Author Topic: Commercial Crew (CCtCAP) - Discussion Thread  (Read 207823 times)

Offline brickmack

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Re: Commercial Crew (CCtCAP) - Discussion Thread
« Reply #900 on: 03/04/2017 12:10 AM »
The Justification mentions "Spacedesign Corporation" put in a bid. Funny that a semi-defunct software company would bid on a crew delivery vehicle. I bet NASA was unamused.

Offline psloss

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Re: Commercial Crew (CCtCAP) - Discussion Thread
« Reply #901 on: 03/05/2017 05:36 PM »
FWIW, a revision of CCT-REQ-1130, "ISS Crew Transportation and Services Requirements Document" showed up on NTRS recently:
https://ntrs.nasa.gov/search.jsp?R=20170001943

(Attached here, as well.)

Offline yg1968

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Re: Commercial Crew (CCtCAP) - Discussion Thread
« Reply #902 on: 03/06/2017 02:48 AM »
Loss of crew is now at 1 in 200 (but it includes orbital debris hazards while docked to the ISS):

Quote from: page 34 of Document CCT-REQ-1130
3.2.1 Crew Safety
3.2.1.1 Loss of Crew Risk

The CTS shall safely execute the objectives defined in Section 3.1 with the following Loss of
Crew (LOC) requirements for the various mission phases.

a. The overall LOC probability distribution for an ISS mission shall have a mean value no
greater than 1 in 200 without utilizing operational controls implemented by the ISS, such as
TPS inspections.

b. The LOC probability distribution for the combined ascent and entry phases of an ISS mission
shall have a mean value no greater than 1 in 500. [R.CTS.030]

Rationale: The LOC requirement is consistent with NASA's defined goals and thresholds for
crewed vehicles. The LOC values are part of the overall certification process for the
commercial launch vehicle and spacecraft and establish a basis for decision making relative
to safety enhancing features in the design, including failure tolerance. The LOC requirement
represents a design robustness criteria to be managed by the commercial provider alone.
« Last Edit: 03/06/2017 02:55 AM by yg1968 »

Offline AnalogMan

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Re: Commercial Crew (CCtCAP) - Discussion Thread
« Reply #903 on: 03/06/2017 10:03 AM »
Loss of crew is now at 1 in 200 (but it includes orbital debris hazards while docked to the ISS):

Quote from: page 34 of Document CCT-REQ-1130
3.2.1 Crew Safety
3.2.1.1 Loss of Crew Risk

The CTS shall safely execute the objectives defined in Section 3.1 with the following Loss of
Crew (LOC) requirements for the various mission phases.

a. The overall LOC probability distribution for an ISS mission shall have a mean value no
greater than 1 in 200 without utilizing operational controls implemented by the ISS, such as
TPS inspections.

b. The LOC probability distribution for the combined ascent and entry phases of an ISS mission
shall have a mean value no greater than 1 in 500. [R.CTS.030]

Rationale: The LOC requirement is consistent with NASA's defined goals and thresholds for
crewed vehicles. The LOC values are part of the overall certification process for the
commercial launch vehicle and spacecraft and establish a basis for decision making relative
to safety enhancing features in the design, including failure tolerance. The LOC requirement
represents a design robustness criteria to be managed by the commercial provider alone.

Revision: D-1 (March 23, 2015) has exactly the same text.

Offline yg1968

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Re: Commercial Crew (CCtCAP) - Discussion Thread
« Reply #904 on: 03/06/2017 02:03 PM »
The number recently changed. It was still 1 in 270 at the end of 2015 according to ASAP. NASA decided to reduce it to 1 in 200 in order to take into account MMOD damage while docked at the ISS. See the 2015 ASAP report for more on this:

Quote from: page 17 of the ASAP 2015 Report
The CCP has a requirement to achieve a LOC risk of no worse than 1 in 270 (1:270). Analysis of current designs indicates that they fall short of that limit. The primary risk contributor is MMOD damage. The strategy that is being taken to meet the LOC requirement is to back off to 1:200 for the spacecraft themselves, but to require that the design and vehicle capability be the sole means to achieve that level without consideration of operational adjustments. Any potential inspections or other operational workarounds will be put aside and left for later consideration. Both companies are now considering potential changes to their vehicles to address the MMOD risks. While there will always be risk from MMOD, NASA wants the providers to do as well as they can in using the spacecraft design to provide primary prevention before looking at other ways to improve safety through secondary preventive techniques such as inspection. There is some evidence that this strategy will have a positive result.

