Gnaskar Posted July 27, 2012 Report Share Posted July 27, 2012 Re: More space news! Thank you! They are separating the rover 20 meters above the surface, and lowering it on a cable 21 feet long. Platform does not hover but continues downward as the cable is being played out? The rockets come within 21 feet of the surface and this is far enough away to not kick up any dust? Let me do the math on that one. This is all ball park math done mostly from memory, may not be entirely accurate. Hydrazine has an exhaust velocity of about 2,000 m/s (compared to methane/LOX's 3,000 and H2/LOX's 4,000). We want the rocket to hover on Mars (3.8 m/s^2 gravity). Assume it masses a bit more than a ton at this point. Mass times gravity gives us weight: roughly 4,000 newtons. To keep it hovering we need mv = 4,000 Ns per second (solved for propellant mass). [EDIT: That is, the momentum of the propellant with respect to the rocket must equal the impulse inflicted on the rocket by gravity] That gives us about 2 kg of hydrazine hitting the surface at 6 times the speed of sound each second. But while this is going on, we're also shedding horizontal velocity and slowing down towards a hovering state, so lets say 5 kg instead. It strikes me that when doing this kind of ballpark math, there's no functional difference in plume impact velocity between the hover rocket and a landing rocket (20ft of martian air isn't going to slow down the rocket propellant significantly). The difference is in where the impact occurs. The rockets on the sled don't point straight down, but point out at about 30 degrees (eyeballed from video). Trigonometry gives us 12 feet between the landed rover and where the rocket plumes hit. Note however that the force of the plume impact is directed away from the rover, neatly functioning like a leaf blower to clear the area surrounding the rover of dust. In a desperate attempt to actually use the math I've already done, I'll calculate how much energy force is being used to push the dust directly away from the rover (the rest is pushing the dust upward). The plume hits with a 60 degree angle relative to the ground, and assuming a mostly elastic collision, that means the dust is going to be flying in a cloud that averages 30 degrees relative to the ground. the momentum of the collision (which is preserved) is the total mass times velocity of the system. Before the collision that is 5kg of propellant moving at 2,000 m/s for 10,000 Ns each second. The energy that's going into moving this away from the rover is N times cos(30) = 8,660 N. Say about half the energy momentum is lost heating up the soil, making dust into glass and what not, and we find about 5,000N is going into pushing dust away each second and about 700N is going into lifting it. So, assuming we only care about airborne dust, each second pushes about 200 kilo of dust away from the rover at 25m/s. Compared to the rocket lander that can lift up to half a ton of matter* per second (about 30% of which is pointed directly at the lander). TL;DR: There's half the dust, its 12ft further away, and being pushed away from the rover with about 5,000 newtons of force. * 5,000 netwons pointed strait down (the other 5,000N being heat loss lost as heat) can lift 1,300 kg of the martian ground, but that's with barely enough force to counteract gravity. I just assumed an average dust velocity of 10m/s to arrive at 500kg of matter. Assuming different averages can cause radically different results. Hybridization. Send out your robots to explore, build a communications array, build infrastructure from local materials (Option 4). By that time we may have a faster way to get there. If noting else, equip the vessel with a light sail, use all available fuel on the outbound leg, deceleration provided by huge laser built by the robots at the destination. Send your cold seed and cold sleep ships to already built infrastructure (Option 3 & 2). If we get the ability to get beyond .5 c we gain some extra time by relativistic time dilation. Once you have you biosphere set up, send out the next wave of robot explorers. Number of settled star systems increase exponentially, in the blink of an eye (geologically/astronomically speaking) we have settled every suitable star in the galaxy. Why hasn't anyone done this yet? We're achieved solar escape velocity. Barely. We've landed robots on a grand total of two exo-planetary bodies, one of which orbits our home world. We've had one program involving landing people on an exo-planetary body, and no permanent or semi-permanent bases further than 500km away from the surface. Lets learn to crawl before we start sprinting. But, it's definitely time to start crawling. Also, why are people so obsessed with other star systems? with 8 planets and 168(ish) moons, there's plenty of real estate left in this one. Quote Link to comment Share on other sites More sharing options...
