Slashdot Mirror
Messenger En Route To Mercury
Soft writes "NASA's Messenger space probe has lifted off on its second try on a Delta 2-Heavy rocket.
As mentioned earlier on Slashdot, it is poised to orbit Mercury in 2011 after three flybys, as well as two flybys of Venus and one of Earth for course corrections.
It will be the first probe to visit the innermost planet since Mariner 10 in 1974 and 1975.
Stories on the BBC and SpaceflightNow."
When a launch is canceled due to mechanical failures, weather, or any other reason, it's considered a try as long as the launch procedure has been started. Since launch procedures can range from 6 hours to 6 days, there are a lot more tries than launches.
Yoda wisdom or no Yoda wisdom, you're still wrong.
(With rockets, if you try and don't succeed, its pretty much SOP - most things don't launch on the first attempt. Now, if you were to say "ignite" instead of try, you'd be correct - most rockets don't do too well on a second ignition.)
---
Mod me down, you fucking twits. Go ahead. I dare you.
(I read with sigs off.)
The spacecraft cannot fly straight to Mercury; it does not carry nearly enough fuel. So it will fly once past Earth, twice past Venus and three times past Mercury and make 15 loops around the sun before slowing enough to slip into orbit around the small, hot planet.
The following statement is false.
The previous statement is true.
Welcome to my world.
MESSENGER stands for MErcury Surface, Space ENvironment, GEochemistry and Ranging
Though ion drives are really effective in terms of specific impulse (you need little fuel for gaining unit momentum), they are not much mass-effective (thrust per unit engine mass) at all. a trip to Mercury is a kind of parachute jump, you have to go really slowly or you're Sunburnt :). so if you want to get there faster, you first have to accelerate, and step on brakes afterwards. Russians say -- going slowly, get farther. :)
Sig. No Sig.
Also, remember the Earth is in orbit around the sun, so to get to the orbit of Mercury you need to lose a lot of the energy Earth's higher 'altitude' gives you to start with. Plus you need to slow down enough to where you don't need an ungodly amount of fuel to slow down into orbiting Mercury itself.
Mix the failings of Usenet with the shortcomings of the World Wide Web and the result is slashdot.
..They are not much mass-effective (thrust per unit engine mass) at all.
Current Ion drives can deliver >10x more power overall per Kg compared to rockets - but they do it slowly, over months/years.. Rockets can deliver "punch" at a spacific time. Advantages/Disadvantages both ways really.
Messanger as-is carries 1/2 its weight as fuel, so if you can reduce that 10 fold, or get 10 times the power, thats a good thing. Faster missions are less expensive in terms of keeping support staff too, and less risky. I think a solar-ion mission that spirals inwards as it decelerates would be way more efficient than the current plan. And would be much less dependant on celestial mechanics for launch dates.
Anyone from NASA here know why they dont use solar-ion drives for these missions? Is there some sort of political bias against solar & pro old fashioned rockets or nuclear? (And yes, I know nuclear (RTG) is needed for deep space - at least for electric power for the science instruments..)
Here is a better link for SMART-1..
"You lied to me! There is a Swansea!"
Why aren't ion drives used more?
2 1072826.htm. (And enter "ion engine" at NASA's main site for a huge number of links.) So, it's not only ESA that have their fingers in this pie.
That's actually quite a good question, given the huge amount of power available from sunlight in the inner solar system. A continuous-burn trajectory to Mercury would probably be very much shorter than the current one; the thrust may be small, but craft speed builds up rapidly under such continuous acceleration. You'd only need to carry enough conventional chemical propellant for the final orbital insertion.
NASA has been very active on the ion-engine front -- last year it successfully completed a pretty advanced test: http://www.sciencedaily.com/releases/2003/11/0311
Maybe the answer is that ion engines still need a few more years of development? Certainly not long though, since small ion thrusters are already in use, as you point out.
"The question of whether machines can think is no more interesting than [] whether submarines can swim" - Dijkstra
Actually it's a combination of *decreasing* velocity (each flyby will take speed away from the craft, causing it to have a smaller orbit) and the final position in orbit (the final orbit has to be very ellipitcal, and very near polar).
The number of times around the sun is merely a side effect of a) the number of flybys needed and b) the fact that Messenger needs to orbit for a while before it can reach the planet needed for flyby.
Gilthalas
Software Engineer, Space Dept, JHU/APL
Support Space Science!
No, there isn't. The official terminology acknowledges attempts as tries, as does the English language. Do you think trying to launch starts when they hit "Go" on the main motors? It starts a lot earlier than that; launch procedure usually starts with fueling (for liquid-fueled motors). Solid rockets have much shorter launch procedures, but are generally not used for launch all by themselves (only as strap-on boosters, for the most part).
The writeup is correct as written. 'NASA made two launch tries, and succeeded in launching on the second try'. This sentence is equivalent to 'NASA made two launch attempts, and succeeded in launching on the second attempt.' There is no difference in the two. NONE.
And here are the common English definitions, just to drive the point home:
Attempt - To try to perform, make, achieve.
Try - To make an effort to do or accomplish (something); to attempt (something).
Admit you were wrong and move on.
---
Mod me down, you fucking twits. Go ahead. I dare you.
(I read with sigs off.)
I, for one, WELCOME our joke recycling overlords.
Not power - specific impulse, which is effectively propellant ejection velocity.
Usually specific impulse is given in units of seconds, but this is an archaic convention - it's really velocity (they divide by the acceleration of gravity at ea level to get seconds).
