bobjengr, I had a similar thought when I read TJ's post--this is part of the larger efforts to reduce space junk, as well as part of larger efforts to extend the usable life of (very expensive spacecraft.
Its funny, as you stand at a distance and view the entire timeline of space flight history, (now at a brief 50+ years), who would have imagined at the beginning that Design for Demise (D4D) would have been a serious initiative. I humorously think back at JFK's inspiring speech, challenging to the US Space program to put a man on the mood before the end of the decade – then add this embellishment: " -- and be sure the craft breaks up properly to keep outer space green for centuries to come!" My, how priorities change.
Excellent Post Ann. NASA has for some time been concerned with "space junk". These tanks will definitely help lessen this huge issue for our planet. I posted an article through Word Press some months ago highlighting real problems space junk provides.
The overwhelming number of particles are smaller than one centimeter; i.e., 0.39 inches, but others are of considerable size. Estimates are as follows:
· 1,500 pieces of debris weighing more than 100 Kg or 200 pounds.
· 19,000 pieces of debris measuring between 1 to 10 centimeters; 3.9 inches.
· An unestimated number of particles, mostly dust and paint "chips" resulting from collisions that have occurred with larger objects also orbiting. Some "guesses" put that number into the millions.
For the most part, the debris can be categorized as follows:
· Jettisoned garbage from manned spacecraft, purposefully disposed of into lower earth orbit
· Lost equipment; i.e. cameras, tools, measuring devices, fabric hold-down straps, nuts, bolts, cotter pins, etc.
· Debris from collisions tearing apart structures either jettisoned or lost
· Rocket boosters that orbit yet remain in space. Some, over time, experience decaying orbits, eventually falling to earth.
· Satellites that no longer function but still orbit in LEO (Low Earth Orbit) or HEO (High Earth Orbit). Generally satellites operate between 435 to 800 miles above the earth. When these satellites "die", they do not accomplish reentry but simply stay aloft as dormant objects. Think of the number of telecommunication devices now orbiting the earth. Most will eventually fade and no longer fulfill their purpose, being replaced with newer technology.
Hi, I was the principle investigator for GSFC's GPM demiseable tank (now retired). the effort spanned about 10 years. Last year we published a number of papers in JANNAF, AIAA, SAMPE and had an artlcle in the Compsoites World trade magazine. While the goal of the effort was to produce a spacecraft propellant tank which demised (ablated) upon reentry. The goal of the entrie spacecraft was to do the same so that we would not need to waste propellant or curtail the useful life of the spacecraft just to force it to reenter to a safe splash down location (usually the Pacific Ocean). Your question had to do with fragmentation due to impacts or over pressurization. The tank was designed to not fracture in a brittle fashion. Most spacecraft propellant tanks including monolithic metallic tanks will rupture violently but the result is usually a number of sizeable chunks rather than shards such as is the case for a ruptured glass bottle. COPV's have the added benefit of having the composite and metal liner firmly bonded to each other which should also reduce the number of small fragments. For space debris fields it's the cloud of small fast pieces rather than a few large chunks tha tis the bigger worry - shot gun vs cannon ball. Hope this helps answer your question. BTW, the hidden beauty of a demiseable spacecraft is that it can be left to itself to die a natural death as it ages and gets less reliable rather than needing to be forced to reenter while it is healthy enough to do so. With spacecraft like GPM coming in at $500M - $1000M one can see that extending its life by even a year is very attractive
Ann, my thoughts were incomplete, please excuse me. The tanks burn up better on reentry, but what about if the tank does not reenter atmosphere? More than a few tanks ruptured catastrophically on orbit when the fuel in them heated up, expanding to rupture the tank. This happens with spent upper stages that do not reenter shortly after launch. Most agencies now reignite the spent stage after separation from IRS payload to consume all possible fuel and oxidizer; or have a way to vent to prevent this problem. Several times in the last shuttle flights, one could see the external tank venting after separation from the shuttle.
TJ, the whole point of making this tank partly out of composites instead of out of all metals was to help it disintegrate more easily, completely and harmlessly. NASA began R&D on demiseable craft a few years ago after a couple of notorious incidents involving spacecraft debris causing potential hazards on reentry.
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