Author Topic: Basic Rocket Science Q & A  (Read 277465 times)

Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #660 on: 08/22/2011 03:22 PM »
A modern ICBM is able to hit multiple targets using multiple independently targetable reentry vehicles with an accuracy of 150 meters and very high reliability. 

Weapon systems reliability is not same as for space launch.  The make up for failures with numbers.   Also the weapon system payloads are passive for launch.

Offline DarkenedOne

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Re: Basic Rocket Science Q & A
« Reply #661 on: 08/22/2011 05:21 PM »
A modern ICBM is able to hit multiple targets using multiple independently targetable reentry vehicles with an accuracy of 150 meters and very high reliability. 

Weapon systems reliability is not same as for space launch.  The make up for failures with numbers.   Also the weapon system payloads are passive for launch.

The Trident missile system has had 135 consecutive successful tests.  That is pretty much the best space launch systems to date.

Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #662 on: 08/22/2011 05:30 PM »

The Trident missile system has had 135 consecutive successful tests.  That is pretty much the best space launch systems to date.

When it can put 50klb spacecraft into LEO then use it as example.

Offline Tcommon

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Re: Basic Rocket Science Q & A
« Reply #663 on: 08/22/2011 05:57 PM »

The Trident missile system has had 135 consecutive successful tests.  That is pretty much the best space launch systems to date.

When it can put 50klb spacecraft into LEO then use it as example.

DarkenedOne, that's an excellent example. Launching with fewer people reliably is clearly possible, as shown with your example. Its the kind of new technology and designs that NASA should be working on.

It's a clear tip-off when Jim slams questions like this without offering any significant  technical rationale.
« Last Edit: 08/22/2011 05:58 PM by Tcommon »

Offline AS-503

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Re: Basic Rocket Science Q & A
« Reply #664 on: 08/22/2011 06:13 PM »
ICBM does not equate to manned space launch.

Apples to Oranges.

Almost no commonality. Trajectory, mission type, ground support equiptment, facilities...etc.etc.

I stand by Jim's assertion.

Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #665 on: 08/22/2011 06:16 PM »

The Trident missile system has had 135 consecutive successful tests.  That is pretty much the best space launch systems to date.

When it can put 50klb spacecraft into LEO then use it as example.

DarkenedOne, that's an excellent example. Launching with fewer people reliably is clearly possible, as shown with your example. Its the kind of new technology and designs that NASA should be working on.

It's a clear tip-off when Jim slams questions like this without offering any significant  technical rationale.

"50klb spacecraft into LEO" is significant technical rationale.
Trident SLBM are not space launch vehicles.  And RV's are not spacecraft.  or even manned spacecraft.

It has nothing to with "new technology".  It has to do with complexity of the task and the complexity of the payload.  That is the difference between the vehicle.

Sticking with SRM's.

You have excluded the team to build up the trident, that is not part of the submarine crew nor the ICBM launch teams for Minuteman.
Look at a Minotaur launch team, it is in the 40 to 50 range (including the techs to build it up)


Offline mmeijeri

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Re: Basic Rocket Science Q & A
« Reply #666 on: 08/22/2011 06:24 PM »
Also the weapon system payloads are passive for launch.

Can you explain what you mean by that? I sometimes hear "spacecraft on internal power" or words to that effect in launch audio feeds, but what exactly does a spacecraft actively do before and during ascent?
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Offline Tcommon

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Re: Basic Rocket Science Q & A
« Reply #667 on: 08/22/2011 06:50 PM »
"50klb spacecraft into LEO" is significant technical rationale.
Trident SLBM are not space launch vehicles.  And RV's are not spacecraft.  or even manned spacecraft.

It has nothing to with "new technology".  It has to do with complexity of the task and the complexity of the payload.  That is the difference between the vehicle.,

And yet SLBMs have independently targeted payloads and so are more complicated, at least in one respect

Quote
Sticking with SRM's.

You have excluded the team to build up the trident, that is not part of the submarine crew nor the ICBM launch teams for Minuteman.
Look at a Minotaur launch team, it is in the 40 to 50 range (including the techs to build it up)

I wouldn't suggest launching from a submarine as a way to reduce launch personnel.

Jim you're saying what is, I'm asking what's possible by way of examples that show it can be done, reliably. But you don't get something for nothing. Reducing launch personnel would certainly entail a redesign of the carrier rocket, facilities and operating procedures, if not the entire company that launches it.  And would probably require less flexible standards that the payload must meet.


Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #668 on: 08/22/2011 06:56 PM »
I'm asking what's possible by way of examples that show it can be done, reliably.


