NASA budget to increase dramatically...

Dan Foster wrote in
:

In article , Joe D.
wrote:
"Michael R. Grabois ... change $ to "s""
wrote in message ...

STS-51F had the engine shut down, resulting in an abort-to-orbit
(ATO).

Interestingly the media often depicts the 51-F ATO as not a big deal.
Many times I've heard media commentaries say had they lost a
2nd SSME (which they almost did) it would have forced a "risky"
trans-Atlantic abort (TAL).

In actuality, close examination of the time/velocity chart vs
pre-51L abort options shows loss of a 2nd SSME within about 15-20 sec
of the 1st would have probably resulted in loss of crew and
vehicle. This is somewhat counter-intuitive since the 1st
SSME was lost at 345 sec, at a pretty high velocity, very roughly
13k ft/sec.

Before about 360 sec there's insufficient energy for TAL, and
they had no bailout capability, and ditching wasn't survivable.

Slight clarification - before 360 there's insufficient energy for a
*single-engine* TAL. That was clear from context in Joe's original post,
but with people replying to it I fear the context will be lost.

Interesting. Why wouldn't RTLS have had been an option (even if not a
real desirable one, ordinarily) in such a scenario with two SSMEs out?

In the case of 51-F, it was because the first SSME failure occurred after
Negative Return, the point beyond which an RTLS is not possible.

Just curious. Seems to me that if it had enough energy to almost make
it for the TAL case, it would theoretically have more than sufficient
energy margin to make it for a RTLS or ECAL landing.

Keep in mind that an RTLS requires a *reversal* of course, so there comes a
point (Negative Return) where the shuttle has too much momentum going
downrange for it to make it back to KSC, especially with two SSMEs out.

(I'm not sure if ECAL abort capability was pre or post-51L, though.)

Post-51L, and only for high-inclination launches at that. Low-inclination
launches can do a kind of pseudo-ECAL to Bermuda, though.


--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
think one step ahead of IBM.

"Dan Foster" wrote in message
...
Interesting. Why wouldn't RTLS have had been an option (even if not a real
desirable one, ordinarily) in such a scenario with two SSMEs out? Just
curious. Seems to me that if it had enough energy to almost make it for
the
TAL case, it would theoretically have more than sufficient energy margin
to
make it for a RTLS or ECAL landing.

Distance, as far as I understand. They'd have to get off the tank and honk
it back around, and if they're too far to do that, well... I imagine the
turn required would be pretty wide, which would eat up a lot of energy.

Plus, I don't know how stressful it would be to turn all the way around at
Mach 13.

Slight clarification - before 360 there's insufficient energy for a
*single-engine* TAL. That was clear from context in Joe's original post,
but with people replying to it I fear the context will be lost.

So after a single SSME failure and negative return (which is when?), you
have a "black hole" in the abort tree until 360s - at least before the post-
51L changes which made bailout possible? Duh.

Jan

Jan C. Vorbrüggen wrote in
:

Slight clarification - before 360 there's insufficient energy for a
*single-engine* TAL. That was clear from context in Joe's original
post, but with people replying to it I fear the context will be lost.

So after a single SSME failure

Sorry, I see my "clarification" was nothing of the sort: "Single-engine
TAL" means a TAL with one engine remaining, two engines failed.

and negative return (which is when?),

Varies, always after T+3:40.

you have a "black hole" in the abort tree until 360s - at least before
the post- 51L changes which made bailout possible? Duh.

No. For a single engine failure, all the abort boundaries overlap so that
there is always an intact abort available. First TAL overlaps Negative
Return, last TAL overlaps Press to ATO.

There are black zones for two- and three-engine-out scenarios, though.


--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
think one step ahead of IBM.

Sorry, I see my "clarification" was nothing of the sort: "Single-engine
TAL" means a TAL with one engine remaining, two engines failed.

Sorry, my fault, I had understood that.

and negative return (which is when?),

Varies, always after T+3:40.

There are black zones for two- and three-engine-out scenarios, though.

That's what I meant to say: for about 360-220=140s, you're one failure
away from a black hole after the first SSME failure. And in real life,
it will be longer because MECO will be later (depending, of course, on
when the first engine failed). Uncomfortably long - that's about 30% of
time-to-MECO.

The non-linearity is always a little surprising...at 6 minutes, you don't
have enough energy to get across the 6000 km Atlantic, at 8 minutes you're
(almost) in orbit...

Jan

Well, not necessarily - not all of the gaps are considered black zones,
just the ones where crew survivability is low. There are plenty of two- and
three-out scenarios that are survivable, and NASA has spent a considerable
amount of attention on closing black zones.

I'mm sure they did...but with TAL not yet and RTLS no longer possible,
bailout is the only option - and that wasn't available before 51L, right?

And you loose an orbiter in any case.

Jan