Slashdot Mirror

Following the Tsiolkovsky equation, rockets do most of their acceleration when they are almost empty, see this graphics for the Saturn V. NASA actually had to turn off one of the Saturn V engine towards the end of the first stage burn otherwise acceleration would have been too great for the astronauts. So the last few minutes of the burn are important.

Basically the Musk approach is that you have to lift some of the fuel, which is not used for lifting but for landing. It may be more costly than it looks. Science is not alway "obvious", you have to crunch the numbers and see.

Now the Musk approach may work because his rocket first stages have many small engines and using only one for landing is enough. Most other rockets have a small number of large engines. It may be that other agencies did they math correctly but for their own rockets, which are not as well suited to returning and landing than Musk's.

Generally, rockets begin a roll maneuver that starts them heading downrange very soon after clearing the tower. For instance, the Saturn V would perform its roll maneuver about 20-30 seconds after liftoff.

A huge fraction (90% ?) of the energy an object must gain in order to reach orbit is tangential velocity. By comparison the gain in potential energy from gaining altitude is relatively small.

Plutonium dioxide is already oxidized. It's chemically impossible for it to catch fire, and again, dense and heavy with a high melting point.

Never underestimate the power of chemistry to make unintentionally broad statements concerning lack of ability to catch fire look silly. You assume burning in air. Chemists merely look for a stronger oxidizer. Muahahaha....

Are rockets launched with thousands of kilos of fluorine-based oxidizer?

I'm assuming we're talking about a rocket launch failure of a plutonium-dioxide based RTG. These devices have a long history of safe operation by now, with the most extreme test being the lunar lander splashdown after Apollo 13 where the RTG survived the crash intact. Prior to that there have been several instances of rupture, but provided they remain rare, the risks posed these uncommon events are still low.

Wow. Rather than acknowledge that your statement, which I took pains to highlight was unintentionally overbroad, was contradicted by a rather cool video of some more common oxides catching fire, you felt the need to be an ass by dragging in a number of points which neither the post that you responded to, your original post, or the specifically quoted statement actually reference.

1. Are rockets launched with thousands of kilos of fluorine-based oxidizer? Possibly What ISP do you want? Nevermind that plutonium dioxide is "burned" with fluorine in some plutonium enrichment processes. Thank you, Wikipedia.

2. We're talking about a rocket launch failure involving an RTG? The parent wasn't, and you weren't in your response, both of which were referring to a nuclear pile fire. I sure as hell wasn't. However, I'm happy to assume that we're talking about a fluorine-oxidized rocket fuel so long as one person can unilaterally assume things for the other.

3. RTGs have a long history of safe operation. Irrelevant. You mentioned an oxidation state, then said that it is "chemically impossible for plutonium dioxide to catch fire." Not a word about an RTG, a rocket explosion, limits on the chemicals involved... nada. Well, there are more oxidizers in heaven and earth than are dreamt of in your meager visions of chemistry.

I suggest that you learn to deal with minor mistakes in more self-deprecating manner. Ass.

"IIRC most of the article was not about the costs themself but about the discrepencies between NASAs figures and Europes figures.": Sure, but that doesn't make the data any less valid, I just picked the first reference I found on Google, if you have reference to prove your point, you're free to share them.

By definition, using old antiquated date does make it less valid. Plus, I don't need a reference to prove my point. I'm not even trying to prove it. You are trying to disprove it, so the burden is all yours. Good luck, too, because you will find that with valid data, the numbers won't work out.

"One has to wonder why so cheap since none of the costs have come down. Most analysts believe it is because they are in desparate needs of funds and like the airlines, an discounted seat brings in more revenue than an empty one.": I'd like to see this analysis, because SpaceX is estimating their crewed Dragon would be priced at $140 million, which is even cheaper.

Ok, first you were saying the Soyuz was the way to go at $60M to LEO, now you are saying that Dragon is cheaper at $140M. Last time I checked, $140 is not less than $60M. Also, as you point out, SpaceX is estimating their price at $140M. Even the outdated study you used talked about the price sensitivity of launches and it is forseeable that a launch could be 50% higher in cost than the estimates show, so that would bring it to $210M. Even still, that is a small craft going to LEO, not something able to sustain a crew for three years round trip to Mars, where you have to take everything with you.

"Comparing the Soyuz to another group is like comparing apples and oranges. You are comparing different lift vehicles, different launch sites, different capitalization patterns and a host of other things.": I didn't start the comparison, if you have an apple to apple comparison please just make it.

