Why Has Moon Exploration Declined Despite Advances in Space Travel?

[dgtech]

I've been always wondering, if it was possible to visit the moon so many years ago, why is no one bothering today?

My question is related directly with the fact we have a space station in orbit, so no need to use rockets. Everything needed to reach the moon is a small craft with just enough fuel to navigate in space, it would be so easy reaching the moon from Earth's orbit ISS astronauts can go there every other weekend.

 

[mgb_phys]

I've been always wondering, if it was possible to visit the moon so many years ago, why is no one bothering today?

Because we have proved that our Germans are better than their Germans, and there isn't much more reason to go.

My question is related directly with the fact we have a space station in orbit, so no need to use rockets. Everything needed to reach the moon is a small craft with just enough fuel to navigate in space,

You still need the energy to go from being 300km above Earth to being 350,000km above earth.
Getting above the atmosphere into LEO is a big step in terms of aerodynamics but is nothing in the total energy requirment.

 

[dgtech]

Reaching orbit takes almost all the fuel of the craft. Not having to escape the gravity well of the planet is a tremendous saving that you downplay :)

Also, by leaving the ISS you already are accelerated at its speed - almost 28 000 km/h, or more than 2/3 of the top speed of the fastest Apollo.

It's 1:44 in the morning here and I am not in math mood, but it is obvious it will need only a fraction of the energy used in the Apollo missions.

Anyway, nice to see someone actually recognizes the fact it was the Germans all along ;) Sometimes I wonder what would happen if Oppenheimer's father did not move to the US and his son was still in Germany when he made the atom bomb...

 

[turbo]

Given the state of our propulsion technology, we still need to use rockets, and we still need to loft the propellants into LEO. There is no compelling need to return to an arid dusty rock right now, and once our manned craft get outside the Earth's protective magnetic field, the occupants are at risk for getting fried if the Sun throws a tantrum. We still don't have a means of adequately shielding the occupants, and they will almost certainly die if exposed to a large solar event. We got lucky during the Apollo program.

 

[mathman]

Oppenheimer didn't do it by himself. He was the director, but the technical work was done by others, many of whom were refugees from the Nazis.

 

[mgb_phys]

Reaching orbit takes almost all the fuel of the craft. Not having to escape the gravity well of the planet is a tremendous saving that you downplay :)

Low Earth orbit hasn't escaped the gravity well.
You are only about 7% of the radius of the Earth further away than at the surface.
Graviational energy (J per kg) = 400,000 / R (km)
So the difference to LEO is = 400,000/6360 - 400,000/(6360+500)
Almost the same as the gravitational potential energy at the surface.

At the moon the object is almost out the Earth's gravity at 400,000/406,000 = 1 J/kg

Also, by leaving the ISS you already are accelerated at its speed - almost 28 000 km/h, or more than 2/3 of the top speed of the fastest Apollo.

But not in the direction of the moon

Everything you need to take to get to the moon will have had to have been lifted through the atmopshere into LEO.

Sometimes I wonder what would happen if Oppenheimer's father did not move to the US and his son was still in Germany when he made the atom bomb...

The atom bomb was largely the invention of Leo Slizard - a Hungarian, what would have happened if the inventors of the Rubik cube had got the bomb

 

[dgtech]

Thats the other curious thing, in the last 40 years computers have evolved exponentially, and yet we still use practically the same rocket engines Von Brown made for NASA.

Heck, a desktop pc today has more computing power than all the space program computers put together back in those days.

If you are moving the speed of the ISS you already have escape velocity, you simply have to change trajectory and maintain velocity. I know on the ISS gravity is almost the same as here, they only appear in zero g because they are constantly falling :)

 

[Hurkyl]

Heck, a desktop pc today has more computing power than all the space program computers put together back in those days.

But nowhere near the amount of thrust.

 

[dgtech]

Who needs thrust ;) It seems that theoretical science, numbers and computers are set to displace practical science... sadly... I'd rather visit the moon, as uninteresting as it may be, instead of reading all those theories which have no practical implications

Everything you need to take to get to the moon will have had to have been lifted through the atmopshere into LEO.

Sure, but you can do it only once, and then reuse it a lot of times. Plus you won't need atmosphere reentry shielding and other equipment that's also saving energy.

 

[turbo]

But nowhere near the amount of thrust.

The "back to the Moon'ers" seem to have little appreciation for physical law.

 

[IcedEcliptic]

Because we have proved that our Germans are better than their Germans, and there isn't much more reason to go.

