Author Topic: SpaceX Falcon 9 - CRS-8 Dragon - NET April, 2016 - DISCUSSION  (Read 374713 times)

Offline Jim

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Did you mean that out of the more than 3700 pounds of down mass, more than 2700 pounds is trash? Why don't they use the Cygnus for trash?

"Hundreds of pounds" goes up to 1900lb before it becomes a ton.  And multiple vehicles are used for trash, including Dragon.

I guess it is a case of lost in translation. In my language (non-English), "hundreds" only goes up to 999. More than that we call it "thousand(s)".
Even the total mass is "hundreds" as in 37 hundred lbs.

Offline Jim

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So now Elon's providing a contract laundry service to NASA?!??


Always was providing that service from Day 1.

Offline the_other_Doug

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Did you mean that out of the more than 3700 pounds of down mass, more than 2700 pounds is trash? Why don't they use the Cygnus for trash?

Getting rid of trash is a challenge for ISS, you can't just throw something out the window or wash and reuse clothes. Any vehicle leaving gets trash in it, otherwise you have to store it and wait.

So now Elon's providing a contract laundry service to NASA?!??  It never occurred to me before that maybe it's really the smell of dirty laundry that awaits the lucky first to open Dragon after splashdown.  :o  ;D

"The laundry basket's over on the left there, under those science experiments."

Since downmass is limited (and, in the case of Dragon and Soyuz, more volume-limited than mass-limited), it seems to me that most of the "trash" thrown out in either craft is used to pack more delicate items.

Think of it as using your old laundry to wrap up your drinking tumblers when you move.  You're not doing it because you need to move the old laundry, you're doing it to protect the delicate glassware.

So, on the Dragons, dirty underwear = bubble wrap... ;)
-Doug  (With my shield, not yet upon it)

Offline sevenperforce

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Did you mean that out of the more than 3700 pounds of down mass, more than 2700 pounds is trash? Why don't they use the Cygnus for trash?

"Hundreds of pounds" goes up to 1900lb before it becomes a ton.  And multiple vehicles are used for trash, including Dragon.

I guess it is a case of lost in translation. In my language (non-English), "hundreds" only goes up to 999. More than that we call it "thousand(s)".
Even the total mass is "hundreds" as in 37 hundred lbs.
To be fair, the original comment was "couple of tons" so hundreds of pounds vs a couple of (short) tons would definitely break at 1999 pounds.

Online Robotbeat

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Did you mean that out of the more than 3700 pounds of down mass, more than 2700 pounds is trash? Why don't they use the Cygnus for trash?

"Hundreds of pounds" goes up to 1900lb before it becomes a ton.  And multiple vehicles are used for trash, including Dragon.

I guess it is a case of lost in translation. In my language (non-English), "hundreds" only goes up to 999. More than that we call it "thousand(s)".
Even the total mass is "hundreds" as in 37 hundred lbs.
To be fair, the original comment was "couple of tons" so hundreds of pounds vs a couple of (short) tons would definitely break at 1999 pounds.
Another way of saying this is that you all are in violent agreement.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Arb

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This discusses a waiver SpaceX requested for CRS-8 having to do with ship-borne impact hazard but also mentions the previous ASDS landings and a USAF evaluation of the overall launch hazard.

https://www.federalregister.gov/articles/2016/05/10/2016-09685/waivers-of-ship-protection-probability-of-impact-requirement

Would someone who's read it kindly do a TL:DR for the busy, busy. Thanks.

Offline joek

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This discusses a waiver SpaceX requested for CRS-8 having to do with ship-borne impact hazard but also mentions the previous ASDS landings and a USAF evaluation of the overall launch hazard.

https://www.federalregister.gov/articles/2016/05/10/2016-09685/waivers-of-ship-protection-probability-of-impact-requirement

Would someone who's read it kindly do a TL:DR for the busy, busy. Thanks.

The FAA has a number of risk calculations and thresholds--threshold which you cannot exceed without a waiver (collectively or individually) in order to obtain a launch license.  This waiver is due to one of those risk calculations exceeding a threshold.

The FAA has previously issued several similar waivers to SpaceX and ORB/ATK (among others), and for similar (if not exactly) the same reasons.

FYI... There is an FAA rule change pending that would eliminate the need for some of these waivers, which was first put forth by the FAA in Jul-2014.  For more information than you probably want, see CHANGING THE COLLECTIVE RISK LIMITS FOR LAUNCHES AND REENTRIES AND CLARIFYING THE RISK LIMIT USED TO ESTABLISH HAZARD AREAS FOR SHIPS AND AIRCRAFT.

Online Retired Downrange

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I can see how in the past, the FAA would have a risk threshold for a possible ship impact hazard, but now the object of the test is that SpaceX "AIMS" to hit the ship.

Times change...

Offline joek

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I can see how in the past, the FAA would have a risk threshold for a possible ship impact hazard, but now the object of the test is that SpaceX "AIMS" to hit the ship.

