Assuming the cable doesn't snag or break, your suggestion leads to the payload impacting the surface at slightly under the velocity of the lowest possible circular orbit, about 1700 m/s. That's at the end of the deceleration the anchor can provide, your trajectory intersects the surface after that. The cable of course must first survive impact at the initial 2.4+ km/s in order to provide this deceleration. This is not a realistic requirement.
There are other possibilities (momentum exchange tethers particularly stand out), but they require support infrastructure either on the moon or in orbit.
A mass driver has severe limitations in reachable orbits and imposes very strict limits on payload mass and volume. It also means higher accelerations, which makes it a poor fit for launching people. It is also still less efficient, even the highest mountain is far deeper in the atmosphere than first stage separation, so the mass driver is limited to lower velocities. SpaceX would have needed to build several of them in order to launch to all the orbits the Falcon 9 can reach, and it would have needed to rebuild them for the Falcon 9 v1.1. The Falcon Heavy would have been impossible, that payload increase would have needed a completely new, much larger mass driver. And many of the payloads they've launched simply wouldn't have survived mass driver accelerations. And of course, there's the little issue of not having a conveniently located mountain to put those mass drivers on.
Mass drivers are a complex, expensive, difficult, limited, and impractical way of reducing the size of the first stage. SpaceX is taking the much simpler approach of just recovering and reusing the first stage. They have already made drastic reductions in launch costs and are making steady progress on further reductions...all without a single megastructure. Musk seems to know what he's doing.
If it worked, the end point of this suggestion is a planet with a viciously toxic ~60 atm nearly-pure-O2 atmosphere, and a surface covered in a thick layer of explosively flammable algae dust. You would be explosively flammable as well, especially if your suit is at ambient pressure, which would require a breathing gas mix that's almost entirely hydrogen. Following the inevitable inferno, you would once again have a CO2 atmosphere.
It doesn't work though, because there's not enough water for plant life to lock more than a tiny fraction of the CO2 away in carbohydrates and lipids. You need to import hydrogen, lots of it...almost 10% of the mass of the current atmosphere in hydrogen. Then you have plenty of water, and get to work on the nitrogen problem...there's about 3 Earth atmospheres worth of it there.
My favorite is the Pioneer Venus Multiprobe, a set of 4 little *atmospheric* probes. One continued sending data for over an hour after hitting the surface, despite not being designed as a surface probe...the atmosphere's just so thick that the terminal velocity was survivable.
We now have silicon carbide electronics that can operate at ambient surface temperature, and numerous other ways of dealing with high temperatures and harsh environments, so we could build Venus surface probes that would have indefinite operating lifetimes. RTGs would be a useful power source, the "cold side" temperature of RTGs that have to radiate waste heat in vacuum is similar to the surface temperature on Venus.
You realize geothermal power involves boiling water and spinning turbines as well, don't you?
And solar panels don't just magically appear in a truck, they have to be manufactured, a complex and high-energy industrial process involving a wide array of hazardous substances. The panels themselves frequently contain hazardous materials, and need to be collected for recycling or safe disposal at the end of their life...provided the operator is willing to pay for it.
They also don't have much available power to convert, generally actually make use of less than 30% of that, and your investment will spend half its time in the dark, not doing anything useful, so you have to cover the landscape with them and build gigantic energy storage systems to handle the variations in production...real "elegant".
Space probes use assists *by planets* to adjust their velocity around *the sun*. The maneuver can not be used for changing the speed relative to the object it's being done around. You can not slingshot around the moon and reduce your velocity relative to the moon. If you are on a trajectory that intersects the lunar surface, your kinetic energy will reach a maximum and potential energy a minimum at impact.
You could use gravitational assists around the moon to adjust the orbit around Earth into one that makes it easier to reach the moon, but you can't do anything to gravitationally brake an object coming in for landing. Such an object is trading gravitational potential energy for kinetic energy, and its velocity will be at a maximum at impact. No gravitational trick can make that potential energy disappear.
