Beta
×

Welcome to the Slashdot Beta site -- learn more here. Use the link in the footer or click here to return to the Classic version of Slashdot.

Thank you!

Before you choose to head back to the Classic look of the site, we'd appreciate it if you share your thoughts on the Beta; your feedback is what drives our ongoing development.

Beta is different and we value you taking the time to try it out. Please take a look at the changes we've made in Beta and  learn more about it. Thanks for reading, and for making the site better!

Comments

top

Fusion Reactor Concept Could Be Cheaper Than Coal

cjameshuff Re:Fusion isn't "expensive", it's lossy (315 comments)

Scaling the reactor is nothing at all like that joke. For one thing, simple realities of available room generally make use of superconducting magnets impractical on small reactors. Further, every reactor benefits from larger sizes simply due to square-cube scaling, with less surface area for heat loss for a given volume of fusing plasma, and the various plasma and electromagnetic field behaviors follow their own scaling laws, dependent on the design but frequently favoring larger scales. The Polywell, for example, is expected to have power output proportional to the seventh power of size.

You are assuming that increasing the size of the reactor is no different from building duplicates of the reactor. The reality is that they're nothing at all alike.

about two weeks ago
top

NASA Asks Boeing, SpaceX To Stop Work On Next-Gen Space Taxi

cjameshuff Re:Ridiculous (139 comments)

Price was supposedly the highest-weighted factor for this particular contract, so they aren't entirely unjustified in their complaint. However, NASA also has good justification for their decision: there's quite a bit of uncertainty with the DreamChaser. For instance, they apparently haven't settled on something as basic as a propulsion system. There's talk of them replacing the hybrids with ORBITEC's Vortex engines, but at a recent presentation they appeared to still be undecided (https://twitter.com/jeff_foust/status/517341940073787392). That's somewhat of a significant shortcoming.

about two weeks ago
top

Update: Mangalyaan's Main Engine Test Fired, Maven In Orbit

cjameshuff Re:I hadn't heard of Mangalyaan (25 comments)

It's a precursor, but not one that's stable in an atmosphere exposed to sunlight in the long term. Early Earth may have had some delivered by icy impactors. Titan has a significant quantity in the atmosphere, but even out in Saturn orbit there's enough sunlight that it's constantly being broken up and recombining into heavier hydrocarbons and other photochemical smog components. Titan is largely composed of ices and cryovolcanism is a likely source of replacement methane. There's no obvious sign of similar reserves on Mars, and traces of methane could be a sign of microbial life that are actively producing it.

about a month ago
top

SpaceX and Boeing Battle For US Manned Spaceflight Contracts

cjameshuff Re:Safe choice? (123 comments)

Dragon actually is man-rated and has actually had people inside it, while in orbit and attached to the ISS, without killing anyone. It's just not a man-rated *launcher*, which would require a launch escape system, various additions to support people, etc. The requirements for man-rating Dragon 2 and the Falcon 9 are more extensive but not overwhelmingly different. They've already had people bouncing around inside the Dragon while in orbit, there's no reason to think they won't get this done.

And 12 launches without a single loss of vehicle or failed primary mission, and one partial failure of a secondary mission due to ISS safety rules is hardly "an abysmal safety record". It's arguably a better start than either the Atlas V or Delta IV had...the first 12 launches of both of which included a partial failure that left the *primary* payload in the wrong orbit.

about a month and a half ago
top

Anomaly Triggers Self-Destruct For SpaceX Falcon 9 Test Flight

cjameshuff Re:Government Lawsuit? (113 comments)

This was a modified Falcon 9 first stage with only 3 engines and no second stage, put together as a testbed for developing the landing capabilities. It launches off support blocks on a concrete foundation instead of a full launch pad, does various maneuvers, and lands on bare concrete right next to the launch site.

It wasn't an orbital launch of a standard vehicle, it was a test flight with heavily modified experimental hardware and software operating under rather unusual conditions, so it really shouldn't impact other things like their attempts to compete for military launches...the actual Falcon 9 launches have actually all gone without losing a single vehicle, though there have been some minor failures and one somewhat exciting unplanned demonstration of the engine-out capability. Attempting to hold tests to the same standards as launches would be quite foolish, deterring companies from performing those tests...definitely not the desired outcome.

about 2 months ago
top

How To Make Espresso In Space

cjameshuff Re:Air pressure (192 comments)

They *are* in a pressurized container. The ISS maintains a pressurized environment equivalent to sea level on Earth.

about 4 months ago
top

Lepton Universality In Question, a Standard Model Assumption

cjameshuff Re:How convenient! (62 comments)

