Skyler4856

For Questions That Don't Merit Their Own Thread

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Could Orion get to the moon now? With existing rockets such as the Delta IV and its current design? Not necessarily a landing, but a flyby perhaps?

No. The Delta IV Heavy is the largest rocket in the US inventory, yet it could only send Orion into a high orbit with an apogee of 5900 km. The Moon is at distance of 384000 km. The only rocket that can send Orion to the Moon will be SLS.

There are no plans to ever fly Orion on Delta IV again because Delta IV isn't man rated. Orion has no life-support systems yet, so a manned flight is out of question until Orion is finished.

If not, what would it take? Will such a mission be capable with the initial version (as we expect it to be) of the SLS? If THAT'S the case then how come a possible lunar mission is so far away? I'd have thought such a thing would've been high on the list, if only for the prestige factor. After all, if we have the technology and all that jazz.

SLS will be perfectly capable of sending an Orion around the Moon. In fact, its first flight (EM-1) is likely to be an unmanned circumlunar flight, but you'll have to wait until 2019.

The second flight (EM-2) will likely be a manned circumlunar flight around 2021. They wanted to do the asteroid retrieval mission for EM-2, but it's a bit risky for a first manned flight.

There are no further missions planned for Orion at this time. Only 2 service modules have been ordered from ESA and nobody is working on mission modules or landers, so it really can't do anything else than fly around the Moon.

If we started working on a Moon lander today (which isn't going to happen), it would take at least 10 years. That means that Orion and SLS will be sitting around gathering dust for years with no flights, which isn't sustainable budget-wise. It will probably be cancelled before any mission modules are ever built.

Edited by Nibb31

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If we started working on a Moon lander today (which isn't going to happen), it would take at least 10 years. That means that Orion and SLS will be sitting around gathering dust for years with no flights, which isn't sustainable budget-wise. It will probably be cancelled before any mission modules are ever built.

This cancellation seems dubious. Flying to an asteroid, and a fly-by around the moon are excellent from a PR standpoint, even if the flights are rare

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They could be really subtle. If they gently pressure SpaceX and the like to adopt a standard docking system (which I believe they already have), then they may be hoping that SpaceX will be/is working on their own lander for the Moon and such. They know SpaceX is going to be building it regardless of NASA asking them to.

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This cancellation seems dubious. Flying to an asteroid, and a fly-by around the moon are excellent from a PR standpoint, even if the flights are rare

PR is secondary. NASA isn't in the entertainment business.

Flying to an asteroid or a circumlunar flight has very little scientific or technological value. They are just stunts that don't demonstrate or validate any new technology. They are just poor attempts at self-justifying Orion.

The truth is, Orion was designed to fly to the Moon as part of the Constellation. Constellation was cancelled, but Orion wasn't, and now that NASA has Orion, and isn't going to the Moon, they are trying to shoehorn it into missions that it wasn't designed for. Mars is one them. So is the asteroid mission. If you want to visit Mars, Orion isn't particularly necessary. If you want to study an asteroid, Orion isn't the best way to do it.

If NASA or Congress or the POTUS want to use Orion, then they need to stick a lander on top of that SLS and return to the Moon.

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They could be really subtle. If they gently pressure SpaceX and the like to adopt a standard docking system (which I believe they already have), then they may be hoping that SpaceX will be/is working on their own lander for the Moon and such. They know SpaceX is going to be building it regardless of NASA asking them to.

All the commercial crew vehicles use a variant of the IDS adapter.

SpaceX is only going to fly something that they get paid to fly. If NASA does an RFP for lunar hardware, they'll bid.

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No. The Delta IV Heavy is the largest rocket in the US inventory, yet it could only send Orion into a high orbit with an apogee of 5900 km. The Moon is at distance of 384000 km. The only rocket that can send Orion to the Moon will be SLS.

Falcon Heavy ought to be capable of setting it up for a free-return fly-by, and it will be ready long before SLS, so it seems worth considering.

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Falcon Heavy ought to be capable of setting it up for a free-return fly-by, and it will be ready long before SLS, so it seems worth considering.