"If I can use an orbit to accelerate myself away from a body,"
You can't. The speed relative to the gravitating body in a "slingshot" maneuver is exactly the same on the way out as it was on the way in. The maneuver is useful because it allows for a change of direction and because depending on the approach, the change of direction can mean adding or subtracting the motion of the gravitating body relative to a third body. Slingshotting around the moon can put you in a higher or lower orbit around Earth or allow a cheaper transition between Earth orbit and a Mars transfer orbit, it's not going to help soft-landing on the moon.
The moon has its own gravity, enough to accelerate an object dropped from a large distance to around 2.4 km/s by the time it reaches the surface. It is also in a circular orbit around Earth, and anything reaching it from Earth will be either have a much lower orbital velocity at the high end of an elliptical orbit, or be on a high energy trajectory that has a similar orbital velocity in a quite different direction. And no, it is not possible to slow down a trip to the moon. If you're not going fast enough, you simply don't reach the moon.
And aerobraking at Mars doesn't have to bring you to a stop on the surface to be a benefit. Yes, you still have to carry propellant, but you don't need the vast majority of your craft to be propellant. If 2/3 of the mass you send is payload instead of 1/9th, you're sending 6 times as much payload for a given mass sent to Mars.
The big advantage of the moon is proximity. It's reachable with small craft that only need to operate for days at a time, and it's close enough for equipment on the surface to be monitored and remote operated in near-realtime, with a couple seconds of lightspeed lag instead of up to 40 minutes. Emergency evacuation means reaching Earth in a few days, and delivery of equipment to address failures or unforeseen needs is mostly limited by the time needed to prepare a launch.
There may be extremophiles living in the rock, but they're nothing that would cause problems for us. There's plenty of the chemical substances we need for survival, just not enough for such an extraordinarily wasteful operation as terraforming the planet. And perchlorates are not "highly toxic"...the LD50 for potassium perchlorate is 2100 mg/kg. Compare to 3000 mg/kg for...table salt. Given a bowl full of pure potassium perchlorate, it would be extremely difficult to eat enough of it to be fatal.
Dealing with perchlorate only requires doing things we'd likely be doing anyway. Process the regolith a bit before turning it into soil for growing stuff in...it's eroded salt flat and sea bed material, you're going to do that anyway. Perchlorates are unstable and easy to decompose, so there's options for further soil treatment if necessary. Test occasionally or use supplements to make sure you're getting enough iodine (perchlorate does substitute for iodine, inhibiting uptake). Problem dealt with.
In Python, that could easily have been one or more statements that were unintentionally made conditional or removed from the conditional, perhaps while adjusting the indentation of adjacent just-moved code so the interpreter would put it in the right block. Python's indentation significance doesn't improve things one bit. If you want a fix for this problem, make the end delimiter non-optional, which would make it much more difficult to accidentally put a statement in the wrong block.
And of course, the presence of delimiters does nothing to prevent a language from requiring indentation or producing warnings when it finds inconsistencies between indentation and delimiters.
Except that never actually happens, because there's always enough information there to determine the meaning of the code. The process of restoring sensible indentation can even be automated.
Thank you. The "why don't you like indentation?" argument is nothing but a ridiculous straw man...the issue is not the use of indentation to reflect structure (which, as you point out, Python actually interferes with in some cases...it gets worse with higher dimensional cases such as voxel maps), it's with the lack of properly delimited blocks. With blocks being implied by indentation, you lose an important visual anchor and cross-check of intent with the compiler, and what do you gain? Potential problems with tab characters, code truncation errors that are undetectable until you attempt to execute the code, huge headaches if you have to use code that has had its indentation broken...there are no positives here, unless the proponents are seriously objecting to the onerous burden of typing a few } characters or "end" keywords.
Indentation significance is a design flaw, and it's disappointing to see it repeated yet again...
A solar storm causes problems by producing shifts in Earth's magnetic field. It's many orders of magnitude away from being anything like a MRI, and wouldn't scramble hard drives directly, it would disrupt power grids and copper communication lines. The only impact on hard drives or other electronic devices on Earth would be from power surges, while satellites would have increased ionizing radiation to deal with.
