The thread for space cadets!

[Borachio]

Link to video.

 

[warpus]

Construction of the ISS

 

[Thorgalaeg]

Fascinatng. It is funny how they relocated that Gigantor xl solar array when the station got larger and more complex. I wonder if it was planned since the beginning or was a later improvisation.

 

[warpus]

People are stupid

 

[El_Machinae]

http://www.sciencedaily.com/releases/2015/01/150116093052.htm

NASA's Kepler Space Telescope has discovered a star with three planets only slightly larger than Earth. The outermost planet orbits in the 'Goldilocks' zone -- where surface temperatures could be moderate enough for liquid water and perhaps life to exist. The star ranks among the top 10 nearest stars known to have transiting planets. The star's close enough for astronomers to study the planets' atmospheres to determine if they could possibly be conducive to life.

I can't tell you how excited I am about the idea of spectroscopic analysis of distant atmospheres. Sometimes I feel my desires for anti-aging progress is merely so that I'll get to see progress in space science. Ugh, I just want the different sciences to move faster.

 

[hobbsyoyo]

Well what did they expect after landing on a giant rubber ducky at 40,000 miles per hour?

Several of the systems used to plant the lander on the comet failed to work, which contributed to the bounce. Another huge problem is that we simply don't understand the surface constitution of comets very well which means any landing system is based on best guesses of what they need to do. Part of the mission of the lander was/is to characterize the surface constitution of the comet in order to aid future mission design.
______________

So SpaceX has been trying to retrieve the first stage of their Falcon 9 rockets for reuse. Here is a test landing at sea:

Link to video.
In these early attempts, they were just trying to hit a target zone that was on the square kilometers scale in size.

Now they are attempting to land on a floating barge at sea of the square meters scale in size:

Link to video.

Thought it failed, it was really extraordinary that they came so close!


They say the failure was the result of running out of hydraulic fluid - I believe they lost the ability to gimbal the engines right before touch down which resulted in the off-kilter landing.


Impressive stuff

 

[Thorgalaeg]

The problem i see with that idea is that the ammout of fuel needed to safely bring back and land the rocket. Wouldnt that waste a lot of delta-v?

 

[hobbsyoyo]

The problem i see with that idea is that the ammout of fuel needed to safely bring back and land the rocket. Wouldnt that waste a lot of delta-v?

Yes and no. It does 'waste' enough delta v that some higher mass missions (or those going to particularly high orbits or orbital inclinations) can't be launched on reusable rockets.

Also, as SpaceX originally outlined in their plan of bringing their rocket all the way back to the launch pad, yes it would also be extremely wasteful.

But landing on a pad downrange of launch isn't too too wasteful. The first stage isn't going that fast or is that high at that point in the flight and the atmosphere will slow it down a bit as it descends and deploys the landing legs which have a lot of intentional drag.

The main benefit is reusing the rocket stage itself which saves a ton of money in and of itself - more than offsetting losses due to 'wasted' deltav.

 

[hobbsyoyo]

How is jerkiness of the deployment cause any torque on the whole thing? There should be nothing around to generate force against. Because of conservation of angular momentum, the whole device should not have more angular momentum after the deployment than before.

Am I missing something?

(I never saw this before I left for a bit)

Yeah you're certainly right on that. I know enough of physics to get me into trouble.

Is not the mass involved a fairly small fraction of the overall mass of the craft?

Probably, yes.

 

[warpus]

That they were able to get so close to landing on that barge is nothing short of amazing. It's like asking a supermodel for her number and actually getting it. They haven't gotten lucky yet, but they are that much closer to accomplishing what they set out to do. I bet this test taught them a lot about how to get in that supermodel's pants.

 

[Michkov]

It's not like they did this on the first try mind you. SpaceX have been taking incremental steps towards landing and recovering the first stage intact for a while now. This time the new thing was the barge.

 

[hobbsyoyo]

That they were able to get so close to landing on that barge is nothing short of amazing. It's like asking a supermodel for her number and actually getting it. They haven't gotten lucky yet, but they are that much closer to accomplishing what they set out to do. I bet this test taught them a lot about how to get in that supermodel's pants.

lol true story

And as to what they learned from the crash landing - they increased their hydraulic fluid margins by 50% for the next attempt.

It's not like they did this on the first try mind you. SpaceX have been taking incremental steps towards landing and recovering the first stage intact for a while now. This time the new thing was the barge.

None of that really detracts from any way from the achievement when you think about it.

Particularly when you put it into the context that no one is paying SpaceX specifically to carry out this research and test landings.

 

[bhsup]

That probe isn't a complete write-off yet, is it? I thought they were thinking it would be able to power up later as it got closer to the sun, yes?

 

[hobbsyoyo]

Yes but the comet is throwing off a lot more dust than originally anticipated and they are also unsure as to the exact orientation of the probe relative to the surrounding terrain which both complicate the situation.

 

[Michkov]

If the comet doesn't break up in the meantime ;-)

None of that really detracts from any way from the achievement when you think about it.

Particularly when you put it into the context that no one is paying SpaceX specifically to carry out this research and test landings.