"Instead of Soyuz, you could have just as easily picked the shuttle, which had an average mission cost of $450million": But the Shuttle orbiter is reused, which means most of the mission cost would be launch cost to send the orbiter up there, what you should use is the orbiter price tag of $1.3 to 2 billion, which is indeed much more expensive than a satellite, but the orbiter is also so much bigger than satellite (100 tons vis a few tons).

You are going to need to lift into orbit enough food and supplies to last at a minimum three years for the crew. In addition, you will need a lot of water, not to drink but for shielding from cosmic radiation as that is the current preferred strategy. Think of launching enough water to enclose a room big enough to house the crew for 18 hours or longer surronded by a meter of water all the way around.

Look at the ISS. Assuming you are sending a similar sized crew to Mars, you will need similar sized quarters plus storage space as you won't be able to send resupply ships (although you could send them now and meet them on the way, but has costs, too). Face it, no matter how you do it, to house humans for 3 or more years you are going to need something much, much larger than the Apollo program ever envisioned. To get all of that into space costs money. To add everything you need for the crew protection costs money. And finally, since we are talking about large masses, the energy required to get it moving and to stop it will cost money.

The Mars landers were small crafts lifted out of orbit on relatively inexpensive rockets. Why? Because they didn't need food and water and habitats and all sorts of other things that human beings need in the hostile environment of space. While we may have the technology to send a person to Mars, it doesn't mean it is the most efficient or effective use of limited space exploration resources.

Face it, the whole man on mars push was a

"IIRC most of the article was not about the costs themself but about the discrepencies between NASAs figures and Europes figures.": Sure, but that doesn't make the data any less valid, I just picked the first reference I found on Google, if you have reference to prove your point, you're free to share them.

"One has to wonder why so cheap since none of the costs have come down. Most analysts believe it is because they are in desparate needs of funds and like the airlines, an discounted seat brings in more revenue than an empty one.": I'd like to see this analysis, because SpaceX is estimating their crewed Dragon would be priced at $140 million, which is even cheaper.

"Comparing the Soyuz to another group is like comparing apples and oranges. You are comparing different lift vehicles, different launch sites, different capitalization patterns and a host of other things.": I didn't start the comparison, if you have an apple to apple comparison please just make it.

"Instead of Soyuz, you could have just as easily picked the shuttle, which had an average mission cost of $450million": But the Shuttle orbiter is reused, which means most of the mission cost would be launch cost to send the orbiter up there, what you should use is the orbiter price tag of $1.3 to 2 billion, which is indeed much more expensive than a satellite, but the orbiter is also so much bigger than satellite (100 tons vis a few tons).

When a company, a non corporeal legal entity, has more rights than the meat sacks something is seriously out of whack.

Companies now hold more of an interest in the inner workings of your own body than you do, and have laid successful claim to elements of orbital mechanics.

What's next? Patents being issued on the revitalizing and energizing properties of sunshine? The hydrating effects of water?

What are 1000 patent lawyers at the bottom of the ocean?

A good start.

Damn typo! I meant to say "See http://www.braeunig.us/space/orbmech.htm#maneuver for more info."

> Given the size differential between the first and later stages, the earlier post is
> somewhat justified in calling LOX and kerosene the primary fuel for Saturn V.

But most of the delta-v comes from the final two stages.
Velocity at first staging was 9,900 km/h. Final velocity was 39,000 km/h.
Source: http://www.braeunig.us/space/specs/saturn.htm

Like, oh, say ClF5 (chlorine pentafluoride). It's a nice oxidizer: dense, liquid at room temperature (given a bit of pressure), and highly energetic. Of course, there's the issue of it being hypergolic with human flesh (and nearly everything else -- asbestos burns in ClF5), but really, it's got a lot of things going for it. Use it with a little hydrazine (N2H4) for full effect. Of course, hydrazine has its own problems (it becomes explosive under pressure, and is carcinogenic if you live through handling it ;), but that doesn't seem to affect its popularity.

Fun facts to know and tell here.

http://www.braeunig.us/space/hoax.htm
http://www.clavius.org/

Those above links seem to cover a lot of the 'evidence' for the Moon Hoax theories.

What is stopping you then from becoming one?... All the other folks out there, they're no smarter than you or else they'd be on TV so they're just a bunch of cooky conspiracy theorists so never mind listening to them, okay?

I actually was very intrigued when I first learned that people thought the landing was faked. I did a lot of research looking at both sides and I finally decided there was more convincing evidence on the side saying the landings were real. There definitely is still a lot of strange occurrences such as how many of the main people involved mysteriously died but I still think the landings were real.

