07 April 2005

Re-entry debris footprints

It seems that a number of government officials are holding to their concern about the prospect that the Titan 4B booster scheduled to carry a classified US NRO payload into orbit from Florida will hit the "massive" Hibernia platform.

To see if we can help allay their almost phallicly-based concerns, here's some added information on the footprint left by falling space debris.

The Titan 4B is a two stage system. That means the payload is placed in orbit after it separates from a second stage that has carried it into space. The first stage and side-mounted boosters will have burned out and fallen back to Earth shortly after the launch.

While the Titan 4B may be a 10, 000 pound system fully loaded, the second stage will be returning to Earth the farthest of all debris from the launch point, will have broken up on reentry to Earth's atmosphere and will therefore consist of smaller bits and pieces than when it was fully assembled.

In the case of the system on the pad at Canaveral for the B-30 launch, there is no second stage. It's a 403B version. Therefore, the bulk of the debris will be even closer to the launch point in Florida.

That said, I draw attention to a description of a "debris footprint" from the FAQ at this site, kept up by the Center for Orbital and Reentry Debris Studies.

In particular pay attention to this paragraph:

"The footprint width is generally determined by the effects of wind on the falling debris objects, with heavy objects affected less, and lightest the most. The width of the footprint may also be affected by the breakup process itself. For example, if the object should explode during reentry, fragments will be spread out across the footprint. A footprint width of perhaps 20-40 km is typical, with the most pronounced effects near the heel of the footprint."

If you look at the nice little graphic on that site you will see a big red area on the map representing the surface area where debris may fall.

Until someone shows me the debris footprint for this particular launch, I am going to go out on a limb and say that the Hibernia and Terra Nova rigs were 15 miles outside the red zone representing the most like region of impact for all the bits and pieces of this Titan 4(03)B.

The odds of any bits striking these platforms was small.

And for the record, I give the Premier some slack when he said something about Americans being concerned about seals but not about missiles dropping on peoples' heads. He was a bit concerned, likely based on a poor briefing. Since he loves drama and hyperbole in equal measures, he could come up with a statement that is as accurate as the one uttered by a future Premier when he talked of turbot hanging on by their fingernails.

Fish don't have fingers.