Remains of Jason 3 easily visible from the road

peterabbit456 · 6時間前

Looks like the pieces are in pretty good shape, considering that they are parts of a structure over 100 feet tall (?), that fell on its side.

peterabbit456 · 13時間前

$177.77 million / 4 = $44.44 million per person launched.

If this were a commercial service they would have less paperwork, and could cut 30% off of the total launch price, based on commercial vs US gov't satellite launch prices. That gives $124.4 million per launch. divide that by 7 for 7 passengers, and you get $17.78 million per passenger per flight.

Dennis Tito was charged $20 million to fly on a Soyuz to the ISS, and to stay for 9 days. So SpaceX can already beat the 2001 price for an orbital flight to space.

peterabbit456 · 13時間前

Not many believe me, but I think Elon used to post here under a false ID, and Gwynne Shotwell still does, also under a false ID, on rare occasions.

peterabbit456 · 13時間前

So what does "learning decision" mean?

Best answer is to quote Elon Musk, at the time he announced they were going to try to do retropropulsion. He first made the announcement at the National Press Club on 2011-09-29 (BTW, the sushi restaurant in the lobby is mediocre.)

So, the pivotal breakthrough that's necessary, that some company has got to come up with, to make life multi-planetary is a fully and rapidly reusable orbit class rocket. This is a very difficult thing to do ...

... It wasn't something that I thought - I wasn't sure it could be solved for a while, but then, just relatively recently - in the last 12 months or so - I've come to the conclusion that it can be solved, and SpaceX is going to try to do it. Now, we could fail. I'm not saying we're certain of success here, but we're going to try to do it, and we have a design that, on paper, doing the calculations, do the simulations, it does work. Now, we have to make sure those simulations and reality agree, because generally when they don't, reality wins. That's yet to be determined, ...

Source: http://shitelonsays.com/transcript/npc-luncheon-with-elon-musk-2011-09-29

Edit: Most people say rocket science isn't really science; it's just engineering. But landing an orbital first stage on its tail has all the characteristics of a scientific experiment, so maybe when SpaceX does rocket science it really is science. The reuse project was undertaken to learn if it could be done, and if it could add to profits and make Mars travel more practical. That is what is meant by a learning decision.

peterabbit456 · 16時間前

"Atmosphere," is an ambiguous term, since the density of the atmosphere drops logarithmically (more or less, with some 2nd order temperature effects). There is a thin bit of atmosphere at 250 km, or whatever altitude the ISS orbits. What we are really talking about here is the altitude at which the atmosphere becomes a danger to the returning stage.

This danger is a function of air density and vehicle velocity. Boundaries or human-defined regions like the stratosphere, mesosphere, thermosphere, troposphere, and Karman line are not relevant. The burn must start in atmosphere so thin it poses no danger, and finish just as the atmosphere becomes thick enough to continue the job of braking the vehicle by terminal velocity.

Finish the burn too soon, and the vehicle will accelerate in too-thin air until it destroys itself when it hits the thicker air below. Finish the burn too late, and the vehicle will already have been damaged or destroyed by traveling too fast through air that was too thick.

Manned capsules have enough shielding so they can take the heat, and they do not need to do a burn before hitting the thick, dangerous parts of the atmosphere, but this might change when really big capsules built to go with the MCT start to fly. We might see manned capsules perform a reentry burn if the fuel needed is less mass than the extra heat shielding required to reenter without a burn. But the altitude of the start and especially the end of the burn will be dictated by density, velocity, and terminal velocity, not by any arbitrary definition of atmosphere.

peterabbit456 · 17時間前

Have you considered that they may have just gotten lucky? If you have ever watched an expert shoot targets (My father and uncle were Olympic - level shots) you know that even when one shoots a perfect score, the group of holes is pretty ragged, but occasionally one goes right through the center of the bullseye. That could be what has happened here. SpaceX's hardware and software might be good enough to ensure that 95% of landings are within a 10 meter circle. That would mean that maybe 1 out of 10 landings are within a 2 meter circle, and maybe 1 in 100 are within a 10 cm circle, of dead center.

peterabbit456 · 17時間前

It is nice to see someone who is right, win an argument on Reddit. Good going.

peterabbit456 · 1日前

I think this document you reference is a bit of an orphan on Reddit, despite its great value. /r/spacex won't have it as a submission because it is not enough about SpaceX, and /r/space will not have it because it was submitted elsewhere first.

I hope I am wrong about this, but I don't think I've seen it anywhere as a submission.

Edit: A more optimistic title for this document would be, "Readiness of needed elements for a Mars Mission: What's not ready for Mars, and What we need to do to get ready."

peterabbit456 · 1日前

If Bigelow builds a private space station they will need 2 or 3 for that. If the US or the Russians build a Moon orbiting station they will need 1 or 2 for that, maybe 3. MCT will probably use the international docking standard, so they will need 1 or 2 for each MCT.

Depending on how many MCTs fly, there could be a lot of these in the sky in a few years. Since it is an international standard, don't expect Boeing to remain the exclusive supplier of IDAs. SpaceX will probably start building them for the MCTs, and if they do that, they might start selling them to Bigelow or other customers.

peterabbit456 · 2日前

The only valid metric is ISP.