I hope that was intended to be humorous (sorry, my humor-meter has been dulled by too much irony of late).  FAA calculation is based primarily on risk to public life-and-limb (Ec); for property they simply demand adequate insurance before granting a launch license.

Offline Joffan

I can see how in the past, the FAA would have a risk threshold for a possible ship impact hazard, but now the object of the test is that SpaceX "AIMS" to hit the ship.

Times change...

The point for me is that the stage is re-entering under control. SpaceX know where they want it to go, and they clearly have at least an 80% chance of putting it exactly there, which should reduce the remaining area risk by a factor of at least 5.
Getting through max-Q for humanity becoming fully spacefaring

Offline joek

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The point for me is that the stage is re-entering under control. SpaceX know where they want it to go, and they clearly have at least an 80% chance of putting it exactly there, which should reduce the remaining area risk by a factor of at least 5.

Hmmm... not sure about that "80% chance of putting it exactly there..." (where does that come from?).  But the FAA seems to be convinced that SpaceX can put it where they want it, as the most recent launch licenses includes "Flight includes landing of the Falcon 9 Version 1.2 first stage as indicated in the license application.".  That was notably absent from any prior FAA launch licenses; probably a good sign.  But even if, as you say, it "should reduce the remaining area risk by a factor of at least 5", it was not enough-and is not enough under current rules--to eliminate the need for a waiver.

Offline OxCartMark

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Hmmm... not sure about that "80% chance of putting it exactly there..." (where does that come from?).
Prior to the grid fin addition during the period that we were made aware of their retro propulsion recovery attempts I don't believe that there were any ocean returns that were not within 10km of the intended point, about as good as you could expect in that configuration.  Since the addition of the grid fins we've had (off the top of my head) 7 aimed at the ASDS and every one of them has made some sort of contact with the ASDS except for once when the ASDS was out of position and even then the F9 was reported to have gone to the right spot.  Additionally we've had one RTLS which did get to the LZ-1.  8 of 8 is on the surface greater than 80% though Its been a long while since I had probability and statistics, maybe there's something that wasn't demonstrated to a specific confidence level yet??
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Offline baldusi

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First you have to assume the probability of failure all over the trajectory, to and (now) from space. Second the probability of killing someone is atrociously low.

Offline deruch

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Moving Discussion from Updates thread to proper place: 

This discusses a waiver SpaceX requested for CRS-8 having to do with ship-borne impact hazard but also mentions the previous ASDS landings and a USAF evaluation of the overall launch hazard.

https://www.federalregister.gov/articles/2016/05/10/2016-09685/waivers-of-ship-protection-probability-of-impact-requirement

To be clear:  THIS WAIVER IS NOT DIRECTLY RELATED TO LANDING ON ASDS.  If it was for ASDS landings, then similar waivers would have been needed for every previous ASDS landing attempt.

Here's the most relevant part: 

Quote from: Federal Register
The FAA found that small boats (too small to have AIS required) located close to the launch point should not produce significant individual risks, given conditions expected in the vicinity of Cape Canaveral. Specifically, sufficient surveillance with other means (e.g., radar, and/or using Coast Guard ships or aerial assets) will be used to ensure individual risks comply with the FAA requirement in  417.107(b)(2). In addition, Notices to Mariners will continue to be issued for the areas where the probability of impact on a ship would exceed 1 10 −5, which is current practice at the ER, and required by  B417.3 and B417.11. Since the FAA's current requirements allow launches to proceed with unquantified residual collective risks to people in waterborne vessels, as long as the collective risk for people on land from each source of hazard (i.e., debris, toxics, or distant focusing overpressure) does not exceed 30 10 −6 E C, and because the launch will not exceed the 30 10 −6 E C with the inclusion of persons on water borne vessels, the FAA finds that the Falcon 9 CRS-8 launch will not jeopardize public health and safety or safety of property, and waives 14 CFR 417.107(b)(3) and Appendix B to part 417, paragraph 417.5(a)'s requirement not to initiate flight absent evacuation.

A more nuanced reading, and the part that could be relevant for ASDS landings, is that it might allow them to stage the recovery support vessels (Go Quest and tug) closer to the ASDS during landings.  i.e. Instead of making them wait 5-7miles away, they might only have to wait 2-3 miles.  This would reduce the time needed to return landed stages to port.  But, without reading SpaceX's actual application, it's hard to understand exactly what they were arguing.  The gist from the Federal Register is that AIS and ship tracking data is sufficient now to determine the Ec including shipboard persons as opposed to just trying to determine the odds of hitting a ship with debris.  And, SpaceX would like to do that as they feel like they're less likely to be forced to scrub a launch by a late intrusion into the hazard area unless the ship in question happens to be a large, passenger carrier. 

