Return to the moon

[Beati Dogu]

Powered landings are the only choice for the Moon and Mars.

While you can land on Mars using just an aeroshell, parachutes and large airbags, this is very limited and only suitable for small robotic vehicles. Mars rovers Spirit and Opportunity were landed this way, although there were also some retro rockets that fired just before they were dropped off above the surface. These vehicles were only are about 185kg each.

Larger Mars landers like Viking and the more recent Perseverance used a combination of an aeroshell, parachutes and propulsive landing to set down gently on the surface. Perseverance Is the size of a car and 1025kg though.

[Panamax]

Beati Dogu said:

Powered landings are the only choice for the Moon and Mars.

Which is the whole double-bind. The faster you get there the more fuel you need to slow down. The more fuel you need to slow down the more fuel you have to lift at takeoff. The faster you want to get there the more fuel you have to lift at takeoff. To lift the additional fuel at takeoff you need even more fuel at takeoff. It's a huge problem. One Apollo Moon mission = 3,000 tons at take-off. Total weight of rocks returned to earth across six missions = 380 kg.

Some planetary exploration missions were "fly by". You can get there in a reasonable timeframe but don't have a prayer of slowing down. If you want to get into orbit or land it's a whole different kettle of kerosene, or whatever. (Fly by can also be used for acceleration or deceleration but not at the place you're trying to get to.)

Then when you've mined your hydrocarbons on the far-off world you're left scratching around to find a handy oxidiser so you can do anything with them.

[Beati Dogu]

Hence why they plan to use In-Situ Resource Utilization (ISRU) and have the methane and oxygen prepared and ready for the first manned crew by the time they arrive.

They can use Mars' CO2 atmosphere to make their own methane and oxygen via the Sabatier process.

CO2 (Carbon Dioxide) + 4H2 (Hydrogen) -------> CH4 (Methane) + 2H20 (Water)

They either need to bring hydrogen with them, or (ideally) obtain it from water ice on or near the surface and extract it via electrolysis.

The hydrogen feeds back into the Sabatier process and the oxygen is stored for life support and for the return journey.

[Simpo Two]

Could you just run the thing on H2 and so save all the chemistry?

[Beati Dogu]

Hydrogen is a bear to work with. Much easier to use methane.

[welshjon81]

Simpo Two said:

Landing a rocket backwards is a clever party trick but is it much use for space exploration?

This is probably the most ignorant thing I've ever read on Pistonheads in all my years. And that really does say something!!!

[Simpo Two]

welshjon81 said:

Simpo Two said:

Landing a rocket backwards is a clever party trick but is it much use for space exploration?

This is probably the most ignorant thing I've ever read on Pistonheads in all my years. And that really does say something!!!

Inform your audience then, so they know more. For example, how does landing backwards on the Moon make the voyage better/safer? Can it carry more payload?

[glazbagun]

That's been discussed above. Powered landing is the only way to land on the moon (in one piece at least!)

[Eric Mc]

NASA looked at landing backwards back in the early days of Apollo and quickly abandoned the idea.
It would be a bear to try and do with manually using visual references.

However, with modern "smart" systems and quick reaction computers, it might be a lot more feasible now.

After all, those Falcon 9 boosters seem to be "landing backwards" with monotonous regularity these days.

For me the issue with landing a large, tall booster on the lunar surface is the unpredictability of the nature of the surface you are landing on. The Lunar Module was squat and stable for a reason. And even the Lunar Module could not cope with a slope of more than about 5 degrees.

[Simpo Two]

glazbagun said:

That's been discussed above. Powered landing is the only way to land on the moon (in one piece at least!)

Power, yes. The issue here is about turning round and landing backwards, and why it is supposed to be better. We await the answer!

[LunarOne]

glazbagun said:

So is there any medium-term economic case for Earth-based humans going beyond the moon? I can't think of one beyond getting really good at jetting around space for it's own sake. The ultimate offshore tax haven?

If there's nothing in the solar system that would be worth the expense of bringing it to earth the only alternative would be to send labour to space which, again, doesn't really benefit those down here unless you're making something which can only be made elsewhere. If there were hydrocarbons on Mars at least you could burn them to your hearts content, but there aren't as far as we know.

We're only one medium-sized asteroid away from oblivion. It may not come for another 65 million years, but it may come this decade. And even if we magically manage to escape destruction by asteroid, the Sun will eventually go supernova and swallow us up. The sooner we get off planet Earth and find a way to survive and even thrive elsewhere, the sooner we can assure the future of the human race. Assuming we want to do such a thing. If not, why are we worrying about climate change? It's possibly going to take centuries before we can venture out into space on generational ships, and I seriously doubt we'll ever have Star-Trek like ships with artificial gravity and faster-than-light propulsion. But we probably can create an artificially powered ecosystem that can survive away from the influence of a star, and we can assure our future. But we'll have to start some time. That time is now.

