Quote from: baldusi on 12/10/2014 03:11 pmQuote from: Zappa on 12/10/2014 01:55 amQuote from: ChrisWilson68 on 12/08/2014 11:09 pmGetting back on topic, this thread is about an Astrobotic mission supposedly launching in 2015. They have to launch in 2015 to have any chance to win the GLXP, which is the whole point of the mission. I think we can all agree SpaceX will not have any engine other than Draco and SuperDraco that will be able to restart to do a lunar insertion burn before the end of 2015, yes? So Falcon 9 itself won't be putting the Astrobotic payload into lunar orbit.Could a Falcon 9 just continuously burn it's second stage engine for a TLI burn? Or restart it shortly after entering LEO?Forgive me if this is a dumb question. It's just that they are offering payload services to the Moon and seem quite confident in accepting money for the job.I believe you are not quite clear on the terms. Falcon 9 would make a single burn of its upper stage, until the upperstage and payload are on TLI. For reasons of efficiency that's done as fast as possible on the opposite side of the Earth as is the Moon. After that, the whole stack will take a few days of coasting until they are close to the Moon. During those days, a couple of adjustment maneuvers might be required.Once they reach the gravity field of the Moon, they are still going too fast to be captured by the Moons gravity. Depending on initial conditions, without some serious retropropulsion at that time you either crash the moon, get deviated to some Earth orbit or you return to Earth (the famous Free Return Trajectory that saved Apollo 13).Having a stage that can do a burn four or five days after initial launch is not something easy, and certainly nothing that's usual since even the most complicated missions to Earth orbit are 9hrs top. Thus, the Falcon 9 upper stage would be probably dead by that time and the Astrobotic lander would have to do the retropropulsion by itself. Since the upper stage would be dead mass for the trajectory correction maneuvers, the logical thing would be that the payload separates from the upper stage as soon as it shuts down.Hi Baldusi, I don't believe that is correct (emphasis mine). You would do your TLI roughly when the Moon rises above horizon.You need to set your apogee to where the Moon will be when you get there, not where it is at the time of the burn. Hence TLI burn is not done at spacecraft/Moon opposition, but rather at 90-120-ish degrees.
Quote from: Zappa on 12/10/2014 01:55 amQuote from: ChrisWilson68 on 12/08/2014 11:09 pmGetting back on topic, this thread is about an Astrobotic mission supposedly launching in 2015. They have to launch in 2015 to have any chance to win the GLXP, which is the whole point of the mission. I think we can all agree SpaceX will not have any engine other than Draco and SuperDraco that will be able to restart to do a lunar insertion burn before the end of 2015, yes? So Falcon 9 itself won't be putting the Astrobotic payload into lunar orbit.Could a Falcon 9 just continuously burn it's second stage engine for a TLI burn? Or restart it shortly after entering LEO?Forgive me if this is a dumb question. It's just that they are offering payload services to the Moon and seem quite confident in accepting money for the job.I believe you are not quite clear on the terms. Falcon 9 would make a single burn of its upper stage, until the upperstage and payload are on TLI. For reasons of efficiency that's done as fast as possible on the opposite side of the Earth as is the Moon. After that, the whole stack will take a few days of coasting until they are close to the Moon. During those days, a couple of adjustment maneuvers might be required.Once they reach the gravity field of the Moon, they are still going too fast to be captured by the Moons gravity. Depending on initial conditions, without some serious retropropulsion at that time you either crash the moon, get deviated to some Earth orbit or you return to Earth (the famous Free Return Trajectory that saved Apollo 13).Having a stage that can do a burn four or five days after initial launch is not something easy, and certainly nothing that's usual since even the most complicated missions to Earth orbit are 9hrs top. Thus, the Falcon 9 upper stage would be probably dead by that time and the Astrobotic lander would have to do the retropropulsion by itself. Since the upper stage would be dead mass for the trajectory correction maneuvers, the logical thing would be that the payload separates from the upper stage as soon as it shuts down.
