itself. The computer ran continuing “It was my first interplanetary mission,”
system checks, Hill said, and if any system he said. “The other projects I had worked
veered out of its optimal operating range, on involved satellites in Earth orbit. If
the computer would take corrective ac- you can’t launch the satellite today, you
tions, which could include shutting down could always come back tomorrow, or the
“I’ve enjoyed and
the system and activating a backup. day after, and try it then.
played with comput-
The Hubble was repaired during a 1999 “With interplanetary space shots, there is
mission of the Space Shuttle. “The a tight window, and if you can’t hit it, you
ers as long as I can
astronauts did a space walk,” he have to wait months or years before there
recalled, “and replaced the old computer. is a chance to do it again. Every time
remember,” said
I was in the control center at Goddard, there is a change, you have to recalculate
watching as the astronauts yanked out the trajectories, and the possible observa-
Hill. “And my father
the old computer and put our new tions and experiments.”
one in. That was special.”
bought me my first
In addition, once an interplanetary flight
“But after the Hubble was fixed, I started is launched, it is gone – there is no chance
computer in ninth
to get antsy and was looking for new for astronauts to come up on the Space
challenges.” Shuttle and fix problems, as they did for
grade. I’ve really
the Hubble Telescope. All interplanetary
He found what he was seeking the follow- systems have to work perfectly, or be fixed
loved computers all
ing year at the Johns Hopkins University in flight.
Applied Physics Laboratory in Laurel,
my life.”
Md., a research facility which handled That is particularly critical on Messenger,
government projects from the ocean floor an ambitious exploration of Venus and
to deep space. They had a mission called Mercury which was launched August 3,
MErcury Surface, Space, ENvironment, 2004, from Cape Canaveral Air Force Sta-
GEochemistry and Ranging, or tion, Fla., and will enter its Mercury orbit
Messenger. in March, 2011. Messenger is following a
circuitous route, first using Earth’s
gravity well as a sling shot to boost speed
and hurl it to Venus, where it flew by the
solar system’s second planet in October,
2006, and will dive into its gravity well
again next June before hurling towards
Mercury, reaching speeds of 137,604
miles an hour as it orbits the small planet.
“We will be orbiting every 12 hours in a
highly elliptical orbit,” the 42-year-old
engineer explained from his office near
Mission Control at the APL. “The reason
is that some of the instruments, like imag-
ers which map the surface, work better up
close, and other instruments work better
further away. So each instrument will get
to work at its optimal position.”
These deep space probes have nowhere
near the electrical power available to
Earth-orbiting systems like the Space
Shuttle, since there are strict limits on the
size of the payloads the Boeing Delta II
launch rocket can handle.
“The entire Messenger space craft runs
Alice Bowman: Space Commander
on about 600 watts,” said Hill, “and that
includes the computer, all instruments,
24 USBE & Information Technology I January/February 2007
http:www.blackengineer.com
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