Delta IV Heavy Failure

Brian Thorn wrote in
:

On 22 Dec 2004 12:24:43 -0800, "Ed Kyle" wrote:

As of midday 12/22/04, many of the better news outlets
have figured out that the inaugural Delta IV Heavy mission
failed, but others haven't. For some reason, the Australian
press is more accurate than the US media on this so far.

I'm willing to bet that too much of the SOFI was burned away at
ignition and they had greater boil-off during ascent than expected,
hence running out of prop ten seconds early.

Those scorched black LH2 tanks just *don't* look right. If that
happened to a Shuttle at liftoff, NASA launch controllers would be
keeling over in cardiac arrest.

http://www.spaceflightnow.com/delta/...launch/03.html

I think they need to add a lot more of those "sparklers" around the
pad to get rid of the free hydrogen before engine ignition.

The problem's with the amount of hydrogen used to chill down
the RS-68s just before ignition; different from the SSMEs, somehow.
This was enough of a problem (with an aborted SSME firing) at
the Vandenberg pad that a steam injection system had to be
installed to flush the unburned gas away from the orbiter.
Something similar might have to be installed at the Delta IV pads,
if it's an actual problem. Or the chilldown procedure might have
to be modified.

The hydrogen flare for the Heavy was really impressive. I'm not
convinced it's a real problem, but it looks scary.

--Damon

On Thu, 23 Dec 2004 12:07:07 -0600, in a place far, far away, Brian
Thorn made the phosphor on my monitor glow in such
a way as to indicate that:

I'm willing to bet that too much of the SOFI was burned away at
ignition and they had greater boil-off during ascent than expected,
hence running out of prop ten seconds early.

Ten seconds of propellant burn is a *lot* of propellant. The SOFI is
to prevent boiloff between the time the vehicle is fueled and MECO,
not launch and MECO. I'd bet that there wouldn't be significant
boiloff if they launched with no insulation at all, at least not
enough to result in measurably shortened burn time. The fireball is a
Bad Thing, but I have trouble buying this theory.

"Damon Hill" wrote in message
31...
The problem's with the amount of hydrogen used to chill down
the RS-68s just before ignition; different from the SSMEs, somehow.
This was enough of a problem (with an aborted SSME firing) at
the Vandenberg pad that a steam injection system had to be
installed to flush the unburned gas away from the orbiter.
Something similar might have to be installed at the Delta IV pads,
if it's an actual problem. Or the chilldown procedure might have
to be modified.

Mmmm, maybe somewhat true. The main cause, according to our resident RS-68
guy, is that the start sequence of the RS-68 includes opening the H2 valves
at T-3 sec (IIRC), and the fireball is the result of all that hydrogen
gushing through the combustion chamber.

The hydrogen flare for the Heavy was really impressive. I'm not
convinced it's a real problem, but it looks scary.

Boeing doesn't think it's a problem.

-Kim-

Henry Spencer wrote:

Agreed that a bit of damage to the insulation doesn't seem enough to
account for the early cutoff, though.

You know, a great big hydrogen fire at ignition wouldn't make
me worry just about *fire* damage to the vehicle. Instead, I'd worry
about overpressure from a detonation. Maybe the escaped hydrogen
didn't detonate this time, but what about next time? The peak
pressure is going to depend on the details of mixing, which
will depend on winds, ambient temperature, etc. It's not
going to take all that much overpressure to break the vehicle.

Paul

"Henry Spencer" wrote in message
...
In article ,
Rand Simberg wrote:
Ten seconds of propellant burn is a *lot* of propellant. The SOFI is
to prevent boiloff between the time the vehicle is fueled and MECO,
not launch and MECO...

The main purpose of insulating LH2 tanks is to prevent liquid-air
condensation while on the pad (both because it's hazardous in itself, and
because it ruinously increases LH2 boiloff rates). During ascent... hmm,
I'm not sure whether you could get away without it.

Agreed that a bit of damage to the insulation doesn't seem enough to
account for the early cutoff, though.

Nah... that's more easily explained. They used US Gallons when they meant
to use Imperial Gallons.


--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

"Paul F. Dietz" wrote in news:0JmdneARdKXQa1bcRVn-
:

Henry Spencer wrote:

Agreed that a bit of damage to the insulation doesn't seem enough to
account for the early cutoff, though.

You know, a great big hydrogen fire at ignition wouldn't make
me worry just about *fire* damage to the vehicle. Instead, I'd worry
about overpressure from a detonation. Maybe the escaped hydrogen
didn't detonate this time, but what about next time? The peak
pressure is going to depend on the details of mixing, which
will depend on winds, ambient temperature, etc. It's not
going to take all that much overpressure to break the vehicle.

That's why the chilldown hydrogen was immediately ignited as
it left the engine nozzles. It's a large enough quantity to make
for a very impressive flare. Minimizing that might require
non-trivial changes to the engine and/or launch pad, but if it
causes the loss of one launch, Boeing will be obliged to do
something.

This was obviously anticipated; that's why the aft end of the
CBC has a shield covering nearly the entire engine. I assume
there's a nitrogen purge of the interior as well, as is done
with the Shuttle's engine compartment.

--Damon

In article ,
Damon Hill wrote:

"Paul F. Dietz" wrote in news:0JmdneARdKXQa1bcRVn-
:

You know, a great big hydrogen fire at ignition wouldn't make
me worry just about *fire* damage to the vehicle. Instead, I'd worry
about overpressure from a detonation. Maybe the escaped hydrogen
didn't detonate this time, but what about next time? The peak
pressure is going to depend on the details of mixing, which
will depend on winds, ambient temperature, etc. It's not
going to take all that much overpressure to break the vehicle.

That's why the chilldown hydrogen was immediately ignited as
it left the engine nozzles. It's a large enough quantity to make
for a very impressive flare. Minimizing that might require
non-trivial changes to the engine and/or launch pad, but if it
causes the loss of one launch, Boeing will be obliged to do
something.

This was obviously anticipated; that's why the aft end of the
CBC has a shield covering nearly the entire engine. I assume
there's a nitrogen purge of the interior as well, as is done
with the Shuttle's engine compartment.


Still more reasons why it's silly to use hydrogen on a first stage.