Tiangong-1 is currently predicted by The Aerospace Corporation on 2018 April 1st to reenter the Earth’s atmosphere around April 2nd, 2018 00:30 UTC ± 1.7 hours.
The United States Strategic Command’s Joint Space Operations Center, “provides Trajectory Impact Prediction messages concerning space debris to many locations” informs the FEMA operations centers, “which monitor the data for the FEMA Administrator,” according to FEMA’s National Warning Systems operations manual.
The National Warning System “is a 24-hour continuous private line telephone system used to convey warnings to federal, state, local, tribal, and territorial government and public safety officials,” a FEMA spokesperson told Gizmodo. The organization pays closer attention to nuclear objects or those that may have poisonous fuels.
Once the authorities are notified, they would use the Integrated Public Alert and Warning System to warn people in danger.
Warning the right people could be difficult, though—the projected location is wildly unpredictable.
As the ESA writes in the same FAQ, “Even 7 hours before the actual reentry, the uncertainty on the break-up location is a full orbital revolution—meaning plus or minus thousands of km!”
The strike itself would litter debris spread over an area a hundred miles long and a few miles wide, says Harvard Astrophysicist Jonathan McDowel.
Launched: 2011 September 30 @ 03:16:03.507 UTC
Site: Jiuquan Satellite Launch Center, China
Mission: Tiangong-1, First Chinese Space Station
Mass: 8500 kg at launch (18,740 lbs, or 9.4 tons)
Length: 10.5 m (34 ft)
Diameter: 3.4 m (11 ft)
Solar panels: 2 panels (approx. 7 m x 3 m)
In a written statement, a spokesman from Aerospace's Center for Orbital and Reentry Debris Studies (CORDS) wrote: 'Potentially, there may be a highly toxic and corrosive substance called hydrazine on board the spacecraft that could survive re-entry.
'For your safety, do not touch any debris you may find on the ground nor inhale vapors it may emit.'
Hydrazine, (also known as N2H4, UDMH , or 1,1-dimethylhydrazine, or Unsymmetrical Dimethyl Hydrazine, an organic amine) is a colorless, oily liquid or sometimes white crystalline compound with a very highly reactive base.
UDMH (and its derivatives) is usually mixed with nitrogen tetraoxide (N2O4) to form a bi-propellant architecture.
It has a number of industrial, agricultural and military uses, including in rocket fuel.
WHY IS IT ON THIS SPACE STATION?
Spacecraft and satellites require hypergolic propellants because their thrusters are used for reaction control, which requires thrusters to fire intermittently and for short bursts. Due to the complexity in igniting a rocket engine with pyrotechnics, the ignition sequences is usually measured in multiple seconds, which makes short burst firings impossible.
HOW MUCH HYDRAZINE WAS ABOARD THIS THING?
Titanium hydrazine tanks range from 58-litre to 177-litre capacity. The 58-litre model is a bladder tank, the others being surface tension tanks.
I FIND NO RELIABLE REPORT OF HOW MANY OR WHAT SIZE TANKS ARE ATTACHED TO TIANGONG-1.
WHAT ARE THE KNOWN HAZARDS OF HYDRAZINE?
Symptoms of short-term exposure to high levels of hydrazine include irritation of the eyes, nose, and throat, dizziness, headache, nausea, pulmonary edema, seizures, and coma, according to the United States Environmental Protection Agency (EPA).
Long-term exposure can also damage the liver, kidneys, and central nervous system in humans.
The liquid is corrosive and may produce dermatitis from skin contact in humans and animals.
Increased incidences of lung, nasal cavity, and liver tumours have been observed in rodents exposed to hydrazine.
The EPA has classified hydrazine as a Group B2, a probable human carcinogen.
The combustion of UDMH/N2O4 also produces large quantities of nitrogen oxides, which can further react with water vapor and sulfate in the atmosphere to form small particles containing nitric acid.