[LunarOne]

Simpo Two said:

Cupramax said:

Am I the only one looking at this and seeing after all this time all they’ve managed is to build a new Saturn V which went to moon originally, meanwhile Musk is landing rockets after use

I'll take the moon anytime over the 'landing a rocket after use'.

A brief summary of manned spaceflight:

1961: First man in orbit
1969: First men on the moon
1972: Last men on the moon

Nobody's left Earth orbit for 50 years.

Correction: Nobody's left Earth orbit at all. And nobody will until we venture towards Mars.

[SpudLink]

LunarOne said:

Correction: Nobody's left Earth orbit at all. And nobody will until we venture towards Mars.

In the past I've said (in jest) "going to the Moon isn't really space". Obviously nonsense, but it was to make the same point. Man hasn't yet escaped Earth's orbit.

[CrutyRammers]

Simpo Two said:

glazbagun said:

That's been discussed above. Powered landing is the only way to land on the moon (in one piece at least!)

Power, yes. The issue here is about turning round and landing backwards, and why it is supposed to be better. We await the answer!

Purely because you only need one rocket motor and all associated plumbing.

[dukeboy749r]

Eric Mc said:

NASA looked at landing backwards back in the early days of Apollo and quickly abandoned the idea.
It would be a bear to try and do with manually using visual references.

However, with modern "smart" systems and quick reaction computers, it might be a lot more feasible now.

After all, those Falcon 9 boosters seem to be "landing backwards" with monotonous regularity these days.

For me the issue with landing a large, tall booster on the lunar surface is the unpredictability of the nature of the surface you are landing on. The Lunar Module was squat and stable for a reason. And even the Lunar Module could not cope with a slope of more than about 5 degrees.

This is why the Artemis astronauts are having a real dilemma with the Space X proposal.

You get all the way there and a human might say 'I can land this' whereas the Space X automated system aborts the landing.

It is the terrain and not the technology that is part of the determining factor.

Space X's approach/proposal is adding a layer of difficulty to the task of putting someone back on the Moon.

[Eric Mc]

LunarOne said:

Correction: Nobody's left Earth orbit at all. And nobody will until we venture towards Mars.

In fact, all of the Apollo lunar missions did indeed leave earth orbit - for part of their journey's to the moon. The SIVB stage gave enough velocity to enable the combined Apollo Command and Service Module plus Lunar Module plus itself into an independent orbit around the sun. Indeed, some of the SIVB upper stages continue to orbit the sun to this day.

However, the Command/Service Module - Lunar Module combination used its Service Propulsion System engine, fired in a retrograde manner, to slow the "escaping" spacecraft to a speed at which it could be captured by the moon's gravity and go into orbit around the moon (which, of course, is also an earth orbiting path).

So, having achieved eath gravity escape velocity, they deliberately slowed themselves down again to allow capture by the moon.

[LunarOne]

Eric Mc said:

LunarOne said:

Correction: Nobody's left Earth orbit at all. And nobody will until we venture towards Mars.

In fact, all of the Apollo lunar missions did indeed leave earth orbit - for part of their journey's to the moon. The SIVB stage gave enough velocity to enable the combined Apollo Command and Service Module plus Lunar Module plus itself into an independent orbit around the sun. Indeed, some of the SIVB upper stages continue to orbit the sun to this day.

However, the Command/Service Module - Lunar Module combination used its Service Propulsion System engine, fired in a retrograde manner, to slow the "escaping" spacecraft to a speed at which it could be captured by the moon's gravity and go into orbit around the moon (which, of course, is also an earth orbiting path).

So, having achieved eath gravity escape velocity, they deliberately slowed themselves down again to allow capture by the moon.

In that case, you could say that the vast majority of humankind who have not participated in an orbital manoeuvre have never been in Earth's orbit. Until we exceed Earth's escape velocity, we are essentially on a ballistic path towards the centre of the earth, stopped only by the surface of the Earth's crust, a chair, the floor of a building, or whatever flying machine we choose. Until the periapsis of our path no longer intersects the surface of the Earth or its atmosphere, we are not technically in orbit at all!

[glazbagun]

dukeboy749r said:

This is why the Artemis astronauts are having a real dilemma with the Space X proposal.

You get all the way there and a human might say 'I can land this' whereas the Space X automated system aborts the landing.

It is the terrain and not the technology that is part of the determining factor.

Space X's approach/proposal is adding a layer of difficulty to the task of putting someone back on the Moon.

Would a lunar rover not be a worth sending first to scope out a good spot and maybe add a beacon?

[Eric Mc]

glazbagun said:

Would a lunar rover not be a worth sending first to scope out a good spot and maybe add a beacon?

Possibly some sort of orbital radar mapping would give a better indication of the levelness of potential landing sites.

The moon has the same surface area of Africa. A (very) slow moving rover would take forever to cover the mileage.

[Simpo Two]

LunarOne said:

the vast majority of humankind who have not participated in an orbital manoeuvre have never been in Earth's orbit.

I am in orbit around the sun, but am not in orbit around the Earth.