https://forum.nasaspaceflight.com/index.php?topic=39380.msg1481015#msg1481015

See also the 2016 report on the same issue:

Quote from: page 8 of the ASAP 2016 Report
The ASAP was informed that the LOC goal of 1 in 270 may not be able to be met without additional spacecraft mitigations due to Micrometeoroid and Orbital Debris (MMOD)-associated risks, which are a dominant factor in the LOC calculation. Since the designs of proposed spacecraft systems are not fully mature and are still in a state of flux, it is impossible to determine what the final configurations will yield with respect to LOC. There may be a limit to what can be achieved by design considérations alone, and operational mitigations may be required to achieve the LOC goals. Also, we note that in considering LOC goals, we recognize that there is a fairly large uncertainty band around any calculated LOC number. This issue is currently under review and has the potential to impact budget, schedule, and crew safety.

https://oiir.hq.nasa.gov/asap/documents/2016_ASAP_Annual_Report.pdf

Offline A_M_Swallow

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Re: Commercial Crew (CCtCAP) - Discussion Thread
« Reply #905 on: 03/06/2017 02:34 PM »
At some point putting a Kevlar cover around visiting vehicles becomes a viable option against MMOD damage. I suspect that Bigelow will be happy to sell more of his product.

Offline AnalogMan

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Re: Commercial Crew (CCtCAP) - Discussion Thread
« Reply #906 on: 03/06/2017 04:54 PM »
The number recently changed. It was still 1 in 270 at the end of 2015 according to ASAP. NASA decided to reduce it to 1 in 200 in order to take into account MMOD damage while docked at the ISS. See the 2015 ASAP report for more on this:

[...]

Clearly the Commercial Crew Program had already decided to change the number to 1 in 200 (before operational mitigations) by the time they issued Rev D-1 of the requirements document in March 2015.

[Document attached]

Offline yg1968

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Re: Commercial Crew (CCtCAP) - Discussion Thread
« Reply #907 on: 03/06/2017 07:08 PM »
Thanks! ASAP may not have been aware that the requirements had already changed earlier in 2015.

As you say, it was changed in 2015. I didn't follow all of the changes but I know that back in 2011, it was originally 1 in 270. See below for the 2011 version:

Quote from: page 28 of 2011 version of CCT-REQ-1130
3.2.1.3 The CTS shall safely execute the objectives defined in Section 3.1 with the
following Loss of Crew (LOC) requirements for the various mission phases.
a. The overall LOC probability distribution for an ISS mission shall have a mean value no greater than 1 in 270.
b. The LOC probability distribution for the ascent phase of an ISS mission shall be no greater than 1 in 1000.
c. The LOC probability distribution for the entry phase of an ISS mission shall be no greater than 1 in 1000.

3.2.1.4 The CTS Loss of Mission (LOM) probability distribution for an ISS mission shall have a mean value of no greater than 1 in 55.
a. The overall LOC mission risk in 3.2.1.2 and the LOM risk in 3.2.2 assume docked mission duration of 210 days.
b. A spacecraft failure that requires the vehicle to enter earlier than the pre-launch planned EOM timeframe shall be considered a loss of mission.

Rationale: These LOC and LOM requirements are a direct flow down from the NASA ESMD Exploration Architecture Requirements Document (EARD) and are consistent with NASA‟s defined goals and thresholds for crewed vehicles. The overall LOC mission risk in 3.2.1.3 and the LOM risk in 3.2.1.4 assume docked mission duration of 210 days. A spacecraft failure that requires the vehicle to execute a deorbit/entry/landing earlier than the planned EOM timeframe is considered a loss of mission. Launch vehicle ascent cases that run out of fuel prior to achieving the orbit target are also considered a loss of mission. The LOC values are part of the overall certification process for the commercial launch vehicle and spacecraft and establish a basis for decision making relative to safety enhancing features in the design including failure tolerance.

https://forum.nasaspaceflight.com/index.php?topic=26489.msg795150#msg795150
« Last Edit: 03/06/2017 07:30 PM by yg1968 »

Offline yg1968

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Re: Commercial Crew (CCtCAP) - Discussion Thread
« Reply #908 on: 03/08/2017 04:01 PM »
ECLSS Systems Put to the Test for Commercial Crew Missions:
https://www.nasa.gov/feature/eclss-systems-put-to-the-test-for-commercial-crew-missions

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