Quote from: ChrisWilson68 on 12/08/2014 11:09 pmGetting back on topic, this thread is about an Astrobotic mission supposedly launching in 2015. They have to launch in 2015 to have any chance to win the GLXP, which is the whole point of the mission. I think we can all agree SpaceX will not have any engine other than Draco and SuperDraco that will be able to restart to do a lunar insertion burn before the end of 2015, yes? So Falcon 9 itself won't be putting the Astrobotic payload into lunar orbit.Could a Falcon 9 just continuously burn it's second stage engine for a TLI burn? Or restart it shortly after entering LEO?Forgive me if this is a dumb question. It's just that they are offering payload services to the Moon and seem quite confident in accepting money for the job.
Getting back on topic, this thread is about an Astrobotic mission supposedly launching in 2015. They have to launch in 2015 to have any chance to win the GLXP, which is the whole point of the mission. I think we can all agree SpaceX will not have any engine other than Draco and SuperDraco that will be able to restart to do a lunar insertion burn before the end of 2015, yes? So Falcon 9 itself won't be putting the Astrobotic payload into lunar orbit.
You're more right than me, of course. Well, I didn't wanted to go into specifics. What I tried to say in non technical terms was that for the Oberth effect efficiency you want a single powerful burn at perigee (i.e. on the opposite of where you want your apogee to be). Of course the Moon will move around while you reach it. What I never seem to get right is if the moon orbits in the same direction or the opposite of the Earth's rotation. From what I remember most TLI are done on a retrograde orbit to get the free return. Thus, the moon would actually catch on you?
There are many strategies to get to Moon and land there, even recent orbiter probes have used a bunch of different trajectories. For example see LADEE trajectory, LRO and Artemis
One super-scary way to reduce lander mass is lithobraking. Basically, build a lander that looks a bit like the MSR landing pod - air-bags around a tetrahedral pod. Then have the TLI trajectory Moon-intercepting. A relatively simple solid-propellent retro-motor blasts off lots of the energy, then the probe deploys the landing bags and uses friction with the Moon's surface to slow to a stop. Then the airbags deflate and the way the pod opens ensures that the instrumentation is always the right side up, no matter what attitude it finally stopped rolling.This also allows for U/S disposal because it will just crash into the lunar surface a few minutes and several dozen miles behind the lander.
This news item today suggests a reschedule by as much as a year:http://www.bizjournals.com/pittsburgh/news/2014/12/11/astrobotics-lunar-landing-mission-date-may-change.html
yeah Barcelona moon team has an actual launch contract on CZ-2C in June 2015, on a Change'3-derived lander.CGWIC stands a chance of "winning the commercial moon race".
Quote from: nadreck on 12/11/2014 07:10 pmThis news item today suggests a reschedule by as much as a year:http://www.bizjournals.com/pittsburgh/news/2014/12/11/astrobotics-lunar-landing-mission-date-may-change.htmlThey continue to tout themselves as the first commercial lunar landing, however there was another team who announced they are launching in the Summer. Either they are postponing launch until 2016 and counting on the other team not launching and the Xprize deadline being moved back or they are announcing they are launching earlier in 2015, perhaps this Spring. They are announcing the new launch date next week.
With such minimal gravity and no atmosphere to provide air resistance, how big a bounce do you imagine that would have?
Quote from: savuporo on 12/11/2014 08:59 pmyeah Barcelona moon team has an actual launch contract on CZ-2C in June 2015, on a Change'3-derived lander.CGWIC stands a chance of "winning the commercial moon race".IIRC they too have slipped the launch date some time ago - not sure if it's still in 2015.
Quote from: Galactic Penguin SST on 12/11/2014 09:24 pmQuote from: savuporo on 12/11/2014 08:59 pmyeah Barcelona moon team has an actual launch contract on CZ-2C in June 2015, on a Change'3-derived lander.CGWIC stands a chance of "winning the commercial moon race".IIRC they too have slipped the launch date some time ago - not sure if it's still in 2015.They talked about the slip to Jun 2015 in Sept 2013, and as of now everyone that tracks launch schedules still lists them there.But yeah 27. (Varsi's Law) Schedules only move in one direction.
bouncing doesn't make much sense on the Moon. Airbags only help to at most 30m/s, maybe less, so you already have to be VERY close. Also, all those airbags and petals mean a lot of mass overhead. 30m/s of extra propellant is a lot less. Better off just using the tried-and-true lander method. Kick stage to drop out of orbit, then thrusters for the rest.
