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Spacecraft Buzzes By Mercury
Riding with Robots writes "The robotic spacecraft MESSENGER is making its second fly-by of the first planet today, skimming just 200 kilometers above the surface. The fly-by will reveal portions of the planet that have never been seen before, but the main purpose of the maneuver is to prepare for an orbital insertion in 2011. The mission site offers extensive information, along with the first pictures that are already arriving on Earth, with many more expected in the coming hours and days."
Larry Niven's first published short story was titled "The Coldest Place" (collected in 3 Books of Known Space ), based on the idea that the regions of Mercury not hit by the sun would be the coldest place in the solar system. The story was infamous out of date by the time it hit print, as some studies of Mercury had shown that it never got that cold. Nonetheless, reading the story as a child awoke a certain interest of that planet which never gets as much attention as the sexier Mars or Venus or the gas giants. I look forward to following this mission.
Are you prepared for insertion?
Do you even lift?
These aren't the 'roids you're looking for.
Typical slashdotters long dream of insertion, but are never actually ready.
"I don't have to think. I only have to do it. The results are always perfect, but that's old news." - Meat Puppets
Oddly enough, fat bottomed girls are nowhere to be found.
I thought this kinda thing wasn't happening when I read the No Space Porn article?
Oddly enough, fat bottomed girls are nowhere to be found.
they are, but hidden behind event horizon
Anybody read the headline and get really excited for a second? Must be because I'm reading through Hitchhikers Guide to the Galaxy (again).
Sex. Drugs, and Unix.
At least be thorough - you forgot to mention the chips in our heads.
Well at least we finally got to insert it before the world ends...
Could someone please explain why according to the web site the orbit insertion is going to take another pass and another 3 years. Does it really take that long to slow the spacecraft down?
I thought Virgin Galactic said "No" to space porn.
Why, without your clothes, you're naked, Miss Dudley!
I'm no expert on orbital mechanics or anything, but it seems to be due to the massive change in velocity or "delta-v" (or call it vector). No way to carry enough fuel to effect that much speed change without using various orbits and the gravity of the planets around which they swing to change that vector enough that the amount of fuel on the craft can then make the smaller corrections required for orbit.
but, venus is hotter, lets do that next.
Because it is energetically tough to get to Mercury they are trying to get into with as little fuel expenditure as possible, to send as much payload as possible. Since there is no atmosphere, aerobraking is not possible, and thus they are using gravity assists to help reduce the orbital insertion delta-v to a manageable number. Each flyby speeds up the spacecraft a little, to better match Mercury's orbital velocity, and they decided on 3 of these to get the performance they wanted. There is a synodic period (the orbital beat period) between each such opportunity, so it takes a while to complete three flyby gravity assists.
The mission FAQ has more information on this.
sorry - "speeds up" should be "slows down," above.
The flybys and the ridiculously indirect route are not to speed up the craft, its actually to slow it down. Mercury is a very small planet, a little bigger than our moon, so the flybys are meant to slow down the craft enough so that it can be "caught" in the very low energy level orbit of Mercury.
Because it is energetically tough to get to Mercury they are trying to get into with as little fuel expenditure as possible, to send as much payload as possible. Since there is no atmosphere, aerobraking is not possible, and thus they are using gravity assists to help reduce the orbital insertion delta-v to a manageable number. Each flyby speeds up the spacecraft a little, to better match Mercury's orbital velocity, and they decided on 3 of these to get the performance they wanted. There is a synodic period (the orbital beat period) between each such opportunity, so it takes a while to complete three flyby gravity assists.
The mission FAQ has more information on this.
Ah, thanks! Very interesting.
That's because they didn't want to have to rename the company to "Whores Galactic".
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.
It's so much like the Moon that it's quite boring to me.
Yeah, the core is slightly different and all but really, come on, it's just like our Moon in almost every way.
Moving around in space is all about changing your velocity. There are a number of ways to effect that change - gravitational slingshot, aerobraking, big sails, thrusters ... Each has advantages and disadvantages. For example, direct thrust may provide the most direct path to your objective, but the fuel requirement may be impractical. The mission designers have chosen a method of getting MESSENGER (about 1000kg of payload) to it's objective with enough fuel on-board to perform it's mission. Many variables have been considered - launch vehicle requirements, time to arrival, duration of mission, required consumables, etc. It's a horribly complex optimization.