Falcon Heavy payload to TLI is about 15 tons. Would require cut-down service module for a free-return flight.

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That SM mass includes over 7T of propellant. It's a touch over 13T total empty. So you could either dump some fuel or use it for a boost. Either way, you can get to TLI on a Heavy.

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SpaceX is only going to fly something that they get paid to fly. If NASA does an RFP for lunar hardware, they'll bid.

I wasn't meaning they would do it for free. More what I was meaning is that SpaceX is going to be designing a lander regardless of what NASA says or does. Remember, the point of SpaceX isn't to be just another rocket contractor, it is Musks private space program for colonizing Mars. While the conditions are of course not the same, it wouldn't be too much of a stretch for him to tell his engineers to figure out a variant of his lander that can touch down on the Moon. So NASA could be saying "Let's just work on getting our own special bus up and running, devoting as much of the budget as we can do it, once we get closer to our deadlines for needing a lander, we can evaluate if SpaceX (or whoever) has an option that we could buy rather then engineer our own." Even if Musk's system doesn't meet NASA standards, it is far cheaper for NASA to pay for a re-engineering of a complete lander (that honestly, I'd be surprised if it didn't meet NASA specs for safety and the like, he knows what's up.) than it is to design one from scratch.

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By my calculations, you could do a Free Return Trajectory in 2 launches with a Delta IV Heavy. One to launch the spacecraft itself, one to put a booser up, Orion docks with the booster, and between the booster and the Orion SM engine, you can get about 3100 m/s of Delta-V, which is just about enough. You'd have to do it in two stages, first, boost the Orion's orbit with the booster, then turn the Orion around so you can perform a TLI burn at perigee.

Of course, why you would want to do such a thing is another matter.

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Remember, the point of SpaceX isn't to be just another rocket contractor, it is Musks private space program for colonizing Mars.

Even Musk can only colonize Mars if he finds people willing to buy tickets to colonize Mars. Which is already a stretch. Only millionaires will be able to afford a ticket, and millionaires don't typically become candidates for colonization.

While the conditions are of course not the same, it wouldn't be too much of a stretch for him to tell his engineers to figure out a variant of his lander that can touch down on the Moon.

And that is another stretch.

And well, a lunar lander is not the same as a Mars lander.

Edited by Nibb31

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Suppose an alien-made space probe the size of Voyager 1 enters the solar system from interstellar space, having a perisol just below Mercury's orbit. It has no engines, nor is it transmitting anything; its power systems are already depleted. It comes in cold, completely powerless and unable to do anything besides simply following its current trajectory.

How early (or late) can we detect such a spacecraft, and determine that it's actually a spacecraft and not some metallic asteroid?

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Suppose an alien-made space probe the size of Voyager 1 enters the solar system from interstellar space, having a perisol just below Mercury's orbit. It has no engines, nor is it transmitting anything; its power systems are already depleted. It comes in cold, completely powerless and unable to do anything besides simply following its current trajectory.

How early (or late) can we detect such a spacecraft, and determine that it's actually a spacecraft and not some metallic asteroid?

With current technology, we'd be hard pressed to detect it at all. The only way I can think of would be to have a massive radio telescope that just happens to be pointing right at it at the exact moment a glint of sunlight reflects off it.

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How early (or late) can we detect such a spacecraft, and determine that it's actually a spacecraft and not some metallic asteroid?

Likely never detected if not close to earth, and probably not found to be a spacecraft. For a body orbiting within the solar system I'd say definitely not, but a macroscopic object from outside the solar system would be a first and attract considerable scientific interest.

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Can you use hydrogen peroxide as rocket fuel?

Yes. Read the wiki page.

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I don't quite want this thread to die yet, it's a nice thing to have around (says the guy who practically only lurks, but's that's neither here nor there).

Anyway, I have a couple of questions:

1. What type of radiation is primarily responsible for endangering astronauts (and flight hardware) both inside and outside the Van Allen belts? Is it mostly gamma rays or other high energy photons or different particles? Or, alternatively, am I completely misunderstanding the situation?

