From "Celestial Mechanics and Astrodynamics",1964, Victor Szebehely, editior, p. 56, there is a 36 hour trajectory to the Moon suggested. It's seems like a lead and shoot trajectory. Lead the Moon by a certain amount, fire off the rocket, and hit (not land, necessarily), 36 hours later.It prompted me to ask about the delta-vee penalty for flying to the Moon, basically as fast as possible.
Quote from: Robotbeat on 09/20/2011 04:25 amQuote from: notsorandom on 09/20/2011 03:19 amQuote from: mmeijeri on 09/20/2011 01:50 amQuote from: 93143 on 09/20/2011 01:38 amOne of SLS's advantages, especially for Mars, is that it can launch very large pieces (both mass-wise and size-wise) in one shot, which helps with architecture design.No, it doesn't, not if you allow for propellant transfer, as you should. As for crowds of anti-SLS posters: this whole site is pro-SLS by 2:1...Propellant transfer doesn't solve the problem of Mars EDL. To land humans on the surface of mars the lander needs an entry mass of 100-150mt....That's just plain false.If you land an empty ascent vehicle beforehand that becomes filled with ISRU-derived propellants, nothing even near 100mT is needed as an entry mass (probably could make do with just 10mT or less landed dry mass at a time...). And besides, 100mT entry mass still requires ballutes or other more difficult EDL technology.Heck, the Apollo lunar module, which could probably fit 3 in a pinch (after all, Apollo 17 had over 100kg of samples, plus the two astronauts), and had enough delta-v for a Mars ascent vehicle (if not thrust) weighed only about 4 or 5 tons dry and could have considerable weight shaved off if it used modern electronics and batteries and aluminum-lithium alloysIt also depends if you want a crew of 8 (like some of the Mars architectures had) or a smaller crew of 6, 4, or even 2 (say, for the short-stay missions... some crew could stay on orbit, ala Apollo).I spent the evening looking over a few proposed Mars missions. Haha I didn't have anything better to do. Your claim that 10mt or less could would work doesn't seem doable. DRM 5 thinks 40mt is the smallest individual piece. Mars Direct uses ISRU and it requires the ability to land 28,500 kg on the Martian surface. The habitat, power, and life support is over 10mt for a crew of four. Its something that can't really be split up into smaller pieces.That doesn't include any consumables, lab equipment, space suits, rovers, backup spares, or astronauts. A crew of four is going to require 10.4mt of consumables alone. The ISRU parts don't fit under 10mt either. For safety reasons the crew is going to need to land with plenty of consumables, a long range rover, and a habitat in case they land too far the other mission elements such as their ride home. A lot has to land with the astronauts in order to reduce the risk of an off target landing. Once again going by the Mars Direct figures that is going to be more then 10mt. The lowest mass landed element I can realistically and safely cobble together is at least 16mt from the elements in Mars Direct. I bet there was good reason to not even go that small by the study's authors. I'm not saying that the full 130mt SLS is needed for a Mars mission. However, it looks like the Falcon Heavy is too small for the job even with advanced EDL technology, ISRU, and propellant depots. Its been proposed that the core version of SLS with a 70-100mt payload and propellant depots could be the best way to go. There would need to be more study of this concept but personally I am leaning in that direction. Its interesting that in many proposed Mars mission I read over while compiling this post a lander mass around 130mt kept showing up. Anyone want to bet where the 130mt SLS payload requirement came from?
Quote from: notsorandom on 09/20/2011 03:19 amQuote from: mmeijeri on 09/20/2011 01:50 amQuote from: 93143 on 09/20/2011 01:38 amOne of SLS's advantages, especially for Mars, is that it can launch very large pieces (both mass-wise and size-wise) in one shot, which helps with architecture design.No, it doesn't, not if you allow for propellant transfer, as you should. As for crowds of anti-SLS posters: this whole site is pro-SLS by 2:1...Propellant transfer doesn't solve the problem of Mars EDL. To land humans on the surface of mars the lander needs an entry mass of 100-150mt....That's just plain false.If you land an empty ascent vehicle beforehand that becomes filled with ISRU-derived propellants, nothing even near 100mT is needed as an entry mass (probably could make do with just 10mT or less landed dry mass at a time...). And besides, 100mT entry mass still requires ballutes or other more difficult EDL technology.Heck, the Apollo lunar module, which could probably fit 3 in a pinch (after all, Apollo 17 had over 100kg of samples, plus the two astronauts), and had enough delta-v for a Mars ascent vehicle (if not thrust) weighed only about 4 or 5 tons dry and could have considerable weight shaved off if it used modern electronics and batteries and aluminum-lithium alloysIt also depends if you want a crew of 8 (like some of the Mars architectures had) or a smaller crew of 6, 4, or even 2 (say, for the short-stay missions... some crew could stay on orbit, ala Apollo).
