Author Topic: 1st reignition of a cryogenic rocket engine in Europe  (Read 19691 times)

Offline meiza

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Re: 1st reignition of a cryogenic rocket engine in Europe
« Reply #20 on: 08/17/2007 08:27 pm »
Of course you don't need constant 1 g, that was just an exaggeration to make a point, what I'm asking is, are there any differences in engines and their settling needs for restart...

Offline spacediver

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Re: 1st reignition of a cryogenic rocket engine in Europe
« Reply #21 on: 08/18/2007 11:42 pm »
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meiza - 16/8/2007  11:54 PM

Surely a design approach was picked for the whole stage, long before the engine was even started to being built

The design of the ECB began several years ago in parallel with the ECA. It was set on hold after the failure of the first ECA flight.
I've seen some drawings of the ECB in Bremen last year.

The design of the ECA is similar to the ECB because the ECA was originally planned as a "quick and dirty" interims solution to shorten the gap until the ECB would be available.

The LH2-tank of the ECB is more or less the same as for the ECA. It is stretched a bit, but the tank domes are the same. The LOX-tank has a lens shape and shares a common bulkhead with the LH2-tank. The LOX-tank of the ECA is practically the same used in the L10-stage of the Ariane 4 and is placed directly under the LH2-tank without a common bulkhead.

This shows that the LH2-tank of the ECA (especially the domes) was designed to fit the later ECB-configuration and not the ECA interims solution. This design leads to an unhealthy high empty mass fraction of the ECA compared to other upper stages.  

Spacediver

Offline meiza

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Re: 1st reignition of a cryogenic rocket engine in Europe
« Reply #22 on: 08/19/2007 12:56 am »
Many stages have a skinny LOX tank with a big LH2 tank, . And Centaur is skinny the whole way.

Offline spacediver

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Re: 1st reignition of a cryogenic rocket engine in Europe
« Reply #23 on: 08/19/2007 08:51 pm »
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meiza - 19/8/2007  2:56 AM

Many stages have a skinny LOX tank with a big LH2 tank, . And Centaur is skinny the whole way.

Hello Meiza

You're right, but the problem with the ESC-A is that the LOX-tank, thrust frame and engine have been derived from the Ariane 4 without mayor change and therefore maintain the diameter of the original L10 stage.

To mate this LOX-tank to the new LH2 tank (that was designed for the ESC-B-stage) a massive framework of about 30 - 40 aluminum tubes is necessary.
This framework looked very massive and heavy to me when I stood under the first ESC-A dynamic test stage some years ago.
 
Another problem is that the LH2-tank is far away from the ideal spherical shape for a tank. The tank surface is therefore quite large for the tank volume.

Another aspect is that the design of the LOX-tank was designed for Ariane 4 flight loads and is not optimized for the ESC-A stage.

All this leads to a extremely high empty mass fraction of approximately 23% for the ESC-A.
Most cryogenic upper stages have an empty mass of <10%.
Please have a look to the annexed sketch.

In short:
The design of the whole stage, especially the LH2 tank, was optimized for the ECB.
The ECA is, in so far, a compromise.

Spacediver


Offline meiza

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Re: 1st reignition of a cryogenic rocket engine in Europe
« Reply #24 on: 08/19/2007 09:11 pm »
Whoa, that sure looks serious. Let's hope ECB is funded through. Thanks for the clarification!

Offline neviden

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Re: 1st reignition of a cryogenic rocket engine in Europe
« Reply #25 on: 08/20/2007 09:04 am »
If ECB get's finished, would it replace ECA version?
What would ECB cost be compared to ECA?
Would ECB be able to place ATV into LEO and how much would it be able to lift to LEO?

Offline pierre

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Re: 1st reignition of a cryogenic rocket engine in Europe
« Reply #26 on: 08/20/2007 01:31 pm »
AFAIK (someone please correct me if I'm wrong) Ariane 5 ECB is optimized for GEO, the Moon and escape trajectories and not LEO, but it can still put 23 t in a 300 km x 300 km / 51.6° (ISS) orbit.

So, yes, it can easily put an ATV and even heavier payloads into LEO.

I guess that if it were an US launcher it would be called Ariane 5 "heavy". ;)

Offline spacediver

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Re: 1st reignition of a cryogenic rocket engine in Europe
« Reply #27 on: 08/20/2007 04:07 pm »
Quote
neviden - 20/8/2007  11:04 AM

If ECB get's finished, would it replace ECA version?
What would ECB cost be compared to ECA?
Would ECB be able to place ATV into LEO and how much would it be able to lift to LEO?

Hello Neviden

The ECA was planned only as an interim solution. I'm sure that it will be completely replaced if the ECB will ever be put into service. It does not make sense to keep two different engine production lines busy.

I don't have information about the cost of the stages, but I think that the recurring production cost for the ECB upper stage should not be significantly higher than for the ECA once the serial production is running.

The ATV’s will be launched on an Ariane 5 ES using the hypergolic EPS upper stage. This stage is still in production (at an extremely low rate!) only for this purpose because a reignitable stage is required to reach the ISS. This can not be done with the ECA stage because it has no reignition capability.

In so far the ECB should be capable to reach ISS.
I don’t have any numbers about the payload capacity for such a mission, but it must be much higher than with the ES-version.  

All Ariane versions are optimized for GTO trajectories because this is where real money is earned!
LEO was always only a very small fraction of the Ariane flights.

Spacediver

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