Re: Plutonium on Next Atlas V - Bad Idea?

On Mon, 15 Aug 2005 14:06:55 -0500, Damon Hill
<damonunoseisuno@xxxxxxxxxxxx> wrote:

>Cardman <do-not@xxxxxxxxxxx> wrote in
>news:7in1g1l1su1ahmf57738e249j6n5nhaeso@xxxxxxx:
>
>> Sounds fair enough. Although should one of those SRBs fail, then I
>> guess that the main engine could compensate.
>
>Unlikely. A failure to ignite means the dead weight of propellant
>and loss of energy will prevent the payload from achieving the
>necessary escape velocity.

Well, New Horizons seems to be going for rather a fast trip, where it
seems possible that it could still make escape velocity. Those SRBs
come off a lot more early in the flight.

The main problem is that you would lose that extra thrust, which I
presume would put you at a slower speed in a more general direction.

In the end I have no idea if recovery would be possible. It would
certainly get up there, but just not quite where it should be.

>Might not even make it into low orbit.

I do not see that things would be that bad. This rocket is clearly
going for a high escape velocity.

This Atlas V 551 configuration can put 8672kg into GTO. This weight
would be the New Horizons payload and the Star 48B third stage. What
the real weight is I cannot say, but I have a strong feeling that it
is a lot less than 8672kg.

>Those are pretty big solids and represent quite a bit
>of energy, for a very high-energy mission.

Yes they are.

However, the Mars Reconnaissance Orbiter (what they call "Mr O" and I
call "Mr Oh Dear. Something has gone wrong!") used the basic 401
configuration to go to Mars.

In other words I am quite sure that those 4 extra SRBs could move the
dead weight of 1 SRB in order for this probe to make escape velocity.

>A busted nozzle might not doom the flight, but it'd sure be
>dicey. If the expended motor case fails to separate, see above
>paragraph.

Now that one is a lot more interesting. Having it stuck on for the
full flight time of the 1st stage sounds to me like this probe would
end up even more away from where it should be.

I guess that they could have built some backup plan in the 2nd or 3rd
stages, but then I have no idea. Still, usually when a probe or
satellite fails to reach the correct orbit, then they can sometimes
recover it.

>There ARE risks but they seem to be low enough to take
>the chance, else we'd never get anything done.

I would be happy with it. So are they it seems.

Cardman.
.