Consider how long it took to gather enough of the right events to be reasonably certain about the Higgs, the various false alarms that vanished as more data was collected, etc. Another version just a bit rarer could easily be lost in the noise. Or the two could be similar enough that their signals aren't distinguishable from each other yet.

about 5 months ago
top

Are Glowing, Solar Smart Roads the Future?

cjameshuff Re:WTF is wrong with you? (193 comments)

I didn't say it couldn't be done. I said it was a terrible idea, and that your claimed advantage (guarantee of being free from obstruction) didn't actually exist. The same solar cells placed in a solar farm located in a sunny area without a thick layer of textured, dirty glass, leaves, vehicles, etc between them and the sun could easily produce several times the output. The electronics and cabling used to collect the power and convert it to a useful form would be put to far better use in such a farm, in a road most of the capacity will be wasted due to the non-ideal location and orientation, frequent obstructions, etc.

about 5 months ago
top

Are Glowing, Solar Smart Roads the Future?

cjameshuff Re:WTF is wrong with you? (193 comments)

"As far as roads go, here's an opportunity to leverage a massive area of square footage that is guaranteed to be clear of plants or other obstructions"

Uh...no, it's actually guaranteed to be obstructed frequently, by cars, leaves, snow and ice (the suggestion of melting these away is absurd, there's nowhere near enough power for it), dust and dirt, machine grime, nearby trees, its own textured surface, etc. In addition, with all the stuff embedded in them and the enormous quantity of modules needed, things are going to break frequently, and maintenance access requires shutting down roads. Beneath the road surface is a *terrible* place for solar panels.

about 5 months ago
top

US Should Use Trampolines To Get Astronauts To the ISS Suggests Russian Official

cjameshuff Re:SpaceX isn't ready (272 comments)

How is that in any way "vital"? Having people inside doesn't prevent you from using the robot arm berthing system used by the cargo Dragons. It's a planned feature of the manned version, but that has little to do with it being manned.

about 6 months ago
top

US Should Use Trampolines To Get Astronauts To the ISS Suggests Russian Official

cjameshuff Re:SpaceX isn't ready (272 comments)

On the man-rating...the cargo Dragon is actually already man-rated. Once it's up at the ISS, people have to open the door and go inside to unload supplies and load experiments for return to Earth. What it lacks is a launch escape system. Well, and seats.

On the versatility...apart from carrying more cargo and more crew, the Dragon is equipped with heat shielding that can handle return from lunar or Mars trajectories, and for reuse. It's even adaptable for landing on other bodies such as Mars, as in the Red Dragon proposal. It's launcher can operate in single core or three core variants, eventually with varying degrees of core reuse depending on payload/orbit requirements.

So the OP's claim that Soyuz is "much more versatile" is really rather bizarre...

about 6 months ago
top

SpaceX Looking For Help With "Landing" Video

cjameshuff Re: SpaceX always have an excuse for failure (110 comments)

It's entirely possible it actually was recorded in some buoyant piece of hardware, just in case...but it'd probably have been intended to be picked up out of the debris field of a descent failure in fair weather. Where would it have ended up after the storm tore the rocket apart?

They could engineer a ruggedized black box with a tracking beacon and deployment system...but that's a bit much when they've only got a few water landings left, and those are unlikely to happen in storms. I think they were more concerned with making the rocket land itself.

about 6 months ago
top

SpaceX Looking For Help With "Landing" Video

cjameshuff Re: SpaceX always have an excuse for failure (110 comments)

They claim it was successfully able to return to the surface and perform a soft "landing". Which it did...and it did so in thoroughly bad weather, in high winds and on heavy waves instead of solid ground. Their mission objectives were met completely the moment the rocket cut its engine and started tipping over. Actually fishing the thing out of the ocean intact would have been a nice bonus, but it has nothing to do with their actual plans for recovery and reuse...and the only reason it didn't happen is that nobody wanted to attempt it during the storm.

about 6 months ago
top

SpaceX Looking For Help With "Landing" Video

cjameshuff Re:A 2nd backup camera? (110 comments)

You *do* realize the power output of a rocket engine isn't electrical, right?

