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[ar81]

I have a question. Are nuclear engines pollutant?

 

[insane_alien]

like most things it depends on the design.

an orion type nuclear engine where its basically a thermonuclear warhead chucked out the back and detonated would be the worst case and a thermal nuclear rocket where the fuel never comes into direct contact with the nuclear fuel elements would be the best case and non-polluting.

of course, you have to account for pollution in this case is reffecing to radioactive contamination rather than the traditional pollutants which cause disruption by chemical means.

 

[Urwumpe]

Just watched the interviews, and Alan Bond(M.D.) seems quite upbeat. Interesting comment toward the end. He says when the current generation of expendable rockets need to be replaced, there would have to be good reasons for not using Skylon/Sabre technology. I assume he means the Arianne series, wonder if he's told ESA yet...

Well, IMHO Alan Bond is in the position to have some confidence. Of course, he would have to do his own homework, but for the limited resources he has, he as achieved a lot. Also, don't forget: Ariane V will be due for replacements, in the current pace of things, in just seven years. Too early for Reaction Engines to be bothered and his technology will likely not find use in the heavy lift segment. But in a bit more time, Soyuz will be due for replacement inside ESA. And in that window, Reaction Engines could indeed have a viable alternative to offer and get a development contract. Especially if the expected happens and EADS gets the Ariane 6 contract.

---------- Post added at 03:15 PM ---------- Previous post was at 03:12 PM ----------

I have a question. Are nuclear engines pollutant?

Depends on the engine mode. In general, you have to say yes. In special, the nuclear thermal engines are not pollutant in nominal operation, as the nuclear fuel is encased and moderated by the fuel flow around them.

 

[movieman]

In general, you have to say yes. In special, the nuclear thermal engines are not pollutant in nominal operation, as the nuclear fuel is encased and moderated by the fuel flow around them.

However, if it's a fission engine then the engine itself becomes a pollutant after use: you have to be careful about how you dispose of it. For the NERVA tests, for example, NASA planned to launch the Saturn on a trajectory which would result in the NERVA upper-stage crashing in or near Antarctica if it failed to achieve escape velocity... that put a lot of constraints on the launch.

 

[Notebook]

Not sure about the replies chaps, isn't the Sabre engine a non nuclear design?

 

[Urwumpe]

Yes, but the technology inside the Sabre engine is also useful for nuclear engines (especially the advanced heat exchangers), that Reaction Engines also is involved in a NTR project.

 

[Notebook]

Was it this:-

http://www.reactionengines.co.uk/downloads/REL_Engine_Names.pdf


SERPENT na 8000 Liquid Hydrogen Nuclear rocket engine study.



N.

 

[Spike Spiegel]

About the intake of this engine....

Someone mentioned closing the cone of it. I assume that you'd want it closed off during re-entry. (Correct me if I'm wrong.) What I'm trying to picture in my head is the shape and operation of the closing mechanism/doors. How do you properly seal off a circular area like that?

 

[Notebook]

I don't know! However these links may help.

http://www.reactionengines.co.uk/sabre.html

http://www.reactionengines.co.uk/images/sabre/library/sabre-nacelle-m.jpg

Also during this animation

http://www.reactionengines.co.uk/skylon_ops_anim.html

The Sabre engine has an opening, then somehow the intake is blocked? I blame it on the animators.

N.

 

[Urwumpe]

No, like on the SR-71, the intake cone gets moved. When switching the pure rocket mode, the intake closes by extending the cone fully forward.

 

[Spike Spiegel]

And I guess moving the cone would allow enough closure to protect against re-entry heat?

What's the other purpose for moving the cone? You mentioned the SR-71 did this as well. Does it have something to do with engine operation at different altitudes?

 

[Urwumpe]

Yes, the position of the nose cone relative to the lip of the air intake defines the compression because of reflected shock waves. The intake should "capture" the shock of the cone. By moving the cone, you make sure that at different Mach numbers, the shock hits the intake lip and does not arrive earlier (missing the intake) or later (getting reflected in the wrong direction, causing a intake stall)

 

[movieman]

Yeah, from what I remember the SR-71 intake cones are controlled by an analog computer and took a lot of testing to get them working correctly: even then Lockheed had to add an automatic restart capability for when engine cut out at Mach-3.

 

[Urwumpe]

Yeah, from what I remember the SR-71 intake cones are controlled by an analog computer and took a lot of testing to get them working correctly: even then Lockheed had to add an automatic restart capability for when engine cut out at Mach-3.

No, the analog computer actually required a manual intake restart, AFAIR, the newer digital computer did it automatically and so fast that the pilot had not even a chance to notice that a restart took place.

Intake restart is not the same like an engine restart. The engine restarts required full reignition of the engines, costing precious TEB chemicals, the intake restart alone required extending the nose cone until airflow resumed.

 

[Spike Spiegel]

Might it be possible to use air-breathing rocket engines like the Sabre to launch a rocket vertically? Would there be sufficient thrust, or is the thrust low enough that aerodynamic lift is a required component of the ascent?

 

[Notebook]

From Reaction Engines Sabre page:-

The thrust during airbreathing ascent is variable but around 200 tonnes. During rocket ascent this rises to 300 tonnes but is then throttled down towards the end of the ascent to limit the longitudinal acceleration to 3.0g.

Thats for two engines.

Here is a video of Richard Varvill talking about the engine:-

http://www.space.co.uk/DataBank/Vid...Varvill-Of-Reactiion-Engines-At-IAC-2008.aspx

So for one engine, if your launch mass is less than 100 tonnes, you should go straight up!
Where do you put the air inlet though?...

 

[tblaxland]

Here is a video of Richard Varvill talking about the engine:-

A nice video actually. Good to see someone not afraid to get into some technical detail and to use proper units (except for thrust in tonnes...).

Where do you put the air inlet though?...

Ummm, on the front? Perhaps I have misunderstood the question...

 

[Notebook]

Another attempt at humour fails, such is life!

I was thinking of a Thunderbird 1? rocket type, with the engines on pods, probably rotating as the pitch changes.

Got my Thunderbirds wrong, 3 was the rocket.

N.

 

[tblaxland]

Another attempt at humour fails, such is life!

I was thinking of a Thunderbird 1? rocket type, with the engines on pods, probably rotating as the pitch changes.

Got my Thunderbirds wrong, 3 was the rocket.

N.

Now I see what you mean. That went straight over my head the first time round

 

[Spike Spiegel]

Thanks guys, and yes, I was thinking of something along the lines of that Thunderbirds thing.