Author Topic: Basic Rocket Science Q & A  (Read 270914 times)

Offline Eerie

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Re: Basic Rocket Science Q & A
« Reply #220 on: 05/24/2009 04:07 PM »
Just musing about how dangerous the technology, plans etc of these private rockets are if they fall into the hand of states such as Iran, Syria etc.. ?

SpaceX will have to use Falcon-9 with Dragon to nuke someone. ICBM needs a reentry vehicle.

Hmm, I wonder how many megatons you can stuff into Dragon...

Offline duane

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Re: Basic Rocket Science Q & A
« Reply #221 on: 05/24/2009 05:14 PM »

My question is how much of a step up in technology or avionics etc would need to go into the rocket system to convert it to a small ICBM ?

None.  A space launch vehicle is just a ICBM with longer range.

Well that kinda sounds frightening!

Could something like a Falcon be accurate enough with just a dumb reentry vehicle (no manuevering) to hit a county (30X30 miles) ?

Do modern launch vehicles still use Intertial Navigation Units or do they use GPS systems, or a combination of both ?

Thanks a bunch!
Duane

Offline Danny Dot

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Re: Basic Rocket Science Q & A
« Reply #222 on: 05/24/2009 05:31 PM »

My question is how much of a step up in technology or avionics etc would need to go into the rocket system to convert it to a small ICBM ?

None.  A space launch vehicle is just a ICBM with longer range.

Well that kinda sounds frightening!

snip

Duane

Thus all the fuss about ITAR.

Danny Deger
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Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #223 on: 05/24/2009 05:36 PM »

1. Could something like a Falcon be accurate enough with just a dumb reentry vehicle (no manuevering) to hit a county (30X30 miles) ?

2.  Do modern launch vehicles still use Intertial Navigation Units or do they use GPS systems, or a combination of both ?


1.  yes

2. INS

Offline duane

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Re: Basic Rocket Science Q & A
« Reply #224 on: 05/24/2009 06:34 PM »
Thanks Jim and Danny

I wont bother another question about accuracy. I have a feeling its probably a order or two of magnitude better than 30X30 miles, which is even more scary a thought.

Duane

« Last Edit: 05/24/2009 06:38 PM by duane »

Offline ginahoy

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Re: Basic Rocket Science Q & A
« Reply #225 on: 05/25/2009 03:13 AM »
Does anyone know the typical g forces astronauts were/are subjected to in the various vehicles during ascent and reentry? Seems like I recall during Project Mercury, the centrifuge trained up to about 10 g's. Soyuz ballistic reentry is probably the highest, but I don't think it's anywhere close to 10.
David

Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #226 on: 05/25/2009 03:24 AM »
Does anyone know the typical g forces astronauts were/are subjected to in the various vehicles during ascent and reentry? Seems like I recall during Project Mercury, the centrifuge trained up to about 10 g's. Soyuz ballistic reentry is probably the highest, but I don't think it's anywhere close to 10.
David

8 with Gemini and 6 with Apollo during ascent

Online hop

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Re: Basic Rocket Science Q & A
« Reply #227 on: 05/25/2009 03:33 AM »
Does anyone know the typical g forces astronauts were/are subjected to in the various vehicles during ascent and reentry? Seems like I recall during Project Mercury, the centrifuge trained up to about 10 g's. Soyuz ballistic reentry is probably the highest, but I don't think it's anywhere close to 10.
David
8-9 for ballistic Soyuz reentries. This shouldn't really qualify as "typical" since it only happens in the event of a malfunction. ISTR a nominal lifting Soyuz reentry peaks around 4. Launch escape is 15+.

Apollo lunar reentries were in the 6-7 range.

Offline ginahoy

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Re: Basic Rocket Science Q & A
« Reply #228 on: 05/25/2009 04:14 AM »
8-9 for ballistic Soyuz reentries. This shouldn't really qualify as "typical" since it only happens in the event of a malfunction. ISTR a nominal lifting Soyuz reentry peaks around 4.

Apollo lunar reentries were in the 6-7 range.


What's the nominal Shuttle reentry force?

Here's an interesting interview Whitson gave to CBS News, in which she discusses the BE at length:

http://www.shroomery.org/forums/showflat.php/Number/8356943

Quote
Launch escape is 15+.

Holy Moses!! Talk about a kick in the pants!

Offline Jorge

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Re: Basic Rocket Science Q & A
« Reply #229 on: 05/25/2009 04:27 AM »
8-9 for ballistic Soyuz reentries. This shouldn't really qualify as "typical" since it only happens in the event of a malfunction. ISTR a nominal lifting Soyuz reentry peaks around 4.

Apollo lunar reentries were in the 6-7 range.


What's the nominal Shuttle reentry force?