They aren't valid examples.  launching a small warhead is not the same as launching a large spacecraft.

An RV is rugged and self contained.

Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #669 on: 08/22/2011 06:58 PM »

And yet SLBMs have independently targeted payloads and so are more complicated, at least in one respect



That isn't that complicated.
a.  The warhead does some of the maneuvering.
b. the target is stationary.

Offline agman25

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Re: Basic Rocket Science Q & A
« Reply #670 on: 08/22/2011 07:31 PM »
I have a question about lattice structures on interstages. It has been my understanding that these are designed to dissipate any fuel or oxidizer that may leak from the upperstage.

I see a simillar structure on the Agni-II, which is a solid fuelled IRBM. Can anybody explain why this design was used when there is no chance of fuel leakage. Does it have any other benifits.
« Last Edit: 08/22/2011 07:33 PM by agman25 »

Offline Jorge

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Re: Basic Rocket Science Q & A
« Reply #671 on: 08/22/2011 07:33 PM »
I have a question about lattice structures on interstages. It has been my understanding that these are designed to dissipate any fuel or oxidizer that may leak from the upperstage.

I see a simillar structure on the Agni-II, which is a solid fuelled IRBM. Can anybody explain why this design was used when there is no chance of fuel leakage. Does it have any other benifits.

The primary purpose of such structures is to allow "fire in the hole" staging, as opposed to separating first and then firing the upper stage.
JRF

Offline agman25

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Re: Basic Rocket Science Q & A
« Reply #672 on: 08/22/2011 07:37 PM »
Thanks.

Offline AS-503

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Re: Basic Rocket Science Q & A
« Reply #673 on: 08/22/2011 07:41 PM »
The Apollo LM had "fire in the hole" for lunar ascent and descent abort capability.

I think the S-1b that launched the LM for the "fire in the hole" unmanned test flight was the booster from the Apollo 1 fire.

I wonder what the gas pressure on various portions of the Apollo LM was like given the lack of venting with respect to the previously mentioned lattice structures as an interface. 

Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #674 on: 08/22/2011 07:45 PM »
It went around the descent engine

Offline clongton

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Re: Basic Rocket Science Q & A
« Reply #675 on: 08/22/2011 11:11 PM »
An ICBM is little more than a sophisticated gigantic artillery shell whose properties are so well known that its trajectory can be calculated to within a few meters of accuracy for ground impact. The main difference is that the solid propellant for an artillery shell is explosive while the solid propellant for an ICBM is not. The mass of all 10 of those MRVs combined don't come anywhere near the mass of a manned spacecraft. Plus once you launch an ICBM it will go where it is sent, provided something doesn't act on it from outside. If it goes off trajectory it cannot be controlled and is destroyed. Not so for a manned spacecraft. If it starts to go off trajectory you correct the trajectory if you can. The LV has that capability while the ICBM does not. If it can't be corrected you abort the spacecraft to a safe landing. Try doing that with any one of the MRVs.

The comparison is completely off the wall insane.
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Offline mmeijeri

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Re: Basic Rocket Science Q & A
« Reply #676 on: 08/22/2011 11:21 PM »
If that were true then Atlas and Titan could never have been converted to space launch systems.
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Offline clongton

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Re: Basic Rocket Science Q & A
« Reply #677 on: 08/22/2011 11:34 PM »
If that were true then Atlas and Titan could never have been converted to space launch systems.

We were comparing modern solid fuel ICBM's to a manned launcher. Atlas and Titan were liquid fuel.
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Offline Tcommon

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Re: Basic Rocket Science Q & A
« Reply #678 on: 08/22/2011 11:38 PM »
If that were true then Atlas and Titan could never have been converted to space launch systems.

We were comparing modern solid fuel ICBM's to a manned launcher. Atlas and Titan were liquid fuel.

No, not solid ICBMs specifically. No, not manned launchers specifically.
http://forum.nasaspaceflight.com/index.php?topic=13543.msg796429#msg796429

Offline yinzer

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Re: Basic Rocket Science Q & A
« Reply #679 on: 08/23/2011 03:48 AM »
The ICBM to launch vehicle comparison is not completely off-the-wall insane, as should be obvious when you consider that there are current launch vehicles that are barely modified ICBMs, eg: Dnepr.

The size of the launch crew and the length of the countdown are essentially design requirements, and the people buying ICBMs want both to be very small while the people buying space launches largely don't care.

In order to meet these requirements ICBM designers do things like include extensive automated test equipment, use solid or storable fuels, house their rockets in silos, buy and build all their rockets ahead of time and in significant quantity, and do regular test flights.  All of these things costs money, both on the launch vehicle side and the payload side.
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