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MSL Landing Timeline: What To Expect Tonight
An anonymous reader writes "When the Curiosity rover lands on Mars later tonight, it'll be executing a complex series of maneuvers. JPL will be relying on the Mars Odyssey orbiter to relay telemetry back to Earth in time-delayed real-time, and if all goes well, we'll be getting confirmation on the success (or failure) of each entry, descent, and landing phase, outlined in detail here."
Telemetry will be continuously relayed back to earth, true, but with not much less than about a 15 minute latency, owing to the fact that Mars roughly a quarter of a light-hour from earth right now.
That IS indeed real time. Relativity tells us nothing can have an effect here in less time. I don't know if you're trolling or just ignorant, but by your definition you can never look at the stars, galaxies or nebulae in the sky in real time either because they're all at varying distances and we're seeing light that originated anything from about 4 to several million years ago. With telescopes you can go back billions.
Don't forget the imperial to metric conversions!
I'm really excited, but I doubt the live broadcast will measure up to the bitchin' action movie NASA made of Curiosity's "Seven Minutes of Terror!"
http://www.youtube.com/watch?v=pzqdoXwLBT8 Enjoy!
Ask me about my sig!
True, but for a blueworlder, the blueworld-received-time is real-time, for any definition of real-time consistent with relativity.
Speaker K'Breel knows the instant the Martian Defense Force succeeds in its mission, or fails, and either way he has enough time to throw a Junior Reporter's gelsac beneath the spot where the Skycrane will crash-land. At the moment of impact/invasion, the most recent transmissions from his spies on the Blue World will show a clock dated 10:14 PDT, but that's irrelevant. As far as the blueworlders are concerned, they find out at 10:31 PDT. Loyal Martian Citizens can start celebrating/covering their gelsacs early, but have to wait another 15 minutes (until their view of the blueworlders' clocks show 10:31) before they can enjoy true schadenfreude at the blueworlders' pain, or have hopefully protected their gelsacs in preparation for the ever-merciful Speaker for the Council's reaction to his view of the blueworlders' whoops of joy.
Dust. You don't want martian dust stirred up by the rockets covering all of the mechanics once you have landed.
Not many people know this, but the Stonehenge scene in "This is Spinal Tap" was based on something that really happened to Black Sabbath. The band wanted a life-sized replica of Stonehenge for their stage show, just like in the movie. They drew up the plans, but at some point (nobody's sure where) 14 feet became 14 meters... So they wound up with this giant thing that cost way more than they planned, and worst of all, it wouldn't even fit on any of the stages they were playing. After this, and a series of similar mishaps, NASA stopped hiring members of Black Sabbath.
Just noticed a typo in the article -- it's actually PDT, not PST.
NASA has a convenient countdown timer here:
http://www.nasa.gov/mission_pages/msl/index.html
. The whole thing has an amazingly sci-fi feel to it, like it's the opening scene of a sci-fi blockbuster movie. We really do live in amazing times when you think about it.
The skycrane/rover detach from the parachute at around 2:00 and you can watch as the sky crane lowers the rover at 2:48. It does seem a little too elaborate, and my gut feeling watching it is that using such a complicated landing mechanism is just asking for something to go wrong. But then again... well, think about it. Pulleys are pretty simple machines, and we've been using them for thousands of years. There are a lot of machines on this rover that are vastly more complicated than pulleys and cables- the heat shield, the parachute, the nuclear reactor, the onboard computer, the antenna, the camera that finds the landing site, the rocket motors, the software.
I sure as hell hope it all works, though. Unlike the last mission, there's just the one rover, and there's a hell of a lot riding on it. With the cuts to NASA's planetary science program, we won't be headed back to Mars for a long, long time, and it will be a lot harder to get the program started again if Curiosity fails.
It all has to do with shifting the center of mass. From the official NASA press kit: http://mars.jpl.nasa.gov/msl/news/pdfs/MSLLanding.pdf
After the turn to entry, the back shell jettisons two solid tungsten weights, called the “cruise balance mass devices.”