Quote from: mmeijeri on 09/20/2011 01:50 amQuote from: 93143 on 09/20/2011 01:38 amOne of SLS's advantages, especially for Mars, is that it can launch very large pieces (both mass-wise and size-wise) in one shot, which helps with architecture design.No, it doesn't, not if you allow for propellant transfer, as you should. As for crowds of anti-SLS posters: this whole site is pro-SLS by 2:1...Propellant transfer doesn't solve the problem of Mars EDL. To land humans on the surface of mars the lander needs an entry mass of 100-150mt....
Quote from: 93143 on 09/20/2011 01:38 amOne of SLS's advantages, especially for Mars, is that it can launch very large pieces (both mass-wise and size-wise) in one shot, which helps with architecture design.No, it doesn't, not if you allow for propellant transfer, as you should. As for crowds of anti-SLS posters: this whole site is pro-SLS by 2:1...
One of SLS's advantages, especially for Mars, is that it can launch very large pieces (both mass-wise and size-wise) in one shot, which helps with architecture design.
Unless you used an aeroshell or hypercone or something.
Quote from: notsorandom on 09/20/2011 07:07 amIts interesting that in many proposed Mars mission I read over while compiling this post a lander mass around 130mt kept showing up. Anyone want to bet where the 130mt SLS payload requirement came from?Some of it seems to be circular reasoning, given a 130 tonne Ares V launcher what Mars mission can we design ( DRM 5.0 ) - its not surprising it came up with requiring a 130 tonne HLV.
Its interesting that in many proposed Mars mission I read over while compiling this post a lander mass around 130mt kept showing up. Anyone want to bet where the 130mt SLS payload requirement came from?
{snip}All the astronauts REALLY need to land with in case of an off-nominal landing is a small unpressurized rover, a couple of space suits with enough consumables to last a day or so while they drive to their landing spot. OR, you make an off-nominal landing so unlikely that those things aren't required, or that even an off-nominal landing would be within walking distance or a remote-controlled rover with enough range can be pre-landed, etc.
Quote from: notsorandom on 09/20/2011 07:07 amI spent the evening looking over a few proposed Mars missions. Haha I didn't have anything better to do. Your claim that 10mt or less could would work doesn't seem doable. DRM 5 thinks 40mt is the smallest individual piece. Mars Direct uses ISRU and it requires the ability to land 28,500 kg on the Martian surface. The habitat, power, and life support is over 10mt for a crew of four. Its something that can't really be split up into smaller pieces.That doesn't include any consumables, lab equipment, space suits, rovers, backup spares, or astronauts. A crew of four is going to require 10.4mt of consumables alone. The ISRU parts don't fit under 10mt either. For safety reasons the crew is going to need to land with plenty of consumables, a long range rover, and a habitat in case they land too far the other mission elements such as their ride home. A lot has to land with the astronauts in order to reduce the risk of an off target landing. Once again going by the Mars Direct figures that is going to be more then 10mt. The lowest mass landed element I can realistically and safely cobble together is at least 16mt from the elements in Mars Direct. I bet there was good reason to not even go that small by the study's authors. I'm not saying that the full 130mt SLS is needed for a Mars mission. However, it looks like the Falcon Heavy is too small for the job even with advanced EDL technology, ISRU, and propellant depots. Its been proposed that the core version of SLS with a 70-100mt payload and propellant depots could be the best way to go. There would need to be more study of this concept but personally I am leaning in that direction. Its interesting that in many proposed Mars mission I read over while compiling this post a lander mass around 130mt kept showing up. Anyone want to bet where the 130mt SLS payload requirement came from?Mars DRMs are not the minimum required for landing humans. I'm talking about the minimum size, not even necessarily the optimum size.So, you made lots of assumptions:1) minimum surface crew size 4 (again, no reason why 4 is the minimum required for a short-duration mission)2) precision landing can't be relied on (the lunar-roving-vehicle had a mass of only 210kg, and had a range with 2 astronauts of almost 100km... modern batteries could do better, maybe twice as long)3) the size of power, consumables (for less than 30 days), etc, can't be reduced4) Mars Direct is the best possible option for lowest mass elements (it already assumes an HLV, so if the conclusion after looking at Mars DIRECT is that you should use an HLV, you are begging the question).All the astronauts REALLY need to land with in case of an off-nominal landing is a small unpressurized rover, a couple of space suits with enough consumables to last a day or so while they drive to their landing spot. OR, you make an off-nominal landing so unlikely that those things aren't required, or that even an off-nominal landing would be within walking distance or a remote-controlled rover with enough range can be pre-landed, etc.Halving the crew could have the effect of nearly halving the minimum entry mass. We have a 6-person manned outpost right now that has crew that gets there and back with only a 3-person spacecraft. So, even if you lower the minimum crew to 2 or 3 doesn't mean your outpost can't support higher numbers. Far more important than having large numbers is getting there at all, in my opinion.