In reality, spacecraft have strictly limited power budgets. The booster's electronics are running off battery power from the moment the umbilicals disconnect. It also flew above the bulk of the atmosphere, so you can't exactly rely on air cooling to keep the transmitter from frying itself...and there's plenty of other power-consuming, heat-producing electronics that have rather more important functions. And a more powerful transmitter would be completely unnecessary for the solid-ground landings, which SpaceX hopes to start by the end of the year.

about 6 months ago
top

SpaceX Looking For Help With "Landing" Video

cjameshuff Re:A 2nd backup camera? (110 comments)

Stronger signals take bigger transmitters with higher power consumption. They don't normally require such a signal: for launch (and eventual solid-ground landings) they have line of sight with big receivers, and when they actually recover a stage, they'll be able to get recordings. The splashdown was below the horizon from the launch site, and the video signal was picked up from a chase plane. To top it all off, weather was lousy and deteriorating fast.

They'll have a lot more launches and landings, another water-landing test is coming up soon. Getting video on an early test that was given a 60-70% chance of failure and wasn't even an actual solid-ground landing was a lower priority than trying to make it succeed.

about 6 months ago
top

SpaceX Files Suit Against US Air Force

cjameshuff Re:What about the DC-X? (176 comments)

The DC-X was a small scale experimental vehicle built to demonstrate vertical takeoff and landing under rocket power. It was never able to or intended to fly very high or very fast.

This was the first stage of a Falcon 9 orbital launch vehicle, returning after boosting the second stage and payload, on a launch that actually delivered a payload to the ISS. It's far bigger (the empty Falcon 9 first stage masses about as much as the fully fueled DC-X), far more capable, and it's currently being mass produced. It also uses a cheaper and easier to handle fuel and a more efficient and flexible staged architecture than the SSTO architecture envisioned for the launchers derived from DC-X.

about 6 months ago
top

SpaceX Launches Load to ISS, Successfully Tests Falcon 9 Over Water

cjameshuff Re:Not sure about the recovery test (125 comments)

Those boosters were hollow steel tubes, open at the back. Seawater partially flooded them, that's why they popped up. The Falcon 9 first stage is mostly empty tanks that aren't going to flood (barring severe damage from the waves). If held vertical, the weight of the entire stage wouldn't push it down even two meters into the water...its diameter is greater than that. The engines aren't that heavy, half the mass of the vehicle is in those very long tanks...it's going to float very high in the water, on its side.

about 6 months ago
top

SpaceX Launches Load to ISS, Successfully Tests Falcon 9 Over Water

cjameshuff Re:Cost breakdown (125 comments)

NASA is paying for Dragon missions to the ISS, not just mass to orbit. They're getting a lot more than the launch: delivery of a Dragon loaded with supplies to the ISS, a brand new man-rated spacecraft that people will be working inside while it's at the ISS, return of more payload to Earth than any other option currently available, and operations in orbit and recovery. And probably also various other expenses and extra work involved in working with NASA and the other ISS partners. Their defense launches are also priced higher for the same reason, working with the DOD involves extra work that the customer demanding it has to pay for.

about 6 months ago
top

SpaceX Launches Load to ISS, Successfully Tests Falcon 9 Over Water

cjameshuff Re:Not sure about the recovery test (125 comments)

It doesn't need to brake to a complete stop and then retrace its outgoing path, it needs to bend it's largely-upward trajectory into one that comes back down over the landing site, and manage its velocity so it doesn't go too high and hit the atmosphere too fast on the way back down. As for the difference in separation speed, the flight profile for the reusable flights may very well take a more vertical trajectory during the first stage burn, the first stage taking on more of the gravity losses and going more for altitude rather than speed, and the ratio of propellant loading between the first and second stages may be different for reusable flights...they could oversize both at a minor cost in mass and tweak the ratio to suit the launch, the maximum loading being set by the first stage thrust rather than the total tank capacity.

about 6 months ago
top

SpaceX Launches Load to ISS, Successfully Tests Falcon 9 Over Water

cjameshuff Re:Not sure about the recovery test (125 comments)

It got up there while carrying a lot more propellant and a whole second stage. The braking burn uses only 3 engines to limit the acceleration and ends with just enough propellant left to stop it when it reaches the ground. On top of this, it gets passive aerodynamic braking the whole way down.

The mass ratio for the first stage burn, burdened with the second stage and braking propellant, is probably around 4, and a braking burn with equal delta-v would need the same mass ratio, except with no second stage and ending with the rocket empty. The overall first stage mass ratio is around 30, so all else being equal, a return would take around 3/29 = 10% of the propellant on the first stage. But all else is not equal, the returning rocket is mostly empty tanks descending through a thick atmosphere that provides plenty of braking, so the final burn only has to bring it to a halt from terminal velocity, and I omitted the second stage propellant. Overall, 4% sounds quite reasonable.

about 6 months ago

Submissions

cjameshuff hasn't submitted any stories.

Journals

cjameshuff has no journal entries.

Slashdot Login

Need an Account?

Forgot your password?