SpaceX is a go for April 30th: 1st commercial launch to space station

[YellowSubmarine]

Mark_Nguyen wrote:

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Not quite - space.com is reporting that they may have to move the scheduled docking from tomorrow to Sunday. Not a HUGE problem, but there's fresh fruit on board! :P

They let the fruit spoil? Next up Wikipedia designates the mission a partial failure. Serves SpaceX right for their sloppy performance.

[sojourner]

Yeah, the fix came way too late for rendevous tomorrow. That was off the table pretty early in. Sunday is a good bet if NASA and SpaceX are comfortable that the issue is settled as far as safety is concerned..

[Mark_Nguyen]

In any case, I didn't know they could get to the ISS in a day now? The Shuttle and Soyuz are usually a two-day trip to get there...

Mark

[sojourner]

Technically, with the right timing and accuracy, you could get there in hours. Caution would prohibit such a rapid approach though for just such a reason as we saw today.

[YellowSubmarine]

Then again, if you were trying to get there in hours the thrusters would attempt to go online even when the computer tells you not to, possibly by defaulting to cycling the oxidizer valves or something, because risking the cargo is less important than risking the station, and there would be a dumb emergency source of thrust to get you out of the orbit as quick as possible should the need arise.

[YellowSubmarine]

Dragon is cleared to dock. Orbital manoeuvres towards the station begin in seven hours. I hope I'm awake whenever they get to the docking.

[publiusr]

Safe and sound
http://www.nasaspaceflight.com/2013/...nday-berthing/

In some ways, it has the kinds of problems you want to have, in that it shows how rugged your craft is--same with the engine that came apart in the last launch.

Knowing you have redundant thrusters, engine-out, etc.--and that you can brute force your way into salvaging a mission is far better than having to have a lesser vehicle with no margin have to perform perfectly every time.

There are good problems and bad problems.

[sojourner]

The problem did highlight a single point of failure on Dragon. Using one helium tank to pressurize the oxy tanks for 4 sets of thrusters was not great thinking. My guess is they will go to a second He tank and have it pressurize 2 diametrically opposed thruster pods. There by if one tank fails they still have 2 opposing thruster pods to ensure control.

[YellowSubmarine]

sojourner wrote:

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The problem did highlight a single point of failure on Dragon.

Hm? Wikipedia says Dragon uses nitrogen tetroxide, not oxygen? What am I missing?

[gturner]

That when people talk about the "oxidizer tank" they're not necessarily referring to liquid oxygen.

This is obviously a serious failure because it set their schedule back a whole day whereas having a main engine explode saw them arrive 30 minutes early.

[publiusr]

It's always the little things, isn't it?

Big first stage engine loss? No problem--we've engine out. Stuck thruster with not much more thrust than a can of Aqua-Net hairspray--you're done (almost).

That was one of the reasons that I am so impressed with footage like this:
http://www.viddler.com/v/b8fda424

That thing is rock-steady in hover, something a KKV isn't even supposed to do--support it's own weight on a column of thrust. That's what billions can buy

Now compare that with Carmak's contraptions.That is what millions buy.

Small craft can be very hard to control, what with the computer often faster than the plumbing, as it were. Rather like getting your shower perfectly between scalding hot and freezing cold.

Energia had time to gimbal even with dead-weight Polyus on its side. The smaller something is, the easier it is to get out from under you.

[sojourner]

Wait, you're saying a KKV doesn't need a high t/w ratio? Dude, you might want to think on that a little. That KKV is doing exactly what it's supposed to do.

If Armadillo was actually trying to replicate the KKV's capabilities, I have no doubt they could. There's no billion dollar technology in that video. Just some hypergolic thrusters and a microcontroller.

[Crazy Eddie]

Thing is, Armadillo's trying to construct a relatively large spacecraft that can make a controlled descent and landing on the surface of the moon. You can strap some model rocket engines to a gyroscope and make it hover for a few seconds, but that's a far cry from a functional landing craft (or, for that matter, a functional Dragon space capsule).

There's also the fact that the multiple kill vehicle has effectively been scrapped because they couldn't get the smaller projectiles to synch up properly. Hell, they can barely get the one-shot version to work correctly; according to some reports, it doesn't work at all. But that's beside the point, because it's not designed to actually shoot down incoming ICBMs, it's designed to deter America's nuclear-armed enemies (whoever the hell that's supposed to be) from launching missiles at us.

[publiusr]

sojourner wrote:

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Wait, you're saying a KKV doesn't need a high t/w ratio? Dude, you might want to think on that a little. That KKV is doing exactly what it's supposed to do.

No, it is launched by a missile to hit a warhead--not hover in place over a net really. It is supposed to have enough precision in its thrusters to hit a very small target. That it could hover is a plus.

Now there was a rumor that the R-36M SATAN (Dnepr) derived from the SS-( (Cyclone) was an armored ICBM with an agile bus, so the kinetic kill vehicle itself would have to manuver more--rather like two people trying to side step each other in a hall(right to right, left to left) and colliding anyway, like Stockholm and Andrea Doria

The KKV is just a payload. It is coasting up when released and thrusting a bit out the sides to line up with the target. If the missile that launched it was itself agile, then the KKV doesn't need enough thrust to support its own weight really, if things are lined up well from the start.

I'm thinking the guys who did this net test expected the actual KKV to use less thrust during an intercept than it did doing this hover. This was a way to show how precise their product was. I really doubt Armadillo could replicate it myself. BMDO has such a head-start and all. I seem to remember a similar test back in the 1980's

Now the anti-missile defense arguements puzzle me a bit. They say striking a warhead with a KKV is all but impossible, and yet there are very complex Mars sample return missions that rely on a bus to scoop up a sample return package smaller than most any warhead--and in space near another planet even. So if I hear someone poo-poo missile defense then talk Mars sample return--its pretty much the same problem.

Now if you can mass produce KKVs as easily as warheads, then you have effective missile defense against a smaller country at least.

But that's an arguement for another time. My point was sometimes it's the little things that can cause the most trouble.

[sojourner]

publiusr wrote:

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Now the anti-missile defense arguements puzzle me a bit. They say striking a warhead with a KKV is all but impossible, and yet there are very complex Mars sample return missions that rely on a bus to scoop up a sample return package smaller than most any warhead--and in space near another planet even. So if I hear someone poo-poo missile defense then talk Mars sample return--its pretty much the same problem.

There are just so many things wrong with this.