Timeline for When going to Mars, how do you measure exact distances to determine course corrections?
Current License: CC BY-SA 4.0
9 events
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| Oct 3, 2019 at 13:38 | comment | added | David Hammen | @export_all_errors - The initial errors at the start of entry, descent, and landing (EDL) are over 3 kilometers along track and 150 meters across track. Without error correction, those initial errors can only grow. As Russell Borogrove mentioned in his comment, this results in an error ellipse on landing whose major axis is tens of kilometers long. If you want to call this "precise", fine. It is a lot more precise than were the initial expeditions to Mars. But it's not "precise" in the sense needed by by the now bankrupt Mars One scam. | |
| Oct 2, 2019 at 20:53 | comment | added | DrSheldon | Good answer. It should also be noted that the burn programs on the Apollo Guidance Computer did mostly the same thing. Tracking was done on Earth; the spacecraft itself only knew its attitude and time. Computers in Houston calculated the parameters of the burn, and the on-board computer executed a burn with those parameters. | |
| Oct 2, 2019 at 2:57 | comment | added | Russell Borogove | @export_all_errors The error ellipses for probes landing at Mars are measured in tens of km currently. (See How precise are our Mars landings? ) I think they do some active aerodynamic maneuvering on entry to compensate for mistakes in the trajectory and/or variations in atmospheric conditions. | |
| Oct 1, 2019 at 21:00 | comment | added | chyeaaah | @DavidHammen Great insight - thanks. But it still leaves the original question open. Specifically, how a probe is able to adjust course and velocity SO INCREDIBLY PRECISELY that it is able to enter the atmosphere of Mars at exactly the right time and land at pretty much exactly where you intended. I imagine if the probe is off by a few tens of meters in altitude or a few meters per second in velocity when it enters the atmosphere, it will not land at the exact location you intended, right? | |
| Oct 1, 2019 at 18:27 | comment | added | David Hammen | @Paul - The technology doesn't exist yet to do this in space. JPL uses huge antenna, cryogenic receivers and amplifiers, and sometimes uses multiple antennae around the Earth to yield an antenna that is essentially a good chunk of an Earth diameter across. | |
| Oct 1, 2019 at 18:24 | comment | added | David Hammen | @uhoh - The question asks about "course corrections performed in space". Entry, descent, and landing, which is what I think you're hinting at, is a rather different question. | |
| Oct 1, 2019 at 17:59 | comment | added | uhoh | @Paul that's a good new question but it might have been asked before. Until recently now that we have Tesla autopilot and self-navigating quadcopters, it wouldn't have seemed ludicrous. | |
| Oct 1, 2019 at 16:46 | comment | added | Paul | To the untrained eye, it would seem ludicrous that the probes don’t know where they are. Would it be correct to say that it is designed this way to conserve payload mass? Or is this done to reduce complexity of the system? | |
| Oct 1, 2019 at 15:53 | history | answered | David Hammen | CC BY-SA 4.0 |