That is one of the greatest lines I have ever heard!

https://www.youtube.com/watch?v=<object width="640" height="385"><param name="movie" value="http://www.youtube.com/v/kTKn1aSOyOs&hl=en_US&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/kTKn1aSOyOs&hl=en_US&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="640" height="385"></embed></object>

 

[PaulS1950]

Orbital and escape velocities are very different. In order to 'change trajectory and maintain velocity' it takes a consideral amount of fuel. You have to overcome the Earth's gravity well until you enter the Moon's gravity well in order to get to the moon from orbit.
The real reason we are not going to the moon anytime soon is that Obama has told NASA that they need to concentrate on missions to the asteroids instead of the Moon and Mars if they want funding. This was presented in a NASA press release a couple of weeks ago.

 

[Integral]

Remind me, why do we need to go to the moon? Last time we were there, did they forget something we need?

 

[IcedEcliptic]

Remind me, why do we need to go to the moon? Last time we were there, did they forget something we need?

I think someone left their driver's license. Better to go to the moon than your DMV/RMV.

 

[mgb_phys]

That is one of the greatest lines I have ever heard!

Not original I'm afraid - it's from Tom wolfe's The Right Stuff and is an apocryphal explanation of the US-USSR space race to Pres. Johnson.

 

[Redbelly98]

I'd rather visit the moon, as uninteresting as it may be, instead of reading all those theories which have no practical implications

What is the practical implication of going back to the moon?

 

[DaveC426913]

Thats the other curious thing, in the last 40 years computers have evolved exponentially, and yet we still use practically the same rocket engines Von Brown made for NASA.

Computers have only been around for 40 years. Rockets have been around for centuries.

The development curve of a technology tends to be logarythmic over a long time; i.e. it starts off steep and levels off as we perfect the technology. Chemical rockets are currently about as good as they're going to get.

 

[hamster143]

The energy needed to go to the moon is a few times the energy needed to go to low Earth orbit.

Chemical rockets are not easily scalable. A rocket that takes 25 tons to low Earth orbit (which is where established technology is, more or less) is not necessarily going to scale right away to put 200 tons there, or to put 25 tons on the moon. In fact, NASA estimated that it would take 10 years and billions of dollars to develop a rocket that puts 25 tons on the moon.

We don't want to go much lower than 25 tons, because, with all the safety equipment and such, a 25-ton spacecraft would have barely enough room for three passengers and not much else.

We don't have the technology to reassemble and refuel large craft in orbit. Partly because no one bothered to design and test those, partly because it's simply not possible to hold high specific impulse propellants (liquid hydrogen and oxygen) in containers for extended periods of time.

There is a way out. A 200 kW ion thruster engine is scheduled to be tested in real-world conditions on ISS in 2012. When that technology is sufficiently tested and stable, we'll be able to assemble a mini-ISS in orbit and to use solar panels to power ion thrusters that slowly transfer it from Earth to the Moon or anywhere else we want to go.

 

[dgtech]

Why bother feeding yourself when others eat? The same thing about going to the moon - few people might have been there, but you surely haven't. What is the practical implication of going on a trip?


Honestly, no one of you wants to go to the moon?

 

[dgtech]

The energy needed to go to the moon is a few times the energy needed to go to low Earth orbit.

[PLAIN]http://upload.wikimedia.org/wikipedia/en/c/c8/Apollo_8_acceleration.gif

So Saturn V rocket burns all its 3 stages in less than 12 minutes. The trip to the moon takes more than 3 days, so what you basically say is:

5 F-1 Engines total of 33 500 000 Newtons
8 Retro motors total of 3 100 000 Newtons
5 J-2 engines total of 5 000 000 Newtons
8 Ullage motors total of 800 000 Newtons
1 J-2 engine of 900 000 Newtons
4 Retro motors total of 600 000 Newtons
plus a bunch of smaller engines I did not include

Total of about 50 000 000 Newtons of thrust, used up in less than 12 minutes is a few times LESS than what the actual Apollo craft was carrying? From the http://upload.wikimedia.org/wikipedia/commons/b/b2/Saturn_v_schematic.jpg" it seems all other engines besides the 3 stages of the rocket were not for the actual travel from Earth's orbit to the moon, but for the moon landing itself...

In other words, the craft was hardly using any energy once it exited Earth's orbit, drifting all the way to the moon.

And you all say eliminating those 12 minutes which burn well over 90% of the fuel will not be beneficial? Am I missing something here?

 

[Redbelly98]

Why bother feeding yourself when others eat? The same thing about going to the moon - few people might have been there, but you surely haven't. What is the practical implication of going on a trip?

Not the same thing. Eating is necessary to live, traveling to the moon isn't.

Honestly, no one of you wants to go to the moon?

If they sent someone there, it wouldn't be me (even if I wanted to), so that argument doesn't hold up. I'm all for robotic exploration of the solar system, sending people isn't worth the extra cost in my view.