Christopher Posted July 27, 2012 Report Share Posted July 27, 2012 Re: More space news! Also' date=' why are people so obsessed with other star systems? with 8 planets and 168(ish) moons, there's plenty of real estate left in this one.[/quote'] They all want to see if the girls in Orion are really green... Quote Link to comment Share on other sites More sharing options...
Cancer Posted July 27, 2012 Report Share Posted July 27, 2012 Re: More space news! ... We're achieved solar escape velocity. Barely. We've landed robots on a grand total of two exo-planetary bodies, one of which orbits our home world. We've had one program involving landing people on an exo-planetary body, and no permanent or semi-permanent bases further than 500km away from the surface. Lets learn to crawl before we start sprinting. But, it's definitely time to start crawling. Also, why are people so obsessed with other star systems? with 8 planets and 168(ish) moons, there's plenty of real estate left in this one. I'm assuming by "robots" you mean "self-directed mobile robots" in the first statement. We've put non-mobile things on several other surfaces, at least two of which (Venus and Titan) we could not see before the spacecraft got there and had no idea what expect. That said, I agree with you. Even with our abuse of Earth, we are far from having exhausted the wonders of this star system. Quote Link to comment Share on other sites More sharing options...
Zeropoint Posted July 27, 2012 Report Share Posted July 27, 2012 Re: More space news! Gnaskar, your weight calculation looks right, but all the other math in your post is way off; unit analysis is all wrong and you seem to be using Newtons to refer to energy in many places. Quote Link to comment Share on other sites More sharing options...
tkdguy Posted July 27, 2012 Author Report Share Posted July 27, 2012 Re: More space news! I'm okay with exploring our solar system. Most of the links I've provided deal with new discoveries in the solar system. Like I once told a friend, you ought to know what's in your backyard before you cross the street. Quote Link to comment Share on other sites More sharing options...
Gnaskar Posted July 29, 2012 Report Share Posted July 29, 2012 Re: More space news! Theyall want to see if the girls in Orion are really green... I have it on good authority that they're actually a rather unappealing shade of dark purple, but I appreciate the sentiment. I'm assuming by "robots" you mean "self-directed mobilerobots" in the first statement. We've put non-mobile things on several other surfaces' date=' at least two of which (Venus and Titan) we could not see before the spacecraft got there and had no idea what expect.[/size'] That said, I agree with you. Even with our abuse of Earth, we are far from having exhausted the wonders of this star system. Yeah, mobility is a pretty big requirement if the plan is to build the framework for a human colony who's colonists are several light years behind. For taking pictures and soil samples, you can do without. Gnaskar' date='your weight calculation looks right, but all the other math in yourpost is way off; unit analysis is all wrong and you seem to be usingNewtons to refer to energy in many places.[/quote'] As mentioned, it's mostly from memory, and everything is rounded off. So even assuming I've used the right formula, it's only accurate to about the order of magnitude. It still does a pretty decent job explaining why the chose the hover sled option over a lander, though. I can't find any flaws in my unit analysis on a second read through (but feel free to PM me my mistakes), but you are right about the energy thing. Quote Link to comment Share on other sites More sharing options...
tkdguy Posted July 30, 2012 Author Report Share Posted July 30, 2012 Re: More space news! NASA rover closing in on Mars Quote Link to comment Share on other sites More sharing options...
Greywind Posted July 30, 2012 Report Share Posted July 30, 2012 Re: More space news! Think the Martians will shoot this one down? Quote Link to comment Share on other sites More sharing options...
tkdguy Posted July 30, 2012 Author Report Share Posted July 30, 2012 Re: More space news! Think the Martians will shoot this one down? Not if Bugs Bunny and Duck Dodgers did their job. Quote Link to comment Share on other sites More sharing options...
