberg, due to earth’s rotation in the meantime. Actually, this capability was a requirement demanded by the military during the time of Shuttle concept design and development, and it’s also pretty much the sole reason why the Shuttle was designed having those bulky wings. Without this glide range requirement, it would have looked much more like its early concept studies with very short and small wings. As it happened, the military soon lost interest, the Shuttle never launched from Vandenberg, and subsequently carried that dead (and sometimes deadly, as we know) weight around ever since.

  8. Very interesting stuff on the Black Zone, thanks for sharing it. I love to read up on the space shuttle programs and their progress. I'll be back to read more. Enjoy your day!

  9. Hi Wayne.

    Regarding the Gemini ejection seats, and their operating criteria/envelopes:

    There were 3 ‘modes’ of escape from the Titan; 1 using the seats, the other two relying the crew to ride out aborts within the retro-module section:

    1.) The ejection seats were used from the launch pad (Pad 19)to an altitude of 70,000 feet. 2.) Above 70,000 feet, the spacecraft drag was reduced sufficiently to allow separation of the spacecraft by seperating the spacecraft at the retrograde section from the equipment section, and firing all four solid retro rocket motors in a salvo. For this escape mode, the retro section is retained and the resulting configuration was aerodynamically stable – (small end being the reentry module velocity vector has the crew facing in the velocity vector – or nose [recovery section] first). The retro module was separated at the apogee of the escape trajectory. 3.)After staging from the Titan second stage, when dynamic pressure is neglegable; the escape mode involves shutting down the second stage, and seperating with the two translational 100lb rendezvous thrusters located in the aft portion of the equipment section (velocity vector again nose first).

    Off-the pad ejection was supposedly feasable; the apogee of an off- the-pad ejection sequence was approximately 275 feet, with a distance from the pad achieved at ‘astronaut touch-down’ being approximately 700 feet.

    Unlike Shuttles – or Saturns, the Titan II first and second stages strictly used hypergolics, thus an ‘explosion’ like one might see with LOX and RP-1, or LOX and LH2 explosivly combining, would not occur. Explosive overpressures see with hypers are not nearly as strong as one would witness with LOX and RP-1, or LOX and LH2 explosive events, thus the use of escape seats was entirely feasable, (off the pad or in powered flight up to 70,000 feet) during the Gemini Program.

    Final note; thankfully, and luckily in the case of GT-6’s failed launch attempt in Dec. 1965, when Wally Schirra decided not to pull the D-Ring when he sensed the Titan did not liftoff after the first stage engines briefly ignited – and abruptly shut down before full thrust was achieved, those ejections seats were never put to the ultimate test.

  10. I will grant that maneuvers like RTLS and TAL are problematic – maybe not even survivable. The way around this is to reduce the risk of failure during powered flight as much as possible. Instead, NASA has reverted to treating Shuttle as an experimental vehicle on which something could fail at any moment.

    The vehicle’s flight history would seem to belie this notion. Based on past performance, Shuttle components would seem to be operating at near-zero risk of failure. The SSMEs (which are extremely complex pieces of machinery) have a measured failure risk of 1 in more than 360 flight operations – less than that if you include the many static test ops that have been conducted. The SSMEs would seem to be extremely robust. If, however, they are coming back from flights ready to fall apart and have a demonstrated mtbf of 10 minutes, then certainly, NASA’s concern is justified.

    Space Shuttle is a mature system. Despite high g loads during ascent and re-entry, the orbiter airframes are gently used. Even the thermal protection system is performing reliably. It’s kind of a shame that it has to be retired now that it’s working well.

    (It will be interesting to see if the crew-vibration solution works in Ares 1. And, if payload vibration is an issue in Ares 4.)

  11. Early, early shuttle designs, as late as those that had already been reduced to the drop-tank ET and strap-on solids configuration, had solid-rocket escape motors mounted alongside the fuselage above the wings. [Don’t know for sure if this was before or after the fold-out jet engines had been dropped completely from the design.] The idea was that they would be able to pull the shuttle away from a failing/exploding ET/SRB stack, just as Max Faget’s escape tower design was able to pull Mercury & Apollo free from their boosters.

    These side-mounted escape motors were eliminated because the safety margin they offered was minimal at best and they robbed the vehicle of a large chunk of its AF-required payload capability.

    “Intact abort” became the only “crew escape” option that fit inside all the competing design requirements…including the OMB-imposed development cost ceiling…which was violated anyway, partly BECAUSE of that imposed ceiling since that had prompted NASA (in a cost-cutting move) to not test sufficiently at the component level before major subsystem assembly which led to…

    Ah, to ponder what might have been. If only…

  12. This is a great blog! A very interesting, in-depth discussion of an important issue. Keep it up.

    Best regards,

    – Edwin Kite
    Graduate student, Earth and Planetary Science
    University of California, Berkeley

  13. I didn’t know trajectory lofting of that magnitude occurred during STS-1. Very interesting! Thanks for the informative posts.

    Bill Harwood
    CBS News/Kennedy Space Center

Comments are closed.