I spent the evening looking over a few proposed Mars missions. Haha I didn't have anything better to do. Your claim that 10mt or less could would work doesn't seem doable. DRM 5 thinks 40mt is the smallest individual piece. Mars Direct uses ISRU and it requires the ability to land 28,500 kg on the Martian surface. The habitat, power, and life support is over 10mt for a crew of four. Its something that can't really be split up into smaller pieces.That doesn't include any consumables, lab equipment, space suits, rovers, backup spares, or astronauts. A crew of four is going to require 10.4mt of consumables alone. The ISRU parts don't fit under 10mt either. For safety reasons the crew is going to need to land with plenty of consumables, a long range rover, and a habitat in case they land too far the other mission elements such as their ride home. A lot has to land with the astronauts in order to reduce the risk of an off target landing. Once again going by the Mars Direct figures that is going to be more then 10mt. The lowest mass landed element I can realistically and safely cobble together is at least 16mt from the elements in Mars Direct. I bet there was good reason to not even go that small by the study's authors. I'm not saying that the full 130mt SLS is needed for a Mars mission. However, it looks like the Falcon Heavy is too small for the job even with advanced EDL technology, ISRU, and propellant depots. Its been proposed that the core version of SLS with a 70-100mt payload and propellant depots could be the best way to go. There would need to be more study of this concept but personally I am leaning in that direction. Its interesting that in many proposed Mars mission I read over while compiling this post a lander mass around 130mt kept showing up. Anyone want to bet where the 130mt SLS payload requirement came from?
Quote from: MikeAtkinson on 09/20/2011 09:08 amQuote from: notsorandom on 09/20/2011 07:07 amIts interesting that in many proposed Mars mission I read over while compiling this post a lander mass around 130mt kept showing up. Anyone want to bet where the 130mt SLS payload requirement came from?Some of it seems to be circular reasoning, given a 130 tonne Ares V launcher what Mars mission can we design ( DRM 5.0 ) - its not surprising it came up with requiring a 130 tonne HLV.Looks like you may have missed something... [emphasis added]
I don't think we will use fully propulsive Mars landers. Ever tried firing a rocket into a hypersonic jet stream coming at you?
Topic Summary Posted on: Today at 03:56 AMPosted by: mmeijeri Insert QuoteIt is unlikely heavy payloads can be landed without using propulsion for substantially more than final descent and landing. Of course that doesn't mean you don't want to use aerodynamic deceleration to the maximum degree possible.
I agree that other things being equal, you can save a lot of propellant by using aerobraking, but for heavy payloads, that's not trivial. There are faring issues as well. Meanwhile, a fully propulsive Mars lander could be had more or less off the shelf if it were a beefed up Lunar lander.
Quote from: Warren Platts on 09/25/2011 12:56 pmI agree that other things being equal, you can save a lot of propellant by using aerobraking, but for heavy payloads, that's not trivial. There are faring issues as well. Meanwhile, a fully propulsive Mars lander could be had more or less off the shelf if it were a beefed up Lunar lander.Hey, I'm all for that, in fact I've advocated just that. But eventually I think both propulsive braking and aerodynamic deceleration will play substantial roles. Large single-use heatshields that require huge fairings - not so much.
Mars' gravity and atmosphere is not as great as earth, like 35-40% I think.