At least one human is known to have died after 6 months of SUB-LETHAL
exposure to hydrazine hydrate.
[See 9.2.3. Mortality studies at http://www.inchem.org/documents/ehc/ehc/ehc68.htm]
IT HAS ALSO BEEN DETECTED IN STREAMS AND DRINKING WATER HERE ON EARTH.
5.2. General Population Exposure
It has been reported that analyses of hydrazine-treated boiler water and the condensate of steam, which could have been in contact with food, confirmed the presence of hydrazine (US FDA, 1979). District heating water has been mentioned as an additional potential route of accidental human exposure. This water may contain a low concentration of hydrazine as a corrosion inhi- bitor. If this water is used to heat tap water and there is a leak inside the heat-exchanger at the user end, the tap water may be contaminated. Cases have been reported in which hot water became contaminated with levels of up to 10.72 mg/litre and drinking-water, up to 0.47 mg/litre (Bodenschatz, 1986).
Traces of hydrazine have been found in samples of commercial maleic hydrazide, one of the uses of which is to inhibit sucker growth on tobacco.
5.3. Occupational Exposure
Workers may be exposed to hydrazine at facilities producing hydrazine itself and those producing its salts and derivatives, at propulsion testing and rocket launching sites, and at locations where aircraft using hydrazine as an emergency fuel are assembled or refueled. Workers at plants using high- pressure boilers are potentially exposed to relatively dilute solutions of hydrazine.
5.4. Populations at Special Risk
Recently, hydrazine was detected in the plasma of 8 healthy male volunteers taking (the drug) isoniazid for 2 weeks and in
the plasma of 8 out of 14 hypertensive patients treated with, among others, hydralazine. After 2 weeks of dosing with isoniazid, the average level of acid-labile hydrazine in men of a slow acetylator phenotype was 2.7 times higher than in men of a rapid acetylator phenotype (Blair et al., 1985).
Hydrazine can also be formed during the metabolism of these drugs (Noda et al., 1978; Timbrell & Harland, 1979).
WOULD ANYONE REALLY BOTHER TO WARN PEOPLE IN THE PATH, ONCE THE TRAJECTORY IS KNOWN?
“I imagine perhaps if there was a public information plan, it would generate more hysteria than would be warranted for something so unlikely,” Ruth Rand, historian of science, technology, and the environment during the Cold War at the University of Wisconsin told me. “I imagine some people might respond with undue fear and you might have a crisis in your hands.” Instead, it might be better to just give people what information is available, and remind them not to touch any debris with their hands, as it might contain a corrosive fuel called hydrazine.
THERE ARE WORSE, AS IN MORE TOXIC TO HUMANS, MAN-MADE OBJECTS THAT FALL FROM THE SKY.
In 1978, a nuclear-powered Russian spy satellite called Kosmos 954 crashed into Northern Canada with little warning, scattering radioactive debris. Skylab dropped some debris in a small Australian town, and the same discussions seem to come up whenever a satellite is slated to crash into Earth, as happened in 2011 when some of NASA’s Upper Atmospheric Research Satellite (UARS) crashed into Earth.
Our military has a say, too. The U.S. Air Force’s Joint Space Operations Center tracks objects 10 cm and larger in low Earth orbit and about 1 meter and larger in deep space on space-track.org. U.S. Air Force spokesperson Major Cody Chiles said, “We will continue to monitor this reentry and provide more information when it is available.” The USS Erie shot down failed spy satellite USA-193 with a missile back in 2008.
IN FEBRUARY, 2007, A CONSIDERABLE AMOUNT OF HYDRAZINE WAS DUE TO COME BLAZING BACK TO EARTH. WE SENT A MISSILE UP TO PREVENT THAT.
A U.S. missile was launched to destroy a derelict spy satellite before it could, potentially, splash a half ton of toxic hydrazine somewhere on Earth that would result in human injury or death.
