SpaceX COTS Demo 2 Updates

[Lars_J]

No, you need to be able to station-keep with the same accuracy that you need for docking. The object the station arm grabs needs to be virtually still relative to the station. (well as relatively still as two independent objects in orbit can be)

[mr. mark]

According to this article the Dragon trunk solar arrays have been successfully tested.

"In the meantime, he said, SpaceX successfully completed four new milestones that the agency established in December and that were worth $5 million each. These included a plan to test the effect of vibrations on pressurized cargo stowed inside Dragon, followed by the successful demonstration of the test capability at the company’s Hawthorne facility. A third milestone involved fully deploying Dragon’s solar arrays and conducting thermal vacuum tests of some components. Finally, the company completed a ground simulation of the spacecraft’s lidar sensor, used for rendezvous and proximity operations with the space station, at NASA’s Marshall Space Flight Center in Huntsville, Ala".


 http://www.spacenews.com/civil/110107-nasa-boosted-cots-funding.html

[Comga]

No, you need to be able to station-keep with the same accuracy that you need for docking. The object the station arm grabs needs to be virtually still relative to the station. (well as relatively still as two independent objects in orbit can be)

This is at best not obvious.  For docking you need to drive twelve variables, (three position, three attitude, six rates) to precise targets, including centimeters on lateral position and a tightly bound forward velocity.  For berthing capture the position targets can be meters across, and all relative rates go to zero.  How can berthing not be easier?

[Comga]

According to this article the Dragon trunk solar arrays have been successfully tested.

"In the meantime, he said, SpaceX successfully completed four new milestones that the agency established in December and that were worth $5 million each. These included a plan to test the effect of vibrations on pressurized cargo stowed inside Dragon, followed by the successful demonstration of the test capability at the company’s Hawthorne facility. A third milestone involved fully deploying Dragon’s solar arrays and conducting thermal vacuum tests of some components. Finally, the company completed a ground simulation of the spacecraft’s lidar sensor, used for rendezvous and proximity operations with the space station, at NASA’s Marshall Space Flight Center in Huntsville, Ala".


 http://www.spacenews.com/civil/110107-nasa-boosted-cots-funding.html

This is not an unalloyed benefit to SpaceX.  These are tests that Musk did not include in his plan to develop COTS capability.  While there is no doubt that more income is better for them, the tests take time.  The specialists who are working on the COTS-2 Dragon have to take that time to run this extra test.  It is a distraction.  This will inevitably delay future flights, and may be part of the eight months (minimum) delay between COTS-1 and COTS-2.

The statement has been made (don't remember where or who) that NASA, seeing how critically dependent thay are on COTS / CRS succeeding, is adding test to reduce risk.  I have seen NASA programs explode in cost and schedule as NASA adds tests to reduce risk.   

[Antares]

Wrong.  Edit: What proof do you have that this test regime originated with NASA?  Your premise is severely flawed.

[Lars_J]

According to this article the Dragon trunk solar arrays have been successfully tested.

"In the meantime, he said, SpaceX successfully completed four new milestones that the agency established in December and that were worth $5 million each. These included a plan to test the effect of vibrations on pressurized cargo stowed inside Dragon, followed by the successful demonstration of the test capability at the company’s Hawthorne facility. A third milestone involved fully deploying Dragon’s solar arrays and conducting thermal vacuum tests of some components. Finally, the company completed a ground simulation of the spacecraft’s lidar sensor, used for rendezvous and proximity operations with the space station, at NASA’s Marshall Space Flight Center in Huntsville, Ala".


 http://www.spacenews.com/civil/110107-nasa-boosted-cots-funding.html

This is not an unalloyed benefit to SpaceX.  These are tests that Musk did not include in his plan to develop COTS capability.  While there is no doubt that more income is better for them, the tests take time.  The specialists who are working on the COTS-2 Dragon have to take that time to run this extra test.  It is a distraction.  This will inevitably delay future flights, and may be part of the eight months (minimum) delay between COTS-1 and COTS-2.

The statement has been made (don't remember where or who) that NASA, seeing how critically dependent thay are on COTS / CRS succeeding, is adding test to reduce risk.  I have seen NASA programs explode in cost and schedule as NASA adds tests to reduce risk.   

The ground tests are almost certainly worth it. Especially if they discover issues that would cause COTS-2(/3) to be a failure, like for example to a solar array deployment problem. And if they got $5m per item testing - then who can complain? (certainly not SpaceX)

SpaceX may look like they are flying by the seat of their pants, but the COTS1 mission would not have been a success without extensive ground testing.

Due diligence testing is not "analysis paralysis" (which you seem to allude to) - there is a wide gulf between them.

[yinzer]

No, you need to be able to station-keep with the same accuracy that you need for docking. The object the station arm grabs needs to be virtually still relative to the station. (well as relatively still as two independent objects in orbit can be)

This is at best not obvious.  For docking you need to drive twelve variables, (three position, three attitude, six rates) to precise targets, including centimeters on lateral position and a tightly bound forward velocity.  For berthing capture the position targets can be meters across, and all relative rates go to zero.  How can berthing not be easier?

Docking systems can typically handle subtle misalignments and variations in the closing rate.  Current and predicted berthing systems have very tight relative velocity and angular rate limits.

