SSME Ignition Restrictions: No Flameout Recovery Options?

JF Mezei scribbled something like ...

Snidely wrote:

determines whether the engine is restartable. An engine designed to
be restartable is restartable, an engine that requires massive ground
support to start is not restartable.

What sort of ground support is needed to start the SSME engines ?

I'll have to defer the answer to others ... it has been discussed in this
group before, and I've read some of the NASA pages about it, but long
enough ago that I couldn't do any better at finding those pages than you
could, and certainly couldn't quote them accurately without finding them.

Perhaps the Canonical Shuttle Book also provides a detailed description;
the CSB has been on my wishlist but has yet to arrive.

/dps

In article ,
says...

JF Mezei scribbled something like ...

Snidely wrote:

determines whether the engine is restartable. An engine designed to
be restartable is restartable, an engine that requires massive ground
support to start is not restartable.

What sort of ground support is needed to start the SSME engines ?

I'll have to defer the answer to others ... it has been discussed in this
group before, and I've read some of the NASA pages about it, but long
enough ago that I couldn't do any better at finding those pages than you
could, and certainly couldn't quote them accurately without finding them.

I'm in the same boat as you. But suffice it to say that I doubt Ares I
would have ditched the SSME as an upper stage engine if the SSME would
have been relatively easy to air start. And by relatively easy, I mean
easier than simultaneous development of the J-2X *and* the five segment
SRB.

Jeff
--
" Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry
Spencer 1/28/2011

On 03/02/2011 06:26 PM, Jeff Findley wrote:
In ,
says...

JF scribbled something like ...

Snidely wrote:

determines whether the engine is restartable. An engine designed to
be restartable is restartable, an engine that requires massive ground
support to start is not restartable.

What sort of ground support is needed to start the SSME engines ?

I'll have to defer the answer to others ... it has been discussed in this
group before, and I've read some of the NASA pages about it, but long
enough ago that I couldn't do any better at finding those pages than you
could, and certainly couldn't quote them accurately without finding them.

I'm in the same boat as you. But suffice it to say that I doubt Ares I
would have ditched the SSME as an upper stage engine if the SSME would
have been relatively easy to air start. And by relatively easy, I mean
easier than simultaneous development of the J-2X *and* the five segment
SRB.

According to Rocketdyne, airstartable SSME was feasible though not
necessarily "easy". You need to look at the whole picture. The "classic"
ESAS Ares I used:
- 4 seg SRB (existing)
- airstartable SSME (new)

The "classic" ESAS Ares V used:
- 5 seg SRB (new)
- SSME (existing)
- J-2X (new)

so essentially three new engines (airstart SSME, 5 seg SRB, and J-2X).
Post-redesign, Ares I used:
- 5 seg SRB (new)
- J-2X (new)

and Ares V used:
- 5 seg SRB (new, but common with the "new" Ares I)
- RS-68 (existing)
- J-2X (new, but common with the "new" Ares I)

so two new engines (5 seg SRB and J-2X). From a Total Cost of Ownership
perspective this made sense at the time. Both Rocketdyne and CxP program
management agreed SSME airstart was not a showstopper, just that it
represented a third new engine development and therefore was more expensive.

It was only later that Ares V performance shortfalls necessitated 5.5
seg SRB (new) and RS-68B (new), and the divergence between airstartable
single-start J-2X (Ares I) and airstartable-restartable J-2X (Ares V).

The real problem with the redesign is that it shifted many of the costs
*forward* to Ares I, creating a funding squeeze when shuttle RTF cost
more than anticipated.

On Mar 2, 11:37*pm, JF Mezei wrote:
Jorge R. Frank wrote:
According to Rocketdyne, airstartable SSME was feasible though not
necessarily "easy".

What is so different about airstarting an engine such as an SSME ?

Is it just a question of a different ramp up of the turbo pumps ?
pre-heating of certain pipes/turbo pump ?

Since the engines are already rated to operate in vacuum, shouldn't they
be able to ignite in vacuum ?

How many seconds would it take between the pilots pressing the "engine
start" button and full thrust being available ?

Woud this be very different whether at mid atmosphere, high atmosphere
or orbital vacuum ?