L. Marcus Posted July 30, 2012 Report Share Posted July 30, 2012 Re: More space news! They in charge of Nasa's Imperial To Metric Conversion Dept.? Quote Link to comment Share on other sites More sharing options...
tkdguy Posted July 30, 2012 Author Report Share Posted July 30, 2012 Re: More space news! You have to wonder sometimes! Quote Link to comment Share on other sites More sharing options...
L. Marcus Posted July 30, 2012 Report Share Posted July 30, 2012 Re: More space news! I just go , since it's not my money. Quote Link to comment Share on other sites More sharing options...
McCoy Posted July 30, 2012 Report Share Posted July 30, 2012 Re: More space news! Not if Bugs Bunny and Duck Dodgers did their job. They in charge of Nasa's Imperial To Metric Conversion Dept.? That would explain so much! Quote Link to comment Share on other sites More sharing options...
Christopher Posted July 31, 2012 Report Share Posted July 31, 2012 Re: More space news! "7 Minutes of Terror", as narated by former actors of the Star Trek Series: Actor and writer Wil Wheaton*: Actor William Shatner: *You might know him from Star Trek: Next Generation as Wesley Crusher, but he had other projects since. Quote Link to comment Share on other sites More sharing options...
SteveZilla Posted July 31, 2012 Report Share Posted July 31, 2012 Re: More space news! They in charge of Nasa's Imperial To Metric Conversion Dept.? "Engish Units!" "Metric Units!" "Engish Units!" "Metric Units!" "Engish Units!" "Metric Units!" à la Duck/Rabbit season. Quote Link to comment Share on other sites More sharing options...
Zeropoint Posted July 31, 2012 Report Share Posted July 31, 2012 Re: More space news! Well, I guess we'll find out on August 6. Quote Link to comment Share on other sites More sharing options...
Old Man Posted August 1, 2012 Report Share Posted August 1, 2012 Re: More space news! They're going to broadcast the landing live in Times Square. Could this project possibly be any more doomed? Quote Link to comment Share on other sites More sharing options...
dmjalund Posted August 1, 2012 Report Share Posted August 1, 2012 Re: More space news! its going to land in Times Square? Quote Link to comment Share on other sites More sharing options...
L. Marcus Posted August 1, 2012 Report Share Posted August 1, 2012 Re: More space news! Best-case scenario. Quote Link to comment Share on other sites More sharing options...
Christopher Posted August 3, 2012 Report Share Posted August 3, 2012 Re: More space news! Apollo Flags still on the moon, but now white: http://gizmodo.com/5930450/all-the-american-flags-on-the-moon-are-now-white Quote Link to comment Share on other sites More sharing options...
Christopher Posted August 3, 2012 Report Share Posted August 3, 2012 Re: More space news! The Cloud from outer space: www.youtube.com/watch?v=QnodZFD0-RM Quote Link to comment Share on other sites More sharing options...
SteveZilla Posted August 5, 2012 Report Share Posted August 5, 2012 Re: More space news! Not exactly "Space" news, but I think this technology could have a bearing on future space missions. Panasonic Photosynthesis System converts carbon dioxide to organic material with plant-like efficiency Quote Link to comment Share on other sites More sharing options...
tkdguy Posted August 5, 2012 Author Report Share Posted August 5, 2012 Re: More space news! Space weather and the coming storm Quote Link to comment Share on other sites More sharing options...
Christopher Posted August 6, 2012 Report Share Posted August 6, 2012 Re: More space news! NASA's Live Coverage of the Landing of Curiosity: http://www.ustream.tv/nasajpl Quote Link to comment Share on other sites More sharing options...
SteveZilla Posted August 6, 2012 Report Share Posted August 6, 2012 Re: More space news! Two hours till touchdown on Mars... Quote Link to comment Share on other sites More sharing options...
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