Aerospike systems are heavier and have more demanding cooling requirements, due to the central plug surrounded on all sides by hot exhaust, with radiative cooling being largely ineffective, and the increase in plumbing to all the injectors. Their advantage is in being less optimized for a particular atmospheric pressure, increased complexity and weight are tradeoffs. This is mainly a large advantage if you're using the same engines for liftoff and for the burn to orbital velocity once outside the atmosphere, which is why aerospikes are common features of SSTO schemes, but it's much less of a benefit if you have a separate booster stage and upper orbital stage or stages. They're not being held up by patents, there simply hasn't been a great deal of interest in developing them for real-world systems (the launch industry as a whole has had little incentive to do anything new for quite a while).
You get the same with a couple geographically separated launch sites. SpaceX launches to equatorial orbits from Florida and polar orbits from California, and they do so far more cheaply than an air-launch system could, without having to make sacrifices in payload, adding risks due to loss of on-pad test fires and abort capabilities, etc.
Sea launch does look much better than air launch, but it still makes the logistics and operations more difficult. SpaceX doesn't even want to land rockets at sea when they can bring them down on land, and is talking about future plans of refueling the first stages for a short flight back rather than shipping them back on the landing platform. Political issues with launch and landing locations might make it simpler to do things at sea, though...
Which is why they can manage to only be 5x the cost per kg of a Falcon 9 launch, right? Perhaps 10x when SpaceX starts reusing first stages...
Aerodynamic drag losses are only important for the tiniest of rockets. For most launchers, it's only in the area of 100 m/s. Additionally, propellant is a fraction of a percent of launch costs, and the cost of rocket hardware is not simply proportional to its size.
The failure rate of Pegasus has dropped a fair bit. The big problem is the extremely high cost (around $30 million for 400 kg to orbit these days) and the inflexibility and lack of scalability of air launch systems in general. The Stratolaunch system is building the largest aircraft by wingspan to ever fly to launch rockets with less payload than a Falcon 9...and they won't be able to attempt anything larger without building an even bigger aircraft, while SpaceX is already building the Falcon Heavy (with about 8.7 times the payload capacity of Stratolaunch) based on Falcon 9 hardware.
There really is little to gain. Air launch doesn't get you meaningfully closer to orbit to start with. You don't operate heavily loaded aircraft in bad weather, especially not aircraft loaded with multimillion dollar payloads and tens to hundreds of metric tons of hazardous rocket propellant. Especially when loss of the aircraft removes your ability to perform launches until a new custom-built/modified replacement is ready. You don't simply operate aircraft carrying such payloads out of whatever airport you like, you need special ground infrastructure and flight plans. The altitude and speed are more simply, cheaply, and effectively achieved with a rocket stage...see Orbital's own Taurus, which is essentially a Pegasus launched on top of a rocket first stage instead of dropped from an aircraft, and has a 1320 kg payload compared to the Pegasus' 400 kg.
Problem: the original poster got their units messed up, and the surface of Mars has pressure equivalent to about 35000 meters, not feet. That's about 115 thousand feet. That's nearly 3 times the "altitude without payload" figure listed there.
Didn't forget them, they're just not very good for ballooning. With their hydrogen-helium atmospheres, the only way to get a reasonable amount of buoyant lift is by heating your lift gas, and the low density of those gases means even that gives little lift at a given pressure. Better than Mars, but worse than Earth.
Lift (along with drag) is proportional to the *square* of airspeed, all else being equal. But the rotor blades on a Mars helicopter would have airspeeds in the transonic to supersonic region, with very different airflow, so simply applying a scaling law like that isn't very accurate.
Titan's atmosphere has about 1.5 times the surface pressure of Earth, and the atmosphere is even denser due to the cryogenic temperatures (about 20 K lower, less than the difference between your freezer and room temperature, and it'd start raining nitrogen). The only place in the solar system better for balloons is Venus, they're barely possible on Mars.
I *was* using the density of CO2...which at 273 K and 600 Pa is about 0.012 kg/m^3. It might reach 0.020 kg/m^3 when it's coldest, but it sounds high for a typical surface density.
