SpaceX Merlin 1C Engine

[Crispy]

Strictly speaking, isn't T+0 the moment of release, not the moment of ignition?

[Crispy]

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double post

[Jim]

Patchouli - 17/3/2008  3:53 PM

I thought the Saturn performed a post ignition hold down before letting the vehicle go during launch making such a failure at T+0 just a mission abort where you just simply cut the thrust?

T+0 is once the vehicle is released, T-0 is before release

[wingod]

Jim - 17/3/2008  3:32 PM

Patchouli - 17/3/2008  3:53 PM

I thought the Saturn performed a post ignition hold down before letting the vehicle go during launch making such a failure at T+0 just a mission abort where you just simply cut the thrust?

T+0 is once the vehicle is released, T-0 is before release

And there is a gulf of time between the two.

[wingod]

Jim - 17/3/2008  2:48 PM

Patchouli - 17/3/2008  3:45 PM

There was one vehicle that could handle an engine out at any moment in flight that was both Saturn vehicles they both had first stage engine out capability.

Incorrect.  It could not handle losing one at T+0

Agreed.  It is my memory that it could handle one F1 out at +100 ft altitude and then reach orbit which is pretty darn good!

[Jim]

wingod - 17/3/2008  9:57 PM

Jim - 17/3/2008  2:48 PM

Patchouli - 17/3/2008  3:45 PM

There was one vehicle that could handle an engine out at any moment in flight that was both Saturn vehicles they both had first stage engine out capability.

Incorrect.  It could not handle losing one at T+0

Agreed.  It is my memory that it could handle one F1 out at +100 ft altitude and then reach orbit which is pretty darn good!

before that, they thought it would hit the LUT

[Analyst]

Jim - 18/3/2008  12:47 PM

before that, they thought it would hit the LUT

If I remember correctly, it depended on which engine failed or gimbaled into the worst case direction.

Analyst

[Big Al]

I’ve been thinking about the Falcon 9 and the closest thing to it was the Saturn 1. I dug out my Spacecraft Films DVD on the Saturn 1 and reviewed it in relation to the Falcon 9.

The first thing you realize is the tanks and manifold system on the Saturn was more complex than the 9 will be. The Saturn 1 had 5 oxygen and 4 fuel tanks plumed to 8 engines. It would be interesting to see how this system was designed. An interview with one of the chief engineers he said “we had some difficulty with the fuel feed”

They also said that they shut down one of the H-1’s on one of the flights to test its engine out capability. Also on another flight one of the engines shut down do to turbo pump failure. They were able to complete the mission without any problems.


This brings up the issue of what type of failure Spacex is planning for. An uncontained pump failure might require a nomex blanket around the turbo pump. An exploding combustion chamber would be difficult to plan for and require some heavy shielding.

One of the things you notice between the Saturn1 and 1B is the turbo pump exhaust. The early H-1’s must have run a very rich mixture in the combustor for the turbo pump. You can see lots of burning fuel from the turbo pump exhaust. The 1B did mot have this. They said in the film that after flight 4 or 5 they started using an upgraded H-1 that had more thrust.

By the way they said the Saturn 1 was held down for 3.2 seconds before launch to stabilize engine thrust.

A question on the Falcon 9, how many fist stage engines will be gimbaled for steering? On the Saturn 1, I would guess that the outer 4 engines were gimbaled. On the 9 how do the plan to do this? Will they use turbo pump exhaust for roll control?

[Jim]

Big Al - 18/3/2008  4:48 PM

1.  One of the things you notice between the Saturn1 and 1B is the turbo pump exhaust. The early H-1’s must have run a very rich mixture in the combustor for the turbo pump. You can see lots of burning fuel from the turbo pump exhaust. The 1B did mot have this. They said in the film that after flight 4 or 5 they started using an upgraded H-1 that had more thrust.

2.  Will they use turbo pump exhaust for roll control?

1.  they were the same.  The 1B didn't duct it outward and overboard

2.  That only works for single engine vehicles.  Multiple engined vehicles roll control by opposing engines gimbaling in the opposite direction

[Big Al]

One more observation about the Saturn 1 program. I was a very conservative flight program. The first three flights were sub-orbital. In terms of the Falcon 9 wouldn’t it be a good idea to do an early first stage only flight to demonstrate their ability to fly a multi engine rocket. They could even do an engine out demo; I think this would really help their standing in the industry and with potential customers. The question of Spacex’s ability to routinely fly a multi-engine rocket is on everybody’s mind and the sooner they prove themselves, the better off they will be.