Here are a couple links that I liked (and could still find since it has been a while since I researched) which debunked many of the "conspiracy theorists" claims:

http://www.braeunig.us/space/hoax.htm and http://www.redzero.demon.co.uk/moonhoax/ and http://www.thekeyboard.org.uk/Did%20we%20land%20on %20the%20Moon.htm

This is an interesting neutral site: http://www.xenophilia.com/zb0003.htm

Here is one of the "conspiracy theorists" sites I found interesting:

http://www.ufos-aliens.co.uk/cosmicapollo.html

The moon rocks allegedly collected by Apollo astronauts were actually collected and returned to Earth by robotic spacecraft.

Any mission capable of returning over 800 pounds of rock and soil samples would be a massive, complex and difficult undertaking. If NASA could pull this off, then surely they had the technical know-how to land a manned vehicle. In fact, with an astronaut at the controls, a manned mission would likely have greater odds of success than a robotic mission. Perhaps the greatest case for the Apollo landings exists in the variety of rock samples collected. A robotic mission would be limited to a random collection of samples in the lander's immediate vicinity. However, the Apollo astronauts visited vastly different geological sites and were able to roam about the surface looking for particularly interesting and valuable specimens. For example, it is very unlikely that a robot would have been lucky enough to scoop up the "genesis rock" found by Apollo 15 astronauts. Only trained human explorers could collect the diversity of samples credited to the Apollo astronauts.

NOTE: During the 1970s the USSR successfully completed three lunar sample return missions - Luna 16 (1970), Luna 20 (1972) and Luna 24 (1976) - however these missions returned a grand total of only 301 grams (10.6 ounces) of soil.

What happens if the "slug" stops being a slug? (it'd probably take a really hot fireball to do that - where would they find one of those?)

Plutonium melts at 914K and a typical rocket exhaust is 2500K to 3600K. So even if the resulting fireball is half the temperature of the exhaust, it still has the potential to liquify the plutonium. Summary: Stupid people should apologize for trying to influence policy according to their stupidity. Smart people should not apologize for trying to influence policy according to their smartitude

Stupid people make up words too.

20 tons just isn't that big.

The space shuttle masses over 10 metric tons at liftoff itself with its tanks (and for our purposes, metric tons and 2000 pound tons are interchangeable). The shuttle itself is 2 tons and is capable of delivering payloads of up to 25 metric tons.

So a loaded shuttle with enough fuel to take it out of LEO would be good enough - and this spacecraft would be a lot less sophisticated than the shuttle.

Also, given the low thrust requirements for "towing," this could be a good application for the ion drive, which is high efficiency / ultra low thrust.

C'mon people... hasn't anyone taken basic highschool or (gasp) college level physics... orbital mechanics such as that 'slingshot' are damn common and very well understood... it's covered in Keplerian Phyhsics... see http://www.braeunig.us/space/orbmech.htm, section 1.10 (starting just above the marker)... the hidden 'body' is at the extreme 'southern' aspect of that elliptical orbit... meaning that the majority of its orbit is swining away from the 'black hole' ... in the short period of time i is swinging around the black hole, it appears to do so very fast. This is BASIC PHYSICS. I'm explaining it badly, but its no mystery... that slingshot effect is perfectly natural.

The key here is the energy required. Space travel is still dominated by propulsion. That is, the engines and the fuel they need, and the fuel needed to launch that fuel to orbit, etc., is where most of the cost is.

It is important to travel on a trajectory, called the transfer orbit, that requires the least energy. For a high thrust spacecraft, the minimum energy trajectory is called a Holman transfer. Simply, it is an orbit that just touches the orbits of both planets. The periapsis, the closest point to the sun, touches the orbit of the one planet and the apoapsis, the furtherest point, touches the other planet. For this to work, the destination planet needs to be half an orbit away when the spacecraft arrives. This is a lot easier to see in a picture.

For Earth to Mars, the spacecraft launches and then the thrusters fire to change the spacecraft's orbit of the sun from Earth's orbit to the transfer orbit. It then travels half of the transfer orbit and fires its thrusters to change its orbit to match Mars. This can be done by aerocapture, aerobraking or propulsion. The opportunity for a Holman transfer to Mars occurs every 26 years. It is based on the length of the orbit for the bodies being transferred between. The return trip also needs to be a Holman transfer to save fuel. The opportunity does not occur until many months after arrival. I forget the actual number. That is why Mars trips will have a long stay on Mars before returning.