2. What's up with the sublight Alcubierre drive? It seems like it could be pretty crazy helpful for traveling around the solar system at least, but always gets kind of brushed over. I've heard that it wouldn't require negative energy densities, but also that it would (in this very thread), so a little clarification would be nice. Is there some reason it would be tricky?

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In the VA Belts? The excited particles in the belts themselves.

Outside VA Belts? Probably done from solar activity, although the cosmic threat is fairly small.

Besides, it only increases likelihood of cancer later in life. That's worth it if you can go to space.

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1. What type of radiation is primarily responsible for endangering astronauts (and flight hardware) both inside and outside the Van Allen belts? Is it mostly gamma rays or other high energy photons or different particles? Or, alternatively, am I completely misunderstanding the situation?

As usual, main danger is in ionizing radiation. The gamma radiation from Sol is actually pretty low. It's mostly high energy particles. In VA belt specifically, it's going to be charged particles, as these are influenced by Earth's magnetic field, and are much more concentrated in radiation belts.

2. What's up with the sublight Alcubierre drive? It seems like it could be pretty crazy helpful for traveling around the solar system at least, but always gets kind of brushed over. I've heard that it wouldn't require negative energy densities, but also that it would (in this very thread), so a little clarification would be nice. Is there some reason it would be tricky?

It looks like Alcubierre metric specifically requires negative energy density regardless of speed. So even a sublight Alcubierre will require exotic matter. But way less of it. It's proportional to square of the velocity, so a 0.1c drive would take 10,000 times less negative energy than 10c drive.

But that's a specific kind of warp drive. I could not find any confirmation for warp drives in general. There is a strong argument in General Relativity that suggests that any FTL travel requires negative energy density. It's more a conjecture than a proof, but we seem to keep confirming it with special cases, so it's probably true. But can a sublight warp drive operate with positive definite energy densities? There seems to be nothing to contradict such an idea, and yet, I cannot find any literature that would suggest a specific configuration.

And yes, it'd be super useful. You still need to have delta-V to make the transfer, but instead of taking half a year to get to Mars, you could get there in hours without wasting any more fuel. Who wouldn't want that? Not to mention traveling further out in the Sol system. It's no interstellar drive, but it'd be a huge help in getting around the star system.

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Is it possible to use nuclear fusion to manufacture heavy elements from lighter ones, if nuclear fusion power generation technology is available?

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Is it possible to use nuclear fusion to manufacture heavy elements from lighter ones, if nuclear fusion power generation technology is available?

Maybe. Depends. It starts to take more and more energy to fuse the elements, eventually getting to an impossible amount, requiring supernovae to create anything heavier than iron...

Atomic manufacturing by manipulation of the individual particles with some kind of device would be much more practical.

Sort of like molecular manufacturing, but with atoms instead of molecules.

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Sort of like molecular manufacturing, but with atoms instead of molecules.

Yeah, that. Though, I'm not thinking of natural fusion like inside stars, that is, up until iron. I'm thinking about heavier elements further down the periodic table. That is, fusing lighter atoms to get some energy, and using this energy to fuse iron (or heavier) atoms to make things like lead, gold, tungsten, or platinum, in a controlled fashion. Is that process possible?

Edited by shynung

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So you're saying you want a supernova in a box? That's pretty tough...

Not anytime soon. Although, we have been able to use particle accelerators to make atoms. But only a few at a time.

Maybe doable, but with that much energy you could basically build a solar system.

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Its... hard to impossible. See http://en.wikipedia.org/wiki/Triple-alpha_process

You want the reactor to have high density, and high temperature, which is 93.1 keV. Now, normal fusion usually aim for 6-15 keV, with peak reaction rate at 66 keV, while aneutronic fusion, specifically proton+boron reaction, achieve peak reaction at 600 keV. So that narrows down the reactor choice to this list: http://en.wikipedia.org/wiki/Aneutronic_fusion#Current_research

So, its possible. But very very very impractical.

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Would it be possible, and feastable, to use enriched uranium/thorium/plutonium etc, instead of mercury (meant Xenon!) in an ion thruster?

Accelerating the neutrons?

Edited by Dedjal

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