Author Topic: SpaceX Falcon 9/Dragon CRS-2 SpX-2 MISSION GENERAL DISCUSSION (Read 379838 times)

Jim · « **Reply #220 on:** 01/29/2013 11:31 am »

Quote from: beancounter on 01/29/2013 01:54 am

Well if Elon wants to get to fly like commercial airliners do, then cleanrooms and bunnysuits need to be designed out of the systems or at least components etc, need to become sufficiently robust to eliminate the need for this.
Gotta say it does seem like excessive requirements but then, I have no experience with spaceflight so ...

commercial airliners don't have to deal with 0g and debris floating in the cabin and getting into avionics and people's lungs and eyes. Commercial airliners don't use solar cells, radiators and sensors that would have reduced efficiency due to dust and non volatile residues. Commercial airliners don't have to deal with vacuum outgassing and subsequent redepositing on the above systems.

ChefPat · « **Reply #221 on:** 01/29/2013 11:46 am »

Quote from: IRobot on 01/29/2013 11:15 am

And even bakers don't work in a shirt-sleeve environment,

Wanna bet?

dragon44 · « **Reply #222 on:** 01/29/2013 03:59 pm »

Quote from: Jim on 01/28/2013 08:40 pm

The avionics are in the base of the pressure vessel that is useless for cargo.

The base of the pressure vessel is mostly lockers for cargo. See diagrams in http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110014250_2011013540.pdf. Most of the rest of that space is filled with air circulation ducts.

So, avionics are in both the pressure section and the service section. I don't think the location of the batteries and power equipment has ever been released.

I get the impression you are assuming they are in the pressure section because there was space not used by cargo. I don't think that is a good assumption.

Jim · « **Reply #223 on:** 01/29/2013 05:22 pm »

Quote from: dragon44 on 01/29/2013 03:59 pm

Quote from: Jim on 01/28/2013 08:40 pm
The avionics are in the base of the pressure vessel that is useless for cargo.

The base of the pressure vessel is mostly lockers for cargo. See diagrams in http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110014250_2011013540.pdf. Most of the rest of that space is filled with air circulation ducts.

So, avionics are in both the pressure section and the service section. I don't think the location of the batteries and power equipment has ever been released.

I get the impression you are assuming they are in the pressure section because there was space not used by cargo. I don't think that is a good assumption.

No, there are only a few positions on the floor for lockers with cargo, the bulk of volume is avionics

Chris Bergin · « **Reply #224 on:** 01/30/2013 04:24 am »

Hey guys, do we know if there's another ORBCOMM riding on this SpX-2 Falcon 9, or have they halted for the meantime due to the SpX-1 issue?

QuantumG · « **Reply #225 on:** 01/30/2013 04:29 am »

Quote from: Chris Bergin on 01/30/2013 04:24 am

Hey guys, do we know if there's another ORBCOMM riding on this SpX-2 Falcon 9, or have they halted for the meantime due to the SpX-1 issue?

My understanding is that they plan to launch all the ORBCOMM sats on two dedicated Falcon 9 launches. They got what they needed from SpX-1.

Quote

Orbcomm says the data will allow it to focus on completing and launching the OG2 satellites as the primary mission payloads on two planned Falcon 9 launches, the first in mid-2013 and the second in 2014, directly into their operational orbit.

from: http://www.aviationweek.com/Blogs.aspx?plckBlogId=Blog:04ce340e-4b63-4d23-9695-d49ab661f385&plckPostId=Blog%3A04ce340e-4b63-4d23-9695-d49ab661f385Post%3A22278965-7380-449a-9b29-60d608560e40

Chris Bergin · « **Reply #226 on:** 01/30/2013 04:32 am »

That's what I needed, thanks!

russianhalo117 · « **Reply #227 on:** 01/30/2013 05:58 pm »

Quote from: Chris Bergin on 01/30/2013 04:32 am

That's what I needed, thanks!

Yes that is indeed the new plan now.

mlindner · « **Reply #228 on:** 01/31/2013 09:25 am »

Quote from: russianhalo117 on 01/30/2013 05:58 pm

Quote from: Chris Bergin on 01/30/2013 04:32 am
That's what I needed, thanks!
Yes that is indeed the new plan now.

I think its the old plan as well? After the move from F1 to F9, didn't all the launches get consolidated into 2 launches?

Norm38 · « **Reply #229 on:** 02/05/2013 10:21 pm »

Quote from: wolfpack on 01/28/2013 08:40 pm

Quote from: go4mars on 01/28/2013 08:31 pm
Would it be easier from a heat rejection perspective to put power systems in the unpressurized area? Or is there no meaningful difference?

Think about environmental effects. Silicon semiconductors only work reliably from about -40C to +125C and they really hate radiation.

Since power is my field....

Air isn't a great heatsink, but it's better than nothing. Putting the power electronics in a pressurized area allows air to even out the heating and prevent hot spots from forming. Power devices shed a considerable amount of heat to the surrounding air along with the PCB/heatsinks. Of course zero g doesn't allow any natural convection, but small fans are light, cheap and reliable.
If the power supplies are unpressurized then everything has to be mounted to a cold plate, which itself has to then be liquid cooled to get the heat out to a radiator. Thermal management is much easier in air than in vaccum.

