June 2, 2004Fixing Hubble by robot
In an address to the American Astronomical Society at its meeting in Denver, NASA Administrator Sean O'Keefe announced on June 1 that the agency is requesting proposals for robotic missions to service the Hubble Space Telescope (HST). The proposals are due July 16. According to the agency, any robotic serving mission must, at a minimum, be able to deorbit HST safely. An additional capability — one that's "highly desirable" in O'Keefe's words — will be to replace the telescope's gyroscopes and batteries to extend the telescope's operating lifetime. Third in priority is to install new instruments that would enhance or extend HST's capabilities.
At present, HST has four functioning gyros, three of which are used at a time. Steven Beckwith, director of the Space Telescope Science Institute, notes that HST's operations team has developed ways to achieve somewhat diminished science with HST running on just two gyros. With one working gyro (or none), HST goes into a safe mode that holds its orientation fixed in space, making it easy to dock with. Says Beckwith, "HST in safe mode remains a compliant target" in case a servicing mission is delayed. Engineering projections indicate that by the end of 2006, HST likely will be running with just two gyros, which will drop to one by mid-2007 or thereabouts. (Battery life, while also declining, is believed to be adequate through about 2010.) — Robert BurnhamWhat did the Big Bang sound like?
It didn't make a "bang!" — nor did it make a rumble. In fact, the Big Bang was completely silent at first.
Astronomer Mark Whittle (University of Virginia) has reconstructed what the Big Bang would have sounded like. After the initial silence, it was, he says, "a descending scream that built into a deep rasping roar and ended in a deafening hiss."
Naturally, no human being — nothing living, in fact — existed then or could have survived the explosion to hear what it sounded like. But according to Whittle, the minute fluctuations in the cosmic microwave background radiation amount to frozen sound waves from the Big Bang. These fluctuations were mapped in detail by NASA's Wilkinson Microwave Anisotropy Probe, which was launched in 2001.
Unfortunately for lovers of celestial music, the harmonic structure of the fluctuations does not produce pure chords as a musical instrument does. Thus, the sound might best be described as grating. It is also overwhelmingly loud. "[It was] about 110 decibels," Whittle notes, "like a rock concert."
What about the initial silence? "Before the fluctuations had time to develop, the expansion was so smooth it would not have made any noise at all," Whittle explains. — Robert BurnhamSpeed limit for solar eruptions?
It takes 12 hours for material erupted from the Sun in a solar flare to reach Earth, according to astronomer Nat Gopalswamy (NASA Goddard Space Flight Center) and a team of coworkers. Such eruptions are called coronal mass ejections (CMEs). The researchers studied historical records of solar flares and their aftermaths going back to the first flare identified, by Richard Carrington in 1859.
Coronal mass ejections can be thrown from the Sun at various speeds, but the team's finding suggests there's a speed limit built into the process. They think this comes from a natural constraint on the amount of energy that can be stored in the tangled magnetic fields that cause a solar flare.
This finding means that operators have half a day to prepare satellites in Earth orbit, which can have their electronic circuits overwhelmed or destroyed by the arrival of a CME. Also, astronauts in space get the same warning time and can take precautions, such as seeking shelter in parts of the International Space Station where they are surrounded by more shielding. — Robert Burnham