 

[D H]

So Saturn V rocket burns all its 3 stages in less than 12 minutes. ... Am I missing something here?

You are missing a whole lot here. You are looking at launch only. So what are you missing?

• Trans-lunar injection, about 3.1 km/s.
  The maneuver occurred a couple of orbits after launch and was performed by the Saturn V third stage. It placed the combined third stage+command module+lunar lander+ascent vehicle on a trajectory toward the Moon (more specifically, toward where the Moon would be 3.5 days later).
• Lunar orbit insertion and orbit circularization, about 1 km/s.
  These maneuvers placed the combined command module+lunar lander+ascent vehicle in an elliptical orbit and then a circular orbit about the Moon.
• Lunar orbit descent and powered landing, about 2 km/s.
  These maneuvers placed the combined lunar lander+ascent vehicle on an elliptic orbit about the Moon with a very low perilune altitude and then a powered descent to the lunar surface.
• Lunar ascent and docking, about 1.9 km/s.
  These maneuvers launched the lunar ascent vehicle from the lunar surface and then, over a series of maneuvers, docked the ascent vehicle to the command module.
• Trans-Earth injection, about 1 km/s.
  This maneuver placed the command module on a trajectory that would later intersect the Earth's atmosphere.

I'm leaving out small correction burns and such.You want to go from the ISS to the Moon. First off, the fuel and vehicles needed to accomplish that would need to be launched to the ISS. There ain't no such thing as a free lunch. That fuel and equipment taken into low Earth orbit is dead weight as far as the launch vehicle is concerned. What you are proposing about is one of the most expensive ways to get to the Moon: The low Earth orbit rendezvous option.

The low Earth orbit rendezvous option is very expensive even if the rendezvous is in the optimal orbital plane, which is the Moon's orbital plane at the time of lunar orbit insertion. The ISS is not even close to this. It has an orbital inclination of 51.6° (relative to the Earth's equator); the Moon's orbit about the Earth has an inclination of 23.4° ±5.1°. Plane changes are extremely expensive, particularly so in low Earth orbit. Using the ISS as a base for lunar operations is lunacy.

 

[dgtech]

Even so, that doesn't change the fact spacecraft burns the majority of its fuel reaching Earth's orbit. The ISS might not be the best solution in that case, but launching an in orbit space station once and using it as a remote launch pad will save not only immense quantities of fuel but also a lot of failed launches. The percent of successful launches is still pretty low, and a failed craft is a much bigger waste, in both time and resources. Even if we talk about robotic probes, they are not that heavy and can be transported in quantities to the orbital station and then separately launched at their destinations, eliminating the need for each of them to be launched separately with big, expensive and risky rockers, that have to carry not only their payload, but their fuel.

 

[russ_watters]

Reaching orbit takes almost all the fuel of the craft. Not having to escape the gravity well of the planet is a tremendous saving that you downplay :)

Also, by leaving the ISS you already are accelerated at its speed - almost 28 000 km/h, or more than 2/3 of the top speed of the fastest Apollo.

Others have pointed out several misunderstandings here, but have missed an obvious one: there aren't any spacecraft attached to the space station capable of going to the moon. So we'd still need to launch one from earth, go to the ISS, then go from the ISS to the moon. The total trip would be the same as it was for Apollo. [edit: oh, DH caught that - apologies]

It's 1:44 in the morning here and I am not in math mood, but it is obvious it will need only a fraction of the energy used in the Apollo missions...

I'm sorry, but you're basing that on speed only. You haven't even begun to grasp the issue of gravity.

Honestly, no one of you wants to go to the moon?

Of course I want to go to the moon. But currently lacking the $500 billion required, I'd be much obliged if you could loan it to me!

 

[dgtech]

Yes, you sill have to launch it to the orbit, but that's a one time task, after which you can use it multiple times, saving a lot. The whole idea is about eliminating escaping Earth's gravity and atmosphere reentry each and every time.

 

[D H]

I'm all for robotic exploration of the solar system, sending people isn't worth the extra cost in my view.

I beg to differ. I have an admitted bias here. I changed careers 25 years ago from unmanned space exploration to human space exploration. I made that change because, to be blunt, I could not see the value in this unmanned exploration. What's the point? While those unmanned missions look cheap in comparison to human space missions, they are extremely expensive compared to Earth-based science. Except for Earth and solar observation satellites (note well: these are not robotic missions), the scientific/technical/economical/societal return on investment in terms of bang for the buck of the world's space agencies unmanned space programs. The ROI from those robotic missions is tiny compared to that from Earth-based science.

