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NASA Set To Launch Probe To Mercury
antispam_ben writes "CNN is reporting the upcoming Messenger mission to Mercury is set to launch August 2. The spacecraft uses a combination of technologies (insulation, Peltier devices, careful design and orbit, always keeping the shield side toward the Sun) to keep its electronics at room temperature."
There are various definitions of room temperature. The one most often used is 20 degrees C (Err... about 75 degrees F, I think).
While most other planets have been well studied, Mercury has not even had half its surface mapped! Messenger has non-visual light detectors including a laser altimiter which will let it map the whole planet, counteracting its slow rate of rotation. I hope the launch goes well and look forward to the data return. Kudos to NASA for doing some good science on what is considered a less sexy target than some others which seem to hog all the research money.
$#!^ happens, but why does it always have to happen to me???
For more information, see ESA BepiColombo page.
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NASA can explain it better: http://messenger.jhuapl.edu/the_mission/mission_de sign.html
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Remember, the probe is moving further into the Solar System, so it needs to *decelerate* from Earth-normal angular momentum.
--- Ban humanity.
Wouldn't work well on Venus either. You need a sink into which to pump the heat. Given the 800F surface temperature, you'd have to do an awful lot of work to pump to an acceptable temperature in the electronics bays. I'm not saying it's impossible, just hard.
the Mercury mission will work because they're putting a big insulative blanket between the electronics and the sun, to provide shade; and, they're pumping the heat from the electronics bays to the cold side (facing away from the Sun) of the craft where it's -200F
Actually, it's a Peltier device. Peltier devices, also known as thermoelectric (TE) modules, are small solid-state devices that function as heat pumps. A "typical" unit is a few millimeters thick by a few millimeters to a few centimeters square. It is a sandwich formed by two ceramic plates with an array of small Bismuth Telluride cubes ("couples") in between. When a DC current is applied heat is moved from one side of the device to the other - where it must be removed with a heatsink. The "cold" side is commonly used to cool an electronic device such as a microprocessor or a photodetector. If the current is reversed the device makes an excellent heater.
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Can someone explain why such a convoluted and time consuming route is required?
It's all about delta-v... how much can you change your velocity?
Earth orbits the sun at a specific velocity.
Mercury orbits the sun at a much smaller velocity.
But in order to fly straight there, you have to counteract all of the orbital velocity you have at earth, then either free fall or thrust to the new location, and then build up the orbital velocity of Mercury to make orbit. That's a lot of delta v, and a lot of working fluid to put into your thrusters. In fact, even if we felt like paying that fuel bill, we don't really have the technology to build a probe large enough to carry all that fuel, or to get that fuel out of Earth's gravity well in the first place.
So instead what we do is figure out a low-delta v way to launch it, bringing it into the inner solar system and slowing it down on the way. The key to this is slingshot maneuvers - using the gravity wells peppered throughout the solar system to change the direction of velocity without having to spend delta-v on it.
That and the craft makes use of a little-known feature of relativity; the more energy in your fuel, the heavier it is; if you burn the fuel you have deep in a gravity well, it is quite a bit more effective than it would be in space. This is related to the law that predicts you cannot travel at the speed of light; as you go faster, your intertial mass rises, in such a way that it would take an infinite amount of thrust to reach the speed of light.
Sure your craft has more inertial mass, too, but you'll be slowing down as you exit the gravity well, leaving your fuel behind you, and that's where the mathematical magic happens.
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For those that care, here's the link for the NASA site on Messenger. http://www.nasa.gov/mission_pages/messenger/main/i ndex.html
The planet does indeed spin - Mercury rotates on its axis 1.5 times per solar orbit (see http://www.solarviews.com/eng/mercury.htm). Because of this 3:2 resonance, a Mercury solar day (sunrise to sunrise) is equivalent to 176 Earth days.
e sign.html.
So what this means is that for every Earth year Messenger is orbit, 4 Mercury Years will pass, which consists of 2 Mercury Solar Days (see http://messenger.jhuapl.edu/the_mission/mission_d
This gives the spacecraft many passes over the light and dark side of the planet, so much that they can spend one (Mercury) day doing global mapping and the second (Mercury) day doing targeted science investigations.
In terms of heat - the highly elliptical, near polar orbit is designed so that the heat shield always faces the sun, giving the instruments a nice room temperature setting on the other side of the shield. There is the possibility of heat from the surface, but the instruments are designed to take that into account.
Gilthalas
Software Engineer, Space Dept, JHU/APL
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