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View Full Version : How fast is the Shuttle going when it clears the tower.

MrFloppy
10-07-2006, 06:16 PM
Someone told me that the Space Transportation System more commonly known as the Space Shuttle is already travelling at 120mph when it clears the tower.

I have been unable to confirm or disprove this.

Can anyone help?

engineer_comp_geek
10-07-2006, 06:48 PM
According to a couple of sites I found on google, the space shuttle accelerates at about 3g. I couldn't find a height of the tower in a quick google search, but based on the size of the rocket booster I figured about 200 feet or so for a rough ballpark figure. Assuming a constant 3g acceleration, I came up with about 133 mph at 200 feet (assuming I did my math right).

So, yeah, 120 mph sounds about right.

Shagnasty
10-07-2006, 07:01 PM
I swear I heard it was 70 mph at Space Camp (a long time ago) but I could be mistaken. They said it didn't look like much but it was better than many drag racing cars.

susan
10-07-2006, 07:05 PM
But at the point where it clears the tower, it's not at constant acceleration, right? It can't do 0-250 instantly.

susan
10-07-2006, 07:06 PM

Shagnasty
10-07-2006, 07:22 PM
Unfortunately, this video doesn't do what I hoped it would but it is really cool anyway. It is a launch with speed and downrange data shown for a Discovery launch. The readings don't start until several seconds after clearing the tower.

However, speed at 1/2 mile downrange is only 230 mph so that makes me think 130 mph at tower clearance seems high.

I swear they told me 70 mph and my grandmother paid good money to send me to Space Camp.

Shagnasty
10-07-2006, 07:30 PM
I found a message board that looks like it can open up a can of whoop-ass on the SDMB when it comes to space calculations. Maybe we should form an alliance.

Several answers indicate that the space shuttle would be going between 70 mph and the low 80's at the time of tower clearance. Maybe I should just throw away that complaint letter to Space Camp.

Santos L Halper
10-07-2006, 07:40 PM
I found a message board that looks like it can open up a can of whoop-ass on the SDMB when it comes to space calculations. Maybe we should form an alliance.

Actually that's the forum co-run by a former Straight Dope member, The Bad Astronomer (http://boards.straightdope.com/sdmb/member.php?userid=5394). A while back his board merged with one called Universe Today. And yes, they really know their stuff over there. :)

engineer_comp_geek
10-07-2006, 07:41 PM
Note that I was assuming a constant acceleration of 3g. You know what they say about that word "assume"...

If the acceleration is constant, then the math gets really easy.

Speed = acceleration x time
Position = 1/2 acceleration x (time squared)

I put in 200 feet for the position and 96 feet per second squared (1g = 32 feet per second squared, so 3g would be 96) for the acceleration. The tower looks to be a bit taller than that, and I assume that the rockets don't immediately go to full acceleration, but I just wanted a rough figure. I got a time of about 2.04 seconds. If you have a reasonably accurate stopwatch you can look at the video and see how long it takes the shuttle to clear the tower. If it's longer than 2.04 seconds then it wasn't accelerating at 3g and the speed is going to be slower.

I have problems downloading youtube videos on this computer. If someone can get what they think is an accurate time for the shuttle to clear the tower on the video then we can figure out the real acceleration and speed.

engineer_comp_geek
10-07-2006, 08:01 PM
From what I've been able to tell from the video, it takes closer to 4 seconds to clear the tower. This means the acceleration is a lot lower, more like 25 feet per sec squared.

Using this number, I get a speed of roughly 100 feet per sec or 68 mph.

Looks like space camp got it right.

astro
10-07-2006, 08:12 PM
From what I've been able to tell from the video, it takes closer to 4 seconds to clear the tower. This means the acceleration is a lot lower, more like 25 feet per sec squared.

Using this number, I get a speed of roughly 100 feet per sec or 68 mph.

Looks like space camp got it right.

Here are some videos (http://www.eclipticenterprises.com/gallery_rocketcam.shtml)