As for radiation, yes power semiconductors are quite susceptible, depending on the applied voltage and rating of the parts. A MOSFET can be destroyed by a single neutron given the right condition. I did research on this a few years back to explain field failures we were having. MOSFETs suffer from "Single Event Breakdown" (SEB) when they are off and blocking over ~85% of their rated voltage. SEB begins at 100V, is most prevalent above 300V but has been reported as low as 30V.

When FET voltage is near the device rating, a very high strength electric field appears across the die, and across a parasitic PNP transistor in the substrate. If a neutron scattered from a cosmic ray hits the die, it creates an ionization trail and an avalanche current. Usually this is not fatal, but if the angle is right that current flows laterally through the p-base, the parasitic PNP transistor can latch on, enter thermal runaway and destroy the MOSFET by shorting Drain and Source. This isn't a soft failure like a computer reboot. The FET is dead, and there had better be redundancy.

In the study I did, I had an array of 500V FETs that were held off, and were blocking 490V. After 12 weeks, 25% of the FETs had failed short.
When I repeated the test with 600V FETs at 490V (82% of rating), none had failed. Failures of the 600V began at 520V (87%).

For this reason we now limit all MOSFET voltage stresses to 75% MAX.

Thunderbird5 · « **Reply #230 on:** 02/05/2013 11:17 pm »

Wow, very insightful. Thanks norm38.

mlindner · « **Reply #231 on:** 02/05/2013 11:22 pm »

Yes this makes sense. We were flying MOSFETs on cubesats and have been hearing about people experiencing failures in them. Next satellite revision we took much effort to purge every MOSFET from the design (most often use was changing active low lines to active high lines). These were all low voltage MOSFETs though, I believe all were 30V range or below.

kevin-rf · « **Reply #232 on:** 02/06/2013 01:59 pm »

No, Not Semi Device Physic's again... It's been 20+ years and it still wakes me in a cold sweat!

beancounter · « **Reply #233 on:** 02/12/2013 04:36 am »

I'm presuming that this mission is another 'instantaneous' launch. Wonder what the odds are that they'll get off the first time?
For that matter, wonder what the odds are for a launch on schedule?

Lars_J · « **Reply #234 on:** 02/12/2013 06:48 am »

Quote from: beancounter on 02/12/2013 04:36 am

I'm presuming that this mission is another 'instantaneous' launch. Wonder what the odds are that they'll get off the first time?
For that matter, wonder what the odds are for a launch on schedule?

The odds shouldn't be too bad - didn't the last F9 launch on the first 'instant' window?

manboy · « **Reply #235 on:** 02/12/2013 07:24 pm »

Quote from: Lars_J on 02/12/2013 06:48 am

Quote from: beancounter on 02/12/2013 04:36 am
I'm presuming that this mission is another 'instantaneous' launch. Wonder what the odds are that they'll get off the first time?
For that matter, wonder what the odds are for a launch on schedule?

The odds shouldn't be too bad - didn't the last F9 launch on the first 'instant' window?

Yes.

mlindner · « **Reply #236 on:** 02/14/2013 05:06 pm »

Quoted from updates thread:

Quote from: mr. mark on 02/14/2013 04:15 pm

I must be getting old. Most of these SpaceX employees look like they are right out of high school. Well if they can get the job done, that's all that matters. When I was their age I was working at a pizza parlour.

SpaceX is a return to the old Apollo era with the low average age.

Joffan · « **Reply #237 on:** 02/14/2013 10:13 pm »

At what stage does the unpressurized cargo get packed in the trunk?

happyflower · « **Reply #238 on:** 02/14/2013 10:24 pm »

A bit off topic for SPX2 but a general SPX question.

SPX2 is planned to go up on 3/1 and come back down on 3/25. SPX1 didnt stay attached to the ISS for very long either. However, Dragon is supposed to be able to stay in LEO for a considerable time. Are there plan to keep one of the SPX mission attached to the ISS for an extended period of time? To see how the craft will do after a long time in space.

Comga · « **Reply #239 on:** 02/14/2013 10:47 pm »

Around Feb 8 anik's ISS schedule which references CBS News shifted the capture of the CRS-2 Dragon from Flight Day 3 to Flight Day 2. Actually it is T+ 20 hours 20 minutes to capture.

02/28/13..................SpaceX/CRS-2 pre-flight briefing
03/01/13...15:10:09...SpaceX/CRS-2 launch
03/02/13...11:30:23...SpaceX/CRS-2 SSRMS capture (Ford, Marshburn)
03/02/13...13:40:00...SpaceX/CRS-2 berthing (Harmony nadir; time approximate)
03/25/13..................SpaceX/CRS-2 unberthing and splashdown

Does anyone know who made what decisions and what has changed?
To me this indicates a high confidence on the part of NASA in the launch going according to plan.
Does anyone recall the time between capture and berthing for CRS-1 or COTS-2+?

Edit: T-15 days and counting, and nary a slip in the last four months.