The point of these robotic exploration missions that they are precursors to human missions. NASA is very careful to call these robotic missions just that: precursors. There is little reason to do anything in space other than send a few Earth and solar observation satellites into space, plus maybe a token space telescope every now and then without the added impetus that these are precursors.

 

[dgtech]

Humans are risky in terms of behavior, but still have their advantages over machines. Like when a probe loses contact... and that's all, nothing you can do from Earth, no one really knows what happened, but if you have human crew they can eliminate minor malfunctions and return a multi billion dollar craft to operation instead of just losing it...

Those who say it is too risky and poses danger to the human life - that's BS, millions die to hamburgers each year, there are people many people who will volunteer for space missions no matter the risk.

 

[DaveC426913]

Yes, you sill have to launch it to the orbit, but that's a one time task,

Fuel?

after which you can use it multiple times, saving a lot.

Yes, just like the space shuttle did.

The whole idea is about eliminating escaping Earth's gravity and atmosphere reentry each and every time.

What do you mean? The only thing that doesn't go up or down is the empty shell of the transit vehicle. You've got humans, supplies, fuel, repair and maintenance techs, repair and maintenace equipment, etc.

And you still need the same ground-to-Earth vehicle to get all this to the ISS.

I would bet that if you did a comprehensive analysis, you'd find that the mass of these is at least an order of magnitude (10x) more than the empty transit vehicle.



If I were to take my Winnebago across the country, there are two ways to do it:
1] I keep it in the city, where I can maintain it, repair it, test it, keep an eye on it, take it to my local garage, check its supplies, pack it and get in it and go. It's a soog through the city, true, but...

2] I keep it outside the city at a storage facility (which is currently nothing more than four walls and a roof). I don't have to worry about the slog through rush hour traffic, carrying all my stuff. But now everything is a slog through the city in my car, and many more trips. All my spare parts are at home; my more expensive test equipment is at home (the cheaper stuff I'll leave in a bin at the storage facility the Winnebago, but I still have to get the bin there); there are no repair guys out there, all spare parts and new technology are at home; all my supplies I have to bring with me in my car, and that includes all the gas I'm gonig to need, and finally, after I'm done all this, I have to go back and get my family before heading out.

Tell me again which is better?

 

[dgtech]

Shuttles crap out going in and out of the planet, that's the thing that should be avoided. You are right thou, it will take some time before that is possible. Too much resources are being wasted here on Earth, like all the wars, like all the unnecessary stuff the industry is wasting resources making. The human kind is very inefficient in its current form.

 

[D H]

The ISS might not be the best solution in that case

That is an understatement.

but launching an in orbit space station once and using it as a remote launch pad will save not only immense quantities of fuel but also a lot of failed launches.

That is bass-ackwards. Earth orbit rendezvous is one of the most expensive ways to go and requires an enormous number of launches. NASA rejected this option fairly early on in the Apollo program. Mass reduction was one of the key drivers in the selection of the lunar orbit rendezvous approach that was used in the Apollo program.

Yes, you have to launch it to the orbit, but that's a one time task, after which you can use it multiple times, saving a lot.

That too is bass-ackwards. This either requires an extra 3.1 km/s delta V on the return trajectory to perform the reverse of the translunar injection burn or it requires using the Earth's atmosphere as an aerobrake to reduce that delta V requirement. The latter is a completely untested (TRL=1) capability and adds significant mass to the return vehicle. Some kind of protective shield is needed to prevent the vehicle from burning up in the atmosphere.

Delta V is a bit of a misleading figure. Changing the delta V by just a little requires a lot more fuel. The ideal rocket equation is a rather nasty equation. It is essentially exponential. Changing the delta V by a lot requires a lot more than a lot more fuel. It requires new infrastructure, and that alone costs a lot in terms of fuel.

 

[dgtech]

So you suggest orbital stations make no sense, and it would be more efficient to continue launching chemical rockets and trying to defy the huge gravity well our planet is each and every time, with all the costs and risks of failure associated?

 

[D H]

So you suggest orbital stations make no sense, and it would be more efficient to continue launching chemical rockets and trying to defy the huge gravity well our planet is each and every time, with all the costs and risks of failure associated?

That is a straw man argument.

You have claimed that it is cheaper/better/faster to use an orbital space station, and in particular, the ISS, as a base. I, and others, have shown that this is not the case. You are vastly oversimplifying what is a very hard problem.

 

[DaveC426913]

So you suggest orbital stations make no sense, and it would be more efficient to continue launching chemical rockets and trying to defy the huge gravity well our planet is each and every time, with all the costs and risks of failure associated?

The point is, it is only more cost-effective if we also transport most of JFK Space Centre and its satellite manufacturing companies up there as well. And even that doesn't do anything about the fuel problem (there is no water up there to even convert to fuel).