[Comga]

The stated arguments for flying a full up rocket on the first flight are that the upper stage is not very expensive, there is no better way to test an upper stage than without mechanical constraints in the vacuum of high altitude, and that the avionics are in the upper stage so flying without one requires them to be repackaged.

Did they ever fly a Saturn 1 or 1B with a dummy upper stage?

[Analyst]

Big Al - 19/3/2008  12:31 AM

1) One more observation about the Saturn 1 program. I was a very conservative flight program. 2) The first three flights were sub-orbital.

1) It was the dawn of the space age. Experience was low. Compare this to the earlier Jupiter, Thor, Atlas or Titan development and flight testing. Has been even more conservative.

2) The first four (SA1 - SA4) were suborbitaL, they lacked a live upper stage. Some later flights were suborbital too (by design), despite having an upper stage.

Comga - 19/3/2008  7:23 AM

Did they ever fly a Saturn 1 or 1B with a dummy upper stage?

Yes, four flights: SA1 - SA4.

Analyst

[josh_simonson]

In the Saturn 1 development, the first stage was test launched almost a year before the second stage was even test fired.  If the second stage had been available they probably would have done fewer test flights without the second stage.

SpaceX would have to consider things like range costs, insurance, ect, involved with flying a partial stack against the cost of just putting on the second stage and hoping for the best.  It's only 11% more Merlin engines, and they'll have a decent chance at getting to the second stage.

[Big Al]

My thinking was that it looks like Spacex is much further along with development of the F9 first stage than the second stage. A suborbital first stage flight would be a real confidence builder

Also, now I can't find the source, but I read that Spacex is announcing an 18 month delay for the first flight of the Falcon 9.

[Jim]

Big Al - 19/3/2008  1:56 PM

My thinking was that it looks like Spacex is much further along with development of the F9 first stage than the second stage. A suborbital first stage flight would be a real confidence builder

It would be more work.  The one off vehicle configuration means more drawings and more work, more dead end hardware.  Avionics would have to be relocated and different software used.

Since the Saturn I, rocket science has progressed past the use of incremental testing and "all up" launches in the norm.

[Big Al]

Found my source for the F9 delay, Orlando Sentinel.com, dated 2/28/08

[iamlucky13]

Big Al - 18/3/2008  1:48 PM

1.) This brings up the issue of what type of failure Spacex is planning for. An uncontained pump failure might require a nomex blanket around the turbo pump. An exploding combustion chamber would be difficult to plan for and require some heavy shielding.

2.) A question on the Falcon 9, how many fist stage engines will be gimbaled for steering? On the Saturn 1, I would guess that the outer 4 engines were gimbaled. On the 9 how do the plan to do this? Will they use turbo pump exhaust for roll control?

1.) From http://spacex.com/updates_archive.php?page=0605-1205
"Then there is the question of dealing with the comparatively rare case of a chamber rupture. To protect against this, Falcon 9 will have a blast shield protecting the entire base of the vehicle just above the gimbal joints of the engines. In addition, there will be fireproofed Kevlar fragment containment around each engine, similar to those present in jet engine nacelles. The explosive power of a liquid rocket chamber is actually not exceptionally high – it can be thought of as simply a small pressure vessel containing (in our case) 800 psi hot gas. During the development of Merlin, we saw several of what we refer to as RUD (rapid unscheduled disassembly) events and no fragments have ever penetrated more than 2mm of aluminum. Also, the direction of fragments is in a shallow downward cone away from the vehicle.

As additional measures of protection, all propellant and pneumatic lines have either pre-valves or check valves nested up high in the thrust structure. If anything happens to the engine, the flight computer is able to cut off all propellant and pressurant flow immediately."

I love the term "Rapid unscheduled disassembly" :laugh: but I wonder if the Sea Launch failure last year made SpaceX take a little closer look at the danger.

2.) I think Musk in an interview discussed differences between the gimballing and fixed engines, but I don't remember where. I want to say it's the corner engines, but I can't back that up at the moment.

[meiza]

Ha! So their chamber pressure is actually 800 psi = 55 bars. Haven't seen that officially mentioned in the spec sheets.

[Comga]

Analyst - 19/3/2008  1:32 AM

Comga - 19/3/2008  7:23 AM
Did they ever fly a Saturn 1 or 1B with a dummy upper stage?

Yes, four flights: SA1 - SA4.
Analyst

Another 60's skill kept current at NASA: building dummy/boilerplate upper stages and payloads.
Another NASA SOP being bypassed by SpaceX for better or worse.

[Comga]

Jim - 19/3/2008  12:07 PM
Since the Saturn I, rocket science has progressed past the use of incremental testing and "all up" launches in the norm.

Except for Ares-1, it would appear.  But that is a different discussion.