A helium balloon on Mars would only carry about 10 g of per cubic meter. A hot air balloon would carry far less. (given 273 K ambient temperature and 373 K balloon temperature...rather difficult to maintain with the available power...around 3 g/m^3)
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Assuming the cable doesn't snag or break, your suggestion leads to the payload impacting the surface at slightly under the velocity of the lowest possible circular orbit, about 1700 m/s. That's at the end of the deceleration the anchor can provide, your trajectory intersects the surface after that. The cable of course must first survive impact at the initial 2.4+ km/s in order to provide this deceleration. This is not a realistic requirement.
There are other possibilities (momentum exchange tethers particularly stand out), but they require support infrastructure either on the moon or in orbit.
A mass driver has severe limitations in reachable orbits and imposes very strict limits on payload mass and volume. It also means higher accelerations, which makes it a poor fit for launching people. It is also still less efficient, even the highest mountain is far deeper in the atmosphere than first stage separation, so the mass driver is limited to lower velocities. SpaceX would have needed to build several of them in order to launch to all the orbits the Falcon 9 can reach, and it would have needed to rebuild them for the Falcon 9 v1.1. The Falcon Heavy would have been impossible, that payload increase would have needed a completely new, much larger mass driver. And many of the payloads they've launched simply wouldn't have survived mass driver accelerations. And of course, there's the little issue of not having a conveniently located mountain to put those mass drivers on.
Mass drivers are a complex, expensive, difficult, limited, and impractical way of reducing the size of the first stage. SpaceX is taking the much simpler approach of just recovering and reusing the first stage. They have already made drastic reductions in launch costs and are making steady progress on further reductions...all without a single megastructure. Musk seems to know what he's doing.
If it worked, the end point of this suggestion is a planet with a viciously toxic ~60 atm nearly-pure-O2 atmosphere, and a surface covered in a thick layer of explosively flammable algae dust. You would be explosively flammable as well, especially if your suit is at ambient pressure, which would require a breathing gas mix that's almost entirely hydrogen. Following the inevitable inferno, you would once again have a CO2 atmosphere.
It doesn't work though, because there's not enough water for plant life to lock more than a tiny fraction of the CO2 away in carbohydrates and lipids. You need to import hydrogen, lots of it...almost 10% of the mass of the current atmosphere in hydrogen. Then you have plenty of water, and get to work on the nitrogen problem...there's about 3 Earth atmospheres worth of it there.
My favorite is the Pioneer Venus Multiprobe, a set of 4 little *atmospheric* probes. One continued sending data for over an hour after hitting the surface, despite not being designed as a surface probe...the atmosphere's just so thick that the terminal velocity was survivable.
We now have silicon carbide electronics that can operate at ambient surface temperature, and numerous other ways of dealing with high temperatures and harsh environments, so we could build Venus surface probes that would have indefinite operating lifetimes. RTGs would be a useful power source, the "cold side" temperature of RTGs that have to radiate waste heat in vacuum is similar to the surface temperature on Venus.
You realize geothermal power involves boiling water and spinning turbines as well, don't you?
And solar panels don't just magically appear in a truck, they have to be manufactured, a complex and high-energy industrial process involving a wide array of hazardous substances. The panels themselves frequently contain hazardous materials, and need to be collected for recycling or safe disposal at the end of their life...provided the operator is willing to pay for it.
They also don't have much available power to convert, generally actually make use of less than 30% of that, and your investment will spend half its time in the dark, not doing anything useful, so you have to cover the landscape with them and build gigantic energy storage systems to handle the variations in production...real "elegant".
Space probes use assists *by planets* to adjust their velocity around *the sun*. The maneuver can not be used for changing the speed relative to the object it's being done around. You can not slingshot around the moon and reduce your velocity relative to the moon. If you are on a trajectory that intersects the lunar surface, your kinetic energy will reach a maximum and potential energy a minimum at impact.
You could use gravitational assists around the moon to adjust the orbit around Earth into one that makes it easier to reach the moon, but you can't do anything to gravitationally brake an object coming in for landing. Such an object is trading gravitational potential energy for kinetic energy, and its velocity will be at a maximum at impact. No gravitational trick can make that potential energy disappear.
"If I can use an orbit to accelerate myself away from a body,"
You can't. The speed relative to the gravitating body in a "slingshot" maneuver is exactly the same on the way out as it was on the way in. The maneuver is useful because it allows for a change of direction and because depending on the approach, the change of direction can mean adding or subtracting the motion of the gravitating body relative to a third body. Slingshotting around the moon can put you in a higher or lower orbit around Earth or allow a cheaper transition between Earth orbit and a Mars transfer orbit, it's not going to help soft-landing on the moon.
