SpaceX COTS Demo 2 Updates

[Jorge]

Demo 2 Dragon should be considered a first flight article.  None of the things necessary to actually go to Station would have been on this flight.  None of the RPOC hardware and software.  ALL of that has to be completed, AND NASA gets to sign off on whatever interfaces to Station, be it physical or RF, where it didn't have to sign off on anything for Demo 1.  That's why it takes so long.

I think it is quite correct that NASA gets the final say on whatever interfaces with the station, and it is clear to me a lot of things werent present in the COTS 1 flight, SM for one.
Still, the progress made was good - do you think that they'll get permission to dock?

Pet peeve: permission to approach and be berthed, not permission to dock.

The best outcome I guess would be to have quite a long flight - first do all the movements to docking away from the ISS, then take a break and check that everything is ok, and only after that give perhaps the permission to dock, only if everything checked out.
Am I blabbering or is something like this possible?

That is likely how it would be structured. Perform all COTS Demo 2 objectives first, evaluate performance and resolve any anomalies, then go/no-go for COTS Demo 3 objectives.

[Ambassador]

The best outcome I guess would be to have quite a long flight - first do all the movements to docking away from the ISS, then take a break and check that everything is ok, and only after that give perhaps the permission to dock, only if everything checked out. Load it up with t-shirts, tang and vegetables.
Am I blabbering or is something like this possible?

That's what ATV-1 Demo Days was all about on it's first (and only to date) flight.

[duane]

Thanks Jorge!

[iamlucky13]

That is likely how it would be structured. Perform all COTS Demo 2 objectives first, evaluate performance and resolve any anomalies, then go/no-go for COTS Demo 3 objectives.

Agreed. This also means that the actual need for COTS 3 will not be known until COTS 2 is launched and most of the way through the previously untested parts of its mission.

So it seems only reasonable that SpaceX will need to continue to make preparations for COTS 3, even if the conditional combination is given. If COTS 2 does achieve the COTS 3 objectives, then they have the first CRS hardware that much closer to completion. If not, they're only at the readiness level they previously expected to be at, but shouldn't have lost ground on being ready for CRS.

[Lee Jay]

Pet peeve: permission to approach and be berthed, not permission to dock.

Isn't there a station-keep and grapple in there somewhere?

That is likely how it would be structured. Perform all COTS Demo 2 objectives first, evaluate performance and resolve any anomalies, then go/no-go for COTS Demo 3 objectives.

How different are the actual objectives than those of ATV1 and HTV1?

[Jorge]

Pet peeve: permission to approach and be berthed, not permission to dock.

Isn't there a station-keep and grapple in there somewhere?

Not at this level of detail; the key point I'm trying to bring out is that there is a part Dragon does (approach) and a part that gets done to Dragon (berth). At this level of detail stationkeep gets lumped with approach and grapple gets lumped with berth.

That is likely how it would be structured. Perform all COTS Demo 2 objectives first, evaluate performance and resolve any anomalies, then go/no-go for COTS Demo 3 objectives.

How different are the actual objectives than those of ATV1 and HTV1?

Not much at all.

[Lee Jay]

How different are the actual objectives than those of ATV1 and HTV1?

Not much at all.

Thank you.

It seemed from the point of view of someone not watching as closely as he would have liked that ATV1 and HTV1 were quite different from each other from a timeline perspective.  For example, I distinctly remember ATV1 flying in astonishingly tight formation and then doing an escape maneuver, but I don't remember HTV1 doing the same thing.  Am I just remembering it wrong?

[Ambassador]

The ATV, being fully automated, needed to be put through a different set of tests before docking.  Since it docks autonomously, they needed to make sure it's prox ops were within very tight margins, and would actually respond to manual abort commands sent from the crew and perform its collision avoidance maneuver.  You don't want 2 spacecraft bumping into each other at 17,000 MPH.

The HTV, being a 'grappleoid', just needed to get close enough for the SSRMS to grab it. 

There were also some traffic conflicts with the ATV having to spend a few extra days in parking orbit waiting for the completion of the STS-123 mission.  In fact, I remember watching Endeavour, the ISS, and the ATV all parade across the sky just minutes apart.  Now that was an incredible sight!