The SSRMS-to-Grapple Fixture requirements are within 0.1 fps, 0.2 dps, 3 inches lateral alignment, and 1.5 deg angular alignment.  Soyuz docking requirements are 0.3-0.6 fps closing velocity, 0.3 fps lateral velocity, 0.7 dps angular rates, and 4 deg roll / 6 deg pitch/yaw angular alignment.

So the linear and angular rate requirements for berthing are significantly tighter than for docking.  The requirements are close enough that it's not immediately obvious which is going to be easier.

[Comga]

Thank you, yinzer.  The quantitative requirements make the point unambiguous.
It does seem that the values are quite comparable. 

[Swatch]

On the "birth vs dock" requirements...

Docking requirements are between a large unmaneuverable 'passive' object and a smaller maneuverable 'active' object.  Birthing requirements are between a small maneuverable 'passive' object and a articulated, highly dexterous 'active' arm.   As such, though the actual SSRMS to Grapple Fixture requirements are tighter, the 'capture box' of the capsule may be much greater.  As pointed out, rates are very important when in the capture box and are likely held to tighter requirements, but position and alignment within the capture box should be much looser since the arm has a fair range of motion. The tight tolerance requirements quoted there are made possible by the fact that the arm and it's attached grapple mechanism are more maneuverable than the craft itself.  Comga, am I right?

Also, birthing allows the spacecraft to approach the station and enter a less active state at a still relative (to docking) safe distance before the final birthing process begins. At that point, the station's well-being is largely in its own hands.

[Proponent]

That's "berthing" rather than "birthing".  Requirements for birthing are quite different.

[Nomadd]

That's "berthing" rather than "birthing".  Requirements for birthing are quite different.

 I don't know. If you think of those terms as applying to the surgeon's arm and hand, and the mother delivering the baby, it actually sounds pretty much how a NASA document would describe birthing.

[Swatch]

That's "berthing" rather than "birthing".  Requirements for birthing are quite different.

Uhhh...ummm...err....

It was late... I was tired... I had to much to drink... I liked her, she liked me, one thing led to another...

  Haha!  Whoops!

[billh]

Wrong.  Edit: What proof do you have that this test regime originated with NASA?  Your premise is severely flawed.

I can't find a link that says who actually decided on the solar array thermal vacuum testing, but the original idea to spend more money on COTS risk reduction seems to have originated in the White House FY2011 budget:

http://www.spacenews.com/civil/nasa-raises-bet-commercial-cargo.html

[telomerase99]

I really enjoyed that article. I did not know that that money was available to Orbital and SpaceX, previously it had been said that it was mostly going to Orbital...

[Comga]

Wrong.  Edit: What proof do you have that this test regime originated with NASA?  Your premise is severely flawed.

Who me?  Wrong?  Severely flawed?  Being wrong has happened before, and will happen again and again, but you are so sure.....

As far as we know, SpaceX did not plan for these tests originally.  They were not among the milestones agreed to when COTS was negotiated.  It could have been that these were additional tests that SpaceX wanted to perform but neither included them in the final agreement to meet a funding limit but they didn't mention them publicly as something beneficial.  The notice says that NASA added these tests, these milestones, and is paying $5M apiece.  It sure sounds like added testing, "risk reduction" for NASA.  This would be something I have seen over and over.   You have probably seen it, too.

What evidence do you have that SpaceX went to NASA asking for more testing?  Is there an third way to interpret this?

Remember, this is the group who says that they want to combine COTS-2 and COTS-3 flight.  It doesn't sound to me like they are mired in trepidation.

[Antares]

You should ask yourself the same question you asked me: what evidence you have that SpaceX went to NASA asking for more testing.  Your premise that NASA is levying more tests is still flawed, but you're exhausting the other possibilities one by one.

[Namechange User]

I personally believe the extra money is politically coded as "risk-reduction" because NASA in conjunction with the COTS partners saw the writing on the wall that the vehicles were behind schedule.  Generally, it was likely accepted by all parties that if more money could be thrown at it, then the "risk" of the vehicles slipping further to the right could be "reduced". 

With the decisions that have been made and the generally poor execution of policy over the last 5 years, culminating in the "wasted years" of 2009 and 2010, ISS will be facing a very uncertain future here very soon.  One that is even more unclear if the main link in the resupply chain is removed and there is nothing to even *partially* fill the gap that has been created. 

[mmeijeri]

I personally believe the extra money is politically coded as "risk-reduction" because NASA in conjunction with the COTS partners saw the writing on the wall that the vehicles were behind schedule.  Generally, it was likely accepted by all parties that if more money could be thrown at it, then the "risk" of the vehicles slipping further to the right could be "reduced".   

More importantly, Ares I is so far behind schedule that NASA will now be dependent on these unproven suppliers. If NASA hadn't screwed up on Ares I or if they had chosen one of the COTS proposals using EELVs, then they wouldn't have had to spend extra money on risk reduction now.

[mr. mark]

Elon Musk said in the post flight interview that NASA and Spacex could do additional ground based testing and simulations to reduce the risk of a COTS 2&3 combined mission. Maybe some of this testing is the result of that.

[Namechange User]

Elon Musk said in the post flight interview that NASA and Spacex could do additional ground based testing and simulations to reduce the risk of a COTS 2&3 combined mission. Maybe some of this testing is the result of that.

Which is, of course, schedule related and if successful gets to CRS missions that much sooner.