The moon has its own gravity, enough to accelerate an object dropped from a large distance to around 2.4 km/s by the time it reaches the surface. It is also in a circular orbit around Earth, and anything reaching it from Earth will be either have a much lower orbital velocity at the high end of an elliptical orbit, or be on a high energy trajectory that has a similar orbital velocity in a quite different direction. And no, it is not possible to slow down a trip to the moon. If you're not going fast enough, you simply don't reach the moon.
And aerobraking at Mars doesn't have to bring you to a stop on the surface to be a benefit. Yes, you still have to carry propellant, but you don't need the vast majority of your craft to be propellant. If 2/3 of the mass you send is payload instead of 1/9th, you're sending 6 times as much payload for a given mass sent to Mars.
The big advantage of the moon is proximity. It's reachable with small craft that only need to operate for days at a time, and it's close enough for equipment on the surface to be monitored and remote operated in near-realtime, with a couple seconds of lightspeed lag instead of up to 40 minutes. Emergency evacuation means reaching Earth in a few days, and delivery of equipment to address failures or unforeseen needs is mostly limited by the time needed to prepare a launch.
There may be extremophiles living in the rock, but they're nothing that would cause problems for us. There's plenty of the chemical substances we need for survival, just not enough for such an extraordinarily wasteful operation as terraforming the planet. And perchlorates are not "highly toxic"...the LD50 for potassium perchlorate is 2100 mg/kg. Compare to 3000 mg/kg for...table salt. Given a bowl full of pure potassium perchlorate, it would be extremely difficult to eat enough of it to be fatal.
Dealing with perchlorate only requires doing things we'd likely be doing anyway. Process the regolith a bit before turning it into soil for growing stuff in...it's eroded salt flat and sea bed material, you're going to do that anyway. Perchlorates are unstable and easy to decompose, so there's options for further soil treatment if necessary. Test occasionally or use supplements to make sure you're getting enough iodine (perchlorate does substitute for iodine, inhibiting uptake). Problem dealt with.
Or an actual launch vehicle.
In Python, that could easily have been one or more statements that were unintentionally made conditional or removed from the conditional, perhaps while adjusting the indentation of adjacent just-moved code so the interpreter would put it in the right block. Python's indentation significance doesn't improve things one bit. If you want a fix for this problem, make the end delimiter non-optional, which would make it much more difficult to accidentally put a statement in the wrong block.
And of course, the presence of delimiters does nothing to prevent a language from requiring indentation or producing warnings when it finds inconsistencies between indentation and delimiters.
Except that never actually happens, because there's always enough information there to determine the meaning of the code. The process of restoring sensible indentation can even be automated.
Thank you. The "why don't you like indentation?" argument is nothing but a ridiculous straw man...the issue is not the use of indentation to reflect structure (which, as you point out, Python actually interferes with in some cases...it gets worse with higher dimensional cases such as voxel maps), it's with the lack of properly delimited blocks. With blocks being implied by indentation, you lose an important visual anchor and cross-check of intent with the compiler, and what do you gain? Potential problems with tab characters, code truncation errors that are undetectable until you attempt to execute the code, huge headaches if you have to use code that has had its indentation broken...there are no positives here, unless the proponents are seriously objecting to the onerous burden of typing a few } characters or "end" keywords.
Indentation significance is a design flaw, and it's disappointing to see it repeated yet again...
A solar storm causes problems by producing shifts in Earth's magnetic field. It's many orders of magnitude away from being anything like a MRI, and wouldn't scramble hard drives directly, it would disrupt power grids and copper communication lines. The only impact on hard drives or other electronic devices on Earth would be from power surges, while satellites would have increased ionizing radiation to deal with.