Should the *"according to Rocketdyne" be taken with a grain of salt ?
They wouldn't say it is "easy when they could state it is a complex
project and get billions $ in funding instead of charge NASA $2000 for a
new firmware chip in the engine controlers.

well so far its never been needed, and besides during launch a fault
shutting down a engine probably wouldnt alow time to evaluate what
happened.

so a turbo pump develops a problem the computer shuts it down the
astronaut lacking time pushes restart and boom the vehicle and crew
are lost........

some capabilities arent worth the effort.......

On Mar 2, 6:07*pm, JF Mezei wrote:
Snidely wrote:
determines whether the engine is restartable. * An engine designed to be
restartable is restartable, an engine that requires massive ground
support to start is not restartable.

What sort of ground support is needed to start the SSME engines ?

At time of ignition, aren't the only umbilicals left some electrical
connectors ?

If this is a computer sequencing issue, with modern electronics,
wouldn,t it be fairly simple to just add such alectronics to the SSMEs ?

I know that anything NASA does has to be complex, but in principle,
shouldn't that be fairly simple ?


The SSME are head start engines. They depend the engine being
conditioned to a certain temperature range and the propellants at the
prevalves be at a certain temp range and pressure (head) range. The
engine depends this pressure (which is provided by the propellant
column weight and tank pressure) and vaporization of LH2 to spin up
the turbopumps. Most restartable pump driven engines have a gas
generator that is easy to ignite to start the turbopumps, the SSME
being a closed cycle engine does have a gas generator, it has
preburners.

In article 7c213d9b-79e1-49fd-b15c-1f9faf2efa94
@d26g2000prn.googlegroups.com, says...

The SSME are head start engines. They depend the engine being
conditioned to a certain temperature range and the propellants at the
prevalves be at a certain temp range and pressure (head) range. The
engine depends this pressure (which is provided by the propellant
column weight and tank pressure) and vaporization of LH2 to spin up
the turbopumps. Most restartable pump driven engines have a gas
generator that is easy to ignite to start the turbopumps, the SSME
being a closed cycle engine does have a gas generator, it has
preburners.

Interesting. This would explain why it would be harder to air start the
SSME in flight than on the ground. In flight, the upper stage would be
in "free fall" and would not have any pressure provided by the
propellant column weight.

Jeff
--
" Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry
Spencer 1/28/2011

On Fri, 18 Mar 2011 16:34:58 -0400, JF Mezei
wrote:

Interesting. This would explain why it would be harder to air start the
SSME in flight than on the ground. In flight, the upper stage would be
in "free fall" and would not have any pressure provided by the
propellant column weight.

But with 3g acceleration,

Only if Stage 1 is still firing when Stage 2 with the SSME ignites.
Not. Gonna. Happen.


Brian

On Mar 18, 4:34*pm, JF Mezei wrote:

But with 3g acceleration, there would be plenty of "gravity" pushing the
fuel towards the bottom of the stack. So in fact, there would be greater
* fuel pressure at the pump than the shuttle on the pad when the engines
are started.


There isn't any 3g acceleration when the first stage burns out.

In article ,
says...

Jeff Findley wrote:

Interesting. This would explain why it would be harder to air start the
SSME in flight than on the ground. In flight, the upper stage would be
in "free fall" and would not have any pressure provided by the
propellant column weight.


But with 3g acceleration, there would be plenty of "gravity" pushing the
fuel towards the bottom of the stack. So in fact, there would be greater
fuel pressure at the pump than the shuttle on the pad when the engines
are started.

Actually, I was thinking of air-start for the second stage of Ares I.
In that case, you're in "free fall".

In the case of the shuttle, it makes sense to light the liquids first,
to verify that they're operating properly, before lighting the solids
(which you have far less control over).

Jeff
--
" Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry
Spencer 1/28/2011

In article , bthorn64
@suddenlink.net says...

On Fri, 18 Mar 2011 16:34:58 -0400, JF Mezei
wrote:

Interesting. This would explain why it would be harder to air start the
SSME in flight than on the ground. In flight, the upper stage would be
in "free fall" and would not have any pressure provided by the
propellant column weight.

But with 3g acceleration,

Only if Stage 1 is still firing when Stage 2 with the SSME ignites.
Not. Gonna. Happen.

It's certainly possible to do it this way, and it has been done on other
expendable launch vehicles. But I agree with "not gonna happen", if you
assume that NASA is in charge. Lighting the upper stage with the first
stage still firing with astronauts on top of the stack would likely make
the NASA safety guys go nuts.

Plus, it makes it more difficult to re-use the first stage.

Jeff
--
" Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry
Spencer 1/28/2011