Quote from: Robotbeat on 12/12/2014 01:07 ambouncing doesn't make much sense on the Moon. Airbags only help to at most 30m/s, maybe less, so you already have to be VERY close. Also, all those airbags and petals mean a lot of mass overhead. 30m/s of extra propellant is a lot less. Better off just using the tried-and-true lander method. Kick stage to drop out of orbit, then thrusters for the rest.If you bounce enough times, sooner or later you'll encounter a mountain or crater wall at close to 90 degrees and then you'll lose a lot more than 30 m/s. ;D
Quote from: groundbound on 12/13/2014 04:11 amQuote from: Robotbeat on 12/12/2014 01:07 ambouncing doesn't make much sense on the Moon. Airbags only help to at most 30m/s, maybe less, so you already have to be VERY close. Also, all those airbags and petals mean a lot of mass overhead. 30m/s of extra propellant is a lot less. Better off just using the tried-and-true lander method. Kick stage to drop out of orbit, then thrusters for the rest.If you bounce enough times, sooner or later you'll encounter a mountain or crater wall at close to 90 degrees and then you'll lose a lot more than 30 m/s. The point of the 30 m/s limit is that the acceleration on the first bounce will destroy your payload if your speed is much over 30 m/s.
Quote from: Robotbeat on 12/12/2014 01:07 ambouncing doesn't make much sense on the Moon. Airbags only help to at most 30m/s, maybe less, so you already have to be VERY close. Also, all those airbags and petals mean a lot of mass overhead. 30m/s of extra propellant is a lot less. Better off just using the tried-and-true lander method. Kick stage to drop out of orbit, then thrusters for the rest.If you bounce enough times, sooner or later you'll encounter a mountain or crater wall at close to 90 degrees and then you'll lose a lot more than 30 m/s.
Quote from: ChrisWilson68 on 12/13/2014 05:44 amQuote from: groundbound on 12/13/2014 04:11 amQuote from: Robotbeat on 12/12/2014 01:07 ambouncing doesn't make much sense on the Moon. Airbags only help to at most 30m/s, maybe less, so you already have to be VERY close. Also, all those airbags and petals mean a lot of mass overhead. 30m/s of extra propellant is a lot less. Better off just using the tried-and-true lander method. Kick stage to drop out of orbit, then thrusters for the rest.If you bounce enough times, sooner or later you'll encounter a mountain or crater wall at close to 90 degrees and then you'll lose a lot more than 30 m/s. ;DThe point of the 30 m/s limit is that the acceleration on the first bounce will destroy your payload if your speed is much over 30 m/s.Is it really that low??? That's only about freeway speed... I would have thought those huge airbag systems on Pathfinder were a lot more powerful than that.
Quote from: groundbound on 12/13/2014 04:11 amQuote from: Robotbeat on 12/12/2014 01:07 ambouncing doesn't make much sense on the Moon. Airbags only help to at most 30m/s, maybe less, so you already have to be VERY close. Also, all those airbags and petals mean a lot of mass overhead. 30m/s of extra propellant is a lot less. Better off just using the tried-and-true lander method. Kick stage to drop out of orbit, then thrusters for the rest.If you bounce enough times, sooner or later you'll encounter a mountain or crater wall at close to 90 degrees and then you'll lose a lot more than 30 m/s. ;DThe point of the 30 m/s limit is that the acceleration on the first bounce will destroy your payload if your speed is much over 30 m/s.
They were designed and tested to accommodate grazing angle impacts as high as 28 m/s. However, as the airbags were designed for no more than about 15 m/s vertical impacts, three solid retrorockets were mounted above the lander in the backshell.
Quote from: ChrisWilson68 on 12/13/2014 05:44 amThe point of the 30 m/s limit is that the acceleration on the first bounce will destroy your payload if your speed is much over 30 m/s.Is it really that low??? That's only about freeway speed... I would have thought those huge airbag systems on Pathfinder were a lot more powerful than that.
The point of the 30 m/s limit is that the acceleration on the first bounce will destroy your payload if your speed is much over 30 m/s.
EDIT: I wonder if you could do a lot better if it was specifically designed to survive extreme deceleration... the HARP Project people managed to shoot electronics/sensors out of a naval gun, IIRC, and that's some pretty crazy g forces.