Low thrust is different. Low thrust spacecraft thrust all or most of the time during the trip and the trajectory is more complicated. It is not usable for manned flight because it is to slow but is useful for unmanned spacecraft sometimes.

This is called Celestial Mechanics. When you add propulsion, it becomes Orbital Mechanics.

The best site I have found is NASA's Spacefligh Basics.

Also good is this site.

For explanation of gravity assists see this site.

Also see, Science World at Wolrram

You're wrong on every front.

No. Just the manned launches

Manned launches: 37 Soyuz, 14 Soyuz-T, 23 Soyuz-TM. Total = 74. There may be a couple other types of craft not included there, because I've seen the manned launches as high as around a hundred. Two manned Soyuz failures in 74 is a worse failure rate than two in 113. As mentioned before, the only reason why it has a lower casualty rate is because it carries a lot less people than the shuttle (it carried one and three, respectively, on its accidents. The shuttle carried seven on each).

And, by the way, if you think killing 50 technicians on the ground before one launch alone is irrelevant because it's not the cosmonauts who were killed, I hope for your sake that you never tell that to a technician's face. Same with the deaths of soldiers. That's rather sickening, to be honest.

but it is somewhat safer for the cosmonauts

Not on a per-person-per-trip-to-space basis. The shuttle has launched many more into space. I mean, we could say that the Spruce Goose is tied for the record of "World's Safest Aircraft", but that would be unfair, now wouldn't it, as it only flew a minimal crew one time.

That was a Progress launch

No, it was not. It was a Soyuz-U.

A similar failure of the Shuttle could kill hundreds

No, it could not. The light from the SRBs is visible from 450 miles around. The closest viewing area is outside the designated "blast zone", at 3.5 miles from the twin pads, and that's usually not allowed without a NASA pass. The primary shuttle viewing area is about ten miles away at Space View Park in Titusville, to the west. The shuttle moves east after liftoff.

The high safety of Soyuz ... as evidenced by probably around a hundred total casualties under its belt (including ground crews killed on unmanned launches) and a higher failure rate than the shuttle?

it has safety issues they still haven't solved

And a Soyuz just blew up there years ago. Your point?

Cost of a Space shuttle: $700,000,000 per launch (not counting the latest $2,000,000,000 in upgrades or the initial cost)
22 tons http://www.braeunig.us/space/specs/shuttle.htm

Even taking into account inflation, the Saturn 5 still looks better.

Cost of a Space shuttle: $700,000,000 per launch (not counting the latest $2,000,000,000 in upgrades or the initial cost)
22 tons http://www.braeunig.us/space/specs/shuttle.htm

Even taking into account inflation, the Saturn 5 still looks better.

No, they wouldn't require the same amount of fuel to slow or change the direction of the craft from orbit.

And yes, the shuttle DOES slow down some. It actually comes in completely turned around (IIRC) and starts with a breaking maneuver.

The Orbiter's entire delta-v capability while in orbit (and for re-entry) is 700m/s. Remember that it's moving somewhere in the neighborhood of 7700m/s at the time. If it used the entire 700m/s to decelerate for re-entry, it would drop only 1% of its kinetic energy. The other 99% is left to the atmosphere.

The point is, you have two choices to do most of your braking: aerobraking or rockets; and the latter uses prohibitive quantities of fuel.

Google is your friend. For example, look here.

This is all Newtonian physics. It's not like they're just flinging the spacecraft out there and hoping that it hits the right spot. Knowing Cassini's current position and velocity, they can calculate to very high precision where it will be six months from now. It's still an amazing technological achievement, though, to be able to guide the spacecraft through seven years' worth of maneuvers to get to this point!

In fact Werner von Braun took some interest in the Indian space programme, in the 60s.

India's first satellite was launched 30 years ago, called Aryabhata-I named after the 6th century Indian mathematician, Aryabhata.

Also, the launching station at Thumba is right on the Magnetic Equator. A story covering this can be seen here. Also,

A map of the world's space centers is available.

In fact Werner von Braun took some interest in the Indian space programme, in the 60s.

India's first satellite was launched 30 years ago, called Aryabhata-I named after the 6th century Indian mathematician, Aryabhata.

Also, the launching station at Thumba is right on the Magnetic Equator. A story covering this can be seen here. Also,

A map of the world's space centers is available.

Orbital inclinations which are retrograde are considered to be greater than 90 degrees

SB