Ejecting these devices, which weigh about 165 pounds (75 kilograms) each, shifts the center of mass of
the spacecraft. During the cruise and approach phases, the center of mass is on the axis of the spacecraft’s
stabilizing spin. Offsetting the center of mass for the period during which the spacecraft experiences dynamic
pressure from interaction with the atmosphere gives the Mars Science Laboratory the ability to generate lift,
essentially allowing it to fly through the atmosphere. The ability to generate lift during entry increases this mission’s
capability to land a heavier robot, compared to previous Mars surface missions.
The spacecraft also manipulates that lift, using a technique called “guided entry,” to steer out unpredictable
variations in the density of the Mars atmosphere, improving the precision of landing on target.
During guided entry, small thrusters on the back shell can adjust the angle and direction of lift, enabling the
spacecraft to control how far downrange it is flying. The spacecraft also performs “S” turns, called bank reversals,
to control how far to the left or right of the target it is flying. These maneuvers allow the spacecraft to
correct position errors that may be caused by atmosphere effects, such as wind, or by spacecraft modeling
errors. These guided entry maneuvers are performed autonomously, controlled by the spacecraft’s computer
in response to information that a gyroscope-containing inertial measurement unit provides about deceleration
and direction, indirect indicators of atmospheric density and winds.
After the spacecraft finishes its guided entry maneuvers, a few seconds before the parachute is deployed, the
back shell jettisons another set of tungsten weights to shift the center of mass back to the axis of symmetry.
This set of six weights, the “entry balance mass devices,” each has a mass of about 55 pounds
(25 kilograms). Shedding them re-balances the spacecraft for the parachute portion of the descent.
You draw the line at any signal latency that is too slow to meaningfully respond to in the context that the signal was originally sent from. There's a reason why interrupt handlers in real-time OS's need to finish their job in as few computing cycles as possible.
File under 'M' for 'Manic ranting'
You're both rude and wrong. GP is correct.
"Relativity tells us nothing can have an effect here in less time." True, but that doesn't mean that it's real time. Here are a few examples that show that it's completely ridiculous to call it real time:
The cosmic microwave background is the glow of the hot early universe, from shortly after the Big Bang. No cosmologist would refer to this as seeing the Big Bang "in real time."
It's possible for a ray of light to travel in a circular orbit around a black hole. That means that it would theoretically be possible for me to face in a certain direction, stick out my tongue, and then turn around 180 degrees, look through a telescope, and, some time later, see myself sticking my tongue out at myself. I'm obviously not seeing myself "in real time."
As a third example, there are distant galaxies whose light hasn't gotten to us yet. I don't think anyone would argue that we are seeing them "in real time" -- we haven't even seen them yet.
It sounds like you're misinterpreting something you heard about the nature of simultaneity in relativity. You can define simultaneity in relativity. You simply have to keep in mind that it's relative, not absolute.
In special relativity, the standard way to do this is Einstein synchronization. The relative motions of the bodies in the solar system, as well as all space probes launched so far, is at velocities much less than c, so it doesn't even matter very much whether you talk about doing your Einstein synchronization in the frame of the earth, of mars, or whatever. This is the sense in which the information from Mars is 15 minutes behind "real time." (There are also gravitational time dilations, and they're also quite small.)
Since you brought up astronomy and cosmological look-back times, it's worth addressing that as well. To describe cosmological scales, you need general relativity, and in general relativity Einstein synchronization doesn't work. However, there is a natural notion of clock synchronization in cosmology that is defined as follows. At any spot in the universe, define a frame of reference that is at rest with respect to the cosmic microwave background (or the local flow of galaxies, which amounts to the same thing). Define a time coordinate as measured by a clock that is at rest in that frame. This is what cosmologists mean when they state the age of the universe as so many billions of years. This time coordinate is also the only reasonable definition of "in real time" for use in cosmology.
Next time, please try being more polite and/or getting your facts right.
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