January 4th, 2004

belize

Mars

I'm really fascinated with all the Mars exploration going on. I feel all giddy reading the minute-by-minute news at Spaceflight Now. I was reloading all last night, and I woke up this morning, reloading more. (no RSS feed....)

The "Mission facts" links on the right sidebar are all good reads.

Think about all the areas of knowledge needed to get that rover there: aerospace, math, material sciences, mechanics, software, geology, communications... Must be fun to work at NASA.

Fun tidbits:
Each airbag has double bladders to support impact pressure and, to protect the bladders from sharp rocks, six layers of a special cloth woven from polymer fiber that is five times stronger than steel. The fiber material, Vectran, is used in the strings of archery bows and tennis racquets.
Dealing with temperature:
Batteries and other components that are not designed to survive cold martian nights reside in the warm electronics box. Nighttime temperatures may fall as low as minus 105 C (minus 157 F). The batteries need to be kept above minus 20 C (minus 4 F) for when they are supplying power, and above 0 C (32 F) when being recharged. Heat inside the warm electronics box comes from a combination of electrical heaters, eight radioisotope heater units and heat given off by electronics components.
Slow, reliable computers:
The computer in each Mars Exploration Rover runs with a 32-bit Rad 6000 microprocessor, a radiation-hardened version of the PowerPC chip used in some models of Macintosh computers, operating at a speed of 20 million instructions per second. Onboard memory includes 128 megabytes of random access memory, augmented by 256 megabytes of flash memory and smaller amounts of other non-volatile memory, which allows the system to retain data even without power.
Water:
"Gusev is a big hole in the ground, a crater, and it's got this huge dried up river bed flowing into it," Squyres said. "Now if you can come up with an explanation that says there wasn't a lake there, I'd like to hear it. I mean it was water and it flowed into a hole in the ground.
belize

monobal 0.3

Hot on the heels of the much-revered 0.2 release, I now proudly announce monobal 0.3, the currently stupid but functional C# reverse load balancer that runs on Mono!

http://www.bradfitz.com/share/monobal/monobal-0.3.tar.gz

Things completed since last time:

-- my Socket.cs patches to mono have gone into mono cvs.
-- POST/PUT/etc support. (not just GET)
-- uses Trace for debugging, not Console.WriteLine (.NET tracing is fun!)

Things remaining:

-- everything I said before for the 0.2 release.

Other things I've thought of since:

-- performance (which I haven't cared about yet)
   o watch traces to see if what i expect is happening, and nothing more
   o profile
   o don't create delegates on the fly as needed. just make them once per connection.
-- UsefulStream probably has corner-cases in the BeginGetLine. that's all FIXME annotated still.
belize

Hot tub

I'm really enjoying the hot tub lately, especially with it being all cold and snowy and stormy.

The other day I went out and the friendly neighborhood cat (named "die Katze") was sitting on the hot tub cover. It turns out that one specific place on the cover is warm, right above where the hot water comes up. The rest is all cold. Smart cat!

Speaking of cold and snowy: tonight it's supposed to be really cold (like 22F). And Mr. Snowman is still standind proud in the front yard while all the other snow in the area has melted. He's now a big piece of ice. I don't think he's going anywhere for a while.
belize

More Mars Craziness

http://marsrovers.jpl.nasa.gov/spotlight/navTarget01.html
To land in a precise location on Mars after traveling over 300 million miles, navigators at the Jet Propulsion Laboratory (JPL) had to overcome the head-spinning challenges of calculating the exact speeds of a rotating Earth, a rotating Mars, and a rotating spacecraft, while they all simultaneously are spinning in their own radical orbits around the Sun.

...

, but even the seemingly insignificant solar radiation pressure and thermal radiation forces acting on the spacecraft to a level equal to less than a billionth of the acceleration of gravity one feels on the Earth need to be taken into account. Without knowing the acceleration error to that degree, the spacecraft would have moved off course by 3.7 km (2.3 miles) over 10 days.

...

"We had to know everything from how the iron molten lava in the center of the Earth was churning to how plate tectonic movements were affecting the wobble of the Earth to how the plasma in the atmosphere delayed the radio signals to and from the Deep Space Network stations,

...

Three DSN sites are roughly equally spread around Earth's globe at 120-degree intervals, so that antennas are pointed toward Mars at any given time as the Earth turns. If the exact location of any of these antennas is incorrect by just 5 centimeters (2 inches) on the surface of Earth, that math error builds over the 150 million kilometers (90 million miles) distance between Earth and Mars, creating a 1500-foot (0.3-mile) location error at Mars.

...

The navigation team also used a tongue-tying tracking technique called spacecraft-quasar delta differential one-way range or DDOR (pronounced "Delta Door"), which utilized their knowledge of locations of quasars to a few billionths of a degree to help locate the spacecraft's motion in the "up or down" direction in the sky.