No not at all, I'm just pointing out that it's just one further step towards successfully recovering the first stage. Which is something that is lost on people not keeping track of the program.

 

[hobbsyoyo]

Apologies for the misunderstanding!

 

[LamaGT]

Yes and no. It does 'waste' enough delta v that some higher mass missions (or those going to particularly high orbits or orbital inclinations) can't be launched on reusable rockets.

Also, as SpaceX originally outlined in their plan of bringing their rocket all the way back to the launch pad, yes it would also be extremely wasteful.

But landing on a pad downrange of launch isn't too too wasteful. The first stage isn't going that fast or is that high at that point in the flight and the atmosphere will slow it down a bit as it descends and deploys the landing legs which have a lot of intentional drag.

The main benefit is reusing the rocket stage itself which saves a ton of money in and of itself - more than offsetting losses due to 'wasted' deltav.

Didn't Shuttle engines need to be completely remade after 2-3 launches? I understand that the design here is very different, but wouldn't a similar wear happen in this case too?

 

[hobbsyoyo]

Didn't Shuttle engines need to be completely remade after 2-3 launches? I understand that the design here is very different, but wouldn't a similar wear happen in this case too?

They did essentially have to be rebuilt as you say and even after a single launch they required a massive overhaul. Part of that is just inherent to the nature of rocket engines - extreme pressures and temperatures and high-velocity moving parts (turpopumps, etc). But probably as big of a problem was the engine designs themselves.

Spoiler Long Winded Explanation :

NASA designed them to get the bleeding edge of performance. They are (IIRC) one of the engines with the highest Isp* ever created. *(specific impulse - a measure of efficiency) Bleeding-edge performance does not lend itself well to high re-usability in many cases. In particular, the space shuttle main engines (SSME's) were closed-cycle (also known as stage combustion) which poses a lot of reusability issues.

In most rocket engine designs, a bit of the fuel is burned before it reaches the main combustion chamber and the energy this liberates is used to drive the turbomachinery that is used to move fuel and oxidizer around the engine. In open-cycle engines, this 'pre-burned' fuel and oxidizer is simply dumped out a shaft that runs next to the main engine nozzle after it is burnt. This provides a bit of extra thrust but is not very efficient. Here is a picture of what I am talking about:

Link to video.
The video shows a Merlin engine being test fired. It is an open-cycle engine and you can see that next to the main nozzle is a tube that jets out black smoke as the engine is firing. This is where they are dumping the 'pre-burned' fuel and oxidizer that is used to drive the turbomachinery.

This open-cycle set up has the advantage that you are not routing that hot, reactive, 'pre-burned' fuel and oxidizer around the engine through pipes and other turbomachinery. Because it is hot and reactive, this 'pre-burned' mix really wants to just eat up (chemically attack) everything it touches. By dumping it overboard, you don't have to deal with that.

The penalty is that the engine is therefore less efficient (lower Isp) because that pre-burned fuel/oxidizer still has energy in it that is wasted when you dumped it overboard - it hasn't gone through a complete combustion.

Closed cycle engines such as the SSME's do not dump the pre-burned fuel/oxidizer mix overboard. Instead, they route it back into the main combustion chamber where it finished combusting. This increases efficiency but creates problems because of the reactive nature of this pre-burned mixture which in turn means you have to do more extensive overhaul on the engines.

Short Version:
The Falcon 9's Merlin engines were designed with re-usability from the outset. They specifically wanted to avoid the kind of extensive overhauls that the SSME's had to deal with. I wouldn't go so far as to say that the engines on a Falcon 9 would never need overhaul or replacement but I would say they need it far less frequently than the Space Shuttle. Space X has already demonstrated multiple-reuse on their engines through multiple testing regimes though they have yet to re-use an engine that has gone through a complete launch yet (AFAIK).

 

[hobbsyoyo]

Here's a video that shows the recent Orbital Sciences Antares launch explosion:

Link to video.
The problem was likely with the engines but I haven't yet seen a full report. For those interested, the engines were actually 40+ year old engines that have been sitting in a Moscow warehouse since before the cold war ended. They have an extremely interesting heritage if anyone is interested.

I recently spoke with some Orbital Sciences engineers and they confirmed that the Antares will be switching to the Russian-made RD-191 engines on future launches. There had been speculation that since Orbital Sciences and ATK were merging that the Antares would be switching to one of ATK's solid rocket motors for the first stage (ATK provided the white solid rocket boosters used on Space Shuttle launches) but that isn't happening. It would have required a lot more re-engineering of the Antares structure if they had done that as the acceleration of solid rocket motors is typically much higher, but it would have avoided the issues caused by using Russian engines in the current political climate.

If anyone is interested, I can give a breakdown on the Antares original NK-33 engines and how they went from a warehouse to an American rocket. There is also a cool video on Youtube called 'The Engines That Came in From the Cold' that tells much of the story.

 

[El_Machinae]

I don't know enough about orbital physics. How hard would it be to nudge one of these asteroids into orbit?

http://www.cbc.ca/news/technology/asteroid-2004-bl86-zips-safely-past-earth-1.2929800

I don't even know how to begin to do the calculations.