"A Navy missile, on February 20, 2007, achieved a head-on collision with the five-ton USA 193 satellite and reduced it to impotent shrapnel, dispersing the contents of the vehicle’s propellant tank harmlessly in space.
How dangerous was USA 193?
“Under various assumptions we got different probabilities of human risk from the uncontrolled entry of this satellite,” Johnson told me by telephone. “But they were all much riskier than the accepted standard.” In fact, it wasn’t until last July 20, with the premiere on the cable TV Military Channel of a special program on the satellite intercept, that the actual values were released. General Henry “Trey” Obering, head of the US missile defense effort, disclosed the quantitative results for the likelihood of human casualty: “It varied depending on which experts we talked to, but [we got] anywhere between 1 in 45 and 1 in 25 chance of that occurring.” This translates to a range of 2.2 to 4%.
“Clearly nothing prior to USA 193 rose to that level,” said Nicholas L. Johnson, who has been NASA’s “space debris” guru for many years, leading a team of experts at the Johnson Space Center in Houston.
“The risk posed was much higher than any risk we’ve ever seen.”
MIT scientist Geoff Forden calculated a 3.5% chance of injury if the tank reached the ground, although he doubted it would—and he felt that chance was too small to bother with.
General Kevin Chilton, Commander in Chief of the US Strategic Command, disagreed with Forden.
Chilton confirmed that it was the specific contents of this satellite (THE HYDRAZINE) that elevated the hazards far above the mitigation requirement threshold. “If it had just been hardware we would never consider these extraordinary measures,” he told me. The presence of the toxic chemical, in a tank completely full because the payload had failed immediately after launch, was the unusual driving factor. Johnson concurred: “The odds of injuring many people was much higher then we’d seen in the past,” he had explained. “It was no longer just physical trauma injury.”
A graphic illustration of this nightmare scenario occurred on October 15, 2004 when an off-course Chinese spy satellite’s film canister smashed through the roof of a four-story apartment building in Penglai (southwest Sichuan). Photographs through the smashed roof of the refrigerator-sized capsule sitting among splintered bricks and wood showed what might have happened if it had been carrying toxic chemicals—dozens of people might have been poisoned, many fatally. And in terms of probabilities, this was one of only several hundred uncontrolled landings of similarly-sized space vehicles.
NASA's STUDY STATED THAT THE TANKS CAN VERY LIKELY SURVIVE REENTRY.
NASA’s detailed computations of the tank’s survivability were described in a paper by NASA contractor experts Robert Kelley and William Rochelle in Houston. Their results were summarized at the end of the paper: “Under the initial conditions and modeling techniques described above, it was found that the N2H4 located inside of the titanium tank does not reach its melting temperature. The N2H4 would have needed to absorb 43.15 MJ of energy to reach 275 K [its melting point] from the start temperature of 214 K. It only absorbed 29.34 MJ, or about 68% of that.”
Nor would the tank disintegrate from other forces.
Johnson added that the deceleration forces—perhaps 8 to 10 Gs—were well within the structural strength of the tank to endure.
As to the observation that the hydrazine “exploded” when the tank was actually hit—possibly indicating it would have done the same during the descent—Johnson was equally dismissive.
USA 193 disintegrated due to the immense physical shock of the missile impact, and the scattered hydrazine decomposed at that point, once it had been strewn into empty space. The chemical energy of any hypothetical tank explosion was miniscule compared to the kinetic energy imparted by the collision.
"But if you do get hit and die, take solace in the fact that you’d be the first confirmed death-by-space-debris."
THAT'S COMFORTING, YES?
WHAT IF WE DON'T GET HIT, BUT DO GET SPRAYED WITH HYDRAZINE?
IF OUR GOVERNMENT SAW THE 2007 INCIDENT AS "TOO RISKY" AND BLEW THEIR OWN SATELLITE TO PIECES, WHY NOT DO THE SAME THIS TIME?