About 1.5 during entry. Gets a little higher during TAEM but never above 2.0.

http://spaceflight.nasa.gov/shuttle/reference/green/entare.pdf
JRF

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Re: Basic Rocket Science Q & A
« Reply #230 on: 05/25/2009 04:55 AM »
Also, if I may note, the (de)(ac)celeration figure should also be considered together with the *duration* of that peak load (same goes for thermal loads)  Also whether it's negative or positive.  A very short (milliseconds) even a 15+G peak may be more survivable than a longer 8G peak (same for thermal loads) 

[edit] obviously, after a certain threshold of 'neutral' levels of G's, like 4 perhaps, which can be benign for a while 

[edit2] And *up to* a threshold, of course, at which no short duration will help as things will simply be ripped out/pushed in instanteneously
« Last Edit: 05/25/2009 05:07 AM by lmikers »

Offline Danny Dot

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Re: Basic Rocket Science Q & A
« Reply #231 on: 05/25/2009 03:36 PM »
Does anyone know the typical g forces astronauts were/are subjected to in the various vehicles during ascent and reentry? Seems like I recall during Project Mercury, the centrifuge trained up to about 10 g's. Soyuz ballistic reentry is probably the highest, but I don't think it's anywhere close to 10.
David

The "winner" is a ballistic ascent abort entry and ballistic lunar entry.  These go up to about 20G.  The Russian have done this at least once and the US tested them in centrifuges in the 60s.  Believe it or not, they are OK.

Danny Deger
Danny Deger

Offline ginahoy

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Re: Basic Rocket Science Q & A
« Reply #232 on: 05/25/2009 04:21 PM »
... and ballistic lunar entry.

Elaborate please? Sounds like no retros, therefore surviving the g forces would be a moot point.

Edit - Sorry, I took 'lunar entry' literally. I'm guessing you meant reentry. (I need another cup of java)
« Last Edit: 05/25/2009 04:29 PM by ginahoy »

Offline mmeijeri

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Re: Basic Rocket Science Q & A
« Reply #233 on: 05/25/2009 04:25 PM »
The "winner" is a ballistic ascent abort entry and ballistic lunar entry. 

I read that a normal lunar reentry is mostly ballistic anyway, with only the RCS being used for attitude control. Is this true? And if so, how much difference does the attitude control make?
We will be vic-toooooo-ri-ous!!!

Offline StarStuff

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Re: Basic Rocket Science Q & A
« Reply #234 on: 05/25/2009 05:39 PM »
Apollo attitude during entry was determined by the offset of CG from the axis of symmetry. It could not be changed in flight. The guidance and control were accomplished with roll that moved the direction of lift.


Offline mmeijeri

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Re: Basic Rocket Science Q & A
« Reply #235 on: 05/25/2009 05:57 PM »
Apollo attitude during entry was determined by the offset of CG from the axis of symmetry. It could not be changed in flight. The guidance and control were accomplished with roll that moved the direction of lift.

Is roll rotation around the axis of symmetry? If so, how can it influence lift?
We will be vic-toooooo-ri-ous!!!

Offline Lee Jay

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Re: Basic Rocket Science Q & A
« Reply #236 on: 05/25/2009 06:07 PM »
Apollo attitude during entry was determined by the offset of CG from the axis of symmetry. It could not be changed in flight. The guidance and control were accomplished with roll that moved the direction of lift.

Is roll rotation around the axis of symmetry? If so, how can it influence lift?

If the CG is not located on the geometric axis the craft will come in "crooked" with aerodynamics compensating for the CG offset.  Roll would then control in which direction the "crookedness" (don't know if they called it skew, skid, slip or just AoA) was pointing thereby controlling the direction of lift.

Offline ginahoy

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Re: Basic Rocket Science Q & A
« Reply #237 on: 05/25/2009 06:17 PM »
Is roll rotation around the axis of symmetry? If so, how can it influence lift?

Yaw is rotation around about the 'vertical' axis, which in the case of a capsule, is the axis of symmetry. I get confused because with a capsule, the velocity vector is more or less the same as the vertical axis, whereas with an airplane, they are at right angles. 'Vertical' can be ambiguous because it's referential.

Offline StarStuff

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Re: Basic Rocket Science Q & A
« Reply #238 on: 05/25/2009 06:42 PM »
Think of airplane that has no control of pitch with the nose always  trimmed to a positive attitude.

You would have to descend by rolling upside down. That's what Apollo did.

Offline Danny Dot

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Re: Basic Rocket Science Q & A
« Reply #239 on: 05/25/2009 09:27 PM »
The "winner" is a ballistic ascent abort entry and ballistic lunar entry. 

I read that a normal lunar reentry is mostly ballistic anyway, with only the RCS being used for attitude control. Is this true? And if so, how much difference does the attitude control make?

A guided entry uses roll to put the lift vector largely up.  In a ballistic entry with a capsule, roll rate is set to a constant value and the end result is no effective lift.

In a controlled entry, the capsule ends up flying in much thinner air for a longer period of time.  I think the guided lunar entries were about 9 Gs, while a ballistic is about 20.  I don't think Apollo had a backup lunar ballistic mode.  I saw one short blurb about the Service module putting a dead Command Module heatshield forward and giving it a roll rate, but never saw enough info in the old Apollo documents to know if this procedure was taken to the point it was ready to use.  This would have been an option in Apollo 13, but the LM would have had to have done the maneuvering and I don't know if there would have been enough time to get back into the command module, close the hatch, and jettison the LM in time.

Danny Deger
« Last Edit: 05/26/2009 03:30 AM by Danny Dot »
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