Actually, no. The situation is almost the exact opposite. Efficiency for a deorbit burn or for a Hohman transfer goes up enormously if you have a point thrust, a delta function of almost instantaneous, very high G forces. This is what Hoffman said, and the math agrees.

I also talked with two of the engineers on the Dawn space probe. The ISP of Dawn's ion engines is about 4000, I think. They might be 8000. Some ion drives have ISPs that high. But one of the programmers said to me that while they gain 10-fold efficiency or more from the ion drives, they lose about 30% efficiency by having to thrust continuously in a spiral, instead of applying point thrusts and doing Hohmann transfers, like with chemical engines.

So, while it works, using thrusters to do the deorbit burn gets you the worst of both worlds: low ISP, and long burn time relative to orbit time.

peterabbit456 · 2日前

I've been to meteor crater in Arizona. It is about 80,000 years old, and it is 3 miles across. Such a hit in a major population center could kill hundreds of millions of people.

That is smaller than the threats we worry about on the geological time scale. Every 10-20 million years on the average, we get a meteor hit smaller than the K-T dinosaur killer, but big enough to wipe out the human race. That is the time scale to worry about.

peterabbit456 · 2日前

You have landed yourself smack in the middle of the major fact-deficient debate in the space colonization movement. Everyone from nation states and multi-nation consortia, down to /r/space , /r/spaceX , and individual redditors have weighed in loudly on both sides of this question. A few people and groups are gathering facts and making strong cases, but no clear winner has emerged.

ESA, the Russians, and the Chinese have all declared in favor of the Moon-first approach. Robert Zubrin and Elon Musk have declared in favor of Mars first. Zubrin's closely reasoned plans carry a lot of weight with anyone who listens or reads with close attention. Musk, head of SpaceX, has done something no one else in the world has managed to do: he started with a relatively small amount of capital and built a major orbital launching company from scratch. Such a demonstration of competence deserves to carry enormous weight in the debate. He may win it, just because he and his company are the only ones with the will to carry through.

The world is changing. It is getting richer, and launch services are getting cheaper. Materials are improving, and especially, software is improving. The first sign was in 2004, when Scaled Composites sent 2 men into space, developing a spaceplane with the capabilities of the X-15, for $30 million, with a team of 22 engineers. Think of that. 22 people did what only countries had done before. Now we have SpaceX, with >50 launches on the books or accomplished, and missions going beyond Earth orbit planned and accomplished.

The Moon is a lot easier, and cheaper. You need a substantial Moon base to start orbiting materials for space habitats. It is so expensive to bring the materials from Earth that, not only will it be cheaper to get them from the Moon, it would also be cheaper to get them from Deimos, the outer moon of Mars.

My feeling is that the shorter distance and travel time to the Moon makes it much safer. If something is needed in a month to save the colony, it can be shipped from Earth. That could never happen with Mars, until we have powerful nuclear rockets. If the colony suffers a disaster and needs to evacuate, that can be done from the Moon, but not from Mars.

On the other hand, no one sees how a Moon base can become economically self sustaining. It can only make a profit if there are customers who want Lunar materials to build orbiting habitats, or to build spaceships to go to Mars. The Moon base will be a mining camp, not a country.

Musk knows that if he is to succeed, he has to make a profit almost every step of the way. He would be most happy to start a Lunar shipping line, but only if there are customers asking for the service.

peterabbit456 · 2日前

Establishing life on Mars and the Moon only increases your decentralized ratio by 2.

You have to start somewhere. My personal opinion is that it will be easier to start life on Mars after a large Moon base is constructed, and that life in the asteroid belt will be easier to stage from Mars than directly from Earth. I and some other /r/space contributors did some calculations a few months ago that indicate Cere could support a population of over 1 billion, indefinitely. But it is far easier to colonize Ceres from Mars than it is from Earth, so I am firmly in the "Mars first," or "Mars second," camp.

peterabbit456 · 2日前

the threats are so long-term that we can safely let our successor-species deal with it, or ...

The counter argument to that is that civilization usually lasts for a few centuries, and then a dark age intervenes for 1000 years or more. We might be approaching the end of advanced civilization in the next few decades, or perhaps a century, and succeeding civilizations may not be interested in going to the planets, or they might not have the resources to do it. We have just about used up the oil on this planet, and rockets launch using hydrocarbons.

Perhaps a stronger argument is that space travel from Mars is much easier than it is from Earth, due to the lower gravity. Single stage rockets can get to orbit, and they can refuel at Phobos or Deimos, both of which appear to be much more resource-rich than the Moon. I am convinced that in the late 21st century and throughout the 22nd century, spaceships built on Mars will come to Earth to pick up recruits for Mars colonies, and the deal will be roughly,"You pay your way to Earth orbit, and we will take you to Mars for free." There will be such a labor shortage on Mars that this immigration policy will be profitable for the Mars economy.

