SRB Tanks going up to 41 miles and back down in 400 seconds

http://io9.gizmodo.com/5893615/absolutely-mindblowing-video-shot-from-the-space-shuttle-during-launch?utm_medium=sharefromsite&utm_source=io9_facebook

Maximum height the external fuel tanks reached: 41 miles
Maximum speed: approx. 2937 MPH
Time to reach that speed/height: 197 seconds
Time to fall: 203 seconds
Speed when parachutes deployed: 216MPH

Why post in this forum??

Joat42 wrote:Why post in this forum??

Because it illustrates what a object free falling from orbit does, although the SRBs didn't reach orbit. Similar to what an free-falling object from the OBS would do.

I noted that the final speed of the SRB was approx. 220 mph, even though it began at 41 miles and almost 3000 mph. I am also aware that the final speed of a falling object depends upon its mass. However, I do believe that this illustrates that an unpowered object falling from space does not have as much energy for impact damage as you might think.

Also you might note that the 2 SRBs, although they started out not very far from each other seemed to have landed a fair distance apart, althought not out of sight from each other, indicating that landing unguided is not a good way to bomb a location.

Keith_w wrote:

Joat42 wrote:Why post in this forum??

Because it illustrates what a object free falling from orbit does, although the SRBs didn't reach orbit. Similar to what an free-falling object from the OBS would do.

I noted that the final speed of the SRB was approx. 220 mph, even though it began at 41 miles and almost 3000 mph. I am also aware that the final speed of a falling object depends upon its mass. However, I do believe that this illustrates that an unpowered object falling from space does not have as much energy for impact damage as you might think.

Also you might note that the 2 SRBs, although they started out not very far from each other seemed to have landed a fair distance apart, althought not out of sight from each other, indicating that landing unguided is not a good way to bomb a location.

SRB are extremely poor examples to compare with since they are designed not to easily reach terminal velocity after they have been jettisoned. It's like comparing a leaf to a rock, just watch any video from a booster falling and you will see it tumbling around almost the whole time until the parachute deploys.

You'd be surprised by the amount of energy an object free falling from orbit can liberate on impact if it's designed to do so. The USAF released a report in 2003 where they described an orbital kinetic bombardment system consisting of computer guided tungsten rods 6.1m long and 0.3m in diameter which would after orbital release and free falling reach Mach 10 (12200 km/h or 7600 mp/h) and release energy the equivalent of 11.5 tons of exploding TNT on impact.

Because it illustrates what a object free falling from orbit does, although the SRBs didn't reach orbit. Similar to what an free-falling object from the OBS would do.

What makes you think the OBS uses free-falling projectiles instead of an accelerated one?

Duckk wrote:

Because it illustrates what a object free falling from orbit does, although the SRBs didn't reach orbit. Similar to what an free-falling object from the OBS would do.

What makes you think the OBS uses free-falling projectiles instead of an accelerated one?

The SRBs are hollow, and empty inside. Much drag, little mass.

Of course, if you have an orbiting space bomber and shove the rod out the bomb bay, it won't go much of anyplace. It is still in orbit. To hit the ground, it needs a retrorocket.

Man, this whole topic is so wrong...

The shuttle tank weighs 26650 kg empty, and has a volume of 553358 L. That means its overall density is 0.043 g/cm^3.

For comparison, Styrofoam is ~0.05 g/cm^3.

So a giant solid block of Styrofoam the size and shape of the shuttle main tank would weigh more and have a higher terminal velocity. Probably the least effective projectile imaginable.

On top of that, the main shuttle tank is only ever ballistic, whereas anything in orbit is going to require far more velocity to do anything but plunk back down to the earth's surface. The quoted max velocity for the shuttle tank is 1.34km/s (3000mph). Orbital velocity for LEO IS ~7.8 km/s... Kinetic energy in a projectile increases with the square of velocity... the difference in these velocities gives the orbital projectile more than 30x the energy.

And that 30x is even before the method used to deorbit the projectile. No braking is used... why waste the energy in that direction? Instead, the projectile would be boosted with even more velocity that would put it into a highly elliptical orbit where it's gaining velocity the whole time from its greatest orbital distance (aphelion) from the earth to the point it hits the atmosphere.

Solid tungsten is usually the quoted material, as it has an incredibly high melting point (hence it's use as a lightbulb filament... white-hot and unmelted) and it also has a very high density (nearly 20g/cm^3).

Each projectile is commonly quoted as being akin the size of a telephone pole and would hit with the destructive energy of a small nuke. But no fallout...

For more information, look up "rods from God."
https://en.m.wikipedia.org/wiki/Kinetic_bombardment

You propose " Instead, the projectile would be boosted with even more velocity that would put it into a highly elliptical orbit where it's gaining velocity the whole time from its greatest orbital distance (aphelion) from the earth to the point it hits the atmosphere."

That doesn't work, at least not as described. We start from a nearly circular orbit. If you change the speed over a very short distance, but do not change the direction, when you come back where you started you will be going in exactly the same direction, and will be at perihelion, too high to hit the atmosphere.

samwichse wrote:Man, this whole topic is so wrong...

The shuttle tank weighs 26650 kg empty, and has a volume of 553358 L. That means its overall density is 0.043 g/cm^3.

For comparison, Styrofoam is ~0.05 g/cm^3.

So a giant solid block of Styrofoam the size and shape of the shuttle main tank would weigh more and have a higher terminal velocity. Probably the least effective projectile imaginable.

On top of that, the main shuttle tank is only ever ballistic, whereas anything in orbit is going to require far more velocity to do anything but plunk back down to the earth's surface. The quoted max velocity for the shuttle tank is 1.34km/s (3000mph). Orbital velocity for LEO IS ~7.8 km/s... Kinetic energy in a projectile increases with the square of velocity... the difference in these velocities gives the orbital projectile more than 30x the energy.

And that 30x is even before the method used to deorbit the projectile. No braking is used... why waste the energy in that direction? Instead, the projectile would be boosted with even more velocity that would put it into a highly elliptical orbit where it's gaining velocity the whole time from its greatest orbital distance (aphelion) from the earth to the point it hits the atmosphere.

Solid tungsten is usually the quoted material, as it has an incredibly high melting point (hence it's use as a lightbulb filament... white-hot and unmelted) and it also has a very high density (nearly 20g/cm^3).

Each projectile is commonly quoted as being akin the size of a telephone pole and would hit with the destructive energy of a small nuke. But no fallout...

For more information, look up "rods from God."
https://en.m.wikipedia.org/wiki/Kinetic_bombardment

phillies wrote:That doesn't work, at least not as described. We start from a nearly circular orbit. If you change the speed over a very short distance, but do not change the direction, when you come back where you started you will be going in exactly the same direction, and will be at perihelion, too high to hit the atmosphere.

Yes, I forgot the second burn, which is a brake burn at aphelion.

Sam

phillies wrote:

Duckk wrote:
What makes you think the OBS uses free-falling projectiles instead of an accelerated one?

The SRBs are hollow, and empty inside. Much drag, little mass.

Of course, if you have an orbiting space bomber and shove the rod out the bomb bay, it won't go much of anyplace. It is still in orbit. To hit the ground, it needs a retrorocket.

1) absolutely nothing.
2) Yes I am aware of that, especially after they burn their contents
3) wouldn't that depend on which direction you threw it out of the space bomber and with how much force?