[duane]

Any details on how the solar panel will deploy ? I think Jim put a blurb that they will deploy out of the back of the trunk. All the spacex promo videos show out the sides

Thanks!

[Lars_J]

The ATV, being fully automated, needed to be put through a different set of tests before docking.  Since it docks autonomously, they needed to make sure it's prox ops were within very tight margins, and would actually respond to manual abort commands sent from the crew and perform its collision avoidance maneuver.  You don't want 2 spacecraft bumping into each other at 17,000 MPH.

For spacecraft attempting to dock/station-keep, it is relative motion/velocity to each other that matter. Not 17,000 MPH from an Earth surface reference point.

Still, these are multi-ton vehicles that interact (or ~370 tons in the case of ISS), so even relatively slow impacts can have severe consequences.

The HTV, being a 'grappleoid', just needed to get close enough for the SSRMS to grab it.

Positioning yourself (or a spacecraft) to be grappled by ISS is not much simpler (if at all). The relative motions need to be cancelled out exactly, with a fairly exact parking position relative to ISS. Not too close, yet within the arm's range.

[R.Simko]

The ATV, being fully automated, needed to be put through a different set of tests before docking.  Since it docks autonomously, they needed to make sure it's prox ops were within very tight margins, and would actually respond to manual abort commands sent from the crew and perform its collision avoidance maneuver.  You don't want 2 spacecraft bumping into each other at 17,000 MPH.

For spacecraft attempting to dock/station-keep, it is relative motion/velocity to each other that matter. Not 17,000 MPH from an Earth surface reference point.

Still, these are multi-ton vehicles that interact (or ~370 tons in the case of ISS), so even relatively slow impacts can have severe consequences.

The HTV, being a 'grappleoid', just needed to get close enough for the SSRMS to grab it.

Positioning yourself (or a spacecraft) to be grappled by ISS is not much simpler (if at all). The relative motions need to be cancelled out exactly, with a fairly exact parking position relative to ISS. Not too close, yet within the arm's range.

Hi Lars, I looked up the reach of the robotic arm, but all I keep coming up with are its dementions.   Do you know what the maximum reach is for the arm?  Thanks, Bob

[Lars_J]

Jorge knows

But I found this link that describes some factors that constrain the "capture box" the spacecraft must occupy: http://www.scribd.com/doc/43933900/International-Space-Station (page 38 in the inline doc)

This page mentions 10m away from the SRMSS base for the HTV: http://www.jaxa.jp/countdown/h2bf1/overview/htv_e.html

EDIT: Even better, this document  has an illustration of the position and distances from ISS during the different stages of approach to capture: http://www.nasa.gov/centers/ivv/pdf/482479main_3500_-_2010_IV%26V_Modeling_and_Hazard_Analysis_Using_STPA.pdf (page 12 of the inline PDF)

[R.Simko]

Jorge knows

But I found this link that describes some factors that constrain the "capture box" the spacecraft must occupy: http://www.scribd.com/doc/43933900/International-Space-Station (page 38 in the inline doc)

This page mentions 10m away from the SRMSS base for the HTV: http://www.jaxa.jp/countdown/h2bf1/overview/htv_e.html

EDIT: Even better, this document  has an illustration of the position and distances from ISS during the different stages of approach to capture: http://www.nasa.gov/centers/ivv/pdf/482479main_3500_-_2010_IV%26V_Modeling_and_Hazard_Analysis_Using_STPA.pdf (page 12 of the inline PDF)

Thanks for the Information Lars.

[Jorge]

Jorge knows

I did, but left my brains at work (or at least my references).

But I found this link that describes some factors that constrain the "capture box" the spacecraft must occupy: http://www.scribd.com/doc/43933900/International-Space-Station (page 38 in the inline doc)

This page mentions 10m away from the SRMSS base for the HTV: http://www.jaxa.jp/countdown/h2bf1/overview/htv_e.html

EDIT: Even better, this document  has an illustration of the position and distances from ISS during the different stages of approach to capture: http://www.nasa.gov/centers/ivv/pdf/482479main_3500_-_2010_IV%26V_Modeling_and_Hazard_Analysis_Using_STPA.pdf (page 12 of the inline PDF)

Those give a flavor but give the mistaken impression that this is mainly a positional problem. It's also an orientation (attitude) problem and, crucially, a velocity problem (both translational and angular). Since the grappleoid must mode to free drift prior to capture, the velocity problem is harder than it sounds. It essentially places a tight time constraint on the amount of time the SSRMS operator has to move the arm in and grapple before translational and angular velocity take the grapple fixture outside the capture box. To make the time constraint reasonable, the grappleoid must null rates very precisely prior to moding to free drift. These constraints are no less difficult to meet than the ones on docking vehicles. Unfortunately I do not have the exact numbers memorized.