There are two major problems with ion propulsion - ion thrusters need Kilowatts of power to operate (and so drive the design, mass and cost of the power subsystem), and they have very low thrust. They are also expensive and have limited life. So with ion propulsion, like everything else in engineering; if it's not necessary to do it, then it's necesary NOT to do it.
Helium balloons want to be free.
To reach Mercury orbit, you have to decrease velocity. Remember that in outer space, it's just as hard to slow down as to speed up. (Unless you find a convenient atmosphere to help you brake, which Mercury doesn't have.)
As far as Mercury, it is so close to the Sun that the solar wind is strong enough to blow away any atmosphere it has. It also has a very low mass, and so it has trouble resisting this. Any dust wouldn't settle into rock formations due to a lack of pressure, and would be hardly held down by the low gravity. Look at the dust storms on Mars, which is significantly larger. So dust and light materia are blown away also. This leaves a very solid, very dense core of nickle, and whatever heavy material might survive the heat of the nearby star.
Fnord.
Why arnt ion drives used more?
To put it in simple non-technical terms, you can't slow down fast enough. Yes, you can get a good bit of speed up over several months on a more direct trajectory, but you'd end up having to start slowing down once you're only 1/2 way there.
To make it at all reasonable, you'd have to use a few gravity sling-shots to build up speed and possibly dump speed later. Once you're doing that, you might as well go with the old tried and true chemical propellent that gets you up to speed much quicker.
Ion drives are great if you're going to be going in a straight line for a very long time and don't want to stop, ever. The farther you go, the faster you go, so the less reasonable it is to slow down.
I have even read of deep-space solar-powered mission designs that head in inside mercurys orbit, grab loads of power and then head out beyond Jupiter..
Really? Where do they store all this power? If they used an ion drive, they would need constant power for the entire trip. Sounds a little fishy to me...
Mercury is real hard to observe from Earth-based telescopes since it is so close to the Sun. In the near future, the only way to get higher resolution data is to send the telescopes to Mercury. Even the most fervent remote sensing advocate will have to admit that data quality generally improves with decreasing distance to the target.
Using martian studies as an analogy for mercurian (hermitian?) observations, one can see how spacecraft data provide much more detailed observations over ground-based observations. Earth-based data of Mars obtained during the last opposition last summer (when Mars was closer to Earth than Mercury ever gets) does not compare to spacecraft data in terms of resolution. Earth-based (visible-wavelength) observers of Mars have to content themselves with seeing albedo variations. The geology which caused those albedo variations was largely unknown prior to our sending spacecraft. (Please note that tha "canals" reported by Lowell were likely optical illusions - Lowell's canal maps do not correspond to locations of known martian dry channels.)
Similarly, Earth-based spectroscopic observations of Mars have poor spatial resolutions. I remember one paper from '96 which reported 300 km/pixel resolutions. Two spectrometers currently in orbit around Mars get far better spatialresolution (Thermal Emission Spectrometer gets 3 km/pixel; THEMIS-IR gets 100 m/pixel - although, granted, that's with a low spectral resolution).
Two advantages that Earth-based observations have over spacecraft data are: 1) Earth-based observations are a lot cheaper to obtain and 2) a network of Earth-based observers can look for changes in the target with better time continuity than a singe spacecraft (since the spacecraft may be looking at some other part of the planet).
The true value of a Mercury mission is two-fold. Most obviously, new spacecraft observations will provide geologic context for current ground based observations (Mariner 10 only imaged ~40% of the planet). Additionally, Mercury is considered an end-member planet - a planet that likely formed close to the Sun in the solar nebula from which the solar system formed. As such, understanding how Mercury formed will provide a calibration point for models of solar system formation, which could have implications for formation in other portions of the solar nebula or the early solar system or of other planetary systems.
No, we aren't going to be sending people to Mercury anytime soon, but neither are we going to be sending people to Mars in the near future. (Even Bush's space initiative doesn't plan a Mars landing for at least 20 years - plenty of time to get distracted by other problems.) However, even if people aren't going to those placed, there are still useful things to learn regarding the solar system in which we live.
http://messenger.jhuapl.edu/faq/faq_journey.html#5
Mix the failings of Usenet with the shortcomings of the World Wide Web and the result is slashdot.
You're close, but not quite. It wasn't that the sun's gravity pulled in the lighter elements from the inner planets, but rather, that the solar wind from the sun blew all the lighter material outward, towards the outer solar system (which is why there was so much of it available to form the gas giants). You just have your vacuum in the wrong direction ;).
I dont understand why solar-powered ion drives are not used on missions like this.
Because any spacecraft headed for planets inside earth's orbit will be falling towards the sun anyway, and thus accelerating. This makes a direct trip between Earth and Mercury very difficult because in order to acheive orbit around Mercury, you'd have to slow down a whole lot - more than a chemical rocket could produce and way, way more than an ion drive. Sending a probe on a path like this would essentially give it a stupidly long elliptical orbit around the sun or around Mercury and then the sun.
Also, you don't seriously believe that solar panels could withstand the heat and radiation on Mercury do you? At best they'd overload and burn themselves out, although a more likely scenario would be that they'd just evaporate.
"No problem. I have the capacity to do infinite work so long as you don't mind that my quality approaches zero."-Dilbert
after having gone by Earth on a flyby (2005?)
and by Venus twice on flybys (2007, 2008)
See this link Mercury
After a flyby of Mars in 2008, and another in 2009, it settles down for orbit in 2011.
That last long ago (30 years) visit was only a flyby.
So all that confusion is about getting the right orbital velocity to stay, plus we get good science all along the way.
Letter To Iran