Only days after narrowly avoiding a nasty knock on the noggin by a NASA satellite [U-ARS] another lump of space hardware may or may not be headed our way.
The German ROSAT satellite is busily heading for earth re-entry at the end of this month or the beginning of November.
Unlike NASA’s statements that their citizens, Americans, would be just fine the German’s are a bit clearer: “Might Germany be affected by re-entry?”: “Yes!”.
The orbit of the satellite means that ROSAT overflies regions up to a maximum northerly latitude of 53 degrees. Allowing for some degree of scattering of possible fragments, this means that regions might be affected up to about 53.4 degrees, that is, up to 40 kilometres above the 53rd parallel. This may or may not be exactly where Southam is.
The official advice is not to panic..
It will only be possible a few days prior to re-entry to determine whether or not the calculated ground track for the re-entry of ROSAT might actually cross Germany or Southam.
The Delta II expendable launch vehicle with the ROSAT (Roentgen Satellite): A co-operative space X-ray astronomy mission between NASA, Germany and United Kingdom, was launched from the Cape Canaveral Air Force Station on June 1, 1990.
The likelihood of a person getting injured as a result of the re-entry is extremely low. Taking account of the projected total surface area over which damage might be caused by the fragments that – theoretically – might survive re-entry, the orbital path of the satellite and the distribution of human populations on Earth, it is possible to calculate that the probability of someone somewhere on Earth getting injured is about 1 in 2,000; that is, one person is predicted to be injured for every 2000 de-orbit events of this kind. The probability of someone in Germany [or presumably Southam] being harmed is much lower: about one injury for every 700,000 de-orbit events.
Nevertheless, wearing head protection such as a hat may be a good idea. Asked why they don’t go and get it back instead of allowing the satellite to re-enter the atmosphere DLR, the satellite owners, said: “The technologies for capturing satellites and de-orbiting them under controlled conditions are still at the development stage. It will be a several years, at the earliest, before the first demonstration missions can be launched with the aim of proving the technological feasibility of this kind of operation. However, even once these technologies become available, only a few objects will be selected for controlled re-entry, not the majority of satellites and upper stages of launchers”.
DLR being candid compared to NASA said: “Satellite re-entries cannot be avoided; space debris re-enters Earth's atmosphere on an almost weekly basis. Over the last few years, the total mass of this debris has amounted to about 60 to 80 tons per year. This total includes small items of debris as well as spent upper stages of launchers and satellites of every shape and size. Items of debris have been found on the ground only in very rare cases. The total mass of natural objects reaching the Earth's surface (meteorites) far exceeds that of debris from man-made objects or fragments resulting from activities in space”.
To clarify all the facts, we've got a video to look at:
The launch of the ROentgen SATellite (ROSAT) into space on 1 June 1990 marked the start of a mission that would allow researchers to perform an all-sky survey of X-ray sources with an imaging telescope for the first time. X-rays arise in the Universe in response to unusually hot, high-energy processes, which often entail extreme states of matter such as black holes or neutron stars.
Originally designed for a five year mission, like the original Starship Enterprise mission, ROSAT continued in its extended mission for a further 4 years before equipment failure forced an end to the mission. For some months after this, ROSAT completed its very last observations before being finally switched off on 12 February 1999.
On 25 April 1998, failure of the primary star tracker on the X-ray Telescope led to pointing errors that in turn had caused solar overheating. A contingency plan and the necessary software had already been developed to utilise an alternative star tracker attached to the Wide Field Camera.
ROSAT was soon operational again, but with some restrictions to the effectiveness of its tracking and thus its control. It was severely damaged on 20 September 1998 when a reaction wheel in the spacecraft's Attitude Measuring and Control System (AMCS) reached its maximum rotational speed, losing control of a slew, damaging the High Resolution Imager by exposure to the sun.
This failure was initially attributed to the difficulties of controlling the satellite under these difficult circumstances outside its initial design parameters. A reaction wheel operates by changing its rotational velocity, conservation of angular momentum then causing the more massive satellite to rotate in opposition. Their maximum speed is limited by design, which in turn means they are limited in the rotational velocity they can impart to a satellite.[clarification needed] "Reaching maximum speed" thus means merely that it cannot impart any more r' velocity change, not that it's approaching mechanical damage to itself.
ROSAT could be heading back to earth because of hackers. Nothing is done about hackers so it's not surprising they could do such a thing: In 2008, NASA investigators were reported to have found that the ROSAT failure was linked to a cyber-intrusion at Goddard Space Flight Center. This was also reported through Bruce Schneier's blog, a highly-regarded commentary on IT security issues.
The root of this allegation is a 1999 advisory report by Thomas Talleur, senior investigator for cyber-security at NASA. This advisory is reported to describe a series of attacks from Russia that reached computers in the X-ray Astrophysics Section (i.e. ROSAT's) at Goddard, and took control of computers used for the control of satellites, not just a passive "snooping" attack. The advisory stated: "Hostile activities compromised [NASA] computer systems that directly and indirectly deal with the design, testing, and transferring of satellite package command-and-control codes."
The advisory is further reported as claiming that the ROSAT incident was "coincident with the intrusion" and that, "Operational characteristics and commanding of the ROSAT were sufficiently similar to other space assets to provide intruders with valuable information about how such platforms are commanded,". Without public access to the advisory, it is obviously impossible to comment in detail. However it does seem to describe a real intrusion, there is a plausible "no attack" explanation for ROSAT's failure, and the report is claimed to link the two incidents as no more than "coincident". IT security remains a significant issue for NASA, other systems including the Earth Observing System having also been attacked.
In 1990, the satellite was put in an orbit at an altitude of 580 km and inclination of 53°. Since that time, due to atmospheric drag, the satellite has slowly lost height. As of September 2011[update], the satellite continues to orbit approximately 270 km above the Earth, and is expected to re-enter the Earth's atmosphere in October 2011.
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