Aerospike systems are heavier and have more demanding cooling requirements, due to the central plug surrounded on all sides by hot exhaust, with radiative cooling being largely ineffective, and the increase in plumbing to all the injectors. Their advantage is in being less optimized for a particular atmospheric pressure, increased complexity and weight are tradeoffs. This is mainly a large advantage if you're using the same engines for liftoff and for the burn to orbital velocity once outside the atmosphere, which is why aerospikes are common features of SSTO schemes, but it's much less of a benefit if you have a separate booster stage and upper orbital stage or stages. They're not being held up by patents, there simply hasn't been a great deal of interest in developing them for real-world systems (the launch industry as a whole has had little incentive to do anything new for quite a while).
You get the same with a couple geographically separated launch sites. SpaceX launches to equatorial orbits from Florida and polar orbits from California, and they do so far more cheaply than an air-launch system could, without having to make sacrifices in payload, adding risks due to loss of on-pad test fires and abort capabilities, etc.
Sea launch does look much better than air launch, but it still makes the logistics and operations more difficult. SpaceX doesn't even want to land rockets at sea when they can bring them down on land, and is talking about future plans of refueling the first stages for a short flight back rather than shipping them back on the landing platform. Political issues with launch and landing locations might make it simpler to do things at sea, though...
Which is why they can manage to only be 5x the cost per kg of a Falcon 9 launch, right? Perhaps 10x when SpaceX starts reusing first stages...
Aerodynamic drag losses are only important for the tiniest of rockets. For most launchers, it's only in the area of 100 m/s. Additionally, propellant is a fraction of a percent of launch costs, and the cost of rocket hardware is not simply proportional to its size.
The failure rate of Pegasus has dropped a fair bit. The big problem is the extremely high cost (around $30 million for 400 kg to orbit these days) and the inflexibility and lack of scalability of air launch systems in general. The Stratolaunch system is building the largest aircraft by wingspan to ever fly to launch rockets with less payload than a Falcon 9...and they won't be able to attempt anything larger without building an even bigger aircraft, while SpaceX is already building the Falcon Heavy (with about 8.7 times the payload capacity of Stratolaunch) based on Falcon 9 hardware.
There really is little to gain. Air launch doesn't get you meaningfully closer to orbit to start with. You don't operate heavily loaded aircraft in bad weather, especially not aircraft loaded with multimillion dollar payloads and tens to hundreds of metric tons of hazardous rocket propellant. Especially when loss of the aircraft removes your ability to perform launches until a new custom-built/modified replacement is ready. You don't simply operate aircraft carrying such payloads out of whatever airport you like, you need special ground infrastructure and flight plans. The altitude and speed are more simply, cheaply, and effectively achieved with a rocket stage...see Orbital's own Taurus, which is essentially a Pegasus launched on top of a rocket first stage instead of dropped from an aircraft, and has a 1320 kg payload compared to the Pegasus' 400 kg.
Problem: the original poster got their units messed up, and the surface of Mars has pressure equivalent to about 35000 meters, not feet. That's about 115 thousand feet. That's nearly 3 times the "altitude without payload" figure listed there.
1.5% in Neptune and 2.3% in Uranus, not enough to matter for buoyant craft.
Didn't forget them, they're just not very good for ballooning. With their hydrogen-helium atmospheres, the only way to get a reasonable amount of buoyant lift is by heating your lift gas, and the low density of those gases means even that gives little lift at a given pressure. Better than Mars, but worse than Earth.
Lift (along with drag) is proportional to the *square* of airspeed, all else being equal. But the rotor blades on a Mars helicopter would have airspeeds in the transonic to supersonic region, with very different airflow, so simply applying a scaling law like that isn't very accurate.
Titan's atmosphere has about 1.5 times the surface pressure of Earth, and the atmosphere is even denser due to the cryogenic temperatures (about 20 K lower, less than the difference between your freezer and room temperature, and it'd start raining nitrogen). The only place in the solar system better for balloons is Venus, they're barely possible on Mars.
I *was* using the density of CO2...which at 273 K and 600 Pa is about 0.012 kg/m^3. It might reach 0.020 kg/m^3 when it's coldest, but it sounds high for a typical surface density.
A helium balloon on Mars would only carry about 10 g of per cubic meter. A hot air balloon would carry far less. (given 273 K ambient temperature and 373 K balloon temperature...rather difficult to maintain with the available power...around 3 g/m^3)