NB: This doesn't mean that they wouldn't try to keep any boats/ships out of the hazard zone, including using Coast Guard assets to convince them to GTFO.

TL;DR- A repeat of the SES-9 scrub due to a late intrusion by a barge being towed into the hazard zone isn't going to happen.  Only a large passenger ship (e.g. a cruise ship) going into the hazard zone would be likely to warrant scrubbing the launch.
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Offline Joffan

To be clear:  THIS WAIVER IS NOT DIRECTLY RELATED TO LANDING ON ASDS.  If it was for ASDS landings, then similar waivers would have been needed for every previous ASDS landing attempt.

Right. However note that success in steering the descending stage means that the hazard for the rest of the descent zone would be zero. To make a sensible risk assessment for the rest of that zone, therefore, you need to scale down by the chance of a total failure of that steering. Given the recent successful track record, I resort to my usual rule of thumb of assuming that the next stage descent fails to steer to make a conservative guess at that probability.

A more nuanced reading, and the part that could be relevant for ASDS landings, is that it might allow them to stage the recovery support vessels (Go Quest and tug) closer to the ASDS during landings.  i.e. Instead of making them wait 5-7miles away, they might only have to wait 2-3 miles.  This would reduce the time needed to return landed stages to port.  But, without reading SpaceX's actual application, it's hard to understand exactly what they were arguing.  The gist from the Federal Register is that AIS and ship tracking data is sufficient now to determine the Ec including shipboard persons as opposed to just trying to determine the odds of hitting a ship with debris.  And, SpaceX would like to do that as they feel like they're less likely to be forced to scrub a launch by a late intrusion into the hazard area unless the ship in question happens to be a large, passenger carrier. 

Justifying a reduction in the support  boat offset is tricky to judge for us bystanders. SpaceX will have the data on the trajectory control and how early they bring the impact point  in close to the ASDS. But  I agree with the reading that this is mainly about reducing scrub likelihood due to hazard area incursion.
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Offline cscott

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This discusses a waiver SpaceX requested for CRS-8 having to do with ship-borne impact hazard but also mentions the previous ASDS landings and a USAF evaluation of the overall launch hazard.

https://www.federalregister.gov/articles/2016/05/10/2016-09685/waivers-of-ship-protection-probability-of-impact-requirement

Would someone who's read it kindly do a TL:DR for the busy, busy. Thanks.
TL:DR: Previously calculating the actual probability of impact on a ship and subsequent loss of life was difficult, so the rule was written as "no launching if there are ships in a hazard zone".  The USCG mandate to have AIS transponders on ships above a certain size has allowed the range to develop a more sophisticated approach, where you can compute in real time the probability of human casualty using the known maximum human capacity and location of the AIS-carrying ships and some assumptions about small non-AIS-carrying ships.  This allows a uniform treatment of potential casualties on land and sea.

SpaceX requested a general waiver back in January to use this new casualty-estimation process.  They were then encouraged to request a specific exemption for CRS-8 after the tug boat scrubbed the launch of SES-9, since presumably in that particular case the launch would not have been scrubbed under the new rules since the tugboat had a very small crew and so the risk of casualty would have been sufficiently low.

There seems to be more general rulemaking in progress to make this new standard the default, but the FAA seems willing to give individual flights waivers to use it for now.
« Last Edit: 05/14/2016 11:42 am by cscott »

Offline deruch

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This discusses a waiver SpaceX requested for CRS-8 having to do with ship-borne impact hazard but also mentions the previous ASDS landings and a USAF evaluation of the overall launch hazard.

https://www.federalregister.gov/articles/2016/05/10/2016-09685/waivers-of-ship-protection-probability-of-impact-requirement

Would someone who's read it kindly do a TL:DR for the busy, busy. Thanks.
TL:DR: Previously calculating the actual probability of impact on a ship and subsequent loss of life was difficult, so the rule was written as "no launching if there are ships in a hazard zone".  The USCG mandate to have AIS transponders on ships above a certain size has allowed the range to develop a more sophisticated approach, where you can compute in real time the probability of human casualty using the known maximum human capacity and location of the AIS-carrying ships and some assumptions about small non-AIS-carrying ships.  This allows a uniform treatment of potential casualties on land and sea.

SpaceX requested a general waiver back in January to use this new casualty-estimation process.  They were then encouraged to request a specific exemption for CRS-8 after the tug boat scrubbed the launch of SES-9, since presumably in that particular case the launch would not have been scrubbed under the new rules since the tugboat had a very small crew and so the risk of casualty would have been sufficiently low.

There seems to be more general rulemaking in progress to make this new standard the default, but the FAA seems willing to give individual flights waivers to use it for now.

Good summary! 

For those wondering, the assumptions that they are using for this new calculation are that the ships have the maximum number of passengers possible and they are not adjusting for reasonable % of them actually being on deck (i.e. no protection from being below decks).  So, all told, a pretty conservative set of assumptions.
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

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