The most efficient time/location to make orbital adjustments is apogee or perigee. If you enter into a highly eliptical orbit and wish to circularize at a much lower altitude using only a fractional-Newton thruster, yeah, it'll take a while. MESSENGER has a 650N main thruster, but only about 600kg of propellant. That equates to "not a lot" of thruster time. The main engine has a Specific Impulse (Isp) of 318 seconds. On Earth, you'd get about 318 seconds (5+ minutes) of operation. That gravitational element doesn't really apply out in space, so the available thrust-time will be longer. The NASA PDF indicates that the final orbital insertion burn will consume 30% of the propellant, and will last about 14 minutes. Extrapolating, that indicates that MESSENGER has about 42 minutes of propellant on board.
There's also a nice explanation of the orbital maneuvers on the JHUAPL website, and also a nice PDF showing the orbital insertion cost plots.
Note that MESSENGER used solar sailing to correct its trajectory for this flyby:
http://www.planetary.org/blog/article/00001674/
This is what we should be doing, instead of quibbling over small things like creationism and Paris Hilton. We should launch several satellites orbiting each planet and few satellites for some of the more interesting moons(Europa, io etc)
that means they gave linear velocity to Mercury. It's going faster. The whole space time continuum has now been altered. We're doomed!
I've always said English was my second language. Had Romeo and Juliet been written in C, I might have understood it.
When they eventually build a hotel on Mercury, I want an ice machine that works and doesn't keep running out of ice. So how big would such an ice machine have to be on Mercury? Would they have to charge $3 for a soda? I hate those tacky signs that say "No Filling Ice Chests."
If it was easy, they would have done it before now. We managed flybys of Merc 30 years ago, but those are much easier since you don't have to slow down.
The main engine has a Specific Impulse (Isp) of 318 seconds. [spaceref.com] On Earth, you'd get about 318 seconds (5+ minutes) of operation.
No. Specific impulse, despite being measured in seconds, has nothing to do with how long the rocket can fire. That obviously depends on how much propellant you carry.
Take another look at that Wikipedia article you linked on specific impulse.
Patrick Doyle
I mod down every jackass who puts his moderation policy in his sig. Oh, wait a sec....
Better would be nonvirgin galactic. Or change the V meaning to special place on a woman. :)
How about Mirgin Galactic, if you use a font where the M looks like the special place on a woman + her legs? :)
Ok apparently the rest of the mods are sleeping on the job today. Reading TFA Your first assertion was correct. It's not about slowing down the thing needs to speed up in order to match mercury's orbital velocity of 47.9 km/s which is quite a bit faster than earth's measly 29.8 km/s:
Info on gravity assists for the MESSENGER mission.
There will actually be 6 total flybys (3 of mercury, 2 of venus, 1 of earth) during which the spacecraft will accelerate in order to decrease its orbital period from 365 days (that of earth) to 88 (that of mercury).
Well as another poster in the above thread pointed out, that's incorrect.
To be "caught", you'd want low relative velocity to Mercury, surely.
And just because you missed it, I'll repost oneTheory's link: http://messenger.jhuapl.edu/the_mission/gravity.html
Crap ... typing too fast ... not enough sleep ...
... a little over 47 minutes. At least that's consistent with the other derived number. Sorry about that, Chief.
Fthrust = Isp * (mass flow rate) * (gravity on Earth), which allows us to solve for the mass flow rate:
650N = 318s * MFR * 9.8m/s^2
MFR = 0.209 kg/s
With 600kg of propellant on board, you'd be able to fire the engine for 600kg / 0.209kg/s = 2871 seconds on the Earth's surface
No, that's because no one deserves to be a Zero-G Jizz-Mopper.
With 600kg of propellant on board, you'd be able to fire the engine for 600kg / 0.209kg/s = 2871 seconds on the Earth's surface ... a little over 47 minutes.
True, though your calculation has nothing to do with Earth's surface. (When Isp is measured in seconds, they multiply by the gravity on Earth's surface just for fun.)
Patrick Doyle
I mod down every jackass who puts his moderation policy in his sig. Oh, wait a sec....