From Mars we will colonize the rest of the Solar system. Pluto looks like an especially rich system of planets and moons. There and farther out, fission and fusion will power civilization, so there is not any real block to colonizing the Kuiper belt and the Oort Cloud. The Oort Cloud extends to Alpha Centauri, so even if fast interstellar travel is not invented, we will get to the stars, if very slowly.

peterabbit456 · 2日前

There was a rather speculative talk at JPL a few years ago, about life on Titan. You should look for the video on TED or YouTube. It described some plausible scenarios for life with very different chemistry than life on Earth.

peterabbit456 · 2日前

Mars, despite the harsh conditions, is still very much more like Earth than not.

Yes. There are statistical studies that concluded the chance of life migrating from Earth to Mars, or the other way, is over 99%. The frequency of exchanges averages less than once every 3 million years. I am inclined to believe that when we get to Mars, we will find "living fossils," bacteria species that were last seen on Earth 3 to 10 million years ago.

The outer space treaty will then not be a bar to settling mars, since life on Mars will be found to be essentially the same as life on Earth.

peterabbit456 · 2日前

This sounds like a prime business opportunity, for someone to design chips with most of modern speed and processing power, and more radiation hardness than the latest generations of chips. It should be possible to better for the long term, deep space market than what is available from any supplier right now.

peterabbit456 · 2日前

Voyager 1 has been running on its backup processor for ~>25 years now, I believe. Accurate information is on the Voyager web site. Don't quote me; I have not looked there for months and I may have got details wrong.

peterabbit456 · 2日前

That is the old space approach. I don't know about now, but a few years ago makers of spacecraft circuit boards were paying $1800 each for Motorola 68000 chips, like those used in the original Macintosh in 1984. SpaceX realized they could get faster, better, cheaper, and more reliable by using redundant copies of modern computers.

SpaceX has found all sorts of uses for the thousands of times greater processing power in modern chips. Not least of which is running versions of Linux that allow faster and more reliable software development. The old OSs that run on the old chips were buggy, and software changes required extensive testing. I've talked to JPL programmers about this.

peterabbit456 · 3日前

Here on the surface of the Earth, we have over 100 km of atmosphere above us, which is roughly equivalent to 10 m of water shielding over our heads. Despite this, we are each of us hit by 1000 or more cosmic rays every second, and if standing, 1 or more that go the entire length of our bodies each second. These tend to be single charged particles with a charge of +-1, either muons, protons, or electrons. This is after the atmosphere has stopped a large fraction of the incoming rays.

Every so often one of these cosmic rays strikes a nucleus dead on, and causes a shower of + and - particles. This is the sort of event that causes bit flips. It would take several (~10-20) cm of lead shielding to duplicate what the atmosphere does for us, but that might do more harm than good. Cosmic ray showers from atmospheric nuclei being hit spread out before they hit the ground, but from lead, they shower would still be confined to a small space. The shielding might cause more bit flips due to showers than just letting single charged particles pass through.

The better approach is using redundant computers and voting on the decision. Machines will go wrong, but no 2 will go wrong in the same way, at the same time. Maybe you go to 5 redundant computers for the Mars trip instead of 3. It is clear that SpaceX is going this way, because it is required for manned flight, and they are rehearsing for future manned flights. Also, they are hiring programmers with experince in MMORGs (Is that the acronym for Massively Multiplayer Online **** Games?) where the same sorts of voting and arbitration are part of the programs.

peterabbit456 · 3日前

Don't they do some maintenance also while out at sea? Chip rust? paint?

peterabbit456 · 3日前

Mentioned farther down in the same article, also on Thursday:

BEAM to be inflated on ISS

A prototype habitat is scheduled to take shape early Thursday outside the International Space Station when astronauts and engineers on the ground inflate it with air.

peterabbit456 · 3日前

I second marshallsmedia . Please add this to the wiki.

peterabbit456 · 3日前

The law is a plastic thing. It was made by people; it can be changed by people; it will be changed by people as new circumstances dictate revisions.

The treaty arbitrated by the pope around 1500, that divided the New World between ownership by the Spanish and the Portuguese has influence even today. (See the border between Brazil and Argentina.) But circumstances are completely different now, than in 1500, so in most ways that treaty is now less than a joke. 500 years from now it will be the same with the Outer Space Treaty.

peterabbit456 · 3日前

I'm ~quoting ex-astronaut Jeff Hoffman, now a professor at MIT. He gave a lecture in which he described this exact situation, except he was comparing using the shuttle's OMS engines for a reentry burn vs using the maneuvering thrusters, which was the backup method. I also did the math, for the shuttle case, years ago.

The thrust ratios, mass ratios, and burn times for Dragon reentry and shuttle reentry are very similar. The fuel savings should be proportionally similar. The difference is that on the shuttle, they always held enough fuel in reserve so that they could reenter using thrusters, if thew OMS engines failed at the last minute, and then they had to vent that fuel on the ground. On Dragon 2, that reserve of fuel for deorbit will be used in the touchdown burn. If Dragon 2 has to deorbit using thrusters, then they definitely will not be using the SuperDracos to land on land, and the flight will end with a splashdown in the ocean.

peterabbit456

次のモデレーターです

トロフィーケース

本日のreddit gold目標額達成率