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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."
...well, compared to the melting point of Tin anyway...
'Don't worry' said the trees when they saw the axe coming, 'The handle is one of us.'
Better hope Microsoft isn't watching, they may sue for copyright violation.
Nasa: But it isn't MS Messenger!!
Gates: I don't care, gimme mo' money beeyatch!@#
Der Tod ist der einzige Weg hier raus!
Nasa's Messenger? I wonder if Trillian will cover it...
There are two kinds of people in the world: Those with good memory.
There are various definitions of room temperature. The one most often used is 20 degrees C (Err... about 75 degrees F, I think).
...developed by nVidia for the NV30 launch, but scaled back because they only need to protect Messenger from a class G star as opposed to a modern graphics card.
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.
Auferre trucidare rapere falsis nominibus imperium, atque ubi solitudinem faciunt, pacem appellant.
It doesn't matter what temperature a room is, it's always room temperature.
-- Steven Wright
Yet Another Web Site
"...the spacecraft must swing once past Earth, twice past Venus and thrice past Mercury before slowing down enough to slip into orbit around Mercury"
Her>That's the 2nd time I've seen Mercury! Stop and ask!
Him>I will not ask for directions! I know where we are now
Her>I have to pee! And you promised we'd get some Venutian shopping done!
*NOTE* - It is rather interesting that the craft must maneuver like this to get a stable orbit and not get crushed.
I know thermal issues have always been central to spacecraft design, but this sounds like a nicely engineered approach to temperature control.
I'm reminded of the faulty heater on one of the Mars Rovers. Could such problems be avoided or at least mitigated by use of more passive thermal management (insulation, heat pipes, heat sinking/sourcing)?
I'm also reminded of the Russian probes to Venus which had uderstandably short lives due to both heat and pressure (possibly corrosive gases as well).
I'm firmly in the camp that promotes more unmanned probes, maximizing the power of money spent on advancing spacecraft technology and knowledge from expanded exploration rather than blowing it all on the dubious value of letting a person stand on Mars.
NASA can explain it better: http://messenger.jhuapl.edu/the_mission/mission_de sign.html
--- Ban humanity.
However, you can steal energy from planets using gravity assists. JPL is amazingly good at doing these.
<tinfoilhat> We do need to worry that JPL is slowly robbing orbital energy from the planets they use. I've been worried about our profligate use of this irreplaceable resource for a long time. Worse, JPL seems to be totally blase about using Earth as one of their prime engines- enough gravity assists and the earth will fall into the sun!
Join the League to Conserve the Angular Momemtum of Planets today!
"Seven Deadly Sins? I thought it was a to-do list!"
It shouldn't be all that hard since in space thermal control based almost solely on radiant energy. Even though the side facing the sun will get very hot, the side facing away from the sun is exposed to empty space with a temperature near absolute zero. If you simply reflect most of the sunlight away on the hot side, slow down what gets absorbed with a little insulation, and arrange to radiate what does get through the insulation (along with any internally generated heat) on the cold side, you should be able to maintain a reasonable temperature.
From what I've read, one of the hardest parts about controlling temperature on this probe is to handle the times when it passes in front of Mercury. Then, the near-zero chill on the "cold" side is temporarily replaced with the radiant heat from the > 400 C surface of the planet. At these times the probe has to be closed up like an ice chest to maintain its internal temperature at reasonable levels until it gets away from the planet.
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.
I am disrespectful to dirt! Can you see that I am serious?!
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
FRY: This is a great, as long as you don't make me smell Uranus. Heh heh.
LEELA: I don't get it.
PROFESSOR FARNSWORTH: I'm sorry, Fry, but astronomers renamed Uranus in 2620 to end that stupid joke once and for all.
FRY: Oh. What's it called now?
PROFESSOR FARNSWORTH: Urectum.
...isn't the 5 gigamile trip. It's the launch window. They have a 12 second launch window to either launch it or wait for the next 12 second window-- the next day, at the earliest. Because of the multiple fly-bys, the math gets a little complicated, and error tends to cascade towards failure.
;-)
Talk about performance anxiety!
Wife: OK Honey, I'm ready. You've got 12 seconds.
Enough for a high school boy, I imagine, but not us mighty slash dotters, right?
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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