Timeline for How did the Perseverance rover land on Mars with the retro rockets apparently stopped?
Current License: CC BY-SA 4.0
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| S Mar 2, 2021 at 11:20 | history | suggested | Glorfindel | CC BY-SA 4.0 |
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| Mar 2, 2021 at 10:21 | review | Suggested edits | |||
| S Mar 2, 2021 at 11:20 | |||||
| Feb 25, 2021 at 19:25 | comment | added | Darth Pseudonym | @azot Note that hydrazine decomposition is often visible on earth because the exhaust is mostly a hot plume of nitrogen gas and hydrogen gas. While they are both invisible gasses, as soon as the hot hydrogen mixes with atmospheric oxygen, it tends to catch fire and burn with a dim orange flame. On Mars, the atmosphere is carbon dioxide, so the hydrogen can't burn. | |
| Feb 24, 2021 at 4:34 | comment | added | uhoh | @azot this answer explains that these are hydrazine monopropellant thrusters, you can't compare them to a launch vehicle's engines; way different size and scale and power, and totally different chemical mechanisms. Here's an old, strange video, they have to dim the lights and use a black background to see anything: youtube.com/watch?v=9DqtWjZOVfY In the engine it decompose(s) into ammonia, nitrogen gas, and hydrogen gas and that gas escapes the nozzle. There's no flame. | |
| Feb 24, 2021 at 1:16 | comment | added | Christopher James Huff | @azot so what? A single video where the exhaust was visible is hardly evidence that the exhaust will always be visible. The visibility depends on viewing angle, sun angle, weather, etc. And even in that video, that cluster of much-larger engines produces a plume that has very little contrast against the background, the exhaust of the individual engines being very nearly invisible shortly after liftoff, with any refraction having little visible effect. | |
| Feb 23, 2021 at 23:06 | comment | added | azot | @ChristopherJamesHuff , Watch this video: "Russian Proton-M launch with Spektr-RG X-ray Observatory satellite (7/13/2019)" (youtube.com/watch?v=LfHH6oX1VQg). The exhaust plume of the engines is visible all the time. | |
| Feb 23, 2021 at 16:09 | comment | added | Christopher James Huff | @azot The exhaust from Proton rockets with much bigger and more powerful engines can be nearly invisible at times. How would you expect to see shimmer/distortion from refraction with such a uniform background? | |
| Feb 23, 2021 at 10:08 | comment | added | OrangeDurito | I think Matt Walace also mentions that if you look closely at the rim of the nozzle, you can see a faint pink glow that indicates its burning. Other than that, yes the exhaust is quite clear and now that we have seen it, the animations will follow suit. Exhaust-plume interaction was interesting to look at and that is certainly nobody could have guessed beforehand. | |
| Feb 23, 2021 at 9:48 | comment | added | GremlinWranger | @azot starting writing my own question on plume temperature and then found researchgate.net/publication/… which gives an exit temperature for MSL, original name for Curiosity of 202 Kelvin, well below freezing but still balmy for mars, pressure seems to be four to five Martain atmospheres. Does explain why the rover hanging under the sky crane does not get singed. | |
| Feb 23, 2021 at 9:42 | comment | added | necroncryptek | they claimed that they had test footage on earth that showed the same thing but i haven't seen it. They explained people were curious why animators made plumes coming from the rockets during simulations showing people what it would look like, when both on earth and mars its clear. It was just a mix up and something that wasn't communicated. | |
| Feb 23, 2021 at 9:40 | comment | added | GremlinWranger | @azot - The physics of rocket thrusters means that you want the pressure of the exhaust to be close to ambient, and the temperature to be low for maximum energy extraction (some vacuum thruster operations are visible because the exhaust condenses). Given the Martian atmosphere is pretty close to a vacuum anyway an interesting question what the actual pressure and temperature actually was. | |
| Feb 23, 2021 at 9:25 | comment | added | azot | Is there a video on the net showing hydrazine rocket engines, other than those of Perseverance, burning perfectly clear. In general, even if an object, or jet of gas, is transparent you still see it because its refraction coefficient is different from that of the air. | |
| Feb 23, 2021 at 9:08 | history | answered | necroncryptek | CC BY-SA 4.0 |