[butters]

Won't there be some reasonably close "pre-grapple" position that the SSRMS maneuvers to and aligns with the grapple fixture while the visiting vehicle is in active station-keeping? Then the visiting vehicle goes to free drift and the arm moves in the final few feet to capture?

[Jorge]

Won't there be some reasonably close "pre-grapple" position that the SSRMS maneuvers to and aligns with the grapple fixture while the visiting vehicle is in active station-keeping? Then the visiting vehicle goes to free drift and the arm moves in the final few feet to capture?

Yes.

[zaitcev]

Those give a flavor but give the mistaken impression that this is mainly a positional problem. It's also an orientation (attitude) problem and, crucially, a velocity problem (both translational and angular). Since the grappleoid must mode to free drift prior to capture, the velocity problem is harder than it sounds. It essentially places a tight time constraint on the amount of time the SSRMS operator has to move the arm in and grapple before translational and angular velocity take the grapple fixture outside the capture box. To make the time constraint reasonable, the grappleoid must null rates very precisely prior to moding to free drift. These constraints are no less difficult to meet than the ones on docking vehicles. Unfortunately I do not have the exact numbers memorized.

This is all true but then did you see the blasted videos of HTV capture? They were astonishing. There was absolutely no discernable drift of the vehicle after dead mode was on, for minutes, all the while the arm approached the vehicle at agonizingly slow speed. Japanese made it clear that problem is not just soluble, but is so in the first flight and with a lot of margin to spare.

[Lee Jay]

Those give a flavor but give the mistaken impression that this is mainly a positional problem. It's also an orientation (attitude) problem and, crucially, a velocity problem (both translational and angular). Since the grappleoid must mode to free drift prior to capture, the velocity problem is harder than it sounds. It essentially places a tight time constraint on the amount of time the SSRMS operator has to move the arm in and grapple before translational and angular velocity take the grapple fixture outside the capture box. To make the time constraint reasonable, the grappleoid must null rates very precisely prior to moding to free drift. These constraints are no less difficult to meet than the ones on docking vehicles. Unfortunately I do not have the exact numbers memorized.

This is all true but then did you see the blasted videos of HTV capture? They were astonishing. There was absolutely no discernable drift of the vehicle after dead mode was on, for minutes, all the while the arm approached the vehicle at agonizingly slow speed. Japanese made it clear that problem is not just soluble, but is so in the first flight and with a lot of margin to spare.

Time-lapse of that:

http://forum.nasaspaceflight.com/index.php?topic=18820.msg480220#msg480220

[Jorge]

Those give a flavor but give the mistaken impression that this is mainly a positional problem. It's also an orientation (attitude) problem and, crucially, a velocity problem (both translational and angular). Since the grappleoid must mode to free drift prior to capture, the velocity problem is harder than it sounds. It essentially places a tight time constraint on the amount of time the SSRMS operator has to move the arm in and grapple before translational and angular velocity take the grapple fixture outside the capture box. To make the time constraint reasonable, the grappleoid must null rates very precisely prior to moding to free drift. These constraints are no less difficult to meet than the ones on docking vehicles. Unfortunately I do not have the exact numbers memorized.

This is all true but then did you see the blasted videos of HTV capture? They were astonishing. There was absolutely no discernable drift of the vehicle after dead mode was on, for minutes, all the while the arm approached the vehicle at agonizingly slow speed. Japanese made it clear that problem is not just soluble, but is so in the first flight and with a lot of margin to spare.

I never said or implied it wasn't solvable. I just said the berthing problem was no easier than the docking problem.

[telomerase99]

How is that? It has to be easier to berth than to dock, the berthing window is much larger than the docking window!